CHROMIUM
Chromium is a hard, brittle metal used mainly as an alloying agent in stainless steels, heat-resistant alloys and in titanium alloys. Chromium is also widely used for plating purposes because of its excellent corrosion resistance, due to a thin surface oxide layer.
Typical Analysis:
Process Al C Cr Fe N O P Si S
Electrolytic: 0.015 0.05 99.50 .035 0.02 0.05 0.01 0.04 0.01
Aluminothermic: 0.10 0.05 99.40 0.20 0.02 0.10 0.01 0.10 0.01
Structure:
Crystal Structure: Body centered cubic, cI2 (Im3m); a=0.28844 to 0.28848 nm at 20 oC. Above 1840 oC: face-centered cubic; a=0.3 nm.
Mass Characteristics:
Atomic Weight: 51.996
Density: 7.19 g/cm3 at 20 oC
Thermal Properties:
Melting Point: 1875 oC
Boiling Point: 2680 oC
Phase Transformation Temperature: 1840 oC
Coefficient of Linear Thermal Expansion: 6.2 µm/m ⋅ K
Specific Heat: 0.4598 kJ/kg ⋅ K at 20 oC
Latent Heat of Fusion: 258 to 283 kJ/kg
Latent Heat of Vaporization: 6168 kJ/kg
Thermal Conductivity: 67 W/m ⋅ K at 20 oC, 76 W/m ⋅ K at 426 oC, 67 W/m ⋅ K at 760 oC
Entropy:
Entropy, kJ/kg ⋅ K
Temp (oC) Solid Gas
25 .046 3.35
227 0.71 3.56
727 1.09 3.83
1227 1.36 4.00
1727 1.59 4.13
2227 4.24
2727 4.31
Vapor Pressure:
oC Pa
965 3.2 x 104
1093 2.8 x 103
1197 2.7 x 102
1288 2.4 x 101
1875 9.9 x 102
Electrical Properties:
Electrical Conductivity: 13% IACS at 20 oC
Electrical Resistivity:
oC nΩ ⋅ m
-260 5
20 130
152 180
200 200
407 310
600 400
652 470
1000 600
Temperature Coefficient of Electrical Resistivity: At 0 oC, 0.03 nΩ ⋅ m per K
Electrochemical Equivalent: Valence 3, 0.17965 mg/C; valence 6, 0.08983 mg/oC
Electrolytic Solution Potential: For valence 3,0.5 V versus hydrogen electrode
Hydrogen Over-voltage: 0.38 V
Temperature of Superconductivity: 0.08 K
Work Function: 0.7337 aJ
Magnetic Properties:
Magnetic Susceptibility: Volume: 4.5 x 10-5 mks
Optical Properties:
Color: Steel gray
Reflectance:
67% at λ = 300 nm
63% at λ = 1000 nm
70% at λ = 500 nm
80% at λ = 4000 nm
Refractive Index: 1.64 to 3.28 for λ from 257 to 608 nm
Absorptive Index: 3.69 to 4.30 for λ from 257 to 608 nm
Nuclear Properties:
Stable Isotopes: 50Cr, 4.31% abundant; 52Cr, 83.76% abundant, 53Cr 9.55% abundant, 54Cr 2.38% abundant.
Unstable Isotopes:
Isotope Number Half-life
48 23-24 h
49 41.7 - 41.9 min
51 27.5 - 27.9 days
55 3.52 - 3.6 min
56 5.9 min
Chemical Properties:
Resistance to Specific Corroding Agents: (A 10% solution at 12 oC was used unless otherwise noted.) Chromium is resistant to the following acids: acetic, aqua regia, benzoic (saturated), butyric, carbonic, citric, fatty, formic, hydrobromic, hydroiodic, lactic, nitric, oleic, oxalic, palmitic, phosphoric, picric, salicylic, stearic, and tartaric. Chromium is not resistant to hydrochloric acid or other halogen acids.
Chromium is Resistant to the Following Agents: Acetone, air, ethyl and methyl alcohol, higher alcohols, aluminum chloride, aluminum sulfate, ammonia, ammonium chloride, barium chloride, beer, benzyl chloride,(saturated and 100%) calcium chloride, carbon dioxide, carbon disulfide, carbon tetrachloride (saturated and 100%), dry chlorine, chlorobenzene (saturated and 100%), chloroform, copper sulfate, ferric chloride, ferrous chloride, foodstuffs, formaldehyde, fruit products, glue, hydrogen sulfide (100%), sulfur dioxide (100%), chlorinated water, distilled water, rainwater, zinc chloride, and zinc sulfate.
Mechanical Properties:
Tensile Properties (For Re-crystallized, Swaged, and Arc Cast Electrolytic Chromium):
Tensile Elongation Reduction Modulus of
Strength, Proportional in 25 mm, in Area, Elasticity,
oC MPa Limit, MPa % % GPa
20 83 __ 0 0 248
200 234 __ 0 0 __
300 154(a) 11.7 3 4 290
350 197 105 6 8 168
400 225(b) 132 51 89 227
500 __ __ 30 75 __
600 242 69 42 81 200
700 203 __ 33 85 __
800 180 97 47 92 255
Recrystallized at 1200 oC in hydrogen. Strain rate of testing, 0.017 m/m per min. (a) Yield strength, 131 MPa. (b) Yield strength 140 MPa.