Science and engineering of glass and natural stone in construction
F. Wittel The vitreous state
Institute for Building Materials | | 1
The vitreous state
From melts to glasses: Thermodynamic aspects Micro-structural aspects
Glass in nature Igneous, metamorphic and sedimentary glass
Synthetic glass The discovery of glass Chemical composition of glass Raw materials
Durability of glass
Institute for Building Materials | | Teaching goals:
You will
…learn about the nature of glass from different perspectives and will have a first look into glass formation.
… get to know natural glass
…hear the story of the invention of glass, learn about chemical compositions of the most important building glasses
… learn about raw materials and batch compositions
… combine what you learned to realize that durability of glass is just a consequence of everything.
Institute for Building Materials | |
Understanding glasses: what is it?
Glass is …
… a transparent, shiny body obtained by smelting sand or grave with an alkali and salt, that is used in diverse ways (practical) D.J.G. Krünitz, Oeconomische Encyclopedie 1779 … a solid, non-crystal material (structural) … a super cooled liquid that solidifies without crystallization (Gustaf Tamman (1861-1938) , Der Glaszustand) … an amorphous mixture of basic and acidic oxides (chemical) … and inorganic melting product that solidifies without crystallization (DIN 1259-1) … a solid being constituted by a spatial, disordered network of building blocks with low coordination number (structural) W.L. Zachariasen (1932), B.E. Warren (1933) … all non-crystalline, solid material are in the glassy state
Institute for Building Materials | | Glass basics: The V-T-Diagramm
Network structure Strongly interconnected wide open
Heat expansion by asymmetric potentials +
Instituteexpansion for Building Materials by changes of network structure | |
Glass basics: Dependence on cooling rate
Glass density depends on cooling rate Small rate leads to higher density, higher rate to low density (up to 20%) Reason: Molecule can not reach thermodynamically preferred higher packing due to fast increase in viscosity Glass temperature depends on cooling rates l 1/l th 0 T
Institute for Building Materials | | Basics: Glass – a definition Non-crystal solid with amorphous structure Glassy state Crystalline State Periodic lattices • All bond of identical strength/ energy Experiment: Glass vs. Tin • precise melting point
Vitreous state • Frozen, disordered structure • Increased viscosity when cooled transformation regime • Glass transition at the end of the transformation regime • Sudden change in heat expansion
• Decrease of specific heat cp Institute for Building Materials | |
Glass summary glasses Crystalline materials Transformation regime (TR) Precise melting point T_s Dilatation in TR like liquid Discontinuity in volume at T_s liquid liquid Irregular network Regelar, periodic arrangement, long range order (irregular bonding angles and distances) no long range anisotropic order (like a liquid) isotropic , frozen super cooled liquid melting 19 of extremely high viscosity (10 dPas RT) And cooling Strong and weak bonds neighbour each other Bonds with similar strength Solidification regime Melting point Silica Glass Silica Crystal (rock crystal)
Institute for Building Materials | | The vitreous state Can be taken by quite a number of materials
Institute for Building Materials | |
The vitreous state: Micro-structural aspects
Institute for Building Materials | 9/18/2019| 10 Structure theories: Crystallite hypothesis by A. Lebedev
. Glass as an assembly of minute crystalline ordered regions (~1.5nm), so called micro crystallites . Ordering is highest in the center of the micro crystallites, but decays towards the exteriors . Micro crystallites are bonded to each other by an amorphous intermediate layer.
Submicroscopic crystallites are so small, that they can not be called crystals any more. No difference to network hypothesis Historical value lies in the first hypothesis with focus on inhomogeneity in glasses.
Institute for Building Materials | |
Structure theories: Network hypothesis by Zachariasen and Warren
. Energy difference between vitreous and crystalline state more or less indistinguishable Identical chemical bonding and structural unit . If glass is a frozen super cooled liquid, then the structure of liquids is the one of the solid Molecules are disordered - . Glasses with SiO2 as network former, silicate SiO 4-tetrahedra can be arranged in a regular or an irregular 3D random statistical network. . Symmetry and periodicity is missing. . Differentiation between network formers and modifiers.
