Feed grade silica
Silica is also known as silica and has the chemical formula SiO2. There are two kinds of crystalline silica and amorphous silica in nature.
Crystalline silica is classified into quartz, tridymite and cristobalite due to its different crystal structure. Pure quartz is a colorless crystal, and large, transparent prismatic quartz is called crystal. If crystals containing trace impurities have different colors, there are amethysts, sapphire, and the like. Ordinary sand is a fine quartz crystal with yellow sand (more iron impurities) and white sand (less impurities, purer). In the silica crystal, the four valence electrons of the silicon atom form four covalent bonds with four oxygen atoms, the silicon atoms are located at the center of the regular tetrahedron, and the four oxygen atoms are located at the four vertex angles of the regular tetrahedron, SiO2 It is the simplest form of composition, and it is only the ratio of the number of atoms of silicon and oxygen in the silica crystal. Silica is an atomic crystal.
The diatomaceous earth existing in nature is amorphous silica, which is the remains of lower aquatic plant diatoms. It is a white solid or powdery, porous, light and soft solid with strong adsorption. Insoluble in water.
Carbon black manufacturer feed grade silica chemical properties
The chemical properties are relatively stable. Does not react with water. It is an acidic oxide and does not react with ordinary acids. Gaseous hydrogen fluoride reacts with silica to form gaseous silicon tetrafluoride. It reacts with a hot concentrated alkali solution or a molten base to form a silicate and water. It reacts with various metal oxides at high temperatures to form silicates. Used in the manufacture of quartz glass, optical instruments, chemical vessels, ordinary glass, refractory materials, optical fibers, ceramics, etc. Silica is inactive and does not interact with halogens other than fluorine, hydrogen fluoride, hydrogen halides, and sulfuric acid, nitric acid, and perchloric acid (except hot concentrated phosphoric acid).
Common concentrated phosphoric acid (or pyrophosphoric acid) can corrode silica at high temperatures to form heteropolyacids. Melting borate or boric anhydride at high temperatures can also corrode silica. In view of this property, borate can be used. In addition to the flux in the ceramic firing, in addition to hydrogen fluoride, the acid which dissolves the silica can form a fluorosilicic acid which is easily soluble in water.
The supported silica generally does not react with water, that is, does not form silicic acid upon contact with water, but it is artificially specified that silica is an acid anhydride of silicic acid. The crystallization rate of silica is low enough to be neglected in the temperature range of interest for most microelectronic processes. Although fused silica is not a long-range order, it exhibits a short ordered structure, and its structure can be considered as four oxygen atoms located at the vertices of the tetrahedron. The center of the polyhedron is a silicon atom. Thus, every four oxygen atoms are approximately covalently bonded to the silicon atoms, satisfying the valence shell of silicon. If each oxygen atom is part of two polyhedrons, the valence of oxygen is also satisfied, and as a result, it becomes a regular crystal structure called quartz. In fused silica, certain oxygen atoms become oxygen bridges and are bonded to two silicon atoms. Some oxygen atoms have no oxygen bridge and are only bonded to one silicon atom. It is believed that the thermally grown silica consists primarily of a polyhedral network in any direction. The larger the portion of the aerobic bridge, the greater the adhesion of the oxide layer and the less the tendency to be damaged compared to the anaerobic bridge. The ratio of the aerobic bridge to the anaerobic bridge of the dry oxygen oxide layer is much greater than that of the wet oxygen oxide layer.
