A member of NSG Group1 Application of Inorganic Chemistry in IndustryFlat Glass and Coatings On GlassDr Troy ManningAdvanced Technologist, On-line CoatingsPilkington European Technical CentreHall LaneLathomUKtroy.manning@2 Outline•Overview of Flat Glass industry and NSG/Pilkington•Flat Glass manufacture–Float Glass Process•Coating technology within the glass industry–Chemical Vapour Deposition•Examples of on line coating applications–Low Emissivity/Solar Control–Self Cleaning•Summary•Suggested Reading3 Global Flat Glass MarketGlobal Market 37 million tonnes (4.4 billion sq. m)Building Products 33 m tonnes - Automotive 4m tonnesOf which–24 million = high quality float glass–3 million = sheet–2 million = rolled–8 million = lower quality float (mostly China)Global Value At primary manufacture level €15 billionAt processed level €50 billion4 NSG and Pilkington combined•A global glass leader – the pure play in Flat Glass•Combined annual sales c. £4 billion•Equal to Asahi Glass in scale, most profitable in Flat Glass•Ownership/interests in 46 float lines•6.4 million tonnes annual output•Widened Automotive customer base•36,000 employees worldwide•Manufacturing operations in 26 countries•Sales in 130+ countries5 Manufacture of Flat Glass•Four main methods–Plate Glass (1688) – molten glass poured on to a flat bed, spread, cooled and polished–Sheet Glass (1905) – continuous sheet of glass drawn from tank of molten glass–Rolled Glass (1920) – molten glass poured onto to two rollers to achieve an even thickness, making polishing easier. Used to make patterned and wired glass.–Float Glass (1959) – molten glass poured onto bed of molten tin and drawn off in continuous ribbon. Gives high quality flat glass with even thickness and fire polish finish. ~320 float-glass lines worldwide6 Melting furnaceFloat bathCooling lehrContinuos ribbon of glassCross cuttersLarge plate lift-off devicesSmall plate lift-off devicesRaw material feedThe Float-Glass Process•Operates non-stop for 10-15 years•6000 km/year•0.4 mm-25 mm thick, up to 3 m wide7 The Float Glass Process8 Raw materials9 Melting Furnace10 Float Bath11 Float Glass Plant12 The Float-Glass ProcessFine-grained ingredients, closely controlled for quality, are mixed to make batch, which flows as a blanket on to molten glass at 1500 ºC in the melter. The furnace contains 2000 tonnes of molten glass.After about 50 hours, glass from the melter flows gently over a refractory spout on to the mirror-like surface of molten tin, starting at 1100ºC and leaving the float bath as a solid ribbon at 600ºC. Despite the tranquillity with which float glass is formed, considerable stresses are developed in the ribbon as it cools. 13 Raw Materials•Oxide % in glass Raw material source•SiO272.2Sand•Na2O13.4Soda Ash (Na2CO3)•CaO8.4Limestone (CaCO3)•MgO4.0Dolomite (MgCO3.CaCO3)•Al2O31.0Impurity in sand, Feldspar or Calumite•Fe2O30.11Impurity in sand or Rouge (Fe2O3)•SO30.20Sodium sulphate•C0.00Anthracite14 Raw materials• SiO2Very durable, BUT high melting point (>1700°C)!•+ Na2OMelts at a lower temperature, BUT dissolves in water!•+ CaOMore durable, BUT will not form in bath without crystallisation•+ MgOGlass stays as a super-cooled liquid in bath, no crystallisation•+ Al2O3Adds durability•+ Fe2O3Adds required level of ‘green’ colour for customer15 Chemistry of GlassImportant glassmaking chemistry: basic reactionsNa2CO3 + SiO2 1500ºC Na2SiO3 + CO2Na2SiO3 + x SiO2 Na2SO4 (Na2O)(SiO2)(x+1)Digestion16 Composition of Glass17 Structure of GlassRandom network of [SiO4]- tetrahedral units.Na-O enter Si-O network according to valency – Network FormersCa and Mg – Network Modifiers – make structure