This document discusses applying micromechanical analysis to alkali-activated materials. It identifies the intrinsic Young's modulus of the N-A-S-H gel that forms in alkali-activated fly ash and metakaolin as approximately 18 GPa using nanoindentation testing. It then develops a two-scale homogenization model combined with percolation theory to upscale the intrinsic gel properties to the macroscale, reproducing experimental data. The model also demonstrates how the N-A-S-H gel stiffens with increased packing of solid gel particles during the alkali activation process.
V mn-mcm-41 catalyst for the vapor phase oxidation of o-xylenesunitha81
This document describes a study investigating V and Mn incorporated mesoporous molecular sieves for the vapor phase oxidation of o-xylene. Mesoporous monometallic V-MCM-41, Mn-MCM-41, and bimetallic V-Mn-MCM-41 molecular sieves were synthesized and characterized. Their activity was measured for the gas phase oxidation of o-xylene to phthalic anhydride. Among the catalysts, V-MCM-41 with Si/V = 50 exhibited the highest activity and selectivity towards producing phthalic anhydride under the experimental conditions. The physico-chemical properties of the catalysts, including metal content, surface area,
Effect of Grain Size and Reaction Time in Characterisation of Aggregates for ...IJERA Editor
Concrete can deteriorate as a result of alkali aggregate reaction, an interaction between alkalis present in
alkaline pore solution originating from the Portland cement and reactive minerals in certain types of aggregates.
Potential reactivity of aggregates with regard to alkalis present in concrete mix can be determined by Mortar Bar
method, Chemical Method and Petrographic analysis. Of these the chemical method though is quick and does
not require a large quantity of material for testing yet have its own inherent limitations. It does not ensure
completion of reaction as the observations are limited to 24hour only and also does not assess the effect of
varying the combination of coarse and fine aggregates. A study on chemical method by allowing the reaction for
a prolonged time up to 96 hours and also on different grain size ranged matrix was carried at Central Soil and
Materials Research Station, New Delhi. Simultaneously the test results of the modified method are compared to
the existing Mortar Bar method, Chemical Method and Petrographic analysis The outcome of the studies clearly
reflects that the grain size play an important role in the reaction, the reaction time has a demarked impact on
reactivity, in the cases having a high value of silica release the choice of reduction in alkalinity as an indicator
of degree of reaction is not reliable, instead measuring remaining Na2O concentration in Sodium hydroxide
solution after the reaction seems to be much more meaningful in justifying the silica release.
Equilibrium and Kinetics Adsorption of Cadmium and Lead Ions from Aqueous Sol...theijes
This document summarizes a study on the adsorption of cadmium and lead ions from aqueous solution using bamboo-based activated carbon. Key findings include:
1) Unwashed chemical activated bamboo carbon achieved 87.81% removal of cadmium at pH 5 and 96.45% removal of lead at pH 11.
2) Adsorption equilibrium was reached within 1 hour for cadmium and 2.5 hours for lead.
3) Adsorption isotherm data fitted the Freundlich, Temkin, and Hills isotherm models well, suggesting chemisorption as the adsorption mechanism.
4) Kinetic data correlated best with the pseudo-
The document summarizes research on the adsorption of copper(II) and nickel(II) ions onto a polymeric resin called PMBMNen. Key findings include:
1) The resin showed maximum adsorption (88-90%) of copper and (86-88%) of nickel at pH 6, reaching equilibrium within 60 minutes.
2) Adsorption increased with concentration but decreased with increasing flow rate and volume of metal solutions.
3) Adsorption data fit the Freundlich isotherm model best, and thermodynamic parameters (negative ΔH, ΔS, ΔG) indicated spontaneity and exothermic adsorption.
4) The resin effectively removed
Preparation of γ-Al2O3 and Prioritization of Affecting Factors on the Crystal...A Behzadmehr
In this work, boehmite sol was prepared by a previously applied and validated method; hydrolysis of aluminum chloride hexa-hydrate. In order to obtain precise results, the effect of pH after adding precipitating agent, aging time, peptizing temperature and ultrasonic vibration time on the crystallite size of final precipitate were investigated in a narrow range. The preparation conditions applied in the production step of nanocrystalline boehmite affected on the desired alumina phase. Experiments were set based on the statistical design of experiments (Taguchi method). Furthermore the influence of calcination on crystallization and phase transformation of the precipitate was investigated using X-ray diffractometry (XRD) and simultaneous thermal analysis (STA) techniques. To evaluate the results, the obtained data were statistically analyzed. Considering the statisti cal analysis of experiments, the pH after adding precipitating agent is the major parameter affecting crystallite size. In contrast, aging time has the smallest effect on the crystallite size. In addition, Transmission electron microscopy (TEM) of the samples revealed that the particle size of the powders was well distributed in the nano-size range. Taguchi prediction on the crystallite size was 2.096±0.139 nm (with confidence interval of 95%) which confirmed by a verification experiment (2.064 nm).
Corrosion studies of colmonoy - 6 in nitric acid during gadolinium removal st...RAMASUBBU VELAYUTHAM
This document summarizes a study on the corrosion of Colmonoy-6, a nickel-based alloy used in valves and bearings of nuclear power plant moderator systems, when exposed to nitric acid conditions present during gadolinium removal from the moderator. Specimens of undiluted Colmonoy-6 deposits and Colmonoy-6 coatings on stainless steel with varying levels of dilution were exposed to a nitric acid solution at 65°C, and corrosion rates were estimated through weight loss and electrochemical measurements. Microstructural analysis found the undiluted deposit and multiple layer coatings contained more carbide and boride precipitates than single layer coatings, indicating lower dilution effects.
Optimization of temperature imposed on activator before mixinginventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
V mn-mcm-41 catalyst for the vapor phase oxidation of o-xylenesunitha81
This document describes a study investigating V and Mn incorporated mesoporous molecular sieves for the vapor phase oxidation of o-xylene. Mesoporous monometallic V-MCM-41, Mn-MCM-41, and bimetallic V-Mn-MCM-41 molecular sieves were synthesized and characterized. Their activity was measured for the gas phase oxidation of o-xylene to phthalic anhydride. Among the catalysts, V-MCM-41 with Si/V = 50 exhibited the highest activity and selectivity towards producing phthalic anhydride under the experimental conditions. The physico-chemical properties of the catalysts, including metal content, surface area,
Effect of Grain Size and Reaction Time in Characterisation of Aggregates for ...IJERA Editor
Concrete can deteriorate as a result of alkali aggregate reaction, an interaction between alkalis present in
alkaline pore solution originating from the Portland cement and reactive minerals in certain types of aggregates.
Potential reactivity of aggregates with regard to alkalis present in concrete mix can be determined by Mortar Bar
method, Chemical Method and Petrographic analysis. Of these the chemical method though is quick and does
not require a large quantity of material for testing yet have its own inherent limitations. It does not ensure
completion of reaction as the observations are limited to 24hour only and also does not assess the effect of
varying the combination of coarse and fine aggregates. A study on chemical method by allowing the reaction for
a prolonged time up to 96 hours and also on different grain size ranged matrix was carried at Central Soil and
Materials Research Station, New Delhi. Simultaneously the test results of the modified method are compared to
the existing Mortar Bar method, Chemical Method and Petrographic analysis The outcome of the studies clearly
reflects that the grain size play an important role in the reaction, the reaction time has a demarked impact on
reactivity, in the cases having a high value of silica release the choice of reduction in alkalinity as an indicator
of degree of reaction is not reliable, instead measuring remaining Na2O concentration in Sodium hydroxide
solution after the reaction seems to be much more meaningful in justifying the silica release.
Equilibrium and Kinetics Adsorption of Cadmium and Lead Ions from Aqueous Sol...theijes
This document summarizes a study on the adsorption of cadmium and lead ions from aqueous solution using bamboo-based activated carbon. Key findings include:
1) Unwashed chemical activated bamboo carbon achieved 87.81% removal of cadmium at pH 5 and 96.45% removal of lead at pH 11.
2) Adsorption equilibrium was reached within 1 hour for cadmium and 2.5 hours for lead.
3) Adsorption isotherm data fitted the Freundlich, Temkin, and Hills isotherm models well, suggesting chemisorption as the adsorption mechanism.
4) Kinetic data correlated best with the pseudo-
The document summarizes research on the adsorption of copper(II) and nickel(II) ions onto a polymeric resin called PMBMNen. Key findings include:
1) The resin showed maximum adsorption (88-90%) of copper and (86-88%) of nickel at pH 6, reaching equilibrium within 60 minutes.
2) Adsorption increased with concentration but decreased with increasing flow rate and volume of metal solutions.
3) Adsorption data fit the Freundlich isotherm model best, and thermodynamic parameters (negative ΔH, ΔS, ΔG) indicated spontaneity and exothermic adsorption.
4) The resin effectively removed
Preparation of γ-Al2O3 and Prioritization of Affecting Factors on the Crystal...A Behzadmehr
In this work, boehmite sol was prepared by a previously applied and validated method; hydrolysis of aluminum chloride hexa-hydrate. In order to obtain precise results, the effect of pH after adding precipitating agent, aging time, peptizing temperature and ultrasonic vibration time on the crystallite size of final precipitate were investigated in a narrow range. The preparation conditions applied in the production step of nanocrystalline boehmite affected on the desired alumina phase. Experiments were set based on the statistical design of experiments (Taguchi method). Furthermore the influence of calcination on crystallization and phase transformation of the precipitate was investigated using X-ray diffractometry (XRD) and simultaneous thermal analysis (STA) techniques. To evaluate the results, the obtained data were statistically analyzed. Considering the statisti cal analysis of experiments, the pH after adding precipitating agent is the major parameter affecting crystallite size. In contrast, aging time has the smallest effect on the crystallite size. In addition, Transmission electron microscopy (TEM) of the samples revealed that the particle size of the powders was well distributed in the nano-size range. Taguchi prediction on the crystallite size was 2.096±0.139 nm (with confidence interval of 95%) which confirmed by a verification experiment (2.064 nm).
