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Polyether-ether-2-ketone (PEKK) is a high-performance thermoplastic polymer used in various fields, from aerospace to medical applications, due to its exceptional mechanical and thermal properties. Nonetheless, the mechanical behavior of 3D-printed PEKK still deserves to be more thoroughly investigated, especially in view of its production by 3D printing, where mechanical properties measured at different scales are likely to be correlated to one another and to all play a major role in determining biomechanical properties, which include mechanical strength on one side and osteointegration ability on the other side. This work explores the mechanical behavior of 3D-printed PEKK through a multiscale approach, having performed both nanoindentation tests and standard tensile and compression tests, where a detailed view of strain distribution was achieved through Digital Image Correlation (DIC) techniques. Furthermore, for specimens tested up to failure, their fractured surfaces were analyzed through Scanning Electron Microscopy (SEM) to clearly outline fracture modes. Additionally, the internal structure of 3D-printed PEKK was explored through Computed Tomography (CT) imaging, providing a three-dimensional view of the internal structure and the presence of voids and other imperfections. Finally, surface morphology was analyzed through confocal microscopy. The multiscale approach adopted in the present work offers information about the global and local behavior of the PEKK, also assessing its material properties down to the nanoscale. Due to its novelty as a polymeric material, no previous studies have approached a multiscale analysis of 3D-printed PEKK. The findings of this study contribute to a comprehensive understanding of 3D-printed PEKK along with criteria for process optimization in order to customize its properties to meet specific application requirements. This research not only advances the knowledge of PEKK as a 3D-printing material but also provides insights into the multifaceted nature of multiscale material characterization. [ABSTRACT FROM AUTHOR]

Polymer materials are increasingly widely used in high-fire-risk applications, such as aviation interior components. This study aimed to compare the tensile, thermal, and flame-retardant properties of test samples made from ultra-performance materials, polyetherimide (PEI) and polyetherketoneketone (PEKK), using the fused filament fabrication process (FFF). The tensile tests were performed for these materials at different raster angles (0, 45, and 90°). The thermomechanical tests were done in the axial, perpendicular, and through-thickness directions to the extruded filaments. The impact of printing parameters on the flame retardancy of 3D-printed samples was investigated in vertical burn tests with varying specimen thicknesses and printing directions. Experimentally, it was testified that PEKK had better isotropic behaviour than PEI for mechanical performance, thermal expansion, and fire-resistant properties, which are essential in fabricating intricately shaped products. [ABSTRACT FROM AUTHOR]

In the present paper, the results of a research focused on microstructure investigation of steel welded joints by means of non destructive thermographic technique are presented. In particular, two rough joints obtained by means of irregular manual welding are analyzed. Active lock in thermography phase analysis is applied, basing on the evidence that thermal diffusivity is related to the thermal diffusion length, using the phase contrast trend as a function of the distance from the laser spot. Diffusivity is expected to be dependent on the local microstructure and vary through different directions. By the variation in diffusivity, it is possible to investigate the level of anisotropy.The results are compared with micrographic analysis. The proposed method provides an active lock-in infrared thermography analysis by means of a thermal camera and an exciting laser head to evaluate thermal diffusivity. [ABSTRACT FROM AUTHOR]

Temperature limitations in nickel‐base superalloys have resulted in the emergence of SiC‐based ceramic matrix composites as a viable replacement for gas turbine components in aviation applications. Higher operating temperatures allow for reduced fuel consumption but present a materials design challenge related to environmental degradation. Rare‐earth disilicates (RE2Si2O7) have been identified as coatings that can function as environmental barriers and minimize hot component degradation. In this work, single‐ and multiple‐component rare‐earth disilicate powders were synthesized via a sol‐gel method with compositions selected to exist in the monoclinic C 2/m phase (β phase). Phase stability in multiple cation compositions was shown to follow a rule of mixtures and the C 2/m phase could be realized for compositions that contained up to 25% dysprosium, which typically only exists in a triclinic, P1¯${\rm{\bar{1}}}$, phase. All compositions exhibited phase stability from room temperature to 1200°C as assessed by X‐ray diffraction. The thermal expansion tensors for each composition were determined from high‐temperature synchrotron X‐ray diffraction and accompanying Rietveld refinements. It was observed that ytterbium‐containing compositions had larger changes in the α31 shear component with increasing temperature that led to a rotation of the principal axes. Principal axes rotation of up to 47° were observed for ytterbium disilicate. The results suggest that microstructure design and crystallographic texture may be essential future avenues of investigation to ensure thermo‐mechanical robustness of rare‐earth disilicate environmental barrier coatings. [ABSTRACT FROM AUTHOR]

h-BN is a two-dimensional ceramic material with a lamellar structure, known for its typical orientation characteristics on mechanical and thermal properties. By optimizing the size and arrangement of h-BN grains in the matrix, the anisotropic characteristics of h-BN ceramics can be fully utilized to obtain ceramic materials with high thermal conductivity or high strength. In order to study the effect of grain orientation distribution on the mechanical and thermal properties of materials, the index of orientation distribution (IOP) was used to quantitatively characterize the orientation degree of h-BN grains and analyzed the effect of h-BN grain size on material properties. The results show when the initial h-BN size is 13.50 μm, the ceramic has the highest orientation degree/-507, and the mechanical and thermal properties show obvious anisotropy. While the related properties of BN-YAG ceramics varies significantly with the decrease of initial h-BN grain size. [ABSTRACT FROM AUTHOR]

This research focuses on four thermal characteristics of 3D products printed from the fourteen most common filaments. The softening temperature, coefficient of linear thermal expansion (CLTE), irreversible thermal strain, and thermal conductivity of the 3D printed samples at various measurement directions were evaluated, systematised, and analysed. Semi-crystalline and amorphous, electrically conductive and thermochromic polymer filaments were investigated. Four sets of samples were printed by the Ultimaker S5 3D printer. Printer settings provided the unidirectional orientation of all filament fibres in all specimens and uniform within any specimen's cross section to investigate the anisotropy of their properties. For investigation of the thermal characteristic of the 3D printed samples, thermomechanical analysis (TMA), differential scanning calorimetry (DSC) methods, and method for measurement of the thermal conductivity (Hot-Disk) were used. The penetration test showed that polyetherimide samples had the highest heat resistance, while the samples from polylactic acid (PLA) had the lowest one. The results of TMA demonstrated that the samples of polypropylene (PP), thermoplastic polyurethane (TPU), and Polyamide had the highest CLTE. In general, semi-crystalline polymers had a higher coefficient of thermal expansion than amorphous ones. During the TMA, almost all samples showed an irreversible thermal strain. PLA Red and Co-polyester showed significant shrinkage of 6–9% in the print direction and expansion in the build direction compared to other samples. Samples of PLA LAVA, acrylonitrile butadiene styrene, polycarbonate, PP, and TPU filaments demonstrated more stable thermal behaviour. The thermal conductivity analysis showed that almost all specimens had a certain degree of anisotropy. The highest thermal conductivity value was obtained for print direction for materials with pronounced anisotropic behaviour, except for polyamide samples. DSC study of post-printing relaxation of the structure of printed samples showed that rapidly cooled samples of semi-crystalline PLA material had a non-equilibrium structure with a low degree of crystallinity. Such structures changed with the time up to 400 h after printing, which also affected their stiffness and strength. The annealing of printed samples at temperatures of cold crystallisation allowed a significant increase in their crystallinity degree, thus approaching the upper limit of this degree for semi-crystalline PLA. [ABSTRACT FROM AUTHOR]

