University of Babylon



Glass Batch Formulation:

A combination of batch materials is selected according to the desired glass composition and oxidation state in combination with manufacturing process requirements (including those of mixing, melting, fining, etc.) and product cost. The quantities of each component are calculated to give the required weight of oxide after the volatile components and reaction products, such as water, carbon dioxide, sulfur dioxide, and nitrogen oxides, are lost to the atmosphere.

Batch: mixture of unmelted raw materials. Batches are heated and melted to form melts, which are then cooled to form glasses.

Examples of important raw materials for commercial glasses. Among the more significant ones are:

• Feldspars (albite: Na2O; anorthite: CaO; aplite:

R2O/RO)

• Borax (borosilicate glasses)

• Dolomite

• Limestone

• Nepheline

• Kyanite (aluminosilicate fiber glasses)

• Sand

• Soda ash

•Cullet (recycled glass) is another important commercial batch ingredient

20-40 wt% of batch.

Glass Batch Considerations

Rarely does a commercial process start with an all-oxide batch. This is in part because the expense of the materials would be too great, but mostly because oxides melt at much higher temperatures than the salts of the corresponding metallic elements, thus requiring longer times at higher temperatures to complete the chemical reactions.

Many different combinations of raw materials can yield the same final glass composition. Final choice of raw materials is based on factors such as chemical composition, the level of impurities tolerated, particle size, particle size distribution, and the precision to which these characteristics are controlled (maintained) by the vendor, and price.

Shelby classifies five types of batch components:

1. Glass forming oxides: usually the dominant compositional constituent.

• SiO2, B2O3, P2O5, etc.

2. Fluxes: reduce melting temperatures.

• Na2O, PbO, K2O, Li2O, etc.

3. Property modifiers: added to tailor chemical durability, expansion, viscosity, etc.

• CaO, Al2O3, etc.

4. Colorants: oxides with 3d, 4f electron structures; minor additives ( ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download