Chromium

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Description:

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:

       Crystaline: 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                        0.046               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

Magnetic 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                    Ma             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.