Laser-flash Measurements Research Articles

Acridinedione-phthalimide conjugates: Intramolecular electron transfer and singlet oxygen generation studies for optical and photodynamic therapy applications

We reported herein the synthesis, characterization of hybrid conjugates composed of phthalimide (Phth) and acridine-1,8-diones (Acr) for optical and medical applications. For the synthetic procedure, a three-step synthetic strategy has been utilized. The optical properties of the examined 1,8-acridinedione–phthalimide connected molecules (AcrPhth 1–5) have been examined utilizing various spectroscopic techniques, e.g., steady-state absorption and fluorescence, and time-correlated single photon counting. The steady-state absorption studies showed that AcrPhth 1–5 absorbs the light in the UV and visible region. The fluorescence studies of AcrPhth 1–5 exhibited significant fluorescence quenching compared to the acridinedione control compounds (Acr 1–5) suggesting the occurrence of electron-transfer reactions from the electron donating acridinedione moiety (Acr) to the electron accepting phthalimide moiety (Phth). The rate and efficiency of the electron-transfer reactions were determined from the fluorescence lifetime measurements indicating the fast electron-transfer processes of the covalently connected AcrPhth 1–5 conjugates. Computational studies supported the intramolecular electron-transfer reaction of AcrPhth conjugates using ab initio B3LYP/6-311G methods. In the optimized structures, the HOMO was found to be entirely located on the Acr entity, while the LUMO was found to be entirely on the Phth entity. Further, the synthesized compounds were tested as photosensitizers for generating the singlet oxygen species, which is a key factor in the photodynamic therapy (PDT) applications. The nanosecond laser flash measurements enable us to detect the triplet-excited states of examined Acr and AcrPhth conjugates, determining the triplet quantum yields, and direct detecting the singlet oxygen in an accurate way. From this observation, the singlet quantum yields were found to be in the range of 0.12–0.27 (for Acr 1–5) and 0.07–0.19 (for AcrPhth 1–5 conjugates). The molecular docking studies revealed that compound AcrPhth 2 exhibited high binding affinity with for key genes (p53, TOP2B, p38, and EGFR) suggesting its potential as a targeted anticancer therapy.Graphical abstractEfficient intramolecular electron-transfer reaction for the light harvesting conjugates! In addition, the conjugates can be used as good photosensitizers for PDT

Bismuth Telluride (Bi2Te3) nanocrystallites: Studies on growth morphology and its influence on the thermoelectric properties

Growth of Bismuth Telluride (Bi2Te3) nanocrystallites by solvothermal method resulted in an incomplete hexagonal flake-like (BTFL) structure for surfactant-free growth and complete hexagonal morphologies (BTHP) for the PVP surfactant mixed growth respectively identified through FESEM studies. XRD characterization revealed the crystallization of pure phase of Bi2Te3 at 210 °C for PVP-free growth and at 200 °C for PVP-assisted growth. Raman studies shows a noticeable difference in the appearance of peak positions for hexagonal nanoplatelets. Laser flash measurement of total thermal conductivity (κtot) resulted in the lowest value of 0.39 Wm−1K−1 for the BTFL pellet and 0.44 Wm−1K−1 for BTHP. Estimated lattice thermal conductivity resulted in 0.16 Wm−1K−1 for BTFL pellet and 0.25 Wm−1K−1 for the BTHP pellet. Temperature-dependent electrical conductivity studies reveal semiconductor behaviour for BTFL pellet and semi-metallic behaviour for BTHP pellet. Calculation of figure of merit (ZT) based on the measured values exhibits ZT value of 0.76 for BTFL and 0.64 for BTHP pellet. Details are presented in this paper.

Thermal conductivity of porous refractory material after aging in service with carbon pick-up

Medium Density Insulating Boards, based on vermiculite, are used for the insulating lining of ladles in steel production. In service, carbon monoxide is generated from oxidation of neighbouring Magnesia – Carbon bricks and diffuses through the refractory brick lining to deposit carbon in the colder insulating lining via the Boudouard reaction. Characterization by laser flash and hot disk measurements of original and post-mortem samples reveals an approximate increase by 26% in the overall thermal conductivity of the board to 0.34 W m−1 K−1 at room temperature following 15 months service. This is attributed to carbon and chloride phases detected by X-ray fluorescence and energy dispersive X-ray spectroscopy in the outermost zone of the board, cut into three zones for analysis along the heat flow direction. The increase in thermal conductivity is reduced to 17% when the thermal gradient in service conditions is considered.