Corrosion studies of colmonoy - 6 in nitric acid during gadolinium removal st...RAMASUBBU VELAYUTHAM
This document summarizes a study on the corrosion of Colmonoy-6, a nickel-based alloy used in valves and bearings of nuclear power plant moderator systems, when exposed to nitric acid conditions present during gadolinium removal from the moderator. Specimens of undiluted Colmonoy-6 deposits and Colmonoy-6 coatings on stainless steel with varying levels of dilution were exposed to a nitric acid solution at 65°C, and corrosion rates were estimated through weight loss and electrochemical measurements. Microstructural analysis found the undiluted deposit and multiple layer coatings contained more carbide and boride precipitates than single layer coatings, indicating lower dilution effects.
Optimization of temperature imposed on activator before mixinginventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Magnetic Fe3O4@MgAl–LDH composite grafted with cobalt phthalocyanine as an ef...Pawan Kumar
Magnetically separable layered double hydroxide MgAl–LDH@Fe3O4 composite supported cobalt
phthalocyanine catalyst was synthesized and used for the aerobic oxidation of mercaptans to corresponding
disulfides under alkali free conditions. The catalyst exhibited excellent activity for the oxidation of
mercaptans using molecular oxygen as an oxidant which can be effectively recovered by using an external
magnetic field. In addition, the covalent immobilization of cobalt phthalocyanine to MgAl–LDH@Fe3O4
support prevents the leaching of the catalyst and improves its activity and stability
FIBER OPTIC AIDED SPECTROPHOTOMETRIC DETERMINATION OF GADOLINIUM IN FBR REPRO...ijac123
This document describes the development of a new spectrophotometric method for determining gadolinium concentration using Alizarin Red S as the complexing agent. Key findings include:
1) Gadolinium forms a stable complex with Alizarin Red S at pH 4.6-4.8 that has maximum absorbance at 530 nm.
2) Beer's law is followed in the concentration range of 1-14 μg/mL of gadolinium.
3) The method allows for detection of gadolinium down to 0.264 μg/mL with good precision.
4) The method is proposed for determining gadolinium concentration during solvent extraction studies of gadolinium removal from nuclear
Optical resolution trials and a process-concept assessment of the industrial ...Katalin Nemák
This dissertation discusses the synthesis, optical resolution, and scale-up process for producing the pure enantiomers of pipecolo-anilides and pipecolo-xylidides. 13 model compounds were synthesized and all were resolved into their optical isomers. The resolution processes of the N-alkyl-pipecolo-xylidides were investigated in detail. Temperature dependence and recrystallization were studied to produce the enantiomers in high purity. Binary phase diagrams were applied to purification. A new method was developed to select resolving agents and solvents based on chromatographic retention differences. Supramolecular characterization of the diastereomers was also conducted. Finally, a trial production was carried out and plans were
Chemical Examination Of Sandbox (Hura Crepitans) Seed: Proximate, Elemental A...IOSRJAC
A study in terms of proximate, elemental and fatty acid contents of (Hura crepitans) seed was investigated using standard analytical techniques. The results of proximate composition in % were as follows: moisture 12.82 ± 0.01, crude protein 24.76 ±0.04, crude fibre 10.15 ± 0.03, fat 10.68 ± 0.01, ash 3.16 ± 0.02 and carbohydrate 34.75 ± 0.05. The elemental composition of the seed showed Na, K, Ca and Mg in mg/100g to be 6.00 ± 0.01, 123.00 ± 0.02, 10.40 ± 0.03, 112.00 ± 0.01 respectively while other elements determined in mg/kg were Fe and Zn with 7.10 ±0.04 and 2.60± 0.01. The (%) free fatty acid compositions of the seed oil were as follows: lauric (1.310 ±0.015), palmitic (0.389 ±0.012), palmitoleic (1.211 ±0.013), stearic (2.436 ± 0.004), oleic (6.138 ±0.003), linoleic (8.625 ±0.001) and linolenic (2.469 ± 0.102). The results revealed linoleic and oleic acids to be the most common in terms of abundance while palmitic acid was the least. The seed of Hura crepitans could be described as a good food because it contained significant amount of essential nutrients required by man.
— Previous researches were made on UHMWPE (Ultra-High-Molecular-Weight-Polyethylene) based implant material and its fusion with Ca-alginate. New methods were made for preparing UHMWPE-Ca-alginate blends. If the coating Ca-alginate salt can be achieved on the surface of UHMWPE, it might lead to an implant material which could promote the bone formation. Earlier results show that we can make the coating layer on the polymer powder surface. Our new approach is to modify the method we made earlier, and this way the alginate layer can withstand washing and sterilization as it's shown in the paper. We also realized that the layer slowly can give off Ca2+ ions which can be absorbed with specific cells. Since we modified the surface structure of the UHMWPE samples we carried out wear testing of the new prepared samples. All of these measurements and experiments have been done as preparative ones to make one time real prosthetic material.
This document summarizes a study that determined the concentrations of lead, cadmium, and chromium in spice samples from eastern Ethiopia using atomic absorption spectroscopy. Spice samples of fenugreek, black cumin, garlic, and ginger were collected and digested using microwave digestion with nitric acid and hydrogen peroxide. Lead, cadmium, and chromium concentrations were then measured. The study found detectable levels of all three metals in the samples tested, with the highest lead level found in ginger and the only detectable cadmium found in fenugreek. Microwave digestion was determined to be the optimal sample preparation method compared to dry and wet digestion based on shorter time and smaller deviations in results.
The document investigates the effects of varying deposition parameters on the structure and corrosion resistance of hydroxyapatite (HA) coatings electrodeposited onto Ti-6Al-4V alloy samples. X-ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the coatings deposited under different conditions. Potentiodynamic polarization measurements in simulated body fluid evaluated the corrosion behavior. The optimal deposition parameters were found to be an applied voltage of 9 volts, pH value of 5.5, temperature of 25°C, and deposition time of 30 minutes, which yielded coatings with the best structural and corrosion-resistant properties.
The document investigates the effect of heat treatment on the corrosion behavior of Ti-15V-3Al-3Cr-3Sn alloy (β-Ti alloy) in HCl and NaCl solutions of varying concentrations. Potentiodynamic polarization tests were conducted on samples of the alloy in both the solution treated and aged conditions. The corrosion rates were calculated from the polarization curves. It was found that the corrosion properties of the β-titanium alloy remained intact even after aging heat treatment. The corrosion rates in both HCl and NaCl increased with increasing concentrations but no significant change was observed between the solution treated and aged alloy conditions.
Characterization of Structural and Surface Properties of Nanocrystalline TiO2...Shingo Watanabe (渡邊真悟)
This document characterizes the structural and surface properties of TiO2-CeO2 mixed oxides synthesized using a urea coprecipitation method. Key findings include:
1) The mixed oxides have unimodal nanoporous structures with pore sizes ranging from 3.7 to 5.3 nm and higher surface areas than single TiO2 and CeO2 oxides.
2) XRD and XPS analysis show the mixed oxides have nanocrystalline structures between 4.0-5.4 nm, with distorted lattice structures indicating reduction of Ti4+ and Ce4+ ions at the surface.
3) H2-TPR and NH3-TPD reveal the mixed oxides
Microwave assisted synthesis and IR spectral analysis of a few complexes of 4...IRJET Journal
The document summarizes a study that synthesized chromium complexes of 4-Hydroxy-3-methoxybenzaldehyde (vanillin) using microwave-assisted oxidation with ditertiary butylchromate (TBC) in different solvents. The products were characterized using elemental analysis and Fourier transform infrared spectroscopy (FTIR). Key findings include: (1) Reaction conditions like solvent and substrate/oxidant ratio affected the products' characteristics. (2) FTIR analysis showed the presence of Cr-O, Cr=O bonds and indicated oxidation of the aldehyde group to a carboxylic acid. (3) The most efficiently synthesized product was obtained with a 1:1 substrate/oxidant ratio in 1
Removal of Coke during Steam Reforming of Ethanol over La-CoOx Catalystinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
This document summarizes a study that investigated the effects of fluoridation and densification of hydroxyapatite (HA) composite material with the addition of titanium fluoride (TiF4). Five HA composite samples were prepared with varying weight percentages of TiF4 using a sol-gel technique and sintered at 1250°C. X-ray diffraction analysis showed the presence of fluoridated apatite and other calcium compounds in the sintered samples. Scanning electron microscopy revealed reduced porosity with increasing TiF4 content. The highest relative density of 96.42% was achieved for the sample with 19% TiF4. Mechanical testing demonstrated that Vickers hardness and bending strength increased with TiF4
Studies on Nitration of Phenol over Solid Acid Catalyst | Crimson PublishersDanesBlake
Phenol was selectively nitrated in liquid phase to produce ortho-nitrophenol using dilute nitric acid (30%) at room temperature in presence of hydrochloric acid treated γ-alumina. Initially Al(NO3) and NH4HCO3 were reacted to prepare Al (OH)3 which on successive calcinations at 550 ᴼC for 5h produce γ-alumina. The γ-alumina was characterized by BET, XRD, SEM and NH3-TPD analysis. The XRD profile confirmed the crystalline structure of the solid acid catalyst γ-alumina. The NH3-TPD analysis showed the development of lewis acidity on the surface of hydrochloric acid treated γ-alumina. The effects of various parameters such as concentration of reactants, types of catalyst, weight of the catalyst, solvent, temperature and time of reaction have been studied. The kinetics of the reaction was also investigated.
This document summarizes a study that used response surface methodology to optimize the removal of Zn2+ ions from aqueous solution using a novel biochar-alginate composite adsorbent. The researchers developed a quadratic model to predict Zn2+ removal based on initial Zn2+ concentration, adsorbent dose, and temperature. Their analysis found that initial Zn2+ concentration and adsorbent dose had the largest effect on removal efficiency. The optimum conditions for maximum 85% removal were determined to be an initial Zn2+ concentration of 43.18 mg/L, adsorbent dose of 0.062 g, and temperature of 313.5 K.
A new technique to measure oxygen reduction kinetics underneath coatings using hydrogen permeation from the back side. Huge step towards characterising buried interface reactivity.
