Laser Flash Apparatus Research Articles

Thermophysical Properties' Enhancement of LiNO3-NaNO3-KNO3-NaNO2-KNO2 Mixed with SiO2/MgO Nanoparticles.

The aim of this study is to further enhance the thermal storage and heat transfer performances of a low-melting-point quinary salt. The eutectic salt was prepared using LiNO3, NaNO3, KNO3, NaNO2, and KNO2 as raw materials, followed by the doping of nano-SiO2 and nano-MgO into the base salt using a microwave-assisted method. The thermal properties of the samples were analyzed using a Synchronous Thermal Analyzer and a Laser Flash Apparatus. The co-doping of two types of nanoparticles was found to significantly enhance the specific heat capacity of the base salt. The maximum specific heat reached 2.36 J/(g·K), showing a 50.4% increase compared to the base salt. The thermal conductivity of molten salts can be affected by nanoparticles. An observed sample demonstrated a thermal diffusivity of 0.286 mm2/s, indicating a 19.2% improvement over the base salt, which may be attributed to enhanced phonon thermal efficiency. In addition, this study revealed that while interfacial thermal resistance can enhance specific heat capacity, it can also lead to a decrease in the thermal conductivity efficiency of materials. This work can offer insights and references for the enhancement of molten salt properties.

Temperature and composition dependence of thermophysical properties within a wide temperature range for ternary Si–Ge–Ag alloys

The thermophysical properties of Si–Ge–Ag alloys in a broad temperature range are essential for the design of electronic devices. In this work, relationships between specific heat, thermal expansion, thermal conductivity and temperature, as well as chemical composition of Si–Ge–Ag alloys were clarified. Moreover, various thermophysical properties’ prediction strategies of multicomponent alloys from pure elements were evaluated. The specific heat of Ag–Si, Ag–Ge, Si–Ge, and Si–Ge–Ag alloys was determined by the differential scanning method. The results showed a significant increase with rising temperature at low temperatures followed by a gradual rise at high temperatures. The specific heat reached the maximum value when a small amount of Si/Ge was introduced to Ag. The coefficient of thermal expansion was obtained by a dilatometric method and increased slightly with the increasing temperature, while decreased linearly with the increase in the Si/Ge content. Furthermore, the thermal conductivity was investigated via a laser flash apparatus. It decreased with rising temperature when the Ag content is smaller than 50%, whereas it increased with rising temperature when the Ag content exceeds 50%. The thermal conductivity of Si–Ge alloys decreased with rising temperature and reached the local minimum for Si–Ge alloys with an equiatomic ratio of Si and Ge. More importantly, the experimental results reveal that the thermal expansion that is related to volume can be estimated approximately by pure metals in Si–Ge–Ag alloys. However, this rule cannot be applied to specific heat and thermal conductivity, which is due to the influence of lattice vibration, electronic scattering, and microstructure.

Effects of atmospheric gases and compression load on effective thermal conductivity of Li2TiO3 pebble bed

Tritium breeder material in the solid-type of breeding blanket concepts is usually used in a pebble bed form because of the efficiency and convenience of tritium extraction. The pebble bed is continuously heated by the exothermal reaction between neutron and lithium-6 during the operation of a fusion reactor. Thus, a compression pressure is applied on the pebble bed by the thermal expansion of pebbles and container structure. Therefore, the accurate thermal properties of the pebble bed are one of the important design parameters to ensure a function and stability of the breeding blanket. This study aims at the investigation of the change on effective thermal conductivity of Li2TiO3 pebble beds under the operation conditions of breeding blanket.The measurement of effective thermal conductivities of Li2TiO3 pebble beds has been performed by laser flash technique in several atmosphere gases, such as helium, nitrogen, and air, under the statically compression load controlled by specially design pneumatic device incorporated to the laser flash apparatus. Also, in the case of helium atmosphere, the effects of hydrogen concentration from 0.1 wt.% to 1.0 wt.% on the effective thermal conductivity were also investigated. The effective thermal conductivity of the Li2TiO3 pebble bed was strongly dependent on a kind of atmosphere gases, especially its thermal conductivity, in the relatively low temperature. However, the concentration of hydrogen in the helium atmosphere did not significantly affect the effective thermal conductivity of the pebble bed. Applied axial compression load has influenced on the effective thermal conductivity of the Li2TiO3 pebble bed, especially at high temperature. However, the obvious change of effective thermal conductivity with the value of compression load was not observed.

