Low temperature dilatometer

Abstract

Low temperature dilatometers are described which employ a combination cryostat/furnace made from an elongated block of metal by drilling separate longitudinal tubular chambers for insertion of a specimen tube containing a specimen and at least one electric resistance heater. A separate longitudinally drilled tubular cooling chamber serves as the expansion chamber for a conventional compressed gas refrigeration system, one end of the cooling chamber communicating with the inlet of the refrigerant gas compressor and the other end communicating, through an intermediate heat exchanger, with the outlet of the compressor. The metal construction of the cryostat/furnace and the absence of a conventional ceramic protection tube for the specimen facilitates rapid heat transfer to and from the specimen. The specimen can be brought quickly to the minimum desired temperature by operating the refrigeration system until that temperature is reached and then shutting off the compressor. The temperature then can be raised at a controlled rate to the desired maximum by continuous or intermittant operation of the heater or by alternate operation of the heater and refrigeration system. High and low temperatures also may be cycled readily. Changes in the length of the specimen are transmitted through a ceramic pushrod to a linear variable differential transformer dilation sensor. Specimen holders are described which prevent flexible specimens from bending during dilation measurements.