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Silica sand and glass industry


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Glasses, Raw Materials; Silica sand, Limestone, Soda ash , Glass Manufacturing Process, Glass Forming, Glass Structure, Glass Properties, Glass Types, Soda-lime glasses , Lead glasses , …

Glasses, Raw Materials; Silica sand, Limestone, Soda ash , Glass Manufacturing Process, Glass Forming, Glass Structure, Glass Properties, Glass Types, Soda-lime glasses , Lead glasses , Heat-resistant or borosilicate glasses, High-purity silica glasses, Specialty glasses, Heat Treating Glasses, Annealing glass, Tmpered glass, Chemistry of Glass Manufacture, Recycling of Glass, Virtification

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  • 1. Topic 6: GLASS A short series of lectures prepared for the Third year of Geology, Tanta University 2013- 2014 by Hassan Z. Harraz
  • 2. OUTLINE OF TOPIC 6:  Glasses  Raw Materials: a) Silica sand b) Limestone c) Soda ash  Glass Manufacturing Process  Glass Forming  Glass Structure  Glass Properties  Glass Types: i) Soda-lime glasses ii) Lead glasses iii) Heat-resistant or borosilicate glasses iv) High-purity silica glasses v) Specialty glasses  Heat Treating Glasses: a) Annealing glass b) Tmpered glass  Chemistry of Glass Manufacture  Recycling of Glass  Virtification
  • 3. Question What is Glass? Glass is an amorphous solid. A material is amorphous when it has no long-range order, that is, when there is no regularity in the arrangement of its molecular constituents on a scale larger than a few times the size of these groups. [...]. A solid is a rigid material; it does not flow when it is subjected to moderate forces - Doremus Glass includes all materials which are structurally similar to a liquid. However, under ambient temperature they react to the impact of force with elastic deformation and therefore have to be considered as solids. -Pfaender Glasses have numerous properties in common with crystalline solids, such as hardness and elasticity of shape [...]. The term 'amorphous solid state' has a more comprehensive meaning broader than that of the 'vitreous state'. All glasses are amorphous, but not all amorphous substances are glasses. Feltz, 1993 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 3
  • 4. Glasses Clay products Refractories Abrasives Cements Advanced ceramics optical composite reinforce containers/ household -whiteware -bricks -bricks for high T (furnaces) -sandpaper -cutting -polishing -composites -structural engine -rotors -valves -bearings -sensors Adapted from Fig. 13.1 and discussion in Section 13.2-6, Callister 7e. Taxonomy of Ceramics 13 March 2014 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 4
  • 5. Glasses  A glass can be defined as an inorganic product which has cooled to rigid structure without crystallization.  Glass is hard material normally fragile and transparent common in our life.  Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so called "controlled crystallization" in contrast to a spontaneous crystallization  It is composed of mainly:  Sand  Alkali  Glass-ceramics are mostly produced in two steps:  First, a glass is formed by a glass manufacturing process.  The glass is cooled down and is then reheated in a second step. In this heat treatment the glass partly crystallizes  Two prime characteristics of glass are their optical transparency and the relative ease with which they may be fabricated. Amorphous solid materials No crystal structure No long-range order Resemble “frozen liquids” 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 5
  • 6. RAW MATERIALS Raw Materials Approximate Proportion (wt %) Provides Approximate Proportion in glass (wt %) Soda ash (Na2CO3) 25 Soda (Na2O) 18 Limestone (CaCO3) 10 Lime (CaO) 7 Silica sand (SiO2) 65 Silica (SiO2) 75 Raw materials used in lime-soda glass a) Silica sand  Silica sand suitable for glass manufacture is however relatively rare, because of the need for a high degree of chemical purity.  The essential requirements for silica sand for glass manufacture are that it must be even grain size - more than 90% of grains must lie in the range 125-500µm, and its chemical composition must meet the requirements shown in Table 4. Maximum Cr2O3 Maximum Fe2O3 Minimum SiO2Glass 0.000150.01399.7Opthalmic glass 0.00020.01099.6Tableware, crystal and borosilicate glass 0.00050.03098.8Colourless containers --0.2597.0Coloured containers 0.00010.1099.0Clear flat glass Table 4: Required chemical composition of silica sand for glass manufacture Fig.1: High pure silica sand raw materials