Crystalline quartz (2D/3D) Vitreous quartz (2D/3D)
Institute for Building Materials | | Cation-anion-packing: Sphere model
Coordination- 34 6 8 1220 number
2 3 31 1 21 31 1 2( 5 5) 1 1 3(1 5) 1 rcat/ran 3 2 2 2
Cations have to fill the cation gap entirely. If they are smaller, the structure collapses to the next lower coordination number.
Tetrahedral gap for cation-anion-radii rate of 0.225 Institute for Building Materials | | Network former silica glasses: atomic shell Si: 4 valence electron (like C) Ground state 3s2p2 hybridized sp3 tetrahedral structure (109.5°) 4- [SiO4] Tetrahedron is short range order Hybrid orbital has larger electron cloud than atom orbital large overlap volumes are possible (additional gain of binding energy is the main reason for hybridization) [SiO4] Tetraedron (nesosilicate) 2- 109.47° 4+ Bonding angle 2- 2- 2- Institute for Building Materials | | Excursion: Silicate formations Polymerization of neso-silicated by ≡Si-O-Si ≡ -covalent bondings. Oxygen is bridge forming oxygen. Si-Si distances in SiO-structures Sorosilicate Tectosilicates -quartz Inosilicates Amorphous Silicate Zeolithe Phyllosilicat Institute for Building Materials | | Rules for vitrification Network former / modifier make the molecular skeleton of glass basically no other substances are needed Coordination number of the cation has to be small (3 or 4). (Zachariasen) . Connection of tetrahedra only via joined vertices and not edges or surfaces (max. distance of cations) . Network former mainly acidic oxides with radii ratio cation/oxide anion 0.2-0.4. . Anion should not be bound to more than 2 cations. . Sum of electrons in the p-orbitals divided by the number of atoms has to be >2. Example SiO2: (1*2+2*4)/3=3.33>2 strong tendency for vitrification Institute for Building Materials | | Diezel’s filed strength Dietzel’s Field strength F 22 1 zzezezcat an an cat f 22 , ar cat r an 4400aa Diezels field strength Ion radii and Diezel’s field strength F Element Valence Ionic Most Ionic Field strength Function in at distance of glass Z radius frequent distance for O2 ions Z/a2 (for coordination oxides a in structure CN=6) number CN Å Estimates for the behavior of a certain element rinÅ K 1 1.33 8 2.77 0.13 in a glass network Na 1 0.98 6 2.3 0.19 Li 1 0.78 6 2.1 0.23 Ba 2 1.43 8 2.96 0.24 Pb 2 1.32 8 2.74 0.27 Sr 2 1.27 8 2.69 0.28 Ca 2 1.06 8 2.48 0.33 ~0.1-0.4 2 Mn 2 0.91 6 2.23 0.4 Z/a Fe 2 0.83 6 2.15 0.43 Network modifier Mn 2 0.83 4 2.03 0.49 Mg 2 0.78 6 2.1 0.45 4 1.96 0.53 Zr 4 0.87 8 2.28 0.77 Be 2 0.34 4 1.53 0.86 Fe 3 0.67 6 1.99 0.76 4 1.88 0.85 Al 3 0.57 6 1.89 0.84 ~0.5-1 2 4 1.77 0.96 Z/a Ti 4 0.64 6 1.96 1.04 Intermediate B 3 0.2 4 1.5 1.34 Ge 4 0.44 4 1.66 1.45 Si 4 0.39 4 1.6 1.57 ~1.5- 2 Institute for Building Materials P 5 0.34 4 1.55 2.1 | | Z/a Network former B 3 0.2 3 1.36 1.63 2 After Diezel Natural glasses Earth, moon, meteoroids.. Glasses are abundant in the universe. Glass formation… … by amorphous solidification products of volcanic melts (volcanic glass) … by meteoroid impacts (impactites, tectites) … by lightening strokes (fulgurites) … by rockslides (frictionites) … by shock waves (diaplectic glass) … by biology (glass sponge) Institute for Building Materials | | Apollo 15 pyroclastic green glass Apollo 17 pyroclastic orange Institute for Building Materials lunar volcanic glasses, Apollo 15 mission| | Natural igneous glass: Pyroclastic glass . Volcanic rock in amorphous state No own rock type but a certain structural rock fabric . Originates from quenching of pyroclastic flows by water or ice Pumice