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Extremely low lattice thermal conductivity is always the pursuit of thermoelectric materials research. In this work, we reported an exceptional effect of Ag2S addition in MnTe, an emerging promising mid-temperature thermoelectric material, to enable the realization of minimum lattice thermal conductivity, namely ∼0.4 Wm−1K−1. Such a low lattice thermal conductivity is guaranteed by the incorporation of in-situ formed Ag rich phase (Ag2Te) with ultralow lattice thermal conductivity and further scattering of phonons from the partial doping effects induced point defects and boundaries between various phases. Apart from the dramatically decreased lattice thermal conductivity, the partial doping of Ag and S simultaneously enhance the electrical conductivity, further contributing to enhanced thermoelectric performance. Meanwhile, an inverse sign of Seebeck and Hall coefficient was observed and rationalized by the influence of highly electron-conductive Ag2Te phase. Thanks to the synergetic modulation of electrical and thermal transport properties by in-situ formed composite, a high ZT value of 1.1 was achieved in MnTe based thermoelectric materials, which also demonstrates the importance of compositing approaches to design state-of-the-art thermoelectric materials.

Sodium silicate based ceramic coatings were prepared on the surface of carbon fiber reinforced epoxy resin matrix composite. The coatings were obtained by curing the mixture of silicate adhesive, SiO2 or Na2SiF6 as curing agent, and YSZ and Al2O3 as filler. The effects of adhesive modulus, curing agent, curing temperature and time on curing behavior of the coatings were investigated. The results indicated that the coating obtained from 2.7 modulus of silicate adhesive was dense, cohesiveness, uniform and continuous. As curing agent, SiO2 could promote curing better than Na2SiF6, achieving complete curing of the coating. And the coating containing SiO2 as curing agent was dense, flat and well adhered to the substrate. The curing behavior of coatings was significantly affected by curing temperature and time. The coatings could be cured completely with the increase of curing temperature. The best curing result was obtained at 100 °C curing temperature. Also the experimental results showed that the characteristics of coatings were improved to a certain extent by prolonging the curing time.

We report a detailed analysis of the crystal structure, electronic structure, and thermoelectric (TE) properties of a stoichiometric Mn2CoAl inverse full-Heusler alloy, which has been predicted to ...

Faced with the challenge of high energy ablation problems, especially for laser ablation, effective energy dissipation protective materials fabricate by efficient preparation method is a feasible solution. The Ni-graphite/SiO2 coatings with different Ni content were prepared by plasma spraying method with optimized plasma spraying parameters. All coatings are pure without oxidation and dense. Their ablation behaviors were investigated by high power continuous wave laser. The results indicate that the Ni-graphite/SiO2 coating with appropriate Ni content could realize the purpose of energy consumption by endothermal reaction of graphite/SiO2 and reflection improvement. High Ni content will block the occurrence of endothermal reaction of graphite/SiO2 and increase the heat diffusion to interior part of coating, which can make the ablation situation of coating more serious.

The increasingly serious service condition in aerospace industry has posed a higher requirement to the ablation resistance of hypersonic vehicle structural carbon fabric-reinforced phenolic composites. To further enhance the ablation resistance of the composite, different contents of TaSi2-modified carbon fabric-reinforced phenolic composites were successfully prepared. The ablation behavior and mechanism of these composite were investigated. Results showed that the ablation resistance of the modified composite was significantly improved due to the addition of the TaSi2. When the mass fraction of TaSi2 on the matrix resin was 50 wt%, the mass and liner ablation rate of the modified composites were 30% and 12% lower than those of the unmodified composites, respectively. The formed double-layer structural residue acted as an insulating layer and effectively obstructed the flame flow and oxygen to the inner material. Moreover, the occurrence of the endothermic reactions and the evaporation of the reaction gases further dissipated the heat energy. The multi-effect synergy mechanism effectively reduced the thermal oxidative ablation degree of the modified composites. All these results confirmed that the TaSi2-modified composite exhibits excellent oxidative ablation resistance, which provided a basis for the application of composite to more serious service environments.

