Glass

QuestionWhat 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 - DoremusGlass 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. -PfaenderGlasses 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

GlassesAmorphous solidsNo crystal structureNo long-range orderResemble frozen liquids

Forming a GlassRequirementsMaterial must have high viscosity at melting pointMaterial must have difficulty nucleating crystalProcedureMelt material to eliminate crystal structureCool material quickly through melting temperatureForm supercooled liquidCool until solid

Zachariasens rules glass formation1. No oxygen atom may be linked to more than two cations2. 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

Zachariasens rules glass formationSilica 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

Zachariasens rules glass formationMgOionic 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 polyhedraRules are NOT Satisfied: MgO does not form a glass.Cation CN:Anion CN =6:6

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 formglasses. dominated by ionic bonding; higher CN's

What is the raw material?Sand - SiO2Flux to lower T eg. soda (1700 900C)Stabilizing agent to mitigate water solubility of the glass formed eg. CaO normally added as limestone

72%17%5%6%

Silica SandThree of most common rock forming minerals on earthChemically named: quartz sand / rock crystalProperties:Extremely heat durableChemical stack resistance

World resources of Silica Sand Silica sand resources is abundant on the world. Its extraction is limited bygeographic distributionquality requirements for some usesenvironmental restrictionsExtraction 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.pdfFig. 1

QuartzQuartz is silicon dioxide (silica)Is an excellent network formerSlow cooling forms regular networkFast cooling forms irregular networkHigh viscosity at melting pointHowever, nucleates crystals easilyMelting point of Quartz is very high

Addition of Modifying ionsContinuous 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

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

Types / classes of glassesSoda-limeLead glassesHeat-resistant glassesHigh-purity Silica glassesSpeciality, natural.70% silica+ Fe + MnUsed as surgical blades in heart surgery

Soda-Lime-Silica GlassAdding sodium oxide (soda) lowers melting pointAdding calcium oxide (lime) makes it insolubleSodium and calcium ions terminate the network and soften the glassSoda-lime-silica glass is common glass 90% of all modern glass66% sand; 15% soda; 10% lime

Lead GlassLime and soda replaced with PbOHigh refractive index- clarity sparkleSofter cut and engraveGood electrical resistance - electronics

Heat-resistant - Borosilicate GlassSoda-lime-silica glass expands much when heatedBreaks easily during heating or coolingBoron-oxide-silica glass expands lessTolerates heating or cooling reasonably wellPyrex and Kimax are borosilicate glassesBoron oxide replaces lime and most of soda low thermal expansion coefficientAl2O3 i.s.o. B2O3 aluminosilicate glass with even better heat resistance

High-purity SilicaHighest quality most durable3 processes melting pure SiO2; making 96% silica and flame hydrolysisPure SiO2 pure silica melted @ 1900 C under vacuum96% - Vycor process borosilicate glass heated to grow crystalline sodium borate channels extracted hot HNO3 leaving 96% pure silica after heat reduction @ 1200 C flame hydrolysis SiCl4 in CH4 / O flame (1500 C, produces high-surface silica soot thermally sintered to pure silica at 1723 C)

SpecialityColoured glass MnO2 violet, CoO blue, Cr2O3 - greenOpal 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 processFrosted glass satiny look when exposed to HF

SpecialityCoated 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 lightphototropic darkens upon exposure to light and returns to original clear sate afterwards. AgCl/AgBr

The Process the history

Historical Glass Manufacturing process:Historical method:heating and blowing shape the glass products by hand requires high skills & is time consumingtherefore using glass is considered as luxury in our old world

The Process @ Consul

Tempered GlassTempering glassHeat glass to softening pointCool outside of glass quicklyOutside stiffens while inside is still hotShrinking inside compresses outsideCompressed outside stretches insideResists fractures because surface is compressedCrumbles when cracked because inside is tense

The Float ProcessThe 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.

Glass FormingCasting - moldingPressing pressing second mold into molten glassCore-forming clay core dipped into molten massFusing fusing glass rods together around a moldBlowing blowing air into a glob

Glass FormingFlat glass floating / rollingGlass fibre continuous strands and Crown process for glass wool

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

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 productAnalysis & Testing

Consumption of GlassThree largest consumers: glass packaging (43%)domestic commoditiesconstruction industry

National Glass Usagehttp://www.bisnis.doc.gov/bisnis/country/000727glass_samara.htmFig. 13

Glass IndustriesThe World Glass Industry has a gross production value totaling $82.3 billionFig. 14www.icem.org/events/ bled/matdocen.htm