Removal of cadmium from aqueous solution using cobalt silicate precipitation ...IJSIT Editor
This document discusses the removal of cadmium from aqueous solutions using cobalt silicate precipitation tubes (CoSPT) as an adsorbent. CoSPT was synthesized through a "silica garden" process and found to be an effective adsorbent for cadmium. Batch adsorption studies were conducted to determine the effect of contact time, adsorbent dose, initial cadmium concentration, temperature, and pH. Experimental data fit the Langmuir and Freundlich isotherm models well. Kinetic studies showed that the pseudo-second order model provided the best fit. The maximum adsorption capacity of CoSPT for cadmium was estimated to be 319 mg/g based on
Studies on Nitration of Phenol over Solid Acid Catalyst by Lipika Das, Koushi...crimsonpublisherspps
- Phenol was selectively nitrated to ortho-nitrophenol using dilute nitric acid over gamma-alumina catalyst in liquid phase at room temperature.
- Gamma-alumina was prepared using a controlled precipitation method and characterized using various techniques which showed it had suitable properties for nitration.
- Parameters like concentration of reactants, weight of catalyst, solvent, temperature and time were varied to determine their effect on the reaction. Kinetics of the reaction were also studied.
1. The document examines the adsorptive removal of Acid Blue 45 dye from aqueous solutions using preformed flocs of ferric sulfate, manganese chloride, and manganese sulfate as adsorbents.
2. Batch experiments were conducted to analyze the effects of contact time, pH, adsorbent dosage, and to develop adsorption isotherm models. The maximum dye removal was 90%, 85%, and 65% for ferric sulfate, manganese sulfate, and manganese chloride flocs, respectively.
3. Equilibrium data fitted well to the Langmuir isotherm model, indicating monolayer adsorption on homogeneous sites. This suggests preformed floc ad
The document discusses ground granulated blast furnace slag (GGBFS) as a supplementary cementitious material used in concrete. GGBFS is a byproduct of steel production that is rapidly cooled and finely ground to a fineness similar to cement. When used to replace up to 50% of the cement in concrete, GGBFS improves workability, finishability, pumpability, durability, strength, and resistance to sulfate attack and alkali-silica reaction compared to plain Portland cement concrete. Typical applications include exterior flatwork, general use concrete, and mass concrete where GGBFS replacement rates can be as high as 80%.
Cracking tendency of alkali-activated slag concretefrank collins
This document summarizes a study on the cracking tendency of alkali-activated slag concrete (AASC) when subjected to restrained shrinkage. Key findings include:
1) AASC has higher drying shrinkage than ordinary Portland cement concrete (OPCC) which can lead to greater cracking under restrained conditions.
2) In restrained ring tests, AASC cracked within 7 days while OPCC took 168 days to crack, showing AASC has a higher cracking tendency.
3) To better evaluate cracking, researchers developed a restrained beam test where embedded steel rods or a stress magnifier plate provided restraint. Beams with AASC cracked within hours while OPCC took 9 days, further demonstrating the higher
The document discusses how hazardous air pollution control residue can be transformed into a non-hazardous glass material called Plasmarok through plasma technology. Plasmarok can then be used as a cement replacement to create alkali-activated concretes with high compressive strengths over 90 MPa. The properties of these concretes depend on factors like the particle size, chemical composition, and processing method of Plasmarok. Reducing the particle size and increasing the silicon-to-aluminum ratio can improve the strength. Understanding these influencing factors helps develop consistent concrete materials with desirable properties.
Magnetic Fe3O4@MgAl–LDH composite grafted with cobalt phthalocyanine as an ef...Pawan Kumar
Magnetically separable layered double hydroxide MgAl–LDH@Fe3O4 composite supported cobalt
phthalocyanine catalyst was synthesized and used for the aerobic oxidation of mercaptans to corresponding
disulfides under alkali free conditions. The catalyst exhibited excellent activity for the oxidation of
mercaptans using molecular oxygen as an oxidant which can be effectively recovered by using an external
magnetic field. In addition, the covalent immobilization of cobalt phthalocyanine to MgAl–LDH@Fe3O4
support prevents the leaching of the catalyst and improves its activity and stability
FIBER OPTIC AIDED SPECTROPHOTOMETRIC DETERMINATION OF GADOLINIUM IN FBR REPRO...ijac123
This document describes the development of a new spectrophotometric method for determining gadolinium concentration using Alizarin Red S as the complexing agent. Key findings include:
1) Gadolinium forms a stable complex with Alizarin Red S at pH 4.6-4.8 that has maximum absorbance at 530 nm.
2) Beer's law is followed in the concentration range of 1-14 μg/mL of gadolinium.
3) The method allows for detection of gadolinium down to 0.264 μg/mL with good precision.
4) The method is proposed for determining gadolinium concentration during solvent extraction studies of gadolinium removal from nuclear
Optical resolution trials and a process-concept assessment of the industrial ...Katalin Nemák
This dissertation discusses the synthesis, optical resolution, and scale-up process for producing the pure enantiomers of pipecolo-anilides and pipecolo-xylidides. 13 model compounds were synthesized and all were resolved into their optical isomers. The resolution processes of the N-alkyl-pipecolo-xylidides were investigated in detail. Temperature dependence and recrystallization were studied to produce the enantiomers in high purity. Binary phase diagrams were applied to purification. A new method was developed to select resolving agents and solvents based on chromatographic retention differences. Supramolecular characterization of the diastereomers was also conducted. Finally, a trial production was carried out and plans were
Chemical Examination Of Sandbox (Hura Crepitans) Seed: Proximate, Elemental A...IOSRJAC
A study in terms of proximate, elemental and fatty acid contents of (Hura crepitans) seed was investigated using standard analytical techniques. The results of proximate composition in % were as follows: moisture 12.82 ± 0.01, crude protein 24.76 ±0.04, crude fibre 10.15 ± 0.03, fat 10.68 ± 0.01, ash 3.16 ± 0.02 and carbohydrate 34.75 ± 0.05. The elemental composition of the seed showed Na, K, Ca and Mg in mg/100g to be 6.00 ± 0.01, 123.00 ± 0.02, 10.40 ± 0.03, 112.00 ± 0.01 respectively while other elements determined in mg/kg were Fe and Zn with 7.10 ±0.04 and 2.60± 0.01. The (%) free fatty acid compositions of the seed oil were as follows: lauric (1.310 ±0.015), palmitic (0.389 ±0.012), palmitoleic (1.211 ±0.013), stearic (2.436 ± 0.004), oleic (6.138 ±0.003), linoleic (8.625 ±0.001) and linolenic (2.469 ± 0.102). The results revealed linoleic and oleic acids to be the most common in terms of abundance while palmitic acid was the least. The seed of Hura crepitans could be described as a good food because it contained significant amount of essential nutrients required by man.
— Previous researches were made on UHMWPE (Ultra-High-Molecular-Weight-Polyethylene) based implant material and its fusion with Ca-alginate. New methods were made for preparing UHMWPE-Ca-alginate blends. If the coating Ca-alginate salt can be achieved on the surface of UHMWPE, it might lead to an implant material which could promote the bone formation. Earlier results show that we can make the coating layer on the polymer powder surface. Our new approach is to modify the method we made earlier, and this way the alginate layer can withstand washing and sterilization as it's shown in the paper. We also realized that the layer slowly can give off Ca2+ ions which can be absorbed with specific cells. Since we modified the surface structure of the UHMWPE samples we carried out wear testing of the new prepared samples. All of these measurements and experiments have been done as preparative ones to make one time real prosthetic material.
This document summarizes a study that determined the concentrations of lead, cadmium, and chromium in spice samples from eastern Ethiopia using atomic absorption spectroscopy. Spice samples of fenugreek, black cumin, garlic, and ginger were collected and digested using microwave digestion with nitric acid and hydrogen peroxide. Lead, cadmium, and chromium concentrations were then measured. The study found detectable levels of all three metals in the samples tested, with the highest lead level found in ginger and the only detectable cadmium found in fenugreek. Microwave digestion was determined to be the optimal sample preparation method compared to dry and wet digestion based on shorter time and smaller deviations in results.
The document investigates the effects of varying deposition parameters on the structure and corrosion resistance of hydroxyapatite (HA) coatings electrodeposited onto Ti-6Al-4V alloy samples. X-ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the coatings deposited under different conditions. Potentiodynamic polarization measurements in simulated body fluid evaluated the corrosion behavior. The optimal deposition parameters were found to be an applied voltage of 9 volts, pH value of 5.5, temperature of 25°C, and deposition time of 30 minutes, which yielded coatings with the best structural and corrosion-resistant properties.
The document investigates the effect of heat treatment on the corrosion behavior of Ti-15V-3Al-3Cr-3Sn alloy (β-Ti alloy) in HCl and NaCl solutions of varying concentrations. Potentiodynamic polarization tests were conducted on samples of the alloy in both the solution treated and aged conditions. The corrosion rates were calculated from the polarization curves. It was found that the corrosion properties of the β-titanium alloy remained intact even after aging heat treatment. The corrosion rates in both HCl and NaCl increased with increasing concentrations but no significant change was observed between the solution treated and aged alloy conditions.
Characterization of Structural and Surface Properties of Nanocrystalline TiO2...Shingo Watanabe (渡邊真悟)
This document characterizes the structural and surface properties of TiO2-CeO2 mixed oxides synthesized using a urea coprecipitation method. Key findings include:
1) The mixed oxides have unimodal nanoporous structures with pore sizes ranging from 3.7 to 5.3 nm and higher surface areas than single TiO2 and CeO2 oxides.
2) XRD and XPS analysis show the mixed oxides have nanocrystalline structures between 4.0-5.4 nm, with distorted lattice structures indicating reduction of Ti4+ and Ce4+ ions at the surface.
