Chromium ppt


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Chromium ppt

  1. 1. Kundan Samal
  2. 2.  Appearance-Silvery metallic Atomic number-24 Category-Transition metal Group,period,block-6,4,d Oxidation States-+6 and +3(Strongly acidic oxide) Crystal Structure-BCC(body centered cubic) Isotopes-52Cr, 53Cr,54Cr Ore-Chromite(FeCr2O4)
  3. 3.  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.
  4. 4.  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.
  5. 5.  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.
  6. 6.  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.
  7. 7.  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.
  8. 8.  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.
  9. 9.  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.
  10. 10.  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
  11. 11.  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+.
  12. 12.  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.
  13. 13.  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.
  14. 14.  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