Chromium(VI) is more carcinogenic than Chromium(III). Hexavalent chromium exists in alkaline, strongly oxidizing environments, readily soluble in water. Trivalent chromium exists in moderately oxidizing and reduced environments, sparingly soluble in water.
Used on a large scale in the metallurgical and chemical industries. The metallurgical industry: production of stainless steels, alloy cast iron and nonferrous alloys, plating steel. The chemical industry: pigments and dyes(Cr VI and Cr III), metal finishing and electroplating, wood preservatives (Cr VI only) and leather tanning (Cr III only), Glass manufacturing.
Stainless steel: Fe+Cr(11%) Ni alloy: Used in jet engine and gas turbine due to protective and decorative property. Chrome plating: immersing the metal parts to be plated in a bath of chromium trioxide (CrO3). A direct current is passed through the solution. Wood preservative: Chromate(VI) copper arsenate(CCA) used in timber treatment. Tanning: Chrome alum and Chromium(III) sulfate used to stabilize by cross linking collagen fibers.
Colorimetric, Ion Chromatography, co- precipitation(Ni2+). Cr(VI) uses diphenylcarbohydrazide (DPC) to form an intensely colored complex with Cr(VI). The complex is measured quantitatively by its visible absorption at 520 nm. Dynamic Reaction Cell (DRC) ICP-MS: Overcome mass interference(mass/charge). Use gases like N2O, SF6, CS2, CO2 etc.
An essential elements in human. High concentration of this can lead to DNA damage. Essential to normal glucose, protein, and fat metabolism. Body has several systems for reducing chromium (VI) to chromium (III) in blood before entering to the cell. Dietary supplements: Cr(III)picolinate and Cr(III) polynicotinate.
It is xenotoxic carcinogenic. The respiratory tract is the major target organ for chromium (VI) toxicity, for acute (short- term) and chronic (long-term) inhalation exposures. Kidney damage, liver failure,blood cell damage happens due to it’s oxidation property. pneumonia, asthma, ulcerations of the skin(chrome ulcers), bronchitis.
Hexavalent chromium is transported into cells via the sulfate and phosphate transport mechanism. Inside the cell, Cr(VI) is reduced first to metastable pentavalent chromium Cr(V), then to trivalent chromium Cr(III). Vitamin C and combine with chromate to give Cr(III) products inside the cell.
Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxoanions of Cr in the oxidation state +6. 2[CrO4]2- + 2H+ ⇌ [Cr2O7]2- + H2O The chromate ion is the predominant species in alkaline solutions, but dichromate can become the predominant ion in acidic solution
Chrome plating :Thermal spraying using a tungsten carbide substitute as an alternative to chrome baths. Nickel and tungsten at the atomic level to create a more environmentally friendly alternative to hexavalent chromium. Metals in general composed of many crystal grains, controlling the size of these grains and doing nanoscale manipulation to duplicate the properties of Cr6+.
Trivalent chromium plating baths use a very similar process to that used in hexavalent plating. Low Temperature Arc Vapor Deposition (LTAVD) is a process in which parts to be coated are exposed to a vaporized metal that condenses on the parts, depositing a thin, solid film. Heat treatments and plasma nitriding methods use heat to diffuse elements into the top surface of a substrate metal to form an alloy or layer with desired properties.
Nanocrystalline coatings use electrodeposition, vapor deposition, or spray conversion processing to deposit very small grains of crystalline alloys on a metal substrate. Thermal sprays include high velocity oxy-fuel (HVOF) and plasma sprays. Thermal spray is a coating process in which wire or metallic powder is melted by a high temperature flame and sprayed as particles or droplets onto a substrate.
Chromium as Cr6+: 0.05mg/l(Drinking water) Inland Surface water: 0.1 Public Sewers:2.0 Land of irrigation:0.6 Marine/Costal areas:1.0
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