Abstract:In the brazing process, the powder brazing filler metal is widely used. It is often used not only in the production of some complicated workpieces but also in the process production of repair welding and incomplete penetration. Besides, it can also be used in automated production, with a promising future. Due to their large specific surface area, the silver-based powder filler metal easily suffers an increase in oxygen content. However, few systematic studies have been conducted on the effect of the oxygen content on the performance of silver-based powder brazing filler metals. In this study, both density functional theory (DFT) calculations and a variety of analytical methods were employed to study the effects of increased oxygen content on the melting characteristics and brazed joint mechanical properties. The results revealed that the apparent activation energy of the filler metal increased with the increasing oxygen content, resulting an increased melting time. The tensile strength of the brazed joints decreased nonlinearly with the increasing oxygen content in the filler metal. To ensure good performance of brazing filler metals, the filler metal oxygen content should be controlled to be less than 200 ppm. According to the fatigue testing results, the oxygen induced brazing defects severed as a source of fracture cracks. Our studies provided a detailed mechanism of the oxygen effects on the brazing process of the silver-based powder filler metals.

Abstract:The superplasticity of fine grained Ti-6Al-4V wide sheet was investigated by constant strain rate tensile method in this work. The superplastic tensile tests were carried out at temperatures ranging from 1103K to 1223K and strain rates from 3.2×10-4 s-1 to 1×10-2s-1. The tensile elongation to failure values between 100% and 604% were obtained. Microstructure evolution and deformation mechanism were analyzed. The main deformation mechanism was grain boundary sliding, accommodated by matrix dislocation movement and the intragranular slip of β phase. It was also found that the Ti-6Al-4V wide sheet showed anisotropy when deformed at lower temperatures, which was obviously reduced when deformed at higher temperatures.

Abstract:Four different kinds of TC18 Ti matrix composites containing trace TiB and TiC are fabricated by in-situ synthesis method in this work. The experiments show that the merging of β grains is accelerated with increasing the reinforcements during heat treatment, and the standard deviations of β grain size distributions tend to decrease. The microstructure phenomenon is associated with the influence of the reinforcements on the boundary migration of β grains. It is revealed that the decrease of the pinning capability of the reinforcements on the grain boundary migration plays the most important role in the microstructure refinement law. The plasticities of the composites are excellent during tensile test. However, when the molar ratio of TiB to TiC in the composites is 4:1, the yield ratios of the composites are all higher than 0.96, and gradually increase with the increase of the reinforcements. The grain boundaries absorb the dislocations, which slows down the increase of dislocation strengthening during the strengthening process. It is suggested that the reinforcements accelerate the absorption of dislocations, and thus lead to this result. Just because of this, the contribution of the microstructure refinement to the toughness increases with the increase of reinforcements.

Abstract:The weakness of wear resistance and corrosion resistance of titanium alloy has become a bottleneck restricting the use of titanium alloy. In this work, the micro-arc oxidation coating is performed on TC11 sample in electrolyte prepared by sodium silicate (Na₂SiO₃) and sodium tungstate (Na₂WO₄). Scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness tester are used to observe the coating surface and cross-sectional morphology, micro-hardness of the inner and outer ceramic coating. The coating is mainly composed of TiO₂, γ-Al₂O₃, and Al₂TiO₅. TiO₂ consists of anatase-TiO₂ and a small amount of rutile-TiO₂. The outer coating contains a large amount of amorphous SiO₂. The electrochemical corrosion and general corrosion of the coating are comparatively analyzed in 3.5% NaCl and 30% H₂SO₄ solution, and the coating obtained in the 30% H₂SO₄ solution has a lower self-corrosion current density. Finally, the wear mechanism of the coating is studied by the anti-wear experiment with SiC.

Abstract:As a phase change material for solar energy storage at moderate- high temperature, the molten eutectic chloride salt of a sodium chloride and a magnesium chloride (NaCl-52 wt% MgCl2) is strongly corrosive to metal container and pipes. The corrosion behavior of three kinds of iron-chromium-nickel (Fe-Cr-Ni) alloys and a carbon steel in the molten eutectic salt at 520℃ were studied. Results show that the carbon steel is corroded along grain boundary for a iron atom become ferrous ion (Fe2+) and ferric ion (Fe3+). A thick and compact magnesium oxide (MgO) shell is formed on the carbon steel surface, which protects the specimen from corrosion. The MgO shell also formed on the three kinds of iron-chromium-nickel alloy surface, but the magnesium oxide shell can’t protect them from corrosion in the molten salt. Because a loose skeletal microstructure rich Ni is formed on specimen surface for the chromium element is preferentially corroded. The magnesium oxide (MgO) shell or particles peel off easily. In addition, the higher of the content of the chromium, the more serious of the corrosion As a vessel or pipe material for solar energy storage by molten chloride salt, a cheap iron-based alloy with alloy element nickel is more development prospects.

Abstract:In this paper, series micro-scale powders with composite microstructure in CuFeCoCr system were successfully designed and fabricated by using CALPHAD (Calculated of Phase Diagrams) approach and gas atomization method, respectively. The bulk CuFeCoCr composites were produced by hot pressing technique at 950℃ under a pressure of 45MPa. The effect of Cu content on the microstructure, coefficients of thermal expansion (CTE), thermal conductivity (TC) and micro-hardness (H_V) were systematically studied. The results show that the CuFeCoCr composites present two separate fcc phases (Cu-rich and FeCrCo-rich phase) microstructure. After annealing at 500 °C for 8 h, the CTE of the composites ranged from 5.75 to 11.45×10^_-6 K^_-1 and TC varied from 42.2 to 107.4 W.m^_-1.K^_-1. Particularly, the Cu₅₅(Fe_0.37Cr_0.09Co_0.54)₄₅ composite exhibits excellent comprehensive properties, i.e. CTE of 6.88×10^_-6 K^_-1 and TC of 91.09 W.m^_-1.K^_-1,which matches with the semiconductor in electronic packaging. In addition, all the prepared composites exhibit a higher H_V than that of Cu/Invar composite.

