Silica is an acidic oxide, and the corresponding hydrate is silicic acid. Silica is one of the important compounds of silicon. Chemical properties are relatively stable, insoluble in water and not react with water. It is an acidic oxide and does not react with ordinary acids. Gaseous hydrogen fluoride reacts with silicon dioxide to form gaseous silicon tetrafluoride. React with hot concentrated alkali solution or molten alkali to produce silicate and water. It reacts with various metal oxides to form silicate at high temperature. It is used for manufacturing quartz glass, optical instruments, chemical utensils, ordinary glass, refractory materials, optical fiber, ceramics, etc. Silica is inert in nature and does not react with halogen, hydrogen halide, sulfuric acid, nitric acid and perchloric acid (except hot concentrated phosphoric acid) except fluorine and hydrogen fluoride. The common concentrated phosphoric acid (or pyrophosphoric acid) can corrode silicon dioxide at high temperature and generate heteropoly acid. The molten borate or boron anhydride can also corrode silicon dioxide at high temperature. In view of this property, borate can be used as a flux in ceramic firing. In addition, hydrogen fluoride can also dissolve the acid of silicon dioxide and generate water-soluble fluorosilicic acid.
Silica is the raw material for manufacturing glass, quartz glass, water glass, optical fiber, important components of electronic industry, optical instruments, handicrafts and refractories, and is an important material for scientific research.
Uses of silicon dioxide: flat glass, glass products, casting sand, glass fiber, ceramic glaze, sand blasting for rust prevention, sand for filtration, flux, refractory materials and manufacturing lightweight bubble concrete. Silica has a wide range of uses. Rare crystals in nature can be used to manufacture important parts, optical instruments and handicrafts of electronic industry. Silicon dioxide is an important raw material for manufacturing optical fiber. Generally pure quartz can be used to make quartz glass. The expansion coefficient of quartz glass is very small, which is equivalent to 1/18 of ordinary glass. It can withstand sharp changes in temperature and has good acid resistance (except HF). Therefore, quartz glass is often used to manufacture high-temperature resistant chemical instruments. Quartz sand is often used as glass raw material and building material.