With the development of high-density electronics, polymer-based thermal conductive composites with excellent thermal and mechanical performance are receiving great attention. For the development of polymer-based thermal conductive composites with superior properties, it is essential to reduce the agglomeration of fillers and enhance the interfacial interactions between thermal conductive fillers and the polymer matrix. Among the several thermal conductive materials, graphene nanoplatelets (GNPs) and cellulose nanofiber (CNFs) are attracting attention. However, poor interfacial interaction between GNP and CNF leads to interfacial separation, which in turn, deteriorates its properties. Herein, we synthesized a pyranine-functionalized polyether dispersant (PyPE), which can significantly improve the interfacial interactions between GNPs and CNFs. The effect of PyPE on the dispersion behavior of GNPs and the thermomechanical properties of GNP-CNF composite were monitored. Furthermore, we also performed molecular dynamics (MD) simulations to investigate the impact of applying PyPE dispersant on the interfacial interactions between the GNPs and CNF matrix. The application of PyPE significantly enhanced the dispersibility of GNPs within the CNF matrix, resulting in a 15.5 % increase in-plane thermal diffusivity and a 24.5 % enhancement in tensile strength of the composite, demonstrating their potential applications in high power density electrical equipment and electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• A laser spot periodic heating technique based on sub-region phase fitting is developed in measuring the anisotropic thermal diffusivity of thin films. • The spatial distribution of phase is divided into linear and nonlinear regions for fitting in-plane and out-of-plane thermal diffusivity, respectively. • The thermal diffusivity of the tested films ranges from 5.5 × 10−8 m²/s to 9.6 × 10−4 m²/s. • The present method can accomplish anisotropic thermal diffusivity measurements for thin films with thicknesses ranging from a few to hundreds of microns. The thermal transport properties of thin films have garnered significant research interest due to their diverse applications in new energy sources and thermal management. As the thickness of anisotropic thin films decreases to a few microns, conventional laser flash analyzer and infrared lock-in thermography encounter difficulties in characterizing their thermophysical properties. In response to this challenge, we propose a laser spot periodic heating technique based on sub-region phase fitting for measuring anisotropic thin films. In this method, a thermocouple monitors the temperature response on the sample back surface, and the amplified voltage is subsequently measured using a lock-in amplifier to record the spatial distribution of the phase signal. Finite element simulations indicate that the impact of contact thermal resistance between the thermocouple and the sample can be negligible when measuring in variable locations. The anisotropic thermal diffusivity is then fitted using one-dimensional and three-dimensional unsteady-state heat conduction models, with the spatial distribution of phase lag being partitioned into linear and non-linear regions, respectively. We measure the in-plane and out-of-plane thermal diffusivity of a stainless-steel film, demonstrating the reliability and accuracy of the method. As a showcase study demonstrating the capabilities of our methodology, we test four anisotropic thin films, covering a large spectrum of thermal diffusivity, ranging from 5.5 × 10−8 m2/s to 9.6 × 10−4 m2/s. It is verified that the present method can accomplish anisotropic thermal diffusivity measurements for thin films with thicknesses ranging from a few to hundreds of microns, a capability crucial for advancing the characterization of the thermophysical properties of materials. [ABSTRACT FROM AUTHOR]

Sapphire crystals have a special lattice structure, which causes anisotropy in their processing quality due to anisotropy of the physical and mechanical properties. Laser-induced plasma assisted ablation (LIPAA) is a new processing technology used to process transparent, hard, and brittle materials. LIPAA is regarded as a photoelectric composite processing method that makes the material removal and surface generation mechanisms more complicated. In this study, a surface generated by LIPAA processing showed much higher quality than a surface generated by direct laser ablation. Moreover, LIPAA has the advantage of a lower etching energy threshold than that of infrared laser direct ablation. Infrared laser-induced plasma assisted ablation was performed on different sapphire crystal orientations to explore the influence of anisotropy on LIPAA processing. The LIPAA material removal rates for different sapphire planes were presented and compared with results for direct laser ablation-focused ion beam (FIB) processing. The results showed that thermal removal was most dominant during LIPAA processing of sapphire. The material removal rate was highest in the [10 1 ‾ 0] direction and lowest in the [11 2 ‾ 0] direction. [ABSTRACT FROM AUTHOR]

Efficiently thermal management in electronic devices calls for creating polymer composites that have superior thermal transport abilities. Compared with single-filler composites, hybrid-filler composites have gained significant attention as they not only utilize the advantages of each filler individually but also allow for the potential cooperation in constructing filler networks between them. Differing from the previous research on hybrid-filler size, geometry, composition, and content and their impact on thermal conductivity (TC) in composites, this study aims to examine the spatial distribution effects of hybrid-fillers. A binary-filler strategy comprising of anisotropic 2D h- BN and 0D isotropic S–Al 2 O 3 has been proposed, with the primary h -BN filler aligned to filly utilize its anisotropy and intrinsic TC properties. Furthermore, positioning a small quantity of S–Al 2 O 3 between adjacent parallel h -BN considerably improves TC in the non-oriented direction of silicon rubber (SiR) composites. A special focus is given to the influence of the interstitial S–Al 2 O 3 filler on the individual through-plane TC (λ ⊥) and in-plane TC (λ ⫽) variation of the binary-filler hybrid SiR composites, which are perpendicular and parallel to the oriented h -BN. When incorporating 40 vol% h -BN and 5 vol% S–Al 2 O 3 , the binary SiR composites exhibit the highest concurrent λ ⫽ and λ ⊥ values of 14.581 and 2.132 W/m·K, respectively. The corresponding effects on the ductility, hardness, and dielectric properties of the SiR composites were explained. Moreover, the use of commercially available TC fillers, along with the effortless preparation method, enables the potential to produce h -BN based TIMs materials on a large scale for thermal management usage. [Display omitted] • A binary filler system consisting in-plane oriented 2D h -BN and 0D isotropic S–Al 2 O 3 is designed. • The addition of S–Al 2 O 3 filler between adjacent parallel h -BN flakes facilitates vertical heat transfer. • The binary structure of h -BN/S–Al 2 O 3 exhibits an anisotropic feature in the filler contact thermal resistances. • The binary filler strategy mitigates the trade-off between in-plane and through-plane thermal conductivity. [ABSTRACT FROM AUTHOR]

