Glasses- Raw Materials

Question 1

What is needed to make a typical commercial glass?

Answer 1

Sand, fuel, flux

Question 2

Things to optimise in glass making process

Answer 2

Batch should melt easily to a homogeneous, bubble-free product. Optimum melt viscosity-T curve for forming (large T range for shaping). Appropriate physical and chemical properties. Right colour (or none). Lowest cost

Question 3

Issues with natural minerals

Answer 3

Purity (Fe discolours glass). Wrong particle sizes. Raw materials already in reacted state. Inappropriate chemistry (deliquescent- tend to melt or dissolve).

Question 4

Why is CaO used in glass making?

Answer 4

For chemical durability

Question 5

Where does SiO2 come from?

Answer 5

Sand. Weathered rocks graded by water flow. River deltas

Question 6

Where does Na2CO3 come from?

Answer 6

Is a flux to lower melting temperature dramatically. Soda ash. Naturally in dried-up lakes. Extracted from plant ash. Now derived from NaCl using Solvay process

Question 7

Where does CaCO3 come from?

Answer 7

Is a flux to increase chemical durability. Limestone. UK sources of adequate quality exist

Question 8

Where does CaCO3 and MgCO3 come from?

Answer 8

MgO lowers crystal growth rates. Dolomite. UK sources too much Fe. Use Spain.

Question 9

Where do Na2.Al2O3.6SiO2
K2O.Al2O3.6SiO2
CaO.Al2O3.6SiO2
come from?

Answer 9

Alumina also stabilises glass and improves durability. Feldspars. Cheap source of alkali and alumina. Imported

Question 10

Other raw materials

Answer 10

Cullet- recycled scrap glass (20-100%)
Na2SO4- melting acid (5% soda ash)
Colourants/decolourisers

Question 11

Which contaminants must be minimised?

Answer 11

Fe, Ti, Cr (colourants, slow solution rates)
Refractory minerals (high melting point)
Pollutants (SOx, Cl in Na2SO4)

Question 12

Why must grain size be controlled?

Answer 12

Avoid coarse, slow dissolving grains. Avoid fine grains (more contaminated and cause unhealthy dust and seed- small bubbles)

Question 13

Delivery methods of sand

Answer 13

Small producer uses 50kg bags. Large producer uses air discharge road tanker

Question 14

What are molar compositions and weight %s used for?

Answer 14

Molar composition used for interpretation (academic)

Weight% used commercially for handling, costing

Question 15

How to convert weight% into mole%

Answer 15

Divide each weight% by Mr to find moles of each per 100g. Find total moles in 100g. Divide each by total and times by 100

Question 16

Why would sand have moisture in it?

Answer 16

Water is used to wash the sand by the supplier

Question 17

What does soda ash split into?

Answer 17

Na2O and CO2 (which is released)

Question 18

Sources of error in weight percentage calculations

Answer 18

Wet components and hydrates
Refractory (slowly dissolving) impurities in batch
Solution of furnace refractories
Volatilisation losses (particularly Na2 as NaOH which has high vapour pressure in furnace atmosphere)
Impurities in fuel (high for oil not gas)
Variable solubility of H2O/SO3 with T, gas composition
Components with different redox states like S, Fe