Laser Flash Method Research Articles

Structure and thermal properties of as-fabricated U-7Mo/Mg and U-10Mo/Mg low-enriched uranium research reactor fuels

Aluminum-clad U-7Mo/Mg and U-10Mo/Mg pin-type mini-elements (with a core uranium loading of 4.5 gU/cm3) have been fabricated at the Canadian Nuclear Laboratories for experimental tests and ultimately for use in research and test reactors. In this study, the microstructure and phase composition of unirradiated U-7Mo/Mg and U-10Mo/Mg fuel cores were analyzed using optical and scanning electron microscopy, and neutron powder diffraction. Thermal properties were characterized using a combination of experimental measurements and thermodynamic calculations. The thermal diffusivity was measured using the laser flash method. The temperature-dependent specific heat capacities were calculated based on the linear rule of mixture using the weight fraction of different crystalline phases and their specific heat capacity values taken from the literature. The thermal conductivity was then calculated using the measured thermal diffusivity, the measured density and the calculated specific heat capacity. The resulting thermal conductivity is practically identical for both types of fuel. The in-reactor temperatures were predicted using conjugate heat transfer simulations.

A study of the heat capacity of coated metal materials by the laser flash method

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.

Thermal conductivity of Kapton-derived carbon

Heat treatment of translucent Kapton®HN polyimide films conducted in inert atmosphere yields black residues. Micro-Raman spectroscopy revealed that the residues obtained between 600°C and 1200 °C are mainly constituted of disordered carbon. Aside its standard application in the structural identification of carbon, the Raman technique has also been used as a means of evaluating the thermal conductivity of Kapton-derived carbon. The aim of this study is to know whether such a tool can also be appropriate for disordered carbon with coherent diameters lower than 2 nm and with variable quantities of heteroatoms (H, O, N). To achieve this aim, a comparative study was undertaken using two other conventional techniques, namely laser flash analysis and photothermal radiometry. It has been found that thermal conductivity increases linearly with the heat-treatment temperature of Kapton and reaches 1.905 Wm−1K−1 for the film heat-treated at 1200 °C. The comparison of the experimental results shows that the Raman thermometry is particularly sensitive for sp2 carbon and predicts quite well the general trend of thermal conductivity of materials. However, the precision is rarely better than 20%.

Application of Hot-wire Method for Measuring Thermal Conductivity of Fine Ceramics

Ceramic substrate is preferred in high density packaging due to its high electrical resistivity and moderate expansion coefficient. The thermal conductivity is a key parameter for packaging substrates. There are two common methods to measure the thermal conductivity, which are the hot-wire method and the laser-flash method. Usually, the thermal conductivities of porcelain is low and meet the measurement range of hot-wire method, and the measured value by hot-wire method has little difference with that by laser-flash method. In recent years, with the requirement of high-powered LED lighting, some kinds of ceramic substrates with good thermal conductivity have been developed and their thermal conductivity always measured by the means of laser flash method, which needs expensive instrument. In this paper, in order to detect the thermal conductivity of fine ceramic with convenience and low cost, the feasibility of replacing the laser flash method with hot wire method to measure thermal conductivity of ceramic composites was studied. The experiment results showed that the thermal conductivity value of fine ceramics measured by the hot-wire method is severely lower than that by the laser-flash method. However, there is a positive relationship between them. It is possible to measure the thermal conductivity of fine ceramic workpiece instantly by hot-wire method via a correction formula.DOI: http://dx.doi.org/10.5755/j01.ms.22.4.12543

Sol–gel followed by urea–acetone spherodization for preparation of lithium titanate ceramics pebbles and preliminary characterization

Lithium titanate ceramics pebbles were prepared by chemical method of sol. gel followed by urea-aceton spherodization technique. Lithium titanate having monoclinic phase was obtained. Laser flash method was used to study thermal conductivity and diffusivity of the ceramics. At near 472K the average value of diffusivity was around 0.0052cm2s−1 while the specific heat capacity was 3101.3Jkg−1K−1 while the same two parameters had values of 0.0041cm2s−1 and 3894.4Jkg−1K−1 at a temperature 1050K. The crush strength of pebble was measured on Universal Testing Machine (UTM) and was found as 37.08N. The density was measured and found to be 2.8g/cc (81.63% of TD of value 3.43g/cc).

