A new high sensitivity thermobalance

Abstract

A new thermobalance is described which gives a direct plot of percentage weight loss versus sample temperature, without the need for replotting the results. The unit operates over the range ambient to 1000~ and features a miniature water-cooled furnace in conjunction with an electronic microbalance, giving sensitivities of 1 --250 mg for full scale deflection on a potentiometric recerder. Heating rates of 1--100~ are available and the furnace will cool from 1000~ to 50~C in less than four minutes. Typical applications of the unit are illustrated by reference to a number of inorganic and polymer systems.Although recent years have seen considerable development in the field of differential thermal analysis instrumentation, thermobalance design has not proceeded to such a high level of sophistication. Thus samples of the order of 50-200 mg are still widely used, requiring slow heating rates to obtain good resolution. This, coupled with the slow cooling rate of conventional furnaces, makes thermogravimerry a fairly lengthy process.In addition, the so-called "buoyancy effect" which causes an apparent increase in sample weight [l], requires the results to be replotted before a graph of percentage weight loss versus sample temperature can be obtained.The aim of the present design was to construct a thermobalance which would enable samples of the order of a few mg to be studied with good resolution at high heating rates, with minimum cool-down time between experiments. It was also required that "buoyancy effects" should be reduced to a level where it was possible to obtain a direct reading of the weight changes.

Applications of thermal analysis

“…Instrumentation used in the applications discussed below has been fully described elsewhere [6,7] but a brief mention here is appropriate, For work on the characterisation of fuel oils and fossil fuels the Stanton Redcroft simultaneous thermal analyser, the STA 781, has been used. Its advantages are (a) that it simultaneously measures TG-DTG-DTA and (b) that it is designed to give extremely close atmosphere control, in that the sample and reference head is suspended in a micro environmental ceramic cup with a series of ceramic discs and spacers sitting on the lid (Fig.…”