What is silica and what are its properties?

Silicon dioxide (SiO2) is the most abundant of all minerals. ? The silica existing in nature is called silica, which accounts for about 12% of the total weight of the earth's crust. There are three different crystal forms of silica: Yingshi, tridymite and FangShi Ying. It is the most stable at room temperature, and the other two are stable at high temperature. They also exist at room temperature because they are converted into time slowly. Some timely mines have special names. For example, a large and transparent crystal is called a crystal and contains trace impurities? And purple is amethyst, light yellow, gold and brown are called cigarettes? The black and almost opaque crystal is called Mo Jing. Chalcedony, agate and jasper are gem minerals with various colors when microcrystals are mixed with other substances in time. Does the village contain iron oxide and emeralds? Bone marrow contains magnesium. Ruby mixed with fine dispersed goethite? (Fe2O3 H2O). Ordinary sand contains impurities. ? There are a large number of high-quality silica minerals in the north of China. Sandstones are widely distributed in southern China, in Qinghai, Yunnan, Guangdong and Guangxi. And there are crystal mines in Guizhou province. Pure natural silica crystal is a hard, fragile and insoluble colorless and transparent solid.

physical features

quartz

Density: 2.2? G/cm3

Melting point: 1723℃

Boiling point: 2230℃

Refractive index: 1.6

Solubility: insoluble in water

chemical property

The chemical properties are relatively stable. Does not react with water. It has high fire resistance, high temperature resistance, small thermal expansion coefficient, high insulation, corrosion resistance, piezoelectric effect, resonance effect and its unique optical characteristics. ? It is an acidic oxide and does not react with ordinary acids. Hydrofluoric acid reacts with silicon dioxide to produce gaseous silicon tetrafluoride. React with hot concentrated alkali solution or molten alkali to form silicate and water. React with various metal oxides at high temperature to form silicates. Silicon dioxide is inactive, and does not react with halogen, hydrogen halide, sulfuric acid, nitric acid and perchloric acid except fluorine and hydrogen fluoride (except hot concentrated phosphoric acid).

Common concentrated phosphoric acid (or pyrophosphoric acid) can corrode silicon dioxide to form heteropoly acid at high temperature, and molten borate or boric anhydride can also corrode silicon dioxide at high temperature. In view of this property, borate can be used as a flux in ceramic firing, and hydrogen fluoride can also be an acid, which can dissolve silicon dioxide and generate water-soluble fluorosilicic acid.

SiO2+4HF=SiF4↑+2H2O

6HF+SiO2=H2SiF6+2H2O

Silica +2 sodium hydroxide (concentrated) = silica sodium +H2O

SiO2+Na2CO3=Na2SiO3+CO2↑？ (high temperature)

SiO2+CaO=CaSiO3

SiO2+2C=2CO↑+Si