The exact measurement of the specific heats of solid substances at high temperatures. VI. The specific heats of vanadium, niobium, tantalum and molybdenum

Abstract

In the following are communicated the results of the measurements of the specific heats under constant pressure, made with the metals vanadium. niobium, tantalum and molybdenum, which all, in the shape of massive bars, could be obtained by us in a very pure state. If necessary, all these metalls were preliminarily brought into their "stabilized" condition by a suitable thermal treatment, as formerly described.T h e measurements a t a definite temperature were always repeated several times and the indication of the thermocouples, as well as their corrections, often controlled by intercalated determinations of the specific heats of stabilized platinum. T h e exactness and reproducibility of the measurements proved to be 0.1 -0.2 of the values indicated. 4 2. Vanadium. Purest vanadium in the form of preliminarily melted and then solidified droplets was most kindly furnishefl us by Mr. J. Strauss. Chief Research Engineer of the Vanadium Corporation of America of Bridgeville (Pa). It was enclosed in a vacuum platinum crucible of the construction formerly described I ) and the specific heats were determined with the usual care. The weight ot V d was :14.367 g, that of the platinum: 30.540 g ; the temperatures were checked several times by means of ?,-determinations of purest platinum, with the purpose of avoiding wrong indications of the thermocouples b y occasional contamination. According to Bolton ' ) vanadium melts a t 1680' C, according to Ruff3) a t about 1720' C, the now accepted value being: 1715' C. T h e metal, like niobium, tantalum, etc., crystallizes in the cubic system '), with a body-centred lattice: a,= 3.04 A : its density is: 5.98. I) F. M. Jaeger and E . Rosenbohrn, Rec. trav. chim. 51, 2 (1932).

Effect of Thermal Vacancy on Thermodynamic Behaviors in BCC W Close to Melting Point: A Thermodynamic Study

“…Figure 1 shows the calculated heat capacity for bcc W using the presently obtained Gibbs energy expression in comparison with the experimental data [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. As can be seen in the figure, excellent agreement between the calculations and the experiments is obtained.…”

“…Taking body cubic centered (bcc) W that has been proposed for use in the divertor of future fusion devices [ 4 , 5 ], for example, its thermal vacancy concentration can be larger than 0.02 at its melting point [ 6 , 7 ]. With such a large thermal vacancy concentration, the heat capacity of bcc W over the high-temperature region shows a strong non-linear increase, as demonstrated by most of the experimental data available in the literature [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] and plotted in Figure 1 . Such strongly non-linear behavior on heat capacity in the region close to the melting point is related to the dramatic increase of thermal vacancy.…”

“… Arrhenius plots of thermal vacancy concentration of bcc W. Symbols: Experimental data at melting point from [ 9 , 10 ]. Solid line: Calculated thermal vacancy concentration of bcc W according to the presently established Gibbs energy for bcc W. A clear curvature is obtained for the Arrhenius plot of thermal vacancy concentration of bcc W. …”

Ab initio inspection of thermophysical experiments for zirconium near melting

“…Thermochemical Table NIST [75] provides an approximation of seven enthalpy studies [87,[92][93][94][95][96][97] between 300 K and 1135 K and four [87,93,94,96] over the temperature range 1135-2125 K.…”