Glass raw materials are relatively complex, but can be divided into main raw materials and auxiliary raw materials according to their functions. The main raw materials constitute the main body of glass and determine its main physical and chemical properties. Auxiliary raw materials endow glass with special properties and bring convenience to the production process.
1. The main raw materials of glass
(1) Silica or borax: The main component introduced into glass by silica or borax is silicon oxide or boron oxide, which can melt into the main body of the glass during combustion, determining the main properties of the glass, and is correspondingly called silicate glass or borate glass.
(2) Soda or mirabilite: The main component introduced into glass by soda and mirabilite is sodium oxide, which can form fusible complex salts with acidic oxides such as silica sand during calcination, playing a melting aid role and making the glass easy to shape. But if the content is too high, it will increase the thermal expansion rate of the glass and decrease its tensile strength.
(3) Limestone, dolomite, feldspar, etc.: The main component introduced by limestone into glass is calcium oxide, which enhances the chemical stability and mechanical strength of the glass. However, excessive content causes glass to break and reduce heat resistance.
Dolomite, as a raw material for introducing magnesium oxide, can improve the transparency of glass, reduce thermal expansion, and improve water resistance.
As a raw material for introducing alumina, feldspar can control the melting temperature and improve durability. In addition, feldspar can also provide potassium oxide composition, improving the thermal expansion performance of glass.
(4) Crushed glass: Generally speaking, glass is recyclable, and when making glass, not all new raw materials are used, but 15% -30% of the broken glass is added.
2. Auxiliary raw materials for glass
(1) Bleaching agent: Impurities such as iron oxides in raw materials can bring color to glass. Commonly used as bleaching agents are soda ash, sodium carbonate, cobalt oxide, nickel oxide, etc. They present a complementary color to the original color in the glass, making the glass colorless. In addition, there are color reducing agents that can form light colored compounds with coloring impurities, such as sodium carbonate that can oxidize with iron oxide to form iron dioxide, causing the glass to turn from green to yellow.
(2) Colorant: Some metal oxides can directly dissolve in glass solution to make glass colored. Iron oxide can make glass appear yellow or green, manganese oxide can appear purple, cobalt oxide can appear blue, nickel oxide can appear brown, copper oxide and chromium oxide can appear green, etc.
(3) Clarifier: Clarifier can reduce the viscosity of glass melt, making bubbles generated by chemical reactions easier to escape and clear. Commonly used clarifying agents include white arsenic, sodium sulfate, sodium nitrate, ammonium salt, manganese dioxide, etc.
(4) Opaque agent: Opaque agent can turn glass into a milky white translucent substance. Commonly used opacifiers include cryolite, sodium fluorosilicate, tin phosphide, etc. They can form 0.1-1.0 μ M particles are suspended in glass, causing it to opacify.