Abstract:An extruded AZ31 alloy was compressed along the extrusion direction at room temperature. Profuse tensile twins were activated. Paired twins including the connected twin pairs and randomly paired twins (unconnected twins) were studied by a combined analysis of Schmid factor and strain compatibility factor. The results show that the nucleation of connected twin pairs preferentially occurs in the neighboring grains with the misorientation of 25°. About 88% of the connected twins have high Schmid factor and around 76% show high strain compatibility factor. The occurrence of connected twin pairs with low values of Schmid factor is well interpreted by their high values of strain compatibility factor. Around 22% of the unconnected twin pairs have the strain compatibility factor values of zero.

Abstract:Octahedral Pt-Ni nanoparticles surrounded by (111) facet are considered as promising oxygen reduction reaction (ORR) catalysts. It has been reported that the ORR activities of Pt-Ni octahedral nanoparticles are greatly influenced by the Pt:Ni atomic ratio. The relationship between the Pt:Ni atomic ratio of Pt-Ni octahedron and the corresponding ORR activity is presented as a volcano plot without explanation. Herein, by synthesizing Pt-Ni octahedral nanoparticles with composition of Pt₃Ni, PtNi and PtNi₂, we found an abnormal ORR specific activities in the order of Pt₃Ni> PtNi₂> PtNi. Meanwhile, with the same Pt loading, the sequence of ORR mass activity is Pt₃Ni≈ PtNi₂> PtNi. The surface lattice contraction and the utilization of Pt were considered to explain these phenomenon. The extent of surface lattice contraction is decreased as Pt₃Ni> PtNi₂> PtNi, consistent with the sequence of ORR specific activity, which challenges the previous experience that the more Ni was incorporated into the Pt lattice, the higher the surface lattice contraction yielded. While the mass activity is a balance between specific activity and surface Pt utilization. The results indicated that the ORR activity can be adjusted by tuning the surface tension and surface Pt utilization.

Abstract:Six diffusion couples of Ni-Cr-W ternary alloys were prepared, annealed at 1473 K for 72 hours and measured by using the electron probe microanalysis combined with Whittle and Green method in order to determine the interdiffusion coefficients. The experimental interdiffusion coefficients were critically assessed to obtain the atomic mobilities by means of DICTRA software package. A good agreement has been obtained by comprehensive comparison between the experimental data and the model-predicted diffusion properties, which verifies the reliability of the atomic mobilities of Ni, Cr and W in Ni-Cr-W alloys. The diffusion phenomena, such as diffusion paths and the concentration-distance profiles in the Ni-Cr-W ternary system can be reasonably described by the presently obtained atomic mobilities.

Abstract:Surface aluminizing for magnesium alloy is an effective method to improve corrosion resistance. This research introduces surface nanocrystallization as the pre-process of aluminizing. AZ91D magnesium alloy is processed by high energy shot peening (HESP) to achieve surface nanocrystallization, and then vacuum solid state aluminum diffusion to obtain aluminized layer. The morphology of the aluminized layer is observed with Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). It shows that the surface of the nanocrystalline grain size of 100 nm was obtained after HESP of AZ91D magnesium alloy. After HESP, the depth of the aluminized layer is thicker than that of the aluminized layer without HESP. After diffusion of 12 hours under the temperature of 440 ℃, the depth of aluminized layer increases to 70 mm. The corrosion resistance of AZ91D magnesium alloys are characterized by electrochemical method. It shows that the aluminized layer obviously decreases the corrosion rate of AZ91D magnesium alloy. Therefore, high energy shot peening(HESP)was beneficial to surface aluminizing and can improve the corrosion resistance of magnesium alloy.

Abstract:The porous NiTi alloys were prepared by microwave sintering with different Ni/Ti powder particle sizes, and the effect of particle size on the microstructure and mechanical properties of the porous NiTi alloys was systematically investigated. The results show that the undesired Ti2Ni and Ni3Ti phases in the porous NiTi alloys decrease and the Ni phase disappears with decreasing the particle sizes. At the same time, the pore shapes of the porous NiTi alloys change from the irregular shape with sharp angles to the suborbicular shape. Moreover, both of the porosities and pore sizes of the porous NiTi alloys increase with increasing the particle sizes, while all of the Rockwell hardness, compressive strength and bending strength decrease. Therefore, the decrease of particle sizes can be beneficial to obtain the microwave sintered porous NiTi alloys with desired microstructure (pure phase composition and uniform pore structure) and high mechanical properties.

Abstract:For the core-shell structured immiscible alloys within the immiscible gap, whether the shell is composed of a phase with lower or higher melting point, there is no exact answer yet. Based on the Cu-Sn-Pb calculated phase diagram given by reference, the phase separation of 14Sn-73.1Cu-12.9Pb, 14Sn-64.5Cu-21.5Pb, Cu-65Pb and Cu-75Pb alloys have been experimentally investigated by casting method. An anomalous core-shell structure with a CuSn-rich shell and a Pb-rich core formed in 14Sn-64.5Cu-21.5Pb alloy, which differed from the viewpoint that a lower melting point phase generally formed the shell as Cu-75Pb alloy showed. This anomalous phenomenon may be explained by that the liquid separation reaction was suppressed due to undercooling generated during casting process and the monotectic reaction took place before the liquid separation reaction. This work may provide a method to modify the structure of immiscible alloys through controlling solidification path.