3) H2-TPR and NH3-TPD reveal the mixed oxides
Microwave assisted synthesis and IR spectral analysis of a few complexes of 4...IRJET Journal
The document summarizes a study that synthesized chromium complexes of 4-Hydroxy-3-methoxybenzaldehyde (vanillin) using microwave-assisted oxidation with ditertiary butylchromate (TBC) in different solvents. The products were characterized using elemental analysis and Fourier transform infrared spectroscopy (FTIR). Key findings include: (1) Reaction conditions like solvent and substrate/oxidant ratio affected the products' characteristics. (2) FTIR analysis showed the presence of Cr-O, Cr=O bonds and indicated oxidation of the aldehyde group to a carboxylic acid. (3) The most efficiently synthesized product was obtained with a 1:1 substrate/oxidant ratio in 1
Removal of Coke during Steam Reforming of Ethanol over La-CoOx Catalystinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
This document summarizes a study that investigated the effects of fluoridation and densification of hydroxyapatite (HA) composite material with the addition of titanium fluoride (TiF4). Five HA composite samples were prepared with varying weight percentages of TiF4 using a sol-gel technique and sintered at 1250°C. X-ray diffraction analysis showed the presence of fluoridated apatite and other calcium compounds in the sintered samples. Scanning electron microscopy revealed reduced porosity with increasing TiF4 content. The highest relative density of 96.42% was achieved for the sample with 19% TiF4. Mechanical testing demonstrated that Vickers hardness and bending strength increased with TiF4
Studies on Nitration of Phenol over Solid Acid Catalyst | Crimson PublishersDanesBlake
Phenol was selectively nitrated in liquid phase to produce ortho-nitrophenol using dilute nitric acid (30%) at room temperature in presence of hydrochloric acid treated γ-alumina. Initially Al(NO3) and NH4HCO3 were reacted to prepare Al (OH)3 which on successive calcinations at 550 ᴼC for 5h produce γ-alumina. The γ-alumina was characterized by BET, XRD, SEM and NH3-TPD analysis. The XRD profile confirmed the crystalline structure of the solid acid catalyst γ-alumina. The NH3-TPD analysis showed the development of lewis acidity on the surface of hydrochloric acid treated γ-alumina. The effects of various parameters such as concentration of reactants, types of catalyst, weight of the catalyst, solvent, temperature and time of reaction have been studied. The kinetics of the reaction was also investigated.
This document summarizes a study that used response surface methodology to optimize the removal of Zn2+ ions from aqueous solution using a novel biochar-alginate composite adsorbent. The researchers developed a quadratic model to predict Zn2+ removal based on initial Zn2+ concentration, adsorbent dose, and temperature. Their analysis found that initial Zn2+ concentration and adsorbent dose had the largest effect on removal efficiency. The optimum conditions for maximum 85% removal were determined to be an initial Zn2+ concentration of 43.18 mg/L, adsorbent dose of 0.062 g, and temperature of 313.5 K.
A new technique to measure oxygen reduction kinetics underneath coatings using hydrogen permeation from the back side. Huge step towards characterising buried interface reactivity.
Removal of cadmium from aqueous solution using cobalt silicate precipitation ...IJSIT Editor
This document discusses the removal of cadmium from aqueous solutions using cobalt silicate precipitation tubes (CoSPT) as an adsorbent. CoSPT was synthesized through a "silica garden" process and found to be an effective adsorbent for cadmium. Batch adsorption studies were conducted to determine the effect of contact time, adsorbent dose, initial cadmium concentration, temperature, and pH. Experimental data fit the Langmuir and Freundlich isotherm models well. Kinetic studies showed that the pseudo-second order model provided the best fit. The maximum adsorption capacity of CoSPT for cadmium was estimated to be 319 mg/g based on
Studies on Nitration of Phenol over Solid Acid Catalyst by Lipika Das, Koushi...crimsonpublisherspps
- Phenol was selectively nitrated to ortho-nitrophenol using dilute nitric acid over gamma-alumina catalyst in liquid phase at room temperature.
- Gamma-alumina was prepared using a controlled precipitation method and characterized using various techniques which showed it had suitable properties for nitration.
- Parameters like concentration of reactants, weight of catalyst, solvent, temperature and time were varied to determine their effect on the reaction. Kinetics of the reaction were also studied.
1. The document examines the adsorptive removal of Acid Blue 45 dye from aqueous solutions using preformed flocs of ferric sulfate, manganese chloride, and manganese sulfate as adsorbents.
2. Batch experiments were conducted to analyze the effects of contact time, pH, adsorbent dosage, and to develop adsorption isotherm models. The maximum dye removal was 90%, 85%, and 65% for ferric sulfate, manganese sulfate, and manganese chloride flocs, respectively.
3. Equilibrium data fitted well to the Langmuir isotherm model, indicating monolayer adsorption on homogeneous sites. This suggests preformed floc ad
The document discusses ground granulated blast furnace slag (GGBFS) as a supplementary cementitious material used in concrete. GGBFS is a byproduct of steel production that is rapidly cooled and finely ground to a fineness similar to cement. When used to replace up to 50% of the cement in concrete, GGBFS improves workability, finishability, pumpability, durability, strength, and resistance to sulfate attack and alkali-silica reaction compared to plain Portland cement concrete. Typical applications include exterior flatwork, general use concrete, and mass concrete where GGBFS replacement rates can be as high as 80%.
Cracking tendency of alkali-activated slag concretefrank collins
This document summarizes a study on the cracking tendency of alkali-activated slag concrete (AASC) when subjected to restrained shrinkage. Key findings include:
1) AASC has higher drying shrinkage than ordinary Portland cement concrete (OPCC) which can lead to greater cracking under restrained conditions.
2) In restrained ring tests, AASC cracked within 7 days while OPCC took 168 days to crack, showing AASC has a higher cracking tendency.
3) To better evaluate cracking, researchers developed a restrained beam test where embedded steel rods or a stress magnifier plate provided restraint. Beams with AASC cracked within hours while OPCC took 9 days, further demonstrating the higher
The document discusses how hazardous air pollution control residue can be transformed into a non-hazardous glass material called Plasmarok through plasma technology. Plasmarok can then be used as a cement replacement to create alkali-activated concretes with high compressive strengths over 90 MPa. The properties of these concretes depend on factors like the particle size, chemical composition, and processing method of Plasmarok. Reducing the particle size and increasing the silicon-to-aluminum ratio can improve the strength. Understanding these influencing factors helps develop consistent concrete materials with desirable properties.
This document summarizes a study on the strength and shrinkage properties of alkali-activated slag concrete (AASC) placed in a large concrete column. Key findings include:
1) The AASC had improved workability over time compared to ordinary portland cement concrete, with minimal slump loss over 2 hours.
2) The temperature development in the AASC column was similar to a blended cement column and slower than an ordinary portland cement column, with a smaller temperature difference between the interior and exterior.
3) The compressive strength of the AASC column was identical to ordinary portland cement concrete and stronger than blended cement concrete at 28 and 91 days.
4) Embedded strain gauges
This document describes the development of a numerical model to analyze the cracking behavior of alkali-activated slag concrete (AASC) beams subjected to restrained shrinkage. The model accounts for the time-dependent properties of different concrete mixtures, including shrinkage, elastic modulus, creep, and tensile strength. Experimental data on these properties was used to develop time-dependent relationships in the model. The model aims to better understand the contributions of these parameters to cracking risk by comparing model results to experimental cracking data from restrained beam tests of various concrete mixtures.
The document describes research into developing alkali-activated slag concrete (AASC) for construction use that achieves high early strength. The researchers created a dry powdered activator by blending sodium silicate and hydrated lime that could be pre-blended with slag. When used to make AASC, this resulted in minimal slump loss over time and compressive strengths similar to ordinary Portland cement concrete at one day. However, AASC exhibited higher drying shrinkage than OPCC. Various methods were investigated to reduce the shrinkage of AASC, such as curing regimes and use of shrinkage-reducing admixtures or porous aggregate, with some success in lowering crack tendency and widths.
The Leading manufacturers, Suppliers, importers and exporters of a varied range of Carbon Products Calcined Petroleum Coke, Petroleum Coke, Cement & Cement Clinker, Petroleum ProductsPetroleum Products
This paper investigates the workability and mechanical properties of concrete containing alkali-activated slag as the binder. Two types of activators were used: sodium hydroxide with sodium carbonate, and sodium silicate with hydrated lime. The fresh and hardened concrete properties of these alkali-activated slag concretes were compared to ordinary portland cement concrete. The results showed that concrete activated with powdered sodium silicate and lime had minimal slump loss over 2 hours and achieved similar 1-day compressive strengths as portland cement concrete when cured at normal temperatures. However, it exhibited higher drying shrinkage. Overall, alkali-activated slag concrete shows potential as a viable alternative to portland cement concrete.
This document summarizes the results of a study investigating the effects of ultra-fine materials on the workability and strength of concrete containing alkali-activated slag as the binder. It was found that:
1) Partial replacement of slag with ultra-fine fly ash improved workability but had similar strength development as ordinary portland cement concrete.
2) Partial replacement with condensed silica fume or ultra-fine slag showed significantly greater strength than alkali-activated slag concrete at ages greater than one day, though condensed silica fume reduced workability.
3) Of the mixes tested, concrete with partial replacement of slag with condensed silica fume achieved the highest compressive strength over 91 days of
Early age strength and workability of slag pastes activated by sodium silicatesfrank collins
This document reports on an investigation into activating blast furnace slag with sodium silicates to achieve equivalent one-day strength to Portland cement at normal curing temperatures and reasonable workability. The effects of varying sodium silicate activator dosages on strength and workability are discussed. Tests on pastes, mortars and concretes showed that equivalent one-day strength to Portland cement is possible using sodium silicate activation at normal curing temperatures, with the strength decreasing as the silicate modulus increases. Workability was also found to decrease with increasing activator dosage.
This document discusses microcracking and strength development in alkali activated slag concrete (AASC) subjected to different curing regimes. The main points are:
1) AASC cured without moist curing ("exposed") exhibited higher levels of microcracking compared to AASC with moist curing ("bath" or "sealed"), as measured by surface crack detection, water sorptivity, and mercury intrusion porosimetry tests.
2) Exposed AASC also showed significantly reduced compressive strength development compared to bath or sealed cured AASC. Strength of exposed AASC was 54% and 41% lower than bath and sealed AASC at 365 days.