Temperature effect on thermal conductivity of oxidised coal associated with its predictive model during coal pyrolysis

To explore the heat transfer characteristics of oxidised coal, four kinds of bituminous coal from Shilawusu coalmine (SLWS), Huangling coalmine (HL), Ewirgol coalmine (AWEG), and Sangshuping coalmine (SSP) respectively, were collected and oxidised at 80, 120, 150, and 200 °C in air. The thermal conductivity of each coal were measured by laser flash apparatus with 30–300 °C. Main proximate analysis indexes influencing the thermal conductivity of oxidised coal were received by grey correlation method. A predictive model was established to forecast the thermal conductivity of oxidised coal. The results indicated that, when the temperature enhanced from 30 to 300 °C, the thermal conductivity of each coal gradually increased, the thermal conductivity for SLWS, HL, AWEG, and SSP increased by 12.0–12.6%, 9.2–10.9%, 7.0–9.6%, and 7.6–8.7%. At fixed temperature, the thermal conductivity of each coal increased linearly, which was markedly affected by the change of fixed carbon, ash, and volatiles in coal. Furthermore, a predictive model was established to forecast accurately the thermal conductivity of oxidised coal with a low relative error. Such findings can deepen the understanding of heat transfer in oxidised coal, and provide a theoretical basis in the prevention and intervention of coal fires.

Enhancing thermal conductivity of TiC nanopowder with cryogenic treatment

This paper deals with determining the thermal conductivity and thermal diffusivity of TiC nano powder before and after deep cryogenic treatment. Deep cryogenic treatment is done at −196 °C for 24 h on Tic nanopowder material. The thermal conductivity and thermal diffusivity were found out by using laser flash apparatus. It is found that the thermal conductivity of TiC nanopowder is improved by 21% due to deep cryogenic treatment.

Experimental Studies of Thermophysical Properties and Microstructure of X37CrMoV5-1 Hot-Work Tool Steel and Maraging 350 Steel.

Measurements of thermal diffusivity, heat capacity and thermal expansion of X37CrMoV5-1 (1.2343) hot-work tool steel and Maraging 350 (1.6355) steel in the temperature range from -50 °C to 1000 °C were carried out in this paper. Both X37CrMoV5-1 and Maraging 350 are tested for military use as barrel steels. Thermophysical properties were tested using specialised test stands from NETZSCH. Thermal diffusivity was studied using both the LFA 427 laser flash apparatus in the temperature range of RT-1000 °C and the LFA 467 laser flash apparatus in the temperature range of -50 °C-500 °C. Specific heat capacity was investigated using a DSC 404 F1 Pegasus differential scanning calorimeter in the range RT-1000 °C, and thermal expansion was investigated using both a DIL 402 Expedis pushrod dilatometer in the range -50 °C-500 °C and a DIL 402 C in the range RT-1000 °C. Inconel 600 was selected as the reference material during the thermal diffusivity test using LFA467. Tests under the light microscope (LM), scanning electron microscopy (SEM) and Vickers microhardness measurements were carried out to detect changes in the microstructure before and after thermophysical measurements. This paper briefly characterises the research procedures used. In conclusion, the results of testing the thermophysical properties of X37CrMoV5-1 hot-work tool steel and Maraging 350 steel are compared with our results on 38HMJ (1.8509), 30HN2MFA and Duplex (1.4462) barrel steels. The thermophysical properties of X37CrMoV5-1 (1.2343) hot-work tool steel and Maraging 350 (1.6355) steel are incomplete in the literature. The paper presents the thermophysical properties of these steels over a wide range of temperatures so that they can be used as input data for numerical simulations of heat transfer in cannon barrels.

