SCANNING CALORIMETRY WITH VARIOUS INDUCING VARIABLES AND MULTIOUTPUT SIGNALS

Scanning calorimetry controlled by an independent thermodynamic variable is further developed by simultaneous measurements of the rate of heat evolution and of the variations of the dependent variable. An instrument of this type is presented for use over the pressure interval from 0.1 to 400 MPa at temperatures from 213 to 503 K. The calorimeter is automated on the basis of digital feedbacks by the use of a 8255 I/O card and a PC. The typical low scanning rates of the three basic thermodynamic variables are as follows: P: 5 kPa/s, T: 8 10(-4)K/s, and V: 2 10(-5)cm3/s. Measurements can be made under isothermal, isobaric or isochoric conditions. The direct output signals are: the rate of heat evolution and the variations of the dependent variable or their rate. The total volume of the sample can be varied from 0.5 to 2.5 cm3 depending on the kind of measurement. The sample can be loaded once into the calorimeter and the phenomenon under investigation observed on different thermodynamic planes. The performence of the instrument is exemplified by investigation of the first-order phase transition in benzene, and phase transitions in 4-n-pentyl-phenylthiol-4'-decyloxybenzoate (10S5BARBAR) liquid crystal.