Laser Flash Method Research Articles

Microstructure, Mechanical and Thermal Properties of Mg-0.5Ca-xZr Alloys

To evaluate the potential values in heat dissipation applications, this study investigated the microstructure, mechanical and thermal properties of the Mg-0.5Ca-xZr alloys (x = 0.5 and 1 wt.%) under the as-cast, as-extruded and aged states. The phase constituents of the Mg alloys were examined by X-ray diffraction analysis, and the microstructure was inspected by optical microscopy and scanning electron microscopy. The thermal conductivity and mechanical properties of the Mg alloys were measured by the laser flash method and tensile tests, respectively. The results showed that the Mg alloys exhibited the equiaxed microstructure which is composed of α-Mg, Zr and compound Mg2Ca. Both the extrusion process and increase of Zr content remarkably enhanced the mechanical strength of the Mg alloys and deteriorated the thermal performance simultaneously. It was also found that the thermal conductivity and mechanical strength of the Mg alloys increased gradually with the increase of aging time due to the higher precipitation of Zr and compound Mg2Ca during the aging treatment. TheMg-0.5Ca-0.5Zr alloy aged at 473 K for 48 h demonstratedhigher thermal conductivity than the required values of the Mg alloys used as heat dissipation materials. Moreover, theMg-0.5Ca-0.5Zr alloy exhibited similar mechanical strength to the commonly-used Mg alloys, highlighting its potential become a potential heat dissipation material in the future due to its good combination of high thermal performance and mechanical strength.

3D Printing Processability of a Thermally Conductive Compound Based on Carbon Nanofiller-Modified Thermoplastic Polyamide 12.

A polyamide (PA) 12-based thermoplastic composite was modified with carbon nanotubes (CNTs), CNTs grafted onto chopped carbon fibers (CFs), and graphene nanoplatelets (GNPs) with CNTs to improve its thermal conductivity for application as a heat sink in electronic components. The carbon-based nanofillers were examined by SEM and Raman. The laser flash method was used to measure the thermal diffusivity in order to calculate the thermal conductivity. Electrical conductivity measurements were made using a Keithley 6517B electrometer in the 2-point mode. The composite structure was examined by SEM and micro-CT. PA12 with 15 wt% of GNPs and 1 wt% CNTs demonstrated the highest thermal conductivity, and its processability was investigated, utilizing sequential interdependence tests to evaluate the composite material behavior during fused filament fabrication (FFF) 3D printing processing. Through this assessment, selected printing parameters were investigated to determine the optimum parametric combination and processability window for the composite material, revealing that the selected composition meets the necessary criteria to be processable with FFF.

Optimization of the composition of Al-Mg alloy films for laser-driven flyer

Laser-driven flyer technology attracts tremendous interests owing to the advantage of generating high pressure shocks at a relative simple and low-cost way. However, low energy conversion efficiency between flyer and laser restricts the further application of this technology. To improve the energy conversion efficiency in a laser-driven flyer assembly, Al-Mg alloy films with three varied compositions were fabricated via magnetron sputtering. The composition, surface morphology, light absorption and thermal properties of the films were investigated using energy dispersive spectrometer, atomic force microscopy, ultraviolet–visible spectrophotometer and laser flash method. The reflectivity of the Al-Mg alloy film at 1064-nm wavelength decreases from 87.2% to 69.3% in comparison with Al film. Moreover, the thermal diffusivity of all the Al-Mg alloy films is lower than that of Al film and varies with the composition. The behavior of the plasma induced shock wave evolution was investigated by shadowgraph imaging technique, indicating that the spatial and temporal evolution of the shock wave agrees well with the form of a Taylor-Sedov spherical shock and the calculated shock wave energy of the Al-Mg alloy films can reach up to 1.19 times that of Al film. Furthermore, the ability to launch a 17-μm-thick Al flyer was characterized by a Photonic Doppler Velocimetry, and there is a 20.9% and 46.12% increase in the terminal velocity and energy conversion efficiency of the Al flyers for Al-Mg alloy films compared with Al film, respectively. Therefore, the performance of laser-driven flyer can be significantly improved by adjusting the composition of Al-Mg alloy films.

