Quasi-aligned aluminum nitride (AlN) nanofibers were formed through a nitriding combustion synthesis reaction using aluminum and aluminum nitride powders with yttria and ammonium chloride additives. Scanning electron microscope images showed the aluminum particles maintained their original ball-like shape after combustion, with a thin crust layer on the surface covering quasi-aligned AlN nanofibers grown in the interior. This novel morphology is believed to form through a two-stage process where the crust acts as a micro-reactor allowing nitridation and fiber growth inside the molten aluminum core.
1) The study examines the corrosion behavior of electrodeposited Ni-Al composite coating containing 1μm aluminum particles in 3.5% NaCl + 0.05 M H2SO4 solution.
2) Open circuit potential measurements showed the aluminum particles shifted the Ni corrosion potential to more negative values. Potentiodynamic polarization tests revealed the aluminum particles increased the corrosion rate of the Ni coating by enhancing both the cathodic and anodic reactions.
3) XPS characterization confirmed the aluminum corrosion products were highly soluble in the test solution. This disturbed the formation of a continuous protective nickel corrosion product layer, as shown by SEM analysis.
This document describes a study that investigated various techniques for preparing a nickel oxide (NiO) catalyst coating on an FeCrAl substrate for use in catalytic converters. Specifically, it examined applying nickel to the substrate through electroplating with and without ultrasonic treatment, and then oxidizing the nickel to form a NiO layer. The techniques aimed to develop an innovative and simpler method for adhering catalyst powder to the substrate. The study assessed the techniques based on weight gain during oxidation testing and analyzed the resulting oxide growth and microstructure.
The document characterizes the electrochemical corrosion behavior of a Ni-28wt.%Al composite coating compared to a pure Ni coating after 24 and 72 hours of immersion in 3.5% NaCl solution. Open circuit potential and polarization tests showed that the Al particles in the composite shifted the potential more negatively and increased the anodic dissolution rate after 24 hours compared to pure Ni. However, after 72 hours the composite exhibited lower anodic current density and slightly higher cathodic current than pure Ni. XPS analysis indicated the composite surface rapidly formed a protective Ni(OH)2 layer that thickened over time and became enriched with the highly corrosion resistant Al2O3, decreasing the corrosion rate and susceptibility to pitting for the composite
This document summarizes the synthesis, characterization, and properties of nickel ferrite (NiFe3O4) nanoparticles. Nickel ferrite was synthesized using a sol-gel technique and sintered at 600°C. X-ray diffraction analysis confirmed the formation of nickel ferrite and showed structural changes due to ion shifting between lattice sites. Scanning electron microscopy images showed agglomerated, porous nanoparticles with an average size of 0.21μm. AC conductivity measurements showed a conductivity of 1.0 x 10-4 S/cm due to dipole polarization. Dielectric properties were also measured as a function of frequency.
This document analyzes the hot corrosion behavior of laser melted GP1 stainless steel powder when exposed to a molten chloride and sulphide environment. The study found that the corrosion followed a parabolic rate law, with higher corrosion rates initially. Surface examination revealed pitting and scaling. Phase analysis identified oxides like Fe2O3 and Cr2O3 as well as other reaction products like NiFe2O4 and NiCr2O4, indicating the material underwent oxidation, chloridation and sulphidation during exposure. The results provide insight into corrosion mechanisms during additive manufacturing processes involving laser powder melting.
The document describes a novel method for growing aluminium nitride (AlN) whiskers through the direct nitridation of an Al-NH4Cl mixture. NH4Cl promotes the growth of AlN whiskers through a vapor-phase reaction mechanism rather than the normal liquid-gas mechanism. Thermodynamic analysis confirms that AlN whiskers can grow via spontaneous chlorination-nitridation reactions in the vapor phase. The addition of NH4Cl not only enhances the nitridation reaction but also enables the production of homogeneous AlN nanowhiskers less than 150 nm in diameter.
The document summarizes a study on increasing the salt fog corrosion resistance of plasma nitrided AISI 4340 steel through a pulsed plasma post-oxidation process. Key findings:
1) Post-oxidation treatment produces an oxidized layer on the nitrided surface that fills and seals pores, improving corrosion resistance.
2) Samples post-oxidized for 15 minutes showed the best corrosion performance when exposed to salt fog, with only 1/16 as much red rust as nitrided samples alone.
3) X-ray diffraction analysis found the oxidized layer consisted mainly of magnetite iron oxide, which provides high corrosion resistance.
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.
1) The study examines the corrosion behavior of electrodeposited Ni-Al composite coating containing 1μm aluminum particles in 3.5% NaCl + 0.05 M H2SO4 solution.
2) Open circuit potential measurements showed the aluminum particles shifted the Ni corrosion potential to more negative values. Potentiodynamic polarization tests revealed the aluminum particles increased the corrosion rate of the Ni coating by enhancing both the cathodic and anodic reactions.
3) XPS characterization confirmed the aluminum corrosion products were highly soluble in the test solution. This disturbed the formation of a continuous protective nickel corrosion product layer, as shown by SEM analysis.
This document describes a study that investigated various techniques for preparing a nickel oxide (NiO) catalyst coating on an FeCrAl substrate for use in catalytic converters. Specifically, it examined applying nickel to the substrate through electroplating with and without ultrasonic treatment, and then oxidizing the nickel to form a NiO layer. The techniques aimed to develop an innovative and simpler method for adhering catalyst powder to the substrate. The study assessed the techniques based on weight gain during oxidation testing and analyzed the resulting oxide growth and microstructure.
The document characterizes the electrochemical corrosion behavior of a Ni-28wt.%Al composite coating compared to a pure Ni coating after 24 and 72 hours of immersion in 3.5% NaCl solution. Open circuit potential and polarization tests showed that the Al particles in the composite shifted the potential more negatively and increased the anodic dissolution rate after 24 hours compared to pure Ni. However, after 72 hours the composite exhibited lower anodic current density and slightly higher cathodic current than pure Ni. XPS analysis indicated the composite surface rapidly formed a protective Ni(OH)2 layer that thickened over time and became enriched with the highly corrosion resistant Al2O3, decreasing the corrosion rate and susceptibility to pitting for the composite
This document summarizes the synthesis, characterization, and properties of nickel ferrite (NiFe3O4) nanoparticles. Nickel ferrite was synthesized using a sol-gel technique and sintered at 600°C. X-ray diffraction analysis confirmed the formation of nickel ferrite and showed structural changes due to ion shifting between lattice sites. Scanning electron microscopy images showed agglomerated, porous nanoparticles with an average size of 0.21μm. AC conductivity measurements showed a conductivity of 1.0 x 10-4 S/cm due to dipole polarization. Dielectric properties were also measured as a function of frequency.
This document analyzes the hot corrosion behavior of laser melted GP1 stainless steel powder when exposed to a molten chloride and sulphide environment. The study found that the corrosion followed a parabolic rate law, with higher corrosion rates initially. Surface examination revealed pitting and scaling. Phase analysis identified oxides like Fe2O3 and Cr2O3 as well as other reaction products like NiFe2O4 and NiCr2O4, indicating the material underwent oxidation, chloridation and sulphidation during exposure. The results provide insight into corrosion mechanisms during additive manufacturing processes involving laser powder melting.
The document describes a novel method for growing aluminium nitride (AlN) whiskers through the direct nitridation of an Al-NH4Cl mixture. NH4Cl promotes the growth of AlN whiskers through a vapor-phase reaction mechanism rather than the normal liquid-gas mechanism. Thermodynamic analysis confirms that AlN whiskers can grow via spontaneous chlorination-nitridation reactions in the vapor phase. The addition of NH4Cl not only enhances the nitridation reaction but also enables the production of homogeneous AlN nanowhiskers less than 150 nm in diameter.
The document summarizes a study on increasing the salt fog corrosion resistance of plasma nitrided AISI 4340 steel through a pulsed plasma post-oxidation process. Key findings:
1) Post-oxidation treatment produces an oxidized layer on the nitrided surface that fills and seals pores, improving corrosion resistance.
