Differential thermal analysis of transitions in finely-divided solids suspended in liquid media.
The experimental difficulties associated with differential thermal analysis (DTA) are reviewed. Quantitative work has always required calibration of the equipment, and conventional solid diluents have serious disadvantages. It is shown that calibration is not strictly necessary, given appropriate conditions. Dilute suspensions of polymer crystals in organic liquids provide ideal media for DTA when used as diluent and as reference material. Convection currents are suppressed and the medium can support fine particles of the solid under test, even when the solid has a relatively high specific gravity. The new theory and techniques have been tested experimentally by measuring the heats of fusion of two inorganic salt hydrates. The results are in excellent agreement with literature values. A novel arrangement with a double thermocouple junction is shown to have considerable potentialities as a means of making precise measurements quite simply.
Blackadder
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Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, U.K.
Roberts
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