Precision of Quartz Crystal and Mercury Differential Thermometers in Heat-Of-Hydration Test

摘要

The precision of a quartz crystal thermometer was directly compared with that of a mercury differential thermometer in the determination of the heat of solution of a type II low-heat portland cement and a hardened paste made with the cement. The standard calorimeter apparatus was altered to permit (a) the insertion of one crystal probe into the calorimeter and a second crystal probe into the thermal jacket of the calorimeter and (b) the storage of the sample within the calorimeter enclosure. The calorimeter temperature rise was determined during solution of zinc oxide, dry cement, and 7-day hydrated paste. The test precision obtained using the quartz crystal thermometer was far poorer than expected, due to its low thermal mass in contrast to the high thermal mass of the rest of the calorimeter system. It was concluded that improved precision would require a low thermal mass calorimeter and closely controlled ambient temperature. The precision obtained with the differential thermometer was better than expected and was improved by storage of the sample within the calorimeter enclosure. The test results indicated that calibrated differential thermometers are not needed for this test procedure. The test results also indicated that properly prepared zinc oxide does not dissolve at the same rate as dry cement, but dissolves at a rate two to three times as fast as the dry cement. (Author)