2) Samples post-oxidized for 15 minutes showed the best corrosion performance when exposed to salt fog, with only 1/16 as much red rust as nitrided samples alone.
3) X-ray diffraction analysis found the oxidized layer consisted mainly of magnetite iron oxide, which provides high corrosion resistance.
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.
Synthesis, Characterization and Phase Transition of Highly Porous γ - Alumina...AnuragSingh1049
Alumina is an important metal oxide used in a
wide range of applications. It is a challenge to synthesize
stable γ-alumina nanoparticles because; γ-phase of alumina
is not as stable as α phase of alumina. But γ-alumina owns a
higher surface area making it a good candidate for many
industrial applications such as catalyst, catalytic support for
petroleum refining, absorbent, alcohol dehydration,
catalytic reduction of automotive pollutants like NOx, CO
and hydrocarbons. This research focuses on synthesis,
characterization and study of phase identification of pure γ-
alumina nanoparticles.
Modified “Pechini method” (Danks, Hall, and
Schnepp (2016); Huízar-Félix, Hernández, de la Parra,
Ibarra, & Kharisov, 2012; Naskar, 2010; Zaki, Kabel, &
Hassan, 2012) was used for the synthesis. Transesterification
of citrate and ethylene glycol makes a covalent polymer
network with trapped Al atoms. Continuous stirring of the
reaction mixture while maintaining an optimum
temperature is an important factor affecting this reaction.
Calcination was carried out at different temperatures to
identify phase transitions of alumina nanoparticles. In order
to further reduce the particle size and increase the surface
area, reactant ratio of citric acid: aluminum acetate was
modified to 1:1, volume of ethylene glycol was increased up
to 90% of volume of the solution and Triton X was used as a
surfactant.
PXRD confirmed the pure γ-alumina phase
(JCPDS No. 00-010-0425) in samples calcined at 900 °C. At
1000 °C γ-alumina is conve+rted to α-alumina (JCPDS No.
00-083-2080). After the modifications, γ-alumina was
identified at 700 °C. FTIR-ATR analysis shows peaks
around 1127 cm-1
indicating the presence of Al-O-Al
asymmetric bending modes and the peaks around 500 cm-
1
-
750 cm-1
correspond to γ-AlO6 octahedral sites and 800 cm-1
correspond to AlO4 tetrahedral sites in γ alumina spinel
structure. Resulted product of low temperature, pure γ-
alumina nanoparticles will facilitate the industrial
development in various applications.
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.
The document summarizes a study that investigated the corrosion behavior of annealed 2205 duplex stainless steel in sulphuric acid environments. Potentiodynamic polarization tests were conducted on annealed and untreated 2205 duplex stainless steel samples in 0.1M and 3M sulphuric acid. The results showed that the annealed samples exhibited lower corrosion resistance than the untreated samples in both acid environments, indicating that annealing heat treatment reduces the corrosion resistance of 2205 duplex stainless steel in sulphuric acid.
The document discusses MOCVD (Metalorganic Chemical Vapor Deposition) technology and material growth. It covers the MOCVD growth system, common metalorganic compounds used as sources, gas phase and surface reactions during growth, characterization techniques for analyzing materials, and some issues related to growing GaN and related materials by MOCVD.
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.
1991_Sensitivity to Iron Impurity Content of Corrosion Rate of Mg-15Al_Cotton...James D. Cotton
The corrosion rates of extrusions produced from rapidly-solidified Mg-15wt%AI alloy powder containing varying levels of iron (Fe) impurity (0.003-0.020wt%) were studied. Trace amounts of Fe were found to have a strong exponential effect on the corrosion rate, consistent with previous studies. However, the sensitivity to Fe content was markedly lower for the rapidly-solidified alloys compared to conventionally-cast alloys. This effect is explained by the microstructural refinement produced by rapid solidification, which decreases the scale of microstructure and distributes corrosion more evenly. Both pitting and filiform corrosion were observed and characterized using various microscopy techniques.
Surfactant-assisted Hydrothermal Synthesis of Ceria-Zirconia Nanostructured M...IOSR Journals
CeO2–ZrO2 oxides were prepared by the surfactant-templated method using cetyl trimethyl ammonium bromide (CTAB) as template and modified with chromium nitrate. These were characterized by XRD, FT-IR, TEM, SEM, BET and TPD-CO2. The XRD data showed that as prepared CeO2-ZrO2 powder particles have single phase cubic fluorite structure. HRTEM shows mesoscopic ordering. Average particle size is 12-13 nm as calculated from particle histogram. The nitrogen adsorption/desorption isotherm were classified to be type IV isotherm, typical of mesoporous material. The presence of uni-modal mesopores are confirmed by the pore size distribution which shows pore distribution at around 60 A°. Catalytic activity was studied towards liquid-phase oxidation of benzene.
This document summarizes research on the thermal properties of green alumina porcelain. Thermal conductivity, diffusivity, density, and specific heat were measured on samples fired from 100-1320°C using transient plane source methods. Differential thermal analysis, thermogravimetry, and thermodilatometry were also performed to study structural changes during firing. Dehydroxylation of kaolinite occurred around 580°C, while crystallization of spinel happened at around 975°C. After sintering was complete, thermal conductivity increased by 700% and thermal diffusivity rose by 400% compared to the green material.
1) The study examined the electrochemical characteristics of an ultra-fine grain γ/–Ni3Al coating after exposure to 3.5% NaCl solution, using various electrochemical techniques.
2) The ultra-fine grain γ/–Ni3Al coating was fabricated by annealing an electrodeposited Ni-Al composite at 600°C for 1 hour, resulting in a refined microstructure.
3) Testing found the ultra-fine grain γ/–Ni3Al exhibited a more positive corrosion potential and lower corrosion current density compared to an arc-melted γ/–Ni3Al alloy. This was attributed to the refined microstructure of the ultra-fine grain coating promoting a faster formation of a protective
Graphene oxide was synthesized from graphite powder and functionalized with ethanolamine to produce GO-EA. GO-EA was successfully redispersed in an ethylene glycol solution. X-ray photoelectron spectroscopy analysis showed the expected functional groups on GO and the appearance of new peaks indicating successful functionalization of GO-EA. Future work will verify the increased thermal conductivity of the solution and explore GO-EA's catalytic properties.
Effect of Adding Indium on Wetting Behavior, Microstructure and Physical Prop...Editor IJCATR
Effect of adding indium on microstructure, wetting process, thermal, electrical and mechanical properties of tin- zinc eutectic alloy have been investigated. Microstructure (started base line, lattice parameters, unit cell volume, crystal size and the shape of formed crystalline phases) and measured physical properties of tin- zinc eutectic alloy changed after adding different ratio of indium content. A little variation occurred in thermo-graph (Endo-thermal peaks) of Sn91Zn9 alloy after adding indium. The contact angle, melting temperature and specific heat of Sn91Zn9 alloy decreased after adding indium content. Also elastic modulus and internal friction values of Sn91Zn9 alloy decreased after adding indium content. But electrical resistivity and Vickers hardness values of Sn91Zn9 alloy increased after adding indium content. The SnZn9In5 alloy has adequate properties for solder applications.
1) The document examines the high temperature oxidation behavior of a nickel-based superalloy produced by mechanical alloying. Samples were mechanically alloyed, sintered, hot-deformed, and underwent secondary recrystallization.
2) Isothermal oxidation tests were conducted on the samples at 1000°C for up to 100 hours. SEM and XRD analysis found that a protective chromium oxide (Cr2O3) film formed on the surfaces. Weight change results indicated the samples gained a small amount of weight over time, exhibiting sub-parabolic oxidation behavior.
