CHROMIUM COMPOUNDS
Chromium (symbol Cr and atomic number 24) occurs in the oxidation states 0, +2, +3, and +6 states. Element (0) and divalent chromium, however, are unstable. Chromium (0) immediately produce a thin oxide layer. Divalent chromium is easily oxidized to the trivalent form in air. The trivalent and hexavalent oxidation states are important in industry, which exit in their divalent anions called chromate and dichromate respectively and an chromic anhydride form called chromium trioxide (CrO3) and chromic oxide (Cr2O3). In industrial, chromium trioxide is called chromic acid. The principal uses of chromium are in the metallurgical processing of ferrochromium and other metallurgical products to impart corrosion resistance, chiefly stainless steel. There are applications in chrome plating, anodizing aluminium, and refractory processing of chrome brick. When combined with oxygen together other metallic elements such as lead and potassium, it forms various inorganic pigments. Chromium is used in chemical processing to produce chromic acid and chromates. Chromates are strong oxidants which will produce many organic and inorganic materials and used in the purification of chemicals. Chromates are used as rust and corrosion inhibitors in diesel engines. Dichromate is converted to chromic sulfate for tanning of leather. The reaction of chromium with collagen raises the hydrothermal stability of the leather and renders it resistant to bacterial attack. The reaction with collagen is useful reaction in screen printing application and in photography as a sensitizer for gelatin coatings. This Chromates and dichromates are used as pigments in paints and in dyeing. Chrome colors include black, red, orange, green, and yellow. Chromate salts contain the chromate ion, CrO4-2, and have an intense yellow color. Dichromate salts contain the dichromate ion, Cr2O7-2, and have an intense orange color. Chromates are used as mordant in dyeing cloth.Chromic acid ( chromium trioxide, CrO3) is an odorless red deliquescent solid. Chromium trioxide is produced commercially by the reaction of sodium dichromate with concentrated sulfuric acid. It has been used mainly for chromium plating particularly in the production of automobiles and as a colorant in ceramics. Uses in other metal-finishing operations include aluminium anodizing, particularly on military aircraft; chemical conversion coatings, which provide both decoration and corrosion protection; and the production of phosphate films on galvanized iron or steel. It is a powerful oxidant and are utilized by controlled oxidations in organic synthesis. This compound is sensitive to moisture.
Another significant oxygen compound, chromic oxide is prepared by calcining sodium dichromate with boric acid or by reducing sodium dichromate with carbon. Anhydrous chromic oxide is produced commercially from chromic hydroxide, dry ammonium dichromate, or sodium dichromate by heating with sulfur. Chromic oxide is a dark green, amorphous powder, forming hexagonal crystals on heating that are insoluble in water or acids. Most chromic oxide is used as a pigment. Anhydrous chromic oxide is known as the most stable green pigment used when heat, light and chemical resistance is required for glass, ceramics, and polymers. Its hydrate form is called Guignet's green and used as a green pigment, particularly for automotive finishes.
Chromic compounds are also used in metallurgy in the manufacture of chromium metal and aluminium-chromium master alloys, in refractory brick, and as a chemical intermediate. They have good resistance to alkali and find application as colorant for latex paints. They are used in asphalt roofing and in camouflage paints. They are used as catalyst in the preparation of methanol, butadiene and high-density polyethylene. When used as a mild abrasive for polishing jewellery and fine metal parts, it is known as ‘green rouge’
Chromic compounds are used extensively as pigments. Chromic acid finds applications in:
