Thermal Conductivity Of Samples Research Articles

Thermal Conductivity of Some Marble Stones Available in South Aceh District

Thermal conductivity is a fundamental property for insulating purposes when they are used as a building material. It controls the temperature distribution within the building. In this paper, the thermal conductivities of marble samples from the South Aceh District are reported. The samples were collected from three different areas in South Aceh District. The thermal conductivities of the samples were determined by using laboratory measurements. The results showed that samples of marble stones existing in South Aceh District have low thermal conductivity values. It revealed that marble stones existing in South Aceh District are appropriate to be applied as thermal insulating material.

On investigations of thermal conductivity, circumferential compressive strength, and surface characterization of 3D-printed hybrid blended magnetostrictive PLA composite

In past two decades, the 3D printing of thermoplastic-based composite matrix has been widely explored for different engineering applications. But hitherto little has been reported on the preparation of polylactic acid (PLA) composite-based 3D-printed circular disc to ascertain its circumferential compressive strength, thermal conductivity, and morphological properties for possible structural engineering applications. The present investigation outlines the circumferential compressive strength, thermal conductivity, and morphological properties (Shore D hardness, surface voids using fractured surface analysis) of 3D-printed PLA composite matrix. Based upon the thermal conductivity test, it has been ascertained that sample printed on fused deposition modeling (FDM) setup with infill density of 100%, infill angle of 90°, and infill speed of 70 mm/s has shown maximum thermal conductivity (0.278 W/mK). Further it has been observed that with the increase in infill density, thermal conductivity of the sample has improved. Circumferential compressive testing has been performed on universal tensile testing machine setup (with in-house developed fixtures), and from printer setting optimization viewpoint, it has been ascertained that infill density has maximum contribution for peak and break strength. Further morphological studies (surface hardness, fractured surface analysis, and surface roughness (Ra) data) have supported the observed behavior of circumferential compressive strength and thermal conductivity of 3D-printed samples.

The relationship between thermal conductivity and electrical resistivity of silty clay soil in the temperature range − 20 C to 10 C

With increasing engineering projects carried out in cold regions, the analysis and evaluation of the thermal conductivity and electrical resistivity of frozen soil have become important considerations in engineering construction and theoretical research. Through experiments performed on silty clay, the effects of the initial water content and soil temperature on the thermal conductivity and electrical resistivity of silty clay soil were analyzed. Theoretical models were also formulated for the soil thermal conductivity and electrical resistivity. The results showed that the variations in the thermal conductivity and electrical resistivity can be discussed as three stages: the freezing prophase, freezing metaphase and freezing anaphase. The electrical resistivity increases rapidly in the temperature range − 2 °C to −6 °C. The thermal conductivity increases rapidly from −2 °C to −4 °C and then decreases slightly from −4 °C to −6 °C due to the development of frost heave cracks in samples with higher water contents (15%, 18% and 20%). However, the thermal conductivity of samples with a water content of 10% continues to increase under these conditions. At the same temperature, the thermal conductivity increases linearly with water content in general. The electrical resistivity decreases approximate linearly with water content from 10 °C to −4 °C and increases with increasing water content from −4 °C to −20 °C. The thermal conductivity is inversely proportional to electrical resistivity from 10 °C to −4 °C and is proportional to electrical resistivity from −10 °C to −20 °C. The results of the experiments performed on silty clay soil verify the soundness of the proposed model for the thermal conductivity and electrical resistivity of unfrozen and frozen soil.