more complex to prevent crystallisation 18 Body-tinted GlassIonResulting Colour of GlassFerrous (Fe2+)BlueFerric (Fe3+)YellowFe2+ + Fe3+GreenSelenium (SeO2)BronzeCobalt (Co2+)Grey/BlueNickel (Ni2+)Grey19 CIE L a* b* colour space20 CIE L a* b* colour space21 Functions of a Window•Light in – homes, offices•Light out – shops, museum displays•Heat in – heating dominated climates•Heat out – cooling dominated climates•Can change properties of glass by applying coatings to the surface22 Making a window functional - coatings•A wide variety of coating technologies are utilised by the glass industry–Spray Pyrolysis–Powder Spray–Chemical Vapour Deposition–Sputter Coating–Thermal Evaporation Coatings–Sol Gel Coatings•These are applied–On Line i.e. as the glass is produced on the float line–Off Line i.e. coating not necessarily produced at the same location23 Variations of CVD•Atmospheric Pressure – APCVD•Low Pressure - LPCVD•Aerosol Assisted - AACVD •Metalorganic – MOCVD•Combustion/Flame – CCVD•Hot Wire/Filament – HWCVD/HFCVD•Plasma Enhanced - PECVD•Laser Assisted – LACVD•Microwave Assisted – MWCVD•Atomic Layer Deposition – ALD24 Chemical Vapour Deposition25 Chemical Vapour DepositionMain gas flow regionGas Phase ReactionsSurface DiffusionDesorption of Film PrecursorBy ProductsDiffusion to surface26 Chemical Vapour DepositionAnimation kindly supplied by Dr. Warren Cross, University of Nottingham27 CVD processes and parametersProcessParametersTransportPrecursorsGas phase reactionPressure, temperature, flow conditions, boundary layer thickness, gas phase concentration, precursors, carrier gasDiffusionPressure, temperature, flow conditions, boundary layer thickness, gas phase concentrationAdsorptionTemperature, gas phase concentration, number and nature of sitesSurface reactionTemperature, nature of surfaceDesorption of by-productsTemperature, pressure, nature of surfaceDiffusion to lattice siteTemperature, surface mobility, number of vacant sites28 CVD Precursor Properties•Volatile – gas, liquid, low melting point solid, sublimable solid•Pure•Stable under transport•React/Decompose cleanly to give desired coating – minimise contaminants•Can be single source or dual/multi-source29 CVD Precursors•Single Source – pyrolysis (thermal decomposition) e.g Ti(OC2H5)4 TiO2 + 4C2H4 + 2H2O (>400 ºC)•Oxidation e.g SiH4(g) + O2(g) SiO2(s) + 2H2(g)•Reduction e.g. WF6(g) + 3H2(g) W(s) + 6HF(g)•Dual source e.g. TiCl4(g) + 4EtOH(g) TiO2(s) + 4HCl(g) + 2EtOEt(g)30 Dual Source and Single Source PrecursorsFilmDual SourceSingle SourceGaAsGaCl3 + AsH3Me2Ga(AsH2)TiNTiCl4 + NH3Ti(NMe2)4WSiWCl6 + SiH4W(SiR)4TiO2TiCl4 + H2OTi(OiPr)4CdSeCdMe2 + H2SeCd(SeR)231 Transport of Precursors•Bubbler for liquids and low melting solids• Direct Liquid Injection – syringe and syringe driver for liquids and solutions• Sublimation for solids – hot gas passed over heated precursor•Aerosol of precursor solutions32 Effect of Temperature on Growth RateIndependent of temperature33 Flow conditionsLaminar Flow regimeTurbulent Flow Regime34 Reynolds Number•Dimensionless number describing flow conditionsr = r = Mass density related to concn and partial pressureu = average velocitym= viscosityL = relevant length, related to reactor dimensionsIf Re < 10 Laminar flowIf Re >> 1000 fully turbulent flowReality is between the two extremes35 Dimensionless Numbers•Reduces the number of parameters that describe a system•Makes it easier to determine relationships experimentally•For example: Drag Force on a SphereVariables: Force = f (velocity, diameter, viscosity, density)Can be reduced to 2 “dimensionless groups”:Drag coefficient (CD) and Reynolds number (Re)36 