Description
Calcium Silicate is a hydrous or anhydrous silicate with varying proportions of calcium oxideand silica. many different calcium silicates occur in nature in mineral form (e.g.,wollastonite, afwillite, grammite). The stoichiometry of the hydrate in cement paste is variable and the state of the chemically and physically bound water in its structure is not clear. Thus, calcium silicate can be prepared by calcining the oxide with silica, SiO2, at an elevated temperature: CaO + SiO2+ heat→CaSiO3. Calcium orthosilicate is commonly used as a safe alternative to asbestos for high-temperature insulation materials. Industrial grade piping and equipment insulation are often fabricated from calcium orthosilicate.
Chemical Properties
Calcium silicate occurs as a crystalline or amorphous white or off white material, and often exists in different hydrate forms. It consists of different ratios of CaO and SiO4, including tricalcium silicate (3CaO.SiO2) and dicalcium silicate Ca2SiO4. It is insoluble in water and forms a gel with inorganic acids. The pH of 5% suspension is 8.4~10.2.
Uses
Calcium Silicate is an anticaking agent that exists in different forms,
which are insoluble in water. it is used in salt to enhance flowability
under extremely high humidity conditions. it is also used in baking
powder and fabricated chips to absorb water or other liquids.
Application
The main applications of calcium silicate relate to its anticaking properties, and it has therefore been used in dusting powders and a range of different cosmetic products (e.g. face powders, eye shadow). It is also used as anticaking agent in table salt, foods, pharmaceuticals, and agricultural pesticides; replacement for asbestos in thermal insulation; Constituent (produced in situ) of lime glass, portland cement; reinforcing filler in elastomers and plastics; absorbent for liquids, gases, vapors; as anti-caking agent, suspension agent, pigment and pigment extender; binder for refractory material; in chromatography; in road construction.
Preparation
Calcium silicate is a naturally occurring mineral, but for commercial applications it is usually prepared from lime and diatomaceous earth under carefully controlled conditions.
Production Methods
Calcium silicate is made in various ways by reacting siliceous material (such as diatomaceous earth) and calcium compounds (such as calcium hydroxide (Ca (OH) 2).The refinement of wollastonite ore into high-grade wollastonite was originally done by manual selection at many mines. This process is now performed by screening and magnetic separators, sometimes in combination with flotation and vacuum filtration. Grinding and milling operations can produce variable mesh powders or aggregates.
Hazard
Irritating dust. Use in foods restricted to
5% in baking powder, 2% in table salt. Upper res-
piratory tract irritant. Questionable carcinogen.
Health Hazard
The toxicity of calcium silicate
depends on particle size, aspect ratio, and
amount of silica and respirable fiber.1 Synthetic
nonfibrous calcium silicate is considered to be
a nuisance dust.
Skin irritation was reported in a worker
exposed to an atmosphere permeated with calcium silicate.1 A study of 104 wallastonite (a
naturally occurring calcium silicate mineral)
miners showed no relationship between the
prevalence of chronic bronchitis or airflow
obstruction with increasing exposure.1 In a
cohort mortality study of wollastonite quarry
workers the observed numbers of deaths from
all cancers combined and lung cancer were
lower than expected.
Flammability and Explosibility
Not classified
Pharmaceutical Applications
Calcium silicate (Ca2SiO4) is used in the pharmaceutical industry as an anticaking agent. Anti-caking agents absorb moisture and allow products to flow freely during the manufacturing process. It is also used as a filler aid for oral pharmaceuticals. It has also been used in pharmaceutical preparations as an antacid.
Industrial uses
Calcium silicate compounds belong to a complicated class of silicates. Among their many industrial applications, calcium silicates are heavily used as a building material as they constitute the main ingredient in today’s cement clinker.
Safety Profile
A nuisance dust
Safety
GRAS listed. Included in the FDA Inactive Ingredients Database (oral dosage forms). Included in nonparenteral (oral, orodispersible, effervescent and enteric-coated tablets) formulations licensed in the UK.
calcium silicate is generally recognized as safe (GRAS) when used at levels not exceed 2% in table salt and 5% in baking powder.
storage
Calcium silicate is chemically stable and nonflammable, but it
should be protected from moisture. Store in airtight containers in a
cool, dry place.
Incompatibilities
None reported [Note: After prolonged contact with water, solution reverts to soluble calcium salts & amorphous silica.]
Regulatory Status
Calcium silicate (E552) is listed in Commission Regulation (EU) No 231/2012 as an authorised food additive and categorized as “additives other than colours and sweeteners”. It is an approved ingredient in Australia and New Zealand with the code number 552.
