Chromium metal is used as an alloying element to harden steel and to manufacture stainless steel. Chromium compounds are used for chrome plating (e.g. protective coatings for automotive and equipment accessories), as dyes, as inorganic paint pigments, for leather tanning, as fungicides and wood preservatives, and as catalysts. More applications are in the photographic industry (sensitiser), in industrial water treatment (including treatment of cooling tower water), as medicinal astringents and antiseptics, and in nuclear and high temperature research. Chromium (III) compounds are employed as pigment, as catalyst, as tanning agent in the tanning industry, in the production of pure chromium metal and chromium (VI) compounds, and in the production of refractory bricks. More specifically, chromium (III) oxide is used as a paint pigment, a fixative for certain textile dyes and as a catalyst. Chromium (III) acetate is used to fix certain textile dyes, to harden photographic emulsions and as a catalyst. Chromium (III) nitrate is used in the preparation of chrome catalysts, in textile printing operations, and as a corrosion inhibitor. Chromic sulfate is used in tanning, green paints, inks and text dyes and in ceramics.
Substance name: Chromium (III) compounds
CASR number: 16065-83-1
Molecular formula: Cr3+
Synonyms: Chromic ion, Chromium ion, Trivalent chromium
Trivalent chromium compounds include:
chromic oxide (CASR# 1308-38-9),
chromium acetate (CASR# 1066-30-4),
chromium nitrate (CASR# 13548-38-4),
chromium chloride (CASR# 10025-73-7),
chromium phosphate (CASR# 7789-04-0), and
chromium sulfate (CASR# 10101-53-8)
Chromium is a white, hard, lustrous and brittle metal that is extremely resistant to ordinary corrosive agents.
Atomic Number: 24
Atomic Mass: 52.0
Melting Point: about 1860°C
Boiling Point: about 2670°C
Specific Gravity: 7.2
Properties vary widely depending on the particular compound. Chromic oxide is a bright green hygroscopic powder with melting point of 2435°C, boiling point of 4000°C and specific gravity of 5.2. Chromium acetate is a grey-green to blue green pasty mass. Chromium nitrate is a pale green powder. Chromium chloride is a hygroscopic compound with melting point of 1152°C and specific gravity of 2.8. All chromium compounds have no taste or odour.
The most stable oxidation state of the element chromium is chromium (III), found in chromite. Chromite is the most important chromium ore mined for the recovery of chromium. Another oxidation state of practical importance is chromium (VI) (CASR# 18540-29-9), but whilst there are some natural sources for chromium (VI), the majority originates from industrial activities. Chromium is chiefly found in its trivalent form in natural environments, except in sea water where chromium in its hexavalent state is prevailing, but at extremely low concentrations. Compared to chromium (III), chromium (VI) is assumed to be about 100 to 1000 times more toxic. Although each form can be converted to the other form under certain conditions, chromium (III) is not oxidised to chromium (VI) in the natural soil environment. Water solubility of chromium and its salts ranges from low to high, e.g chromium (III) oxide is insoluble in water, and chromic (III) acetate, chromium (III) nitrate and chromium (III) sulfate are soluble in water. Pure chromium metal (oxidation state of 0) which dissolves readily in non-oxidising mineral acids such as hydrochloric and sulfuric acids is not found in nature. Chromium (VI) compounds are dealt with elsewhere in the NPI.
The National Pollutant Inventory (NPI) holds data for all sources of chromium (III) compounds emissions in Australia.
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