3) XRD analysis identified the primary oxide as Cr2O3. The intensity of Cr2O3 peaks in XRD
A solid solution is a single phase that exists over a range of chemical compositions. It occurs when two elements form similar crystal structures and have properties like atomic radii and electronegativity that allow them to substitute for each other in the crystal lattice. There are two main types: substitutional solid solutions where one atom substitutes for another, and interstitial solid solutions where atoms occupy spaces in the lattice that are normally unoccupied. A good example is the copper-nickel system, where copper and nickel atoms can substitute for each other to form a continuous range of solid solutions due to their similar properties. The extent of solid solubility depends on factors like temperature, size differences between atoms, and relative positions in the electrochemical series
The document discusses different methods for producing alumina nanoparticles, including sol-gel, spray pyrolysis, and emulsion combustion methods. Sol-gel produces nanoparticles below 30 nm and allows control of particle properties. Spray pyrolysis controls particle size below 400 nm using an ultrasonic spray of precursor solutions decomposed at 700°C. Emulsion combustion combines emulsion and combustion processes to continuously produce hollow spherical alumina nanoparticles 200-800 nm in size with 10 nm shells.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
This document summarizes research on a nickel-chromium composite material reinforced with tungsten, aluminum, titanium, and molybdenum disulfide developed using powder metallurgy. Tests were conducted to analyze the material's high-temperature oxidation behavior and friction/wear performance. Results showed the oxidation kinetics followed a parabolic rate law, with oxide scales consisting of chromium oxide and nickel-chromium spinel. Friction decreased with increasing temperature up to 400°C, below which wear rate also decreased, but wear rate was highest at 600°C. The dominant wear mechanism at 600°C was oxidative wear.
The document describes a novel method for growing aluminium nitride (AlN) nanowires. Specifically:
1) AlN nanowires were grown by nitridating a mixture of aluminium and ammonium chloride powders at 1000°C for 1 hour under flowing nitrogen gas.
2) SEM images showed the production of homogeneous AlN nanowires between 40-150nm in diameter without droplets at the tips, suggesting vapor-phase growth.
3) A thermodynamic analysis supported that the nanowires were grown via spontaneous vapor-phase chlorination and nitridation reactions of intermediate species produced from the aluminium, ammonium chloride and nitrogen.
Improving the properties of Ni-Based Alloys by Co AdditionIRJET Journal
1) The document discusses improving the properties of nickel-based alloys through the addition of cobalt.
2) Cobalt addition leads to grain refinement in the alloys, which influences both microstructure and corrosion resistance. Finer grain size improves hardness.
3) Samples of Ni-5Cr-5Al-xCo (where x is the cobalt content from 0-30%) were produced by vacuum arc melting and characterized through XRD, optical microscopy, and Vickers hardness testing.
4) Results showed that increasing the cobalt content refined grain size and improved hardness, while also enhancing corrosion resistance properties over the substrate material alone.
Nitrogen containing carbon nanotubes as supports fortshankar20134
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had significantly higher catalytic activity for methanol oxidation compared to a commercial platinum on carbon catalyst.
Nitrogen containing carbon nanotubes as supports for pt–alternate anodes for ...tshankar20134
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon black catalyst.
Nitrogen containing carbon nanotubes as supports formadlovescience
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon black catalyst.
Nitrogen containing carbon nanotubes as supports for pt–alternate anodes for ...madlovescience
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotubes with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had significantly higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon catalyst.
Synthesis, Characterization and Phase Transition of Highly Porous γ - Alumina...AnuragSingh1049
Alumina is an important metal oxide used in a
wide range of applications. It is a challenge to synthesize
stable γ-alumina nanoparticles because; γ-phase of alumina
is not as stable as α phase of alumina. But γ-alumina owns a
higher surface area making it a good candidate for many
industrial applications such as catalyst, catalytic support for
petroleum refining, absorbent, alcohol dehydration,
catalytic reduction of automotive pollutants like NOx, CO
and hydrocarbons. This research focuses on synthesis,
characterization and study of phase identification of pure γ-
alumina nanoparticles.
Modified “Pechini method” (Danks, Hall, and
Schnepp (2016); Huízar-Félix, Hernández, de la Parra,
Ibarra, & Kharisov, 2012; Naskar, 2010; Zaki, Kabel, &
Hassan, 2012) was used for the synthesis. Transesterification
of citrate and ethylene glycol makes a covalent polymer
network with trapped Al atoms. Continuous stirring of the
reaction mixture while maintaining an optimum
temperature is an important factor affecting this reaction.
Calcination was carried out at different temperatures to
identify phase transitions of alumina nanoparticles. In order
to further reduce the particle size and increase the surface
area, reactant ratio of citric acid: aluminum acetate was
modified to 1:1, volume of ethylene glycol was increased up
to 90% of volume of the solution and Triton X was used as a
surfactant.
PXRD confirmed the pure γ-alumina phase
(JCPDS No. 00-010-0425) in samples calcined at 900 °C. At
1000 °C γ-alumina is conve+rted to α-alumina (JCPDS No.
00-083-2080). After the modifications, γ-alumina was
identified at 700 °C. FTIR-ATR analysis shows peaks
around 1127 cm-1
indicating the presence of Al-O-Al
asymmetric bending modes and the peaks around 500 cm-
1
-
750 cm-1
correspond to γ-AlO6 octahedral sites and 800 cm-1
correspond to AlO4 tetrahedral sites in γ alumina spinel
structure. Resulted product of low temperature, pure γ-
alumina nanoparticles will facilitate the industrial
development in various applications.
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.
The document summarizes a study that investigated the corrosion behavior of annealed 2205 duplex stainless steel in sulphuric acid environments. Potentiodynamic polarization tests were conducted on annealed and untreated 2205 duplex stainless steel samples in 0.1M and 3M sulphuric acid. The results showed that the annealed samples exhibited lower corrosion resistance than the untreated samples in both acid environments, indicating that annealing heat treatment reduces the corrosion resistance of 2205 duplex stainless steel in sulphuric acid.
The document discusses MOCVD (Metalorganic Chemical Vapor Deposition) technology and material growth. It covers the MOCVD growth system, common metalorganic compounds used as sources, gas phase and surface reactions during growth, characterization techniques for analyzing materials, and some issues related to growing GaN and related materials by MOCVD.
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.
1991_Sensitivity to Iron Impurity Content of Corrosion Rate of Mg-15Al_Cotton...James D. Cotton
The corrosion rates of extrusions produced from rapidly-solidified Mg-15wt%AI alloy powder containing varying levels of iron (Fe) impurity (0.003-0.020wt%) were studied. Trace amounts of Fe were found to have a strong exponential effect on the corrosion rate, consistent with previous studies. However, the sensitivity to Fe content was markedly lower for the rapidly-solidified alloys compared to conventionally-cast alloys. This effect is explained by the microstructural refinement produced by rapid solidification, which decreases the scale of microstructure and distributes corrosion more evenly. Both pitting and filiform corrosion were observed and characterized using various microscopy techniques.
Surfactant-assisted Hydrothermal Synthesis of Ceria-Zirconia Nanostructured M...IOSR Journals
CeO2–ZrO2 oxides were prepared by the surfactant-templated method using cetyl trimethyl ammonium bromide (CTAB) as template and modified with chromium nitrate. These were characterized by XRD, FT-IR, TEM, SEM, BET and TPD-CO2. The XRD data showed that as prepared CeO2-ZrO2 powder particles have single phase cubic fluorite structure. HRTEM shows mesoscopic ordering. Average particle size is 12-13 nm as calculated from particle histogram. The nitrogen adsorption/desorption isotherm were classified to be type IV isotherm, typical of mesoporous material. The presence of uni-modal mesopores are confirmed by the pore size distribution which shows pore distribution at around 60 A°. Catalytic activity was studied towards liquid-phase oxidation of benzene.
This document summarizes research on the thermal properties of green alumina porcelain. Thermal conductivity, diffusivity, density, and specific heat were measured on samples fired from 100-1320°C using transient plane source methods. Differential thermal analysis, thermogravimetry, and thermodilatometry were also performed to study structural changes during firing. Dehydroxylation of kaolinite occurred around 580°C, while crystallization of spinel happened at around 975°C. After sintering was complete, thermal conductivity increased by 700% and thermal diffusivity rose by 400% compared to the green material.