Hydrazine-nitrate combustion synthesis of BaCeO3 preceramic powders: structure, morphology and thermophysical properties

In the present work, preceramic nanocrystallite barium cerate (BaCeO3) was successfully synthesized using the hydrazine-nitrate combustion method. Using carbon-free hydrazine (N2H4) as fuel significantly reduced the formation of carbonate by-products. Subsequent annealing of combustion products in the air atmosphere at temperatures in the range of 500–1000 °С yielded preceramic powders based on chemically and phase-pure BaCeO3. Characterization of the as-received powders was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), simultaneous thermal analysis (DTA-TGA) and adsorption-structural analysis (N2, 77 K). Thermophysical properties of the sample annealed at 1000 °С were investigated using laser flash analysis (LFA) in the temperature interval of 1000 °С. As a result of a comprehensive study, the sequence of chemical and phase transformations that lead to the formation of barium cerate with a rhombic structure (Pnma, a = 6.2145 Å, b = 8.7776 Å, c = 6.2337 Å) during the thermal processing of combustion products was investigated. It was established that the average size of the obtained nanocrystals is 38 ± 3 nm and that they form micron-sized agglomerates with a specific surface area of the powder of 4.8 m2/g. It was shown that the sintered sample of barium cerate is characterized by thermal diffusivity values of 0.28 to 0.20 mm2/s and thermal conductivity values of 0.41–0.35 W/mK, depending on temperature. These results, given the impact of porosity on the sample (~40%), show very good agreement with the thermophysical characteristics of densely sintered ceramics based on BaCeO3—a solid oxide electrolyte SOFC. Consequently, the proposed method of hydrazine-nitrate synthesis of barium cerate presents itself as a promising approach to obtaining preceramic powders and ceramics in the area of solid oxide fuel cells.

Possibility of Advanced Modified-Silica-Based Porous Materials Utilisation in Water Adsorption Processes—A Comparative Study

Due to a high risk of power outages, a heat-driven adsorption chillers are gaining the attention. To increase the efficiency of the chiller, new adsorbents must be produced and examined. In this study, four newly developed silica–based porous materials were tested and compared with silica gel, an adsorber commonly paired with water. Extended sorption tests using mercury intrusion porosimetry, gas adsorption, and dynamic vapor sorption were performed. The morphology of the samples was determined using a scanning electron microscope. The thermal properties were defined using simultaneous thermal analysis and a laser flash method. Metal organic silica (MOS) nanocomposites analysed in this study had thermal properties similar to those of commonly used silica gel. MOS samples have a thermal diffusivity coefficient in the range of 0.17–0.25 mm2/s, whereas silica gel of about 0.2 mm2/s. The highest water adsorption capacity was measured for AFSMo-Cu and equal to 33–35%. For narrow porous silica gel mass uptake was equal about 25%. In the case of water adsorption, it was observed that the pore size of the sorbent is essential, and adsorbents with pore sizes higher than 5 nm, are most recommended in working pairs with water.

The influence of blackening in a laser spot periodic heating method and a laser flash method

In a measurement of thermal property, to raise emissivity of sample surface is sometimes important. Blackening of the sample surface is a standard way to raise its emissivity for the measurement by a laser spot periodic heating method and a laser flash method. The blackening brings not only an increase of sensitivity but also an influence on the result of thermal property measurement, and then we should evaluate it in a quantitative way. In this research, thermal diffusivities of the four types of samples whose thickness of blackening layer are different were measured by periodic heating method and laser flash method. The relationship between apparent thermal diffusivity and thickness of blackening layer were obtained. Thicker the blackening layer is, lower the apparent thermal diffusivity is. The tendency of relationship between thickness of blackening layer and apparent thermal diffusivity are same in both of periodic heating method and laser flash method. Interfacial thermal resistance of samples is estimated by the comparison between experimentals and theoretical simulations of laser flash method.

