The vitreous state · … a solid being constituted by a spatial, disordered network of building...

||Institute for Building Materials

Science and engineering of glass and natural stone in construction

The vitreous stateF. Wittel

1


The vitreous state

From melts to glasses:Thermodynamic aspectsMicro-structural aspects

Glass in natureIgneous, metamorphic and sedimentary glass

Synthetic glassThe discovery of glassChemical composition of glassRaw materials

Durability of glass


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.


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


Glass basics: The V-T-Diagramm

Network structureStrongly interconnected wide open

Heat expansion by asymmetric potentials+

expansion by changes of network structure


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

Glass basics: Dependence on cooling rate

01 /th

ll

T


Basics: Glass – a definitionNon-crystal solid with amorphous structure Glassy state

Crystalline StatePeriodic lattices

• All bond of identical strength/ energy• 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

Experiment: Glass vs. Tin


Glass summaryglasses 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(irregular bonding angles and distances) no long range

order (like a liquid) isotropic , frozen super cooled liquid of extremely high viscosity (1019dPas RT)

Regelar, periodic arrangement, long range order anisotropic

Strong and weak bonds neighbour each otherSolidification regime

Bonds with similar strength Melting point

Silica Glass Silica Crystal (rock crystal)

meltingAnd cooling


Can be taken by

quite a number of materials

The vitreous state

||Institute for Building Materials 9/18/2019 10

The vitreous state: Micro-structural aspects


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.


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)


Cation-anion-packing: Sphere model

Coordination-number

3 4 6 8 12 20

rcat/ran2

3 13

31

2 2 1 3 1 1

2 2 ( 5 5 ) 1 12 3 (1 5 ) 1

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<rcat/ran<0.414.

Structures are not allowed to rattle when being vibrated.

Example: r(Si4+)=0.041nm; r(O2-)=0.14nm rcat/ran=0.293


Network former silica glasses: atomic shellSi: 4 valence electron (like C)

Ground state 3s2p2 hybridized sp3 tetrahedral structure (109.5°)

[SiO4]4- 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)

109.47°Bonding angle

2-

4+

2-

2-

2-


Excursion: Silicate formations

Polymerization of neso-silicated by ≡Si-O-Si ≡ -covalent bondings.

Oxygen is bridge forming oxygen.

Si-Si distances in SiO-structures

Zeolithe

Tectosilicates

Phyllosilicat

Inosilicates

Sorosilicate -quartz

Amorphous Silicate


Rules for vitrificationNetwork 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


Diezel’s filed strength

2 2

2 20 0

1,

4 4c a t a n a n c a t

c a t a n

D ie ze lsf ie lds tr e n g thF

z z e z e zf a r r

a a

Dietzel’s Field strength F

Ion radii and Diezel’s field strength

Estimates for the behavior of a certain element in a glass network

Element Valence

Z

Ionic

radius(forCN=6)

r in Å

Most

frequentcoordinationnumber CN

Ionic

distance foroxides a inÅ

Field strengthat distance ofO2 ions Z/a2

Function inglass

structure

K 1 1.33 8 2.77 0.13

Net

wor

km

odifi

er

Z/a

2 ~0.

1-0.

4

Na 1 0.98 6 2.3 0.19Li 1 0.78 6 2.1 0.23Ba 2 1.43 8 2.96 0.24Pb 2 1.32 8 2.74 0.27Sr 2 1.27 8 2.69 0.28Ca 2 1.06 8 2.48 0.33Mn 2 0.91 6 2.23 0.4Fe 2 0.83 6 2.15 0.43Mn 2 0.83 4 2.03 0.49

Inte

rmed

iate

Z/a

2~

0.5-

1

Mg 2 0.78 6 2.1 0.454 1.96 0.53

Zr 4 0.87 8 2.28 0.77Be 2 0.34 4 1.53 0.86Fe 3 0.67 6 1.99 0.76

4 1.88 0.85Al 3 0.57 6 1.89 0.84

4 1.77 0.96Ti 4 0.64 6 1.96 1.04B 3 0.2 4 1.5 1.34

Net

wor

kfo

rmer

Z/a

2~

1.5-

2

Ge 4 0.44 4 1.66 1.45Si 4 0.39 4 1.6 1.57P 5 0.34 4 1.55 2.1B 3 0.2 3 1.36 1.63After 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 lunar volcanic glasses, Apollo 15 mission

Apollo 17 pyroclastic orange

Apollo 15 pyroclastic green glass


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%.


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


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



Markus Kayser – Solar Sinter Project

Sand Babel Wolkenkratzer


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.