Publisher’s Note: “Nanoscale laser flash measurements of diffuson transport in amorphous Ge and Si” [APL Mater. 10, 041111 (2022)

Publisher’s Note: “Nanoscale laser flash measurements of diffuson transport in amorphous Ge and Si” [APL Mater. 10, 041111 (2022)

Nanoscale laser flash measurements of diffuson transport in amorphous Ge and Si

The thermal properties of amorphous materials have attracted significant attention due to their technological importance in electronic devices. In addition, the disorder-induced breakdown of the phonon gas model makes vibrational transport in amorphous materials a topic of fundamental interest. In the past few decades, theoretical concepts, such as propagons, diffusons, and locons, have emerged to describe different types of vibrational modes in disordered solids. However, experiments can struggle to accurately determine which types of vibrational states carry the majority of the heat. In this study, we use nanoscale laser flash measurements (front/back time-domain thermoreflectance) to investigate thermal transport mechanisms in amorphous Ge and amorphous Si thin-films. We observe a nearly linear relationship between the amorphous film’s thermal resistance and the film’s thickness. The slope of the film’s thermal resistance vs thickness corresponds to a thickness-independent thermal conductivity of 0.4 and 0.6 W/(m K) for a-Ge and a-Si, respectively. This result reveals that the majority of heat currents in amorphous Si and Ge thin films prepared via RF sputtering at room temperature are carried by diffusons and/or propagons with mean free paths less than a few nanometers.

Neck formation and role of particle-particle contact area in the thermal conductivity of green and partially sintered alumina ceramics

Sintering ceramics involves neck formation, densification and eventually grain growth. A simplified model is developed to describe the effects of pore fraction, average grain size and the contact area between particles due to neck formation on the thermal conductivity of the green or partially sintered ceramic. Laser flash measurements on green bodies of alumina powders with different average particle sizes reveal similar thermal conductivity values close to 0.5 Wm−1K−1, corresponding to thermal resistances for equivalent planes of contacts in the range 10-7 to 2 10-6 m2KW−1. BET specific surface area measurements were then used to estimate the contact area due to neck formation in partially sintered alumina ceramics fired from 400 °C to 1200 °C. As predicted by the model, there is a strong increase in thermal conductivity. Such information is relevant as input data for numerical modelling of the green body behaviour during thermal treatment.

Aerosol jet printed 3 omega sensors for thermal conductivity measurement.

The 3 omega (3ω) method is a trusted technique for measuring thermal conductivity-a fundamental material property of critical importance in a broad range of applications. However, traditional 3ω sensor processing requires some form of physical vapor deposition, such as metal evaporation or sputtering. These 3ω sensor deposition techniques limit the materials and sample sizes applicable to the 3ω method. This work demonstrates an aerosol jet printing method to directly printsilver 3ω sensors that yield accurate temperature-dependent measurement up to 300°C on materials with thermal conductivity ranging from 1 to 150 W/m K. The interrelationship between printed sensor geometry, sensor thermal stability, and applicability to the 3ω method is examined. Thermal conductivity measurement with 3ω sensors conventionally sintered at 300°C agrees to independent laser flash measurement within 4% from room temperature to 150°C. An unconventional rapid high-temperature sintering method is shown to produce sensors that agree within 3% of the laser flash measurements from room temperature to 300°C. The rapid sintering profiles also reduced the sensor-substrate thermal boundary resistance of the printed sensors by as much as 88%. The direct printing of 3ω sensors creates opportunities for measurement of thermal transport properties in applications previously inapplicable to the 3ω method.