1) The study examined the electrochemical characteristics of an ultra-fine grain γ/–Ni3Al coating after exposure to 3.5% NaCl solution, using various electrochemical techniques.
2) The ultra-fine grain γ/–Ni3Al coating was fabricated by annealing an electrodeposited Ni-Al composite at 600°C for 1 hour, resulting in a refined microstructure.
3) Testing found the ultra-fine grain γ/–Ni3Al exhibited a more positive corrosion potential and lower corrosion current density compared to an arc-melted γ/–Ni3Al alloy. This was attributed to the refined microstructure of the ultra-fine grain coating promoting a faster formation of a protective
Graphene oxide was synthesized from graphite powder and functionalized with ethanolamine to produce GO-EA. GO-EA was successfully redispersed in an ethylene glycol solution. X-ray photoelectron spectroscopy analysis showed the expected functional groups on GO and the appearance of new peaks indicating successful functionalization of GO-EA. Future work will verify the increased thermal conductivity of the solution and explore GO-EA's catalytic properties.
Effect of Adding Indium on Wetting Behavior, Microstructure and Physical Prop...Editor IJCATR
Effect of adding indium on microstructure, wetting process, thermal, electrical and mechanical properties of tin- zinc eutectic alloy have been investigated. Microstructure (started base line, lattice parameters, unit cell volume, crystal size and the shape of formed crystalline phases) and measured physical properties of tin- zinc eutectic alloy changed after adding different ratio of indium content. A little variation occurred in thermo-graph (Endo-thermal peaks) of Sn91Zn9 alloy after adding indium. The contact angle, melting temperature and specific heat of Sn91Zn9 alloy decreased after adding indium content. Also elastic modulus and internal friction values of Sn91Zn9 alloy decreased after adding indium content. But electrical resistivity and Vickers hardness values of Sn91Zn9 alloy increased after adding indium content. The SnZn9In5 alloy has adequate properties for solder applications.
1) The document examines the high temperature oxidation behavior of a nickel-based superalloy produced by mechanical alloying. Samples were mechanically alloyed, sintered, hot-deformed, and underwent secondary recrystallization.
2) Isothermal oxidation tests were conducted on the samples at 1000°C for up to 100 hours. SEM and XRD analysis found that a protective chromium oxide (Cr2O3) film formed on the surfaces. Weight change results indicated the samples gained a small amount of weight over time, exhibiting sub-parabolic oxidation behavior.
3) XRD analysis identified the primary oxide as Cr2O3. The intensity of Cr2O3 peaks in XRD
A solid solution is a single phase that exists over a range of chemical compositions. It occurs when two elements form similar crystal structures and have properties like atomic radii and electronegativity that allow them to substitute for each other in the crystal lattice. There are two main types: substitutional solid solutions where one atom substitutes for another, and interstitial solid solutions where atoms occupy spaces in the lattice that are normally unoccupied. A good example is the copper-nickel system, where copper and nickel atoms can substitute for each other to form a continuous range of solid solutions due to their similar properties. The extent of solid solubility depends on factors like temperature, size differences between atoms, and relative positions in the electrochemical series
The document discusses different methods for producing alumina nanoparticles, including sol-gel, spray pyrolysis, and emulsion combustion methods. Sol-gel produces nanoparticles below 30 nm and allows control of particle properties. Spray pyrolysis controls particle size below 400 nm using an ultrasonic spray of precursor solutions decomposed at 700°C. Emulsion combustion combines emulsion and combustion processes to continuously produce hollow spherical alumina nanoparticles 200-800 nm in size with 10 nm shells.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
This document summarizes research on a nickel-chromium composite material reinforced with tungsten, aluminum, titanium, and molybdenum disulfide developed using powder metallurgy. Tests were conducted to analyze the material's high-temperature oxidation behavior and friction/wear performance. Results showed the oxidation kinetics followed a parabolic rate law, with oxide scales consisting of chromium oxide and nickel-chromium spinel. Friction decreased with increasing temperature up to 400°C, below which wear rate also decreased, but wear rate was highest at 600°C. The dominant wear mechanism at 600°C was oxidative wear.
The document describes a novel method for growing aluminium nitride (AlN) nanowires. Specifically:
1) AlN nanowires were grown by nitridating a mixture of aluminium and ammonium chloride powders at 1000°C for 1 hour under flowing nitrogen gas.
2) SEM images showed the production of homogeneous AlN nanowires between 40-150nm in diameter without droplets at the tips, suggesting vapor-phase growth.
3) A thermodynamic analysis supported that the nanowires were grown via spontaneous vapor-phase chlorination and nitridation reactions of intermediate species produced from the aluminium, ammonium chloride and nitrogen.
Improving the properties of Ni-Based Alloys by Co AdditionIRJET Journal
1) The document discusses improving the properties of nickel-based alloys through the addition of cobalt.
2) Cobalt addition leads to grain refinement in the alloys, which influences both microstructure and corrosion resistance. Finer grain size improves hardness.
3) Samples of Ni-5Cr-5Al-xCo (where x is the cobalt content from 0-30%) were produced by vacuum arc melting and characterized through XRD, optical microscopy, and Vickers hardness testing.
4) Results showed that increasing the cobalt content refined grain size and improved hardness, while also enhancing corrosion resistance properties over the substrate material alone.
Nitrogen containing carbon nanotubes as supports fortshankar20134
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had significantly higher catalytic activity for methanol oxidation compared to a commercial platinum on carbon catalyst.
Nitrogen containing carbon nanotubes as supports for pt–alternate anodes for ...tshankar20134
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon black catalyst.
Nitrogen containing carbon nanotubes as supports formadlovescience
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotube surface with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon black catalyst.
Nitrogen containing carbon nanotubes as supports for pt–alternate anodes for ...madlovescience
1) Nitrogen-containing carbon nanotubes were synthesized and used to support platinum nanoparticles as an alternative anode catalyst for direct methanol fuel cells.
2) The platinum nanoparticles were uniformly distributed on the nitrogen-containing carbon nanotubes with an average particle size of 3 nm.
3) Cyclic voltammetry studies showed that the platinum nanoparticles supported on nitrogen-containing carbon nanotubes had significantly higher catalytic activity for methanol oxidation compared to a conventional platinum on carbon catalyst.
2018 khodan an-porous monoliths consisting of aluminum oxyhydroxide nanofibrilsAnatoleNKhodan
Abstract We present a study on the chemical and structural transformations in highly porous monolitic materials consisting of the nanofibrils of aluminum oxyhydroxides (NOA, Al2O3·nH2O) in the temperature range 20– 1700 °C. A remarkable property of the NOA material is the preservation of the monolithic state during annealing over the entire temperature range, although the density of the monolith increases from ~0.02 up to ~3 g/cm3, the total porosity decreases from 99.3 to 25% and remains open up to 4 h annealing at the temperature ~1300 °C. The physical parameters of NOA monoliths such as density, porosity, specific area were studied and a simple physical model describing these parameters as the function of the average size of NOA fibrils—the basic element of 3D structure—was proposed. The observed thermally induced changes in composition and structure of NOA were successfully described and two mechanisms of mass transport in NOA materials were revealed. (i) At moderate temperatures (T ≤ 800 °C), the mass transport occurs along a surface of amorphous single fibril, which results in a weak decrease of the length-to-diameter aspect ratio from the initial value ~24 till ~20; the corresponding NOA porosity change is also small: from initial ~99.5 to 98.5%. (ii) At high temperatures (T > 800 °C), the mass transport occurs in the volume of fibrils, that results in changes of fibrils shape to elliptical and strong decrease of the aspect ratio down to ≤ 2; the porosity of NOA decreases to 25%. These two regimes are characterized by activation energies of 28 and 61 kJ/mol respectively, and the transition temperature corresponds to the beginning of γ-phase crystallization at 870 °C.
