Chromium Plating and Chromating

About 1910 three discoveries, independent of each other, were made  

As an alloying element chromium has a ferrite-forming effecL One consequence of this is that the structure of these steels is similar to that of unalloyed iron. Corrosion and scaling resistance are, however, much better because of the passive layer Even at 12-13% Cr they withstand attacks of water and of oxidizing acids like nitric acid, but the steel has no resistance to the non-oxidizing adds, sulfuric and hydrochloric acids. 

In 2000 the world production of stainless steels was 20 million tonnes. Of this quantity 73% was austenitic. Stainless steels are important for growing economies. 

The remarkable changes of stainless steel production in China testifies this in 1998 0.88, in 2000 1.73 and in 2002 2.92 million tons. 

It is important to be aware of the difference between the two techniques chromium plating and chromating. The former creates a chromium metal layer on the substrate, while the latter gives a conversion coating as a foundation for lacquering or painting. 

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Exchange resins are also employed for the concentration of ions present in very dilute solutions instances are the recovery of silver from photographic residues, chromate from the waste liquor of chromium plating and magnesium from sea water. They have also been used for the separation of rare earths (p. 426), and of uranium, plutonium and radio-active fission products (p. 437), and for plutonium and uranium-233 purification. A striking application was the historic separation of single atoms of mendelevium on a sulphonated polystyrene resin and their elution therefrom, at 87 , with a-hydroxyisobutyrate (Seaborg, 1955). 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

The most common toxic metals in industrial use are cadmium, chromium, lead, silver, and mercury less commonly used are arsenic, selenium (both metalloids), and barium. Cadmium, a metal commonly used in alloys and myriads of other industrial uses, is fairly mobile in the environment and is responsible for many maladies including renal failure and a degenerative bone disease called "ITA ITA" disease. Chromium, most often found in plating wastes, is also environmentally mobile and is most toxic in the Cr valence state. Lead has been historically used as a component of an antiknock compound in gasoline and, along with chromium (as lead chromate), in paint and pigments. 

Theoretically, HCrOj is the predominant species between pH 1.5 and 4.0, HCr04 and CrO exist in equal amounts at pH 6.5, and Cr04 predominates at higher pH values. Chromium plating wastewater is generally somewhat acid, and the acid chromate ion HCrO is predominant in this wastewater. 

The lARC has concluded that there is sufficient evidence in humans for the carcinogenicity of chromium(Vl) compounds as encountered in the chromate production, chromate pigment production, and chromate plating industries. In experimental animals there is sufficient evidence for the carcinogenicity of calcium chromate, zinc chromates, strontium chromate, and lead chromate. ... 

Specialty Chromium-Plating Baths. Chromic acid baths using sodium chromate and sodium hydroxide to form a tetrachromate (92) have had limited use. Porous chromium is used in lubricated wear applications, and is made by chemically etching regular chromium plate, sometimes with light grinding after the etch. Black chromium is used on solar collector surfaces (see PHOTOVOLTAIC CELLS Solarenergy). Baths are sulfate-free, and include fluosilicic acid or acetic acid (91). 

No studies were located regarding death in humans after acute inhalation of chromium or chromium compounds. An increased risk of death from noncancer respiratory disease was reported in retrospective mortality studies of workers in a chrome plating plant (Sorahan et al. 1987) and chromate production (Davies et al. 1991 Taylor 1966) (see Section 2.2.1.2, Respiratory Effects). However, a number of methodological deficiencies in these studies prevent the establishment of a definitive cause-effect... 

A list of industries that may be sources of chromium exposure is given in Table 5-5. For most occupations, exposure is due to both chromium(III) and chromium(VI) present as soluble and insoluble fractions. However, exceptions include the tanning industry, where exposure is mostly from soluble chromium(in) and the plating industry, where exposure is due to soluble chromium(VI). The typical concentration ranges of airborne chromium(VI) to which workers in these industries were exposed during an average of 5-20 years of employment were chromate production, 100-500 pg/m3 stainless steel welding,... 

Toxicity and health effects Occupational exposure to chromium through inhalation occurs more with stainless steel welding, chromate production, chrome plating, and chrome pigment industries, primarily to hexavalent chromium. Chromium (HI) is an essential nutrient that helps the body use... 

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