Chromium is a silvery transition metal that occurs naturally in ores like chromite. It has several important industrial uses including in stainless steel production and metal plating. Chromium exists in two main oxidation states, Cr3+ and Cr6+, with Cr6+ being more toxic and carcinogenic. Alternative plating methods are being developed to replace the use of hexavalent chromium due to its health and environmental risks.

1. Kundan Samal

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.  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.  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.  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.  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.  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.  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.  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.  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.  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.  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.  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.  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