INVESTIGATION OF MECHANICAL AND THERMAL BEHAVIOR OF BASALT CUTTING WASTE (BCW) ADDED CLAY BRICK

Porous clay bricks produced by adding 5%, 10%, 15% and 20% by weight of Basalt Cutting Waste (BCW) were manufactured by semi-dry pressing process. BCW (Karacadağ, Diyarbakir, Turkey) was added to brick raw material as an additive in order to increase porosity and strength. The chemical composition and thermal behaviors of raw materials were investigated and SEM analysis was performed. Brick mixes containing different proportions of BCW were formed and then fired at 900 and 1000° C for two hours. Porosity, water absorption, compressive strength, thermal conductivity and microstructure of the samples were examined . It was observed that the porosity ratios were increased by up to 34% with the addition of BCW, however, compressive strength (at least 28 MPa) decreased. However, the compressive strength was found to be higher than the required standards. The thermal conductivity of samples with the addition of 20% BCW decreased from 0.98 up to 0.72 W / mK compared to the reference sample, which also corresponds to a reduction of 26.5% in proportion to the reference sample along with the increase in porosity. The increase in firing temperature also affected the mechanical and physical properties of the samples. In conclusion, this study revealed that the brick samples produced could be evaluated and used as insulating materials by adding BCW to building materials in construction applications.

Enhanced thermoelectric performance of a simple method prepared polycrystalline SnSe optimized by spark plasma sintering

In this study, polycrystalline SnSe was synthesized via a rapid, cost-effective, and large-scale synthesis route. The obtained SnSe powders were pressed into pellets via spark plasma sintering (SPS) at different temperatures. Powder X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) were used to characterize the crystal structures and morphology of the SnSe samples. The XRD results indicate that the orientation factors increase monotonously with the increase of sintering temperature. The FESEM images show that sintering temperatures have no obvious influence on the particle size. Positron annihilation measurements indicate that vacancy defects exist in all the sintered SnSe samples, and they recover gradually with increasing sintering temperatures. These vacancy defects are responsible for the lower lattice thermal conductivity in samples sintered at lower temperatures. The electrical conductivity, power factor, thermal conductivity, and figure of merit ZT show nearly the same variation trend, which increases initially with the increasing sintering temperature up to 550 °C then decreases with further increase of the sintering temperature, which is possibly due to slight oxidation of SnSe. A maximum ZT value of ∼0.47 at 430 °C was achieved for the 550 °C sintered sample, which is higher than those reported for undoped polycrystalline SnSe around this temperature. Thus, we provide a simple, energy-saving, and effective method to synthesize polycrystalline SnSe in large quantities, and SPS is an effective method to optimize thermoelectric performance.

Effect of Sample-Shape Imperfection on Uncertainty in Measurements of the Thermal-Conductivity by the Laser-Flash Method

The effect of the geometric shape of the samples on the uncertainty in measurements of the thermal conductivity coefficient of materials by the laser-flash method is investigated. A mathematical model simulating the process of measuring the thermal conductivity of samples made of graphite, Mg2Si0.4Sn0.6, and bismuth telluride by the laser-flash method is created in the Comsol Multiphysics software. Cylindrical samples with plane-parallel sides, samples shaped as a truncated cylinder, as well as parallelepiped-shaped samples with a square base are investigated. It is shown that the uncertainty in the measurements does not exceed 2% for the samples with plane-parallel sides and sizes up to 12.7 mm. For the samples shaped as a truncated cylinder with a diameter of 3 mm and at an inclination angle of φ = 1.5°, the measurement uncertainty does not exceed 3%. With increasing sample diameter and angle φ, the measurement uncertainty increases significantly.

Recycling of industrial waste iron tailings in porous bricks with low thermal conductivity

Abstract To meet the requirement of thermal insulation material in buildings, porous bricks with high porosity, high strength and low thermal conductivity were fabricated by foam-gelcasting technology using industrial waste iron tailings as raw materials. The effects of preparation parameter on phase composition, microstructure and mechanical strength of synthesised bricks were investigated in reference to Gibson model. The results showed that sintering temperature, soaking time and milling time had significant effects on porosity, compressive strength and microstructure of the porous tailing ceramics. Extending soaking time, meanwhile decreasing sintering temperature could effectively improve the compress strength of sample with similar porosity. The thermal conductivity of the porous tailing bricks could reach the lowest value of 0.032 W/(m·K) with the porosity of 89%. The thermal conductivity of samples with varied porosity is comparable with the calculated values deduced from the universal model, which make a good description of the relationship between porosity and thermal conductivity. It is a new way to recycle industrial waste into porous tailing brick which can be used as a building insulation material or filter material.

