TABLE OF CONTENTS Measurements of changes in sample mass with temperature ( thermogravimetry, see Table 1.2) are made using a thermobalance (sometimes referred to as a thermogravimetric analyzer). (Note that mass is a measure of the amount of matter in a sample, whereas weight refers to the effect of the gravitational force on a mass and thus varies from one geographical location to another.) A thermobalance is a combination of a suitable electronic microbalance with a furnace, a temperature programmer and computer for control, that allows the sample to be simultaneously weighed and heated or cooled in a controlled manner, and the mass, time, temperature data to be captured. The balance should be in a suitably enclosed system so that the nature and pressure of the atmosphere surrounding the sample can be controlled (see Figure 3.1). Care is usually taken to ensure that the balance mechanism is maintained at, or close to, ambient temperature, in an inert atmosphere.
Several types of balance mechanism are possible [1], [2], [3], [4]. Null-point weighing mechanisms are favoured in TG as they ensure that the sample remains in the same zone of the furnace irrespective of changes in mass. Various sensors have been used to detect deviations of the balance beam from the null-position, e.g. in the Cahn RG electrobalance (Figure 3.2.) an electro-optical device has a shutter attached to the balance beam. The shutter partly blocks the light...