Abstract:Sol-gel method was used to prepare La3+-doped TiO2 Nanopowders. The sample was characterized with XRD, TEM, HRTEM, STEM-EDS, XPS and ultraviolet-visible (UV-Vis) spectroscopy. The changes of the La3+-doped TiO2 in the phase transition were discussed on the aspects of its phase composition, the average grain size, the microstructure, the chemical states and UV-Vis absorption spectroscopy. Doping with La3+ significantly suppressed the phase change and grain growth of TiO2. It effectively improved the TiO2 dispersibility and reduced the average particle size of TiO2. With the increase of the calcination temperature, the second phase La4Ti19O24 gradually precipitated from the La3+-doped TiO2 and formed an incoherent interface with the Brookite TiO2 phase, which precipitated in the form of irregular spheres from the surface of the TiO2 base. Secondary phases are originated from segregation of point defects at grain boundaries in La3+ doped TiO2. The segregation driving force is mainly the elastic strain energy. With the increase of calcining temperature, the atomic percentage of the O1S in the La3+-doped TiO2 gradually decreased, and that of the La3d gradually increased. There was an energy loss peak at the higher binding-energy side of the main peak of the La3d, and Ti3+ existed after the calcination. La3+ Doping makes the optical absorption bandedge of the TiO2 red-shifted. But with increasing calcination temperature, the optical absorption bandedge was blue shifted.

Abstract:As the miniaturization of multilayer ceramic capacitors (MLCCs) is a major trend, well-fabricated ferroelectric materials such as barium titanate (BaTiO₃, BTO) with small grain and well crystallinity are increasingly in demand. Compared with other synthetic routes, solid-state reaction (SSR) is a more feasible route to prepare BaTiO₃ nanoparticles without lattice imperfections. In contrast to other researches about SSR that mainly focus on exploring improved processes to obtain BaTiO₃ nanoparticles with high tetragonality, investigations on the phase, microstructural transformation and reaction mechanism of BaTiO₃ nanoparticles were made in this study. Experiments results reveal that the reaction mechanism of forming tetragonal BaTiO₃ via SSR can be ascribed to two main reaction stages, including the formation of cubic BaTiO₃ and the cubic-tetragonal transformation of BaTiO₃. Finally, BaTiO₃ powders with a tetragonality of 1.0086 (c/a) and average particle size of 180 nm was acquired after optimizing the calcination parameters.

Abstract:The BaTi2O5 (BTO) and 35La2O3-65Nb2O5 (LNO) amorphous microspheres without conventional network-forming oxides were fabricated by a containerless flame-spraying technique. The results showed that transparent BTO and LNO glass microspheres were successfully prepared. All the BTO glass microspheres have smooth surfaces and no crystalline traces, indicating they are amorphous glass with diameters ranging from 8 to 40 μm. Most of the LNO glass microspheres have diameters of 10 to 40 μm, which are amorphous glass with smooth surfaces. And a small number of LNO microspheres have large particle diameters, which possessing micron-sized grains on their surfaces. The BTO and LNO glass microspheres have high refractive index of 2.20 and 2.23, respectively, which are very promising to be applied as window, lens and reflection film materials.

Abstract:In order to improve the shielding ability of spacecraft against space debris hypervelocity impact, the B₄C-Al based composites prepared by pressureless presintering and aluminium infiltration in vacuum were designed as the front bumper of Whipple shielding configuration, and the hypervelocity impact tests were carried out on a hypervelocity impact range to evaluate the shielding performance of B₄C-Al bumper and Al alloy bumper under the impact velocity of 3 km/s ~ 6.5 km/s. By comparising the bumper penetration, the rear wall damage state and the debris clould structure of the two different bumper materials under various impact velocity as well as the SEM and EDS results, the relationship among the bumper material properties, the cratering mechanics of rear wall and the debris cloud characteristics was discussed. The research results indicated that the B₄C-Al bumper can break the projectile into smaller pieces and even make the debris melt, and the impact damage of debris cloud on rear wall was alleviated significantly, meanwhile, the good toughness of Al metallic phase can keep this bumper structure intact. Hence, both the pulverized small debris and the decreased impact kinetic concentration of debris cloud are the main reasons to obtain higher shielding capability of B₄C-Al bumper. This primary investigation provided theoretical and technical instructions for the design and application of B₄C-Al based composite materials in space debris shielding configuration.

Abstract:In this paper, the effects of the compression, assembly and heat exposure temperature on the elastic properties of the braided spring using as the elastic support of thermal barrier seals were investigated systematically, and the reason for elastic failure of the braided spring on high temperature was also discussed. The results show that the oxidation of alloy is the main reason for reduced resiliency of braided spring on high temperature, and the resiliency of braided spring is more than 95% when the compression is less than 50% below 800℃, which indating that the as-prepared braided spring may have broad application prospects in aerospace thermal barrier.

Abstract:Fine-grained compact 10 mol% scandia stabilized zirconia (10ScSZ) bulks were sintered by SPS using powders synthesized by the combustion method as raw materials. The densification process of as-processed powders was investigated by measuring the real-time ram displacement of SPS during heating. It was estimated that the densification temperature of this material was around 1200 ℃ at which the ram displacement is minimum. In order to verify the effectiveness of the approach, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃ were chosen as the sintered temperature to prepared bulk samples respectively. The results revealed that the 10ScSZ sample sintered at 1150 °C had the highest density, reaching 99.4%, and a fine grain structure with an average grain size of 194 nm, which was basically consistent with the speculated results. In this study, an efficient and reliable method was proposed and confirmed for judging the proper SPS sintering temperature through the densification development.

Abstract:glycine-nitrate process (GNP) was used to synthesis Ce0.65La0.35O1.825 (LDC) powders. The samples were obtained by sintering for 10 h at 1400 ℃. The phase composition and morphology were characterized by XRD and SEM. We measured the current change with time of specimen at different temperatures and thus calculated the transferred number of ions and the DC conductivity. Almost all the mobile ions will shift around their positions, but only tiny portion can migrate through a few lattice length. The number of transferred ions increased with temperature, but far smaller than the total number of oxygen vacancies. The transferred ion number and temperature follows Arrhenius relationship with the activation energy of 0.83 eV.