The determination of the thermoelastic properties of polyimide (PI) fibers is important for their applications, however, these properties are difficult to measure directly, especially the transverse thermoelastic properties. Here, the transverse thermoelastic properties of PI fibers, including transverse Young's modulus (2.12 GPa), shear modulus (0.94 GPa), Poisson's ratio (0.05), and coefficient of thermal expansion (45.68 μm/m°C), were estimated by combining dynamic and static thermo-mechanical techniques, as well as various relevant micromechanical models. The transverse Young's modulus of PI fibers was only 1/46th of the longitudinal one, and the transverse coefficient of thermal expansion of PI fibers was positive, unlike the longitudinal one, which was negative, showing the typical anisotropy of PI fibers. Finally, the thermoelastic properties of the PI fibers were in turn used to predict the thermoelastic behavior of the PI fiber-reinforced composites, thus validating their effectiveness. [Display omitted] [ABSTRACT FROM AUTHOR]

Based on density functional theory, this paper uses first-principles methods to study the stability, electronic properties, anisotropy, thermodynamic properties, and optical properties of compound MB2 (M = V, Nb, Zr). The enthalpy of formation indicates that the compound MB2 is energy stable. Studying its electronic properties, it is concluded that the compound MB2 (M = V, Nb, Zr) has metallic properties from the band structure and density of states diagram. The analysis of the differential charge density shows that the binding force between B–M and M–M atoms is greater than that of B–B. The results of elastic performance research show that VB2, NbB2, and ZrB2 exhibit brittleness and are brittle materials. Moreover, VB2, NbB2, and ZrB2 also meet the mechanical stability standards. Research shows that the anisotropy of MB2 is: NbB2 > VB2 > ZrB2.The quasi-harmonic Debye model is used to study the thermodynamic properties of compound MB2 (M = V, Nb, Zr). We analyzed the change curve of heat capacity, volume, thermal expansion coefficient, and Debye temperature at 0–1600 K and 0–100GPa. According to the analysis of thermodynamic properties, MB2 also satisfies the thermal stability condition. Finally, this paper studies the absorption and reflection of light by MB2. It is found that absorption and reflection are relatively strong in the ultraviolet region. [ABSTRACT FROM AUTHOR]

• Despite relatively weak hydrogen bonds, tetracarboxylic-based frameworks (TCFs), a three-dimensional (3D) HOF, show relatively high thermal conductivity. • Electrostatic interactions in TCFs dominate thermal conductivity and anisotropy but central atoms in the monomers show negligible impact. • Electrostatic interactions sustain phonon modes with frequencies of 5–25 THz to carry heat and are key to maintaining high crystallinity in TCFs. Hydrogen-bonded organic frameworks (HOFs), an emerging class of porous molecular materials assembled through hydrogen bonds (H-bonds), have shown intriguing latent for multifunctional materials or devices. Understanding thermal transport in HOFs is crucial to guiding the functional material design with desired thermal properties. Here, we report thermal transport properties in HOFs and reveal the significance of electrostatic interactions (H-bonds and π-π interactions) to heat conduction with molecular dynamics simulations. It is found that despite relatively weak H-bonds, tetracarboxylic-based frameworks (TCFs), a three-dimensional (3D) HOF, show relatively high thermal conductivity compared with known 3D porous covalent organic frameworks and metal-organic frameworks. Electrostatic interactions in TCFs dominate thermal conductivity and anisotropy but central atoms in the monomers show negligible impact. The structural analysis and x-ray diffraction patterns highlight the importance of electrostatic interactions in maintaining the high crystallinity of TCFs. The vibrational density of states and spectral thermal conductivity further demonstrate that phonon modes with frequencies below 25 THz contribute about 90 % of total thermal conductivity in TCFs, and electrostatic interactions sustain phonon modes with frequencies of 5–25 THz to carry heat. These findings provide a fundamental understanding of structure-thermal conductivity relation in HOFs and advance their applications for multifunctional materials and devices. [ABSTRACT FROM AUTHOR]

Heat dissipation material with programmable anisotropic property is very challenging, yet can realize the controllable thermal diffusion for heating device. In this work, anisotropic Si3N4 ceramics with oriented grains are prepared to adjust and improve the mechanical and thermal properties under the applied stress field by rolling film forming technology. Through the design of the sintering aids in the process of liquid‐phase sintering, the orientation degree of the Si3N4 grains is programmable as well as the mechanical property and the thermal property of the Si3N4 ceramics. As a consequence, the obtained Si3N4 ceramics show significant anisotropy in mechanical properties and thermal conductivity. The typical fracture toughness and thermal conductivity along the grain orientation direction are 10.6 MPa⋅m1/2 and 45.45 W/(m⋅K) while they are 4.5 MPa⋅m1/2 and 66.42 W/(m⋅K) in the direction perpendicular to the oriented grain, respectively. This grain orientation method paves the way for the thermal performance design and the production of programmable heat dissipation material. [ABSTRACT FROM AUTHOR]

The anisotropic mechanical and thermal conduction properties of unidirectional aligned alumina aerogels (AAs) were investigated in our part II. The anisotropic structure characteristics are the main factors to decide the physical properties of AAs. The results show that the brittle failure behavior reflects the fracture of the long pore walls along ice-crystal growth direction, but the excellent strain and low compressive strength are ascribed to the weak second structures. The structural difference in the direction of heat transfer results anisotropic thermal conduction. The heat transfers layer-by-layer at intervals of solid walls and air pores is more effective for the heat insulation. [ABSTRACT FROM AUTHOR]

Abstract The thermoelectric transport properties of artificially textured polycrystalline CrSiTe 3 samples have been investigated for elucidating their correlations with a crystal structure and the corresponding charge density distribution. We verified that the low mobility of 13–27 cm2 V−1 s−1 attributing poor electronic transport properties is originated from the discrete charge density distribution in the covalently bonded layer. Also, the modulation of thermal conductivity values from 3.5 to 5.4 W m−1 K−1 with varying the texture was confirmed in pristine CrSiTe 3. Thus, we suggest that the electronic and thermal transport properties of layer structured CrSiTe 3 are strongly correlated with crystallographic features. Graphical abstract Image 1 Highlights • Thermoelectric transport properties of CrSiTe 3 compounds. • Strong correlation between structure and thermoelectric properties. • The charge density distributions are strongly localized without no overlaps. • In-plane electronic transport properties depend on charge density distributions. • Anisotropy in thermal conductivity inherited from crystal structure. [ABSTRACT FROM AUTHOR]