stone cellular, porous glass formed by explosive eruptions of gaseous magma. Obsidian; volcanic glass with different names, depending on chemical composition. rhyolitic (silica rich), phonolitic, andesitic etc. obsidian. Water content < 1%. Institute for Building Materials | | Natural metamorphic glass: Glass from Meteorite impacts Impactite • Meltet material at the impact location • Melt quenches at the place of impact with inclusions from the impactor • Can be found in the surrounding of the crater • Examples: Libyan desert glass (LDG), Suevite Tektite • Impact of big meteorides • Plasma is ejected into the atmosphere and cooled down without inclusions • Can be found several hundred of km distant • Example: Moldavit, Indochinite Institute for Building Materials | | Natural metamorphic glass: Formed by lightening strikes . Lightening strikes in sandy soils (Beach) T> 1800°C . Fulgurite (lat. fulgur=thunderbolt) «petrified lightening" . Natural hollow glass tubes with diameter up to several cm and length of several meters with branches . Penetration depth up to 15 meters below the surface . Color and composition depends on the soil type (black to white) . Very smooth interior with small blisters, rough outside with sand grains . Lightening strike in solid rock exogenic fulgurite Institute for Building Materials | | Institute for Building Materials | | Markus Kayser – Solar Sinter Project Sand Babel Wolkenkratzer Institute for Building Materials | | Natural glass: vitrification by shock metamorphis . Vitrification not by a super cooled melt, but by an external force by shock waves lattice structure of crystals is destroyed without going through the liquid phase . Shock waves by meteorite impacts or nuclear weapon tests . In meteorites Maskelynite is found, that is a diaplectic glass with the composition of Plagioklas Special type of impact glasses that originate from shock wave metamorphis. Lunar sample 78235. Institute for Building Materials | | Devitrification Glass is as old as the universe. But why are there no volcanic glasses as old as the universe or even the Precambrian (>4.5Billion years)? Glasses are in a metastable state Devitrification (crystallization) in geological time scales Thermodynamic stable crystal structure starting form crystal seeds. today entirely recrystallized. Snowflake obsidian is in the state of Crystallization to SiO2 Cristobalit Institute for Building Materials | | Devitrification Crystallization below the transformation regime. Aging by pressure and temperature. Exsolution of crystalline silica and field spar crystals. Loss of strength, increased hardness, anisotropy, increased opacity. 24-48 hours close to the melting point and slow cooling. Reaumur’s porcelain. Quartz glass is strongly endangered. Devitrification layer that grows into the material (ß-Cristobalit). Institute for Building Materials | | The discovery of synthetic glasses Discovery about 5000B.C. by Phoenician traders in Lebanon (following Plinius the Elder «Historia naturalis» 23-79n.Chr.) Fireplace in between nitrate blocks on the beech Liquefaction of the blocks with the sand by the temperatures of the fire Opaque, glassy substance Reaction to form sodium silicate (Soluble glass) ≡Si-O-Si≡ + Na-O-Na ≡Si-O-Na + Na-O-Si ≡ Network Network former modifier Soluble glass Stabilization: ≡Si-O-Na + Na-O-Si≡ + Ca-O ≡Si-O-Ca-O-Si ≡ + Na-O-Na Soluble glass Stabi- Stabilized SiO2 Sodium lizer backbone Oxide Institute for Building Materials | | Network former The condition of electro neutrality leads to the rule that only