Barium chromate

The first naturally occurring barium chromate was found in the country of Jordan. The brown crystals found perched on host rocks were named hashemite in honor of the Hashemite Kingdom of Jordan. The hashemite crystals range in color from light yellowish-brown to a darker greenish-brown and are usually less than 1mm in length.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O₄, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

The hashemite crystals are not composed of pure barium chromate but instead contain some small sulfur content as well. The different crystals contain a range of sulfur impurities ranging from the more pure dark crystals, Ba_1.00(Cr_0.93, S_0.07)_1.00O₄, to the less pure light crystals, Ba_1.00(Cr_0.64, S_0.36)_1.00O₄.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O₄, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

Hashemite was found to be an isostructural chromate analog of baryte, BaSO₄.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O₄, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

It can be synthesized by reacting barium hydroxide or barium chloride with potassium chromate.

:{{chem2 | Ba(OH)2 + K2CrO4 -> BaCrO4↓ + 2 KOH }}

Alternatively, it can be created by the interaction of barium chloride with sodium chromate. The precipitate is then washed, filtered, and dried.

It is very insoluble in water, but is soluble in acids:

:{{nowrap|2 BaCrO₄ + 2 H⁺ → 2 Ba²⁺ + Cr₂O₇²⁻ + H₂O}}{{spaces|6}}K_sp = [Ba²⁺][CrO₄²⁻] = 2.1 × 10⁻¹⁰

It can react with barium hydroxide in the presence of sodium azide to create barium chromate(V). The reaction releases oxygen and water.

:{{chem2 | 4 BaCrO4 + 2 Ba(OH)2}} ->[\ce{NaN3}] {{chem2 | 2 Ba3(CrO4)2 + O2↑ + 2 H2O↑ }}

Barium chromate has been found to be useful in many capacities. The compound is often used as a carrier for the chromium ions.

One such case is the use of barium chromate as a sulfate scavenger in chromium electroplating baths.Jones, Allen R; Meng, John; Newboy, Kenneth R. (1993) Use of barium chromate as a sulfate scavenger in chromium electroplating baths" US Patent No. 5207890 A. Over time the chromium concentration of the bath will decrease until the bath is no longer functional. Adding barium chromate enhances the life of the bath by adding to the chromic acid concentration.

Barium chromate is an oxidizing agent, making it useful as a burn rate modifier in pyrotechnic compositions. It is especially useful in delay compositions such as delay fuses.Espagnacq, Andre; Morand, Philippe. (1997) "Pyrotechnic composition for delay fuses" EP Patent No 0630876 B1.

Barium chromate is used as a corrosion inhibitive pigment when zinc-alloy electroplating surfaces.Fountoulakis, Stavros G; Humayan, Arif; Lezzi, Robert A. (1985) "Electroplated product and method" EP Patent No. 0140564 A2.

When mixed with solid fumaric acid, barium chromate can be used in the removal of impurities and residual moisture from organic dry-cleaning solvents or from petroleum fuels.Jackson, Herman R. (1993) "SOlid fumaric acid-solid barium chromate catalyst for removing impurities and residual moisture and method for its use" US Patent No. 5154726 A.

Barium chromate is also used in the composition of a catalyst for alkane dehydrogenation.Ruettinger, Wolfgang; Jacubinas, Richard. (2013) "Chromia Alumina Catalysts for Alkane Dehydrogenation" US Patent No. 20130072739 A1.

Barium has also been used to color paints. The pigment known as lemon yellow often contained barium chromate mixed with lead sulfate.Douma, M. curator. (2008) Pigments through the Ages. Institute for Dynamic Educational Development. http://www.webexhibits.org/pigments/ Due to its moderate tinting strength lemon yellow was not employed very frequently in oil painting.Kühn, H. and Curran, M., Strontium, Barium and Calcium Chromates, in Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 1: Feller, R.L. (Ed.) Oxford University Press 1986, p. 205 – 207. Pierre-Auguste Renoir and Claude Monet are known to have painted with lemon yellow.[http://colourlex.com/project/lemon-yellow/ Lemon yellow], ColourLex

In 2004 a method was found for making single-crystalline ABO₄ type nanorods. This method consisted of a modified template synthesis technique that was originally used for the synthesis of organic microtubules. Nanoparticles are allowed to grow in the pores of alumina membranes of various sizes. The varying sizes of the pores allow the growth to be controlled and cause the shapes to be reproducible. The alumina is then dissolved, leaving the nanoparticles behind intact. The synthesis can be carried out at room temperature, greatly reducing the cost and constrictions on conditions.Mao, Yuanbing; Wong, Stanislaus S. (2004) "General, Room-Temperature Method for the Synthesis and well as Arrays of Single-Crystalline ABO₄⁻ Type Nanorods." J. Am. Chem. Soc. 126(46), 15245-15252.

In 2010, a study was conducted on four hexavalent chromium compounds to test the carcinogenic effects of chromium. The chromium ions accumulate in the bronchial bifurcation sites, settling into the tissue and inducing tumors. Using zinc chromate as a standard, it was discovered that barium chromate is both genotoxic and cytotoxic. The cytotoxicity was determined to most likely be a result of the genotoxicity, but the cause of the genotoxicity is yet unknown.Wise, Sandra S; Holmes, Amie L; Qin,Qin; Xie, Hong; Kafsifis, Spiros P; Thompson, W Douglas; Wise, John Pierce Sr. (2010) "Comparative Genotoxicity and Cytotoxicity of Four Haxevalent Chromium Compounds in Human Bronchial Cells." Chem. Res. Toxicol. 23, 365-372.

Barium chromate is toxic. Chromates, when pulverized and inhaled, are carcinogens.

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• Kühn, H. and Curran, M., Strontium, Barium and Calcium Chromates, in Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 1: Feller, R.L. (Ed.) Oxford University Press 1986, p. 205 – 207.

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Category:Barium compounds

Category:Chromates

Category:Pyrotechnic oxidizers

Category:Oxidizing agents