Abnormal behavior in adiabatic calorimetry of set dental stone.

Dehydration in set dental stone was studied by employing specific heat measurements. Dehydration proceeds in two steps in air. In the case of bulk samples, especially those made with a lower water-powder ratio, three endothermic reaction stages are observed; a reaction of the dihydrate to the hemihydrate is apparently separated in two, one of which is not inherent. It is thought that the occurrence of a new peak is due to the difficulty for the dehydrated water to escape, depending on the porosity of the set stone.

Effects of the current used on determining a critical temperature by electrical resistivity measurements in dental alloys.

The electrical resistivity measurement to determine a critical temperature (Tc) in a stoichiometric CuAu alloy is discussed on the dependence of the current used. The temperature was measured on two ways: With the thermocouple connected to the specimen by spot-welding, and with them separated. In the latter case, the greater the current, the lower the apparent Tc because of the generation of Joule heat. To obtain a more precise Tc, the current should be as small as possible or the thermocouple should be located as close as possible to the specimen. It is highly desirable for the thermocouple and the specimen to be welded together, if the effects of some contamination can be ignored in measuring system.