  • 7. a) Silica sand  The discolouring impurities iron and chromium occur within the non-quartz mineral fraction of the sands.  Iron can occur as haematite, giving the sand a red colour, or as oxy-hydroxidcs (giving a yellow or brown colour) as well as in silicate minerals.  Chromium occurs as the heavy mineral chromite (FeCr2O4), which is stable during glass manufacture, and so rather than resulting in a discoloured glass, it persists as solid inclusions within the finished product, which can cause it to be brittle. This is especially important for float glass manufacture, where persistence of chromite grains can render useless substantial lengths of glass strip. Because of the difficulties involved in the chemical determination of minor amounts of Cr it may be appropriate simply to count the number of grains of chromite detected optically within a sample of known weight in order to classify a sand as suitable for float-glass.  Alumina is a natural impurity in glass sands, arising from the presence of feldspars, mica or clay minerals, and varies from 0.4% to 1.2% Al2O3 High values in this compositional range are preferred because they help to reduce melting temperatures (yet another component is added) and involve no negative effect on glass colour or other physical properties. The occurrence of aluminium as an impurity may also be beneficial by reducing the need to add aluminosilicates (feldspar, aplite or nepheline syenite) for the manufacture of certain glasses.  Great care is taken to consider the minor components of a glass, as small traces of impurities may have a major positive or negative effect on the quality of the finished product. For example, the presence of traces of iron may give a pale green colour (often visible when examining a pane of glass end on), and this can be tolerated in some applications (such as container glass).  Other minor components might have beneficial effects on the qualities of the glass produced. For example, addition of lithium (reduces the temperature required to melt the glass, and so yields savings in energy costs.
  • 8. b) Limestone • Limestone is required twice in glass manufacture - once to produce sodium carbonate and secondly as an ingredient in the batch to be melted. • As an ingredient in batches to be melted to produce glass, limestone purity is critical. In particular, Fe contents have to be very low, and the amount of MgO, as in dolomite, has to be known. In some glasses MgO is added using pure dolomite, but the amounts have to be controlled. • Like CaO, MgO causes immiscibility in glass melts; the miscibility gap in the system SiO2-MgO is wider than that in the system SiO2-CaO (Fig.4). 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 8
  • 9. Limestone Cycle Limestone CaCO3 Lime Hydrated Lime Milk of Lime Heat CO2 H2OH2O CO2 H2O Slurry Calcium oxide (CaO) Calcium hydroxide (Ca(OH)2 - DRY Calcium Hydroxide Ca(OH)2 - WET
  • 10. Lime (CaO)  Include hydrated lime & quicklime  Only quicklime can use to make glass Extraction of Lime  Quarry of limestone  Transported to crush plants  Undergo Calcination process:  heating limestone or chalk (CaCO3) in kiln till 900oC  CO2 is emitted in this process and calcium oxide (lime) is produced. Calcination Process 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 10 • Calcined lime  Quicklime/Burnt lime/White wash is obtained by heating limestone at temperatures above 900oC in a Kiln: CaCO3  heat CaO + 2CO2 • Hydrated lime  Calcium Hydroxide/Slaked Lime is a dry powder, resulting from the controlled slaking of Calcined Lime with water in a Hydrator: CaO + H2O  Ca(OH)2 • Precipitated Calcium Carbonate  Carbonation of Hydrated lime, also known as purified, refined or synthetic Calcium carbonate: CaO + H2O + CO2  CaCO3 + H2O
  • 11. Vertical Lime Kiln 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 11
  • 12. c) Soda Ash (NaHCO3)  Anhydrous sodium carbonate  Texture: soft  Color: grayish & white  Appearance: lump / powder in nature  Naturally:  Erosion of igneous rock form sodium deposits  Transport by waters as runoffs & collect in basins  When sodium comes in contact water/ CO2, precipitates out sodium carbonate.  Synthetically:  Extraction of Soda Ash(NaHCO3),  Manufactured synthetically through Solvary process by using salt, ammonia & limestone 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 12
