Silica powder, also called silica fume, is usually a by-product of smelting metallic silicon or ferrosilicon alloy. In the process of producing polysilicon and ferrosilicon, a part of SiO2 is reduced to SiO gas, and SiO gas is discharged out of the furnace, and it is oxidized again when encountering oxygen to form fine silica powder. Therefore, it is actually a kind of silicon oxide produced by the vapor deposition method.
The morphology of silica micropowder is standard round sphere, the average particle size is about 0.15??m, the specific surface area is between 15-30m2/g, and it has high chemical activity. Silica powder is non-flammable and is less harmful to the human body.
The content of SiO2 in silica powder is between 87-98%, and its chemical activity is related to the content of SiO2. Generally speaking, the higher the content of SiO2, the greater the surface area and the higher the activity. Generally, the content of SiO2 in the silicon dioxide powder obtained by smelting ferrosilicon alloy is lower than that of the silicon dioxide powder obtained by metal silicon. Moreover, silica micropowders produced by different manufacturers generally have large differences in chemical composition, resulting in large differences in their chemical properties. For example, compared with the silica fine powder collected in the production of metallic silicon, the average particle size of the silica fine powder collected in the production of desiliconized zirconium by using zircon is relatively small, and it contains impurity alkaline oxides. The low content results in a relatively low pH value in the aqueous solution. It can reduce the viscosity of the castable inside the castable, improve the fluidity of the castable and prolong the service life of the castable, so it is in the unshaped refractory castable The dosage is relatively large.