The Thermal Characteristic of Chromium

Chromium is hard, lustrous silvery metal which can take a high polish. It is a transition element with atomic number 24 and atomic weight 51,996. It has body-centered cubic crystalline structure and it is anti-ferromagnetic below 311.5 K and para magnetic above this Neel temperature. Naturally, occurring chromium is composed of four stable isotopes and five radioactive isotopes are known to exist, which half-lives ranging from 3.5 minutes for Cr-55 to 27.8 days for Cr-51. The most abundant isotopes from chromium is Cr-52 which has a constitutes about 83.76%.

Chromium in nature cannot move free as an unsure, but it stable with a compound called chromite (FeO.Cr2O3), from which the metal can be obtained directly by reduction with aluminum. Chromium is widely used in alloys as a hardening and anti-corrosion agent. It is the critical ingredient in all stainless steels. In combined form it is also used as a coloring agent, since all of its compounds are highly colored. In addition, it has many uses as a chemical catalyst. The structural stability of its ore, chromite, under heating makes it a useful form material in refractory processing.

Thermal Conductivity. At low temperatures a series of measurements is reported by Harper et al. On chromium specimens of increasing purity, with residual resistance ratios from 47-217 range. Below about 20 K the intrinsic thermal resistivity does not correlate well with the static defect scattering parameter beta, and consequently interpolating at these temperatures is uncertain. At higher temperature up to about 50 K, however, it is dependence for the intrinsic thermal resistivity as expected.

At temperatures above 100 K, within 1 percent with an earlier set reported for the measurement on iodide chromium having 280 of Residual Resistance Ratios (RRR). At high temperatures the thermal conductivity is obtained as a product of thermal diffusivity, specific heat, and density with thermal diffusivity. These derived thermal conductivity values lie about 3-4 percent and at temperature 1500 K and up to 1650 K the values decrease rapidly, about 20 percent at 1650 K. This reduction is attributed to effects of vacancy formations.

The recommended values for thermal conductivity are given for well-annealed chromium of purity 99.99 percent or higher. At temperatures below 100 K however, they are applicable only to chromium with residual resistivity of 0.616 nano-ohm-meter as obtained from the Wiedemann-Franz law.