The laser-matter interaction contains complex thermophysical and thermochemical responses. The variation of energy and composition happen in thermophysical and thermochemical process will totally change the interaction behaviors. In order to obtain an accurate mechanism and promote the understanding of laser-matter interaction, all thermophysical and thermochemical responses, especially the thermochemical part, should be considered and investigated. In this study, a coupled heat-matter diffusion model based on thermodynamic chemical equilibrium finite-element method and thermochemical ablation theory was established. The materials with complex reaction enthalpy change in high temperature environment were chosen to validate the model. The results show that this model is accurate, as the maximum error of back-surface temperature response is just 4.0% between experimental and calculation values. The detailed variations of composition, temperature and optical reflection were obtained and analyzed, which is in good agreement with the experiment. This coupled heat-matter diffusion model including all thermophysical and thermochemical response has the great potential in nearly all laser-matter interaction involved application.

Laser, especially high energy continuous-wave (CW) laser, can destroy traditional structure material of aircrafts or vehicles easily. Therefore, anti-laser damage is gradually becoming a major concern. In this case, calcium carbonate (CaCO3)-filled phenolic matrix composite coatings have been designed and prepared to prevent from high energy CW laser damage. Laser ablation behavior of the coating is deeply studied by varying the laser parameters including laser power density and irradiation time. The results show that the phenolic resin keeps decomposing into residual char caused by the high temperature during laser irradiation. The porous structure of phenolic resin of residual char provides an excellent thermal insulation property for the coating. In addition, the decomposition reaction of CaCO3 consumes a large amount of laser energy, which has a cooling effect on the residual char. CaO that is produced during the decomposition of CaCO3 has a high melting temperature and can lead to the thermal stability improvement of the residual char. Due to the introduction of CaCO3, the back-surface temperature of sample is decreased from 94 °C to 64 °C when irradiated at 500 W/cm2 for 10 s and the anti-laser property of the coating is improved. All the analysis indicate that the designed coating can perform as a shield to prevent from high energy CW laser.

In this paper, copper–graphene composites were fabricated by using two different processing routes (ball milling (BM) and ultrasonication) followed by spark plasma sintering. Vickers hardne...

Faced with the challenge of ultra–high–temperature ablation problems, multi-synergy and efficient energy dissipation method is a feasible solution. A structure-modified silica-graphite composite with multiple copper layers was prepared by hot-pressing. The ablation behaviors and mechanisms were analyzed in detail. During the laser ablation, the designed composite exhibits excellent ablation resistance with a multi-synergy effects strategy. As ablation time increases, the ablation mechanisms change from reflection and horizontal thermal diffusion to reaction and horizontal thermal diffusion and vertical heat insulation. Moreover, the gap generated by the reaction volume contraction can further insulate against heat transfer in the vertical direction. The rate of increase of back-surface temperature can be further reduced. This multi-synergy effects strategy and designed structure accompanied with appropriate materials can greatly enhance the ablation resistance ability of the composite.

Further utilization of aircraft structural materials is threatened by the fact that high-intensity continuous lasers are widely used in the field of military defense. To protect the aircraft structure from laser damage, ammonium polyphosphate filled polybenzoxazine composite coatings were prepared on the substrate. The anti-laser ablation characteristics of the coatings were investigated. Results showed that the addition of the inorganic filler improved the anti-laser ablation performance of polybenzoxazine. The back-surface temperature of substrates covered with the composite coatings was more 50% lower than that in the case of a pure polybenzoxazine coating after laser ablation. Further, the residue of the composite coating could be vertically divided into three distinct regions, with the dense surface char layer and the porous pyrolysis layer acting as shielding layers for the laser beam and preventing any heat-related transformations from occurring. The addition of the inorganic particles improved the surface reflectivity of the coatings resulting in much more laser energy dissipation. The decreased pyrolysis rate ensured that the pneumatic cooling effect of pyrolysis gas was more lasting and stable, owing to which the composite coatings could act as effective thermal protection layer for longer. These results confirmed that the inorganic filler modified polybenzoxazine coating exhibits excellent anti-laser properties and are suitable for protecting structural materials from laser-related damage.

