A dynamic pulse-heating method has been developed for measuring with an error of less than 2% the specific heats of metal wires from room temperature to 1000°C. The method consists essentially of recording the resistance of the sample wire while it is being heated by a pulse of large current and short time duration; then obtaining the temperature of the wire throughout the pulse with the aid of the measured resistance as a function of temperature; and finally computing the specific heat of the sample from the temperature as a function of time during the pulse, the measured power input to the wire, and the theoretically computed heat loss corrections. Results are given for high-purity iron over the temperature range 25° to 1050°C. Variations of the specific heat near the phase transitions are shown in detail.
In stitu te for A tom ic R e s e a rc h and D e p a rtm e n t of P h y s ic s Iowa State U n iv e rs ity , A m es, Iowa « -A b s tra c t-T h e e le c tr ic a l r e s is tiv ity of Nax W O j, and K xWO3 has been m e a s u re d at H>0*K, T he range of x -v a lu e s w as 0. 25 < x < 0 .9 . All r e s is tiv itie s w e re c h a r a c te r is tic of a m etal and lie on a single c u rv e . An e x tra p o la tio n of the c o n ductivity c u rv e to s e ro conductivity in dicated that the tu n gsten b ro n s e s should be se m ic o n d u c to rs for x < 0 .2 5 . The r e s i s tiv itie s th at have b een m e a s u re d for tu n gsten b ro n s e s with x < 0. 25 show* d se m ico n d u ctin g b eh av io r. The r e s is tiv ity of L ixWO^ ex h ib ited an an o m alo u s peak in the p vs T c u rv e . The Hall co efficien t of Li© 3 7 WO3 in d icated one fre e e le c tro n p e r alk ali a to m a» w as p re v io u s ly /o'uiH for N a^O j . The Seebeck co efficien t of N a^W O j depended lin e a rly on x "^"* as ex p ected * fro m fre e e le c tro n th e o ry . The im p lica tio n s of th ese and so m e o th e r d ata a r e d is c u s s e d .
A modified Ångström method for measuring thermal diffusivity and hence thermal conductivity of metals has been developed. Like previously reported dynamic methods, this method uses a heat source, whose temperature varies sinusoidally with time, located at one end of an effectively infinite rod. Unlike these methods, only one period of the heat pulse is required to eliminate the unknown coefficient determining the heat lost by radiation since both velocity and amplitude decrement of the heat pulse are measured. In addition to providing greater reliability at high temperatures by using only one period, the new method is faster in taking data and simpler in computation. The thermoelectric potentials from two thermojunctions are amplified and plotted on a Brown electronic recorder in order to obtain a permanent record of all necessary data for computing the thermal diffusivity. Results for copper, nickel, and thorium over the temperature range 0–500°C are given.
The electrical resistivities of the nonstoichiometric compounds NaxWO3 have been measured as a function of sodium concentration from x=0.48 to x=0.88, and as a function of temperature from T=4°K to T=873°K. The minimum in electrical resistivity near x=0.75, which had been reported by earlier investigators, was absent in single crystals which were selected to be electrically homogeneous. Above room temperature, the electrical conductivity increased approximately linearly with sodium concentration; at liquid-helium temperatures, the electrical conductivity increased approximately as the fourth power of sodium concentration.
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