Zinc chromate

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Zinc chromate
Zn2+.svg
Chromat-Ion2.svg
Zinc-chromate-3D-vdW.png
Names
IUPAC name
Zinc chromate
Identifiers
ChemSpider
ECHA InfoCard 100.033.511 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 236-878-9
PubChem CID
RTECS number
  • GB3290000
UNII
UN number 3288 3077
Properties
ZnCrO4
Molar mass 181.403 g/mol
Appearanceyellow-green crystals; yellow powder
Density 3.43 g/cm3
Melting point 316 °C (601 °F; 589 K)
Boiling point 732 °C (1,350 °F; 1,005 K)
insoluble
Hazards
GHS labelling:
GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H302, H317, H350, H410
P201, P202, P261, P264, P270, P272, P273, P280, P281, P301+P312, P302+P352, P308+P313, P330, P333+P313, P363, P391, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
2
0
0
OX
Lethal dose or concentration (LD, LC):
0.5 to 5 g/kg
NIOSH (US health exposure limits):
PEL (Permissible)
0.1 mg/m3 [1]
Related compounds
Other anions
Zinc dichromate
Other cations
Potassium chromate
Sodium chromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Zinc chromate, Zn Cr O4, is a chemical compound, a salt containing the chromate anion, appearing as odorless yellow powder or yellow-green crystals, but, when used for coatings, pigments are often added. [2] [3] [4] It is used industrially in chromate conversion coatings, having been developed by the Ford Motor Company in the 1920s. [5]

Production

A process known as the Cronak process is used to create zinc chromate for use in industry. This process is done by putting zinc or a zinc plated metal in a solution of sodium dichromate and sulfuric acid for a few seconds. [6] Zinc chromate can also be synthesized by using neutral potassium chromate (K2CrO4) and zinc sulfate (ZnSO4), which forms a precipitate. [7]

K2CrO4 + ZnSO4 → ZnCrO4 + K2SO4

Uses

Zinc chromate's main use is in industrial painting as a coating over iron or aluminium materials. [8] It was used extensively on aircraft by the US military, especially during the 1930s and 1940s. It is also used in a variety of paint coatings for the aerospace and automotive industries. [9] Its use as a corrosion-resistant agent was applied to aluminium alloy parts first in commercial aircraft, and then in military ones. During the 1940 and 1950s it was typically found as the "paint" in the wheel wells of retractable landing gear on US military aircraft to protect the aluminium from corrosion. This compound was a useful coating because it is an anti-corrosive and anti-rust primer. [8] Since it is highly toxic, it also destroys organic growth on the surface. Zinc chromate is also used in spray paints, artists' paints, pigments in varnishes, and in making linoleum. [5]

When used as a pigment, it is known as Zinc Yellow, [2] Buttercup Yellow or Yellow 36. [10] It is rarely used in art because the pigment degenerates into a brown color. This effect can be seen in Georges Seurat's famous painting A Sunday Afternoon on the Island of La Grande Jatte . [11] The degradation of zinc yellow in Seurat's painting was thoroughly investigated [12] and these findings were subsequently employed in a digital rejuvenation [13] of the painting. [14] [15]

Zinc chromate putty was used as sealant in addition to two O-rings between sections of the failed solid rocket booster on Space Shuttle Challenger. Blowholes in this putty may have been a minor contributor to its catastrophic loss. [16]

Toxicity

Recent studies have shown that not only is zinc chromate highly toxic, it is also a carcinogen because it contains Cr(VI). [17] Exposure to zinc chromate can cause tissue ulceration and cancer. [1] [3] A study published in the British Journal of Industrial Medicine showed a significant correlation between the use of zinc chromate and lead chromate in factories and the number of cases in lung cancer experienced by the workers. [18] Because of its toxicity the use of zinc chromate has greatly diminished in recent years.[ citation needed ]

Related Research Articles

<span class="mw-page-title-main">Chromium</span> Chemical element, symbol Cr and atomic number 24

Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.