Dimensionless NumbersLaminar flow regimeTurbulent flow regimeExperimental values of CD for spheres in fluid flows at various Re37 Boundary Layer – gas velocityFrictional forces against reactor walls decrease gas velocity The boundary layer thickness can be estimated from:38 Boundary Layer - temperatureContact with hot surfaces increases temperature39 Boundary Layer – precursor concentrationDepletion of precursor decreases gas phase concentration40 Nucleation and GrowthVan der Waals type adsorption of precursor to substratePrecursors then diffuse across surfacePrecursors diffuse across boundary layer to surfaceAnd can be desorbed back into main gas flowOr can find low energy binding sites to coalesce into filmMain Gas Flow41 Nucleation and GrowthSubstrate TemperatureGrowth RateSurface DiffusionCrystallinityLowHighSlow relative flux of precursorsAmorphous – no crystalline structureHighLowFast relative to flux of precursorsEpitaxial – replicates substrate structureIntermediateIntermediateIntermediatePolycrystalline42 Growth Mechanisms(b) Frank - van der MerweLayer growth(c) Stranski - KastanovMixed layered and island growth(a) Volmer - WeberIsland growth43 Thin Film Analysis•Many techniques are used to characterise thin films•Examples include–XRD – crystallinity, phase–XRR – layer thickness, layer roughness–SEM/EDX/WDX – morphology, thickness, composition–Raman – phase, bonding–FTIR – phase, bonding–XPS – composition, depth profiling, doping–SIMS – composition, depth profiling, doping–AFM – roughness, surface morphology–TEM – crystalline structure, crystal defects–Analysis of functional properties44 CVD on GlassFor on-line coating of glass we require:•High growth rates – required thickness in <2 s•Stable chemistry – uniform coatings for continuous operation for many days•Good adhesion to glass•High efficiency – reduce costs45 APCVD Strengths and WeaknessesStrengthsWeaknessesResultOn-line coating possibleReduced flexibilityReduced labour costs, high volume manufactureFresh substrate surfacesNo washing step, enhanced adhesionHigh deposition ratesNeed to match line speedThick films possible with high throughputHard filmsImproved processability and performanceStructure control possible e.g. crystallinityRough surfaceImproved functional properties and durabilityVolatile precursors requiredLimited range of materials46 On-Line Coating PositionsLoad raw materialsMeltingFloatingCoolingCutting and Stacking25 ºCGlass ribbon600 ºC1050 ºC40 ºC1500 ºCPossible positions for CVD coating systems47 Laminar Flow CVD CoaterGlassGlassGlass Ribbon FlowGlass Ribbon FlowUp-Stream ExhaustUp-Stream ExhaustDown-Stream ExhaustDown-Stream ExhaustPrecursorPrecursor gases gasesOutside Outside AtmosphereAtmosphere48 APCVD Applications on Glass•Coating technology allows us to add functionality to glass•Coating technology is today used for a variety of products–Low Emissivity coatings to reduce heating bills–Solar Control coatings to reduce solar heat gain–Technical products e.g. TCO’s for LCD displays, solar cells–Anti-Reflective Products–Hydrophobic Coatings–Self Cleaning Coatings–Smart Coatings e.g. electrochromics, thermochromics, photochromics49 Low-Emissivity Coatings•Designed to reduce heating billsIn a double glazed unit, a low-emissivity coating on the inner pane blocks radiative heat trying to escape into the cavity 50 Emissivity•Emissivity is the ratio of radiation emitted by a blackbody or a surface to the theoretical radiation predicted by Planck’s law. •Surface emissivity is generally measured indirectly by assuming that e = 1 - reflectivity, usually at a specified wavelength 51 Solar SpectrumWe have to distinguish