High-temperature simultaneous thermal analysis (STA) techniques comprise both differential thermal analysis (DTA) and thermogravimetry (TG). A mass spectrometer (MS) is attached to the STA instrument for evolved gas analysis. The Stanton Redcroft STA shown above operates in a manner similar to a differential scanning calorimeter (DSC). Two sample crucibles are heated or cooled at a precisely controlled rate in a controlled environment. One crucible contains a standard of known thermal response; the unknown is placed in the second crucible. Differences in the thermal behavior of the two materials caused by differences in specific heat, occurrence of an exothermic or endothermic reaction, or a phase change result in a temperature difference between the two crucibles.

Temperature differences, measured with a Pt vs. Pt-10Rh differential thermocouple, permit properties of the unknown to be determined relative to that of the standard. Simultaneously, any change in mass of the specimen during a heating cycle can be measured with a microbalance as a function of temperature. During the thermal cycle, a capillary leak allows samples of the gaseous environment in the immediate vicinity of the specimen to be drawn into a quadruple mass spectrometer. Evolved gases can thus be identified by the mass-charge ratios of molecules, fragments, or atoms in the gas.

Features:

• DTA and TG measurements from 25 to 1500^oC
• Mass change determinations to +/- 0.01 mg
• Simultaneous quadruple mass spectrometric (MS) analysis of evolved gases with sensitivity in ppm level and mass range to 600 amu
• All systems fully computer controlled

Applications:

STA can be used to follow the course of chemical reactions, thermal decompositions, or phase changes as a function of temperature. Both endothermic and exothermic reactions can be detected, and semiquantitative values for the heats of reaction obtained. The sensitive balance associated with the TG capability of the system allows the mass change of a specimen to be measured as a function of temperature. Simultaneous DTA, TG and mass spectrometer measurements provide information about the cause of mass changes.