stoichiometry has to be fulfilled.: M2X3 MX2 M2X5 Electron sum Silicon dioxide SiO2 x3.33 Bor trioxide B2O3 x2.8 Phosphor pentoxide P2O5 x3.71 Germanium GeO2 x3.3 Arsenic / Diarsenic trioxid As2O3 x3.6 Antimony Sb2O5 x3.71 Institute for Building Materials Ion radii | | Quartz crystal Network modifier Since glasses have no texture, the properties have to be influences via chemistry of bondings via foreign ions! Network modifiers split up the network and reduce the number of connections smaller glass temperature and viscosity. Modifiers are normally alkaline oxides with large cations: Sodium oxide (Na2O) ↓ Lime (CaO) chemical resistance ↑ Potassium oxide (K2O) glass is getting longer; Lithium oxide (Li2O) ↓↓ More rare: Barium oxide, Niobium oxide, Rubidium oxide, Strontium oxide, Cesium oxide (CsO), Tantalum(V)-oxide, Tellurium oxide Institute for Building Materials | | Network modifiers Manipulation of structure and hence mechanical and chemical properties of glasses SiO2 content high lower High corrosion resitance against Decrease of viscosity acids and bases Increase of electrical High glass temperature conductivity Production from inexpensive carbonates: Institute for Building Materials | | Network modifier for soda-lime glass Opening of the SiO network by calcium and sodium oxide 1. Formation of independent chain endings: Soluble glass [SiO4] Tetrahedron covalent bonding (BO) Ionic bond (NBO) 2. Closing of endings/ ionic bond with metal cation: O- Institute for Building Materials | | Intermediates . Take position in between network formers and modifiers. . Can not form one component glass Examples: Manganese(II)-oxide (MnO) glass gets longer Alumina (Al2O3) glass gets longer, mech. strength ↑, chem. resistance ↑ Lead oxide (PbO) Tg ↓, diffraction number ↑, el. resistance ↑, absorption of X-rays ↑ Titanium dioxide (TiO2) diffraction number ↑, acidic resistance ↑ Zirconium(IV)-oxide(ZrO2) chemical resistance↑, opacifying agent for enamel Zinc oxide ZnO hardness ↑, acts as flux, Tg ↓, devitrification ↓, degassing ↑; Polonium oxide (PoO) Tin(II)-oxide (SnO) Cadmium-oxide (CdO) Beryllium oxide (BeO) Thorium- oxide (ThO2) Selenium(IV)-oxide(SeO2) Iron(II)-oxide (FeO) Iron(III)-oxide (Fe2O3) Nickel(II)-oxide (NiO) Cobalt(II)-oxide (CoO) Institute for Building Materials | | Glass recipes - glasses become transparent Institute for Building Materials | | Glass recipes – glasses become transparent «Take 60 parts of sand, 180 parts of ash from marine plants, 5 parts of char – and you get glass» oldest glass recipe by the Assyrian king Assubanipal (7. B.C.) Glass does not have a clearly defined chemical composition, it is a mixture of metallic oxides and other chemical elements and components. Building blocks of glasses are oxides of Si, B, Al, Mg, Ca, Ba, Pb, Zk, Li, Na, K Chemical analysis always refers to the element in form of its oxide. Institute for Building Materials | | Composition of some important glasses Glass type SiO Al O Na OKOMgOCaOBO PbO TiO FAsSeGeTe / weight % 2 2 3 2 2 2 3 2 Quartz glass 100 – – – – – – – – – – – – – Soda-lime glass* 72 2 14 - - 10 - - - - – – – – Float glass 72 1,5 13,5 - 3,5 8,5 - - - - – – – – Lead glass 60 8 2,5 12 - - - 17,5 - - – – – – Boro-silicate glass 80 3 4 0,5 - - 12,5 - - - – – – – E-glass 54 14 - - 4,5 17,5 10 - - - – – – – Enamel 40 1,5 9 6 1 - 10 4 15 13 – – – – Chalcogenide glass 1 – – – – – – – – – – 12 55 33 – Chalkogenide glass 2 – – – – – – – – – – 13 32 30 25 Institute for Building Materials | | Overview glass types Institute for Building Materials | | Classification of