Abstract:The lattice dynamics, thermodynamic properties and thermal transport properties of CeO₂ are calculated by the finite displacement method and the Boltzmann equation based on density functional theory. The calculated results are in good agreement with the corresponding experimental results. The important role of optical phonons in enhancing the lattice anharmonicity and phonon scattering rates is revealed by analyzing the vibration frequency, Grüneisen coefficient and scattering rate of all phonon modes. Moreover, by calculating the relationship between the cumulative lattice thermal conductivity and the phonon free path, it is found that the thermal conductivity of CeO₂ is mainly contributed by phonons with a phonon free path between 1 and 10 nm.

Abstract:Al₂O₃-based ceramic cores were prepared by dry-pressing and subsequent pressureless sintering, where the Al₂O₃ powders were used as the matrix and the silicone resin powders were used as the binder. The effect of the silicone resin content on the properties of Al₂O₃-based ceramic cores was investigated. Results showed that the new mullite phase was formed by the reaction between Al₂O₃ and silica which was formed by the decomposition of silicone resin. Weight loss of sintered Al₂O₃-based ceramic cores was mainly caused owing to the release of gases during the cross-linking and decomposition process of silicone resin. And the release of gases inhibited the shrinkage caused by the sintering drive force. Therefore, with the increase of silicone resin content, more and more gases were released. As a result, the weight loss of Al₂O₃-based ceramic cores gradually increased and the shrinkage rate gradually decreased. The increasing silicone resin content made the apparent porosity increase and the bulk-density decrease, leading to the decrease of bending strength in sintered Al₂O₃-based ceramic cores. Although the addition of silicone resin decreased the bending strength, the dimensional precision was improved markedly.

Abstract:A series of multiferroic 1-x(0.71BiFeO3-0.29BaTiO3)-xLaFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics were synthesized by solid state reaction. The effects of LaFeO3 content in 0.71BiFeO3-0.29BaTiO3 system on structure, microstructure, electric and magnetoelectric properties were investigated. All the ceramics form a single phase perovskite structure, and structural phase transition is formed with the increase of LaFeO3. The ceramics show good microscopic appearance. The grain sizes are uniform and decrease obviously with increasing of LaFeO3, which acts as an inhibitor for grain growth. The dielectric constants are decreased by the doping level of LaFeO3. The ceramic of x = 0.1 exhibits low leakage current density J with the value around 10-7~10-8 A/cm2. With the increase of LaFeO3, the remnant polarization and the magnetoelectric coefficient aME of the ceramics attain maximum at x = 0.1, with the value of Pr = 0.45?C/cm2 and aME = 132.21 mV/cm?Oe, respectively. These results suggest that the ferroelectricity properties and ferromagnetism effect can be improved simultaneously by adding suitable LaFeO3.

Abstract:Graphite is an important structural material and moderating material in high temperature gas-cooled reactor (HTGR). Improving the oxidation resistance of graphite is an important guarantee to improve the safety of HTGR. SiC coating is one of the most widely used coating materials at present. In this paper, a dense SiC antioxidant coating was prepared by fluidized bed chemical vapor deposition process on matrix graphite sphere. And its oxidation behavior and mechanism were analyzed at 1400℃. The results show that the atmosphere has a significant effect on the oxide layer thickness. In the case of single steam, the thickness of the oxide layer obtained is thinner than that in the mixed atmosphere. The surface oxidized by single steam has a smoother surface, slighter point cracks and smaller linear cracks than that oxidized by mixed atmosphere. The oxidation of dense SiC coatings occurs on the surface without destroying the structure of the dense layer. The oxidation mechanism analysis shows that the surface morphology, crack formation and thickness change of the dense SiC coating are all related to the oxidation competition reaction and oxidation intermediates. In the oxidation process of dense SiC coatings in different environments such as air and water vapor, a certain thickness of SiO2 self-healing layer can be formed on the surface. After 10 hours of oxidation, the oxidation depth of the coating is only within 3.5 μm of the surface, and the structure of the dense layer is not destroyed.

Abstract:Carbon-based ceramic tile is urgently needed high-temperature anti-insulation materials in the thermal protection system of hypersonic vehicles due to the high temperature resistance, low density, and low thermal conductivity. But the material is easy to destroyed by oxidation erosion and ablation. In this experiment,, the Ni-Cr spinel high-emission ablation-resistant anti-oxidation coating was prepared by atmospheric plasma spraying technology on the surface of a carbon-based ceramic thermal insulation tile substrate on which a ZrB2-SiC-glass inner coating has been prepared. The phase structure and microstructure of the powder and coating were examined by XRD and SEM, and the coating was ablated by oxygen-acetylene flame. The results show that when the mole ratio of Cr2O3 and NiO is 1: 1.2, the pure NiCr2O4 spinel powder can be obtained by the solid phase reaction at 1200 ℃ for 2 h. To get complex spinel powder, 15 wt.% TiO2 and 25 wt.% MnO2 were added to the former consititute system and the same manufacture method was applied. The emissivity of NiCr2O4 high-emission coatings and NiCr2O4-doped high-emission coatings reached 0.955 and 0.954 respectively in the 1-22 μm band. The NiCr2O4 was slightly decomposed after spraying, and the emissivity was reduced. The Mn-Ti doped NiCr2O4 phase structure was stable, no decomposition, and the emissivity was stable. The result of the ablation shows that the surface temperature of Mn-Ti doped NiCr2O4 coating lower than NiCr2O4 coating by 240 ℃ and the infrared radiation performance is far higher than NiCr2O4 coating, when the flame temperature is 2000 ℃. Mn-Ti-doped NiCr2O4 coating is more stable than NiCr2O4 coating at high temperature, which keeps high emission performance. The Mn-Ti doped NiCr2O4 coating keeps stable after the 2000 ℃, 300 s ablation assessment, which perform a better radiation and ablation resistance.