Investigation of the influence of technological factors on the uncertainty of the results of measuring thermal conductivity by the method of laser flash

The estimation of the deviation in the measurements of thermal conductivity by the laser flash method for materials with different thermal conductivity coefficients, arising due to the presence of a graphite coating on the sample and the small thickness of the sample, is carried out. A computer model of the method was created in the Comsol Multiphysics software environment. For bulk samples with a graphite coating thickness of 20 μm, the deviation is 5.5%. The thickness of bulk samples does not affect the measurement results. For materials with low thermal conductivity, a sharp increase in the deviation is observed, reaching 60%. For thermally conductive materials, the deviation is 16-18%. For thin samples less than 10 μm thick, the thickness of the graphite coating does not affect the measurement results. The decisive factor is the duration of the laser pulse. Keywords: laser flash method, thermal conductivity, relative deviation.

Влияние фотонной обработки на повышение термоэлектрической добротности твердого раствора Bi2Te3 − Bi2Se3

In the present work, the phase compositions, morphology, structure, and thermal conductivity of Bi2Te3 – хSeх-based semiconductor wafers before and after the photon treatment (PT) were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and laser flash methods. The semiconductor plates 10 × 10 × 2 mm in size were prepared by electric discharge cutting from the briquettes, synthesized by hot pressing of Bi2Te3 – хSeх powder. Then, the plates were annealed at 570 K in an argon atmosphere for 24 h. The PT was carried out in an Ar atmosphere by irradiation of gas-discharge xenon lamps with pulses of 1.0 and 1.4 s and energy density ranging from 125 to 175 J/cm2. As revealed, the PT initiates the formation of a thin surface layer with an inhomogeneous nanocrystalline structure and an arbitrary nanocrystals orientation. The volume of material manifests a large-block textured crystalline structure with the original elemental and phase compositions formed during the extrusion. Thereby, a gradient nanostructured region composed of nano-sized and large Bi2Te3 – хSeх crystals with tunneling contacts is formed in the process of PT. We revealed that the PT changes the material bandgap slightly, decreases the concentration of charge carriers, increasing their mobility. The scattering of carriers and photons on linear defects dominates in a wide temperature range in the studied samples. Thereby, the figure of merit rise s by 8 % after PT, due to a decrease in the phonon component of thermal conductivity.

Thermal decomposition and crystallization behavior of Yb/Y co-doped SrZrO3 precursor used in the suspension plasma spray process

A double rare-earth (Yb/Y) co-doped SrZrO 3 [Sr 1.0 (Zr 0.9 Yb 0.05 Y 0.05 )O 2.95 ] thermal barrier coating was prepared via suspension plasma spraying (SPS). The rare-earth nitrates [Zr(NO 3 ) 4 ·5H 2 O, Sr(NO 3 ) 2 , Yb(NO 3 ) 3 ·6H 2 O, Y(NO 3 ) 3 ·6H 2 O] and NH 4 (C 2 O 4 ) 2 ·H 2 O were used to prepare the precursor suspension by co-precipitation. The thermal decomposition and crystallization of the precursor suspension powders calcined at 1200 °C were characterized with X-ray diffraction and a synchronous thermal analyzer coupled with quadrupole mass spectrometry . Zr 2 (C 2 O 4 ) 2 (OH) 4 decomposed into Zr(C 2 O 4 ) 2 , ZrO 2, and H 2 O initially, followed by the decomposition of Zr(CO 3 ) 2 into ZrO 2 . The SrC 2 O 4 precursor decomposed into SrCO 3 and SrO consecutively. The ZrO 2 reacted with SrO (Yb 2 O 3 , Y 2 O 3 ) to generate the Yb/Y co-doped SrZrO 3 . And the Yb/Y co-doped SrZrO 3 coating with a columnar crystal structure was prepared by SPS, which was analyzed with scanning electron microscopy, an inductively coupled plasma atomic emission spectrometer, and a laser flash analyzer. The thermal conductivity of the as-prepared coating was 1.77 W·m −1 ·K −1 at 1000 °C, which was more than 19% lower than that of the SPS SrZrO 3 coating. • The precursor suspension was prepared by co-precipitation using Zr(NO 3 ) 4 ·5H 2 O, Sr(NO 3 ) 2 , Yb(NO 3 ) 3 ·6H 2 O, Y(NO 3 ) 3 ·6H 2 O and NH 4 (C 2 O 4 ) 2 ·H 2 O. • The phase evolution of the precursor suspension was investigated. • The Yb/Y co-doped SrZrO 3 coating was prepared by suspension plasma spray using the prepared precursor suspension. • The Yb/Y co-doped SrZrO 3 coating has a low thermal conductivity of 1.77 W·m -1 ·K -1 at 1000 °C compared to SrZrO 3 coating.