Highlights • The anisotropic turbulent mixing model for rod bundle with spacer grid is proposed. • Simulation result agrees well with experimental result with anisotropic turbulent mixing model. • Detailed thermal-hydraulic performance of rod bundle with spacer grid is analyzed. Abstract The interchannel mixing effect is very important for the thermal-hydraulic performance of fuel assembly subchannels in Pressurized Water Reactor (PWR), especially for that of the fuel assembly with spacer grid. In this study, an anisotropic turbulent mixing model with a turbulent mixing coefficient matrix is developed and embedded in an in-house code to analyze the thermal-hydraulic performance of the fuel assembly. The validation of the present turbulent mixing model has been performed by comparing the numerical results with the experimental results for the outlet temperature distribution of the fuel assembly. Then, the thermal-hydraulic performance of 5 × 5 rod bundle with spacer grid is analyzed by comparing the present turbulent mixing model and the conventional isotropic turbulent mixing model which uses a constant value to consider the average mixing effect. It is found that stronger diversion crossflow, more uniform outlet temperature distribution, higher Critical Heat Flux (CHF) and higher Departure from Nuclear Boiling Ratio (DNBR) of the fuel assembly are achieved when using anisotropic turbulent mixing model. In summary, the anisotropic turbulent mixing model depicts the interchannel mixing characteristics of spacer grid more reasonably. [ABSTRACT FROM AUTHOR]

Abstract In this work, highly anisotropic thermally conductive polyimide/boron nitride (PI/BN) composites were successfully prepared by a simple method called "ball milling, high-pressure compression and low-temperature sintering". The in-plane thermal conductivity of the PI composites with 30wt% BN reached as high as 2.81 W/mK, while the out-of-plane thermal conductivity was 0.73 W/mK, about 3.2 times and 2.4 times of pure PI, respectively. The great improvement of the thermal conductivity was attributed to the in-plane alignment of BN platelets, which constructed highly connected thermally conductive pathways. The thermally conductive BN networks were observed to be more dense and sufficient in the in-plane direction, more favorable for the heat dissipation, compared to the out-of-plane direction. [ABSTRACT FROM AUTHOR]

Abstract In this work, we used the first-principles calculations to study structural properties, elastic constants and moduli, polycrystalline elastic moduli, anisotropic properties and thermal conductivities of tetragonal LnB 2 C 2 (Ln = Rare Earth) compounds. The polycrystalline elastic modulus, Poisson's ratio, hardness and Debye temperature were calculated based on the single crystal elastic constant. Estimation of elastic anisotropy was carried out by elastic anisotropy index and surface projection. The elastic anisotropy for these compounds is a sequence of LuB 2 C 2 > TmB 2 C 2 > ErB 2 C 2 > LaB 2 C 2 > HoB 2 C 2 > TbB 2 C 2 > DyB 2 C 2 > NdB 2 C 2 > PrB 2 C 2 > CeB 2 C 2. The calculated minimum thermal conductivity and Debye temperature are in the same order of LaB 2 C 2 > TmB 2 C 2 > LuB 2 C 2 > ErB 2 C 2 > HoB 2 C 2 > CeB 2 C 2 > DyB 2 C 2 > NdB 2 C 2 > PrB 2 C 2 > TbB 2 C 2. The obtained sound velocities and minimum thermal conductivity of LnB 2 C 2 compounds are also anisotropic. [ABSTRACT FROM AUTHOR]

Abstract The transient plane source (TPS) technique has recently garnered attention due to its ability to measure thermal properties of an extensive range of isotropic materials such as solids, liquids and powder. It also can be employed to measure thermal properties of anisotropic materials at a low cost and reduced time scale; however, it requires that thermal capacity be determined a priori in a separate experiment. In this study, a new methodology has been theoretically established to characterize the transport coefficients of anisotropic materials in both directions without requiring the measurement of heat capacity. We propose a new experimental configuration of the TPS setup which allows for measurement of the conductivity ratio of anisotropic materials and is coupled with the conventional TPS technique for anisotropic material to measure all transport coefficients, including thermal capacity. This is accomplished by measuring the samples in two different orientations and deriving a relation between the conductivity ratio and the time ratio through a specific time window during the measurement time, which depends on the sample size. The viability of this method was verified numerically by simulating the proposed approach for an ABS polymer composite material. The numerical model is further used to examine the proposed approach for different anisotropic thermal conductivity ratios ranging from 1.225 to 4. The effect of other factors—such as the influence of sensor thermal capacity and heater power—were explored. The results show that the error in predicting the thermal conductivity ratio ranges from 0.26% at an anisotropic ratio of 1.225–1.5% at an anisotropic ratio of 4. The numerical model was revised to represent a realistic embodiment of an experimental apparatus. The revised model shows that the predicted error in testing this approach experimentally will be approximately less than 8%, which demonstrates the viability of the experimental implementation of this technique. [ABSTRACT FROM AUTHOR]

The first-principles calculations were used to predict the anisotropic elasticity and thermal properties of hexagonal ( hP 4-WB 3 , hP 8-WB 3 and hP 16-WB 3 ) and trigonal ( hR 24-WB 3 ) WB 3 triborides. The single-crystal and polycrystalline elastic properties were computed from the stress-strain method and Voigt-Reuss-Hill approximations, respectively. Based on the obtained elastic modulus, two theoretical models were used to theoretically calculate Vickers hardness H V of WB 3 . The results showed that hP 16-WB 3 and hR 24-WB 3 are potential candidates for superhard materials. The elastic anisotropies of WB 3 were characterized by elastic anisotropic indexes ( A U , A comp and A shear , and A 1 , A 2 and A 3 ), three-dimensional views and projections of bulk, shear and Young's moduli. The anisotropic elasticity is ordered as hP 8-WB 3 >  hP 4-WB 3 >  hR 24-WB 3 >  hP 16-WB 3 . Furthermore, the thermal properties such as Debye temperature and sound velocity were computed from the elastic constants and moduli. Finally, the directional sound velocities were also discussed. [ABSTRACT FROM AUTHOR]

Herein, we report a fabrication of epoxy resin/oriented BN composites via a facile hot-pressing strategy. Benefitting from the force exerted vertically on the BN platelets, a well-ordered BN microstructure in the composites has been achieved, which renders the prepared composites an elevated thermal conductivity up to 6.09 W m −1 K −1  at 50 wt% loading, while it is only 2.44 W m −1 K −1 for epoxy resin/random BN composites. In addition, the composites show an enhanced tensile strength (31.79 MPa) and Young's modulus (4.63 GPa) when comparing with epoxy resin/random BN composites at the same 50 wt% loading (21.21 MPa and 1.48 GPa). We attribute the improved thermal conductivity to the well-aligned BN platelets in higher heat conduction direction based on the anisotropic thermal conduction ability of BN. The enhanced mechanical properties are ascribed to the increased friction area along the tensile in-plane direction and the decreased defects which are easily incorporated during the fabrication process. This study sheds a light for exploring future thermal management materials to meet the increasing heat dissipation demands. [ABSTRACT FROM AUTHOR]