During the fabrication of functional high-endothermic-enthalpy graphite/SiO2 composite coating, the oxidation and vaporization of raw materials have become serious issues in hyperthermal preparation environment. In this study, these issues were addressed through densification and modification of the feedstock powder. Then, the corresponding coating was prepared by optimized plasma-spraying parameters. By investigating the modified feedstock powder and the resulting splats and coatings by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy, we realized an optimized composite feedstock powder preparation process and an ideal coating structure. The compactness of the powder reached its optimum after treating at 1400 °C for 2 h. After heat treatment densification and Ni shell covering processes, the modified powder exhibited good oxidation resistance, vaporization resistance, and spreading performance during plasma spraying. Thus, a pure and dense composite coating was prepared. Positive laser resistance performance was observed during the initial laser ablation test, which proved that this modified graphite/SiO2 coating has good application potential in the laser protection field. Moreover, this study provides an experimental basis and a feasible method for difficult-to-spray composite coatings’ preparation, such as graphite/SiO2 composite.

Full-Heusler compounds exhibit a variety of magnetic properties such as non-magnetism, ferromagnetism, ferrimagnetism and anti-ferromagnetism. In recent years, they have attracted significant attention as potential thermoelectric (TE) materials that convert thermal energy directly into electricity. This chapter reviews the theoretical and experimental studies on the TE properties of magnetic full-Heusler compounds. In Section 1, a brief outline of TE power generation is described. Section 2 introduces the crystal structures and magnetic properties of full-Heusler compounds. The TE properties of full-Heusler compounds are presented in Sections 3 and 4. The relationship between magnetism, TE properties and order degree of full-Heusler compounds is elaborated.

The using performance of carbon fabric reinforced phenolic composites in the aerospace industry is determined by the fibre/matrix interfaces performance and ablation resistance. To enhance these properties, a functionalized ZrSiO4 sol was prepared and sprayed onto carbon fabric, and then the coated fabric was impregnated with resin to fabricate the composite. The ablation resistance and interlaminar shear strength of the composite were investigated. Results showed that the functionalized ZrSiO4 sol had positive effect on composite modification. Due to the improved interfacial adhesion between the carbon fabric and resin, the shear strength of the functionalized ZrSiO4 sol modified composite increased by 11% compared to the unmodified composite. Furthermore, the mass ablation ratio of the functionalized ZrSiO4 sol modified composite was 30% lower than that of the unmodified composite. The surface ceramic layer with a main phase composition of ZrO2 provided an oxygen insulating effect and protected the inner material from serious oxidative ablation. These results confirm that the interlaminar shear strength and ablation resistance of the composite were both significantly enhanced, making this composite be suitable for more severe ablation environments.

To explore full-Heusler compounds with positive Seebeck coefficient, we calculated thermoelectric (TE) properties of several Co- and Mn-based full-Heusler compounds. Relatively high Seebeck coefficients were obtained in the calculation, indicating a potential of full-Heusler compounds as TE materials. As a candidate, we prepared a Mn2VAl sample and measured its TE properties. As predicted in the calculation, the Mn2VAl sample exhibited a positive Seebeck coefficient from 315 K to 1020 K. The maximum power factor was 2.7 × 10−4 Wm−1 K−2 at 717 K. This study embodies great significance for future study on design and fabrication of full-Heusler compounds with high TE properties.

Lead-free manganese telluride has been considered to be a promising candidate for mid-temperature thermoelectric materials. In this work, we report point defect scattering-induced reduction of thermal conductivity in MnTe with Se alloying, fabricated by a facile method combining mechanical alloying and spark plasma sintering. A low lattice thermal conductivity of 0.56 W/mK was obtained for MnTe0.92Se0.08, which is quite close to the amorphous limits. A detailed Debye model analysis reveals the underlying mechanism of phonon scattering and well predicts the thermal conductivity with different contents of Se. Meanwhile, a slight increase of carrier concentration was also observed after Se alloying, accompanied by a variation of energy gap that may be associated with the competition among anions in trapping charges. Further Na doping leads to enhanced electrical transport properties, achieving a maximum ZT value of 1.03 at 873 K. An average ZT of 0.52 and a calculated efficiency of more than 9% also suggest ...

