G.J.K. van den Berg

Construction of an adiabatic calorimeter measurements of the molar heat capacity of synthetic sapphire and of n-heptane

Abstract The construction of an adiabatic calorimeter for the temperature range between 10 and 350 K is described. Emphasis is given to the construction of the cryostat and the regulation of the shields. For a measurement of heat capacity from 5 to 100 K about 3 to 4 dm 3 of liquid helium is needed. The performance of the apparatus was checked by measuring the molar heat capacity of a standard sample of synthetic sapphire and of a sample of n -heptane. Results are within 0.2 per cent of the accepted literature values.

An isothermal displacement calorimeter for positive excess enthalpies

Abstract An isothermal displacement calorimeter has been constructed on the basis of the successful design of the Armidale group.(1,2) The most important changes in the design are (a) a stainless-steel construction was used instead of a glass one, (b) the dead space has been elimiated by introducing the stirrer shaft from below, (c) the degassed liquids are injected without any contact with air, and (d) the energy is measured by using a pulsed heater circuit instead of the conventional time-switching method. Calibration was carried out using benzene + carbon tetrachloride and benzene + cyclohexane at 298.15 K. The standard deviation are 0.10 and 0.45 J mol−1 respectively. Our results are in good agreement with those obtained by other investigators.

Tetraethoxysilane, Si(OC2H5)4: heat capacity and thermodynamic properties at temperatures from 0 to 440 K

The low-temperature heat capacity of tetraethoxysilane, Si(OC 2 H 5 ) 4 (s, 1), has been measured by adiabatic calorimetry at temperatures from 5 to 362 K. Two transitions were observed in this temperature range, a solid-to-solid transition at T = 187.72 K with Δ trs H o m = 13.20 kJ · mol −1 , and a solid-to-liquid transition at T = 190.97 K with Δ fus H o m = 11.14 kJ · mol −1 . From the results the thermodynamic functions have been calculated up to T = 440 K, the boiling temperature of tetraethoxysilane.

The construction of a sensitive microcalorimeter

Abstract The construction of a small differential calorimeter with a temperature range between 273 K to 373 K is described. The calorimeter is power compensated with adiabatic surroundings. The sample volume is 2 ml. In the most sensitive mode the noise level is below 0.4 microwatt. The α-β phase transition in paradichlorobenzene is used to demonstrate its performance.