Changes in thermal properties of 7075 aluminium alloy by aging heat treatment

This study investigated the effects of aging heat treatment on the change of thermal properties of 7075 Al alloy using differential scanning calorimetry and a laser flash apparatus. The thermal diffusivity showed different trends in the three temperature ranges: In the range from room temperature to 160°C, the thermal diffusivity increased with increasing temperature. Between 160 and 240°C, the thermal diffusivity increased with an increase in the temperature of the specimen. Precipitation was completed at 240°C or higher, and the thermal diffusivity decreased with an increase in the temperature of the specimen. The amount of precipitation of η′ and η phases did not affect the change in thermal diffusivity but only contributed to the improvement of micro-hardness.

Novel Method for the Production of Titanium Foams to Reduce Stress Shielding in Implants.

Titanium foams have potential applications in orthopedic and dental implants because of their low elastic modulus and good bone in-growth properties. In the present study, a novel method for the preparation of three-dimensional interconnected microporous titanium foams has been developed. This method is based on the insertion of a filler metal into the titanium metal by arc melting, followed by its removal by an electrochemical dealloying process for the development of foams. Complete removal of the filler metal by the electrochemical dealloying process was confirmed by an X-ray diffractometry (XRD) analysis, whereas scanning electron microscopy (SEM) analysis of the developed foams showed the development of interconnected porosity. Ti foams with different levels of porosities were successfully developed by varying the amount of the filler metal. Mechanical and thermal characterizations of the developed foams were carried out using compression testing and laser flash apparatus, respectively. The yield strength and elastic modulus of the developed foams were found to decrease by increasing the volume fraction of pores. The elastic modulus of the developed titanium foams (15.5-36 GPa) was found to be closer to that of human bones, whereas their yield strength (147-170 MPa) remained higher than that of human bones. It is therefore believed that the developed Ti foams can help in reducing the problem of stress shielding observed in orthopedic implants. The thermal diffusivity of the developed foams (4.3-0.69 mm2/s) was found to be very close to that of human dentine.

Sintering behaviors and thermal properties of Li2SiO3-based ceramics for LTCC applications

A series of new Li2SiO3+4 wt% Al2O3-xK2O–B2O3–SiO2 (x = 1–4 wt%) LTCC materials were prepared by standard traditional solid-state method and their bulk density, microstructure and crystalline phase composition were shown in detail. The sintering behavior, heat conduction and thermal expansion of the samples were all thoroughly studied. And their microwave dielectric properties were also demonstrated. The bulk density of the samples was enhanced with the addition of 3 wt% KBS glass, and the sintering temperature was reduced from 1020 °C to 900 °C. Meanwhile, the thermal diffusivity of the samples was determined using the LFA447 laser flash apparatus and the specific heat was calculated, according to the results of thermal diffusivity and specific heat, all samples possessed high thermal conductivity ranging from 5.5 ± 0.02 W/mK to 8.6 ± 0.08 W/mK. Furthermore, the attractive flexural strength and average coefficient of thermal expansion reach to 270 MPa and 15.7 × 10−6/K (at 100 °C), respectively. The reduction of the sintering temperature is attributed to the addition of KBS glass which reduces the crystallization activation energy of the samples. Besides, increasing bulk density can substantially reduce pores in the grain boundary, which has great effects on phonon scattering, improving the thermal conductivity.