In this paper, aluminium phosphate binders were synthesized using $$\hbox {Al}(\hbox {OH})_{3}$$ and $$\hbox {H}_{3}\hbox {PO}_{4}$$ as the raw materials. These binders, with the curing agent MgO and filler $$\hbox {ZrO}_{2}$$ , were used to prepare coatings by brush painting on the carbon fibre-reinforced epoxy resin matrix composites. The influences of synthesis conditions such as the P/Al ratio, concentration of the reactant and reaction temperature on the viscosity of binders and the bonding strength of corresponding coatings were investigated by using a viscometer and a universal testing machine. The structures and compositions of aluminium phosphate binders were characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. The results show that with a decrease in the ratio of P/Al, the degree of polymerization of the aluminium phosphate binder increases, the viscosity increases, while the bonding strength of the coating decreases. When $$\hbox {P}/\hbox {Al}=3{:}1$$ , the reaction product is $$\hbox {Al}(\hbox {H}_{2}\hbox {PO}_{4})_{3}$$ with the best properties of bonding strength. As the concentration of phosphoric acid solution increases in the range of 60–80%, the viscosity increases on account of larger quantity of viscous molecules in a unit volume and higher extent of polymerization of the phosphorus oxygen tetrahedron. The compositions of aluminium phosphate binders are almost the same when the reaction temperature changes from 120 to $$180{^{\circ }}\hbox {C}$$ , so the viscosity of the binder and the bonding strength of the coating do not exhibit obvious changes along with temperature.

Recently, metals with graphene and graphene oxide have been extensively used to enhance the mechanical and anisotropic thermal properties of composites. A novel facile fabrication approach of layer by layer self-assembly followed by hot press sintering was adopted to make copper–reduced graphene oxide composites. The microstructure and heat dissipation properties of pure copper and copper–reduced graphene oxide composites were analyzed with the help of SEM and continuous laser machine analysis. Thermal diffusivity of pure copper and copper–reduced graphene oxide composites was examined in different directions to measure the anisotropic thermal properties by using different volumetric percentages of reduced graphene oxide in the composites. Extraordinarily high anisotropic thermal conductivity of the copper–reduced graphene oxide composites was obtained at a very low concentration of 0.8 vol% reduced graphene oxide, with the difference between the thermal conductivity in-plane and through-plane being a factor of 8.82. Laser test results confirmed the highly anisotropic behavior of our copper–reduced graphene oxide composite with the remarkable property of heat dissipation. The three point bending test was also performed to check the flexural strength of the composites. At 0.6 vol% rGO, the flexural strength was noted (∼127 MPa), and it is 22% higher than that of pure sintered Cu. The high value of anisotropic thermal conductivity and higher flexural strength exhibited by the copper–reduced graphene oxide composite produced using a simple two-step fabrication method give us new hope to use these materials as heat sinks in thermal packaging systems.

Here, the author fabricated copper-reduced graphene oxide composites by using conventional powder metallurgy technique by varying the amount of reduced graphene oxide. SEM and Raman analysis were used to characterize micro-morphology and disorder in the bulk composites. Tensile, thermal and microhardness testing were conducted to observe the behaviour of Cu-rGO composites. Interesting results were obtained after testing; the materials ultimate tensile strength, ductility, thermal conductivity and hardness were increased significantly compared to pure Cu. An increase in 31% ultimate tensile strength, ~200% ductility, 9.5% thermal conductivity and 90% hardness were noticed by using a very small amount of rGO 0.5 wt%. Laser irradiation test was also proved the good heat dissipation properties of Cu-rGO composites by increasing the amount of rGO. This extraordinary simultaneous increase in mechanical and thermal properties is remarkable and gave us a new way for the fabrication of higher strength-ductility and strength-conductivity based composites.

Full-Heusler compounds have three crystal structures with a different order degree; the highly ordered L21, partially disordered B2, and completely disordered A2 structures. To reveal the effects of the order degree on thermoelectric (TE) properties of the full-Heusler compounds, Mn2VAl samples with varied L21 and B2 order degrees are prepared by changing preparation conditions, and their Seebeck coefficients and electrical conductivities are measured in a wide temperature range. As the B2 order degree becomes higher, the Seebeck coefficient increases, leading to the increase of the power factor (PF). The maximum PF is 2.84 × 10−4 Wm−1 K−2 at 767 K for the Mn2VAl sample with the highest B2 order degree. This study demonstrates that the TE properties of Mn2VAl can be enhanced by increasing the fraction of the B2 phase. A relation between the Seebeck coefficient and crystal structures is also discussed based on the calculation of the electronic density of states of Mn2VAl with the L21 and B2 structures.

