ACCURATE THERMOGRAVIMETRY IN FLOWING GASES

A review of the sources of error in continuous weighing at high temperatures shows that the following precautions must be taken in the design of accurate thermobalances: (i) insulation of microbalance from furnace heat; (ii) accurate control of the reaction temperature; (iii) effective earthing of glass components to avoid electrostatic charging; (iv) correction of weight readings for buoyancy forces; (v) use of a narrow reaction tube to minimize turbulence. A new thermobalance has been designed with these precautions in mind. It also incorporates a novel divided gas flow system whereby the aerodynamic drag on the specimen from flowing gas is exactly balanced by a controlled opposite moment arising from a secondary gas flow. The thermobalance incorporates a Sartorius 4102 microbalance and weighs 1·5 g specimens to ±2 μg at 1273°K in flowing gas (e.g. O2 at 0·25 ml s-1 and atmospheric pressure).