A. Cezairliyan

A high-temperature laser-pulse thermal diffusivity apparatus

A high-temperature laser-pulse apparatus for the measurement of thermal diffusivity in the temperature range from 1500 to 2500 K has been designed. constructed, and tested at the National Institute of Standards and Technology. A curve-fitting method is introduced by which the entire experimental temperature history curve is fitted with the theoretical curve under the boundary condition of radiative heat losses. The new apparatus and the curve-fitting method permit thermal diffusivity measurements with an uncertainty of not more than 3%.

Transient interferometric technique for measuring thermal expansion at high temperatures: Thermal expansion of tantalum in the range 1500–3200 K

AbstractThe design and operational characteristics of an interferometric technique for measuring thermal expansion of metals between room temperature and temperatures in the range 1500 K to their melting points are described. The basic method involves rapidly heating the specimen from room temperature to temperatures above 1500 K in less than 1 s by the passage of an electrical current pulse through it, and simultaneously measuring the specimen expansion by the shift in the fringe pattern produced by a Michelson-type polarized beam interferometer and the specimen temperature by means of a high-speed photoelectric pyrometer. Measurements of linear thermal expansion of tantalum in the temperature range 1500–3200 K are also described. The results are expressed by the relation:

Hemispherical total emissivity of niobium, molybdenum, and tungsten at high temperatures using a combined transient and brief steady-state technique

\begin{gathered} (l - l_0 )/l_0 = 5.141{\text{ x 10}}^{ - {\text{4}}} + 1.445{\text{ x 10}}^{ - {\text{6}}} T + 4.160{\text{ x 10}}^{ - {\text{9}}} T^2 \hfill \\ {\text{ }} - 1.309{\text{ x 10}}^{ - {\text{12}}} T^3 + 1.901{\text{ x 10}}^{ - {\text{16}}} T^4 \hfill \\ \end{gathered}

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

where T is in K and l0 is the specimen length at 20°C. The maximum error in the reported values of thermal expansion is estimated to be about 1% at 2000 K and not more than 2% at 3000 K.

Measurement of the heat capacity of molybdenum (Standard Reference Material) in the range 1500–2800 K

Measurements of the radiance temperature of graphite at 655 nm have been performed in the vicinity of its triple point by means of a rapid pulse-heating technique. The method is based on resistively heating the specimen in a pressurized gas environment from room temperature to its melting point in less than 20 ms by passing an electrical current pulse through it and simultaneously measuring the radiance temperature of the specimen surface every 120 μs by means of a high-speed pyrometer. Results of experiments performed on two different grades of POCO graphite (AXM-5Q1 and DFP-1) at gas pressures of 14 and 20 MPa are in good agreement and yield a value of 4330±50 K for the radiance (or brightness) temperature (at 655 nm) of melting graphite near its triple point (triple-point pressure, ∼ 10 MPa). An estimate of the true (blackbody) temperature at the triple point is made on the basis of this result and literature data on the normal spectral emittance of graphite.

A combined transient and brief steady-state technique for measuring hemispherical total emissivity of electrical conductors at high temperatures: Application to tantalum

The hemispherical total emissivity of three refractory metals, niobium, molybdenum, and tungsten, was measured with a new method using a combined transient and brief steady-state technique. The technique is based on rapid resistive self-heating of a solid cylindrical specimen in vacuum up to a preset high temperature in a short time (about 200 ms) and then keeping the specimen at that temperature under steady-state conditions for a brief period (about 500ms) before switching off the current through the specimen. Hemispherical total emissivity is determined at the temperature plateau from the data on current through the specimen, the voltage drop across the middle portion of the specimen, and the specimen temperature using the steady-state heat balance equation based on the Stefan–Boltzmann law. Temperature of the specimen is determined from the measured surface radiance temperature and the normal spectral emissivity; the latter is obtained from laser polarimetric measurements. Experimental results on the hemispherical total emissivity of niobium (2000 to 2600 K), molybdenum (2000 to 2700 K), and tungsten (2000 to 3400 K) are reported.

Thermal diffusivity of POCO AXM-5Q1 graphite in the range 1500 to 2500 K measured by a laser-pulse technique

AbstractThe linear thermal expansion of tungsten has been measured in the temperature range 1500–3600 K by means of a transient (subsecond) interferometric technique. The tungsten selected for these measurements was the standard reference material SRM 737 (a standard for thermal expansion measurements at temperatures up to 1800 K). The basic method involved rapidly heating the specimen from room temperature up to and through the temperature range of interest in less than 1 s by passing an electrical current pulse through it and simultaneously measuring the specimen temperature by means of a high-speed photoelectric pyrometer and the shift in the fringe pattern produced by a Michelson-type interferometer. The linear thermal expansion was determined from the cumulative shift corresponding to each measured temperature. The results for tungsten may be expressed by the relation