Corrosion Behaviour of 6061 Al-SiC Composites in KOH MediumEditor IJCATR
The present research work deals with the corrosion behaviour of 6061 Al-15% (vol) SiC(P) composites. The addition of the
reinforcement like SiC to Aluminium has been reported to decrease the corrosion resistance of the matrix due to several reasons, one
of them being galvanic action between the reinforcement and the matrix. In the present work, the corrosion behaviour of 6061 Al-15%
(vol) SiC(P) composites in KOH at different concentration (0.5M, 1M, 1.5M) and different temperature (300C, 350C, 400C, 450C, 500C)
was determined by Tafel extrapolation technique. The inhibition action of 8-Hydroxyquinoline on corrosion behaviour of 6061 Al-
15% (vol) SiC(P) composites in KOH at different concentration of inhibitor (200ppm, 400ppm); different concentration of medium
(0.5M, 1M,1.5M) and different temperature (300C, 350C, 400C, 450C, 500C) was investigated. The results indicate that corrosion rate
of Al-SiC composite in KOH increases as the concentration of medium increases and also as temperature of medium increases. The
results indicate that the inhibitor is moderately effective in inhibiting the corrosion of 6061 Al-15% (vol) SiC(P) composites. As the
inhibitor concentration increases, the corrosion rate decreases. The surface morphology of the metal surface was investigated using
scanning electron microscope (SEM). Activation energy was evaluated using Arrhenius equation, and enthalpy of activation and
entropy of activation values were calculated using transition state equation
Electrospun Nanofibers Reinforced Aluminium Matrix Composites, A Trial to Imp...IJAMSE Journal
A comparison between TiO2 nanofibers and carbon nanofibers as fibers reinforced metal matrix composites with respect to mechanical properties improvements have been made in this paper. Al and Mg have been chosen as metal matrices. The used carbon and ceramic nanofibers (Titanium Oxide) were successfully synthesized using electrospinning technique. Various weight percentage of calcined
electrospun TiO2 and carbon nanofibers (1, 3, 5 and 10%) were mixed with metal matrix and fabricated by route of powder metallurgy using High Frequency Induction heat Sintering (HFIHS). Mechanical properties of the sintered composites have been investigated. The manufactured pellets were tested for compression test, hardness and microstructures by the field emission scanning electron microscopes (FESEM), which reveals the homogeneous distribution of nanofibers in the Al/Mg matrices. In addition,
energy-dispersive X-ray spectroscopy (EDS) was employed to obtain the chemical analysis of each composite. The result shows that, the ultimate compressive strength increased to 415 MPa at 5% TiO2, which is 13.5% more than the pure Al. The hardness increased up to 64% in case of using the ceramic nanofibers as reinforcement. While using CNFs as reinforcement to the Al matrix deteriorates the
mechanical properties.
The document summarizes research on LiMn2O4 cathode material for lithium-ion batteries. It describes the spinel crystal structure of LiMn2O4 and discusses synthesis using solid state combustion with oxalic acid. Characterization with XRD and SEM showed that adding 5 wt% oxalic acid produced smaller, more homogeneous particles. Electrochemical analysis indicated 5 wt% oxalic acid yielded the highest initial capacity of 108.5 mAh/g. Cyclic voltammograms and charge-discharge curves demonstrated better reversibility and electrochemical activity for the 5 wt% sample. The research suggests surface modification could further improve performance of the LiMn2O4 material.
Investigation of heat transfer through cnt composites focusing on conduction ...iaemedu
This document summarizes a study that investigated the heat transfer properties of carbon nanotube (CNT) composites, with a focus on conduction mode heat transfer. Multi-wall carbon nanotubes were synthesized using chemical vapor deposition inside anodic aluminum oxide templates to create aligned CNT composites. Randomly oriented CNT and graphite films were also prepared. Specific heat capacity and thermal conductivity measurements from 300-400K revealed that aligned CNT composites had higher thermal conductivity than randomly oriented films, demonstrating the anisotropic heat transfer properties of aligned CNT structures. Randomly oriented CNT and graphite films showed similar thermal properties.
Investigation of heat transfer through cnt composites focusing on conduction ...IAEME Publication
1. The document investigates heat transfer through carbon nanotube composites, focusing on the conduction mode.
2. It summarizes the synthesis and preparation of aligned multi-walled carbon nanotube samples embedded in anodic aluminum oxide templates, as well as randomly oriented films of multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphite powder.
3. The specific heat and thermal conductivity of the samples are measured from 300 to 400K. The specific heat of the aligned nanotube sample has weaker temperature dependence than the random films and bulk graphite. The thermal conductivity of the aligned sample increases with temperature, while the random films and graphite show a
Investigation of heat transfer through cnt composites focusing on conduction ...IAEME Publication
This document summarizes a study that investigated the heat transfer properties of carbon nanotube (CNT) composites, with a focus on conduction mode heat transfer. Multi-wall carbon nanotubes were synthesized using chemical vapor deposition inside anodic aluminum oxide templates to create aligned CNT composites. Randomly oriented CNT and graphite films were also prepared. Specific heat capacity and thermal conductivity were measured for the different materials from 300-400K using an AC calorimetric technique. Results showed the aligned CNT composite had higher thermal conductivity than the random films, demonstrating the anisotropic heat transfer along the CNT axes.
Investigation of heat transfer through cnt composites focusing on conduction ...iaemedu
1. The document investigates the heat transfer properties of carbon nanotube composites, focusing on the conduction mode of heat transfer.
2. It analyzes the specific heat and thermal conductivity of aligned multi-walled carbon nanotubes embedded in anodic aluminum oxide templates, as well as randomly oriented films of multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphite powder.
3. The results show that the specific heat of the randomly oriented films is similar to bulk graphite powder, while the aligned nanotubes have a weaker temperature dependence. The thermal conductivity of the randomly oriented films behaves similarly to graphite and is dominated by phonon boundary scattering, while
Investigation of heat transfer through cnt composites focusing on conduction ...IAEME Publication
1. The document investigates the heat transfer properties of carbon nanotube composites, focusing on the conduction mode of heat transfer.
2. It analyzes the specific heat and thermal conductivity of aligned multi-walled carbon nanotubes embedded in anodic aluminum oxide templates, as well as randomly oriented films of multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphite powder.
3. The results show that the specific heat of the randomly oriented films is similar to bulk graphite powder, while the aligned nanotubes have a weaker temperature dependence. The thermal conductivity of the randomly oriented films behaves similarly to graphite and is dominated by phonon boundary scattering, while
An equiaxed, submicron grain size distribution was generated in an Al (0.1 wt.% Sc) alloy by
processing through equal channel angular pressing followed by a low temperature pre-
ageing heat treatment. The alloy was subsequently annealed for various times at 300, 350,
400 and 450° C for investigating the thermal stability of the deformation microstructure. It
was found that up to 400° C, the submicron grain structure coarsens slowly and uniformly by
a process of continuous recrystallization.
1) Nickel-copper-phosphorus layers were electrolessly deposited on anodized aluminum and aluminum alloys to improve their surface characteristics.
2) Polarization and impedance tests showed the Ni-Cu-P coating improved corrosion resistance for anodized Al7075 but decreased corrosion resistance for anodized Al2014.
3) Scanning electron microscopy images indicated the anodized aluminum surfaces were uniform, while the alloy surfaces were more defective, influencing how well the Ni-Cu-P layer adhered.
Carbon-cuprous oxide composite nanoparticles
were chemically deposited on surface of thin glass tubes of spent
energy saving lamps for solar heat collection. Carbon was
obtained from fly ash of heavy oil incomplete combustion in
electric power stations. Impurities in the carbon were removed by
leaching with mineral acids. The mineral free-carbon was then
wet ground to have a submicron size. After filtration, it was
reacted with concentrated sulfuric/fuming nitric acid mixture on
cold for 3-4 days. Potassium chlorate was then added drop wise on
hot conditions to a carbon slurry followed by filtration.
