Sample Digital DTA Apparatus

One of the first precise vacuum or inert-atmosphere instruments was designed and constructed by Whitehead and Breger (37). The furnace was constructed from an alundum core, 9 in. in length by 2 in. ID, wound with Chromel A resistance wire. The core was shielded by four sheet-nickel cylinders, mounted on three posts, and the entire assembly was placed inside a 12 x 24-in. Pyrex bell jar. All electrical connections were made through the bottom of the bell jar mounting base. The sample block was made in the dimensions shown from Type 446 or 309 stainless steel. The furnace heating rate was controlled by a Leeds and Northrup Micromax controller the differential temperatures were recorded on a Beckman Photocell recorder. 

A low-temperature DTA apparatus, capable of operation in the temperature range — 190-4Q0°C, has been described by Reisman (40). With the Dewar container filled with liquid nitrogen, the heating rate of the sample block was controlled by increasing the voltage into the heater coils, while cooling was accomplished by varying the pressure of the gas present in the outer chamber. Commercially available dc amplifiers and recorders were employed in the apparatus to record the DTA curve. 

An extremely rugged DTA furnace and sample holder has been described 

DTA has been described (97, 98). An earlier apparatus has been described by Stone and Rase (42). 

Radio-frequency heating oflarge samples of rubber has been described by Wald and Winding (99). The sample is placed between two parallel plates which are connected to a rf generator. Sample temperature is detected by a thermocouple located in the center of the sample. 

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