  • 13. The Solvay process for the manufacture of Soda Ash (NaHCO3) media_portfolio/22.html
  • 14. Impurity  The Na2O and CaO decrease the softening point of this glass from 1600oC to 730oC  So that soda lime glass is easier to form.  An addition of 1 – 4% MgO is added to Soda lime glass to prevent cracks. Magnesium can be substituted for a proportion of the calcium content by the use of dolomite instead of limestone  In addition of 0.5 – 1.5% Al2O3 is used to Increase the durability. Alumina is a widespread component of glasses in addition to soda ash and silica, and helps improve resistance to weathering.  Boric oxide (to produce heat-resistant glasses such as 'Pyrex' and 'Vycor') and  Lead oxide (for lead crystal tableware).  Potassium can be substituted for some of the sodium with the use of feldspar, aplite or nepheline syenite.  fluorides.: used to produce Opaque glasses .  Lithium (Li2O) is added to the glass composition: The amounts required are very small, frequently ~1 to <4%. Lithium is added to glasses for several reasons, because it reduces liquidus temperatures; it improves moulding properties (reduces viscosity); it improves thermal properties ('Pyrex', ceramic hobs) and it improves strength. 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 14
  • 15. Ingredients To Obtain Glass There are following main ingredients used in the manufacturing of glass:  Sand (SiO2), Quartz, or Silica sand 72%  Flux → to lower T – e.g. Soda or Soda Ash (NaHCO3) 17%; (1700 – 900oC)  Stabilizing agent → to mitigate water solubility of the glass formed – e.g. CaO normally added as Limestone {Lime 5%} What is the raw material? Percentage of Ingredients in Glass silica sand soda ash lime other ingredien 72% 17% 5% 6% 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 15
  • 16. Glass Manufacturing Process 1. Silica sand, limestone, soda ash and cullet (recycled glass or broken glass) are keep dry and cool in a batcher house in silos or compartments 2. Mixing and weighting into proper proportion 3. Send to furnaces in hoppers:  operated by natural gas  heat the mixture at 1300-1600oC into soften or molten state 4. Molding (or Casting ): molten glass flows to forming machine to mold into desire shapes 5. Annealing lehrs : reheating the glass in an oven  to ensure even cooling of glass for strengthening of the products 6. Cooling process: Cool for 30 min to an hour for safe to handle. 7. Glass products are then decorated, inspected again and finally packaged and shipped to our customers. Glass Furnace Cooling Systems 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 16
  • 17. The Process 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 17
  • 18. Glass Forming Flat glass – floating / rolling Glass fibre – continuous strands and Crown process for glass wool 1) Casting : molding 2) Pressing: pressing second mold into molten glass 3) Core-forming: clay core dipped into molten mass 4) Fusing : fusing glass rods together around a mold 5) Blowing: blowing air into a glob 13 March Prof. Dr. H.Z. Harraz Presentation Glass 18
  • 19. Glass Fabrication Methods • Pressing: GLASS FORMING Adapted from Fig. 13.8, Callister, 7e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.) Gob Parison mold Pressing operation • Blowing: suspended Parison Finishing mold Compressed air plates, dishes, cheap glasses -mold is steel with graphite lining • Fiber drawing: wind up PARTICULATE FORMING CEMENTATION
  • 20. Blow Molding Softened glass Softened glass Pressed Glass Processing 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 20
  • 21. Float Glass: The Process Image from Prof. JS Colton, Ga. Institute of Technology Modern Plate/Sheet Glass making:
  • 22. Glass Structure • Quartz is crystalline SiO2: • Basic Unit: • Glass is amorphous • Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+) • Impurities: interfere with formation of crystalline structure. (soda glass) Adapted from Fig. 12.11, Callister, 7e. SiO 4 tetrahedron 4- Si 4+ O2- Si 4+ Na + O2- 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 22
  • 23. Glass Properties  Specific volume (1/r) vs Temperature (T): • Glasses:  do not crystallize  change in slope in spec. vol. curve at glass transition temperature, Tg -- transparent - no crystals to scatter light  Crystalline materials:  crystallize at melting temp, Tm  have abrupt change in spec. vol. at Tm Adapted from Fig. 13.6, Callister, 7e. T Specific volume Supercooled Liquid solid T m Liquid (disordered) Crystalline (i.e., ordered) T g Glass (amorphous solid) 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 23
