Novel results on thermal diffusivity measurements on anisotropic materials using photothermal methods

Photothermal radiometry has been widely used to measure the thermal diffusivity of bulk materials. In the case of thin plates and filaments, a one-dimensional heat propagation model including heat losses has been developed, predicting that the thermal diffusivity can be obtained by recording both the surface temperature amplitude and phase profile slopes ("slope method"). However, this method has given highly overestimated values of the thermal diffusivity of poor-conducting films and filaments. In this paper we analyze the effect of the experimental factors affecting the thermal diffusivity measurements of thin plates and filaments using infrared thermography, in order to establish the experimental conditions needed to obtain accurate and reliable values of the diffusivity of any kind of material using the slope method. We present the calculations of the surface temperature of thin isotropic and anisotropic plates heated by a modulated and tightly focused laser beam, showing that the slope method is also valid for this kind of pointlike heating. Special attention is paid to the effect of surface heat losses (convective and radiative) on the diffusivity measurements of small-dimension and poor-conducting materials. Lock-in thermography measurements performed in the best experimental conditions on a wide set of samples of different thermal properties (thin isotropic and anisotropic plates and filaments) confirm the validity of the slope method to measure accurately the thermal diffusivity of samples of these shapes.

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“…Slabs have been covered by a 200 nm thick graphite layer. The error is 5%.References 15,17,18,25,and 26. …”

mentioning

confidence: 92%

Thermal diffusivity measurements of thin plates and filaments using lock-in thermography

Mendioroz

Fuente²,

Apiñaniz³

et al. 2009

Review of Scientific Instruments

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“…It is also convenient to introduce the inverse quantity of the thermal diffusivity rϭ1/k, which we have called the resistivity to heat diffusion. 9 In a classical modulated photothermal setup with pointlike excitation and surface absorption, spherical thermal waves diffuse through the sample. As a consequence, the surface temperature isophases are concentric and equidistant circumferences ͑see Fig.…”

Section: Isotropic Materialsmentioning

confidence: 99%

“…[12][13][14] We focus our attention on the photothermal signal generation in such materials and, in particular, on the photothermal methods for thermal diffusivity measurements. 6,[9][10] Moreover, we introduce the notation that will be used throughout the paper.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, some works devoted to the study of the photothermal signal generation in anisotropic media and, in particular, to the measurement of the thermal diffusivity have been published. [2][3][4][5][6][7][8][9][10] The interest has mainly focused on the measurement of the thermal diffusivity along the principal axes that define the thermal diffusivity tensor. Because anisotropic materials have isotropic behavior along the principal directions, all the photothermal methods developed for thermal diffusivity measurement on isotropic materials can be applied directly to measure the thermal diffusivity tensor.…”

Section: Introductionmentioning

confidence: 99%

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Photothermal characterization of anisotropic materials with buried principal axes

1997

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We study theoretically and experimentally the ability of photothermal techniques to thermally characterize the anisotropic materials whose principal axes are not contained at the sample surfaces. We first determine the thermal diffusivity tensor when the directions of the principal axes are known. Inversely, we calculate the directions of the principal axes in a sample whose thermal diffusivities are given. Measurements validating our theory are presented for a sample of pyrolytic graphite (PG), which has a high anisotropy, by means of two photothermal techniques: IR radiometry and the mirage effect. © 1997 Society of Photo-Optical Instrumentation Engineers.Subject terms: photoacoustic and photothermal science and engineering; photothermal techniques; isotropic materials; anisotropic materials; principal axes.Paper PPS-12

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“…El ajuste de la parte lineal a la ecuación anterior permite obtener su difusividad térmica. Este mismo método se puede aplicar a la medida de la difusividad térmica de materiales anisótropos, de forma que estudiando la fase de la temperatura (o de la desviación "mirage") a lo largo de las direcciones principales se obtiene el tensor difusividad térmica (7).…”

Section: -Medida De La Difusividad Termicaunclassified

Aplicación de las técnicas fototérmicas al estudio de materiales

Salazar¹,

Sánchez‐Lavega²,

Terrón³

et al. 2000

Bol. Soc. Esp. Ceram. Vidr.

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En este trabajo presentamos una descripción detallada de las técnicas fototérmicas y de sus aplicaciones al estudio de materiales. En particular, nos vamos a centrar en aquellas técnicas desarrolladas en nuestro laboratorio: radiometría infrarroja, termorreflectancia y efecto "mirage", junto con los resultados más importantes que hemos obtenido en el estudio de las propiedades térmicas de una amplia gama de materiales y en la detección y caracterización de defectos subsuperficiales en sólidos opacos. Palabras clave: Técnicas fototérmicas, ondas térmicas, difusividad térmica, ensayos no destructivos. Application of the photothermal techniques to the study of materialsIn this paper a general description of the photothermal techniques and its applications is presented. In particular, we concentrate our effort in those developed in our laboratory: infrared radiometry, photothermal reflectance and mirage effect. We also present their application to the measurement of the thermal diffusivity of a wide variety of materials and to the detection and characterization of subsurface features in opaque solids. Key words: Photothermal techniques, thermal waves, thermal diffusivity, nondestructive evaluation. 1.-INTRODUCCIONLa contínua sintetización de nuevos materiales con posibles aplicaciones tecnológicas ha impulsado el diseño y puesta a punto de nuevas técnicas que permiten la caracterización de sus propiedades y de su estructura interna. Durante los últi-mos 20 años las técnicas fototérmicas se han consolidado como herramientas útiles en el estudio de las propiedades ópticas, electrónicas y térmicas de materiales, y en el ensayo no destructivo de sólidos opacos.Las técnicas fototérmicas se fundamentan en la detección de las ondas térmicas que se generan en un material como consecuencia de la absorción de un haz de luz de intensidad variable (modulado o pulsado). Las características que definen la onda térmica (longitud de onda y velocidad de fase) están determinadas por las propiedades térmicas del material. Si éste es homogéneo las ondas térmicas se propagan libremente, pero sufrirán un proceso de "scattering" cuando en su avance se encuentren con inhomogeneidades. En consecuencia, las ondas térmicas llevan información sobre las propiedades ópticas y térmicas del material, así como de su estructura interna. Para extraer esta información se han desarrollado diversas técnicas de detección de las ondas térmicas. Entre las más utilizadas podemos citar: La radiometría infrarroja, la termorreflectancia, la fotodeformación, la técnica "mirage" (espejismo) y la fotoacústica. Para una revisión general sobre las técnicas fototérmicas y sus aplicaciones recomendamos consultar las referencias (1-3).En este trabajo vamos a describir las técnicas fototérmicas que hemos desarrollado en nuestro laboratorio, junto con los resultados más importantes que hemos obtenido en el estudio de las propiedades térmicas de una amplia gama de materiales y en la detección y caracterización de defectos subsuperficiales en sólidos opacos. 2.-CARACTERIS...

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Novel results on thermal diffusivity measurements on anisotropic materials using photothermal methods

Cited by 27 publications

References 10 publications

Thermal diffusivity measurements of thin plates and filaments using lock-in thermography

Thermal diffusivity measurements of thin plates and filaments using lock-in thermography

Photothermal characterization of anisotropic materials with buried principal axes

Aplicación de las técnicas fototérmicas al estudio de materiales

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