Nanocarbon sample was mixed with 5% by weight PVA to help
adhesion to the glass surface. Carbon so deposited was doped with
copper nitrate solution. After dryness, the carbon/copper nitrate
film was dipped in hydrazine hydrate to form cuprous oxide -
carbon composite, It was then roasted at 380-400 °C A heat
collector testing assembly was constructed of 5 glass coils
connected in series with a total surface area of 1250 cm2
. Heat
collection was estimated by water flowing in the glass coils that
are coated with the carbon/copper film,. Parameters affecting the
solar collection efficiency such as time of exposure and mass flow
rate of the water were studied. Results revealed that the prepared
glass coil has proven successful energy collector for solar heat.
The document summarizes a study that characterized the corrosion of a nickel-aluminum (Ni-Al) composite coating compared to a pure nickel coating after 72 hours of immersion in 2M NaCl solution. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used, and scanning electron microscopy was used to examine the corrosion product layers. Results showed the Ni-Al composite had a porous, cracked corrosion product layer that decreased corrosion potential and increased corrosion currents compared to the more protective layer formed on pure nickel. Thus, the Ni-Al composite exhibited lower corrosion resistance than pure nickel in the higher chloride concentration solution.
The document summarizes research on upgrading metallurgical-grade silicon from aluminum-silicon alloys produced by aluminothermic reduction of Egyptian sand. Key points:
1) Aluminum-silicon alloys were leached with hydrochloric acid to produce silicon powder and an aluminum chloride solution. Nearly pure (99.3%) silicon was obtained by optimizing particle size, temperature, time, solid/liquid ratio, and acid concentration.
2) Process parameters like temperature, time, acid concentration, and liquid/solid ratio were studied to determine their effect on aluminum removal efficiency. Near complete removal was achieved at 50°C, 20 minutes, 6.24M HCl concentration, and 9:
1) Researchers successfully produced SiAlON ceramics from industrial wastes like silicon sludge and aluminum dross using a nitriding combustion process.
2) The nitriding combustion process allows synthesis of ceramic powders in an energy efficient way while recycling wastes.
3) Specifically, the process was used to synthesize SiAlON powders from silicon sludge generated in silicon wafer production and from aluminum dross from aluminum smelting. Desert sand was also used to synthesize silicon oxynitride powder.
This document summarizes research on enhancing the thermal conductivity of polymer composites by filling them with three-dimensional (3D) brushlike aluminum nitride (AlN) nanowhiskers. The 3D brushlike AlN nanowhiskers were synthesized using a simple combustion method. Polymer composites filled with 47% by volume of the 3D brushlike AlN nanowhiskers achieved a thermal conductivity of 4.2 W/m-K, which was over 2 times higher than composites filled with the same amount of commercial equiaxed AlN particles. The enhanced thermal conductivity is attributed to the 3D brushlike nanowhiskers promoting a more effective percolating network with
This document summarizes a study on the synthesis of barium hexaferrite (BaFe12O19) nanoparticles through co-precipitation and calcination. The researchers investigated the effect of the Fe3+/Ba2+ molar ratio and addition of surface active agents on the structural and magnetic properties of the synthesized nanoparticles. They found that decreasing the Fe3+/Ba2+ ratio from the stoichiometric value of 12 to 8 and increasing the calcination temperature to 1000°C or higher promoted the formation of single phase BaFe12O19 nanoparticles. The addition of surface active agents also helped form homogeneous BaFe12O19 nanoparticles as small as 113 nm at the lower calcination temperature of 800°C, with
This document describes research into producing crack-free functionally graded materials (FGMs) composed of stainless steel 316L and alumina through spark plasma sintering (SPS). Initial experiments studied sintering the individual powders and their composites to determine optimal SPS conditions that yielded high density. Subsequent experiments fabricated FGM pellets with varying numbers of interlayers but still encountered cracking near alumina-rich layers. Adding yttrium-stabilized zirconia to the interlayers helped reduce cracking by lowering residual stresses. A crack-free FGM pellet was successfully produced using 19 interlayers between the stainless steel and alumina ends, with the hardness varying steadily throughout the gradient.
This document summarizes research on spark plasma sintering (SPS) of tungsten carbide (WC) and cemented carbides. SPS allows for faster sintering times compared to conventional methods, enabling better control of WC grain size growth. Studies have shown SPS can produce fully dense WC materials with nano-sized or sub-micron WC grains and hardness values up to 28 GPa. SPS of WC-Co powders can achieve high density at temperatures as low as 1050-1100°C, retaining initial nano/sub-micron grain sizes better than conventional sintering. However, truly nano-scale WC grain sizes below 100nm have not been achieved
This document describes a new synthesis route for producing dense silicon oxynitride (Si2N2O) ceramics using desert sand as the raw material. The process involves:
1. Combusting a mixture of desert sand and silicon metal under pressurized nitrogen via self-propagating high-temperature synthesis to produce pure Si2N2O powder.
2. Densifying the Si2N2O powder via spark plasma sintering with 5 wt.% calcia-alumina additive to achieve 99% theoretical density in only 6 minutes of heating and holding.
3. The resulting dense Si2N2O ceramic exhibits a Vickers hardness of 18.7 GPa, fracture tough
1. Growth of Quasi-Aligned AlN Nanofibers by Nitriding
Combustion Synthesis
Mohamed Radwanw
and Yoshinari Miyamoto*,
**
Department of Nano/Micro Structure Control, Smart Processing Research Center, Joining and Welding Research
Institute, Osaka University, Osaka 567-0047, Japan
Quasi-aligned AlN nanofibers were formed by the nitriding
combustion synthesis according to a unique micro-reactor
model. A charge composed of aluminum and aluminum nitride
diluent powders (40/60 mol%) with a mixture of yttria and
ammonium chloride as additives (5 wt% each) was combusted
at low nitrogen gas pressures of 0.25 MPa. The FE-SEM
images of as-synthesized AlN product showed the formation of
ball-like grains (same shape and size as the original Al reactant)
that consisted of a thin surface nitride layer or crust cover
quasi-aligned AlN nanofibers grown in the interior. The cross-
sectional view is sea anemone like. Formation of this novel mor-
phology is believed to occur through a two-stage process. The
first one occurs at the preliminary stage of the combustion out-
side Al particles. After the ignition, the heat generated causes
the sublimation and dissociation of ammonium chloride into
various gaseous species. This effectively interrupts the combus-
tion and slows down the increase of reaction temperature. In
addition, yttria interacts with the native oxide layer present on
the surface of Al particles and forms a stable Al–N–Y–O crust.
The second stage begins by the infiltration of various gaseous
species such as HCl(g), NH3(g), and N2(g) through the crust into
the molten Al cores. The ‘‘crust–core’’ systems function as ‘‘mi-
cro-reactors’’ where both the nitridation and growth processes
occur inside. The molten Al cores are spontaneously halogenated
to AlCl3 vapors and the nitridation proceeds by the gas–gas
reaction of AlCl3 and NH3/N2 vapors. The AlN nanofibers
are then grown from the vapor phase quasi-aligned inside the
micro-reactors by VLS and VS mechanisms.