Plasma electrolytic oxidation thermal barrier coating for reduced heat losses in IC engines

The work involved the development and on-engine testing of a new “thermo-swing” barrier coating for reduced wall heat transfer and increased thermal efficiency in future diesel engines utilizing aluminium alloy pistons. Such swing coatings, of low thermal conductivity and low specific heat capacity, have recently been proposed to produce a dynamic thermal barrier layer that rapidly changes the temperature of the upper surface of the piston crown in response to the adjacent in-cylinder gas temperature. The new coating tested in this work was formed directly from the piston substrate material using an optimised plasma electrolytic oxidation process, with a silica top coat subsequently applied to entrap air within coating pores. Benchtop laser flash measurements were undertaken to quantify coating thermal properties and provide the required empirical data for future thermal simulation. Coatings of varying features were tested in a bespoke thermodynamic single cylinder diesel engine instrumented for precision measurements of in-cylinder pressure, fuel consumption and legislated engine-out emissions. The optimum coating applied across the full piston crown and bowl enabled up to 3% improvement in indicated thermal efficiency under idealised part load operating conditions. The coating reduced heat transfer during combustion, leading to elevated engine-out NOx. By retarding combustion phasing slightly from the optimum, the NOx increase could be mitigated while still retaining most of the fuel consumption benefit, with the remaining benefit associated with reduced heat transfer during the remaining power stroke. The emissions of other key pollutants (CO, unburned hydrocarbons and soot) were less affected under the part load conditions tested.

Thermal conductivity of SLM deposited H13 steel

Hot-worked H13 tool steel was deposited using selective laser melting (SLM) process in different deposition conditions. The samples were deposited in 2 different directions: parallel and perpendicular to the base plate of SLM device. Thermal conductivity of the deposited samples was calculated on the base of laser flash measurements up to 700°C. Furthermore, the thermal expansion, specific heat, and thermal diffusivity of the deposited samples and their variations with different deposition conditions are also presented. To explain the measured differences in thermal properties, some metallographic studies together with porosity investigation are also provided. It was shown that all measured thermal properties of the samples are affected by temperature and that the microstructural defects play an important role for the resulting thermo-physical properties.

Dependence of Heat Transport in Solids on Length-Scale, Pressure, and Temperature: Implications for Mechanisms and Thermodynamics.

Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. When L is several mm, D∞(T) = FT−G + HT, where F is constant, G is ~1 or 0, and H (for insulators) is ~0.001. The attenuation parameter b = 6.19D∞−0.477 at 298 K for electrical insulators, elements, and alloys. Dimensional analysis confirms that D → 0 as L → 0, which is consistent with heat diffusion, requiring a medium. Thermal conductivity (κ) behaves similarly, being proportional to D. Attenuation describing heat conduction signifies that light is the diffusing entity in solids. A radiative transfer model with 1 free parameter that represents a simplified absorption coefficient describes the complex form for κ(T) of solids, including its strong peak at cryogenic temperatures. Three parameters describe κ with a secondary peak and/or a high-T increase. The strong length dependence and experimental difficulties in diamond anvil studies have yielded problematic transport properties. Reliable low-pressure data on diverse thick samples reveal a new thermodynamic formula for specific heat (∂ln(cP)/∂P = −linear compressibility), which leads to ∂ln(κ)/∂P = linear compressibility + ∂lnα/∂P, where α is thermal expansivity. These formulae support that heat conduction in solids equals diffusion of light down the thermal gradient, since changing P alters the space occupied by matter, but not by light.

The thermal and mechanical properties of hafnium orthosilicate: Experiments and first-principles calculations