Enhanced thermal characteristics of CuO embedded lauric acid phase change material

A new composite Phase change material (PCM) was fabricated by adding 0.05, 0.1, 0.15, 0.2 wt% CuO nanoparticles (NPs) into lauric acid, separately. Scanning electron microscopy (SEM) was used to observe the morphological structures of as-prepared nanoparticles, and XRD analysis was used to characterize their crystalline structure. The phase change properties (phase change temperatures and latent heats) of lauric acid and composite PCMs were obtained using differential scanning calorimetry (DSC). Using a laser flash analyzer (LFA), the thermal conductivity enhancement of the composite PCMs was evaluated. The thermal reliability analysis was implemented to ascertain the results of the composite PCMs over long periods.

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The estimation of the deviation in the measurements of thermal conductivity by the laser flash method for materials with different thermal conductivity coefficients, arising due to the presence of a graphite coating on the sample and the small thickness of the sample, is carried out. A computer model of the method was created in the Comsol Multiphysics software environment. For bulk samples with a graphite coating thickness of 20 μm, the deviation is 5.5 %. The thickness of bulk samples does not affect the measurement results. For materials with low thermal conductivity, a sharp increase in the deviation is observed, reaching 60%. For thermally conductive materials, the deviation is 16-18%. For thin samples less than 10 μm thick, the thickness of the graphite coating does not affect the measurement results. The decisive factor is the duration of the laser pulse.

Исследование влияния технологических факторов на неопределенность результатов измерения теплопроводности методом лазерной вспышки

The estimation of the deviation in the measurements of thermal conductivity by the laser flash method for materials with different thermal conductivity coefficients, arising due to the presence of a graphite coating on the sample and the small thickness of the sample, is carried out. A computer model of the method was created in the Comsol Multiphysics software environment. For bulk samples with a graphite coating thickness of 20 μm, the deviation is 5.5 %. The thickness of bulk samples does not affect the measurement results. For materials with low thermal conductivity, a sharp increase in the deviation is observed, reaching 60%. For thermally conductive materials, the deviation is 16-18%. For thin samples less than 10 μm thick, the thickness of the graphite coating does not affect the measurement results. The decisive factor is the duration of the laser pulse.

Investigation on Electrical, Thermal, and Mechanical Properties of Silicone Rubber ATH Nanocomposites

In the present study, investigations have been carried out by choosing the nano-sized ATH (30 – 50 nm) particles as filler content in silicone rubber to acquire a deep insight to understand the use of nano ATH fillers in silicone rubber on its performance, to use it as insulation structure as an outdoor insulator. Variation in the surface condition of silicone rubber nanocomposites due to corona aging and the recovery characteristics analysis carried out through contact angle measurement. Nano ATH added in silicone rubber, up to 3 wt% of filler, shows increased dielectric constant with less loss factor. Water droplet-initiated discharges on silicone rubber nano ATH composites under DC voltage measured using UHF technique and the damage caused zone analyzed through AFM studies and by surface potential measurement, which indicates higher surface roughness and increased charge trap depth. It is observed that negative DC voltage has higher CIV followed by positive DC and AC voltage. Laser Induced breakdown studies (LIBS) show a direct correlation between plasma temperature and material surface hardness. Also, on laser shining on the surface of the specimen, its temperature was measured on the backside of the specimen through thermal imaging confirming increased diffusivity of temperature. Laser flash analysis shows a direct correlation between filler content in base polymer and thermal conductivity and diffusivity. Higher storage modulus and activation energies measured from the dynamic mechanical analysis indicate the significance of prepared composites as an excellent mechanical support structure for the power system network.

