Glass and Cement

©2009 Dr. B. C. Paul

Acknowledgement is given to the following sources, SME Industrial Minerals

Glass• Glass is an inorganic amorphous solid• Main Ingredients

– Glass former• Silicon dioxide Quartz• Boric Oxide Borax

– Glass Modifiers to lower melting point• Soda Ash Trona

– Glass Stabilizers• Formers and modifiers are water soluble• Having Glass Dissolve would defeat its purpose• Lime is most common - Limestone or Dolomite

– Other• Alumina is a glass former, viscosity control, and prevent

devitrification – in ceramics it acts as a flux to lower melting point• Feldspars, Kaolin, and Nephaline Syenite provide• Fluxing agents to and surface tension control (prevents foaming)

– Flourspar• Variety of minerals can provide color

Quartz

SiO2

S.G. 2.6 - 2.65, Average = 2.62 Hardness 7Color Brown, Colorless, Violet, Gray, Yellow. Fluorescence Triboluminescent Magnetic No

Quartz Sandstone

Glass making purity

What is Quartz Worth?

Around $20+ per ton

Feldspar Composition

Feldspars with lotsOf Alakali metals(Sodium andPotassium areThe AlkaliFeldspars

Range fromAlbiteTo OrthoclaseAndMicrocline

Those more rich in CalciumLike Anorthite formThe Plagioclase seriesBetween Albite and Anorthite

Albite

NaAlSi3O8

S.G. 2.61 - 2.63, Average = 2.62Hardness 7Color White, Gray, Greenish gray, Bluish green, Gray. Fluorescence NoneMagnetic NoAl2O3 (Alumina) 20.35 % 

AnorthiteCaAl2Si2O8 S.G. 2.72 - 2.75, Average = 2.73 Hardness 6Color Colorless, Gray, White, Red,Reddish gray.

Fluorescence NoneMagnetic NoAl2O3 (Alumina) 35.84 %

Microcline

KAlSi3O8 S.G. 2.56 Hardness 6Color Bluish green, Green, Gray, Grayish yellow, Yellowish. Fluorescence NoneMagnetic NoAlumina 18.32 %

Orthoclase

KAlSi3O8 S.G. 2.56 Hardness 6Color Colorless, Greenish, Grayish yellow, White, Pink. Fluorescence NoneMagnetic NoAlumina 18.32 %

Nepheline Syenite

A rock with about 22% Nepheline(a feldspathoid) and 66% FeldsparWithout quartz.

Cement

• Objective is to produce dry ingredients that react with water and form an artificial rock– The artificial rock forms a paste that holds loose

aggregate together to form concrete• Dry stuff that sets with water is made of

– Ca3SiO5 Tricalcium Silicate 45%– Ca2SiO4 Dicalcium Silicate 27%– Ca3Al2O6 Tricalcium Aluminate 11%– Ca4Al2Fe2O10 Tetracalcium Aluminoferrite 8%

• No big natural sources of such chemicals exist so we make them by throwing other minerals in a rotary kiln and baking them to cement clinker

The Raw Materials

• Need an alumina and silicate source– Classic source is a natural glass such as volcanic ash– We like to use power plant fly ash

• It has the alumina, silica, and iron– Can get silica from

• Sand, clay, and shale– Can get alumina from

• Bauxite, shale, clay

• Calcium attacks the glass to form water reactive compounds– Calcium sources

• Limestone, Marble, Oyster Shells

Moderating the Reaction

• The cement clinker from the kiln is ground to powder– Its very water reactive

• Too much heat to fast will destroy the strength of the artificial rock– We add gypsum as a retarder to slow down

the reaction– Gypsum is added during the grinding step

Volcanic Ash

Consists mostly of shards of high temperature Christobalite Quartz with someFeldspars.

Power Plant Fly Ash

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

20-60 5-35 10-40 1-12 0-5 0-4 0-4 0-3

F Type Fly Ash oxide % 15-45

10-25

4-15

15-40

3-10

0-10

0-6

0-4

C Type Fly AshOxide %

F type fly ash is highIn iron and low inCalcium and AlkalisC type is high in CalciumAnd alkalis

Crystobalite

SiO2 High temperature form of quartzVery brittle and reactiveIs the primary form of silica thatProduces occupational and exposureRelated disease.