Chemical Properties
Amorphous silica, the noncrystalline form of SiO2, is a transparent to gray, odorless, amorphous powder
Uses
None; produced only as a by-product.
Definition
Produced by the volatilization and vaporization of furnace feed materials during the production of ferrosilicon and silicon metals. Consists primarily of silicon dioxide with carbon and trace elements.
Application
Silica-fume forms most of the dust and other
particulates in the off-gases produced during the electrothermal production of ferrosilicon
(Fe-Si) or silicon (Si). The dust is collected in baghouses and bagged without further treatment. Due to its high surface area, microsilica reacts readily with hydrated calcium silicates
forming strong bonds, and for that reason it is sometimes called reactive silica. Therefore the
addition of microsilica to hydraulic cements improves their mechanical strength, reduces
their permeability, and enhances their workability, cohesiveness, and flowing properties and
hence is extensively used as an additive to cements and monolithic refractories.
Health Hazard
Amorphous silica fume exposure
is associated with recurrent fever, similar
to metal fume fever, and nonprogressive pulmonary
changes.More recently, the importance of silica
fume particle size on toxicity has been noted.8
Specifically, particles of the ultrafine size range
may be expected to have higher toxicity compared
with particles of larger size.
Safety Profile
An inhalation hazard. Much less toxic than crystalline forms. Does not cause silicosis. See also other silica entries
Potential Exposure
Amorphous fumed silica is used as a mineral, natural or synthetic fiber. A potential danger to those involved in the production and handling of fumed silica for paint pigments or catalysts. Diatomaceous earth is used in clarifying liquids, in manufacture of fire brick and heat insulators; used as a filtering agent; as a filler in construction materials; pesticides, paints, and varnishes. A potential danger to those involved in mining of diatomaceous earth or fabrication of products there from.
Incompatibilities
Silica, amorphous is a noncombustible solid. Generally unreactive chemically. Incompatible with fluorine, oxygen difluoride, chlorine trifluoride. Soluble in molten alkalis and reacts with most metallic oxides at high temperature.
Toxics Screening Level
The initial threshold screening level (ITSL) for the amorphous silica compounds (Silica Fume) is 60 μg/m3 based on an 8-hour averaging time.
Waste Disposal
Sanitary landfill.