DevitrificationGlass 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


DevitrificationCrystallization 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).


Sodium Oxide

Stabilized SiO2 backbone

Stabi-lizer

Soluble glass

Soluble glassNetwork former

Network modifier

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

Stabilization:

≡Si-O-Na + Na-O-Si≡ + Ca-O ≡Si-O-Ca-O-Si ≡ + Na-O-Na

Reaction to form sodium silicate (Soluble glass)

≡Si-O-Si≡ + Na-O-Na ≡Si-O-Na + Na-O-Si ≡


Network formerThe condition of electro neutrality leads to the rule that only stoichiometry has to be fulfilled.:

Quartz crystal

M2X3 MX2 M2X5 Electron sum

Silicon dioxide SiO2 x 3.33

Bor trioxide B2O3 x 2.8

Phosphor pentoxide P2O5 x 3.71

Germanium GeO2 x 3.3

Arsenic / Diarsenic trioxid As2O3 x 3.6

Antimony Sb2O5 x 3.71

Ion radii


Network modifierSince 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


Network modifiers

Manipulation of structure and hence mechanical and chemical properties of glasses

Production from inexpensive carbonates:

High corrosion resitance against acids and bases

High glass temperature

Decrease of viscosity

Increase of electrical conductivity

SiO2 content

high lower


Network modifier for soda-lime glassOpening of the SiO network by calcium and sodium oxide

1. Formation of independent chain endings:

covalent bonding (BO) Ionic bond (NBO)

2. Closing of endings/ ionic bond with metal cation:

[SiO4] Tetrahedron

Soluble glass

O-


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)


Glass recipes - glasses become transparent


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.


Composition of some important glasses

Glass type/ weight % SiO2 Al2O3 Na2O K2O MgO CaO B2O3 PbO TiO2 F As Se Ge Te

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


Overview glass types


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 glasses

Chalcogenide glass

Non-silicate glass like borate glass, phosphate glass

Metallic glass

Polymeric glasses like PS, PMMA …


Oxidic glasses: silicate glass

Aluminosilicate glass Lead silicate glass

high contents of aluminum oxide Al2O3

(15-25%) along with low sodium oxides

high amounts of lead oxide (>10% up to 30%)

High electrical resistanceHigh chemical resistance

Increased light refractionLow electrical conductivityLow viscosity and melting temperatureIncreased absorption of X-rays

LCD flat panel displaysFiber-glass (E-glass)Fire protection glazingHalogen lightsCombustion pipes

Optical glassRadiation protection glazing


Oxidic glasses: silicate glass

Quartz glass (Silica glass) Soda-Lime-Glass

SiO2 100% Silicon dioxide with network modifiers like Sodium oxide and limeSiO2 72%; Na2O 14.5%; CaO 8.5%Al2O3 1.5%; MgO 3.5%

Low heat expansion coefficientHigh UV- transmissivityExtremely good chemical resistivityTemperature resistant up to 1400°CHigh electric conductivity

Low softening temperatureLow chemical resistivityHigh heat expansion coefficient

Chemical glassware, glass fibers Window glass, mold glass, packaging glass


Oxydic glasses: Glass mixtures

Boro-silicate glass (Duran)

Mixtures of silica and boro trioxide with additions: Na2O-B2O3-SiO2

Good fusabilityHigh chemical resistivityLow heat expansion coefficientHigh thermal resistivity

Lab glass

TechnicalBoro silicate glass:

in wt% Jenaer Geräteglas 20

Jenaer Duranglas

Jenaer Rasothermglass

Pyrex (USA)

SiO2 76 74 78 80.8

B2O3 7 14 12.5 12

Na2O 6.5 4.5 5.5 4.3

BaO 4.0 3.0 - -

Al2O3 4.5 3.5 3.0 2.2

Thermal expansion 10-7 [-/K] a10-100=46 a10-100=38 a10-100=33 a10-300=33

Tb [°C] 550 534 527 560


Oxydic glasses: Non-silicate glasses

Borate glass Phosphate glass

B2O3 40%Al2O3 30%CaO 30%

P2O + Additions

High electrical resistanceAddition of PbOHigh light diffractionLow chemical resistivity

Addition of BaOHigh light diffractionLow chemical resistivity

Optical glasses Heat insulation glass, optical glass


Adjustment of glass propertiesStatistical 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.

Crystallization or phase changes are not allowed to happen within the scheme

01 1

n n

i i ik i ki k

G la s s p ro p e r ty b b C b C C

b variable coefficientn number of glass componentsC concentration of component



Variations in density 2-6g/cm3; Density SiO2 as quartz 2.65/ glass 2-2.2g/cm3

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.