Hafnium orthosilicate (HfSiO4: hafnon) has been proposed as an environmental barrier coating (EBC) material to protect silicon and silicon-based ceramic materials at high temperatures and as a candidate dielectric material in microelectronic devices. It can naturally form at the interface between silicon dioxide (SiO2) and hafnia (HfO2). When used as an EBC its coefficient of thermal expansion (CTE) should match that of the protecting layer (e.g. silicon and SiC composites) to reduce the stored elastic strain energy, and thus the risk of failure of these systems. In this work, the physical, mechanical, thermodynamic and thermal transport properties of hafnon have been investigated using a combination of density functional theory (DFT) calculations and experimental assessments. The average linear coefficient of thermal expansion (CTE) calculated using the quasi-harmonic approximation increase from 3.06 × 10−6K − 1 to 6.36 × 10−6K − 1, as the temperature increases from 300 to 1500 K, in agreement with both X-ray diffraction lattice parameter and dilatometry measurements. The predicted thermal conductivity from Boltzmann transport theory is approximately 16.1 W/m.K at 300 K. The thermal conductivity of our samples using both hot disk and laser flash measurements gave a value of 13.3 W/m.K. This slightly lower value is expected and is indicative of residual disorder in the experimental samples, which is absent in the theoretical analysis. First-principles calculations and nanoindentation techniques are used to assess the ambient temperature elastic constants and bulk modulus respectively. The elastic properties obtained by both approaches agreed to within 5%, validating the computational approach and its future use for the study of the thermomechanical properties of other oxides or silicates.

Multiple shots averaging in laser flash measurement.

The laser flash method is a well-known procedure to determine the thermal diffusivity of a wide range of materials. However, in some cases there is the need of limiting the input power, measuring materials with high thermal capacity, or investigating thick samples. These conditions lead to a reduction of the signal-to-noise ratio. Therefore, we propose a new laser flash control and data acquisition system, that is able to repeat multiple times the emission of the laser impulse and the measurement of the thermal response of the specimen. With the average of several measurements, it is possible to obtain a decrease of the noise when working with low power inputs.

Graphene enhanced thermoelectric properties of cement based composites for building energy harvesting

Cement based thermoelectric materials can convert the available ambient heat absorbed by the building surfaces in summer into electrical energy. These materials can have an impact on the improvement of indoor climate of buildings, reduction of energy consumption and energy harvesting applications especially in the urban areas. In this paper, the thermoelectric properties of cement based composites with graphene nanoplatelets (GNP) inclusions were reported for the first time. GNP-cement mixtures were prepared by planetary ball milling and compressed subsequently to form bulk composites. We report the maximum electrical conductivity of 16.2 Scm−1 and Seebeck coefficient of +34.0 µVK−1 in this work. Hall measurement was performed to determine the material type and carrier concentration. It was found that all specimen exhibit p-type semiconductor behavior. Thermal diffusivity measurements were carried out using laser flash measurement technique. The highest figure of merit 0.44 × 10−3 was achieved at about 70 °C. Enhanced thermoelectric properties of graphene nanoplatelets cement based composites have a promising prospect in the urban heat island effect alleviation, thus saving electricity consumption and energy harvesting.

Influence of Morphological Changes in a Source Material on the Growth Interface of 4h-Sic Single Crystals.

In this study, the change of mass distribution in a source material is tracked using an in situ computer tomography (CT) setup during the bulk growth of 4H- silicon carbide (SiC) via physical vapor depostion (PVT). The changing properties of the source material due to recrystallization and densification are evaluated. Laser flash measurement showed that the thermal properties of different regions of the source material change significantly before and after the growth run. The Si-depleted area at the bottom of the crucible is thermally insulating, while the residual SiC source showed increased thermal conductivity compared to the initially charged powder. Ex situ CT measurements revealed a needle-like structure with elongated pores causing anisotropic behavior for the heat conductivity. Models to assess the thermal conductivity are applied in order to calculate the changes in the temperature field in the crucible and the changes in growth kinetics are discussed.

Erratum to “Thermal Conductivity of Oxide Scale Thermally Grown on Iron Substrate Corrected by Temperature-dependent Interfacial Thermal Resistance in Laser Flash Measurement” [ISIJ International, Vol. 59 (2019), No. 3, pp. 398–403

Erratum to “Thermal Conductivity of Oxide Scale Thermally Grown on Iron Substrate Corrected by Temperature-dependent Interfacial Thermal Resistance in Laser Flash Measurement” [ISIJ International, Vol. 59 (2019), No. 3, pp. 398–403