Materiale compozite pe baza de deseuri de beton celular autoclavizat si rasina poliesterica nesaturata

This paper presents an experimental study on the potential use of new type of composite as insulation material. The composite material (AACW-UPR) was synthesised through mixture between the Autoclaved Aerated Concrete Waste (AACW) as filler and Unsaturated Polyester Resin (UPR) as matrix. Several samples of the composite material with different UPR concentrations (50 and 70 vol.%) and different AACW particle size (0.2-1 mm, 1.5-2.5 mm, 3-6 mm) were prepared. The thermal behaviour and the water absorption capacity of the AACW-UPR composite materials were studied. Also, the influence of water absorption capacity on thermal resistance and thermal conductivity was studied. During the investigations we noticed the following: good chemical compatibility between the AACW particles and the UPR matrix; a decrease in thermal conductivity for samples with 50 vol.% UPR and inserted particles size between 3-6 mm and an increase in water absorption capacity with the increase in the filler content in the matrix. The increasing water absorption capacity determined a decrease in thermal resistance and a reduction of the composite features as insulating material.

Ambiguous temperature difference in aerodynamic levitation process: Modelling, solving and application

The aerodynamic levitation provides an efficient technique for the research on thermophysical properties and solidification behavior of refractory materials. However, there is a nonnegligible temperature differences across sample, causing unexpected uncertainty of measurement, such as, thermal expansivity and undercooling limit. We establish thermal filed model with properly simplified boundary condition, and derive quantitative expressions of this ambiguous temperature difference. Here we show that the temperature difference not only related to the average temperature, relative size and thermal conductivity of sample, but significantly influenced by the rotation pattern of sample. A huge temperature differences is almost inevitable when the sample with low thermal conductivity and high melting point is smelted in stationary suspension pattern, however, a drastically reduction of temperature difference can be fulfilled by simply making the sample rotation in up to down pattern. The thermal filed simulation was used to confirm the validity of these theoretical expressions. This work shed light on temperature difference in aerodynamic levitation. Based on this work, one can simply estimate the extent of temperature difference across the sample, and regulated that conveniently if needed, which benefit for novel material preparation and solidification mechanism study based on this technique.

The Effect of Surface Active Substances on the Mechanical Properties of a Copper-Matrix Nanocomposite

The presented work reviews the research in the field of production of nanostructured composite materials based on copper, reinforced with carbon nanostructures. Particular attention is paid to the use of composites with high thermal conductivity as structural materials. The method of manufacturing a composite material based on copper is described in detail: modes of preliminary annealing, pre-pressing, hot isostatic pressing. The characteristics of the matrix and alloying components are given, and also preliminary treatment of copper powder and carbon nanotubes is described. Different mechanisms of component mixing are considered, the process of mechanical alloying in a planetary mill is described in detail, the results of measuring the thermal conductivity of samples are given. The mechanical characteristics of the samples are considered in detail: ultimate strength, yield strength, elongation. The degree of influence of surfactants on the uniformity of the distribution of alloying components and the mechanical properties of the composite material is determined.