I. Introduction
DURING the past two decades, aluminum nitride (AlN) has
attracted considerable interest in the electronics industry
because it possesses an excellent combination of material
properties, including high intrinsic thermal conductivity (B320
W/mK), wide band gap (6.2 eV), high electrical resistivity
(41010
O Á cm), low dielectric constant (8.6), high mechanical
strength, chemical stability, and low thermal expansion coeffi-
cient (4.2Â 10À6
1C)À1
matches to both Si and GaN semicon-
ductors. AlN components and substrates are used for various
applications in power electronics (electrical engines), microelec-
tronics (LSI circuits, sensor carriers), naval radio and defense
systems, railway systems, aeronautical systems, and environ-
mental systems.1–3
Recently, the growth of one-dimensional (1-D) AlN nano-
structures such as nanowhiskers,4
nanowires,5–8
nanofibers,9
nanobelts,10
nano-pillars,11
nanoribbons,12
nanotubes,13–15
nanocones,16,17
nanotips,18
and nanorods19
has become the
focus of scientific research and proposed promising applications
such as field emitters, flexible pulse-wave sensors, and nanome-
chanical resonators.16,18
Several methods have been developed
for the preparation of 1-D AlN nanostructures, mostly by the
nitridation at elevated temperatures of 10001–13501C in con-
ventional horizontal-type tube furnaces. These methods can be
categorized as follows:
(i) A halide-assisted direct nitridation of starting charges
contains halide compounds such as Al/AlX3,4,12
AlX3,14
or
Al/NH4X7,9
where X: Cl, F, or I. The Al halide acts as a trans-
port agent and supports the nitridation in the vapor phase and
unidirectional growth by a vapor–solid (VS) mechanism.
(ii) A catalyst-assisted direct reaction of metallic Al
and NH3/N2. In general, a small amount of a metallic catalyst
(0.5–1.0 mmol/1 g Al) such as Ni,6
Co,10,13
or Au18,19
is used. It
forms eutectic quasi-molten droplets that act as active nucle-
ation sites and promote the vapor–liquid–solid (VLS) growth
mechanism of 1-D AlN nanostructures.6
(iii) A template-assisted carbothermic reduction and nitr-
idation of Al2O3/Al mixtures.5
AlN nanowires have been syn-
thesized in bulk from carbon nanotubes (CNTs), which act as a
carbon source and template for confined carbothermic reduc-
tion and nitridation reactions. The synthesis mechanism was
described by space-limited nucleation and the growth occurred
from the vapor phase along the template channels.
Oriented growth of 1-D AlN nanostructures has been report-
ed by halide-assisted nitridation and deposition on catalyzed
substrates (halide-CVD on catalyst-coated silicon or quartz
wafers) at moderate temperatures of 7001–8501C,11,16,17
and the
direct nitridation of Al in NH3/N2 at 11001C under confinement
of a Ni-catalyzed alumina template.8
The combustion synthesis (CS) method (also called the self-
propagating high-temperature synthesis or SHS) is considered
to be an economical approach for the production of pure AlN
powder.20–23
It involves the direct nitridation of metal alumi-
num, which is a typical exothermic reaction as follows:
Al þ 1
2N2 ! AlNðDH
¼ À318 kJ=molÞ (1)
The heat evolved sustains the reaction so that no extra energy
is needed except the small amount used for initiating the reac-
tion and the reaction is completed very quickly within seconds.
High conversions can be attained by careful selection of the
combustion parameters such as nitrogen pressure, amount and
type of diluents, etc. However, the literature of CS of AlN shows
that the product morphology is complex and often consists of
various grain morphologies such as agglomerated particles,
whiskers, faceted particles, rods, pyramids, etc.24–26
Although
a uniform morphology is very important to engineer the
properties of AlN-based materials or devices, a morphology-
controlled synthesis condition has not yet been realized. In this
paper, we report novel observation of the growth of quasi-
aligned AlN nanofibers inside the reacting Al particles during
the combustion under a low nitrogen pressure. A new growth
B. Derby—contributing editor
Radwan is deeply grateful to the Japan Society for the Promotion of Science (JSPS) for
the postdoctoral fellowship grant.
*Member, The American Ceramic Society.
**Fellow, The American Ceramic Society.
w
Author to whom correspondence should be addressed. e-mail: radwan@jwri.
osaka-u.ac.jp
Manuscript No. 22004. Received July 12, 2006; approved January 25, 2007.
Journal
J. Am. Ceram. Soc., 90 [8] 2347–2351 (2007)
DOI: 10.1111/j.1551-2916.2007.01747.x
r 2007 The American Ceramic Society
2347
2. model is proposed to explain the formation of this unique
morphology. As far as we know, this mode of growth has not
been reported in the literature before.
II. Experimental Procedure
High-purity Al powder (99.9%, Toyo Aluminum KK, Tokyo,
Japan), AlN diluent powder (type H, 99.9%, Tokuyama
K.K., Hino, Tokyo, Japan), NH4Cl (99%, Nacalai Tesque,
Inc., Kyoto, Japan), and Y2O3 (99.9%, Shin-Etsu Chemical Co.,
Tokyo, Japan) were used as the starting materials. Figure 1
shows the morphological characteristics of Al and AlN powders;
the average particle size is 23 and 0.5 mm, respectively. The re-
action charge was composed of Al, AlN (Al/AlN 5 40/60
mol%), and promoting additives of NH4Cl and Y2O3 (5 wt%
each). The reaction powders were mixed using mortar and pestle
for 10 min and then sieved through a 212-mm sieve to disperse
any large agglomerates. Fifty grams of the powder mixture was
poured into a porous graphite container (f42 mm  90 mm H)
and packed by tapping to a relative density B60% of the the-
oretical density. The density was estimated by measuring the
weight of the powder mixture in a fixed volume of the container.
The graphite container was then placed in the combustion
chamber. Two W–Re thermocouples (connected to a data ac-
quisition system) were inserted into the center of the charge (one
at the middle and another near the top surface) at a fixed dis-
tance of 30 mm and used to record the temperature–time pattern
of the combustion and determine the combustion speed by mea-
suring the time lapsed for the wave passage between the two
thermocouples. The chamber was evacuated and subsequently
filled with high-purity N2 gas (99.999%) up to 0.25 MPa pres-
sure. The combustion was initiated from the bottom by igniting
a 2-g ignition pellet (Al1AlN, 1:1) placed at the bottom of the
packed powder by passing an electric current (60 A, 20 V) for 10
s through a carbon ribbon under the pellet. The combustion re-
action was completed in about 5 min and the chamber was then
cooled to room temperature in B30 min. The reaction product
was visually observed. The product phases were identified by X-
ray powder diffraction (XRD; JEOL, JDX-3530, Tokyo, Japan)
using CuKa radiation. The morphology of as-synthesized pow-
der was observed by field emission scanning electron microscopy
(FE-SEM; ERA-8800, ELIONIX, Tokyo, Japan). Samples for
SEM observation were coated with thin films of sputtered gold
to reduce electrical charge-up.
III. Results and Discussion
The content of diluent (60 mol%) in the reaction mixture was
chosen according to a previous study for the relationship be-
tween Al molar ratio and nitrogen pressure on the yield and
properties of AlN product.27,28
It is used to reduce the reaction
temperature and prevent coagulation of melted aluminum
particles. The as-synthesized AlN cake was very fragile with
only a white color.
The microstructure of as-synthesized AlN powder was
observed by FE-SEM using representative samples from three
different locations in the product cake: top surface, side surface,
and middle center. The grain morphologies of as-synthesized
AlN particles are given in Fig. 2. The microstructure consists of
two major types: aggregates of irregular particles (B0.5 mm,
same as original AlN diluent) and ball-like grains (same size and
shape as original Al particles) consist of thin crust (r150 nm)
covers unique quasi-aligned AlN nanofibers grown in the inte-
rior. Their cross-sectional view is similar to oval disk of the sea
anemone. Figure 3 shows the XRD pattern of the as-synthesized
product. The diffraction lines are assigned to a hexagonal AlN
structure similar to the bulk AlN powder reported (JCPDS-file
25–1133). Residual metallic Al has not been detected.
From the SEM observations, one can conclude that:
(1) The AlN diluent did not participate in the formation of
AlN particles and played only a passive role in controlling the
combustion temperature and dispersing the Al particles.
(2) There was no grain growth or sintering for both the
formed and original AlN diluent particles.
(3) The quasi-aligned AlN nanofibers were formed inside
the reacting Al particles.
As far as we know, this mode of growth, encapsulation in
reacting particles, has never been reported before. The question
is how were these balls of quasi-aligned AlN nanofibers formed?
