Heat Transmission Configuration Research Articles

Measurement of the thermal expansion coefficient of Guadua angustifolia-Kunth using the photoacoustic technique

In this paper, the Linear Thermal Expansion Coefficient of Guadua angustifolia- Kunth samples was measured using the Photoacoustic (PA) technique in a heat transmission configuration and considering the thermoelastic bending as a PA signal generation mechanism in addition to the thermodiffusion ones. The obtained value of (27±7)x10-6K-1 is a reasonable value compared with that reported for similar materials such as wood.

A method for heat capacity measurement by photoacoustics

In this paper a photoacoustic method is proposed for specific heat capacity measurements in solids using a heat transmission configuration, where illumination takes place at the reference–sample interface. The method involves the use of a liquid reference sample so that it becomes free of instrumental function influence due to effects dependent on the detection cell, the frequency dependence of the microphone response and of the involved electronics. The method is validated with measurements performed in test samples of different materials.

A practical model for the determination of transport parameters in semiconductors

In this paper a new and practical model for the determination of transport parameters of crystalline semiconductors, by means of the photoacoustic technique is reported. The model is based on the calculation of the photoacoustic signal for the so-called heat transmission configuration, and considers that the thermal response to periodical heating, due to light absorption, in semiconductor materials has mainly two contributions: (a) the vibrations of the crystal lattice (phonon contribution) and (b) the diffusion and recombination (bulk and superficial) of the photogenerated charge carriers. Considering these contributions as the heat sources, and using unmixed Dirichlet and Neumann boundary conditions, the solution of the heat diffusion equation, necessary for the calculation of the photoacoustic signal is obtained. In addition, an expression—describing a particular transport regime—that can be used as practical fitting function, for the more available experimental conditions, is developed. Finally, values of transport parameters for silicon wafers are obtained by fitting this model to the experimental data, showing a good agreement with the values quoted in literature.

Influence of the thiourea/CdCl2 concentration ratio used for the chemical bath deposition of CdS thin films, upon the CdS/CdTe interface recombination velocity in CdTe/CdS/glass structures.

In this work we study the influence of the thiourea/CdCl2 concentration ratio used for the chemical bath deposition of CdS thin films on glass substrates, upon the CdS/CdTe interface recombination velocity in CdTe/CdS/glass structures, where the CdTe layer was grown on the CdS thin film by close space vapor deposition (CSVT)-hot wall technique. The interface recombination velocity was measured by means of the photoacoustic (PA) technique in a heat transmission configuration, in which minority carriers are photoexcited at the CdTe layer after illumination through the substrate and the CdS thin film. For data processing, a theoretical model was developed for the generation of the PA signal. We show a reduction in the value of the recombination velocity respecting those obtained for samples where CdS was grown by CSVT, and we observe that a minimal value appears for a thiourea/CdCl2 ratio in the CdS deposition solution equal to 5. These results show a good correlation with those of electrical measurements performed in solar cell devices.

Photoacoustic measurement of thermal properties of polystyrene metal oxide composites

Thermal properties (diffusivity, effusivity and conductivity) of polystyrene filled with low content of metal oxide (ZnO and MnO) particles are measured using heat transmission configuration of photoacoustic technique. The results show that ZnO changes thermal transport properties of polymer more effectively than MnO. The obtained data of the thermal conductivity are well explained by Lichtenecker's equation for thermal conductivity of two phase system. The experimental values of thermal conductivity of the composites have been used to estimate thermal conductivity of metal oxides. The data presented here show that this method is sensitive enough to detect variations in thermal properties of polymers due to addition of slight amount of particulate solids.

Thermal Characterization of Calcium Phosphates for Biomedical Use

Photoacoustic spectroscopy (PAS) has been used for thermal characterization of diverse materials. The use of PAS has become an important tool since it is a nondestructive technique. Furthermore, its use to measure also optical absorption spectra has advantages over the usual transmission measurements due to important features such as the fact that scattered light does not disturb the measurements significantly and also the sample does not need to be prepared to have good quality surfaces. By using a heat transmission configuration of the photoacoustic technique, the thermal properties of biological samples have been investigated. In the present study, the photoacoustic technique is applied to obtain the thermal diffusivity of hydroxyapatite (HA) [Ca10(PO4)6(OH)2]. Complementary studies of X-ray diffraction and energy dispersion spectroscopy (EDS) were performed.

Thermal Diffusivity Measurement in Solids by means of the Photoacoustic Technique

ABSTRACTWe report thermal diffusivity measurements for samples of silicon, gallium arsenide and cupper by means of the photoacoustic technique in a heat transmission configuration in order to obtain a comparison between the results obtained with the use of the conventional RG-model and our SP-model (based in a square periodical heat source) in the fitting process to the experimental data. Our results show that our SP-model is accurate to obtain a good fitting with the experimental data and it improves notably the results obtained with the RG-model.