<i>A Sunday Afternoon on the Island of La Grande Jatte</i> Painting by Georges Seurat

A Sunday Afternoon on the Island of La Grande Jatte was painted from 1884 to 1886 and is Georges Seurat's most famous work. A leading example of pointillist technique, executed on a large canvas, it is a founding work of the neo-impressionist movement. Seurat's composition includes a number of Parisians at a park on the banks of the River Seine. It is held in the collection of the Art Institute of Chicago.

<span class="mw-page-title-main">Chromate and dichromate</span> Chromium(VI) anions

Chromate salts contain the chromate anion, CrO2−
4. Dichromate salts contain the dichromate anion, Cr
2O2−
7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

<span class="mw-page-title-main">Barium sulfate</span> Inorganic chemical compound

Barium sulfate (or sulphate) is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs in nature as the mineral barite, which is the main commercial source of barium and materials prepared from it. Its opaque white appearance and its high density are exploited in its main applications.

Lithopone, C.I. Pigment White 5, is a mixture of inorganic compounds, widely used as a white pigment powder. It is composed of a mixture of barium sulfate and zinc sulfide. These insoluble compounds blend well with organic compounds and confer opacity. It was made popular by the cheap production costs, greater coverage. Related white pigments include titanium dioxide, zinc oxide, zinc sulfide, and white lead.

<span class="mw-page-title-main">Potassium dichromate</span> Chemical compound

Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in laboratories because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.

Chrome yellow is a bright, warm yellow pigment that has been used in art, fashion, and industry. It is the premier orange pigment for many applications.

Metal fume fever, also known as brass founders' ague, brass shakes, zinc shakes, galvie flu, galvo poisoning, metal dust fever, welding shivers, or Monday morning fever, is an illness primarily caused by exposure to chemicals such as zinc oxide (ZnO), aluminium oxide (Al2O3), or magnesium oxide (MgO) which are produced as byproducts in the fumes that result when certain metals are heated. Other common sources are fuming silver, gold, platinum, and chromium.

<span class="mw-page-title-main">Potassium chromate</span> Chemical compound

Potassium chromate is the inorganic compound with the formula K2CrO4. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.

<span class="mw-page-title-main">Chromate conversion coating</span> Chemical treatment of metals

Chromate conversion coating or alodine coating is a type of conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys. The coating serves as a corrosion inhibitor, as a primer to improve the adherence of paints and adhesives, as a decorative finish, or to preserve electrical conductivity. It also provides some resistance to abrasion and light chemical attack on soft metals.

<span class="mw-page-title-main">Lead(II) chromate</span> Chemical compound

Lead(II) chromate is an inorganic compound with the chemical formula PbCrO4. It is a yellow orange solid that is very poorly soluble in water. It occurs also as the mineral crocoite. It is used as a pigment.

<span class="mw-page-title-main">Zinc molybdate</span> Chemical compound

Zinc molybdate is an inorganic compound with the formula ZnMoO4. It is used as a white pigment, which is also a corrosion inhibitor. A related pigment is sodium zinc molybdate, Na2Zn(MoO4)2. The material has also been investigated as an electrode material.

<span class="mw-page-title-main">Barium chromate</span> Chemical compound

Barium chromate, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions.

<span class="mw-page-title-main">Chrome orange</span> Chemical compound and inorganic pigment

Chrome orange is a mixed oxide with the chemical formula Pb2CrO5. It can be made by treating a lead(II) salt with an alkaline solution of a chromate or by treating chrome yellow (PbCrO4) with strongly basic solution.

<span class="mw-page-title-main">Calcium chromate</span> Chemical compound

Calcium chromate is an inorganic compound with the formula CaCrO4, i.e. the chromate salt of calcium. It is a bright yellow solid which is normally found in the dihydrate form CaCrO4·2H2O. A very rare anhydrous mineral form exists in nature, which is known as chromatite.

<span class="mw-page-title-main">Environmental effects of paint</span>

The environmental effects of paint can vary depending on the type of paint used and mitigation measures. Traditional painting materials and processes can have harmful effects on the environment, including those from the use of lead and other additives. Measures can be taken to reduce its environmental effects, including accurately estimating paint quantities so waste is minimized, and use of environmentally preferred paints, coating, painting accessories, and techniques.