Влияние фотонной обработки на структуру и субструктуру термоэлектрического материала Bi2Te3 – хSeх

X-ray diffractometry, scanning electron microscopy and transmission electron microscopy techniques were used to study the phase composition and morphology as well as structure and substructure of semiconductor plates based on Bi2Te3 –xSex before and after photon treatment (PT) by radiation of high-power xenon lamps (spectral range λ = 0.2–1.2 μm) in an Ar atmosphere. It was found that the PT results in recrystallization of the near-surface layers (~2 μm) of the Bi2Te3 – xSex solid solution with the formation of inhomogeneous structure in the form of microcrystals surrounded by nanocrystalline grains. It also changes the chemical composition of the near-surface layer (~5 μm) associated with an increase in the concentration of selenium. More than a 40-fold increase in the area of intergrain boundaries and the formation of nanocontacts along the boundaries of the microcrystalline phase make a significant contribution to the scattering of phonons, and a change in the concentration of tellurium and selenium leads to a decrease in the electronic component of thermal conductivity. Substructural changes correlate with a significant (up to 5%) reduction in the thermal conductivity of samples of Bi2Te3 – xSex solid solution with a surface layer modified as a result of PT.

Effects of 2D boron nitride (BN) nanoplates filler on the thermal, electrical, mechanical and dielectric properties of high temperature vulcanized silicone rubber for composite insulators

Degradation of the silicone rubber in the composite insulators is usually caused by thermal and electrical stressing. The thermal conductivity of the composite insulator can be improved by adding a second phase with high thermal conductivity. Boron nitride is a new kind of two-dimentional (2D) materials, with a microstructure similar to the popular graphene but electrically insulating. Such unique properties make BN a promising candidate for increasing the thermal conductivity while maintaining the electrical insulating properties of the silicone rubber. In this report, we systematically studied the effects of BN nanoplates as a filler on the thermal diffusivity/conductivity, electrical breakdown strength, mechanical performance, dielectric behavior, as well as hydrophobicity properties of high temperature vulcanized silicone rubber. A series of samples were prepared with different BN filler loadings up to 32 wt% (∼25 vol%). We found that after adding BN nanoplates the sample's thermal conductivity can be increased by 30%. Surprisingly the electrical breakdown strength and hydrophobicity were also improved by the BN filler. However, the mechanical strength was deteriorated to some extent. Our results provide new thoughts in optimizing the performance of the silicone rubber for composite insulators. More studies need to be done in order to reveal the effects of BN additives in real composite insulators.

Fabrication of β-Si3N4 with high thermal conductivity under ultra-high pressure

In this work, the Silicon nitride composite ceramics (β-Si3N4) by ultra-high pressure sintering were investigated. And the effect of sintering temperature, hold time and α-Si3N4 powders on the sintering process had been analyzed in detail. These experimental results showed the larger particle size and lower porosity had an obvious effect on the thermal conductivity. Meanwhile, the addition of α-Si3N4 powder could be also attributed to thermal conductivity. We had been calculated the porosity of β-Si3N4 composite ceramics that the sample D (0.26%) was lower than the others samples. For a comparison, the thermal conductivity of sample D was up to 64.6 W/m K that was also attributed to its higher diffusion rate and small grain size.

Preparation of Lightweight Mullite-Anorthite Refractories by Different Routes

Mullite-anorthite as a kind of lightweight refractory combines the low thermal conductivity of anorthite and the excellent thermal properties of mullite. In this work, mullite beads and calcium aluminate cement was used as the main component and bonding agent. The lightweight mullite-anorthite refractory was prepared by difference routes including foaming method, addition of pore-forming agent and sacrificial template method. The phase composition, bulk density, apparent porosity and thermal conductivity of samples were compared. The results showed that anorthite formed as the consequence of the reaction of cement and mullite. Extra addition of foam, cornstarch and polyurethane sponge could decrease the bulk density of samples. The pore size of samples prepared by foaming method was the smallest. The apparent porosity of samples obtained by sacrificial template method was largest, but the thermal conductivity was the highest due to the open pores.