glasses 1 Hard glass Soft glass High resistivity againt chemical attacs Low production costs High cooling temperatures Easyer melting and forming High thermal resistivity Boro-silicate glasses Soda-lime glass; lead glass; non-silicate glasses Oxydic glass Non-oxydic glass Silicate glasses ; Soda-lime glass Nitrateglass, Fluorideglass Mixtures of diverse glasses like boro-silicate Chalcogenide glass glasses Non-silicate glass like borate glass, phosphate Metallic glass glass Polymeric glasses like PS, PMMA … Institute for Building Materials | | Oxidic glasses: silicate glass Aluminosilicate glass Lead silicate glass high contents of aluminum oxide Al2O3 high amounts of lead oxide (>10% up (15-25%) along with low sodium to 30%) oxides High electrical resistance Increased light refraction High chemical resistance Low electrical conductivity Low viscosity and melting temperature Increased absorption of X-rays LCD flat panel displays Optical glass Fiber-glass (E-glass) Radiation protection glazing Fire protection glazing Halogen lights Combustion pipes Institute for Building Materials | | Oxidic glasses: silicate glass Quartz glass (Silica glass) Soda-Lime-Glass SiO2 100% Silicon dioxide with network modifiers like Sodium oxide and lime SiO2 72%; Na2O 14.5%; CaO 8.5% Al2O3 1.5%; MgO 3.5% Low heat expansion coefficient Low softening temperature High UV- transmissivity Low chemical resistivity Extremely good chemical resistivity High heat expansion coefficient Temperature resistant up to 1400°C High electric conductivity Chemical glassware, glass fibers Window glass, mold glass, packaging glass Institute for Building Materials | | Oxydic glasses: Glass mixtures Boro-silicate glass (Duran) Mixtures of silica and boro trioxide with additions: Na2O-B2O3- SiO2 Good fusability High chemical resistivity Low heat expansion coefficient in wt% Jenaer Jenaer Jenaer Pyrex (USA) High thermal resistivity Geräteglas 20 Duranglas Rasothermglass SiO 76 74 78 80.8 Lab glass 2 B2O3 7 14 12.5 12 Na2O 6.5 4.5 5.5 4.3 BaO 4.0 3.0 - - Technical Al O 4.5 3.5 3.0 2.2 Boro silicate glass: 2 3 -7 Thermal expansion 10 [-/K] a10-100=46 a10-100=38 a10-100=33 a10-300=33 T [°C] 550 534 527 560 Institute for Building Materials b | | Oxydic glasses: Non-silicate glasses Borate glass Phosphate glass B2O3 40% P2O + Additions Al2O3 30% CaO 30% High electrical resistance Addition of BaO Addition of PbO High light diffraction High light diffraction Low chemical resistivity Low chemical resistivity Optical glasses Heat insulation glass, optical glass Institute for Building Materials | | Adjustment of glass properties Statistical analysis based on glass-datenbancs like SciGlass or Interglas. Large databanks for glass properties (SciGlass> 360.000 different glass compositions). Prediction of diverse compositions by regression analysis. Basically all physical and chemical properties of glasses and glass forming melts. • Different interpolation schemes for wide ranges of concentration. • Ternary phase diagrams for vitrification • Optical spectra. b variable coefficient nn n number of glass components Glass property b0 bii C b ikik C C C concentration of component ik11 Crystallization or phase changes are not allowed to happen within the scheme Institute for Building Materials | | Institute for Building Materials | | Adjustment of glass properties: Density 3 3 Variations in density 2-6g/cm ; Density SiO2 as quartz 2.65/ glass 2-2.2g/cm Loosened structure, path dependent Addition of alkali oxides increases glass density: opening of the network vs. filling of voids Due to higher atomic weight, the density increases. 