Microstructure and Thermal Diffusivity of Ceramic Powders

For the first time, the thermal diffusivity (α) in red clay samples has been determined as a function of the annealing time, for a furnace temperature above 900 ◦ C. The thermal diffusivity measurements on the samples were obtained by means of the photoacoustic technique in a heat transmission configuration. A complementary microstructure analysis using X-ray diffraction (XRD) and energy dispersion spec- troscopy (EDS) has been performed. The ceramic material used in this work is widely used in the fabrication of several kinds of building materials such as bricks and roof tiles in the north oriental region of Colombia (Cucuta). The importance of these results is in the determination of conditions to obtain manufactured products with the desired heat transport capacity.

Determination of Thermal Diffusivity of the Pb0.88Ln0.08Ti0.98Mn0.02O3 (Ln = La, Eu) Ferroelectric Ceramic System by Photoacoustic Technique

Thermal diffusivities of the Pb0.88(Ln)0.08Ti0.98Mn0.02O3 (Ln = La, Eu) ferroelectric ceramic system are investigated by using Open Photoacoustic Cell (OPC) technique. The preparation of the ceramics was performed in our laboratory by using the oxide-mixing conventional ceramic method. It should be noted that these ceramics were taken in an unpoled state. For the thermal characterization, measurements at room temperature, of the photoacoustic amplitude signals as a function of the light modulation frequency, were performed by using OPC technique. Experimental data were fitted to the OPC theoretical expression in the heat transmission configuration for optically opaque samples. The thermal diffusivity values obtained for these ceramics are close to those results reported for BaTiO 3 based ferroelectric ceramics.

Thermal Diffusivity and Microstructure in API5L-X52 Carbon Steel

The determination of the thermal diffusivity of API5L-X52 carbon steel at room temperature, by means of the photoacoustic technique in a heat transmission configuration, is reported for the first time. Since literature values of thermal diffusivity for this low carbon steel do not exist, comparisons among our thermal diffusivity (α) results for API5L-X52 steel and those reported in the literature for steels with similar compositions are reported. Moreover, a study of the microstructure of this low carbon steel by means of scanning electronic microscopy (SEM) and X-ray diffraction (XRD) is presented.

Heat capacity measurement in solids by means of the photoacoustic technique

We report a method for determining the specific heat capacity in solids by means of the photoacoustic (PA) technique in a heat transmission configuration. This method involves a modulation frequency range where the samples are thermally thin and a liquid (i.e., distilled water) as a reference sample. It is free of PA cell parameters and was tested in some metals and semiconductors. The results agree very well with literature reported values for these samples.

H2SO4corrosion of API5L-X52 pipeline steel: Thermal diffusivity and microstructure

The effect of corrosion by H 2 SO 4 on the values of room temperature thermal diffusivity (a) and the microstructure of APISL-X52 pipeline steel are studied. The samples were exposed for 3, 6, 9, 12 and 15 days in a corrosive solution in an atmosphere with relative humidity of 57.16% in average and at temperature of 23.6 °C. The a values were measured by the photoacoustic technique in a heat transmission configuration. Our results show a a decrease with the corrosion time (t), with a behavior described by an exponentially decreasing curve. Microestructural study on the samples revealed the appearance of irregular surfaces with corroded grain frontiers, porosity and fractures of micrometer size as a consequence of corrosion, as well as a presence of phases mainly composed by tetra hydrated iron and manganese sulphates. The decreasing evolution of a vs t show the activity-passivity behavior in the corrosion process.

Thermal characterization and determination of recombination parameters in CdTe films on glass substrates by using open photoacoustic cell technique

CdTe is a semiconductor with a wide variety of applications and perspectives for electronic industry (high-efficiency photoelectric cells, infrared radiation detectors, etc.). In the present work, we used photoacoustic (PA) technique to study the thermal properties and the surface recombination velocity in CdTe/glass samples. Experimental PA phase signal as a function of modulation frequency in a heat transmission configuration was fitted to the theoretical expression for PA signal, which takes into account the heat sources resulting from the absorption of light in semiconductors and the nonradiative processes involved, which depend on their thermal, optical and electronic transport properties. By this procedure, it was possible to determine the thermal diffusivity and the surface recombination velocity in these samples. The studied samples were thin polycrystalline CdTe film deposited on glass slides. CdTe layers were deposited by a hot-wall closed-spaced vapor transport method, known as gradient recrystallization and growth. The values for the deposition parameters used in this study were the following: 700°C for the source temperature and 450 and 550°C for the substrate temperatures with three different deposition times from 5 to 20 min (then three different film thicknesses were obtained). A clear increment in the surface velocity and surface roughness is observed as the film thickness is increased.