Abstract:Home-synthesized FHA powder were used to obtain a water-based suspension. And the FHA coating was fabricated on a Ti substrate by suspension plasma spraying technique. The effect of spraying power on the microstructure and properties of coatings was studied. The crystalline phases and chemical compositions of the coatings were characterized through XRD. The result showed that all coatings contained a HA major phase and the decomposition phases (α-TCP, β-TCP and TTCP). FT-IR and XPS confirmed the presence of fluorine in the as-sprayed coatings. The solubility result showed that the substitution of fluorine into the HA structure had a positive effect on the dissolution resistance of the HA. The corrosion behavior was studied in a SBF solution using potentiodynamic polarization test, and the results indicated that the coatings enhanced the corrosion resistance of the Ti substrate.

Abstract:La₂Mo₂O₉ is expected to have an extremely low thermal conductivity. However, the α-β phase transition at 580 oC seriously affects its performance and applications. In this work, the effect of Gd^₃₊ doping on the phase stability and thermal conductivity was investigated. The results show that the phase transition of La₂Mo₂O₉ is effectively suppressed with the doping of Gd^₃₊ ions. The samples show a β-phase when x ≥ 0.2. Moreover, the thermal conductivity decreases firstly and then increases with the increase of doping content of Gd^₃₊ ions with a minimum value at x = 0.2 at room temperature. The thermal conductivities of all samples are below 1 W/(m.K).

Abstract:ZrC, Si and C powders were used as the sintering aids to enhance the densification and the mechanical properties of HfB2, due to the in-situ reaction between ZrC-Si-C at sintering temperature. Dense HfB2-ZrSi2-SiC ceramic composites have been fabricated by reactive spark plasma sintering at 1600 ℃ for 10 min under a pressure of 40 MPa. With the amount of ZrC-Si-C increasing, the Vickers hardness, the flexural strength and fracture toughness of the sintered samples increased first, then decreased. HfB2-10wt.% ZrC-Si-C composites showed the the best comprehensive mechanical properties. The Vickers hardness, flexural strength and fracture toughness of HfB2-10wt.% ZrC-Si-C composites were 26.80±1.2 GPa, 504±40 MPa and 4.66±0.21 MPa.m1/2, respectively.

Abstract:Gd₂Zr₂O₇-SrZrO₃ (GZSZ, Gd₂Zr₂O₇:SrZrO₃=7:3) composite ceramic powder was synthesized by solid state reaction. Spray drying and atmospheric plasma spray (APS) method were used to prepare corresponding spray powders and coatings, respectively. The phase compositions and microstructures of the spray dried powders and APS coatings were characterized by X-ray diffraction and scanning electron microscopy. The thermal diffusivity, thermal expansion coefficient and sintering coefficient of the coatings were characterized by a laser flash method and a high-temperature dilatometer. Both GZSZ composite powders and coatings are composed of Gd₂Zr₂O₇ and SrZrO₃. The Gd₂Zr₂O₇ powder has a pyrochlore structure, while the Gd₂Zr₂O₇ coating has a fluorite structure. And both the SrZrO₃ powders and coatings have a perovskite structure. The porosity of the coating is ~14%, and its thermal expansion coefficient after heat treatment at 1400℃ for 5 h is 9.8~11.2×10^_-6 K^_-1. The thermal conductivity of the as-sprayed GZSZ coating is ~0.8 W?m^_-1?K^_-1, which is ~20% lower than that of the SrZrO₃ coating (~1.0 W?m^_-1?K^_-1). And the thermal conductivity of the GZSZ coating increases to ~1.5 W?m^_-1?K^_-1 after heat treatment at 1400℃ for 360 h. The results showed that the GZSZ coating is a promising thermal barrier coating material.

Abstract:La₂Ce₂O₇ is a fluorite-structured ceramic material with lower thermal conductivity and better high-temperature phase stability than 8YSZ, thus, it is considered as a new thermal barrier coating ceramic material. The solution precursor plasma spraying (SPPS) method is a novel coating preparation method for preparing nanostructured ceramic thermal barrier coatings in recent years. The prepared SPPS coatings have an inter pass boundary (IPB) structure, with low thermal conductivity and long lifetime. In this paper, the decomposition processes of the La₂Ce₂O₇ coating precursor were studied, and the La₂Ce₂O₇ coating was prepared by SPPS method. The nitrate solution with a molar concentration of 3.08 mol/L was used as the precursor solution, and its viscosity and surface tension were 7.17 mPa.s and 76.9 mN/m, respectively. The decomposition process of the La₂Ce₂O₇ dried precursor was characterized by STA-FTIR-QMS. The decomposition temperature and decomposition process of the precursor were evaluated, and the preheating temperature of substrate was determined to be 450 °C. The optimized spary parameters were the atomization pressure of 1.2 bar, the current of 700 A, and the liquid feed rate of 17 ml/min, determined by the Taguchi experiments. The La₂Ce₂O₇ coating prepared by using the optimzed spray parameter had a thickness of 121.59 μm after 20 times spraying, relative density of 92.4%, and hardness of 2.1 GPa. The prepared coatings were characterized by SEM, XRD, EDS and laser flash method. The results showed that the La₂Ce₂O₇ thermal barrier coating with low thermal conductivity, uniform element distribution and fluorite structure is obtained.

Abstract:Carbon nanofibers can be produced from graphene, graphite powder and carbon nanotubes by nozzle-less electrospinning and following stabilization and carbonization process. The prepared carbon nanofibers were used for the adsorption of Cr(VI) ions, and the adsorption performance of Cr(VI) ions under different test conditions were studied. It was found that carbon nanotubes-based nanofibers exhibit a large surface roughness, the best degree of graphitization, more ordered crystal structure, and the largest specific surface areas. This features contribute to increasing the adsorption performance of adsorbent materials on Cr(VI) ions. Their adsorption capacity for Cr(VI) ions can reach 52.8 mg/g at pH=3, 25℃. Moreover, the adsorption capacity can remain about 60% of the initial adsorption capacity after five cycles. Therefore, the carbon nanotubes-based nanofibers exhibit the best adsorption performance. Hence, carbon nanotubes-based nanofibers have a promising in practice for applications in heavy metal ions adsorption due to their high specific surface area, high porosity, excellent surface chemistry and good adsorption performance.