Characterisation and Performance Optimisation of WC-MC/M(C,N)-Co Hardmetals

WC-MC/M(C,N)-Co hardmetals with 10 wt% Co were prepared in undoped, as well as in either Cr- or V-doped form. The starting formulations contained 5 wt% TiC or 5% (TiC+TiN), the latter with two different TiC/TiN ratios, and 10 wt% (Ta,Nb)C. For each composition, a low-C grade (Ms ≈ 75%) and a high-C grade (Ms ≈ 88%) was adjusted by C or W addition, to end up with 18 different hardmetal formulations, prepared in an industrial process. Model alloys, MC and M(C,N) phases with a composition reflecting the composition of these phases in the hardmetal were prepared, too. A variety of data was collected: binder phase and hard phase compositions of model alloys by wavelength-dispersive electron-probe microanalysis (WDS-EPMA), liquid phase formation temperatures in model alloys with free C and eta by differential thermal analysis (DTA), respectively, thermal conductivities of MC and M(C,N) phases and hardmetals by laser-flash temperature conductivity and heat capacity measurements up to 950 °C, crystallite-size distribution by electron backscatter diffraction EBSD, hardness HV30, Palmqvist-Shetty fracture toughness KIC, Weibull evaluation of the transverse rupture strength (TRS), oxidation resistance in air as well as milling tests on coated hardmetals with Ti(C,N)/Al2O3 and (Ti,Al)N layers.

Thermal Conductivity of Oxide Scale Thermally Grown on Iron Substrate Corrected by Temperature-dependent Interfacial Thermal Resistance in Laser Flash Measurement

Thermal Conductivity of Oxide Scale Thermally Grown on Iron Substrate Corrected by Temperature-dependent Interfacial Thermal Resistance in Laser Flash Measurement

SiO2-Modified Al2O3@Al-Supported Cobalt for Fischer–Tropsch Synthesis: Improved Catalytic Performance and Intensified Heat Transfer

SiO2-modified high thermal conductivity Al2O3@Al composites were synthesized and supported cobalt for Fischer–Tropsch synthesis to improve the catalytic performance and intensify the heat transfer within a fixed-bed reactor. FTS results showed that the CO conversion and C5+ selectivity increased whereas CH4 selectivity decreased, which could be attributed to the reduced metal–support interaction via modification of SiO2 on the surface of Al2O3@Al. The heat transfer coefficients of the Co/SAl2O3@Al–x were more than 30 times those of conventional Co/Al2O3 according to the laser flash measurement. The thermal conductive study showed that a homogeneous radial temperature gradient was maintained within the catalyst bed for Co/SAl2O3@Al-x even without using a heat diluter, indicating good thermal conductivity within the reactor. In addition, the temperature of the catalyst bed for Co/SAl2O3@Al-x was easier to reach a “steady state” compared to the reactor packed with traditional low thermal conductive Co/Al2O3,...

Grain boundary thermal resistance and finite grain size effects for heat conduction through porous polycrystalline alumina

Design of high performance materials for thermal insulation or heat sinking requires understanding of the mechanisms controlling heat flow. The effect of grain size on the effective thermal conductivity of porous alumina ceramics has been investigated. After uniaxial pressing of a fine α-alumina powder, control of firing temperature and duration yielded ceramics with variations in grain size. Values of thermal conductivity corresponding to equivalent 100% dense ceramics were determined from laser flash measurements using Landauer’s relation to take porosity into account. These exhibited a strong decrease from 33 W m−1 K−1, for grain sizes larger than 2 μm, down to 8 W m−1 K−1 for an average grain size of 0.25 μm.A method to separate the contributions of localized thermal resistance (Kapitza resistance) at grain boundaries and grain conductivity for each sample is presented. The larger grain size samples (>0.5 μm) yield values for the effective grain boundary thermal resistance in the range 0.6–0.8 × 10−8 m2 K W−1 and a grain conductivity close to 35 W m−1 K−1. For smaller grain samples (<0.5 μm), the grain boundary thermal resistance increases to 2 × 10−8 m2 K W−1 while the grain conductivity reduces to 23 W m−1 K−1. Thus grain size controls both the number of grain boundaries in the heat path and the grain conductivity itself.

Thermoelectric stability of Eu- and Na-substituted PbTe

The out-of-equilibrium samples show highest values of figure-of-merit, ZTmax, up to 2.1.