Method for Direct Measurement of On-Axis Carbon Fiber Thermal Diffusivity Using the Laser Flash Technique

Mechanical and thermal property values of carbon fiber-reinforced polymer (CFRP) composites are readily available. However, the small diameter and thermal anisotropy of the carbon filaments pose significant challenges for measuring thermal diffusivity of the constituent fibers. As a result, the literature describes many techniques to address this issue. Here, a new method for the direct, bulk measurement of on-axis thermal diffusivity of a matrix-free carbon fiber bundle is reported. Aligned carbon fiber tows were uniformly compacted into a collimated, cylindrical bundles using heat-shrink tubing, and fixed such that the fibers remained unwetted, in the center of an epoxy disk, which was subsequently analyzed for thermal diffusivity using laser flash analysis.

Thermal Conductivity Measurement using Thermoelectric Module

In this study, thermoelectric module is used as a heater for thermal conductivity measurement of solid materials. Principle of temperature gradient is adopted in this measurement. Stainless steel is utilized as a reference material. Each temperatures are measured by t-type thermocouple and the thermal conductivity is then calculated. The result shows that the thermal conductivity of tested materials is 0.303 W/mK with maximum uncertainty of 3.79%. To assure the result of this measurement, the thermal conductivity of tested material is also measured by laser flash method. The difference result of both measurement is below 5%.

Effect of CuO-TiO<sub>2</sub> Eutectic on Thermal and Electrical Conductivities of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Ceramics

In this work, CaCuxTiyO12 ceramics (2.7 ≤ x ≤ 3.3 and 3.25 ≤ y ≤ 4.75), related to excess and deficiency of CuO-TiO2 eutectic phase have been synthesized by coprecipitation method. The crystalline phases in the ceramics were identified by X-ray diffraction patterns, and the pellets have mainly presented CCTO and also exhibited CuO, TiO2 and CaTiO3 as secondary phases. The thermal conductivity of the ceramics was determined using the laser flash method in the temperature range of 300-1000 K. It was observed a decrement in thermal conductivity values as the amount of the eutectic phase decreased. The electrical DC conductivity has been measured by the two-probe method from 300-1000 K and it has been noted that both grain size and amount of eutectic phase influenced the electrical conductivity results.

An Experimental Study of Thermophysical Properties for Quinary High-Entropy NiFeCoCrCu/Al Alloys**Supported by the National Natural Science Foundation of China under Grant Nos 51571163, 51371150, 51271150 and 51327901

Two quinary high-entropy alloys (HEAs) with equiatomic concentrations formed by doping either Cu or Al elements into the quaternary NiFeCoCr alloy are produced by arc melting and spray casting techniques. Their entropy of fusion, thermal expansion coefficient and thermal diffusivity are experimentally investigated with differential scanning calorimetry, dilatometry and laser flash methods. The NiFeCoCrCu HEAs contain a face-centered cubic high-entropy phase plus a minor interdendritic (Cu) phase and display a lower entropy of fusion and the Vickers hardness. The NiFeCoCrAl HEAs consist of two body-centered cubic high-entropy phases with coarse dendritic structures and show higher entropy of fusion and the Vickers hardness. Both the thermal expansion coefficient and the thermal diffusivity of the former Cu-doped alloy are significantly larger than those of the latter Al-doped alloy. Although the temperature dependence of thermal diffusivity is similar for both HEAs, it is peculiar that the thermal expansion curve of the NiFeCoCrAl alloy exhibits an inflexion at temperatures of 860–912 K.

