Thermal and electrical properties of dilute Cr-Ni base alloys

Abstract

The ferro-paramagnetic phase transition in dilute Cr-Ni base alloys is investigated through a qualitative study of their thermal conductivity as a function of temperature in the near vicinity of the transition. A single apparatus was used to measure the thermal and electrical conductivities and the specific heat of three thin rod samples having Cr concentrations of 0.12, 0.51 and 1.13 at. %.A voltage-temperature (V-0) realign was applied to measure the ratio between the thermal and electrical conductivities. The thermal conductivity data were then evaluated by using the electrical resistivity results obtained from the measured current-voltage (I-V) characteristic curves. A model describing the effect of Cr concentration on the I-V curve is proposed and tested. The effect of Cr concentration on specific heat is also presented.There have recently been several experimental and theoretical investigation on the nature of the magnetic phase transition in ferromagnetic metals and alloys. The study of transport properties such as electrical and thermal eonductivities and thermoelectric power has a good deal of attention [1][2][3][4][5]. In the present work the ratio between thermal and electrical conductivities (K/o) has been measured by the direct passage of an electric current through the specimen and by making use of V-0 relation.The electrical resistivity (p) is evaluated directly from the I-V characteristic curves. The obtained data agree quite well with those determined previously for the same samples by using the four-probe method [4]. In order to understand the effect of Cr concentration on the I-V curve and consequently on the electrical resistivity, the following relation is proposed:

Measurements of thermal conductivity and specific heat of dilute metallic alloys in the form of small samples by electrical method

“…5 and amounts to be 498 J kg-1 K -1 at 300 K, which is nearly close to the predetermined value [12]. In order to obtain other values of Cp at different temperatures, microfurnaces should be included at the ends of the sample.…”

“…In an attempt to avoid such difficulties, measurements on ferromagnetic metals and alloys were made by an indirect method to investigate the variation of thermal conductivity with temperature in the region around the Curie temperature [2--4]. The method depends upon a relation between the temperature and the potential distributions in a current-carrying conductor kept under vacuum.In the present work, measurements were performed on dilute Ni base Cr alloy sample up to 640 K. The electrical resistivity "Q" was accurately measured [5], and it has been found that the temperature coefficient of resistivity \~ d-~j diverges logarithmically at the Curie temperature Tc. The quantity "K" can be obtained by plotting the potential difference (V) across the sample against "0.,", where "0,," is the maximum temperature attainedfor a given current in the conductor the ends of 3*…”