New sample levitation initiation and imaging techniques for the processingof refractory metals with an electrostatic levitator furnace

Two new methods that substantially ease the processing and study of refract ory metals, when an electrostatic levitation furnace is used, are reported. The first technique is concerned with preheating the sample on a pedestal, prior to launch, to a temperature (similar to 1500 K) at which thermionic emission dominates all other charging/discharging mechanisms that may be go ing on simultaneously. Launched into levitation at that temperature, the sa mple can be quickly heated to its molten state without encountering further charge loss problems. This procedure thus shortens substantially the time it takes to bring the samples to their final high temperature states at whi ch their thermophysical properties can be measured. This technique can be a pplied to most materials whose melting temperatures are higher than their t hermionic temperatures. The second technique described is an ultraviolet-ba sed sample imaging configuration. Due to the excellent sample-background co ntrast it continuously provides during all phases of processing (from solid to overheated liquid sample), it allows the measurements of the density an d the ratio of constant pressure heat capacity over hemispherical total emi ssivity of refractory metals. This method, compared with other imaging tech niques, leads to more accurate density data at very high temperatures and t o density temperature coefficients closer to those reported in the literatu re. This is exemplified in this article with zirconium and niobium liquid s amples. (C) 2001 American Institute of Physics.