3) Microcracking in
Effect of activator dosage... (2014, SAICE, Shekhovtsova J)Maxim Kovtun
This document provides biographies of three researchers - Julia Shekhovtsova, Elsabe Kearsley, and Maxim Kovtun - from the University of Pretoria, South Africa. It discusses their educational backgrounds and fields of research, which include the use of fly ash in alkali-activated cement binders and building materials. The document also provides their contact details.
This document discusses how the pore size distribution affects drying shrinkage in alkali-activated slag concrete (AASC) compared to ordinary Portland cement concrete (OPCC). The main points are:
1) AASC exhibited higher drying shrinkage than OPCC even though OPCC lost more moisture during drying.
2) The pore size distribution of AASC pastes showed a much higher proportion of pores in the mesopore region compared to OPC pastes.
3) The radius of pores where the meniscus forms during drying seems to be a more important factor for shrinkage than the total moisture loss. This supports the theory that capillary tensile forces from drying cause shrinkage.
1) A trial was conducted injecting an enhanced calcium sorbent called Sorbacal® SPS at Great River Energy's Stanton Station to reduce SO2 emissions and meet regional haze compliance targets.
2) The trial successfully achieved over 85% SO2 removal and emission rates below 0.14 lb/MMBtu, meeting the target.
3) Monitoring of the electrostatic precipitator performance showed only minimal impacts from the sorbent injection, indicating good compatibility between the enhanced calcium sorbent and ESP operation.
This document summarizes the development of geopolymer applications over 30 years by Prof. Joseph Davidovits and his research organizations. It describes early successes with fire-resistant wood panels in the 1970s, followed by applications of geopolymers in ceramics, bricks, and cement from the 1970s-1980s. A key innovation was developing a low-temperature process to transform kaolinite clay into a geopolymer binder. This led to liquid geopolymer binders in the 1980s and the invention of high-strength geopolymer cement in 1983 through a collaboration between Prof. Davidovits and Lone Star Industries.
Challenges for Concrete. Presenterat av professor Karen Scrivener, vinnare av Swedish Concrete Award 2015, på Träffpunkt Betong 15 den 7 oktober i Stockholm.
Feasibility studies of geopolymer as a coating materialzerohead
The document discusses a study on the feasibility of using geopolymer as a coating material. The experimental program involved testing different raw materials and molar ratios to determine optimal properties. Results showed that a polysialate-siloxo type geopolymer with a Si/Al ratio of around 4.0, Na/Al ratio of 0.4-0.6, Si/Na ratio of 0.8-1.2, and H2O/Na ratio of 13-17 provided good workability, fast strength development, and potential as an environmentally friendly coating material. The conclusions determined composition ranges that achieved these qualities. Further studies could continue optimizing geopolymer for coating applications.
The document discusses the constituents and applications of concrete. The key constituents of concrete are cement, water, sand, coarse aggregate, and chemical or mineral admixtures. Common cements used are OPC, PPC containing fly ash, and PSC containing slag. Blended cements like PPC and PSC provide benefits like improved workability and reduced heat development. The appropriate type of cement is chosen based on the application and exposure conditions of the concrete.
Magnesium carbonate trihydrate, nesquehonite, is proposed as a precursor for the production of a construction material similar to plasterboard,
in a unique carbon capture and utilisation process [1]. The hardening process is thought to follow a similar mechanism to gypsum in the manufacture
of plasterboard, where the hardening is produced in the recrystallization of gypsum crystals. However, nesquehonite [2], during hardening,
converts into hydromagnesite, releasing CO2
and H2
O during the transformation. In this work, samples of nesquehonite were hardened by forcing
their conversion into hydromagnesite in enclosed cubes [3]. The influence of the curing temperature (50 ℃-80 ℃) and time (0-72 hours) on the
compressive strength has been studied and correlated to the conversion of nesquehonite into hydromagnesite [4]. Compressive strength values up
to 6MPa are easily achievable in the studied conditions and it was observed that at higher temperatures time has a detrimental effect on the strength.
The probable overpressure within the cubes, generated by released CO2
and water at the higher temperatures, is thought to be the main cause for
the loss of strength [5].
Enhanced fluidized bed methanation over a Ni Al2O3 catalyst for production of...Pengcheng Li
This document summarizes a study that investigated the fluidization behavior and CO methanation performance of a Ni/Al2O3 catalyst in a fluidized bed reactor for producing synthetic natural gas. The researchers found that the pure Ni/Al2O3 catalyst failed to properly fluidize on its own due to particle sizes between 10 and 100 μm, but fluidization was improved by adding larger Al2O3 particles. Methanation performance in the fluidized bed reactor increased substantially with the Al2O3 addition. Temperature was found to control the methanation reaction mechanism, with surface reactions dominating at lower temperatures and external diffusion controlling at higher temperatures. Stability tests showed the fluidized bed reactor had higher CO conversion, methane selectivity
1) The document examines the role of various catalysts (HCl, H2SO4, CH3COOH, HF, NH4OH) in the fabrication of silica films using a sol-gel process.
2) It was found that different catalysts can have dramatic effects on the porosity, optical quality, shrinkage, thickness, structural evolution during thermal treatment, and stress of the films. For example, using H2SO4 instead of HCl as the catalyst increased the porosity of thermally treated films from 2.8% to 31%.
3) Experiments were conducted to study the effects of various catalysts on silica films fabricated via spin coating of precursor solutions and subsequent thermal
The document evaluates the effect of temperature on polyethylene terephthalate (PET)-coated electrolytic chromium-coated steel plates immersed in an acetic-acetate medium. Samples with flat and rippled walls were immersed at 40, 60, and 80°C. Raman spectroscopy showed the temperature had no effect on acid absorption by the PET coating. The rippled samples had greater amorphousness due to mechanical deformation during manufacturing. Higher temperatures slightly reduced crystallinity near the steel interface but did not compromise the steel plate. The medium increased failures and deterioration of manufacturing defects on the PET surface. A combination of techniques characterized the PET coating's protective capacity on the steel plates.
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
This document summarizes research on incorporating polyamide 6 nanofibrous structures into glass fiber-reinforced epoxy composites to improve their mechanical properties. Experiments showed that the nanofibers had a catalytic effect on the curing of the epoxy resin, lowering its activation energy. Composites with nanofibers deposited on or between fiber layers showed increased stress at failure compared to a control without nanofibers. The deposited nanofibers in particular improved load transfer to the glass fibers. While nanofibers did not significantly increase modulus, their inclusion helped prevent delamination cracks in the composites. The research demonstrates that nanofibers can enhance some mechanical properties of glass fiber-ep
Equation of state for technetium from x‐ray diffraction and first principle c...Konstantin German
This document presents an experimental and theoretical study of the equation of state (EoS) of technetium metal under high pressure. Key points:
1) X-ray diffraction was used to measure the structure of technetium up to 67 GPa in a diamond anvil cell. The hexagonal close-packed structure was found to be stable over this pressure range.
2) First-principles calculations were also performed to model the compression behavior of technetium up to 273 GPa.
3) By fitting both the experimental and calculated volume-pressure data to different equations of state, the Vinet equation of state with B0 = 288 GPa and B' = 5.9(
In this work, we synthesized and characterized mesoporous thin fims
of SiO 2 and NiTiO3 structured by a surfactant called Brij58. These fims
were fabricated by the method of dip coating and the best conditions for
well-structured thin fims were investigated as a function of surfactant
concentration and diffrent types of substrates. These fims have been
characterized by X-ray reflctivity which was calculated using the matrix
formalism. We demonstrated that the silicon substrate had a great effct
on the structure and porosity of the fabricated fims for both SiO2 and
NiTiO3. Furthermore, we found that mesoporosity has been increased
as a function of the surfactant concentration in the solution. This experimental procedure allows also to produce NiTiO3 powders which have
been characterized by X-ray diffaction. The XRD coupled to the crystallographic software “Maud”shows that the samples are constituted by 98,
2% NiTiO 3 powders.
This document discusses the structural, vibrational, and microwave dielectric properties of double perovskite ceramics with the formula Ba2Zn1-xCaxWO6 (x = 0-0.4). The samples were sintered at temperatures between 1300-1400°C and characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The analysis showed that the tolerance factor and temperature coefficient of resonant frequency decreased with increasing calcium content. Microwave dielectric properties such as relative permittivity and quality factor were measured and found to vary with sintering temperature and calcium concentration.
1. The document describes a study on using organosilane nanovessels created via chemical vapor deposition of organosilanes using a polystyrene nanosphere template for crystallizing alkanes at the nanoscale.
2. The nanovessels were found to have an average volume of around 284,000 nm3 and contact angle of 82±6°, and were able to concentrate deposited alkane materials near the vessel structure.
3. Factors investigated included the reaction vessel size, with smaller 100 mL jars producing multilayered nanostructures due to faster heating and higher vapor pressures, while larger 3 L desiccators resulted in monolayer structures. Reaction time studies found rings forming quickly within 10
Highly stable pt–ru nanoparticles supported on three dimensional cubic ordere...tshankar20134
This document describes the synthesis and characterization of Pt-Ru nanoparticles supported on cubic ordered mesoporous carbon (Pt-Ru/CMK-8) and their evaluation as electrocatalysts for methanol oxidation in direct methanol fuel cells. Two types of CMK-8 carbon with different pore sizes were synthesized using two different mesoporous silica templates. Pt-Ru was deposited on the CMK-8 using sodium borohydride reduction. Characterization showed the CMK-8 had high surface areas over 1000 m2/g and pore volumes over 1.26 cm3/g. Electrochemical testing found the Pt-Ru/CMK-8-I catalyst had a high specific mass activity of 487
Deactivation Modeling through Separable Kinetics of Coking On Ni/CZ Catalyst ...IOSR Journals
Abstract : Steam methane reforming (SMR) is a very significant technique to produce hydrogen from fossil fuels. In this particular work, nickel is used as the active metal and ceria-zirconia (CZ) bi-metallic oxide is used as the support. The foremost challenge to this process is sooting or coking over the catalyst surface and blocking the active sites. For the economic viability of the catalyst, it is very significant to make it coke deposition resistant. This is the reason that the kinetic modeling of the deactivation is very important. Therefore, this paper is aimed to model the deactivation and activity of the catalyst. A rate model of the deactivation process is also developed using separable kinetics. A comparison with commercial catalyst is also reported to show that the Ni/CZ catalyst is much more stable towards the coking. Keywords –Coking, Deactivation, Methane, Separable kinetics, Steam reforming.
