chromate


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chromate

any salt or ester of chromic acid. Simple chromate salts contain the divalent ion, CrO42--, and are orange

Chromate

 

any one of a group of salts of chromic acid and isopolychromic acids. The salts of chromic acid, H2CrO4, namely monochromates or simply chromates, are discussed below.

Chromates are stable only in an alkaline medium; upon acidification, they are converted to dichromates. Potassium chromate and sodium chromate are the most important chromates.

Potassium chromate, K2CrO4, is a yellow crystalline substance, with a density of 2.732 g/cm3 and a melting point of 968.3°C. It is readily soluble in water: 62.9 g at 20°C and 79.2 g at 100°C in 100 g of water. It is produced by the action of potassium hydroxide, KOH, on potassium dichromate, K2Cr2O7.

Sodium chromate, Na2CrO4, is also a yellow crystalline substance, with a density of 2.72 g/cm3 and a melting point of 790°C. A hygroscopic compound, it is soluble in water: 80.2 g in 100 g of water at 19.5°C. It is produced by roasting the natural chromite FeCr2O4 with dolomite and sodium carbonate at 1150°–1200°C, then leaching out Na2CrO4 from the sintered mass formed, and finally subjecting the solution to evaporation and crystallization.

Sodium chromate and potassium chromate are used as chemical reagents, as mordants for dyeing textiles, and as components of tanning solutions in the leather industry. They are also used for seed treatment and as wood preservatives.

REFERENCE

Pozin. M. E. Tekhnologiia mineral’nykh solei, 4th ed., parts 1–2. Leningrad, 1974.

A. B. SUCHKOV

chromate

[′krō‚māt]
(inorganic chemistry)
CrO42-
An ion derived from the unstable acid H2CrO4.
A salt or ester of chromic acid.
(mineralogy)
A mineral characterized by the cation CrO42-.

chromate

To coat a metal surface with a rust-inhibiting primer of lead or zinc chromate.
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(24.) Furbeth, W, Stratmann, M, Williams, G, McMurray, HN, "Chromate Inhibition of Corrosion-Driven Organic Coating Delamination Studied Using a Scanning Kelvin Probe Technique," / Electrochem.
CONCLUSIONS: These data illustrate that repetitive exposure to particulate chromate induces chronic injury and an inflammatory microenvironment that may promote Cr(VI) carcinogenesis.
Chromate pigment production involves reacting sodium chromate with zinc or lead to produce insoluble zinc chromate and lead chromate, respectively.
Wide range of inorganic pigments include ultramarine blue, lead chromates, chrome oxide, iron oxide, pearlescents, phosphoroescents, luminescents, cadmium, mixed metal oxides, titanium dioxide and predispersed flush pigments.
Employing kaolinite as a substrate, Zachara and others (1988) observed that [CrO.sub.4] = protonation was an important reaction affecting chromate adsorption, especially at lower pH intervals where Cr adsorption was observed to be greater.
If it hasn't, or if there is any question, it is important to note that the molybdate corrosion inhibitors (possible replacements for chromates) are not as easy to deal with as are chromate inhibitors.
Investor, Mr Buck said: "In my 40 years in the industry, we have been searching for a comparable anticorrosion pigment that delivers the same results as lead and chromate complexes.
As of 2015, the company says it is no longer producing any pigments containing lead chromate.
It concerns the following substances: formaldehyde, oligomeric reaction products with aniline (technical MDA); arsenic acid; dichromium tris(chromate); strontium chromate; potassium hydroxyoctaoxodizincatedichromate; pentazinc chromate octahydroxide; bis(2-methoxyethyl) ether (diglyme); N,N-dimethylacetamide (DMAC); 1,2-dichloroethane (EDC); 2,2'-dichloro-4,4'-methylenedianiline (MOCA).
With a modified eluent (30 mmol/L LiOH + 24 mmol/L [Li.sub.2] [SO.sub.4]), chromate [Chromium (VI)] analysis is also possible with the ion exchange columns Metrosep A Supp 10 - 75/4.0 and Metrosep A Supp 15 - 100/4.0.
Abstract Chromate conversion coatings are commonly deposited on plated zinc to improve the corrosion resistance of the substrates, and to increase the adherence of painted films.