Abstract:_{:In this paper, we find a broth formulation that is stable at room temperature for 15h and does not solidify and it is good for forming gel microspheres. And we use a capillary microfluidic device assisted internal gel process to prepare successfully small size (<120μm) ZrO2 ceramic microspheres. The factors affecting the size of ZrO2 microspheres are analyzed. The results show that under the same conditions, the larger the flow rate or the viscosity of the silicone oil, the smaller the size of the ZrO2 microspheres. The larger the flow rate of the broth or the larger the throat size of the capillary microfluidic device, the larger the size of the ZrO2 microspheres; the CV value of the ZrO2 microspheres are less than 5% by image recognition, indicating that the ZrO2 ceramic microspheres prepared by the method are uniform in size and monodisperse; the sintered microspheres are dense and showing a cubic phase by SEM and XRD.}

Abstract:_{: Phosphate adhesive were prepared with the H3PO4 and Al (OH)3 as the matrix and nano CuO as the inorganic fillers. The influence of nano CuO on the water resistance of phosphate adhesives was investigated by soaking mullite joints that were bonded by the adhesive in artificial seawater for 168h. The results show that the nano CuO could improve the water resistance of the adhesive. The shear strength of mullite joint was 7.13MPa which is the best strength after immersed in artificial water whenthe content ofnano CuO was 20wt% in matrix. It has good water resistance within the whole heat-treatment temperature range from 150^oC to 1300^oC. The lowest shear strength is 2.31MPa after heat-treatment at 1300^oC and immersed in artificial seawater. The effects of nano CuO on the water resistance of phosphate adhesive were analyzed by XRD and SEM.}

Abstract:ZTA-TiC-Fe cermet composite materials were prepared by high gravity combustion synthesis technology. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Variable temperature X-ray diffraction were used to study the phase composition, microstructure and microstructure evolution of the cermet during heating and cooling process. The results show that ZTA-TiC-Fe cermet can be fabricated directly by high gravity combustion synthesis melting-casting method; The ZTA eutectic ceramics formed by t-ZrO₂ and Al₂O₃ with a three-dimensional network structure, and TiC-coated Fe are filled in the three-dimensional ZTA ceramics skeleton. The inefficacy mechanism of ZTA-TiC-Fe: the phase transformation of Fe and ZrO₂ occurs at about 750℃; The volume changing of phase transformation of Fe and ZrO₂ during heating and cooling and the internal stress release caused by the different thermal expansion coefficients of each component lead to the thermal expansion of the ZTA-TiC-Fe cermet. In the aerobic environment, the oxidation rate of Fe phase in the surface layer increases when the temperature exceeds 550℃, resulting in porous red-brown Fe₂O₃. The oxidation of Fe phase produces about 8 times volume expansion, resulting in the irreversible rupture of three-dimensional ceramic skeleton.

Abstract:Abstract: Zirconium carbide (ZrC) coatings were deposited on graphite substrate at 1200°C by low pressure chemical vapor deposition (LPCVD) from the Zr-Br2-C3H6-H2-Ar system. The effect of total flow rate on the morphology and growth mechanism of ZrC coatings were investigated. As the total pressure increased, the deposition rate increased firstly and then decreased slowly, the maximum value was 3.37 g-3?cm-2?h-1. Meanwhile, the preferential orientation of ZrC coatings changed evidently, the (200) plane was the preferential orientation of ZrC coatings at the total flow rate of 600~800 ml/min. XPS showed that the C/Zr ratio of ZrC coatings increased from 0.85 to 1.49. At the total flow rate below 200 ml/min, the ZrC coatings were dense and composed of equiaxed gain structure. As the total flow rate increased from 400 to 800 ml/min, the ZrC coatings were well-faceted pyramidal-shaped crystals. When the total flow rate above 1000 ml/min, the ZrC coatings with a loose complex island-like gains. The variations of ZrC coatings can mainly be attributed to boundary layer with increasing the total flow rate.

Abstract:Three kinds of TiN-Ni cermets containing Ni 30vol%, 50vol% and 70vol% were prepared by hot pressing sintering method. The continuous oxidation behavior of TiN-Ni cermet at 800 C in static air was studied. The results show that there is no chemical reaction between the TiN phase and the Ni phase during the sintering process, and the adjustment of Ni content contributes to the densification of sintering. The density of TiN/70Ni is the highest, up to 99.6%, which helps to strengthen its high temperature oxidation resistance. Scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X ray diffraction (XRD) were used to study the mechanism of high temperature oxidation of TiN-Ni composites. The oxidation process was divided into rapid oxidation process and slow oxidation process, in which the external diffusion of metal ions and internal diffusion of oxygen ions existed.

Abstract:The rapid development of electric vehicle industry has placed urgent need for solid state battery with large capacity and high energy density. The electrolyte and interface problems are two key issues that limit the performance of solid state battery. The paper introduced PEO buffer layer to the cathode/electrolyte interface to improve contact. First, Li6.4La3Zr1.4Ta0.6O12(LLZTO) with density of 5.25 g/cm3 and ionic conductivity of 8.33×10-4 S/cm was prepared. Second, the paper prepared PEO-LiTFSI-LLZTO buffer layer and LiFePO4 composite cathode slurry. The PEO buffer layer and cathode slurry were coated on the surface of electrolyte by spin coating, respectively. The interfacial resistance was 509 Ωcm2 at 60 °C. The galvanostatic charge and discharge curve of symmetric battery proved excellent interfacial stability. The solid state battery has fist discharge capacity of 145.8mAh/g and coulombic efficiency of over 97%.