  • 24. Glass Viscosity vs. T and Impurities • Viscosity decreases with T • Impurities lower Tdeform Adapted from Fig. 13.7, Callister, 7e. (Fig. 13.7 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.) Viscosity[Pas] 1 102 106 1010 1014 200 600 1000 1400 1800 T(°C) T deform : soft enough to deform or “work” annealing range Tmelt strain point • fused silica: > 99.5 wt% SiO2 • soda-lime glass: 70% SiO2 balance Na2O (soda) & CaO (lime) • Vycor: 96% SiO2, 4% B2O3 • borosilicate (Pyrex): 13% B2O3, 3.5% Na2O, 2.5% Al2O3 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 24
  • 25. Glass Types Five common types of glass: i) Soda-lime glasses ii) Lead glasses iii) Heat-resistant glasses OR Borosilicate iv) High-purity Silica glasses v) Speciality glasses There are the following types:-  Fused silica glass  96% silica glass  Soda lime glass  Lead silicate glass  High lead glass  Boron silicate glass  Alumina borosilicate glass  Low alkali glass  Alumina silica glass  Glass ceramics 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 25
  • 26. i) Soda-Lime-Silica Glasses • 65% sand; 15% soda; 10% lime • In this glass component are:  71 – 73% SiO2  12 – 14% Na2O  10 – 12% CaO • Adding sodium oxide (soda) lowers melting point • Adding calcium oxide (lime) makes it insoluble • Sodium and calcium ions terminate the network and soften the glass • The Na2O & CaO decrease the softening point of this glass from 1600oC to 730oC, So that soda lime glass is easier to form. • An addition of 1 – 4% MgO is added to Soda lime glass to prevent cracks. • In addition of 0.5 – 1.5% Al2O3 is used to Increase the durability • Soda-lime-silica glass is most commonly produced glass which accounts for ~95% of all the glass produced in the world. • Soda-lime-silica glass expands much when heated  Breaks easily during heating or cooling Uses Soda lime glass is used for flat glass, containers, lightening products. It is used where chemical durability and heat resistant are not needed 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 26
  • 27. ii) Lead Glasses • Lime and soda replaced with lead oxide (PbO) • Contains lead oxide (PbO) to improve refractive index • High refractive index- clarity sparkle • Softer –cut and engrave • Good electrical resistance - electronics 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 27
  • 28. iii) Heat-resistant (or Borosilicate) Glasses • Contains Boron oxide, known as Pyrex. • Boron-oxide-silica glass expands less  Tolerates heating or cooling reasonably well • Pyrex and Kimax are borosilicate glasses • Boron oxide replaces lime and most of soda – low thermal expansion coefficient • Al2O3 - B2O3 – aluminosilicate glass with even better heat resistance 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 28
  • 29. iv) High-purity Silica Glasses • Highest quality – most durable • 3 processes – melting pure SiO2; making 96% silica and flame hydrolysis • Pure SiO2 – pure silica melted @ 1900 ºC under vacuum • 96% - Vycor process – borosilicate glass heated to grow crystalline sodium borate channels – extracted hot HNO3 – leaving 96% pure silica after heat reduction @ 1200 ºC • flame hydrolysis – SiCl4 in CH4 / O flame (1500ºC, produces high-surface silica soot thermally sintered to pure silica at 1723 ºC) 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 29 2H2O + SiCl4 SiO2 + 4HCl Flame
  • 30. v) Specialty Glasses • Coloured glass: MnO2 – violet, CoO – blue, Cr2O3 - green • Opal glass: white opaque or translucent glassware colour due to scattering of light from small particle usually NaF/CaF crystals nucleating after a cooling and reheating process • Frosted glass:  satiny look when exposed to HF OHSiFSiOHF 242 24  13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 30
  • 31. v) Speciality (Cont.) • Coated glass:  unique properties  metal / metal oxides Ag+ + RA  Ag mirror  electrically conducting with SnO2 coating (thermal SnCl4 hydrolysis) • Photosensitive glass:–  glass that changes colour upon exposure to light  Phototropic:  darkens upon exposure to light and returns to original clear sate afterwards.  AgCl/AgBr 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 31 Ag+ X-  Ag + X light dark Blue-greycolorless Non-silicate glasses are becoming increasingly important for special optical purposes,  for example in the use of glasses prepared from CaF2, AlF3 and P2O5 for infrared optics or the use of fluoride glasses for optical fibres