100 Estimate: p ii/ i 3 3 Oxide i (g/cm )Oxidei (g/cm ) SiO2 2.24 As2O5 3.33 Al2O3 2.75 CaO 4.3 B2O3 2.9 ZnO 5.94 Na2O 3.2 BaO 7.2 Binary K O 3.2 PbO 10.3 Alkali-silicate glasses 2 Institute for Building Materials MgO 3.25 | | Adjustment of glass properties: Heat expansion Relation between thermal expansion and chemical composition of glass is rather linear. Linear model can be used: 3 kpnn pn percentage of weight of each constituent kn constants High expansion factors of sodium oxide point at low thermal resistance of soda-lime glass. Values factored by 109 for clarity. Oxide constant Oxide constant SiO2 15 MgO 135 Al2O3 52 CaO 489 ZrO2 69 ZnO 21 Na2O 1296 BaO 520 K2O 1170 Institute for Building Materials | | Raw materials for glass facilities Glass products Raw materials energy primary, minerals (Sand, fieldspar, lime stone, Dolomite,….) Primary, synthetic (Soda, Sulfates, colorants) Secondary (cullet) Institute for Building Materials | | Raw materials for glass Quality + Availability = price • Chemical composition: Main • Local / global market components, impurity (e.g. Fe- • Local production vs. Import content), moisture content, etc. dependence (Stability of • Phases: main phase, critical exporting country) phase • Natural vs. Industrially • Grain habitus produced • Grain size distribution • Glass industry main or • Uniformity of quality secondary customer • Transportation distance (needed storage) Institute for Building Materials | | Primary raw materials Element Oxide Raw material Sand cullet Si SiO2 Illmenite, FeTiO TiO Ti TiO2 3 2 Zirconium, ZrSi0 ZrO Zr ZrO2 4 2 fieldspar Nephelinite Metal furnace Phonolith Kaolinite Al Al2O3 (Ba,Ca,Na,K,NH4)(Al,B,Si)4O8 slag Al(OH)3 Al2O3 Borax H BO B O Colemanite Tincal/Borax BB2O3 3 3 2 3 Red iron oxide FeS FeS Fe Fe2O3 2 Cr O K Cr O Cr Cr2O3 2 3 2 2 7 Trona Na CO NaOH Na Na2O 2 3 Potash, K CO KK2O 2 3 Ca CaO Lime stone Mn MnO MnO2 MnCO3 Na So K SO CaSo Gips BaSO SSO3 2 4 2 4 4 4 Pb PbO PbO Pb3O4 Institute for Building Materials | | Mg MgO Dolomite, CaMg(CO3) 2 MgCO3 Soda-lime glass: raw materials Quartz sand: grain size <1mm; almost pure SiO2; small contamination with Fe2O3 (green coloring); network former. Soda: Soda; Na2CO3; NaO-carrier, lowering of melting point of SiO2; flux; network modifier. CO2 is released refining Potash: Potassium carbonate K2CO3; brings Potassium oxide into the batch; network modifier and flux. Field spar: NaAlSi3O8; Increase of hardness and stabilization Lime: Network modifier; Increase of strength and resistance. Dolomite: Carrier for CaO and MgO, acts like Lime. Cullet: Significant decrease of energy use but bad color separation, foreign metals, ceramics and special glasses included not usable for window glass. By careful selection of raw materials, the iron content can be significantly reduced clear glass. Institute for Building Materials | | Raw materials: A glimpse into the past Egypt Rome Europe Syria 1400 Today 1500. BC 100 AD 1300 AD AD SiO2 65 68 53 70 73 Soda, Na2O 20 16 3 12 16 Potash, K2O 2 0.5 17 2 0.5 Lime, CaO 4 8 12 10 5 Magnesium, 40.5733 MgO Batch Plant ash, Quartz Soda, Sand Potash, potash, Synthetic Sand/Quartz Sand/Quartz components Institute for Building Materials | | New processes Leblanc-Process Solvay-process I. II. III. IV. Institute for Building Materials | | New processes Trona-process Trona (trisodium hydrogendicarbonate dihydrate); Na3(CO3)(HCO3)•2H2O Largest deposits close to Green River Wyoming (dried-up, covered lakes) Entirely replaces Solvay-Process in the