Characterization and thermophysical properties of erythritol/expanded graphite as phase change material for thermal energy storage

The main aim of this paper is to enhance the thermal conductivity of erythritol as phase change material (PCM). The expanded graphite (EG, thermal conductivity: 151 W/(m•K)) is dispersed into erythritol (melting point: 118 °C, thermal conductivity: 0.844 W/(m•K)) as the high thermal conductivity additive, in which erythritol can be adsorbed effectively. The 2% EG/erythritol composite PCM has better cycle stability and its thermal conductivity enhances obviously. The 1% calcium pimelate (CaPi) is used as nucleating agent to inhibit the supercooling of the composite PCM further. The 2%EG/1%CaPi/erythritol composite PCM starts to solidify at 98.5 °C and the equilibrium temperature is about 115 °C during 100 cycles. The latent heat is 352.66 J/g and the thermal conductivity measured by the laser flash method is 1.287 W/(m•K), which is 52.5% higher than pure erythritol. Therefore, it is a new candidate to be used in waste heat recovery, solar energy medium temperature heat collection and other fields.

Opto-Thermal Investigation of Additively Manufactured Steel Samples as a Function of the Hatch Distance.

Nowadays, additive manufacturing processes are becoming more and more appealing due to their production-oriented design guidelines, especially with regard to topology optimisation and minimal downstream production depth in contrast to conventional technologies. However, a scientific path in the areas of quality assurance, material and microstructural properties, intrinsic thermal permeability and dependent stress parameters inhibits enthusiasm for the potential degrees of freedom of the direct metal laser melting process (DMLS). Especially in quality assurance, post-processing destructive measuring methods are still predominantly necessary in order to evaluate the components adequately. The overall objective of these investigations is to gain process knowledge make reliable in situ statements about component quality and material properties based on the process parameters used and emission values measured. The knowledge will then be used to develop non-destructive tools for the quality management of additively manufactured components. To assess the effectiveness of the research design in relation to the objectives for further investigations, this pre-study evaluates the dependencies between the process parameters, process emission during manufacturing and resulting thermal diffusivity and the relative density of samples fabricated by DMLS. Therefore, the approach deals with additively built metal samples made on an EOS M290 apparatus with varying hatch distances while simultaneously detecting the process emission. Afterwards, the relative density of the samples is determined optically, and thermal diffusivity is measured using the laser flash method. As a result of this pre-study, all interactions of the within factors are presented. The process variable hatch distance indicates a strong influence on the resulting material properties, as an increase in the hatch distance from 0.11 mm to 1 mm leads to a drop in relative density of 57.4%. The associated thermal diffusivity also reveals a sharp decrease from 5.3 mm2/s to 1.3 mm2/s with growing hatch distances. The variability of the material properties can also be observed in the measured process emissions. However, as various factors overlap in the thermal radiation signal, no clear assignment is possible within the scope of this work.

