J. L. McClure

Simultaneous measurements of normal spectral emissivity by spectral radiometry and laser polarimetry at high temperatures in millisecond-resolution pulse-heating experiments: Application to molybdenum and tungsten

Spectral radiometry and laser polarimetry are two independent techniques for the measurement of spectral emissivity of materials. In this paper, a high-speed system is described for the rapid measurement of normal spectral emissivity of a specimen based on the simultaneous utilization of the two techniques. One of the goals of this work to ascertain the accuracy of the laser polarimetry technique in measurement of normal spectral emissivity at high temperatures. To accomplish this goal, the normal spectral emissivities, in the vicinity of 0.633μm, of molybdenum and tungsten were measured by the two techniques over the temperature range 2000 to 2600 K. The results obtained by the two techniques are in agreement within 1%. The total uncertainty (two-standard deviation level) in measurement of emissivity by either spectral radiometry or laser polarimetry technique is estimated to be not more than + 2%.

Thermophysical properties of solid and liquid 90Ti-6Al-4V in the temperature range from 1400 to 2300 K measured by millisecond and microsecond pulse-heating techniques

The heat capacity and electrical resistivity of 90Ti–6Al–4V were measured in the temperature range from 1400 to 2300 K by two pulse-heating systems, operating in the millisecond and microsecond time regimes. The millisecond-resolution technique is based on resistive self-heating of a tube-shaped specimen from room temperature to melting in less than 500 ms. In this technique, the current through the specimen, the voltage drop along a defined portion of the specimen, and the temperature of the specimen are measured every 0.5 ms. The microsecond-resolution technique is based on the same principle as the millisecond-resolution technique except for using a rod-shaped specimen, a faster heating rate (by a factor of 10,000), and faster data recording (every 0.5 μs). Due to the rapid heating with the microsecond system, the specimen keeps its shape even in the liquid phase while measurements are made up to approximately 300 K above the melting temperature. A comparison between the results obtained from the two systems with very different heating rates shows significant differences in phase transition and melting behavior. The very high heating rate of the microsecond system shifts the solid–solid phase transition from the (α+β) to the β phase to a higher temperature, and changes the behavior of melting from melting over a temperature range to melting at a constant temperature like an eutectic alloy or a pure metal.

Application of laser polarimetry to the measurement of specific heat capacity and enthalpy of the alloy 53Nb-47Ti (mass%) in the temperature range 1600 to 2000 K by a millisecond-resolution pulse heating technique

The determination of the specific heat capacity, enthalpy, and electrical resistivity of the alloy 53Nb–47Ti (mass%) in the temperature range 1600 to 2000 K is described. The method is based on rapid resistive self-heating of a solid cylindrical specimen from room temperature to the maximum temperature of interest by the passage of a subsecond-duration electric current pulse through the specimen and on simultaneously measuring the pertinent experimental quantities. The experimental quantities measured are the current through the specimen, voltage drop across the effective specimen, specimen radiance temperature at two wavelengths, and normal spectral emissivity of the specimen. The present study extends this technique, previously applied to pure metals, to the determination of specific heat capacity and enthalpy of the alloy, 53Nb–47Ti. The measured properties were compared to those calculated from a thermodynamic description of the Nb–Ti system.

A microsecond-resolution transient technique for measuring the heat of fusion of metals: niobium

A microsecond-resolution pulse-heating technique is described for the measurement of the heat of fusion of refractory metals. The method is based on rapid resistive self-heating of the specimen by a high-current pulse from a capacitor discharge system and measurement of the current through the specimen, the voltage across the specimen, and the radiance temperature of the specimen as a function of time. Melting of the specimen is manifested by a plateau in the temperature versus time function. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements gave a value of 31.1 kj · mol−1 for the heat of fusion of niobium, with an estimated maximum uncertainty of ±5%. Electrical resistivity of solid and liquid niobium at its melting temperature was also measured.

Measurement of the heat of fusion of tungsten by a microsecond-resolution transient technique

A microsecond-resolution pulse-heating technique was used for the measurement of the heat of fusion of tungsten. The method is based on rapid (100 to 125μs) resistive self-heating of a specimen by a high-current pulse from a capacitor discharge system and measuring current through the specimen and voltage across the specimen as functions of time. Melting of a specimen is manifested by changes in the slope of the electrical resistance versus time function. The time integral of the power absorbed by a specimen during melting yields the heat of fusion. Measurements gave a value of 48.7 kJ · mol−1 for the heat of fusion of tungsten with an estimated maximum uncertainty of ±6%. The electrical resistivity of solid and liquid tungsten at its melting temperature was also measured.

Measurement of the heat of fusion of titanium and a titanium alloy (90Ti-6Al-4V) by a microsecond-resolution transient technique

A microsecond-resolution pulse heating technique was used for the measurement of the heat of fusion of titanium and a titanium alloy (90Ti-6Al-4V). The method is based on rapid (50- to 100-μs) resistive self-heating of the specimen by a high-current pulse from a capacitor discharge system and measuring, as functions of time, current through the specimen, voltage across the specimen, and radiance of the specimen. Melting of the specimen is manifested by a plateau in the measured radiance. The time integral of the net power absorbed by the specimen during melting yields the heat of fusion. The values obtained for heat of fusion were 272 J · g−1 (13.0 kJ · mol−1) for titanium and 286 J · g−1 for the alloy 90Ti-6Al-4V, with an estimated maximum uncertainty of ±6% in each value.

Radiance temperatures (in the wavelength range 527 to 1500 nm) of palladium and platinum at their melting points by a pulse-heating technique

AbstractThe melting-point radiance temperatures (at seven wavelengths in the range 521 to 1500 nm) of rhenium and iridium were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperature every 0.5 ms with two high-speed pyrometers. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal were determined by averaging results for several specimens at each wavelength. The results are as follows.

Heat capacity and electrical resistivity of liquid niobium near its melting temperature

\begin{gathered} Rhenium Iridium \hfill \\ \overline {2989 K at 521nm} \overline {2458 K at 523 nm} \hfill \\ 2916 K at 614 nm 2402 K at 617 nm \hfill \\ 2891 K at 656 nm 2380 K at 656 nm \hfill \\ 2853 K at 707 nm 2349 K at 711 nm \hfill \\ 2789 K at 807 nm 2297 K at 808 nm \hfill \\ 2719 K at 905 nm 2243 K at 906 nm \hfill \\ 2324 K at 1500 nm 1944 K at 1500 nm \hfill \\ \end{gathered}