A new pretreatment process, namely, Ar + ion beam bombardment and following deposition of a tungsten coating layer on diamond particles for fabricating diamond/copper composites is proposed in this paper. The composites are fabricated by infiltration method, and exhibited excellent thermal properties. Composition of the tungsten coated diamond particles is characterized by the Micro-XRD to investigate the effect of ion beam bombardment on the selectivity of interfacial reaction between the diamond planes and the coating layer. Scanning electron microscopy (SEM) is used to investigate the effect of the ion beam bombardment on interface structure and composition of the composites. A good interfacial adhesion without micro-gaps or cracks in the interfacial region is obtained. In addition to that, the phenomenon of selective interfacial reaction in the composite is no longer taking place, and the metal matrix uniformly adheres to all diamond planes. Therefore, the further enhancing thermal conductivity of the composites reach up to 896 W m −1 K −1 , and coefficient of thermal expansion is only 5.9 × 10 −6 K −1 . The excellent performance can be attributed to the regulated interfacial adhesion and the optimized effective interfacial thermal conductance. [ABSTRACT FROM AUTHOR]

Adding thermal conductive filler is an effective method to improve the thermal conductivity of polymer matrix. In this research, we demonstrated that the polymer composites with much improved thermal conductivity while maintaining low electrical conductivity, which could be achieved via using hybrid 2D stacked filler and controlling the alignment of the filler in polymer matrix. In order to do this, the graphene oxide (GO) was prepared and simultaneously reduced/functionalized by diethylenetriamine (DETA) to obtain NH 2 -functionalized graphene (NfG) which designed to be immobilized on the surface of large-sized insulating hexagonal boron nitride (h-BN) via π-π stacking interaction. In this situation, since the NfG sheets were fixed on the surface of h-BN, the NfG sheets were well separated from each other and participated in the resin curing process. Hence, not only significantly enhanced thermal conductivity (∼3.409 W/m·K, in-plane direction) was obtained, but also a very low electrical conductivity was achieved. The low electrical conductivity was believed to be ascribed to both embedded insulating network of h-BN to inhibit the mobility of charge carrier and well-separated NfG sheets via π-π stacking interaction. In addition, the nanocomposites also exhibited good thermal stability and adhesive properties. We believed that this special structure will provide a new thought for fabricating thermal interface materials (TIMs) with much high thermal conductivity as well as low electrical conductivity. [ABSTRACT FROM AUTHOR]

Uniaxial isothermal compression tests were conducted on cylindrical specimens extracted from an extruded AZ31B rod along both the extrusion and radial directions over the temperature range of 300 °C–500 °C, at strain rates of 10 −3 s −1 –1.0 s −1 . The anisotropy of flow observed at high strain rates in specimens oriented along the extrusion direction can likely be attributed to the dominance of tensile twinning at temperatures below 400 °C, and pyramidal slip for temperatures above 400 °C. The degree of anisotropy increased with deformation strain rate, with specimens deformed at the lowest strain rate of 10 −3 s −1 exhibiting little to no anisotropy. Samples oriented along the radial direction exhibited strong anisotropy of flow at low deformation temperatures, and the extent of anisotropy decreased with increasing deformation temperature. It was determined that the occurrence of basal slip at select locations away from the compression axis likely resulted in preferential elongation of the sample along the circumferential direction of the extruded rod. Moreover, cracking was observed at 300 °C and macroscopic shear bands were observed at deformation temperatures below 450 °C, which suggested that low temperature deformation was less favorable. It was observed that finer dynamically recrystallized (DRX) grains could be obtained by processing at lower temperatures and/or higher strain rates. However, greater microstructural homogeneity was achieved through processing at high temperatures and low strain rates. Furthermore, it was evident that the area fraction of DRX grains increased with strain. Grain growth after deformation occurs rapidly within the first 60 s, and little to no grain growth was observed beyond that. [ABSTRACT FROM AUTHOR]

The subject of the study is development of a quantitative methodology for analyzing the structure of particle reinforced composites. The methodology is based on analytical representative volume element (ARVE) theory, which was developed to determine the effective properties of fiber reinforced composite materials. Further, it can be used for investigation of homogeneous materials. The developed methodology expands the scope of possible applications of ARVE theory to the following issues: (a) comparisons of composite materials of identical composition obtained through different technological processes, (b) assessment of the stability of the technology in the context of obtaining a material of uniform distribution of the reinforcing phase, (c) designation of a minimum area representative of the material, (d) for microscopic examination, detailed analysis of the impact of changes in process parameters on the structure of the composite, etc. The important elements of the developed methodology are the homogeneity and anisotropy parameters of the composite structure. Applied together, they provide additional opportunities to quantify the impact of the selected manufacturing/treatment process parameters on its structure. It is worth noting that the developed methodology is universal and can be applied at different levels, from the reinforcing phase concentration to the effective properties of composite materials. [ABSTRACT FROM AUTHOR]

Enhancing the thermal conductivity of polymers by introducing inorganic fillers with low content remains challenge in modern electronic industries. By homogeneously incorporating both functionalised boron nitride nanosheets and graphene oxide nanosheets at low loading less than 1 wt%, a poly(vinyl alcohol) (PVA) polymer was able to reach in-plane thermal conductivity of 9.90 W/m·K as well as achieve high extensibility and toughness. Synergistic influences of both nanofillers were observed and the improved nanofiller/matrix interfaces and the nanofiller distribution were ascribed to the remarkable enhancement in thermal conductivity. The facile fabrication process has potential to be scaled-up that has significance in preparation of thermal conductive polymers and composites for heat dissipation. [ABSTRACT FROM AUTHOR]

A bottom-up approach to calculate the overall and averaged thermal properties of the jelly roll or electrode stack of Li-ion cells in a generally applicable way is introduced. The model is based on temperature-dependent material properties and is specifically applied to a prismatic hardcase cell. The geometrical properties, such as width, depth, height, porosity, tortuosity, and the saturation with electrolyte are considered. Most of the material properties are determined by own measurements within a wide temperature range and compared with literature data. Anisotropic unit cell properties for homogenised three-dimensional thermal models and the corresponding representative thermal conductivity for one- or two-dimensional models can be calculated. A non-destructive measurement technique to determine the thermal conductivity of prismatic hardcase cell geometries and validate the described model is presented. [ABSTRACT FROM AUTHOR]

Polymer infiltrating filler-network has been actively researched recently to obtain composite materials with enhanced thermal conductivities. However, the long infiltration time blocks its wide application. In this study, we prepared hexagonal boron nitride (h-BN)/poly(vinyl alcohol) (PVA) composite by combining polymer infiltration with filler diffusion through the polymer to reduce infiltration time and form heat conduction paths. Base on this process, the maximum thermal conductivities of the obtained h-BN/PVA composites were 1.63 W/m·K and 8.44 W/m·K along the through-plane and in-plane directions, respectively. In addition, the composites displayed excellent heat dissipation performance when attached on top of a light emitting diode (LED) light strip. The research results indicate our approach is facile and capable of fabricating high performance thermal interface materials. [ABSTRACT FROM AUTHOR]