between :•what comes from the outside to the inside – solar spectrum•what goes from the inside to the outside - heatVisible lightInfra-RedUV52 Outside to InsideOptimal curve for solar control - no UV - all visible light pass - no IROptimal curve for low-e - no UV - all visible light pass - all IR pass53 Inside to Outside – No Glazing5µm50µmHeat radiation (“Black body”) at 23.9 ºC UVVisible lightIR54 Inside to Outside – Low-e Coated GlassLow emissivity coated products limit the black body radiation i.e. the energy losses through the window:K-Glass e=0.1555 Transparent Conducting Oxides•Doped metal oxides displaying n-type conductivity•F- substitutes for O2- in the SnO2 lattice releasing an electron into the conduction band i.e. Sn4+O2-2-xF-xe-x•Close to metallic conductivity (15 W/€) can be achieved but with high optical transmittance (band gap ~4 eV)C. G. Granqvist, Adv. Mater., 2003, 15, 1789-180356 CVD of SnO2:F•SnCl4 + H2O + HF SnO2:F + HCl (~1.5 at% F)–Much gas phase reaction–Gases introduced separately in turbulent flow regime–Very high growth rates >100 nm/s possible–Low precursor efficiency <10%SiCxOy (70 nm)SnO2:F (350 nm)GlassSiH4 + C2H4 + CO2 SiCxOy + H2O + other by-productsUsed as colour suppression and barrier layer57 Low Emissivity Coating•Generally based on SnO2:F (Transparent Conductive Oxide)•SiCO under layer used as colour suppressant58 Low-E and Solar Control Coatings59 Self-Cleaning GlassTwo mechanisms:•Super hydrophilicity•Photocatalytic degradation of organic matter.•TiO2 coating60 SuperhydrophilicityOxygen vacanciesTiO-TiOTiHTiTiTiH+TiOTiOTiTiOTiOTiHHH2O(OH-, H+)Water dropletsUniform water filmUV illumination timeContact angleooooooodarkUV61 Photocatalytic ActivityUltra band gap irradiation of TiO2 Generation of electron hole in valence bandHole migrates to the surface and results in oxidation of organic materialValence BandConductance BandOxidationReductionAA+BB-h+hn62 Semi-conductor PhotocatalysisA. Mills, S Le Hunte, J. Photochem. Photobiol A, 1997, 108, 1-35.63 CVD of ActivTMSiO2 (30 nm)TiO2 (17 nm)GlassSiH4 + O2 + C2H4 SiO2 + by-productsUsed as barrier layer to prevent diffusion of Na ions into TiO2 layerTiCl4 + EtOAc TiO2 + HCl + organic by-productsLaminar Flow regimeReasonable growth rates and precursor efficiency64 ActivTM65 ActivTM66 ActivTM67 Superhydrophilicity15 mins UV Exposure30 mins UV Exposure45 mins UV ExposureBefore UV Exposure68 Photocatalytic Effect UV-AbsorptionO2 -OH*Organic SoilHH2 2O + COO + CO2 2GlassBarrier LayerTiO2 - Layer69 Photocatalytic Effect•The photoactivity of the coating can be measured by monitoring the decomposition of a standard contaminant •A thin film of stearic acid (n-octadecanoic acid, ~200Å) is applied from a methanol solution onto the coating•Stearic acid used as a typical organic contaminant•FTIR (Fourier transform infra-red spectroscopy) used to detect C-H stretch of stearic acid•C-H absorption intensity measured after varying UV exposure70 Stearic Acid DecompositionC-H Absorption Zero UV exposureC-H Absorption ~60 mins UV exposureUV 0.77W/m2 @340nm71 Pilkington ActivTM72 Summary•Scale of the Global Flat Glass Industry•Manufacturing Flat Glass – Float Glass Process•Coating Glass – Chemical Vapour Deposition•Examples of commercial glazing coatings prepared by CVD73 Recommended Reading•D.W. Sheel and M.E. Pemble Atmospheric Pressure CVD Coatings on Glass, ICCG4 2002 http://www.cvdtechnologies.co.uk/CVD%20on%20Glass.pdf•M.L. Hitchman, K.F. Jensen Chemical Vapor Deposition Academic Press, 1993•W.S. Rees, CVD of Non-metals, VCH, Weinheim, 1996 •M. Ohring The Materials Science of Thin Films, Academic Press, 2001•74 First in Glass™75 。