Search

The coatings included: a solid solution of MgO and ZrO2; a true oxide compound, CaZrO3; and two single oxides, Gd2O3 and Y2O3. The compound oxides were applied to specially cleaned ATJ grade graphite-mold hollowcylinder inserts by an oxy-acetylene flame spray method, and the single oxides were applied in similar inserts by a plasma spray technique. The MgO, ZrO3 and CaZrO3 coatings were considered to be insufficiently resistant under casting conditions to qualify as satisfactory barrier coatings. The rare earth oxide Gd2O3 was found to be resistant to molten titanium during casting and to provide a good barrier between the graphite mold substrate and the cast metal, with no significant increases in either oxygen or carbon content. The oxide Y2O3 was found to have the best characteristics as a barrier coating. This oxide did not appear to be wetted by the molten metal cast against it nor to introduce any significant amounts of contaminants into the case metal. The barrier coatings were not effective in altering the high heat extraction capability of the graphite substrate and thus did not provide any improvement in solidification center line shrinkage. (Author)

Current hypotheses were reviewed relative to the contribution of radiant energy to heat transfer in BeO. The problem of radiant energy transmission in BeO was explored by exposing simultaneously, two types of BeO sample materials heated from 1000 to 2000 C, to pulses of radiant energy of known intensity. The effects were monitored with potentiometer and oscilloscope instruments from emf signals obtained from thermocouple detectors. Translucent thin-walled BeO tube material, heated from 1000 to 2000 C, exhibited no sustained transmission of radiant energy when exposed to radiant energy pulses of high intensity. An initial effect from the applied incident radiant energy was detected, however, which was interpreted to be due to the exposed surface of the BeO reaching a high temperature so rapidly that, momentarily, little heat was generated in the mass of the material and no immediate temperature rise occurred in the heated BeO. It was postulated that during this short interval incident radiant energy was transferred in the BeO by a process involving simultaneous emission and absorption of radiant energy in depth. As soon as the BeO temperature began to rise, this process of radiant energy transfer appeared to be replaced by the normal process of radiant energy absorption, conversion to heat, and reradiation. BeO heated above 1800C exhibited no tendency toward an initial rapid transfer of radiant energy. (Author)