1. Glass

2. 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. - Pfaender 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  Feltz, 1993  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, 1993Feltz, 1993Feltz, 1993

3. Glasses  Amorphous solids  No crystal structure  No long-range order  Resemble “frozen liquids”

4. Forming a Glass  Requirements  Material must have high viscosity at melting point  Material must have difficulty nucleating crystal  Procedure  Melt material to eliminate crystal structure  Cool material quickly through melting temperature  Form supercooled liquid  Cool until solid

5. Zachariasen’s rules – glass formation   1. No oxygen atom may be linked to more than two cations   2. The cation coordination number is small: 3 or 4.   3. Oxygen polyhedra share corners, not edges or faces.   4. For 3D networks, at least three corners must be shared

6. Zachariasen’s rules – glass formation   Silica covalent Si-O bond: sp3 hybrid tetrahedral bonding Pauling's packing rule: satisfies Zachariasen's rule #2. Looking at the charge / CN = 4/2 satisfies Zachariasen's rule #1. Crystal structure: sharing four corners: All Rules are Satisfied: SiO2 forms a glass. Cation CN:Anion CN = 4:2

7. Zachariasen’s rules – glass formation   MgO ionic Mg-O bond Pauling's packing rule: violates Zachariasen's rule #2. Looking at the charge / CN = 6/6 violates Zachariasen's rule #1. Crystal structure: edge sharing polyhedra Rules are NOT Satisfied: MgO does not form a glass. Cation CN:Anion CN =6:6

8. In general: *oxides with small cations (and so- small CN's) form glasses; partial covalent bonding → hybridization, low CN geometries *oxides with large, low valence cations (MgO, CaO,… Li2O, Na2O,…) do not form glasses. dominated by ionic bonding; higher CN's

9. 72% 17% 5% 6% What is the raw material?  Sand - SiO2  Flux – to lower T – eg. soda (1700 – 900ºC)  Stabilizing agent – to mitigate water solubility of the glass formed – eg. CaO normally added as limestone

10. Silica Sand TTTThree of most common rock forming minerals on earth CCCChemically named: quartz sand / rock crystal PPPProperties: EEEExtremely heat durable CCCChemical stack resistance

11. World resources of Silica Sand SSilica sand resources is abundant on the world. IIts extraction is limited by ggeographic distribution qquality requirements for some uses eenvironmental restrictions EExtraction of theses resources is dependent on whether it is economic and are controlled by the location of population centers http://minerals.er.usgs.gov/minerals/pubs/commodity/silica/780397.pdf Fig. 1

12. Quartz  Quartz is silicon dioxide (silica)  Is an excellent network former  Slow cooling forms regular network  Fast cooling forms irregular network  High viscosity at melting point  However, nucleates crystals easily  Melting point of Quartz is very high

13. Addition of Modifying ions   Continuous random network (CRN) of the glass former is retained, but that network has been modified by the addition of the second oxide.   These ionic compounds are called Glass Modifiers. Bridging Oxygens link glass forming tetrahedra. Nonbridging Oxygens form the ionic bonds with the modifiers

15. The Solvay process for the manufacture of Soda Ash (NaHCO3). cwx.prenhall.com/petrucci/medialib/ media_portfolio/22.html Fig.6

16. Types / classes of glasses Soda-lime Lead glasses Heat-resistant glasses High-purity Silica glasses Speciality, natural…. 70% silica + Fe + Mn Used as surgical blades in heart surgery

17. Soda-Lime-Silica Glass  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  Soda-lime-silica glass is common glass 90% of all modern glass of all modern glass 66% sand; 15% soda; 10% lime

18. Lead Glass  Lime and soda replaced with PbO  High refractive index- clarity sparkle  Softer –cut and engrave  Good electrical resistance - electronics

19. Heat-resistant - Borosilicate Glass  Soda-lime-silica glass expands much when heated  Breaks easily during heating or cooling  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  Al 2 O 3 i.s.o. B 2 O 3 – aluminosilicate glass with even better heat resistance

20. High-purity Silica  Highest quality – most durable  3 processes – melting pure SiO 2 ; making 96% silica and flame hydrolysis  Pure SiO 2 – pure silica melted @ 1900 ºC under vacuum  96% - Vycor process – borosilicate glass heated to grow crystalline sodium borate channels – extracted hot HNO 3 – leaving 96% pure silica after heat reduction @ 1200 ºC  flame hydrolysis – SiCl 4 in CH 4 / O flame (1500 ºC, produces high-surface silica soot thermally sintered to pure silica at 1723 ºC)

21. Speciality  Coloured glass – MnO 2 – violet, CoO – blue, Cr 2 O 3 - 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

22. Speciality  Coated glass – unique properties - metal / metal oxides Ag+ + RA  Ag  mirror - electrically conducting with SnO 2 coating (thermal SnCl 4 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

23. The Process the history…

24. Historical Glass Manufacturing process: Historical method: hhhheating and blowing sssshape the glass products by hand rrrrequires high skills & is time consuming ttttherefore using glass is considered as luxury in our old world

26. The Process @ Consul

27. Tempered Glass  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

28. The Float Process The equilibrium thickness (T) is given by the relation: where Sg, Sgt, and St are the values of surface tension at the three interfaces shown in the diagram.

31. Glass Forming Casting - molding Pressing – pressing second mold into molten glass Core-forming – clay core dipped into molten mass Fusing – fusing glass rods together around a mold Blowing – blowing air into a glob

32. Glass Forming Flat glass – floating / rolling Glass fibre – continuous strands and Crown process for glass wool

33. Communications are increasingly based on electro-optic systems in which telephones, television and computers are linked by fibre optic cables which carry information by light. Making glass optical fibres is a highly specialised aspect of glass manufacture. Optical fibres consist of two distinct glasses, core of highly refracting glass surrounded by a sheath of glass with lower refractive index between the two glasses, it is guided by total reflection at the core-sheath interface to the other end of the fibre. In theory, a wide range of glasses can be used as long as the difference in refractive index is appropriate but the higher the refractive index of the core relative to that of the sheath glass, the greater the carrying capacity of the fibre. A typical system available commercially comprises a germanium doped silica core and a borosilicate cladding. Optical fibres

34. Analysis and testing is critical to all stages of the glass manufacturing process from the initial starting materials, through the melting and forming to the processes used for manufacturing the final product be it an automotive windscreen, solar control or fire-glazing product Analysis & Testing

35. Consumption of Glass Three largest consumers: 1.g lass packaging (43%) 2.d omestic commodities 3.c onstruction industry National Glass Usage http://www.bisnis.doc.gov/bisnis/country/000727glass_samara.htm Fig. 13

36. Glass Industries The World Glass Industry has a gross production value totaling $82.3 billion Fig. 14 www.icem.org/events/ bled/matdocen.htm