Estimate:

BinaryAlkali-silicate glasses

1 0 0

/i ii

p

Oxide i (g/cm3) Oxide i (g/cm3)

SiO2 2.24 As2O5 3.33

Al2O3 2.75 CaO 4.3

B2O3 2.9 ZnO 5.94

Na2O 3.2 BaO 7.2

K2O 3.2 PbO 10.3

MgO 3.25

Adjustment of glass properties: Density


Relation between thermal expansion and chemical composition of glass is rather linear.

Linear model can be used:

pn percentage of weight of each constituent

kn constants

High expansion factors of sodium oxide point at low thermal resistance of soda-lime glass.

3 n nk p

Oxide constant Oxide constant

SiO2 15 MgO 135

Al2O3 52 CaO 489

ZrO2 69 ZnO 21

Na2O 1296 BaO 520

K2O 1170

Adjustment of glass properties: Heat expansion

Values factored by 109 for clarity.


Raw materials for glass

Glass products

facilities

Raw materials energy

primary, minerals (Sand, fieldspar, lime stone, Dolomite,….)Primary, synthetic (Soda, Sulfates, colorants)Secondary (cullet)


Quality + Availability = price

• Chemical composition: Main components, impurity (e.g. Fe-content), moisture content, etc.

• Phases: main phase, critical phase

• Grain habitus• Grain size distribution• Uniformity of quality

• Local / global market• Local production vs. Import

dependence (Stability of exporting country)

• Natural vs. Industrially produced

• Glass industry main or secondary customer

• Transportation distance (needed storage)

Raw materials for glass


Primary raw materialsElement Oxide Raw material

Si SiO2Sand cullet

Ti TiO2Illmenite, FeTiO3 TiO2

Zr ZrO2Zirconium, ZrSi04 ZrO2

Al Al2O3fieldspar(Ba,Ca,Na,K,NH4)(Al,B,Si)4O8

Nephelinite Metal furnaceslag

Phonolith Kaolinite

Al(OH)3 Al2O3

B B2O3Borax H3BO3 B2O3 Colemanite Tincal/Borax

Fe Fe2O3Red iron oxide FeS FeS2

Cr Cr2O3Cr2O3 K2Cr2O7

Na Na2O Trona Na2CO3 NaOH

K K2O Potash, K2CO3

Ca CaO Lime stone

Mn MnO MnO2 MnCO3

S SO3Na2So4 K2SO4 CaSo4 Gips BaSO4

Pb PbO PbO Pb3O4

Mg MgO Dolomite, CaMg(CO3) 2 MgCO3


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.

Soda-lime glass: raw materials


Raw materials: A glimpse into the past

Egypt1500. BC

Rome 100 AD

Europe 1300 AD

Syria 1400 AD

Today

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, MgO

4 0.5 7 3 3

Batch Plant ash, Quartz Soda, Sand Potash, Sand/Quartz

potash, Sand/Quartz

Syntheticcomponents


New processes

Leblanc-Process

Solvay-process

I.

II.

III.

IV.


New processes

Trona-processTrona (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.


ETH Zürich, HIF E

Chemical attack by…1. Hydrofluoric acid2. Aqueous acids3. Alkali

Water & combined acid/base attack

Glass corrosion


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.


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



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 9/18/2019 59


[SiO4] tetrahedron

Ionic end of chainHydroxide ion

Hydroxideion

Gla

s sk

inV

olu

me

stru

ctu

re



Case 1 passive layer Formationtd c

ted t

Case 2 competing reactionsDiffusion dissolution

c t c t

Case 3 constant dissolution d c ad t

d c a td t

Chemical resistance of glass: EvolutionType I: Formation of a passive surface layer, e.g. silica glass in neutral solution. The dissolution rate is dc/dt ∞ te-at .Type II: Protective layer by leaching of alkali, but 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 dissolution c∞t.Type V: Continuous dissolution of the network without leaching zone. Hydrofluoric acid on silica glass is one example, with a constant dissolution rate of dc/dt∞a.


Chemical resistance of glass: Evolution


Classes of chemical resistivity

DIN 12112 DIN 52322 DIN 12111

Acid class

solubility in acid

Half of the surface weight loss after 6h [mg/dm2]

Caustic class

solubility in base

Surface weight loss after 3h [mg/dm2]

Hydrolytic class

HCl usage

[ml]

Acid equivalent as Na2O

[mg/g]

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


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.


Thank you for your attention.

09.09.2013 65

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The vitreous state · … a solid being constituted by a spatial, disordered network of building...

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