A method was developed to magnetically align multi-walled carbon nanotubes (MWCNTs) as well as graphene nanoplates (GNPs) within a poly (dimethylsiloxane) (PDMS) matrix. The MWCNTs and GNPs polymer composites treated with magnetic field forming chain structures would be expected to produce anisotropic thermal conductivity. Firstly, the MWCNTs and GNPs were functionalized by γ-methacryloxy propyl trimethoxyl silane (KH570) in order to improve their compatibility with polymer matrix, and then different contents of the MWCNTs and GNPs were incorporated into PDMS and cured under a magnetic field up to 10 T to generate anisotropic MWCNTs/PDMS and GNPs/PDMS composites. The polarized Raman spectra and scanning electron microscopy (SEM) were applied to investigate the structures of MWCNTs and GNPs dispersion in the composites. The thermal conductivity of all samples was measured by using hot wire method. The results showed that the magnetically aligned MWCNTs/GNPs polymer composites feature high anisotropy in thermal conductivity. Thermal conductivity in the aligned direction of 10.0 T-treated PDMS composites with 3wt% GNPs content showed enhancements of 174% and 49%, compared to pure PDMS and non-magnetically treated GNP/PDMS composites, respectively. Compared with the MWCNTs fillers, the GNPs showed better performance in improvement of the thermal conductivity of the polymer composites. [ABSTRACT FROM AUTHOR]

The polymer/graphite based products fabricated by conventional molding method possess limited through-plane thermal conductivities (TPTCs) because the graphite flakes are strongly aligned in the in-plane direction. Based on the characteristic of fused deposition modeling (FDM, a trendy technology of 3D printing), rational design of 3D printing (3DP) process can make the graphite flakes orient along the through-plane direction. In this paper, high TPTC of polymer/graphite based products with graphite flakes vertically aligned are achieved via FDM. Although lots of voids generated during the fused deposition process, the optimal product shows a high TPTC as 5.5 W m −1 K −1 because the fluent heat conductive pathways are not blocked by the voids. Finally, a heat sink with good thermally conductive property used for the 3D printer is successfully fabricated and it can well meet the heat dissipation requirement of 3D printer. [ABSTRACT FROM AUTHOR]

In this paper we derive some identities for the solution of the problem of homogeneous and anisotropic micropolar thermoelasticity. These can be applied to proving uniqueness of the solution of the corresponding boundary initial value problem. [ABSTRACT FROM AUTHOR]

Highly anisotropic thermal conductivity, i.e., a limited through-plane thermal conductivity (λ ⊥), is normally observed in polymer composites with asymmetric fillers that are vulnerable to orientate along the flow field during melt-processing. We herein explored the possibility to tailor the filler arrangement and λ ⊥ of polymer composites with asymmetric fillers using nonconductive hollow glass microspheres (HGμS). The results showed that λ ⊥ of ultrahigh-filled polyamide 6/flake graphite (PA6/FG) composites with 70 wt% (54.7 vol%) FG increased by 27% instead of decreasing when replacing 3 wt% FG platelets with HGμS (i.e., 8.1 vol%, and 12.2 vol% HGμS with a diameter of 18 μm and 38 μm, respectively). The increase of λ ⊥ from diluting FG with HGμS was attributed to the reduced structural anisotropy of the FG network, i.e., the in-plane orientation of FG platelets within the polymer matrix was inhibited. A synergistic effect on the improvement of λ ⊥ was achieved by replacing FG platelets with combination of HGμS and alumina (Al 2 O 3) microspheres. This synergy takes the effects from the "bridging" of FG platelets by Al 2 O 3 and the inhibiting of in-plane FG orientation by HGμS. [Display omitted] [ABSTRACT FROM AUTHOR]

The rapid development of integrated circuits and electronic devices with increased power density and heat flux, requires effective heat dissipation for thermal management. Constructing a directional thermal pathway from the vertically aligned thermal conductive fillers in the thickness-direction of polymer-based thermal interface materials (TIMs) is a desirable strategy to form materials with high thermal conductivity. However, due to the complexity of vertical orientation technology, fillers with the poor orientation degree weaken the enhancement of through-plane thermal conductivity. In this work, we prepared short carbon fiber (CF)/olefin block copolymer (OBC) composites with high orientation degree via the melting extrusion method on a basis of sharing force induce alignment. Attributed to the high orientation degree of CF in the vertical direction, the as-prepared material shows a through-plane thermal conductivity (κ ⊥) up to 15.06 W/m K at a 30 vol% CF content, which is ∼10 times that of a parallel structure. The operating temperature difference between vertical and random reached 35.2 °C, surpassing the characters in most works of literature. This study provides an effective way to develop high-oriented degree and electrical insulation polymer composites with superior κ ⊥ for scalable thermal management applications in electronic devices. [Display omitted] • A facile and efficient method to obtain high orientation for polymer-based TIMs. • Excellent through-plane thermal conductivity is obtained via constructing vertical structure. • Outstanding thermal management capability is achieved as an efficient TIM. [ABSTRACT FROM AUTHOR]

Composites with high out-plane thermal conductivity (TC) and great insulation are essential for thermal management in electronic devices. Herein, a transposable, highly thermal conductive silicone rubber (SR)/boron nitride (BN) composite was fabricated by multi-layer stacked hot pressing, in which the orientation of BN was enhanced based on rheological characterizations. Then the pre-pressed films were stacked under 180 °C to get a full-cured and thick composite. The enhanced orientation of BN and the excellent heat transfer capability of the composites were well verified by SEM, XRD, 2D WAXS, finite element analysis (FEA) and infrared thermography, which resulted in a wonderful thermal pathway and low interfacial thermal resistance. The TC of the composite reached 22.08 W/(m·K), and the high in-plane TC could be converted to high out-plane TC after simple vertically cut due to the flexibility and large thickness of composite. Meanwhile, for the first time, the excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τ g). The rheological control was an efficient and potential strategy to get highly thermal conductive composites. • The silicone rubber (SR)/boron nitride (BN) composites with highly oriented BN were prepared by combining optimal pre-orientation based on rheological characterization and multilayer stacked hot pressing. • The enhanced orientation of BN and lower ITR were achieved at low viscosity (135 °C), and the TC of O-SR/BN 83.33 reached 22.08 W/(m·K). • The effect of BN with different degrees of orientation on the TC of the composite was further verified by SEM, XRD, 2D WAXS and FEA. • The excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τ g). [ABSTRACT FROM AUTHOR]