A simple simulation model for oxidative coupling of methaneAlexander Decker
This document describes a study that developed a mathematical model to simulate the oxidative coupling of methane over a La0.6Sr0.4NiO3 perovskite catalyst. The catalyst was prepared using a reverse microemulsion method and characterized using various techniques. Rate equations were developed based on previous studies of similar catalysts. The model can predict that at temperatures of 925°C or higher, with a methane partial pressure of 0.3 and oxygen partial pressure of 0.1, the catalyst will reach around 10% methane conversion and 50% selectivity to C2+ hydrocarbons.
A simple simulation model for oxidative coupling of methaneAlexander Decker
This document describes a study that developed a mathematical model to simulate the oxidative coupling of methane over a La0.6Sr0.4NiO3 perovskite catalyst. The catalyst was prepared using a reverse microemulsion method and characterized using various techniques. Rate equations were developed based on previous studies of similar catalysts. The model can predict methane conversion and selectivity to C2+ hydrocarbons at temperatures of 925°C or higher with methane and oxygen partial pressures of 0.3 and 0.1, respectively, of around 10% conversion and 50% selectivity.
This document summarizes a study on developing a new method for manufacturing porous hydroxyapatite (HA) implants with designed internal architectures. Key points:
1. A lost-mold technique was used involving negative molds made via stereolithography and a highly loaded curable HA suspension. This allowed implants with designed channel patterns to be successfully built.
2. Characterization showed the designed channels in the sintered HA implants had diameters between 366-968 μm with standard deviations of 50 μm or less and porosities between 26-52%.
3. The new technique provides controlled pore structure compared to traditional methods and could produce implants tailored for specific bone defect sites.
This document summarizes research on electrodepositing silver nanoparticles onto carbon sphere surfaces using a pulse current. Key findings include:
1) Silver nanoparticles were successfully electrodeposited with a size of 100-400nm after 2 minutes using a pulse current.
2) Deposition occurred on accessible carbon surface sites, forming a monolayer of scattered nanoparticles. Continued deposition led to larger particles and multilayers.
3) Pulse current helped manage monolayer deposition compared to direct current, controlling particle size and number of layers.
Potential enhancement of thermoelectric energy conversion in cobaltite superl...Anastasios Englezos
This document is a master's thesis submitted by Tasos Englezos investigating the potential enhancement of thermoelectric energy conversion in cobaltite oxide superlattices. The thesis aims to grow superlattices composed of alternating layers of NaxCoO3 and Ca3Co4O9 using pulsed laser deposition, as both materials show promise for thermoelectric applications but also have limitations. Characterization of the superlattices shows the structures maintain crystalline coherence while electrical and thermal properties are preserved at a good level. Further measurements of thermal conductivity are needed to determine if the superlattice approach reduces thermal conductivity and thereby improves thermoelectric efficiency in these cobaltite oxides.
This document describes the preparation and analysis of mesoporous microspheres of nickel oxide (NiO) for use as a pseudocapacitor material. Mesoporous α-Ni(OH)2 microspheres were first synthesized via a hydrothermal method, then calcined at different temperatures between 250-500°C to produce NiO microspheres. The 250°C NiO sample exhibited the highest specific surface area of 295 m2/g and highest specific capacitance of 1,140 F/g. Characterization of the materials showed the pseudocapacitive behavior was more evident for NiO prepared at higher calcination temperatures. The high surface area and mesoporous structure of the 250°C
Batch adsorption experiments were carried out for
the adsorption of cationic dye from aqueous solution onto
composite activated carbon. The composite activated carbon was
prepared from brewer’s spent grain and sea bean shell at a ratio
of 1:1. The equilibrium studies were done at different
concentrations and temperatures. The equilibrium data were
fitted to Langmuir, Freundlich, Dubinin-Radushkevich, and
Temkin isotherm models. The results showed that both Lagmuir
and Freundlich isotherm model fitted the data reasonably well
but Freundlich isotherm fitted better in the temperature range
studied. This confirmed that the adsorption is heterogeneous,
non-specific and non-uniform in nature. Kinetic studies were also
undertaken in terms of first order, second order, pseudo first
order, pseudo second order, Elovich, Boyd, and intra-particle
diffusion models. The results indicated that the data followed
pseudo second order model with surface adsorption and intraparticle
diffusion concurrently operating during the adsorbateadsorbent
interaction. The values of the thermodynamic
parameters computed from Van’t Hoff plot confirmed the
process to be endothermic and spontaneous in nature.
Similar to Application of micromechanics on alkali activated materials (20)
Design of geopolymers integration of economic & enviromentalTran Nam
This document discusses methods for sustainably designing geopolymers by integrating economic and environmental considerations in the early stages of material development. It presents two multi-criteria decision analysis methods - a compensatory method using weighted indicators and an objectives hierarchy, and a non-compensatory dominance concept - for screening raw material options for geopolymers. 58 raw materials were screened using these methods to select the most promising ones for further evaluation based on technical, economic and environmental criteria. The results demonstrate that introducing life cycle thinking early in material development is possible and that screening is an important step to downselect options without losing valuable alternatives.
Choosing a cement for encapsulation of nuclear wastesTran Nam
(1) Cement formulations are commonly used to encapsulate nuclear wastes due to their low cost, ability to form hardened barriers, and compatibility with remote operations. (2) Ordinary Portland cement (OPC) is often used but can lead to high temperatures, so blended cements with fly ash or blast furnace slag are preferred. (3) Alternative cement systems like alkali-activated materials, calcium sulfoaluminate cements, and geopolymers offer options for encapsulating reactive wastes while reducing issues like corrosion and leaching. (4) A "toolbox" approach using the appropriate cement system based on waste chemistry can provide durable solidification of nuclear wastes.
This document summarizes research on geopolymer materials as an alternative to traditional cement. Geopolymers are inorganic polymers synthesized from an aluminosilicate source and alkaline silicate solution at low temperatures, producing a hard, strong material similar to cement but with lower CO2 emissions. The research focuses on characterizing local aluminosilicate sources for geopolymers and investigating their properties. Challenges include controlling setting times and understanding how processing affects strength. Future work will develop geopolymer composite materials and evaluate long-term durability.
Applications of geopolymer technology to waste stabilizationTran Nam
Douglas C. Comrie and colleagues conducted research on using geopolymers to stabilize hazardous wastes. Geopolymers are inorganic binders that solidify wastes into a hard material with high compressive strength. Testing showed geopolymers greatly reduced metal leaching from contaminated soils and wastes, meeting regulatory standards. The research demonstrates geopolymers are effective for both chemically stabilizing wastes and physically encapsulating wastes to isolate them from the environment.
Aluminosilicate polymers influence of elevated temperatures, efflorescenceTran Nam
1) The document discusses the properties of aluminosilicate polymers (ASPs) made from fly ash activated with an alkaline solution.
2) It finds that ASPs have maximum strength when fired at 200°C but strength declines at higher temperatures. Firing above 600°C significantly reduces sodium leaching and efflorescence formation.
3) Sodium is weakly bonded in the ASP structure as Na(H2O)n+ rather than Na+, explaining the material's tendency to efflorescence in humid environments. Firing transforms the sodium bond and greatly reduces leaching.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
Portland cements are hydraulic cements composed primarily of hydraulic calcium silicates. Different types of portland cement are manufactured to meet various requirements for specific purposes. Type I portland cement is a general purpose cement suitable for all uses. Type II cement has moderate sulfate resistance properties and is used where precaution against moderate sulfate attack is important, such as in structures exposed to soil or groundwaters containing higher sulfate concentrations. Portland cement is manufactured through a process involving quarrying and crushing raw materials, blending them into the correct proportions, firing the raw mix in a kiln to produce clinker, cooling and grinding the clinker with gypsum to produce the final cement powder.
This document discusses mineral admixtures used in concrete, including fly ash, blast furnace slag, silica fume, and metakaolin. It provides details on the production, physical and chemical properties, and effects on fresh and hardened concrete of each admixture. For fly ash specifically, it describes the combustion process that produces fly ash, its physical characteristics such as particle size and shape, methods for measuring fineness and specific surface, typical chemical compositions, and influence on properties of concrete such as setting time, workability and strength.
Application of micromechanics on alkali activated materials
1. Application of Micromechanics on Alkali-activated Materials
Vít Šmilauer1, a
, František Škvára2, b
, Jiří Němeček1, c
, Lubomír Kopecký1, d
,
Petr Hlaváček1, e
1
Czech Technical University in Prague, Faculty of Civil Engineering, Department of Mechanics,
Thákurova 7, 166 29 Prague, Czech Republic
2
Institute of Chemical Technology Prague, Department of Glass and Ceramics,
Technická 5, 166 28 Prague, Czech Republic
a
vit.smilauer@fsv.cvut.cz, b
frantisek.skvara@vscht.cz, c
jiri.nemecek@fsv.cvut.cz,
d
kopecky@fsv.cvut.cz, e
petr.hlavacek.1@fsv.cvut.cz
Keywords: Nanoindentation, N-A-S-H gel, fly ash, metakaolin, micromechanics, elasticity,
homogenization
Abstract. Research of alkali-activated materials has been a traditional domain of chemists. This
paper exploits contribution of micromechanics to the subject. Alkali-activation of the fly-ash is
perceived as the volumetric evolution of elastically-invariant components. Nanoindentation
technique identified the intrinsic Young's modulus of N-A-S-H gel as ~18 GPa, which was further
downscaled to the solid gel particles. Percolation theory applied to N-A-S-H gel was introduced to
cover an early-age elasticity. Combination of the two-scale elastic homogenization method,
percolation theory and intrinsic elastic properties of components show a good reproduction of
experimental data obtained from the macroscale. Homogenization model also demonstrates the
stiffening of N-A-S-H gel, induced by increased packing of the solid gel particles.