  • 32. Heat Treating Glass  Annealing:  removes internal stress caused by uneven cooling.  Tempering:  puts surface of glass part into compression  suppresses growth of cracks from surface scratches.  sequence: further cooled tension compression compression before cooling hot surface cooling hot cooler cooler Result: surface crack growth is suppressed. 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 32
  • 33. a) Annealing Glass  Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed.  The process may be carried out in a temperature-controlled kiln known as a Lehr.  Annealing glass is critical to its durability.  Removes internal stress caused by uneven cooling.  Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock.  If glass is not annealed, it will retain many of the thermal stresses caused by quenching and significantly decrease the overall strength of the glass. 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 33
  • 34. b) Tempered Glass • The tempering process consists of the following steps: 1) First the glass is washed and then heated. 2) In order to temper glass, it must reach 1100°F (the softening point for glass.) 3) The glass is then cooled with cold air. Quenching with forced cold air sets up the tension and compression zones. 4) The tempered glass continues down the rollers to cool more and be packed for shipping. Glass to be tempered must be cut to size before the tempering step. • A flow chart in the next slide provides a summary of the tempering process. Tempered Glass: The Process 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 34
  • 35. b) Tempered Glass (Cont.) • Tempering glass:  Heat glass to softening point  Cool outside of glass quickly  Outside stiffens while inside is still hot  Shrinking inside compresses outside  Compressed outside stretches inside • Resists fractures because surface is compressed • Crumbles when cracked because inside is tense  Glass expands when heated  Quenching “freezes” this expansion on the outside  Center cools more slowly, and contracts. Sets up tension and compression zones.  Tempered Glass is required for door products and some windows installed near doors. If tempering is done improperly then distortion can result.  Tempered glass is stronger than annealed glass. If annealed glass (raw float) has a strength factor of “1”, tempered glass would be “4”. 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 35
  • 36. What is the difference between (regular) annealed glass and tempered glass? Annealed (regular) Glass • Advantages:  Cost • Limitations:  Breaks in sharp pieces  Not as strong as Tempered Glass  Size limitations Tempered Glass • Advantages:  4 times the stronger than annealed  Breaks into small, harmless pieces.  Qualifies as Safety Glazing • Limitations:  Must be cut to size before tempering  Optical distortion (roller wave, strain pattern) 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 36
  • 37. Examples of today’s glass products:  Containers (jars and bottles)  Flat glass (windows, vehicle glazing, mirrors, etc.)  Lighting glass (fluorescent tubes, light bulbs, etc.)  Tableware (drinking glasses, bowls, lead crystal, etc.)  Laboratory equipments (test tubes, cylinders, measuring flasks, etc.)  TV tubes and screens  Decorative glass  Fiberglass  Optical glass  Vacuum flasks 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 37
  • 38. CHEMISTRY OF GLASS MANUFACTURE  In general terms, soda-lime-silica glass manufacture involves melting the required raw material mix at 1600°C, which yields a very fluid melt, from which gases can escape (especially carbon dioxide produced by the decomposition of carbonate raw materials).  The glass is then worked to produce the articles required at about 1000°C, followed by annealing at 500-600°C.  Example; the float glass process, used to produce flat panes of glass suitable for windows, illustrates this well (Fig.3). 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 38 Fig.3: Diagram of the float glass process, showing the way a continuous ribbon of glass is drawn from the melting furnace, through the float bath (which gives the perfect surface to the sheet) and then is annealed and allowed to cool before preparation for sale.