Properties of magnesium silicate hydrate (M-S-H) cement mortars containing chicken feather fibres

Fibres derived from waste chicken feathers have been used to reinforce magnesium silicate hydrate (M-S-H) cement mortars and Portland cement mortars using up to 5% of fibres by weight of dry binder. The properties of the feather fibre mortar composites including pH, density, flexural strength, compressive strength, toughness, thermal conductivity and microstructure are reported. Feather fibres bond very effectively into M-S-H cement mortars which has significantly lower pH (∼10.8) than Portland cement mortars (pH ∼ 12.6). Increasing the feather fibre content reduces the density, compressive strength, bending strength and thermal conductivity of samples but increases mortar toughness. The optimal feather fibre addition was determined to be 4 wt% by weight of dry binder content, based on ease of mixing the samples and the strength, toughness and thermal conductivity data. Potential applications for feather fibre reinforced M-S-H cement mortars boards are discussed.

Thermal properties of polyvinyl butyral/graphene composites as encapsulation materials for solar cells

Polyvinyl butyral (PVB) composites were successfully fabricated using graphene as thermal conductivity enhancement filler. The novel composite was prepared via solution blending. Graphene nanoplates (GN) were added to modify thermal conductivity of PVB. Thermal conductivity meter (TCM) and thermo-gravimetric analyzer (TGA) were used to investigate thermal properties of the composites like thermal conductivity and thermal stability respectively. Fourier transformation infrared spectroscope (FT–IR) and X-ray diffractometer (XRD) were used to analyze chemical structure and crystalline phase of the composites respectively. Microstructure of samples was determined by scanning electronic microscope (SEM). The results from the thermal conductivity meter (TCM) showed that the thermal conductivity of sample with a content of 30(Wt%) GN reached 4.521 W/(m K), which was nearly 20.55 times higher than that of pure PVB. The heating and cooling rates of 30(Wt%) GN sample were accelerated noticeably with an enhancement of 28% and 37% respectively, over that of original PVB. The composites have appropriate ionic conductivities as encapsulation materials, which are generally lower than 10−5 S/m. It is forecasted that the prepared composites have considerable prospects in encapsulation of solar cells and cooling of electronic devices.

THERMAL CONDUCTIVITY and TENSILE PROPERTIES OF HOLLOW GLASS MICROSPHERE / POLYPROPYLENE COMPOSITES

In this study, hollow glass microspheres (HGM) filled polypropylene (PP) composites were prepared by melt extrusion method. In order to understand the effect of structure and physical properties on the performance of composites, the morphologies, tensile properties and thermal conductivities of composites were investigated. The surface of HGMs were modified with 3-(Trimethoxysilyl) propyl methacrylate ( TMSM ) silane coupling agent to improve the compatibility between PP matrix and HGMs. The physical properties of silane modified and unmodified HGMs were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM). The effect of HGM content and surface modification of HGM on morphological, mechanical and thermal conductivity properties of composites were evaluated. The results indicated that the surface modification of HGM enhance the interfacial region between HGM and polymer matrix. When 20 wt % modified HGM was added to neat PP, the modulus of the composite obtained was 1057 MPa, increasing by 15.1% compared with that of the PP/unmodified HGM composite. However, any positive or consistent effect of surface modification and HGM addition on thermal conductivity of samples can not be observed.

A study of thermal insulation properties and microstructure of ultra-light 3D-carbon foam via direct carbonization of polymer foam

This paper describes the preparation of ultralight flexible carbon foam (FCF) by direct carbonization of commercial melamine foam (MF). The effect of carbonization temperature on microstructure characteristics and thermal properties in FCF were evaluated. The thermal conductivity of the samples at ambient temperature was measured using the heat flow tester and the thermal conductivity of the samples at various temperatures was measured using water flow plate method. The pore distribution and microstructure morphology of the MF sample and FCF samples were also measured by mercury intrusion porosimetry and SEM imaging, respectively. The results show that the 3D network architecture and the triangle fiber shape of the MF precursor were inherited by the resulting FCF samples despite of a great reduction in volume. The average pore diameter of FCF samples reaches a lowest value for carbonization temperature of 850 °C. The thermal conductivity of FCF samples is considered to be affected by the porosity characteristic of FCF samples. The higher pore diameter of FCF samples, the greater its thermal conductivity.

