High Temperature Structure and Thermal Expansion of Some Metals as Determined by X-Ray Diffraction Data. I. Platinum, Tantalum, Niobium, and Molybdenum

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Abstract
The crystal structure and thermal expansion of platinum,tantalum,niobium, and molybdenum have been determined between 1100° and 2500°K. These metals were found to undergo a uniform thermal expansion over the temperature range of this investigation and to undergo no structural change. The permanent elongation of tantalum wires, produced by annealing at temperatures between 2473° and 2773°K, appears to be caused by reorientation of crystal grains in the specimen and to preferred direction of crystal growth during annealing, rather than to a change in crystal structure. Quadratic equations have been developed for the thermal expansion of platinum,tantalum,niobium, and molybdenum. These equations are represented, respectively, by Δa 0 /a 0 =7.543×10 −6 (T−291)+2.362×10 −9 (T−291) 2 , Δa 0 /a 0 =6.080×10 −6 (T−291)+7.50×10 −10 (T−291) 2 , Δa 0 /a 0 =7.591×10 −6 (T−291)+6.96×10 −10 (T−291) 2 , and Δa 0 /a 0 =0.987×10 −3 +2.40×10 −6 (T−273)+2.20×10 −9 (T−273) 2 . Values of the expansion coefficient α were computed for each of the metals by differentiating the above equations. Our values were compared with those obtained from the Grueneisen theory and indicate that the theory provides a reasonably satisfactory means of extrapolating thermal expansion data obtained at low and moderate temperatures.