Multiple-specimen thermogravimetric gas-flow apparatus for oxidation studies

A thermogravimetric system has been built that is capable of holding six specimens suspended in a flowing test gas at constant temperature (+or-0.1 degrees C) and constant dew point (+or-1 degrees C). The temperature and humidity of the test gas can be varied independently of each other to give gas temperatures from ambient to 200 degrees C and humidities from 30 to 500 Torr of water vapour. Any or all of the specimens can be weighed individually or consecutively at any time interval down to 1 h without removal from the test environment. The use of all-metal components and seals has reduced the leakage of air into the system to the point that it can be operated at the oxygen level in the carrier gas. Statistical methods were used to evaluate the precision of weighings made with this system. Four of these systems have been used to study the oxidation of thorium in humid air and humid nitrogen between 80 and 140 degrees C with water vapour pressures from 27 to 100 Torr.