Temperature Discrepancies in High Temperature Diffractometry
نویسنده
چکیده
Measurements using a Pt-Rh heater strip in a high temperature X-ray diffractometer furnace show that the temperature indicated by a two-colour infra-red pyrometer directed at the upper surface of the strip is within fl “C of the temperature indicated by a Pt/Pt-lO%Rh (type S) thermocouple welded to the lower surface, over the temperature range from 600-l 100 “C. However, the temperature of a powder sample on the heater, as indicated by the two-colour pyrometer, is significantly lower than that indicated by the thermocouple. The discrepancy between the two sets of temperature readings depends on the nature of the powder sample, and increases with temperature and with the thickness of the powder sample. The temperature discrepancy is attributed to thermal gradients within the powder sample, caused by cooling of the same surface due to thermal radiation and by the limited area of contact between the powder particles and the surface of the heater strip. Discrepancies between the temperature readings of the pyrometer and the thermocouple also occur for different atmospheres within the furnace chamber, indicating that the two-color pyrometer must be re-calibrated for each particular atmosphere to be used in an experiment.
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