Thermal and morphological study of paraffin/SEBS/expanded graphite composite phase change material for thermal energy storage

ABSTRACT This work aims to develop a high thermal conducting and leakage-proof composite phase change material (CPCM) for thermal energy storage (TES) applications. A leakage-proof shape-stable phase change material (SPCM) has been prepared by impregnating paraffin into the network of polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SEBS) tri-block copolymer. In order to improve the thermal conductivity of paraffin/SEBS composite, expanded graphite (EG) has been directly incorporated into paraffin/SEBS (4:1) composite. Two different mass fractions of EG, i.e., 1 wt% and 5 wt%, have been chosen for the thermophysical study of leakage-proof SPCM named CPCM1 and CPCM2, respectively. Structural, morphological, and thermal studies of prepared composites have been carried out by XRD, FTIR, SEM, TGA, and DSC. The latent heats of prepared SPCM, CPCM1, and CPCM2 composites have been found as 167.91 J/g, 163.25 J/g, and 146.71 J/g, respectively. The thermal conductivities of composites have been measured by Laser Flash Apparatus (LFA). Results show that the thermal conductivity (TC) of CPCM1 and CPCM2 remarkably increases to 0.501 Wm−1K−1 and 1.301 Wm−1K−1, respectively, which is 2.8 and 7.35 times of paraffin/SEBS composite (0.177 Wm−1K−1). Therefore, findings suggest that the CPCM1 and CPCM2 samples have a great potential for TES application, specifically for solar water heating systems.

Influence of Applied Frequency on Thermal Physical Properties of Coatings Prepared on Al and AlSi Alloys by Plasma Electrolytic Oxidation

In this study, plasma electrolytic oxidation (PEO) was performed on Al and AlSi substrates using a pulsed direct current (DC) power source. The coating process was carried out in a Na2SiO3 electrolyte with the systematic change of pulse frequency (50–1400 Hz). The surface characteristics of the coatings were examined using scanning electron microscopy (SEM). The phase structure was characterized using X-ray diffraction (XRD). A differential scanning calorimeter (DSC) and a laser flash apparatus (LFA) were employed to test heat capacity and heat conductivity, respectively. Results showed that as the discharge frequency increased, the thermal physical properties of Al-PEO and AlSi-PEO coatings changed in different ways. At a high frequency, Al-PEO coatings had low porosity and were closed-pore structured whereas AlSi-PEO coatings had high porosity and large-size open-pore structures could be observed on their surfaces due to concentrated discharges. Based on these findings, it was found that the thermal productivity of coatings is closely correlated with the open-/closed-pore structure instead of porosity. PEO coatings with low heat capacity or low heat conductivity could be obtained with a controlled frequency.

Towards accurate measurements of specific heat of solids by drop calorimetry up to 3000 °C

The French National Metrology Institute LNE-LCM has modified a high temperature Laser Flash apparatus in order to perform the measurement of the specific heat of solids by drop calorimetry. A sample hanging on a thin wire held by a motorised gripper, is heated by the inductive furnace and dropped into a heat-flux Calvet calorimeter maintained at near ambient temperature. The calorimeter is equipped with an in-situ electrical calibration system in order to perform accurate and reliable measurements of energy directly traceable to the International System of Units (SI). The electrical calibration system has been designed for the calibration of the calorimeter by electrical substitution (Joule effect) and remains in-situ during the drop of the heated sample, keeping exactly the same experimental configuration during both steps of calibration and measurement. The metrological features (sensitivity, linearity) of the calorimeter have been evaluated by investigating the influence of the level of energy and dissipation time on the determination of the sensitivity factor of the heat-flux calorimeter. A calibration and measurement procedure was established in order to enable the measurement of the enthalpy increments of solids up to 2700 °C. The first results obtained for the determination of the specific heat of α-alumina (SRM-720), tungsten and graphite, as well as for the measurements of the enthalpy of fusion of pure copper are in good agreement with literature values and a relative uncertainty of 5% can be obtained.