Photoacoustic investigation of intrinsic and extrinsic Si

An open-cell configuration of the photoacoustic (PA) technique is employed to determine the thermal and transport properties of intrinsic Si and Si doped with B (p-type) and P (n-type). The experimentally obtained phase of the PA signal under heat transmission configuration is fitted to that of theoretical model by taking thermal and transport properties, namely, thermal diffusivity, diffusion coefficient, and surface recombination velocity, as adjustable parameters. It is seen from the analysis that doping and also the nature of dopant have a strong influence on the thermal and transport properties of semiconductors. The results are interpreted in terms of the carrier-assisted and phonon-assisted heat transfer mechanisms in semiconductors as well as the various scattering processes occurring in the propagation of heat carriers.

Photoacoustic study of the effect of doping concentration on the transport properties of GaAs epitaxial layers

We report a photoacoustic (PA) study of the thermal and transport properties of a GaAs epitaxial layer doped with Si at varying doping concentration, grown on GaAs substrate by molecular beam epitaxy. The data are analyzed on the basis of Rosencwaig and Gersho's theory of the PA effect. The amplitude of the PA signal gives information about various heat generation mechanisms in semiconductors. The experimental data obtained from the measurement of the PA signal as a function of modulation frequency in a heat transmission configuration were fitted with the phase of PA signal obtained from the theoretical model evaluated by considering four parameters—viz., thermal diffusivity, diffusion coefficient, nonradiative recombination time, and surface recombination velocity—as adjustable parameters. It is seen from the analysis that the photoacoustic technique is sensitive to the changes in the surface states depend on the doping concentration. The study demonstrates the effectiveness of the photoacoustic technique as a noninvasive and nondestructive method to measure and evaluate the thermal and transport properties of epitaxial layers. the effectiveness of the photoacoustic technique as a noninvasive and nondestructive method to measure and evaluate the thermal and transport properties of epitaxial layers.

Effect of Te doping on thermal diffusivity of Bi2Se3 crystals: A study using open cell photoacoustic technique

An open cell configuration has been employed for the photoacoustic measurement of the thermal diffusivity of undoped Bi2Se3 crystals and Bi2Se3 crystals doped with various concentrations of Te. The amplitude of the photoacoustic signal obtained under heat transmission configuration as a function of chopping frequency is used to evaluate the numerical value of thermal diffusivity, α. Doped samples show a substantial reduction in the value of α compared to undoped samples. The variations in the thermal diffusivity of the doped samples are explained in terms of the phonon assisted heat transfer mechanism. It is seen that α is very sensitive to structural variations arising from doping. The experimentally observed results are correlated with X-ray diffraction studies.

Photoacoustic measurement of transport properties in doped GaAs epitaxial layers

The photoacoustic technique under heat transmission configuration is used to determine the effect of doping on both the thermal and transport properties of p- and n-type GaAs epitaxial layers grown on GaAs substrate by the molecular beam epitaxial method. Analysis of the data is made on the basis of the theoretical model of Rosencwaig and Gersho. Thermal and transport properties of the epitaxial layers are found by fitting the phase of the experimentally obtained photoacoustic signal with that of the theoretical model. It is observed that both the thermal and transport properties, i.e. thermal diffusivity, diffusion coefficient, surface recombination velocity and nonradiative recombination time, depend on the type of doping in the epitaxial layer. The results clearly show that the photoacoustic technique using heat transmission configuration is an excellent tool to study the thermal and transport properties of epitaxial layers under different doping conditions.

Thermaldiffusivity of liquid crystalline polymers measured using opencell photoacoustic technique

Thermal diffusivity of two side-chain liquidcrystalline polymers is reported in this paper. An openphotoacoustic cell in the heat transmission configuration isemployed for the measurements. The investigation shows that thethermal transport properties of these materials are mainlydetermined by their molecular structure.

Photoacoustic evaluation of the thermaldiffusivity of coconut shell

In this paper we report the thermal diffusivity of coconut shellmeasured using a laser-induced photoacoustic (PA) technique. An openPA cell in the heat transmission configuration isemployed for the investigation. Laser-induced heating of thecoconut shell is found to result in a thermoelastic bending ofthe sample. Taking into account this effect, an appropriate modification of Rosencwaig-Gersho theory for the PAeffect is made for the calculation of the thermal diffusivity. Ourinvestigation shows that coconut shell possesses a largerthermal diffusivity than ordinary wood.

Photoacoustic studies on <bold>n</bold>-type InP

We discuss an open photoacoustic cell study on sulfer-doped n-type InP wafer. The thermal diffusivity of the sample is evaluated from the phase data associated with the photoacoustic signal as a function of the modulation frequency under heat transmission configuration. Analy- sis is made on the basis of the Rosencwaig-Gersho theory and the re- sults are compared with those from earlier reported photoacoustic stud- ies of semiconductors. Our investigation clearly indicates that the instantaneous thermalization process is the major heat diffusion mecha- nism responsible for the photoacoustic signal generation in an InP sample. © 2002 Society of Photo-Optical Instrumentation Engineers.