  • 39. CHEMISTRY OF GLASS MANUFACTURE (Cont.)  A glass is little more than a rapidly quenched liquid  The term 'Glass' can be applied to many different materials, but in common usage it refers to quenched silicate liquids, , which behaves as a solid but retains the molecular structure of the liquid.  The production of commercial glasses is therefore dictated by the application of phase diagrams which allow the melting behaviour of particular compositions to be predicted and the optimum conditions for glass manufacture to be identified.  The appropriate phase diagram is that for the system SiO2-CaO-Na2O (Fig.4). 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 39
  • 40. CHEMISTRY OF GLASS MANUFACTURE (Cont.) 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 40 Fig 4: Phase relation ships for part of the system SiO2-CaO-Na2O at atmospheric pressure (weight%). The system includes the following crystalline phases: Name Formula Abbreviated formula Cristobalite SiO 2 S Tridymite SiO 2 S Quartz SiO 2 S Pseudowollastonite CaSiO 3 CS Sodium silicate NaSiO 3 NS Sodium disilicate Na 2 Si 2 O 5 NS 2 Sodium calcium silicate Na 4 CaSi 3 O 9 N 2 CS 3 Sodium calcium silicate Na 2 Ca 2 Si 3 O 9 NC 2 S 3 Sodium calcium silicate Na 2 Ca 3 Si 6 O 16 NC 3 S 6 O  Point O is the ternary eutectic, at 725ºC, with the composition 5.2% CaO , 21.3% Na2O and 73.5% SiO2
  • 41.  Liquidus phase relationships within the three-component system SiO2-CaO-Na2O go well beyond those relevant for glass manufacture.  Consequently, Figure 4 focuses on the silica-rich corner of the triangular diagram, as this includes most glass compositions. In this region, the silica mineral on the liquidus is cristobalite, tridymite or quartz (depending on temperature), with very steep temperature gradients particularly towards more sodic compositions. Towards the lime apex, a field of two liquids is drawn; in this field, liquid compositions separate out into two contrasting liquids, one silica-rich and one lime-rich.  These two liquids are immiscible in the same way that oil and water are immiscible, and like a good mayonnaise they are opaque to light and can be quenched to produce an opaque white solid. The other liquidus fields show shallower temperature gradients.  On the boundaries between them arrows are marked to show the "downhill direction". These all converge on a single point, where the temperature at which liquid can exist is lowest, which is a ternary eutectic. The ternary eutectic composition can be read from the compositional axes and corresponds to 5% CaO, 21% Na2O, and 74% SiO2. The minimum temperature can be read from the contours is 725°C.  In order to decide on the optimum blend of ingredients required to make a soda-lime-silica glass, the ternary liquidus diagram can be used to indicate the temperature required to initiate melting. The ternary eutectic composition is therefore the one which appears to be ideal for glass manufacture, as it will begin to melt at the lowest temperature, saving energy and manufacturing costs. Melting is carried out at 1600°C to give enough superheat to ensure that all of the solid grains within the raw materials dissolve within the liquid and to ensure that the viscosity of the liquid is sufficiently low that gases can escape. Compositions which are more silica-rich have a rapidly rising liquidus temperature, and may not completely melt, leaving a glass which contains crystals of a silica mineral or bubbles and appears frosted. It is therefore important to use this and similar diagrams not only to design batch mixes but also to diagnose problems which arise when glasses are not correctly made.  The sources of soda and lime are respectively sodium carbonate (soda ash) and limestone (dolomite is used if magnesium is needed). These materials decompose on heating with the loss of carbon dioxide. Thus, in the formulation of batches consisting primarily of silica sand, limestone and soda ash, proportions must be corrected to take into account the loss of carbon dioxide so that they correspond to the compositions required for the finished glass. In order to carry out this correction, relative atomic masses (atomic weights) are used to determine the proportions of CaO within CaCO3 and Na2O in Na2CO3:  Relative atomic masses: Ca = 12 ; O = 16 ; Na = 23 ; Ca =40  Relative molecular masses: CaO = 56 ; Na2O = 62; CO2 = 44, CaCO3 = 100; Na2CO3 = 106 • Therefore; 100 tonnes of limestone (CaCO3) yields 56 tonnes of CaO and 44 tonnes of CO2. and 100 tonnes of soda ash (Na2CO3) yields 100 x 62/106 = 58 tonnes of soda and 42 tonnes of CO2 CHEMISTRY OF GLASS MANUFACTURE (Cont.)
  • 42. Glass Industries The World Glass Industry has a gross production value totaling $82.3 billion Fig. 14 bled/matdocen.htm 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 42
  • 43. Recycling of Glass • Recycle of glass is mostly used for packaging • Recycle process 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 43
  • 44. Virtification  Definition: a new technology has been discovered to use recycle glass for radioactive waste management  Process:  melt glass together with radioactive waste in barrels or some other container  glass will then bind up with radioactive contamination into a huge glass block  radioactive waste is bond by the glass and become immobilized  keep radioactive waste from interacting with water, stop spreading the waste Fig. 20 vitrification.htm 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 44
  • 45. Good & Bad of Virtification Benefit of virtication:  Prevent radioactive waste pollution  Minimize the amount of glass waste produced  Increase the efficiency of glass use (to stabilize hazardous waste)  High volume reduction of waste  Landfill space can be saved Volume percent of vitrified product compared to the original waste volume Fig. 21 vitrification.htm 13 March 2014 Prof. Dr. H.Z. Harraz Presentation Glass 45