Numerical validation of thermal conductivity of Al6061 based hybrid nano metal matrix composite filled with nanoparticles of Ni and Cr

Aluminum composite matrix materials are regarded as the most popular type of composite materials. Metal matrix composites made of aluminum have better mechanical and thermal properties, including a higher strength-to-weight ratio, tensile strength, hardness, and a low coefficient of thermal expansion. In various types of applications viz, automobile, aviation, the thermal characterization of aluminum metal matrix composites has increased. Thermal conductivity as a function of temperature, thermal diffusivity, and the thermal gradient is one of the essential thermal characteristics of aluminum metal matrix composites needed to understand the material’s behavior. The current work evaluated thermal conductivity as a product of thermal diffusivity, density, and specific heat for Al6061/Ni/Cr hybrid nano metal matrix composites from 50 °C to 300 °C. Al6061 based metal matrix composite reinforced with varying wt.% of Ni and Cr nanoparticles whereas fixed wt.% of graphene and Mg added to improve thermal conductivity, self-lubrication, and wettability. Thermal diffusivity, specific heat, and density were evaluated using laser flash apparatus (LFA 447), differential scanning calorimetry (DSC), and Archimedes principle, respectively. Results revealed that the thermal conductivity of fabricated composites increases with Ni, Cr, Mg, and graphene nanoparticles. With further expansion of reinforced particles of Ni and Cr, the thermal conductivity decreases. Finite element analysis (FEA) has been conducted to determine the thermal gradient and thermal flux using experimental values such as density, thermal conductivity, specific heat, and enthalpy at various temperature ranges to validate the experimental results.

Uncertainty Assessment for Very High Temperature Thermal Diffusivity Measurements on Molybdenum, Tungsten and Isotropic Graphite

The French National Metrology Institute LNE has improved its homemade laser flash apparatus in order to perform accurate and reliable measurements of thermal diffusivity of homogeneous solid materials at very high temperature. The inductive furnace and the associated infrared (IR) detection systems have been modified and a specific procedure for the in situ calibration of the used radiation thermometers has been developed. This new configuration of the LNE’s diffusivimeter has been then applied for measuring the thermal diffusivity of molybdenum up to 2200 °C, tungsten up to 2400 °C and isotropic graphite up to 3000 °C. Uncertainties associated with these high temperature thermal diffusivity measurements have been assessed for the first time according to the principles of the “Guide to the Expression of Uncertainty in Measurement” (GUM). Detailed uncertainty budgets are here presented in the case of the isotropic graphite for measurements performed at 1000 °C, 2000 °C and 3000 °C. The relative expanded uncertainty (coverage factor k = 2) of the thermal diffusivity measurement is estimated to be between 3 % and 5 % in the whole temperature range for the three investigated refractory materials.

Effect of Microstructure on Thermophysical Properties of Heat-Treated Duplex Steel.

The purpose of this study is to investigate the effect of heat treatments and resulting changes in microstructure on the thermophysical properties of commercial 1.4462 duplex stainless steel. Three types of heat treatment and a raw sample were used. In the first heat treatment, a duplex steel bar was annealed in an air atmosphere furnace for one hour at 1200 °C and then quickly cooled in water (1200 °C + water). The second heat treatment was the same as the first, but afterwards, the bar was annealed in an air atmosphere furnace for 4 h at 800 °C and then slowly cooled down in the furnace to room temperature (1200 °C + water + 800 °C). In the third heat treatment, the duplex steel bar was annealed in the furnace in an air atmosphere for one hour at 900 °C and then slowly cooled in the furnace to room temperature (900 °C). As a result, the weight percentages of ferrite and austenite in the samples achieved the following ratios: 75:25, 65:35 and 44:56. Light microscope examinations (LM), scanning electron microscopy (SEM), Vickers micro-hardness measurements and thermophysical studies using a laser flash apparatus (LFA), differential scanning calorimetry (DSC) and push-rod dilatometry (DIL) were performed to reveal the microstructure and changes in thermophysical properties including thermal diffusivity, thermal conductivity, thermal expansion and specific heat. Along with presenting these data, the paper, in brief, presents the applied investigation procedures.

