In this work, the influence of the surface treatment of bulk samples of the single-crystals obser... more In this work, the influence of the surface treatment of bulk samples of the single-crystals observed by means of the Atomic Force Microscopy on the measured thermal diffusivity of the material is presented and discussed. The mixed Zn 1 − x − y Be x Mn y Se crystals were grown from the melt by the modified high-pressure Bridgman method with different Be and Mn contents. The investigated specimens were first ground, then polished, chemically etched and finally annealed in zinc vapor. After each surface technological preparation the AFM images were taken and the thermal diffusivity of Zn 1 − x − y Be x Mn y Se compounds was determined by the photopyroelectric technique in the back configuration. The ground sample exhibited the highest roughness, whereas the annealed sample showed the lowest one. It has also been shown that the thermal diffusivity of the ground sample was significantly lower compared to the samples whose surface has been treated by other procedures. It was assumed that the measured thermal diffusivity had an effective value attained through the mediation of the thermal parameters of the bulk sample with those of the damaged surface layer. To analyze the results, a two-layer model proposed by J.J. Alvarado-Gil was employed. It turned out that the effective thermal diffusivity value depends much stronger on the conductivity of the system than on the diffusivity of the bulk.
Proceedings of the 2014 International Conference on Quantitative InfraRed Thermography, 2014
Lock-in thermography has been used previously for non-destructive testing of materials, but less ... more Lock-in thermography has been used previously for non-destructive testing of materials, but less work has been carried out in medical applications of this technology. Thin vertical cracks located at the interface between tooth and filling are usually difficult to detect by conventional optically stimulated thermography, due to the mainly heat flow generated perpendicular to the surface. The goal of this study is to measure the minimum detectible open crack in cavities restored with classic giomer by lock-in thermography technique, at a given laser intensity that is not harmful for the tooth. In order to check the capabilities of this technique for sealing evaluation and to test its limitations, complementary investigations were carried out by scanning electron microscopy (SEM) and dye penetrant testing. The results obtained by three different methods are also compared.
In this paper, a complete thermal characterization (measurement of all static and dynamic thermal... more In this paper, a complete thermal characterization (measurement of all static and dynamic thermal parameters) of some selected II-VI binary crystals was carried out. The semiconductors under investigation were grown from the melt by high-pressure/high-temperaturemodified Bridgman method. The contact photopyroelectric (PPE) method in back configuration and non-contact infrared lock-in thermography technique were used in order to get the thermal diffusivity of the investigated crystals. The thermal effusivity of the samples was obtained using the PPE technique in the front configuration, together with the thermal wave resonator cavity method. Knowing the values of the thermal effusivity and thermal diffusivity, the remaining two thermal parameters, i.e., thermal conductivity and specific heat were calculated.
ABSTRACT Microwave induced heating is widely used in medical treatments, scientific and industria... more ABSTRACT Microwave induced heating is widely used in medical treatments, scientific and industrial applications. The temperature field inside a microwave heated sample is often inhomogenous, therefore multiple temperature sensors are required for an accurate result. Nowadays, non-contact (Infra Red thermography or microwave radiometry) or direct contact temperature measurement methods (expensive and sophisticated fiber optic temperature sensors transparent to microwave radiation) are mainly used. IR thermography gives only the surface temperature and can not be used for measuring temperature distributions in cross sections of a sample. In this paper we present a very simple experimental method for temperature distribution highlighting inside a cross section of a liquid sample, heated by a microwave radiation through a coaxial applicator. The method proposed is able to offer qualitative information about the heating distribution, using a temperature sensitive liquid crystal sheet. Inhomogeneities as smaller as 1°-2°C produced by the symmetry irregularities of the microwave applicator can be easily detected by visual inspection or by computer assisted color to temperature conversion. Therefore, the microwave applicator is tuned and verified with described method until the temperature inhomogeneities are solved.
The paper is focused on the ability of using two complementary photothermal techniques for the me... more The paper is focused on the ability of using two complementary photothermal techniques for the measurement of all thermal parameters of some porous and/or semi-transparent solid samples whose composition, structure, and geometry do not allow a complete thermal characterization using a single technique. In this work, we combine a contact technique, photopyroelectric (PPE) calorimetry, with a non-contact one, infrared lock-in IR thermography (IRT), in order to investigate some solid samples such as dental composites, building materials, drugs, and semiconductors. The composition and the geometry of the investigated samples make the PPE method (in ''front'' detection configuration together with thermal-wave resonator cavity (TWRC) technique as scanning procedure) suitable for thermal effusivity measurements and IRT for thermal diffusivity investigations. In such a way, this combination of methods leads to a complete thermal characterization of the investigated materials.
ABSTRACT The photopyroelectric method in different experimental configurations was used for therm... more ABSTRACT The photopyroelectric method in different experimental configurations was used for thermophysical characterization of agricultural and biological samples. The study appears important due to the relation of thermal parameters to the quality of foodstuffs (connected to their preservation, storage and adulteration), migration profiles in biodegradable packages, and the mechanism of desiccation tolerance of seeds. Results are presented on the thermal parameters measurement and their dependence on temperature and water content for samples such as: honey, starch, seeds.