Introduction
A group of alkali-activated aluminosilicate materials draws the attention of researchers
worldwide, see [1,2] for a comprehensive review. In comparison with conventional Portland
cement-based composites, these materials generally exhibit excellent durability, fire-resistance, but
may suffer from efflorescense, shrinkage, cumbersome quality control or mastering the technology
[3,4].
In the past, various raw materials (slag, fly-ash, metakaolin, clay) were intermixed with strong
alkaline solutions to synthesize a poorly crystallized inorganic gel binder [5]. Coined nomenclatures
such as “soil cement” [6], “geopolymer” [7] or “inorganic polymer” [2] have characterized more or
less similar dissolution-precipitation processes taking place in a strong alkaline environment due to
different starting materials. Here, the term N-A-S-H gel (aluminosilicate gel) will describe a
binding matrix phase, embedding undissolved inclusions of a remaining raw material.
In the past, alkali-activated materials were characterized by a variety of experimental techniques
including FTIR, ESEM, MAS-NMR, XRD, DTA or calorimetry [4,5]. The majority of experimental
data were linked directly to the atomic scale and nanostructure of N-A-S-H gel. However, all the
above mentioned techniques suffer from data downscaling by several orders of magnitude to the
nanostructure of N-A-S-H gel. In this sense, a traditional chemical description of alkali-activated
materials may be enriched with micromechanics, as proven successfully for the description of
Portland-based materials [8,9].
Micromechanical elastic analysis stems from the definition of intrinsic elastic properties of
constituents. These are considered to remain independent on ongoing chemical reactions with
possible evolution of volume fractions during the alkali-activation. Nanoindentation sensing
1
2. technique enables direct characterization of intrinsic mechanical properties on the micrometer and
submicrometer resolution. The response is obtained directly from a close vicinity of a small indent
without the interaction of distant material. Such measurements have never been performed
systematically in this field, although a few attempts can be found [10].
This paper aims at interconnecting chemical and mechanical disciplines. First, intrinsic elastic
properties are identified from alkali-activated fly ash (AAFA) and alkali-activated metakaolin
(AAMK). Second, a new volumetric model of alkali activation is formulated. Third, two-scale
elastic homogenization combined with percolation upscales the intrinsic properties to the
macrospopic scale.
Materials, Alkali-activation and Curing
The raw fly ash (RFA) was produced in Chvaletice thermal electric power plant, Czech
Republic, with the Blaine specific surface 210 m2
kg-1
. For nanoindentation, RFA was ground in a
small-scale ball mill in the quantity of 8 kg for 180 minutes to crush cenospheres in order to reduce
the porosity. Metakaolin originated from České lupkové závody a.s., Nové Strašecí, Czech
Republic. Chemical compositions of both materials are summarized in Table 1.
Table 1. Chemical composition of fly ash and metakaolin, wt. %.
SiO2 Al2O3 Fe2O3 CaO TiO2 K2O
Fly ash 51.9 32.8 6.3 2.7 1.89 2.12
Metakaolin 48.66 47.41 1.33 0.03 1.99 0.15
The alkali-activator was previously optimized to yield a high compressive strength while
maintaining workability [4]. The activator was prepared by dissolving NaOH pellets in tap water
and adding sodium waterglass. Table 2 summarizes the compositions of the mixtures. The final
properties of the mixture can be controlled by three independent parameters, see Table 2.
Metakaolin requires significantly more activator due to its higher surface area to maintain a
reasonable workability.
Table 2. Composition of alkaline activators and ratii to the activated material.
Activator ratii Activator to solid ratio (wt. %)
Na2O / SiO2 (wt. %) H2O / Na2O (wt. %)
Ground fly ash 0.881 3.925 0.531
Metakaolin 1.669 2.743 1.416
Fly ash or metakaolin was intermixed with the activator for 5 minutes, cast in plastic ampules,
26 mm in diameter and 45 mm in height, gently vibrated for 5 minutes and sealed. Heat-cured fly
ash or metakaolin samples were exposed to 80o
C for 12 hours. Ambient-cured fly ash experienced a
laboratory temperature, approx. 25o
C, for the duration of six months prior to nanoindentation
testing. Both materials are considered to be mature, although polymerization and hardening will
never stop as known from C-S-H aging [11]. After a half-year from casting, the compressive
strength of AAFA samples exceeded 70 MPa and 50 MPa of AAMK.
Methods
Nanoindentation. Activated samples were cut to parallel slices of approx. 10 mm in thickness,
polished on fine emery papers and polishing cloth, and cleaned in an ultrasonic bath.
2
3. Nanoindentation was carried out in a series of grids of 10 x 10 = 100 imprints in three
representative areas. The distance between individual indents varied between 10 and 50 um.
Nanoindentation measurements were performed in a load control regime using the CSM
Nanohardness tester equipped with a Berkovich tip. The trapezoidal loading diagram was
prescribed for all tests with linear loading of 4 mN/min and lasting for 30 s, which produced a
maximum load of 2 mN for all indents. Peak load of 2 mN led to maximum penetration depths
ranging from 100 nm to 400 nm. Fig. 1 shows a typical force/penetration diagram for three
identified material phases.
Figure 1. A typical nanoindentation diagram for alkali-activated fly ash.
The effective depth captured by the tip of the nanoindenter can be roughly estimated as three to
four times of the penetration depth for the Berkovich indentor [12]. It yields the effective depth of
around 1 um from which the elasticity is obtained.
Determination of Open Porosity. Cylindrical samples (diameter 25 mm, thickness 5 mm) of a
well-defined geometry were dried out in an oven at 105o
C. Samples remained in the oven
environment until the weight loss stabilized, which took from 3 to 6 days. Known skeletal density
of fly ash from He pycnometry, known skeletal density of activate fly ash and known sample
volume led to quantification of the open porosity. The open porosity was determined from three
samples and the experiments were repeated during ambient curing of alkali-activated materials to
access the evolution of open porosity.
Results and Discussion
Degree of Reaction. The degree of reaction, DoR, is defined as the amount of consumed fly ash
in the alkali-activation process. Direct simulation of DoR from a known chemical composition is
beyond capabilities of presented models, which do not include reaction kinetics. Instead, the
evolution of DoR is taken from experimental data of Fernández-Jiménez et al. [13] who measured a
progress of reaction degree on AAFA samples activated with 8 M NaOH solution and cured at
85o
C. The extent of DoR was determined by an acid attack with HCl 1:20. Similar results were
observed on calorimetry data, which revealed that the ratio activator/fly-ash is insignificant for the
DoR and that a maximum reaction rate occurs at 8-10 minutes after the contact, ending up to 2
hours at elevated temperatures [14].
Arrhenius equation is utilized to recalculate DoR for various constant temperatures of curing.
For example, the time scaling from 60o
C to 20o
C means a slow down 70-times. The Arrhenius
equation reads
3
4. , (1)
where the activation energy was found 86.2 kJ/mol [4]. The transition from 85o
C to 25o
C predicts
the scaling factor 340. Fig. 2 shows the DoR evolution at 25o
C, recalculated from [13].
Figure 2. Progress of DoR for alkali-activated fly ash by 8M NaOH. The evolution of DoR is showed at a reference
temperature of 25o
C. Original data gathered at 85o
C came from [13].
Porosity and ESEM. AAFA and AAMK samples were crushed to the size of a few millimeters,
dried at 105o
C for 6 hours and intruded by mercury (MIP, Autopore III Micromeritics) or measured
by He-pycnometry (Micromeritics AccuPyc 1330). The combination of MIP and He pycnometry
allowed estimating the “total” porosity from bulk and skeletal densities. The porosity captures the
range from a helium atom (d=0.062 nm) from the bottom range and the limit of MIP from the top
(d=120 um). The pore size distribution obtained from MIP and He pycnometry is depicted in
Fig. 3; for ordinary Portland cement paste and for alkali-activated samples.
Figure 3. Cumulative pore volume by MIP and He pycnometry. OPC paste cured at 60o
C for three months (left) and
alkali-activated materials (right). An asterisk denotes the total volume derived from from the size of a helium atom.
Fig. 4 shows BSE images of AAFA cured under ambient and heat conditions.
4
5. Figure 4. BSE images of AAFA cured under ambient conditions (left) and cured at 80o
C for 12 hours (right).
Identification of N-A-S-H gel's elastic properties and a solid gel particles. Indentation
moduli from 700 locations were gathered and recalculated to Young's moduli. The moduli were
processed statistically to a histogram. Fig. 5 shows the histogram with a deconvolution to four
Gaussian distributions. Deconvolution is generally an ill-posed problem and many solutions exists,
however, the peak for N-A-S-H is clearly and unambiguously defined. Other phases are
hypothesized to present partly-activated slag and unreacted material.
Figure 5. Overall experimental and theoretical probability density functions with segmented four phases in ambient-
cured AAFA samples. Peak are hypothesized to mean A - N-A-S-H gel, B - Partly-activated slag, C - Nonactivated
slag, D - Nonactivated compact glass.
Deconvolution for heat-cured AAFA and AAMK samples yielded similar Young's moduli for
N-A-S-H gel. Table 3 summarizes N-A-S-H gel moduli together with corresponding volume
fraction from the histogram. Volume fraction of N-A-S-H gel in the heat-cured AAFA is lower due
to significant presence of peak B (not showed). Coincidence of the same moduli among different
alkali-activated materials and curing procedures proves the same intrinsic elastic properties of
N-A-S-H gel, irrespective of its origin.
Table 3. Elastic moduli of N-A-S-H gel synthesized from different precursors.
Ambient-cured AAFA Heat-cured AAFA Heat-cured AAMK
Young's modulus of N-A-S-H gel 17.72 ± 3.75 GPa 17.03 ± 3.48 GPa 17.72 ± 4.43 GPa
Volume fraction from histogram 77.50% 50.70% 97.20%
The histogram in Fig. 5 shows no porosity, which should be at least 30 % according to Fig. 3. As
evident from Fig. 3, nanoindentation imprint is much larger than a fine porosity, which is scattered
within a sample. A minor part of porosity is apparently present in the fly ash (cenospheres,
plerospheres) and the major part inside the N-A-S-H gel.