Abstract:A facile one-step hydrothermal process was used to prepare MoS2/CoS2 binary composites with different raw material ratio as electrode material for supercapacitors. Results of electrochemical performances show that MoS2/CoS2 binary composites exhibit competitive specific capacitance (549 F/g at 2 mV/s or 434 F/g at 1 A/g) and excellent cycling stability as the molar ratio of Mo: Co=2:1 in raw material. And microstructure and morphology analyses reveal that the MoS2/CoS2 binary composites were composed of octahedron-shaped CoS2 and flower-liked MoS2. Above all, due to the coupling two species, large surface areas and tunable compositions, the obtained MoS2/CoS2 binary composites electrodes possess the best electrochemical properties.

Abstract:The plunger pump plunger (45 steel) works in high friction and high corrosion environment for a long time, and needs to improve the wear resistance and corrosion resistance of its working surface to improve its working efficiency and prolong its service life. The cermet coating was prepared by cladding the Ni60-TiC mixed powder on the surface of 45 steel by laser cladding technology, and the coatings with different TiC contents (0%, 10%, 20%, 30%) were tested for hardness test and friction and wear test. Corrosion resistance test, at the same time, the surface morphology of the coating was characterized and the microhardness was tested. The results show that the addition of TiC to the coating can effectively improve the wear resistance and corrosion resistance of the coating, improve the hardness of the coating and reduce the friction coefficient. Considering the actual working environment of the plunger pump plunger, the wear resistance and corrosion resistance of the coating are best when the TiC content in the coating is 20%-30%.

Abstract:In this work, three dimensional interconnected porous SiC ceramics were prepared via combining stirring-foaming and freeze-gelcasting. The obtained porous ceramics with tunable porous structure, uniform pore size distribution and multiply porous structure were fabricated successfully. The effect of PVA and stirring speed on porous structure and properties of SiC porous ceramics were investigated.The results showed that porous structure uniformity could be tuned by varying ω(PVA)/ω(SiC) , and until optimum when the values was 1.5. The porosity increased, 1st mode pore size and pore wall thickness decreased with the increasing of PVA content. The porous structure could be improved by increasing stirring speed. When stirring speed was 1600 r/min, the porosity and compressive strength were 88.42 % and 4.36 MPa, respectively.

Abstract:In this paper, barium acetate and tetrabutyl titanate were used as raw materials, and polyvinylpyrrolidone (PVP, Mw=1300000) was used as the viscous agent. The barium titanate nanoparticle with high aspect ratio was prepared by sol-gel method combined with electrospinning technology. XRD results showed that the main phase of BaTiO₃ NFs was cubic phase after calcination at 900 °C. Firstly, this paper investgated the effects of acetic acid-ethanol-deionized water, acetic acid-DMF-deionized water and acetic acid-DMF-acetylacetone on the fibers diameter. The results of SEM showed that when the PVP content was 8.7wt.%, acetic acid-DMF-acetylacetone was the optimized spinning solvent. The BaTiO₃ NFs prepared at this time had a minimum diameter of 200nm and an aspect ratio of 100:1. On the basis of the orthogonal test method, the influence of the spinning parameters such as the distance from the needle to the receiver, the flow rate and the spinning voltage on the aspect ratio of BaTiO₃ NFs was investigated. It was found that the distance from the needle to the receiver was 21cm, flow rate of 0.5mL/h and spinning voltage of 21kV were optimized spinning parameters. The prepared BaTiO₃ NFs have a uniform morphology, diameter of 200nm and aspect ratio ratio of 125:1.

Abstract:In this study, thermal conductive composites with various filling fraction were prepared using angular and spherical AlN powders as fillers and PDMS as organic matrix. The influence of particle morphology, filling fraction and surface treatment on the viscosity and thermal conductivity of composites were deeply investigated. The results indicated that the AlN spherical powders could significantly reduce the viscosity of composites compared with the AlN angular powders, which was in favor of obtaining higher filling fraction and larger composite thermal conductivity. In addition, the surface treatment of AlN powders with KH570 were beneficial to reduce the interface thermal resistance and improve the composite thermal conductivity. When the concentration of KH570 was 2.0wt%, a highest composite thermal conductivity were obtained, which was ~22.5% higher than that of untreated fillers.

Abstract:Lanthanum chromate ceramics with poor tensile properties, high brittleness, difficult deformation and high hardness is difficult to process. Large ceramic components with complex shapes can be fabricated at low cost by ceramic joining technology. In this paper, the lanthanum chromate precursor slurry was used as the interlayer material, and the lanthanum chromate ceramic was joined by spark plasma technology. And then the bonding strength of the joining was measured. The influence of joining temperature and holding time on the strength of the joint was analyzed by means of SEM, EDS and so on.

Abstract:In this paper, oscillatory pressure sintering technique (OPS) was used to prepare high quality zirconia ceramics. The effects of sintering temperature on the density, grain size, microstructure and mechanical properties of zirconia ceramics were firstly investigated. The results show that under the application of oscillatory pressure, the variation of relative densities is not obvious while the grain sizes significantly increase during the increased sintering temperature. All specimens reached a nearly full density as there was scarcely any pores on the polished surface. The highest hardness and bending strength of 16.6 GPa and 1455 MPa, respectively, are reached when the target temperature reaches 1300°C. Compared with conventional pressureless and hot pressure sintering process, the introduction of oscillatory pressure significantly reduces the densification temperature of zirconia ceramics, and evidently enhances mechanical strength and fracture reliability.