Mechanical and thermal performance of additively manufactured copper, silver and copper–silver alloys

On-demand additive manufacturing (three-dimensional printing) offers great potential for the development of functional materials for the next generation of energy-efficient devices. In particular, novel materials suitable for efficient dissipation of localised heat fluxes and non-uniform thermal loads with superior mechanical performance are critical for the accelerated development of future automotive, aerospace and renewable energy technologies. In this regard, this study reports the laser powder bed fusion processing of high purity (>99%) copper (Cu), silver (Ag) and novel copper–silver (CuAg) alloys ready for on-demand additive manufacturing. The processed materials were experimentally analysed for their relative density, mechanical and thermal performance using X-ray computed tomography, destructive tensile testing and laser flash apparatus, respectively. It was found that while Ag featured higher failure strains, Cu in comparison showed a 109%, 17% and 59% improvement in yield strength ([Formula: see text]), Young’s modulus ( E) and ultimate tensile strength, respectively. As such the [Formula: see text], E and ultimate tensile strength for laser powder bed fusion Cu is comparable to commercially available laser powder bed fusion Cu materials. CuAg alloys, however, significantly outperformed Ag, Cu and all commercial Cu materials when it came to mechanical performance offering significantly superior performance. The [Formula: see text], E and ultimate tensile strength for the novel CuAg composition were 105%, 33% and 94% higher in comparison to Cu. Although slightly different, the trend continued with a 106% and 91% rise for [Formula: see text] and ultimate tensile strength, respectively, for CuAg in comparison to industry-standard Cu. Unfortunately, E values for industry-standard Cu alloys were not available. When it came to thermal performance, laser powder bed fusion Ag was found to offer a 70% higher thermal diffusivity in comparison to Cu despite the variation in density and porosity. CuAg alloys however only showed a 0.8% variation in thermal performance despite a 10–30% increase in Ag. Overall, the study presents a new understanding regarding the three-dimensional printing and performance of Cu, Ag and CuAg alloys.

Influences of Heat Treatment on the Thermal Diffusivity and Corrosion Characterization of Al-Mg-Si alloy

The effect of the heat treatment on the Mg2Si phase in Al-Mg-Si alloy was investigated by a laser flash apparatus (LFA), Differential scanning calorimetry (DSC) and corrosion test. The alloy samples were solution treated at 590 oC for a half hour followed by warm water quenching, and then aged in air at 180, 200 and 240 oC for 5 hours. The results showed that the corrosion resistance of the solid solution treated sample was more improved than the as cast sample. Aging treatment also helped increase corrosion resistance at room temperature. It is thought that the fine Mg2Si precipitation phase on the grain had a more positive effect on improving corrosion resistance than crystallization of the Mg2Si phase on the grain boundaries. Corrosion rate also decreased with increasing aging treatment. The corrosion rate of AT240 was reduced to 1.16 MPY compared with the AT180 test piece, which had a corrosion rate of 3.79 MRY. The solution treated sample also showed lower thermal diffusivity than the aged samples. The thermal diffusivity increased as the solute concentration of Mg and Si in the a-Al matrix rapidly decreased during aging treatment. On the other hand, the thermal diffusivity of the aged samples, in which precipitation was completed by the aging process, decreased as the temperature rose. The thermal conductivities of all samples were similar near 250 oC when the β'' phase and β' precipitation was completed.

Experimental investigation on nanoalloy enhanced layered perovskite PCM tamped in a tapered triangular heat sink for satellite avionics thermal management

Miniaturization of circuitry has inherently led to higher heat dissipation which has to be controlled to avoid temperature fluctuation ensuring smooth functioning of the system where developments in the field of PCM provides flexible solutions for avionic Thermal Management (TM). This article focuses to analyse thermal performance of novel tapered triangular finned heat sink along with Vacuum Insulation Panels (VIPs) tamped with nanoalloy (n-LMA) enhanced organo-metallic Mn based layered perovskite Solid-Solid PCM (SS-PCM) to its compatibility for passive TM satellite auxiliary system. An inclusion of 5 wt% nanoalloy (Nano-encapsulated liquid Ga:In eutectic alloy) in SS-PCM increased the thermal conductivity by 21.05% (0.374 W/m-K) and charging and discharging enthalpy by 16.84% (74.56 J/g) and 17.61% (76.32 J/g) respectively. Thermo-physical property values were obtained through Field Emission Scanning Electron Microscope, Scanning Electron Microscope, Differential Scanning Calorimetry and Laser Flash Apparatus. Transient thermal performance analysis was carried out in tapered triangular finned heat sink with specific duty cycles (600s/5400s, 1200s/4800s and 1800s/4200s) for heat fluxes (2 W, 4 W, 6 W, 8 W and 10 W) and with/without VIP for different aspects of SS-PCM and SS-PCM/n-LMA. The effect of n-LMA influences the enhancement in thermal storage and heat transfer performance attributes with a maximum temperature drop of 6.98% over pure SS-PCM. Experimental study reveals better temperature reduction with a maximum of 53.81% decrement in overall heat sink temperature and VIP manifests unidirectional heat transfer through the heat sink reducing overall spatial temperature variation. Further, numerical validation was performed for obtained results with COMSOL application, demonstrating the suitability for real-time passive TM in satellite avionics space applications.