The good interface bonding is the basic requirement of metal-graphene composites to improve their mechanical properties. Here, we fabricated the hybrid composites through traditional powder metallurgy method. SEM and XRD were conducted to elaborate the microstructure and crystal orientation of powder as well as bulk composites. Tensile and hardness test was carried out to check the effect of graphene on copper-titanium carbide composite. Titanium carbide/copper-graphene (0.1 wt%) composite have excellent yield strength, ultimate strength and hardness higher than pure copper and also from copper-titanium carbide composite. The thermal conductivity values and anisotropic thermal conductivity ratio of titanium carbide/copper-graphene (0.1 wt%) composite are also far better than pure Cu. The results of mechanical and thermal properties demonstrate that these materials can be a better candidate to use in the thermal packaging system.

In this study, the effect of novel metal tantalum was investigated on the properties of copper-graphite composites. The complete mechanical behavior of copper-tantalum-graphite hybrid composites was examined. The addition of tantalum increased the compressive, tensile and bending strength of composites as well as the hardness and thermal conductivity. The compression, tensile, bending and hardness values for Cu–Ta-GF (0.5) composites are 20.7%, 138%, 69% and 93% higher than pure Cu and these are also far better than Cu-GF composites. The excellent mechanical and thermal properties with good relation of strength-ductility ratio open up a new window to use these materials as heat sinks in thermal packaging system.

Benzoxazine resin with good heat resistance, low combustion heat release and high char yield is a promising thermosetting resin. Meanwhile, research shows that the inorganic filler can effectively improve the thermodynamic property of the resin. It makes that the inorganic filler modified benzoxazine may have a potential application in laser ablation. The benzoxazine coating with and without inorganic filler ammonium polyphosphate, melamine and pentaerythritol (P-BOZ and BOZ) were prepared by brush and thermal curing method. The ablation properties of these coatings irradiated by high-intensity laser were investigated. The scanning electron microscope, Raman spectroscopy and thermal gravimetric analysis were used to characterize the micrographs, carbon layer structure and thermodynamic property of the sample. Results show that the composite coating has excellent thermal protective properties. The back temperature of 20 wt% P-BOZ coating under different parameter laser power (1000W/cm2, 5s; 1000W/cm2, 10s) are 40% lower than these of the BOZ coating and the 20 wt% P-BOZ has higher mass ablation rate. In the surface layer of the irradiated area, dense carbon layer is produced which reduces the absorb of the laser energy of the interior. In the interior of the sample, a large number of closed bell shaped holes are generated which are beneficial to obstruct the heat conduction.

Copper-reduced graphene oxide composites having good anisotropic thermal conductivity and hardness values fabricated via flake powder metallurgy route. SEM was performed to examine the microstructure of powders and also different composites. Anisotropic thermal diffusivity and micro-hardness test were performed to examine the different concentrations and particle sizes effect on composites. The best thermal conductivity ratio was obtained at 5 wt% reduced graphene oxide (rGO) at 9.5 μm particle size. Moreover, the extraordinarily high value of hardness (85 HV) copper-reduced graphene oxide composite was acquired at 3 wt% rGO with 9.5 µm particle size. Keywords: Metal matrix composites, Different particle sizes, Hardness, Anisotropic thermal conductivity

UASB, bio-contact oxidation, coagulation and floating process was adopted in treatment of juice wastewater. Operation results show that when the main pollutants of COD, BOD and SS in the influent were 6033 mg•L-1, 2512 mg•L-1 and 2200mg•L-1, the effluent could reach 63 mg•L-1, 25 mg•L-1 and 29 mg•L-1, respectively, with the removal rate of 99.0 %, 99.0 %, 98.7 %. The effluent reached the I-class criteria specified in Integrated Wastewater Discharge Standard (GB8978-1996) (COD < 60 mg•L-1, BOD < 20 mg•L-1, SS < 20 mg•L-1). The process provides a practical reference for the similar high concentration organic wastewater treatment processing.