Studies of Thermophysical Properties of Ferrofluids

Thermophysical properties (thermal diffusivity, conductivity and heat capacity) of ferrofluids are investigated by the laser flash method within the interval of magnetic field induction 1.594–3.866 mT while varying the content of added iron powder in the range of 0.1–0.3 g at room temperature.

Temperature dependence of thermal diffusivity of OPC and CAC cement paste

Thermal diffusivity of concrete is an important factor that influences the fire resistance of concrete structures. The temperature dependence of thermal diffusivities of ordinary Portland cement (OPC) and calcium aluminate cement (CAC) paste are studied in this paper. First, the mineral compositions of OPC and CAC paste are investigated by X-ray diffraction analysis. Second, the dehydration process and the microstructure of OPC and CAC paste are characterised by thermogravimetric analysis and environmental scanning electron microscopy, respectively. Finally, the thermal diffusivities of OPC and CAC paste at high temperature are measured using the laser flash method.

Effect of SiC content on electrical, thermal and ablative properties of pressureless sintered ZrB2-based ultrahigh temperature ceramic composites

The effects of SiC content (10–40 vol.%) on electrical, thermal and ablation properties of pressureless sintered ZrB2-SiC composites showing interfacial segregation of W-rich phases have been studied. The electrical resistivity was measured by four-probe method, whereas thermal diffusivity and coefficient of thermal expansion (CTE) were determined using laser-flash method and thermo-mechanical analyzer, respectively. Whereas thermal conductivities calculated from experimentally obtained thermal diffusivity values are found to be the highest for the ZrB2-20 SiC composite, both electrical conductivity and CTE decrease with increasing SiC content. The specimens were subjected to thermal shock by soaking at 800–1200°C, followed by water-quenching. Further, some specimens were exposed to oxyacetylene flame (2200°C) for 10min. The damage was estimated from changes in mass, Young’s modulus, and hardness. The highest thermal shock and ablation resistance have been observed for the ZrB2-20 SiC composite, as thermal properties and formation of protective oxide scale play key role.

Influence of embedded MoSi2 particles on the high temperature thermal conductivity of SPS produced yttria-stabilised zirconia model thermal barrier coatings

To prolong the lifetime of thermal barrier coatings (TBCs) recently a new method of microcrack healing has been developed, which relies on damage initiated thermal decomposition of embedded molybdenum disilicide (MoSi2) particles within the TBC matrix. While these MoSi2 particles have a beneficial effect on the structural stability of the TBC, the high thermal conductivity of MoSi2 may have an unfavourable but as yet unquantified impact on the thermal conductivity of the TBCs.In this work the thermal conductivity of spark plasma sintering (SPS) produced yttria-stabilised zirconia (YSZ) model thermal barrier coatings containing 10 or 20vol.% of MoSi2 healing particles was investigated using the laser flash method. Measurements were performed on free-standing composite material over a temperature range from room temperature up to 1000°C. Microstructural analysis was carried out by SEM combined with image analysis to determine the size, distribution and area fraction of healing particles. The measurements were compared with the results from microstructure-based multi-physics finite element (FE) models and analytical models (the asymmetric Bruggeman model and the Nielsen model) in order to study the effects of the addition of MoSi2 particles as well as the presence of micro-pores on the apparent thermal conductivity. The results show a strongly non-linear increase in the thermal conductivity of the composite material with the MoSi2 volume fraction and a dependence on the aspect ratio of MoSi2 particles. Interparticle connectivity is shown to play a big role too.