Effect of porosity on thermal conductivity of Li2TiO3 ceramic compact

The thermal conductivity of the porous ceramic materials strongly depends on its temperature and porosity. Li2TiO3 ceramic is considered as a tritium breeder material for the Indian fusion blanket concept. Inside the blanket, higher lithium content is vital in terms of lithium burn up, whereas porosity is essential for the diffusion of tritium from its grains to the surface. As the helium gas will continuously pass through the ceramic breeder's pores, all heat transfer modes, i.e. conduction, convection and radiation will appear within the breeder canister. For evaluation of the heat transfer behaviour inside the fusion blanket, it is substantial to determine the porosity dependent thermal conductivity of Li2TiO3 along with a good relationship. In this work, Li2TiO3 compacts of different porosity, i.e. 4–6 %, 11 %, 24 %, 26 % and 39 % are prepared by uni-axial hydraulic pressing. Compacts are sintered at 1073 K, 1173 K, 1273 K and 1423 K for desired porosity. Thermal diffusivity of Li2TiO3 compacts are measured by laser flash apparatus from room temperature to 973 K. Thermal conductivity of porous Li2TiO3 compacts is calculated by multiplication with respective density and specific heat to the measured thermal diffusivity. In this study, the mercury intrusion technique and Scanning Electron Microscopy technique was used for the density, porosity and surface morphology, respectively. The effect of the temperature and porosity on the thermal conductivity of Li2TiO3 are presented here. As the thermal conductivity changes with porosity by virtue of temperature, the correlations are presented by fitting various models such as Maxwell model, modified Maxwell-Eucken model, Loeb model, modified Loeb model, and EMT model. Among these models, the best-fitted model was evaluated. The geometrical factor (β, α) and thermal conductivity at 0 % porosity (k0) for the modified Maxwell-Eucken model and modified Loeb model were calculated. The porosity and temperature-dependent thermal conductivities of Li2TiO3 were calculated with newly obtained coefficients and discussed in this paper.

Increasing the thermal diffusivity of Al–Si–Mg alloys by heat treatment

The objective of this study is to increase the thermal diffusivity of Al–Si–Mg alloys by heat treatment and demonstrate the effect of the eutectic phase distribution on thermal conductivity of Al–Mg–Si alloys. Two types of Al–Si–Mg (Al–0.2Si–0.4Mg and Al–6.5Si–0.4Mg) alloys used in this study were prepared through atmospheric gravity casting. Solid solution treatment was performed at 535 °C for 4–10 h and then quenched in warm water of 80 °C temperature. Artificial aging of specimens was performed at 180 °C for 5 h. After aging treatment, the changes of microstructures due to heat treatment were examined by using optical microscopy. Differential scanning calorimeter analyzed phase transform during the heat treatment. Variations of thermal diffusivity according to the microstructures were investigated by using a laser flash apparatus. Precipitation of Mg2Si and Si phases increased the thermal diffusivity after aging treatment. Moreover, thermal diffusivity of the Al–6.5Si–0.4Mg alloys also increased with increasing solid solution treatment time due to spheroidization of eutectic Si.