Simultaneous determination of thermal conductivity and heat capacity near solid state phase transitions by a photopyroelectric technique

Abstract

An improved technique employing the photopyroelectric effect to measure thermal conductivity and heat capacity simultaneously near solid state phase transitions is reported. A calibration procedure adaptable to the use of a pyroelectric detector on a thermally thick backing medium is described in detail. A quantitative comparison of the predictions of the theory with experimental results on selected known samples is used to test the applicability of the method as a practical technique. The variations of the thermal diffusivity (αs), thermal effusivity (es), thermal conductivity (Ks) and heat capacity (cps) near the para-ferroelectric phase transition in single-crystalline triglycine sulphate at 49.4 °C cut along various axes are reported and compared with available experimental data. The method can be adapted to the measurement of these parameters during any kind of phase transition in solids, the only limitation being the temperature range over which the sensitivity of the pyroelectric detector remains sufficiently high.

Thermal Conduction Across Ferroelectric Phase Transitions: Results on Selected Systems

“…1 is generally used for these measurements (Menon & Philip, 2000). A 120 mW He -Cd laser of = 442 nm, modulated by a mechanical chopper, has been used as the optical heating source.…”

“…At temperatures above room temperature, the boundary conditions involved in the theory of this method are not easy to satisfy, so that application of the method can lead to errors in measurement. A photothermal technique for the simultaneous determination of the thermal conductivity and specific heat capacity near solid state phase transitions using a pyroelectric detector kept in contact with a thermally thick backing medium has been developed by Menon & Philip (2000). The PPE technique has some distinct advantages, such as its simplicity, good sensitivity and ability to perform nondestructive probing, over other photothermal methods.…”

“…The expressions for the temperature dependent PPE amplitude and phase under the above conditions are given by (Menon & Philip, 2000) …”

Enhancement in the Electrical and Thermal Properties of Ethylene Vinyl Acetate (EVA) Co-Polymer by Zinc Oxide Nanoparticles

“…The thermal parameters such as thermal diffussivity (α) and thermal efffusivity (e), the thermal conductivity (k) and heat capacity (C p ) were determined by the technique developed Preethy C menon et al [25]. During the measurement the sample, the pyroelectric detector and the backing should be thermally thick.…”

Thermal diffusion in thin plates and coatings: influence of thickness and substrate material

“…Again, a number of techniques have been developed to measure the thermal diffusivity of bulk samples [5,6]. Of late photothermal techniques employing the photoacoustic [7,8], photothermal deflection [9,10], or photopyroelectric [11,12] effects have become very popular for the measurement of the thermal diffusivity of bulk samples. However, these techniques are limited to bulk samples with minimum thickness of about 1 mm or so.…”