Investigation of a new type of composite ceramics for thermal barrier coatings

In order to explore a novel material for thermal barrier coatings (TBCs), the composite ceramic materials of lanthanum zirconate (La2Zr2O7) and lanthanum phosphate (LaPO4) were prepared by calcining. The phases and micro-structures of La2Zr2O7/LaPO4 composite ceramic materials were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The properties of La2Zr2O7/LaPO4 material, such as thermal conductivity, coefficient of thermal expansion (CTE) and mechanical properties of La2Zr2O7/LaPO4 were investigated using laser flash method, high-temperature dilatometer and micro-hardness test. Based on XRD patterns, the pyrochlore and monazite phases were obtained in La2Zr2O7/LaPO4 composite ceramic material without any chemical reaction. According to SEM morphology, the La2Zr2O7 was closely near to LaPO4 along with a lot of pores, it might cause the decrease of thermal conductivity. The thermal conductivities of composite ceramics were similar to that of La2Zr2O7. The CTE of them were about 10×10−6K−1, which was close to the value of LaPO4. Because of doping LaPO4, hardness and Young's modulus of samples were lower than that of La2Zr2O7. The studies revealed that the La2Zr2O7/LaPO4 composite ceramics had good mechanical and thermal physical properties and could be applied as new candidate materials for TBCs in the future.

Microstructure and Thermal Conductivity of As-Cast and As-Solutionized Mg–Rare Earth Binary Alloys

The microstructure and thermal conductivity of four groups of Mg–rare earth (RE) binary alloys (Mg–Ce, Mg–Nd, Mg–Y and Mg–Gd) in as-cast and as-solutionized states were systematically studied. Thermal conductivity was measured on a Netzsch LFA457 using laser flash method at room temperature. Results indicated that for as-cast alloys, the volume fraction of second phases increased with the increase of alloying elements. After solutionizing treatment, a part or most of second phases were dissolved in α-Mg matrix, except for Mg–Ce alloys. The thermal conductivity of as-cast and as-solutionized Mg–RE alloys decreased with the increase of concentrations. The thermal conductivity of as-solutionized Mg–Nd, Mg–Y and Mg–Gd alloys was lower than that of as-cast alloys. Thermal conductivity of as-solutionized Mg–Ce alloys was higher than that of as-cast alloys, because of the elimination of lattice defects and fine dispersed particles during solutionizing treatment. Different RE elements have different influences on the thermal conductivity of Mg alloys in the following order: Ce

The Characteristics of the Bismuth Telluride Based Materials Via Gas Phase Reaction Method

Bismuth telluride based alloys powders are well known as thermoelectric materials near room temperature in 200~450K. Thermoelectric effect is direct conversion between thermal and electrical energy. Thermoelectric generator has several advantages such as eco-friendly (reusing the waste heat), reliable source of energy, simple maintenance, no-noise, long life time etc. But the low convert energy efficiency and high unit cost of production is still problem to solve. Energy conversion efficiency is involved with figure of merit ZT (ZT=σS2T/κ) where σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, κ is the total thermal conductivity. To enhance the energy conversion efficiency of thermoelectric materials, stoichiometrically dispersed powders within fine sized one particle has an advantage because of its composition uniformity. Spray pyrolysis is well known process as gas phase reaction method. The effects of the morphological, electrical and thermal properties of thermoelectric materials prepared by spray pyrolysis were investigated in this study. The phase of powders and bulk were analyzed by X-ray diffraction (XRD). The microstructures of powders and bulk were characterized by field emission scanning electron microscopy (FESEM). The thermoelectric properties of bismuth telluride based materials were analyzed using ZEM-3 (Ulvac-Rico) and thermal conductivity were calculated by the thermal diffusivity measured by the laser flash method (LFA457, Netzsch).

Yttria-stabilized zirconia–alumina composite sintering temperature effect on thermal diffusivity

Yttria-stabilized zirconia (YSZ) is one of the most common materials used for a ceramic top coat in the thermal barrier coating (TBC). The high operating temperature used in the gas turbine engines causes the stress between the top coat and the bond coat. The stress relaxation can be assured by modifications of YSZ. Hence, studies on how to modify the chemical and phase composition of these coatings are still conducted. The laser flash analysis was used to determine the thermal diffusivity of composite mixture of 8 mol% yttria-stabilized zirconia with α-Al2O3 in the range of temperatures between 20 and 1100 °C. The powders were prepared with 5 and 25 mass% Al2O3 addition to 8YSZ. The particle size distribution was done for each powder to analyse the grain size after milling of the α-Al2O3 with 8YSZ in the ball mill. The density of each powder was measured in the helium pycnometer. The disc-shaped samples were produced by pressing using an isostatic press and then sintered at various temperatures: 1000, 1200, 1400 and 1600 °C.