A facile strategy for effectively constructing in-plane and through-plane thermal conduction paths in polyimide (PI) and its flexible copper clad laminates (FCCLs) was reported by incorporation of hexagonal boron nitride (h-BN) in a controlled manner. The in-plane thermal conductivity pathways resulted from the micron h-BN sheets well mixed within the continuous PI matrix, while the through-plane ones were mainly constructed by the arrayed pillar-like or striped-like high concentration (65.2 wt%) h-BN nano-particles/thermoplastic polyimide (TPI) composites (acting as islands), which were distributed in the above micron PI/h-BN composite (acting as sea) and perpendicular to the direction of thickness. The specific sea-island architecture allowed the preparation of highly thermally conductive flexible PI film and its FCCLs at relatively lower total boron nitride loading. Balanced thermal conductivities and mechanical properties were achieved, for example, in the PI/h-BN composite film containing 30 wt% micron h-BN. The in-plane and through-plane thermal conductivities increased from 0.18 W m−1 K−1 and 0.15 W m−1 K−1 of neat PI film to 2.56 W m−1 K−1 and 0.57 W m−1 K−1, respectively. Meanwhile, the tensile strength and elongation at break can remain at 98.4 MPa and 8.7%. Interestingly, when the pillar-like high concentration h-BN nano-particles/PI composites were present, the in- and out-plane thermal conductivities of the composite films considerably increased to 5.03–6.32 and 1.27–1.29 W m−1 K−1, although the total BN content was only raised by ∼1 wt%. The results of the current work may open a new avenue for promoting the practical application of thermally conductive PI based FCCLs. [Display omitted] 1. High thermal conductive flexible copper clad laminate is made by a simple method. 2. Sea-island structured BN/PI composite favors improving bidirectional heat conduction. 3. Mayer rod coating coupled with hot pressing enhance orientation of BN platelets. [ABSTRACT FROM AUTHOR]

First principles calculations are performed to systematically investigate the electronic structures, elastic, anisotropic and electronic properties of the monoclinic, tetragonal and orthorhombic structures of Si3N4 under pressure. Anisotropy studies show that three Si3N4 phases exhibit a large anisotropy. Furthermore, using the HSE06 hybrid functional, the monoclinic, tetragonal and orthorhombic phases are found to be wide band-gap semiconductors. The pressure induced band gap directindirect transition is found for monoclinic Si3N4. The elastic modulus, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in three Si3N4 phases are also investigated in detail. [ABSTRACT FROM AUTHOR]

Electrically insulating polymeric nanocomposites with high thermal conductivity have great potential for use as thermal-management materials in increasingly high-power-density electronics and optoelectronics. Conventional composite materials require a large amount, over 70 vol%, of electrically conducting fillers such as carbon allotropes to attain thermal conductivities of 1–5 W/mK, [Balandin, 2011] [1] which restricts the utility of these materials to applications that require both electrical and thermal conductivities. Here, we introduce a strategy to achieve the strongest enhancement of thermal conductivity to date at a low level of filler loading (≤15 vol%) in insulating polymer nanocomposites with hexagonal boron nitride (BN) nanosheets. The combination of electric-field switching and the application of fillers with various aspect ratios enables the rearrangement of the BN nanofillers into linear densely packed BN structures (LDPBNs). Flexible nanocomposite films with LDPBNs exhibit electrical resistivity greater than 1.50 × 10 −6 MΩ cm and a thermal conductivity of 1.56 W/mK, a dramatic enhancement over that of pristine polysiloxane with the same BN loading (0.4 W/mK). Our strategy of electric-field-induced BN nanosheet assembly offers insight into the possibility of solving thermal-management problems using ideal thermal interface materials, thus enabling improved next-generation integrated circuits and nanoelectronics. [ABSTRACT FROM AUTHOR]

Polymer composites containing two-dimensional hexagonal boron nitride (h-BN) can achieve enhanced thermal conductivity (TC), and such enhancement is more pronounced along the orientation direction of h-BN platelets. In this paper, an analytical model was developed for simultaneously calculating the anisotropic TC of polymer composites containing aligned h-BN platelets. A unit cell was first abstracted based on the morphological observation in the literature. Then the thermal resistance method and coordinate transformation were used to derive the TC of the composites. The model was successfully validated by the experimental data from two independent literature studies over a large range of filler contents. The dependence of TC on the key parameters of the model, including the orientation angle and geometric dimension of the h-BNs, and the interfacial thermal resistance, were quantitatively analyzed and discussed. [ABSTRACT FROM AUTHOR]

We determined the crystalline characteristics of the hexagonal α-alumina phase by X-ray diffraction at high temperatures between 293 and 2308 K under dynamic vacuum then under constant flow of nitrogen. The experimental values obtained under dynamic vacuum allow to deduce, an anisotropy of the ‘c’ direction compared to the ‘a’ direction of approximately 12% in the range of 293 K–1760 K. On the other side, no anisotropy remains above 1765 K. This anisotropy reflects the fact that aluminum atoms occupy 2/3 of the octahedral sites in the compact hexagonal sublattice formed by the oxygen atoms. We have also reacted alumina when heated under a constant flow of nitrogen. Nitriding alumina occurs around 1765 K and then forms aluminum mononitride, AlN, ZnS-Wurtzite type hexagonal structure. The thermal expansion of this mononitride cell is linear and is characterized by an anisotropy of the direction 'a' in comparison to the direction 'c' of about 17%. [ABSTRACT FROM AUTHOR]

Large crystal of the nonlinear optical and polar oxide Cs 2 TeW 3 O 12 with a size of 20×15×4 mm 3 has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808 °C and melts incongruently. It possesses a large transparent range of 0.415–5.250 μm. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30–390 °C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28 MW/cm 2 with a laser wavelength of 1064 nm and pulse duration of 8 ns. [ABSTRACT FROM AUTHOR]

Ice-templated waxy maize starch. [Display omitted] • Neat anisotropic waxy maize starch cryogels were made via ice-templating method. • The morphology varied from lamellar to sponge-like, controlled by starch concentration. • Cryogels possess anisotropic mechanical and thermal conductivity properties. • Cryogel compression in the transverse direction leads to thermal conductivity decrease. Biodegradable anisotropic neat porous starch materials without any additional cross-linking, plasticizer or any extra matter have been fabricated via facile ice-templating method. Waxy maize was dissolved in water followed by unidirectional freezing and ice sublimation. The influence of process parameters (starch concentration and retrogradation time) on the morphology, density, mechanical properties under the uniaxial compression and thermal conductivity were investigated. The internal morphology and the shape of the pores, from lamellar to sponge-like, was shown to be governed by starch concentration. All porous starches have very low density (0.07–0.15 g/cm3), anisotropic mechanical properties and low thermal conductivity, in particular in transverse direction (0.037–0.048 W/(m·K)). Interestingly, when compressing the ice-templated starches in the transverse direction, the thermal conductivity was further decreased reaching the values of 0.033 W/(m·K). This work provides the guidelines for making fully biobased porous starch materials with controlled morphology and properties. [ABSTRACT FROM AUTHOR]