Viscosity and thermal conductivity of MgO\u2013EG nanofluids

Nanofluids are a group of novel engineering materials that are increasingly being used, particularly in the processes of heat exchange. One of the most promising materials in this group is magnesium oxide–ethylene glycol (MgO–EG) nanofluid. The literature informs that this material is characterized by an significant increase in thermal conductivity with low dynamic viscosity increase. The aim of this paper is to provide experimental data on the dynamic viscosity and thermal conductivity of nanofluids containing MgO nanoparticles with 20 nm average size and ethylene glycol as base fluid. To determine dynamic viscosity and thermal conductivity of samples, a HAAKE MARS 2 rheometer (Thermo Electron Corporation, Karlsruhe, Germany) and KD2 Pro Thermal Properties Analyzer (Decagon Devices Inc., Pullman, Washington, USA) were used. Additionally, a comparison of the experimental results and the predictions of theoretical models was presented. It was presented that the vast majority of theoretical models does not describe in a correct way both viscosity and thermal conductivity. It was also shown that the enhancement of this basic physical properties might be described with good result with second degree polynomials. Finally, evaluation of the heat transfer performance was presented.

Effect of Ga doping on the thermoelectric performance of Cu3SbSe4

The Cu3SbSe4 compound is an environmentally friendly and low-cost medium-temperature thermoelectric material, which is featured by its low thermal conductivity. The disadvantage of this compound lies in its intrinsic poor electrical transport property. In order to improve the electrical conductivity of Cu3SbSe4, in this work we are to increase its carrier concentration by one to two orders of magnitude though elemental doping. The sample composition of Cu2.95GaxSb1-xSe4 is designed to increase the hole carrier concentration by introducing Cu vacancies and substituting Ga3+ for Sb5+. The Cu2.95GaxSb1-xSe4 (x=0, 0.01, 0.02 and 0.04) samples are prepared by melting-quench method. The X-ray diffraction analysis indicates that the obtained samples are of single-phase with the tetragonal famatinite structure, and the energy-dispersive X-ray spectroscopy results show that the actual compositions of the samples are very close to their nominal compositions. The effect of Ga doping on the thermoelectric performance of Cu3SbSe4 compound is investigated systematically by electrical and thermal transport property measurements. According to our experimental results, the hole concentration of the sample is efficiently increased by substituting Sb with a small amount of Ga (x=0.01), which can not only substantially improve the electrical conductivity but also suppress the intrinsic excitation of the sample. The maximum power factor reaches 10 μW/cm·K2 at 625 K for the Ga doped sample with x=0.01, which is nearly twice as much as that of the sample free of Ga. Although the carrier concentration further increases with increasing Ga content, the hole mobility decreases dramatically with the Ga content increasing due to the increased hole effective mass and point defect scattering. Thus, the electrical transport properties of the samples deteriorate at higher Ga content, and the maximum power factors for the samples with x=0.02 and 0.04 reach 9 and 8 μW/cm·K2 at 625 K, respectively. The lattice thermal conductivities of the samples basically comply with the T-1 relationship, suggesting the phonon U-process is the dominant scattering mechanism in our samples. For the samples with x=0 and 0.01, the lattice thermal conductivities at high temperature deviate slightly from the T-1 curve due to the presence of intrinsic excitation. However, these deviations are eliminated for the samples with x=0.02 and 0.04 because the bipolar effect is effectively suppressed with the increasing of Ga content. Thus, Ga doping can reduce the bipolar thermal conductivity at high temperature by increasing the hole carrier concentration. Furthermore, the point defects introduced by Ga doping can also enhance the scattering of high-frequency phonons, leading to slightly reduced lattice thermal conductivities of Ga-doped samples at higher temperature. Finally, a maximum ZT value of 0.53 at 664 K is achieved in Ga-doped sample, which is 50% higher than that of the sample free of Ga.