Papers by Keyword: Thermal Diffusivity

Abstract: This study focuses on the physical and microstructural properties of mullite-based ceramic synthesized by solid-state reaction of rice husk ash (RHA) and alumina (Al₂O₃). Laser Flash analysis (LFA), Field Emission Scanning Electron Microscopy (FESEM) and Energy-dispersive X-ray spectroscopy (EDX) characterized the effects of the mixtures of RHA and Al₂O₃ matrix. The results show that the Al₂O₃rich samples sintered at 1500 °C exhibit the highest thermal diffusivity radiated at 500 °Cwith values varied from 0.258-0.369 mm²/s. The addition of Al₂O₃ (30-60 wt.%) into RHA enhance the crystallization of mullite on the surface of vitreous particles. The presence of diphasic mullite densified the green bodies,and its crystallites size keep increases (400.78-650.52 nm) by theincrement of the sintering temperature (1200-1500 °C). These results suggested that addition of Al₂O₃into RHA enhance the thermal diffusivity as the values closer to the thermal diffusivity of pure mullite and have high potential application as thermal insulation material. The properties of mullite-based ceramics listed above such samples M1, where the composition closes to mullite (3:2) have comparable properties to commercialize mullite ceramics.

Abstract: Thermal lens spectrometry (TLS) technique was used to obtain the thermal diffusivity of electrospun Titania nanofibers (TiO₂), with average diameter size of 50-80 nm, in water. TiO₂ nanofibers have been successfully prepared by sol-gel and electrospining techniques. TLS provides reliable alternative to measure the thermal diffusivities of semitransparent materials and low thermal diffusivities. The results show that the nanofluid thermal diffusivity increases with the presence of nanofibers. Complementary techniques: scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were employed to characterize the nanofibers morphology, average fiber diameter and chemical composition, respectively.

Abstract: The mathematical model of a wood polymeric sand composite has been developed, which allows studying the thermal insulation properties of a composite material, taking into account the ratio of wood filler to the other components, the method for obtaining samples, and the type of wood filler. The technique of modeling and analysis of the obtained results is given. By mathematical modeling it was established that the wood polymeric sand composite has thermal insulation properties 2-3 times better than that of construction materials based on concrete. Construction materials based on the developed composite have a higher heat capacity than pure wood, which allows them to better maintain the constancy of the temperature inside the premises with significant daily fluctuations in the external temperature. A series of practical tests were conducted to evaluate the reliability of the results obtained. The discrepancy between theoretical and practical results does not exceed 5%.

Abstract: This study describes the thermal diffusivity of thin duplex steel plates in the thickness direction measured using the laser-flash method after welding. The work reports the experimental efforts in recording temperature profiles of the grade UNS S32304 duplex steel during autogenous welding. The butt weld autogenous joints were carried out by the GTAW (gas tungsten arc welding) process with either argon or argon - 2% nitrogen atmospheres. The amount of nitrogen in the heat affected regions, after welding, was measured and correlated with the variation of the thermal diffusivity of the studied material. The temperature profiles were obtained using k-type thermocouples connected to a digital data acquisition system. Different thermal cycles and thermal diffusivity values were observed in the heat-affected zone (HAZ) for both samples. In the solidified zone (SZ) was observed similar increase of the thermal diffusivity values for the plates welded with pure argon and argon plus nitrogen atmosphere.

Abstract: This study presents the formation of the zinc silicate from amorphous silica obtained from waste rice ash, with the addition of zinc oxide nanoparticles by conventional solid-state technique. The XRD showed the sharp intensive and small peaks while FTIR results indicated very slight variations in their peaks with the increased of samarium dopant concentrations. The FESEM clearly showed the cracks of zinc silicate doped with samarium the samples. The least thermal diffusivity values from 0.2039 to 0.1392 mm²/s acquired by pure zinc silicate (willemite) sintered at 1000°C. The thermal diffusivity was increasing with dopant concentration and decreasing with the rise in temperature (27-500°C). The thermal diffusivity curves revealed the exponential decay with the pores and cracks in the samples.