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PRODUCT |
CAS # |
FORMULA (M.W.) |
|
Chromium |
7440-47-3 |
Cr (51.996) |
|
Chromium[III] compounds |
||
|
Chromic Acetate |
1066-30-4, 25013-82-5 |
Cr(OCOCH3)3 (229.13) |
| Chromic Chloride Stearate Complex | 15242-96-3 | C18H35Cl4Cr2O3++ (545.28) |
|
Chromic Chloride |
10025-73-7, 10060-12-5 |
CrCl3 (158.36) |
|
Chromic Fluoride |
7788-97-8, 16671-27-5, 68886-78-2 |
CrF3 (108.99) |
|
Chromic Hydroxide |
1308-14-1 |
Cr(OH)3 (103.02) |
|
Chromic Nitrate |
13548-38-4, 20249-21-2, 7789-02-8 |
Cr(NO3)3 (238.01) |
|
Chromic Oxide |
1308-38-9 |
Cr2O3 (151.99) |
|
Chromic Perchlorate |
13537-21-8, 55147-94-9 |
Cl3CrO12 (350.35) |
|
Chromic Phosphate |
7789-04-0 |
CrO4P (146.97) |
|
Chromic Sulfate |
15244-38-9, 10101-53-8 , 39378-25-1 | Cr2O12S3 (392.16) |
| Chromium Hydroxide Sulfate |
12336-95-7, 39380-78-4 |
Cr(OH)SO4 (165.07) |
| Chromium Acetate Hydroxide | 39430-51-8 |
|
|
Neochromium |
64093-79-4 |
Cr(OH)SO4·Na2SO4·H2O |
|
Potassium Chromic Sulfate (Chrome Alum) |
10141-00-1, 14766-82-6, 81827-72-7, 81827-73-8 |
CrKO8S2 (283.20) |
|
Chromium[VI] compounds |
||
|
Ammonium Chromate |
7788-98-9 |
(NH4)2CrO4 (152.07) |
|
Ammonium Dichromate |
7789-09-5 |
(NH4)2Cr2O7 (252.06) |
|
Barium Chromate |
10294-40-3, 12000-34-9, 12231-18-4 |
|
|
Basic Lead Chromate |
1344-38-3, 54692-53-4 |
|
|
Bismuth Chromate |
61204-26-0 |
Bi2O3 Cr2O3 (341.98) |
|
Calcium Chromate |
10060-08-9, 13765-19-0 |
CaCrO4 (156.07) |
|
Chrome Orange Pigments |
1344-37-2, 61513-05-1, 61513-06-2, 61513-07-3, 8012-76-8, 1344-38-3, 54692-53-4, 3564-27-0, 12236-55-4, 11119-70-3, 51329-63-6, 52440-39-8, 15804-54-3, 7758-97-6 |
|
| Chromic[VI] acid | 11115-74-5, 7738-94-5 |
H2CrO4 (118.01) |
|
Chromium[VI] Cholride |
14986-48-2 |
Cl6Cr (264.71) |
|
Chromium Trioxide |
1333-82-0, 12324-05-9, 12324-08-2 |
CrO3 (99.99) |
|
Cupric Chromate |
13548-42-0 |
CuCrO4 (179.54) |
| Dichromic[VI] acid | 13530-68-2 | H2Cr2O7 (218.00) |
|
Lead Chromate |
7758-97-6, 8049-64-7 |
PbCrO4 (323.19) |
| Mercuric Dichromate | 7789-10-8 |
Hg2CrO4 |
| Mercury[I] Chromate | 13465-34-4 | H2CrO4·2Hg (517.17) |
| Mercury[II] Chromate | 13444-75-2 | H2CrO4·Hg(316.58) |
|
Molybdenum Orange |
12656-85-8 |
|
|
Nickel Chromate |
12018-18-7 |
NiCrO4 (174.69) |
|
Potassium Chromate |
7789-00-6 |
K2CrO4 (194.19) |
| Potassium Chromium Oxide | 11073-34-0 | KCrO2 (123.09) |
|
Potassium Dichromate |
7778-50-9 |
K2Cr2O7 (294.17) |
|
Silver Chromate |
7784-01-2 |
Ag2CrO4 (331.73) |
|
Sodium Chromate |
7775-11-3 |
Na2CrO4 (161.97) |
|
Sodium Dichromate |
10588-01-9, 12018-32-5 |
Na2Cr2O7 (261.97) |
|
Stannic Chromate |
|
Sn(CrO4)2 (350.69) |
|
Stannous Chromate |
38455-77-5 |
SnCrO4 (352.71) |
|
Strontium Chromate |
7789-06-2, 54322-60-0 |
SrCrO4 (203.612) |
|
Zinc Chromate Hydroxide |
15930-94-6, 12206-12-1, 66516-58-3 |
|
|
Zinc Chromate |
13530-65-9, 1308-13-0, 1328-67-2, 14675-41-3 |
|
| Zinc Potassium Chromate | 11103-86-9, 12527-08-1, 37809-34-0 | Cr2HO9Zn2·K (418.87) |
Zinc Yellow |
37300-23-5 |
|
|
Other chromium compounds |
||
| Chromium Oxychloride |
14977-61-8 |
Cl2CrO2 (154.90) |
|
Chromium Carbonyl |
13007-92-6, 13930-94-4 |
C6CrO6 (220.06) |
|
Chromic Chromate |
24613-89-6 |
|
|
Chromium[II] Chloride |
10049-05-5 |
|
|
Chromium[IV] Dioxide |
12018-01-8 |
|
|
Chromium [0] alloys |
||
| Chromite | 1308-31-2 | Cr2FeO4, (Fe,Mg)Cr2O4 |
| Nickel Chromium oxide | 12018-18-7 | NiCr2O4 |
|
Cobalt-Vhromium alloy |
11114-92-4, 91700-55-9 |
|
|
Cobalt-Chromium-Molybdenum alloy |
12629-02-6, 8064-15-1, 11068-92-1, 12618-69-8, 55345-18-1 |
|
|
Stainless steel containing Chromium |
60382-64-1, 83272-15-5, 85131-98-2. 94076-26-3, 71631-40-8, 51204-69-4, 59601-19-3, 84723-14-8, 94197-89-4, 98286-69-2 |
|
|
Ferrochrome |
11114-46-8 (11133-75-8, 11143-43-4, 12604-52-3) |
|
| Ferrochromite[III] | 1308-31-2 |
|
|
Iron-Nickel-Chromium alloy |
11121-96-3 |
|
|
Nickel-Chromium alloy |
12605-70-8 |
|
| Copper Chromite | 12053-18-8 | 2CuO·Cr2O3 |