Each type of natural stone has its own geological history, formation conditions, different chemical and mineralogical composition, which influence its possible anisotropy. Knowledge in the natural stones anisotropy represents crucial information for the process of stone quarrying, its correct usage and arrangement in building applications. Because of anisotropy, many natural stones exhibit different heat and moisture transport properties in various directions. The main goal of this study is to analyze several anisotropy indices and their effect on heat transport and capillary absorption. For basic characterization of studied materials, determination of their bulk density, matrix density and total open porosity is done. Chemical composition of particular sandstones is analyzed by X-Ray Fluorescence. Anisotropy is examined by the non-destructive measurement of velocity of ultrasonic wave propagation. On the basis of ultrasound testing data, the relative anisotropy, total anisotropy and anisotropy coefficient are calculated. Then, the measurement of thermal conductivity and thermal diffusivity in various directions of samples orientation is carried out. The obtained results reveal significant differences between the parameters characterizing the heat transport in various directions, whereas these values are in accordance with the indices of anisotropy. Capillary water transport is described by water absorption coefficient measured using a sorption experiment, which is performed for distilled water and 1 M NaCl water solution. The measured data confirm the effect of anisotropy which is qualitatively the same as for the heat transport parameters. Summarizing the obtained results, it can be concluded that the anisotropy of sandstone should always be considered in planning the restoration works on the architectural heritage, in order to ensure compatibility between the original and replacement material. [ABSTRACT FROM AUTHOR]

Two or more multi-component system of didodecyl dimethyl ammonium bromide (DDAB), cholesteryl nonanoate (CN) and ethylene glycol (EG) exhibits an interesting different liquid crystalline cholesteric and induced smectic phases, such as SmA, SmC and SmB, sequentially when the specimen is cooled from its isotropic liquid phase. These phases have been characterized by using optical texture studies. The temperature variations of optical anisotropy, helical pitch measurements and electrical conductivity have been also discussed. XRD results have also been reported. [ABSTRACT FROM AUTHOR]

Dielectric composites aimed for high frequency applications were prepared by using anisotropic hexagonal boron nitride (hBN) particles as a fillers and isotactic polypropylene (iPP) as polymer matrix. Dielectric and thermal properties of the composites were studied, focusing on the filler orientation in the plate-shape specimens and filler concentration up to 40 vol%. The degree of orientation of the filler was controlled by the composite fabrication process. Hot-pressing gave relatively random orientation of the filler in the matrix, while injection molding induced a high orientation. Dielectric constant ( ε r ) of the composites ranged between 2.25 and 3.39. The estimation of ε r based on the Bruggeman mixing model agreed well with the measured value. Low dielectric losses (tan δ ) at microwave frequencies, on the order of 10 −4 , were obtained for all the compositions. Through-thickness thermal conductivity ( k ) of the hot-pressed samples showed a drastic increase with increasing the filler concentration, reaching up to 2.1 W/m K at 40 vol% of hBN. The filler concentration dependence of k was less significant for the injection molded composites. In-plane thermal expansion was almost independent on the filler orientation, while the coefficient of thermal expansion for the thickness direction of the hot-pressed sample was reduced to approximately half of the injection molded counterpart. These differences in thermal conductivity and thermal expansion are thought to arise from the difference in hBN filler orientation. [ABSTRACT FROM AUTHOR]

This paper presents the results pertaining to thermal and magnetic studies of rapidly-cooled samples of the alloy family Fe61Co10B20Y8Me1 (where Me = Nb, Zr, W, Mo). The resulting ribbons, or tapes, have amorphous structure. It has been found that the addition of Me elements alters the thermal and magnetic properties. It is noted that the saturation magnetization decreases with increasing number of unpaired electrons on the valence shells. In addition, the value of the coercivity and effective anisotropy have been determined. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nd:Sr3La2(BO3)4 crystal was grown by the CZ method. [•] The complete set of anisotropic thermal properties was systematically studied. [•] Polarized absorption and fluorescence spectral were measured. [•] CW laser operations at 1.06μm of Nd:Sr3La2(BO3)4 were demonstrated for the first time. [ABSTRACT FROM AUTHOR]

Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti2 AlC and Cr2 AlC, are studied by combining first-principles method and lattice dynamic calculation based on the quasi-harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti2 AlC and Cr2 AlC show different trends: Ti2 AlC exhibits anisotropic thermal expansion while Cr2 AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti2 AlC and Cr2 AlC. In addition, the calculated bulk modulus of Cr2 AlC is higher at ambient temperature but decreases faster than the value of Ti2 AlC as temperature increasing. [ABSTRACT FROM AUTHOR]

Abstract: Starting from theoretical calculations based on LSDA, the authors compute the lattice parameters, cohesive energies and formation enthalpies of monazite-type REPO4 compounds. The calculated values are satisfactory compared with the experimental results from the elastic constants obtained, the mechanical moduli are evaluated using the strain–stress method. The predicted bulk, Young’s and shear moduli are in good agreement with the experiments. It is shown that the mechanical moduli are low (<200GPa) and also increase from LaPO4 to GdPO4. The three-dimensional contours and their planar projections of Young’s modulus are plotted to illustrate the anisotropy in elasticity. It is found that Young’s moduli of all monazite-type REPO4 show strong dependence on direction. The linear thermal expansion coefficients are calculated using the empirical method, and the values are in the range 9×10−6–12×10−6 K−1. Using Clarke’s and Slack’s models, the thermal conductivities of REPO4 compounds obtained are close to the experimental profiles. The observed anomalies of experimental thermal properties of monazite-type GdPO4 are also explained based on the observed monazite to zircon-type transformation in experiment. Solving the Christoffel equation for monoclinic symmetry, the anisotropy in thermal conductivity is investigated. The results indicate that the total lattice thermal conductivities of monazite-type REPO4 show weak dependence on direction. Meanwhile, their sound velocities exhibit strong anisotropic properties. [Copyright &y& Elsevier]

Abstract: The thermal properties of sub-μm nanocrystalline diamond films in the range of 0.37–1.1μm grown by hot filament CVD, initiated by bias enhanced nucleation on a nm-thin Si-nucleation layer on various substrates, have been characterized by scanning thermal microscopy. After coalescence, the films have been outgrown with a columnar grain structure. The results indicate that even in the sub-μm range, the average thermal conductivity of these NCD films approaches 400Wm−1 K−1. By patterning the films into membranes and step-like mesas, the lateral component and the vertical component of the thermal conductivity, klateral and kvertical , have been isolated showing an anisotropy between vertical conduction along the columns, with kvertical ≈1000Wm−1 K−1, and a weaker lateral conduction across the columns, with klateral ≈300Wm−1 K−1. [Copyright &y& Elsevier]