Dielectric Properties of Pinacol Hydrate: Application to Temperature Measurement

Abstract

IN the course of research into the dielectric properties of hydrogen-bonded structures, the dielectric properties of pinacol hexahydrate {(CH₃)₂.C(OH).C(OH).(CH₃)₂.6H₂O} were measured. It was found that in this compound a region of dielectric dispersion occurs centred about a frequency of 80 kc./s. at a temperature of 20° C. For polycrystalline material the relative permittivity falls from 45 to 3 in this dispersion region. The mid-frequency of this dispersion varies rapidly with temperature (Fig. 1) and can be described by the following expression: f = 2 × 10¹⁷ exp(−H/kT) sec.⁻¹, where H is 16.5 k.cal./mol. In the vicinity of 20° C. this means that the centre frequency of the dispersion region has a temperature coefficient of 9 percent per deg. C., and, if measuring at a fixed frequency near the centre, the variation in permittivity is 5.5 per cent per deg. C. The resistance of semiconducting material used in thermistors varies at the rate of 1.5–5 per cent per deg. C. at about room temperature¹. Consequently it would appear that a capacitor made with pinacol hydrate as dielectric could have applications as the thermal-sensitive element in circuits used for the measurement or control of temperature.