In this work, the influence of the surface treatment of bulk samples of the single-crystals obser... more In this work, the influence of the surface treatment of bulk samples of the single-crystals observed by means of the Atomic Force Microscopy on the measured thermal diffusivity of the material is presented and discussed. The mixed Zn 1 − x − y Be x Mn y Se crystals were grown from the melt by the modified high-pressure Bridgman method with different Be and Mn contents. The investigated specimens were first ground, then polished, chemically etched and finally annealed in zinc vapor. After each surface technological preparation the AFM images were taken and the thermal diffusivity of Zn 1 − x − y Be x Mn y Se compounds was determined by the photopyroelectric technique in the back configuration. The ground sample exhibited the highest roughness, whereas the annealed sample showed the lowest one. It has also been shown that the thermal diffusivity of the ground sample was significantly lower compared to the samples whose surface has been treated by other procedures. It was assumed that the measured thermal diffusivity had an effective value attained through the mediation of the thermal parameters of the bulk sample with those of the damaged surface layer. To analyze the results, a two-layer model proposed by J.J. Alvarado-Gil was employed. It turned out that the effective thermal diffusivity value depends much stronger on the conductivity of the system than on the diffusivity of the bulk.
Proceedings of the 2014 International Conference on Quantitative InfraRed Thermography, 2014
Lock-in thermography has been used previously for non-destructive testing of materials, but less ... more Lock-in thermography has been used previously for non-destructive testing of materials, but less work has been carried out in medical applications of this technology. Thin vertical cracks located at the interface between tooth and filling are usually difficult to detect by conventional optically stimulated thermography, due to the mainly heat flow generated perpendicular to the surface. The goal of this study is to measure the minimum detectible open crack in cavities restored with classic giomer by lock-in thermography technique, at a given laser intensity that is not harmful for the tooth. In order to check the capabilities of this technique for sealing evaluation and to test its limitations, complementary investigations were carried out by scanning electron microscopy (SEM) and dye penetrant testing. The results obtained by three different methods are also compared.
In this paper, a complete thermal characterization (measurement of all static and dynamic thermal... more In this paper, a complete thermal characterization (measurement of all static and dynamic thermal parameters) of some selected II-VI binary crystals was carried out. The semiconductors under investigation were grown from the melt by high-pressure/high-temperaturemodified Bridgman method. The contact photopyroelectric (PPE) method in back configuration and non-contact infrared lock-in thermography technique were used in order to get the thermal diffusivity of the investigated crystals. The thermal effusivity of the samples was obtained using the PPE technique in the front configuration, together with the thermal wave resonator cavity method. Knowing the values of the thermal effusivity and thermal diffusivity, the remaining two thermal parameters, i.e., thermal conductivity and specific heat were calculated.
ABSTRACT Microwave induced heating is widely used in medical treatments, scientific and industria... more ABSTRACT Microwave induced heating is widely used in medical treatments, scientific and industrial applications. The temperature field inside a microwave heated sample is often inhomogenous, therefore multiple temperature sensors are required for an accurate result. Nowadays, non-contact (Infra Red thermography or microwave radiometry) or direct contact temperature measurement methods (expensive and sophisticated fiber optic temperature sensors transparent to microwave radiation) are mainly used. IR thermography gives only the surface temperature and can not be used for measuring temperature distributions in cross sections of a sample. In this paper we present a very simple experimental method for temperature distribution highlighting inside a cross section of a liquid sample, heated by a microwave radiation through a coaxial applicator. The method proposed is able to offer qualitative information about the heating distribution, using a temperature sensitive liquid crystal sheet. Inhomogeneities as smaller as 1°-2°C produced by the symmetry irregularities of the microwave applicator can be easily detected by visual inspection or by computer assisted color to temperature conversion. Therefore, the microwave applicator is tuned and verified with described method until the temperature inhomogeneities are solved.
The paper is focused on the ability of using two complementary photothermal techniques for the me... more The paper is focused on the ability of using two complementary photothermal techniques for the measurement of all thermal parameters of some porous and/or semi-transparent solid samples whose composition, structure, and geometry do not allow a complete thermal characterization using a single technique. In this work, we combine a contact technique, photopyroelectric (PPE) calorimetry, with a non-contact one, infrared lock-in IR thermography (IRT), in order to investigate some solid samples such as dental composites, building materials, drugs, and semiconductors. The composition and the geometry of the investigated samples make the PPE method (in ''front'' detection configuration together with thermal-wave resonator cavity (TWRC) technique as scanning procedure) suitable for thermal effusivity measurements and IRT for thermal diffusivity investigations. In such a way, this combination of methods leads to a complete thermal characterization of the investigated materials.
ABSTRACT The photopyroelectric method in different experimental configurations was used for therm... more ABSTRACT The photopyroelectric method in different experimental configurations was used for thermophysical characterization of agricultural and biological samples. The study appears important due to the relation of thermal parameters to the quality of foodstuffs (connected to their preservation, storage and adulteration), migration profiles in biodegradable packages, and the mechanism of desiccation tolerance of seeds. Results are presented on the thermal parameters measurement and their dependence on temperature and water content for samples such as: honey, starch, seeds.
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Papers by D. Dadarlat