The formation of a shell–core system during the course of
nitridation of Al metal is known in the direct nitridation (DN)
method and reported as a ‘‘core–shell’’ model.29–34
In this meth-
od, the nitridation takes place via three steps: nitridation at the
surface of the particles with the formation of a crystalline nitride
shell, breakaway or flowout of molten or vaporized Al core, and
volume nitridation outside the shell with a remaining hole or an
empty core. The final morphology of the AlN product is hon-
eycomb like (a clear SEM photograph of this morphology can
be seen in our recent paper by Radwan and Bahgat34
). In the
combustion synthesis method, both the surface nitridation and
breakaway were also observed when moderate combustions
(low Tmax) were promoted by using small amounts of additives
such as C and NH4Cl35–38
and/or ignition under an appropriate
nitrogen pressure.39–41
The nitride skins were formed at the pre-
heating stage of the combustion and then molten Al flowed out
with the formation of an eggshell-type AlN morphology. Nei-
ther of the previous observations can account for the present
SEM observations, which requires a new growth model without
a breakaway.
The typical temperature–time history of the nitridation reac-
tion (Fig. 4) sheds light on the behavior of the combustion. The
temperature was measured in the middle center of the charge.
The pattern shows a mild combustion with no explosive mode
and has a relatively low rate of temperature increase. It took
B53s to reach 6001C (below melting of Al), B73s to reach
50 µm
(a)
2 µm
(b)
Fig. 1. Scanning electron microscopy micrographs of starting powders: (a) Al and (b) aluminum nitride diluent.
2348 Journal of the American Ceramic Society—Radwan and Miyamoto Vol. 90, No. 8
3. 10001C, B160 s to Tmax (16201C), and lasted B27 s in the
afterburning stage. We noticed that in the temperature–time
histories of other combustion experiments without NH4Cl and
Y2O3 additions, once the combustion wave begins, the temper-
ature increases rapidly close to its maximum value. Owing to the
low combustion temperature, the grain growth and sintering of
AlN particles were avoided. The speed of the combustion reac-
tion was determined by measuring the time lapsed for the wave
passage between two thermocouples inserted into the center of
(e)
1 µm
(b)
10 µm
(d)
5 µm
50 µm
(a)
(c)
10 µm
Fig. 2. Field emission scanning electron microscopy images of the as-synthesized aluminum nitride product.
0
1000
2000
3000
4000
5000
20 30 40 50 60 70 80
2θ (°)
Intensity(a.u.)
·AlN
·
·
·
·
· ·
·
·
·
Fig. 3. X-ray diffraction pattern of the as-synthesized aluminum nitride
product.
Time, s
Combustiontemperature,°C
500
1000
1500
0 50 100 150 200 250 300 350
Fig.4. Temperature–time variation at the combustion front.
August 2007 Growth of Quasi-Aligned AlN Nanofibers 2349
4. the reaction bed at a (vertical) distance of 30 mm. The combus-
tion had a slow speed (0.26 mm/s).
In Fig. 5, we propose a new growth model to explain the
formation of quasi-aligned AlN nanofibers by the CS based on a
‘‘micro-reactors’’ model. The formation of nanofibers occurred
through two stages.
(1) Formation of Micro-Reactors
This stage started in the preliminary stage of combustion and
occurred outside the Al particles through two steps. In the
first step (below 6001C), NH4Cl dissociated into HCl and NH3
vapors (NH4Cl sublimes at 3501C and dissociates at 5201C):
NH4Clðs; vÞ ! HClðgÞ þ NH3ðgÞ (2)
The sublimation and decomposition of NH4Cl are endother-
mic and produce several gaseous species. These reactions absorb
sufficient heat and disturb the direct nitridation of Al particles
with N2 gas, which retards the wave propagation. It also pro-
vides enough time for another endothermic reaction between
yttria and the surface alumina layer (at T ! melting point of Al)
with the creation of a thin crust on the surface of the Al
particles:
Y2O3ðsÞ þ Al2O3ðsÞ þ N2ðgÞ ! Al À Y À N
À OðsÞ stable thin crust
(3)
The energy dispersive X-ray spectroscopy microanalysis
showed the presence of yttrium in the composition of the thin
crust (Fig. 6). The formation of these new crusts also suppresses
the Al–N interaction and slows down the combustion propaga-
tion. Because of the low heat evolution and the presence of new
protective crusts, there was neither breakaway nor explosion of
molten cores.
(2) Nitridation and Growth
The crust–core systems function as unique ‘‘micro-reactors.’’
The various gaseous species present (HCl(g), NH3(g), N2(g))
diffuse through the crust (through pores or cracks) into the
molten AlN cores. Both the nitridation and growth steps then
occur inside the developed micro-reactors. The nitridation pro-
ceeds via spontaneous chlorination–nitridation sequences simi-
lar to that reported in our previous results of direct nitridation
of an Al/NH4Cl mixture.42
Gaseous hydrogen chloride is
very active and spontaneously reacts with molten Al cores to
produce AlCl3 vapors, which are nitrided by a gas–gas reaction
as follows:
AlðlÞ þ 3HClðgÞ ! AlCl3ðvÞ þ 3
2H2ðgÞ (4)
AlCl3ðvÞ þ 1
2N2ðgÞ þ 3
2H2ðgÞ ! AlNðsÞ þ 3HClðgÞ (5)
Ammonium chloride plays a critical role because it produces
hydrogen chloride, which can be considered to be a key inter-
mediate product, acting as a ‘‘catalyst.’’ HCl(v) promotes the
vaporization of molten aluminum cores into volatile aluminum
chloride species and facilitates progress of nitridation through
sequence of spontaneous chlorination and nitridation interme-
diate reactions.
The semi-molten Al–Y–N–O crusts seemed to function as
catalyzed self-substrates and provided active sites that promoted
homogenous nucleation of AlN embryos on the inner surface of
the crusts from the vapor phase by a VLS mechanism. The AlN
nanofibers might condense from the vapor phase, after a critical
(low) degree of supersaturation inside the ‘‘micro-reactors’’ is
attained, and grow on the preceding embryos by a VS growth
mechanism in an epitaxial way according to the classical crystal
growth theory.43
No droplets could be observed at the tips of
these nanofibers. This results in a unique oriented growth in
the interior of the reacting particles normal to the inner crust
surface.
The first stage of the combustion, formation of micro-reac-
tors, was the essential step for the formation of AlN nanofibers
inside reactant particles. The postulation of nucleation of AlN
by VLS in molten droplets or layer with a subsequent fiber
growth through VS mechanism is in close agreement with the
observations of Moya and colleagues.24,44,45
To the best of our knowledge, this mode of growth inside
reactant Al particles has not been observed before and it was
not expected in combustion reactions due to the high increase
Al–N–Y–O
crust
molten
Al core
HCl(g), N2(g),
NH3(g)
Stage I.
1. dissociation of NH4Cl
2. formation of Al-N-Y-O
3. infiltration of gaseous species into core
Stage II.
4. chlorination of molten core
5. gas-gas nitridation reaction
6. nucleation and growth of quasi-aligned AlN nanofibers
quasi-aligned
AlN nanofibers
AlCl3(g)/N2(g)
↓
AlN(s)
native oxide
layer
solid Al
core
Fig. 5. Schematic illustration of the growth model of quasi-aligned aluminum nitride nanofibers by the combustion synthesis method.
Fig.6. Energy dispersive X-ray spectroscopy pattern of the thin nitride
crust.
2350 Journal of the American Ceramic Society—Radwan and Miyamoto Vol. 90, No. 8
5. in nitridation temperature and fast speed of combustion. The
current combustion condition was successful creating new
micro-reactors during the combustion reaction, which promot-
ed this mode of oriented growth inside.
IV. Conclusion
Quasi-aligned AlN nanofibers were formed by the combustion
synthesis according to a new micro-reactor model. This route
might be a possible method for economical growth of AlN
nanofibers, which are obtainable only by complicated nitridat-
ion reactions at elevated temperatures. AlN with this unique
morphology can be used not only for AlN ceramics and
composites but also in nanotechnology applications.
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