Introduction to silicon dioxide, silicon carbide and silicon nitride

Silica

Silica SiO ₂ crystal is colorless, insoluble in water, high melting point, and high hardness
.
Quartz in nature is silica , which is an atomic crystal

The structure of silicon dioxide uses silicon-oxygen tetrahedron as the basic structural unit, and the different connection modes of silicon-oxygen tetrahedron form different crystal types, such as -quartz and β-quartz
.
Siloxane tetrahedrons are also arranged chaotically, such as in quartz glass and silica gel

Porous silica gel can be used as a desiccant
.
Using NaSiO ₃ solution as raw material, acidification causes SiO ₃ ^{2- to} gradually condense and form silicic acid colloid

SiO ₂ is relatively inert at room temperature , but it can react with hydrofluoric acid to produce SiF ₄ or H ₂ SiF ₆
.

SiO ₂ can react with hot strong alkali solution and molten sodium carbonate to form soluble silicate
.

Silicon carbide and silicon nitride

1.
Silicon Carbide

Silicon carbide SiC is commonly known as emery, pure crystals are colorless, and they have different colors if they contain different impurities
.
SiC is an atomic crystal, and both C and Si are tetrahedral bonded, and there are dozens of variants

SiC has many excellent properties, such as high hardness (between diamond and corundum), high temperature resistance (above 1500℃), high stability (decomposition above 2700℃), oxidation resistance, corrosion resistance, high thermal conductivity, etc.
for abrasives, refractory materials, electric components, seals and the like

Industrially, silicon carbide is obtained by reacting high-purity quartz sand and coke in a resistance furnace at 1900-2400℃:

SiO ₂ +3C=SiC+2CO

2.
Nitriding

Silicon nitride Si ₃ N ₄ , pure crystal is colorless (powder is white), gray when it contains impurities
.
Si ₃ N ₄ has high hardness (between diamond and corundum), high temperature resistance, and strong oxidation resistance.

Under the condition of 1300～1400℃, silicon nitride is obtained by direct chemical reaction with elemental silicon and nitrogen:

3Si+2N ₂ =Si ₃ N ₄