Ce1−x Sm x O2−x/2—A novel type of ceramic material for thermal barrier coatings

Abstract In this study, Ce1−x Sm x O2−x/2 ceramics were synthesized by sol–gel route and solid state sintering method. The phase structure was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The morphologies of the synthesized powders and the corresponding bulk samples were observed using scanning electron microscopy (SEM). Their thermal diffusivities and thermal expansion coefficients were measured by the laser-flash method and the pushing-rod method, respectively. Results show that pure Ce1−x Sm x O2−x/2 powders with single fluorite structure are synthesized successfully, and their microstructures of the corresponding bulk samples are very dense. With the increase of Sm2O3 content, their thermal expansion coefficients decrease due to the higher electro-negativity of Sm3+ ions as compared with that of Ce4+ ions. Their thermal conductivities at 1000 °C lie in the range of 1.62–2.02 W/(m·K) due to the phonon scattering caused by the substituted atoms and oxygen vacancies. The Ce1−x Sm x O2−x/2 ceramics can be used as ceramic candidates for novel thermal barrier coatings (TBCs).

Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures

Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the “Reduction-Sintering” process. This methodology can be especially effective in producing components containing refractory metals. Additionally, in situ production of metallic powder from complex oxides containing more than one metallic element may result in in situ alloying during reduction, possibly at lower temperatures. With this motivation, in situ reduction of complex oxides mixtures containing more than one metallic element has been investigated intensively over a period of years in the department of materials science, KTH, Sweden. This review highlights the most important features of that investigation. The investigation includes not only synthesis of intermetallics and refractory metals using the gas solid reaction route but also study the reaction kinetics and mechanism. Environmentally friendly gases like H2, CH4 and N2 were used for simultaneous reduction, carburization and nitridation, respectively. Different techniques have been utilized. A thermogravimetric analyzer was used to accurately control the process conditions and obtain reaction kinetics. The fluidized bed technique has been utilized to study the possibility of bulk production of intermetallics compared to milligrams in TGA. Carburization and nitridation of nascent formed intermetallics were successfully carried out. A novel method based on material thermal property was explored to track the reaction progress and estimate the reaction kinetics. This method implies the dynamic measure of thermal diffusivity using laser flash method. These efforts end up with a successful preparation of nanograined intermetallics like Fe-Mo and Ni-W. In addition, it ends up with simultaneous reduction and synthesis of Ni-WN and Ni-WC from their oxide mixtures in single step.

Thermophysical property measurements and thermal energy storage capacity analysis of aluminum alloys

Ten aluminum alloy samples are prepared using a casting method by carefully designing compositions of Al-Si, Al-Cu, Al-Mg, and Al-Cu-Zn alloys. This paper measures the phase change temperature, latent heat, and specific heat of the samples using a differential scanning calorimeter (DSC), the thermal diffusivity using a laser flash method, and derives the thermal conductivity of each sample. The effects of element addition and temperature on the performance of the aluminum alloy phase change materials (PCM) are comprehensively analyzed. The thermal energy storage (TES) capacities of the samples in different temperature ranges are also analyzed. The results show that adding Cu, Zn, and Si to an aluminum alloy helps reduce the melting point of the alloy. The addition of dense elements such as Cu and Zn in aluminum alloys improves the alloy’s TES capacity per volume unit. Based on experimental results, this paper also recommends fitting formulas for calculating the temperature dependent specific heat and thermal conductivity of the aluminum alloys studied.