<span class="mw-page-title-main">Cadmium chromate</span> Chemical compound

Cadmium chromate is the inorganic compound with the formula CdCrO4. It is relevant to chromate conversion coating, which is used to passivate common metal alloys such as aluminium, zinc, cadmium, copper, silver, magnesium, and tin. In conversion coating chromate reacts with these metals to prevent corrosion, retain electrical conductivity, and provide a finish for the appearance of the final alloy products. This process is commonly used on hardware and tool items. Chromate species take on their distinctive yellow color when coated.

<span class="mw-page-title-main">Strontium chromate</span> Chemical compound

Strontium chromate is an inorganic compound with the formula SrCrO4.

References

  1. 1 2 "OHSA Chemical Sampling Information for Zinc Chromate". Occupational Safety and Health Administration . Retrieved 24 March 2011.
  2. 1 2 National Oceanic and Atmospheric Administration. "ZINC CHROMATE - CAMEO Chemicals" . Retrieved 24 March 2011.
  3. 1 2 "OHSA Guideline for Zinc Chromate". Occupational Safety and Health Administration . Retrieved 24 March 2011.
  4. ↑ Richard P. Pohanish (2004). HazMat data: for first response, transportation, storage, and security. John Wiley and Sons. p. 1155. ISBN   978-0-471-27328-8.
  5. 1 2 Waligorski, Martin. "Everything You Need to Know About Zinc Chromate" . Retrieved 23 March 2011.
  6. ↑ "What is Zinc Chromate Used For". innovateus. Retrieved 11 December 2014.
  7. ↑ Paint and Coating Testing Manual. Philadelphia, PA: American Society for Testing and Aircraft Materials. 1995. p. 241.
  8. 1 2 Tencer, Michal (30 September 2006). "Electrical conductivity of chromate conversion coating on electrodeposited zinc". Applied Surface Science. 252 (23): 8229–8234. Bibcode:2006ApSS..252.8229T. doi:10.1016/j.apsusc.2005.10.039.
  9. ↑ Hall, A.F. (1944). "Occupational contact dermatitis among aircraft workers". American Journal of Medicine. 125.
  10. ↑ "Basic Zinc Chromate". Chemical Land21. Retrieved 24 March 2011.
  11. ↑ Gage, John (1993). Color and Culture: Practice and Meaning from Antiquity to Abstraction . Boston: Little, Brown. pp.  220, 224. ISBN   9780821220436..
  12. ↑ Casadio, F.; Xie, S.; Rukes, S. C.; Myers, B.; Gray, K. A.; Warta, R.; Fiedler, I. (2011). "Electron energy loss spectroscopy elucidates the elusive darkening of zinc potassium chromate in Georges Seurat's A Sunday on La Grande Jatte–1884". Analytical and Bioanalytical Chemistry. 399 (9): 2909–20. doi:10.1007/s00216-010-4264-9. PMID   20953774. S2CID   26844464.
  13. ↑ Digital restoration of paintings, ColourLex
  14. ↑ Berns, R. S.; Byrns, S.; Casadio, F.; Fiedler, I.; Gallagher, C.; Imai, F. H.; Taplin, L. A. (2006). "Rejuvenating the color palette of Georges Seurat's A Sunday on La Grande Jatte—1884: A simulation". Color Research & Application. 31 (4): 278–293. doi:10.1002/col.20223.
  15. ↑ Georges Seurat, A Sunday Afternoon on the Island of La Grande Jatte', ColourLex
  16. ↑ J.A. Hickman (1997). Polymeric Seals and Sealing Technology. iSmithers Rapra Publishing. p. 25. ISBN   978-1-85957-096-8.
  17. ↑ Holmes, A.L. (15 February 2011). "Chronic exposure to zinc chromate induces centrosome amplification and spindle assembly checkpoint bypass in human lung fibroblasts". Chemical Research in Toxicology. 23 (2): 386–395. doi:10.1021/tx900360w. PMC   2822114 . PMID   20030412.
  18. ↑ Davies, J.M. (May 1984). "Lung cancer mortality among workers making lead chromate and zinc chromate pigments at three English factories". British Journal of Industrial Medicine. 41 (2): 158–169. doi:10.1136/oem.41.2.158. PMC   1009277 . PMID   6722042.
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