Any sol-gel system consists of solid particles dispersed in a liquid [15]. Sol-gel is far from
equilibrium and solid particles may aggregate into clusters. If condensation reaction in the system
exists and is irreversible, more and more solid particles appear in the system and grow into fractals
[15]. Linking of clusters continues until they reach a percolation threshold signalized by a sudden
change of many properties such as elasticity.
5
6. C-S-H gel in rather a precipitate than a gel due to the presence of capillary pores and inability to
fill uniformly the space. Reversible condensation reaction dominates C-S-H solidification [15].
Another consequence of reversibility is a constant 28% porosity of the C-S-H gel, irrespective of an
origin or time under normal curing condition [16]. The constant porosity allowed to consider C-S-H
gel as one phase from a micromechanical point of view; solid particles intermixed with the porosity
at the same fraction.
N-A-S-H is a true gel which fills out all available volume. Gel syneresis has been observed many
times in alkali-activated materials; excessive shrinkage accompanied with a strong sample
disintegration might have occurred under the sealed conditions. Due to a true gel nature, no
constant gel porosity, as in the C-S-H, exists and the micromechanical response needs to be
determined from the solid gel particles. The intrinsic elastic properties of the particles are carried
out by a downscaling process. Knowing the elasticity of the N-A-S-H gel and the amount of
porosity, one may determine unknown intrinsic elasticity of the solid gel particles.
Volumetric Model for Alkali-activation. Volumetric model for alkali-activation presents a
stepping stone for the micromechanical analysis. Much inspiration has been gathered from Portland
cement, starting from maturity method [17] and continuing through a famous research carried out
by Powers and Brownyard [16]. Fig. 6 shows volumetric plots for both Portland cement and alkali-
activated fly-ash. Four chemically and mechanically distinctive phases needed to be identified and
described in the alkali-activated fly ash.
Figure 6. Comparison between famous Powers' model for hydrating Portland cement and a newly proposed model for
alkali activation of fly ash.
VFA
Skel
represents the volume fraction fly-ash skeleton. Voids persisting in the fly-ash after the
mixing are quantified with VFA
Voids
. It must be noted that after a few minutes during the mixing, the
activator efficiently destroys a thin shell of plerospheres and opens their porosity. This is
manifested by a partial loss of workability and heat release in isothermal calorimetry. Voids in the
fly ash were obtained from the combination of known skeletal density of fly ash, density of
activating solution and measured volume and weight of mixture immediately after the mixing
process.
VSGP is the volume fraction of solid gel particles. The term “N-A-S-H gel” is intentionally
unused due to the gel composition from solid and liquid parts. No characteristic gel porosity exist,
hence the gel could be treated as the activator plus the solid gel particles. Volume of open
porosity,VOP, describes conveniently a part of accessible porosity by external water. The activator
fills up the major part of open porosity.
6
7. Degree of reaction (DoR) presents a microstructural parameter, which describes the alkali-
activation progress of the fly ash. Expressing all reactions in terms of DoR is more convenient
against time for two reasons:
•Circumventing a logarithmic time scale, needed for a proper plot.
•Mutual comparison for samples cured at various temperatures.
No fly ash becomes activated and consumed at DoR = 0.0, while a complete activation occurs at
DoR = 1.0. To build a simple conceptual model describing basic phenomena, several assumptions
of the volumetric model had to be made:
•The whole activator is treated in the form of evaporable water, disregarding a small solid part
remaining after drying. Under saturation, open porosity is filled with evaporable water.
•No chemical shrinkage/expansion occurs so that the volumetric balance of all liquid and solid
phases is maintained during the activation progress.
•All reactions are time-independent and depend only on DoR. Such simplification neglects
separate contribution of dissolution, precipitation and aging of N-A-S-H gel.
(2)
(3)
(4)
(5)
Parameters for Eq. 2 – Eq. 5 had to be obtained experimentally. The section Methods describes
the assessment of open porosity in the AAFA. VFA
Voids
disappear roughly at the DoR=0.5. Table 4
summarizes fitted parameters for the volumetric model. This conclusion is supported with isooctane
saturation of dried-out samples. The method is described in [18] and is not showed.
Table 4. Fitted parameters for the volumetric model of alkali-activation.
Parameter Fitted value, see Fig. 5
VFA
Skel
(0) 0.58
VFA
Voids
(0)
0.06
VOP (0) 0.36
alpha 0.2
beta 0.12
Downscaling and two-scale homogenization. Elastic properties of the solid gel particles were
obtained by means of a downscaling process. Characterization of N-A-S-H gel by nanoindentation
was considered to occur at DoR = 0.44, which gives the volume fractions summarized in Table 5.
Table 5. Volumetric fractions at DoR = 0.44 and elastic properties of constituents.
Parameter Volume fraction
[-]
Young's modulus
[GPa]
Poisson's ratio
[-]
VFA
Skel
(0.44) 0.324 104.0 0.20
VFA
Voids
(0.44)
0.001 0.001 0.001
7
8. VEW (0.44) 0.325 0.001 0.499924
VSGP (0.44) 0.350 38.2-49.8-59.5a
0.22-0.23-0.24a
Sum 1.000
a
) Three values stem from a standard deviation of N-A-S-H gel indentation moduli.
First, the solid gel particles and evaporable water were considered to form the N-A-S-H gel.
Volumetric fraction of the above-mentioned phases are 0.5185 and 0.485, respectively. Mori-
Tanaka scheme for an isotropic spherical inclusion [19] run with the reference phase of the gel
particles and identified elastic properties of them, see Table 5. Standard deviation of indentation
moduli obtained for the N-A-S-H gel, 17.72 ± 3.75 GPa, see Table 3, led to the variation of elastic
properties of the solid gel particles.
Second, elastic properties of AAFA constituents were connected with the volumetric model for
alkali-activation. Two-level elastic homogenization seemed to give reasonable results. In the first
level, elastic properties of the N-A-S-H gel, composed from the solid gel particles and evaporable
water in the open porosity, were obtained using Mori-Tanaka method with the reference phase of
the solid gel particles. The second level homogenized the gel, fly ash and voids in the fly ash, by
repeating the Mori-Tanaka method with the reference phase of N-A-S-H gel.
Fig. 7 summarizes the results from two-scale homogenization at the level of AAFA.
Experimental data came from a non-destructive measurement by cyclic loading. The load level
attained approximately 0.3 of ultimate load and the load was applied uniaxially on prismatic
samples 40x40x160 mm, equipped with a set of extensometers to control bending induced by the
load eccentricity.
Homogenization solely by Mori-Tanaka method shows a big discrepancy in the beginning of
alkali-activation process. The reason lies in percolation properties of true N-A-S-H gel. Until a
certain point called a percolation threshold, the solid gel particles are mutually separated although
the volumetric model predicts their presence. The assumption of perfect bonding, on which the
homogenization methods are based, is violated at this stage. Percolation problems are known to
occur in early ages of hydration in the system of Portland cement paste [9]. Introducing the
percolation function in the form
p = (DoR – DoRp), (6)
allowed to introduce the percolation threshold DoRp, from which the N-A-S-H gel's modulus
becomes non-zero. The Young modulus from the N-A-S-H gel is multiplied with the Eq. 6.
Calibration to the experimental data yielded DoRp=0.335 and also set the upper limit DoR = 0.405,
above which percolation plays no role and sets p = 1.
The thick line in Fig. 7 shows the elastic prediction in terms of average AAFA's modulus.
Introducing the scatter in the solid gel particles leads to widening the range of validity and seems to
cover almost all experimental points. In addition, self-consistent scheme in Fig. 7 demonstrates that
intrinsic percolation threshold associated with the scheme is in reasonable correlation with
experimental data. However, later elastic properties via the self-consistent scheme would be
seriously underestimated, which denies its application.
8
9. Figure 7. Homogenized elastic properties of alkali-activated fly ash combining the volumetric model, Mori-Tanaka
homogenization method and the percolation theory.
Fig. 8 shows elastic results from the first level of N-A-S-H gel. The percolation function gives a
negligible elasticity when DoRp<0.335. At the percolation threshold, the volume fraction of the
solid gel particles are VSGP=0.2613 and of open porosity VOP=0.3332. It means that the percolation
threshold occurs when the solid gel particles poses a relative volume 0.4395. Rintoul and Torquato
[20] performed an extensive numerical study in the system of identical (monodisperse) overlapping
spheres, resulting in the percolation threshold 0.2895±0.0005. The percolation threshold changes
when a particle size distribution is taken into account. Two distinct sphere diameters were found to
have the percolation threshold as high as 0.70 [21].
Note that the N-A-S-H gel is still stiffening due to increasing fraction of solid gel particles. The
presented model, based on a packing density of the solid gel particles, does not address changes
within the particle, which may occur due to the polymerization on atomistic scale.
Figure 8. Evolution of Young's modulus within the N-A-S-H gel. Results from the volumetric model, Mori-Tanaka
homogenization method and percolation theory.
Conclusions
9
10. The combination of nanoindentation, micromechanical modeling and volumetric model provides
a different point of view on alkali-activated materials, particularly those made from the fly ash. The
N-A-S-H gel is a true gel and the early elastic behavior can be conveniently described with the
percolation theory. The models explain several phenomena occurring during the hardening and
clarify why the hardening occurs within many days at ambient curing temperature and why the
initial and final setting time lay so much far apart. A heat-curing process seems to be a necessity for
the production of these materials on a large scale.
The Young's modulus of the N-A-S-H gel (~18 GPa) is quite similar to C-S-H gels (21.7-
29.4 GPa) [12]. Beyond the point of chemical compatibility, these gels can also coexist well
together from the micromechanical perspective and match of the elastic moduli.
Acknowledgement
Authors gratefully acknowledge the financial support from the Czech Science Foundation, grant
103/08/1639 “Microstructure of inorganic aluminosilicate polymers”.
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