Robert A. Schiffman

Non-contact temperature measurement

Abstract Investigations of three methods for non-contact temperature measurement are presented. Ideal gas thermometry was realized by using laser-induced fluorescence to measure the concentration of mercury atoms in a Hg-Ar mixture in the vicinity of hot specimens. Emission polarimetry was investigated by measuring the spatially resolved intensities of polarized light from a hot tungsten sphere. Laser polarimetry was used to measure the optical properties, emissivity, and in combination with optical pyrometry, the temperature of electromagnetically levitated liquid aluminum. The ideal gas method is difficult to carry out on earth. It would be applicable to temperature measurements on any material in the quiescent gas environment that may be achieved in space-based containerless experiments, if a convenient method for more accurate and precise density measurements by laser scattering were available. The precision of temperature measurements based on the ideal gas law was ± 2.6% at 1500 – 2300K. The polarized emission technique has the capability to determine optical properties and/or spectral emissivities of specimens over a wide range of wavelengths with quite simple instruments. Its accurate use requires a high degree of specimen stability, position control, and modelling of the experimental measurements. These requirements are avoided by the laser polarimetric method for emissivity measurements which is well developed, uses quite simple instruments, provides nearly instantaneous results, and has been used to measure optical properties and emissivities for a variety of liquids and solids at high temperatures. Further development of the laser polarimetric method is in progress for non-contact temperature measurements in containerless space-based experiments, by combining polarimetric measurements of emissivity with spectral radiation pyrometry.

Optical and thermodynamic property measurements of liquid metals and alloys

Abstract Optical properties and spectral emissivities of liquid silicon, titanium, niobium, and zirconium were investigated by HeNe laser polarimetry at λ = 632.8 nm. The metals were of a high purity and, except for zirconium, clean. The more demanding environmental requirements for eliminating oxide or nitride phases from zirconium were not met. Containerless conditions were achieved by electromagnetic levitation and heating. CO 2 laser beam heating was also used to extend the temperature range for stable levitation and to heat solid silicon to form the metallic liquid phase. Corrections to previously reported calorimetric measurements of the heat capacity of liquid niobium were derived from the measured temperature dependence of its spectral emissivity. Property measurements were obtained for supercooled liquid silicon and supercooling of liquid zirconium was accomplished. The purification of liquid metals and the extension of this work on liquids to the measurement of thermodynamic properties and phase equilibria are discussed.

Atomic fluorescence study of high temperature aerodynamic levitation

Ultraviolet laser induced atomic fluorescence has been used to characterize supersonic jet aerodynamic levitation experiments. The levitated specimen was a 0.4 cm sapphire sphere that was separately heated at temperatures up to 2327 K by an infrared laser. The supersonic jet expansion and thermal gradients in the specimen wake were studied by measuring spatial variations in the concentration of atomic Hg added to the levitating argon gas stream. Further applications of atomic fluorescence in containerless experiments, such as ideal gas fluorescence thermometry and containerless process control are discussed.

Stabilised electromagnetic levitation at 2-13 MHz

Abstract SEL, the Stabilized Electromagnetic Levitator, has been developed to exploit the unique design opportunities available in containerless microgravity experiments. Efficiency and versatility are obtained with multiple coils driven by individual broadband amplifiers whose phase and frequency are controlled. The heating and positioning fields are decoupled. Specimen translation, spin, and for liquids, shape, may be adjusted. An open coil structure provides access for optical and diagnostic probes. Results of experiments with a prototype device are discussed. Levitating and heating materials on earth were demonstrated at frequencies up to 13 MHz.