Determination of thermal diffusivity of thin films by applying Fourier expansion analysis to thermo-reflectance signal after periodic pulse heating

The flash methods, which are the most popular transient methods for measuring the thermal diffusivity of solid materials, have evolved into ultrafast laser flash methods by using picosecond or nanosecond pulse lasers as a heating source and a thermo-reflectance technique such as high-speed thermometry. In conventional ultrafast laser flash methods, thermal diffusivity is determined by fitting an analytical equation after single pulse heating to observe thermo-reflectance signals, although actual thermo-reflectance signals are observed after periodic pulse heating. This paper presents an exact analytical solution of the temperature response expressed by Fourier series for one-dimensional heat diffusion after periodic pulse heating. These Fourier coefficients are directly related to the Laplace transformation of the temperature response after single pulse heating. The signal observed for a 100 nm thick platinum thin film on a fused quartz substrate was analyzed by this Fourier expansion analysis and fitted by analytical equations with three parameters: heat diffusion time across thin film, the ratio of heat effusion of the substrate to thin film, and the amplitude of the signal over the entire range of pulse interval in the time domain. Robustness in determining the thermal diffusivity of the thin film by the ultrafast laser flash method can be improved by this new analysis approach.

Thermal diffusivity of corrosion-resistant coating SDP-1

In the present work, the thermal diffusivity of the SDP-1 grade nickel alloy was investigated in the wide temperature range of 300-1476 K. The SDP-1 alloy (Ni-Co-Cr-Al-Y) is the heat-resistant coating for blades of gas turbine plants, providing protection against sulfide-oxide corrosion in the temperature range of 1070-1220 K. The measurements were performed by laser flash method using LFA-427 apparatus. The estimated errors of the obtained data were 2-5% depending on temperature. The thermal diffusivity approximation equations and a table of reference values for various scientific and practical applications were obtained.

Thermophysical properties of NP2 brand nickel

The heat capacity and the thermal diffusivity of NP2 brand nickel were investigated in the temperature interval 296–1000…1375 K of the solid-state, including the region of the magnetic phase transformation. Measurements were carried out on samples from one initial ingot by laser flash technique and method of differential scanning calorimetry using LFA-427 and DSC 404 F1 setups, respectively. The thermal conductivity was calculated based on the measured thermophysical properties. The estimated errors of the obtained results were 2–4%, 3–5%, and 2–3% for thermal diffusivity, thermal conductivity, and heat capacity, respectively. For investigated thermophysical properties the fitting equations and the reference table have been received.

High‐Temperature Thermal Transport in Porous Silica Materials: Direct Observation of a Switch from Conduction to Radiation

AbstractEfficient thermal insulation at high temperatures poses stringent requirements on suitable materials. Low density, porous inorganic structures with pore sizes in the sub‐micrometer range are of particular interest for such materials to control heat conduction. Simultaneously, thermal radiation has to be suppressed, which depends on the optical properties of the constituents. Here, the authors demonstrate a direct observation of the transition from a conduction dominated to a radiation dominated thermal transport mechanism for the case of particulate silica materials at temperatures reaching up to 925 °C. A detailed analysis of the radiative transport through bulk silica as well as solid and hollow silica particles is provided. Optical transparency at high temperatures is the driving force, whereas surface wave modes barely contribute, particularly in case of the insulating particle packings. The existing analytical framework of laser flash analysis is extended to qualitatively describe the radiative and conductive heat transport by two independent diffusive transport models. The analysis provides a better understanding of the challenges to fabricate and analyze efficient thermal insulation materials at high operating temperatures, where multiple heat transport mechanisms need to be controlled.

Development of High Temperature Multi-Layer Laser Flash Artefacts

Delamination of the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of that system. This is even more pertinent for systems at high temperature. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. Multi-layer reference artefacts, with and without, debonded regions are required for validating the thermal characterisation of such systems using LFA. Although some high-temperature bulk candidate reference materials were developed and studied, e.g. in the European Metrology Research Programme (EMRP) funded Joint Research Project (JRP) ENG08 Metrofission, they were not able to meet the requirements for validating thermal measurements of multi-layer systems using LFA. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory is developing multi-layer reference artefacts, including both fully bonded and partially de-bonded systems for validating thermal characterisation of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. This paper details the methodology of production, measurement and validation of isotropic graphite and hafnium based multi-layer systems with, and without, partial debonding. Reproducibility, thermal stability and sensitive parameters concerning the thermal response of the artefacts will be discussed, with recommendation on the usage criteria as LFA multi-layer reference artefacts.