Abstract: In this work, we first present the composition dependence of the magnetocaloric properties in the Y₂Fe_17-xCo_x series.Then, we show preliminary results on our shaping works. In order to use the Y₂Fe_17-xCo_x compounds in magnetocaloric heat conversion systems, we applied powder metallurgy technics at a semi industrial scale to shape it. That involves milling, sintering, and heat treatments.Finally, the emphasis has been laid on the thermal properties of the sintered material, considering their decisive influence on the performance of the system.

Abstract: In this work, new thermally conductive polymer materials (TCPMs) on the base of polymer/graphite composites for cooling system of LED lamps were developed. Heat sinks for LED lamps were fabricated and investigated. Thermal conductivity and thermal diffusivity for all TCPMs were investigated by thermal analyzers XFA 500 and THB 100. Infrared thermal imager was used to study the temperature distribution of the LED lamps. Experimental and numerical investigations have shown high efficiency of polymer/graphite heat sinks for LED lamps.

Abstract: Synthetic fibers are being replaced gradually by natural materials such as lignocellulosic fibers. Compared to synthetic fibers, natural fibers have shown advantages in environmental, societal, economical and technical aspects. Thus, there is a growing worldwide interest in the use of those fibers. The banana fiber, extracted from the pseudo-stem of the plant, displays significant properties yet to be studied. Few thermal properties on banana fiber as reinforcement of epoxy matrix were fully evaluated. Therefore, the present work had as its objective to investigate, by photoacoustic spectroscopy and photothermal techniques the thermal diffusivity, specific heat capacity and thermal conductivity of epoxy composites reinforced with banana fibers .The epoxy matrix was added with up to 30% in volume of continuous and aligned banana fibers. The results indicated that these composites have good insulation capacity.

Abstract: Oxide ceramic is a kind of environmental friendly materials, which has attracted more and more interests for its bunch of advantages such as sound chemical, thermal stability, simple synthetic process, cheap price, harmless and safety. Therefore, Oxide ceramic will be a promising material in the future. In this work, polycrystalline samples of CuAlO₂ were prepared by a solid state reaction method. The mixture of pure CuO and Al₂O₃ powders was firstly pressed under the pressure of 60 MPa, and then 200 MPa to prepare pellets of 5 mm thick and 10 mm in diameter. The green compacts were sintered at five different temperatures (1273 K, 1323 K, 1373 K, 1423 K, 1473 K) for various holding times (5 h, 10 h and 15 h) in the air and then the furnace cooled. The crystalline and microstructures of the sintered CuAlO₂ bodies were detected by XRD and SEM. The properties of density, thermal conductivity were also investigated in detail. The experimental results show that CuAlO₂ bodies were rhombohedral, belonging to R3m space group. It is found that the density and the thermal conductivity of CuAlO₂ ceramics were significantly dependent on the sintering temperatures. The density and thermal conductivity increased with increasing the sintering temperatures. The thermal conductivity of samples sintered at 1273 and 1473 K with the same holding time (10 h) were 9.70 and 35.53 W/mk at the room temperature, 3.41 and 8.29 W/mk at 1100 K, respectively.

Abstract: This paper reports some research findings on the parallel evolutions of microstructural properties and thermal diffusivity in strontium titanate. Strontium titanate samples have been prepared via the high energy ball milling technique and subsequently moulded by a hydraulic pressing and followed by cold isostatic pressing. Nanometer-sized compacted powder samples were sintered from 500 to 1400°C using 100°C increments. Strontium titanate formation was observed at as early as 500°C sintering temperature alongside secondary phases. The full formation of strontium titanate was observed at 800°C sintering temperature and above. Average grain sizes showed a fluctuating trend with increased sintering temperatures due to carbonate decomposition at lower sintering temperatures (500 to 800°C) and grain growth phenomenon at higher sintering temperatures (900 to 1400°C). Parallel characterization of evolving thermal diffusivity showed the same trend of fluctuation at low sintering temperatures as indirect relationship but increased with increased grain size due to a lesser amount of phonon scattering. However, thermal diffusivity values decreased with increased temperatures because of increased phonon-phonon scattering.