USA. Institute for Building Materials | | Glass corrosion Chemical attack by… 1. Hydrofluoric acid 2. Aqueous acids 3. Alkali Water & combined acid/base attack Institute for Building Materials | | ETH Zürich, HIF E Chemical resistance of glass Attack by hydrofluoric acid Hydrofluoric acid dissolves the silicon dioxide backbone and forms SiF. In aqueous solution if further reacts to Fluorosilic acid: SiO2 + HF SiF4 + H2O; SiF4 + 2HF H2(SiF6) Easily dissolvable silicon hexafluoride SiF6 Is formed. Institute for Building Materials | | Chemical resistance of glass Attack by aqueous acids Ion exchange reaction – Protons of the acid replace cations in the glass. Reaction: -Si-O-Na + + H + -Si-OH + Na + Due to the reaction the acid depletes with protons, the pH value increases. A silicate layer, saturated with protons is formed, that acts as a diffusion barrier for further attack passivation Institute for Building Materials | | Chemical resistance of glass Attack by alkali Entire dissolution of the silica backbone, attack on the bridging oxygen. SiO2 molecule is dissolved and washed away. Always new surfaces are formed no passivation Severity of alkali attack decreases in the order: NaOH KOHLiOHNH3 Institute for Building Materials | | Institute for Building Materials | | Institute for Building Materials | 9/18/2019| 59 Chemical resistance of glass Hydroxide ion Ionic end of chain Hydroxide ion [SiO4] tetrahedron Glas skin Institute for Building Materials | | Volume structure Volume Chemical resistance of glass: Evolution Case 1 passive layer Formation Type I: Formation of a passive surface layer, e.g. dc silica glass in neutral solution. The dissolution rate te t is dc/dt ∞ te-at . dt dc at Type II: Protective layer by leaching of alkali, but dt network is unaltered. Example is and aqueous acid on silica glass. Type III: Leaching and surface reaction lead to two protective layers of different constitution, but network remains stable. Type IV: Leaching and dissolution take place simultaneously and leaching layer grows into the network. One example is alkali glass in water. Two competing reactions are diffusion c∞t1/2 and Case 2 competing reactions dissolution c∞t. Diffusion dissolution Type V: Continuous dissolution of the network ct without leaching zone. Hydrofluoric acid on silica ct glass is one example, with a constant dissolution Case 3 constant dissolution rate of dc/dt∞a. dc a dt Institute for Building Materials | | Chemical resistance of glass: Evolution Institute for Building Materials | | Classes of chemical resistivity DIN 12112 DIN 52322 DIN 12111 Acid solubility Half of the Caustic solubility Surface Hydrolytic HCl Acid class in acid surface class in base weight loss class usage equivalent weight loss after 3h as Na2O after 6h [mg/dm2] [mg/dm2] [mg/g] [ml] 1 none 0-0.7 1 Weakly 0-75 1 <0.1 <31 2 Weakly 0.7-1.5 2 moderate 75-175 2 0.1-0.2 31-62 3 Moderate 1.5-15 3 strongly >175 3 0.2-0.85 62-264 4 Strongly >15 4 0.85-2 264-620 5 >2 620-1085 Institute for Building Materials | | Teaching goals: You will …learn about the nature of glass from different perspectives and will have a first look into glass formation. … get to know natural glass …hear the story of the invention of glass, learn about chemical compositions of the most important building glasses … learn about raw materials and batch compositions … combine what you learned to realize that durability of glass is just a consequence of everything. Institute for Building Materials | | Thank you for your attention. Institute for Building Materials | 09.09.2013| 65