Abstract:In order to explore the morphology of Fe element in silicon carbide (SiC) block and the purification technology of SiC powders. The SiC block and powders were used as the main raw materials, respectively. HCl, HNO₃, H₂SO₄ and HF were used as pickling agents, respectively. The phase composition, microstructures and Fe element content of SiC block and powders before and after pickling were characterized by X-ray diffraction, scanning electron microscopy and ICP, respectively. The morphology of Fe element in SiC block under microscopic state and the purification technology of SiC powders were investigated. The results indicated that Fe element existed in the form of Fe_xSi_y solid solution inside the SiC block. It could be seen that Fe element wrapped by free Si in the microscopic state. When the liquid solid ratio about 5:1, the optimum purification technology were considered as follows: The concentration of HF 0.15 mol/L, pickling temperature 70 °C and leaching time 2 h, the removal rate of Fe element could reach 94.1% under this pickling technology.

Abstract:The B₄C/C preforms were prepared by the gel-casting and the B₄C-SiC-Si composites were fabricated based on liquid silicon infiltration process. The effects of different catalysts (Na₂CO₃, NaOH, KOH, Na₂SiO₃ and NaHCO₃)on the microstructure and mechanical properties of B₄C-SiC-Si composites were investigated. The results showed that the catalyst mainly affected the microstructural uniformity of composites and the size of residual Si. The composites were mainly composed of B₄C, B₁₂(B,C,Si)₃, SiC and Si. When NaOH, KOH or NaHCO₃as catalyst, the distribution of residual Si was uniform. With the NaOH as catalyst, the mechanical properties of B₄C-SiC-Si composites were the best：the hardness, flexural strength and fracture toughness were 16.9 GPa, 296 MPa and 4.15 MPa.m^_1/2, respectively.

Abstract:To solve the problem of high toxicity and poor consistency of traditional beryllium oxide microwave attenuation ceramics, a kind of environment-friendly AlN-FeSiAl microwave attenuation ceramics based on aluminum nitride with high thermal conductivity was developed in this paper. The material is added FeSiAl to the AlN matrix and belongs to environment-friendly material. In order to obtain high thermal conductivity and good electromagnetic performance, the effects of different aluminum nitride powders, FeSiAl additive amount and sintering process on composite properties were studied. The results show that adopting Toyo aluminum nitride, adding 10 wt% FeSiAl, vacuum hot pressing sintering under 1650 ℃ and 85 MPa, the high attenuation performance of microwave attenuation ceramics is realized, and material thermal conductivity is 88.2 W/(m.K), close to that of the microwave attenuation ceramics based on aluminum nitride in Ceradyne company.

Abstract:The traditional high temperature resistant coating with high emissivity have the characteristics of large rigidity and obvious brittleness. In order to change these properties in essence, we successfully have produced a kind of scaly and flexible coating with high emissivity and high temperature resistance inspired by structure of the snakeskin in nature. We combine slurry method with sol-gel method, and use silica sol as solvent, MoSi₂ as emittance agent and borosilicate glass as high temperature binder. Compared with the dense coating with the same composition, surface density and sintering process, the scaly coating have high flexibility while ensuring high emittance agent content and emissivity. The mechanical properties, including contact damage resistance, thermal shock resistance and bending strength, have been improved in varying degrees.

Abstract:Using butyl titanate as titanium source and Fe(NO₃)₃.9H₂O as iron source, Fe/TiO₂ nano powders were prepared by sol-gel method and Fe/TiO₂ nano fibers were prepared by sol-electrostatic spinning technology. The photocatalytic activity and practicability of TiO₂ nanomaterials were improved from the aspects of material modification and morphology improvement. By XRD, SEM and TEM, the photocatalytic activity of Fe/TiO₂ nano-materials in visible light region was investigated. The effect of calcination temperature and iron content on photocatalytic performance of Fe/TiO₂ nano-materials was analyzed. The results show that the addition of iron and the improvement of the morphology are helpful to improve the photocatalytic performance of TiO₂.

Abstract:La2O3 nanofibers was synthesized through electrospinning and heat treatment process. The phase structure, morphology and antibacterial performance were characterized by SEM, TEM, XRD, XPS and BET. The result shows that La2O3 nanofibers possessed high length–diameter ratio, uniform morphology and pure phase. The La2O3 nanofibers have an excellent germicidal effect against the high-risk human pathogen Escherichia coli O157. More than 95% inactivation rate of hige concentration bacterial (107 CFU/L) is achieved in 100 minutes by low addition of La2O3 nanofibers (200 mg/L) and no E. coil recovery was detected in following three days. Furthermore, La2O3 nanofibers shows high efficient bactericidal performance against Acinetobacter baumannii and P.aeruginosa, demonstrating its potential application as efficient and broad-spectrum antimicrobial material.

Abstract:Based on the theoretical analysis of the application of Three-Roller Milling (TRM) exfoliating technology in low-carbon carbon-containing refractories, graphite nanoplatelets (GNP) were obtained by exfoliating flake graphite (FG) in phenol formaldehyde resin (PF) via TRM in this study. The effects of the exfoliating times on the structure and morphology of the products were investigated. By using alcohol as the solvent, the product exfoliated from FG by TRM was soaked and washed by ultrasound to remove PF, followed by drying, and then characterized by XRD, SEM, TEM and particle size analysis. It was found that the original FG with 150 μm in size and several microns in thickness was constantly exfoliated. When the exfoliating times were increased gradually to 8 or even 16 times, GNPs were obtained with a size of 10-30 μm and a thickness of 30-100 nm. This technical ideal can be applied in low-carbon and ultra-low carbon refractory industries to reduce carbon content, as well as in resin based carbon fiber composites for aviation industry to improve resin strength.

Abstract:The effect of SiO2 on the sintering rate of YSZ ceramics as well as on the morphology and properties of YSZ during sintering are studied. In this work, YSZ samples of 10% pores with different SiO2 content were prepared. The sample microstructures are characterized by scanning electron microscopy (SEM). The sample porosity was obtained by the Archimedes method. The phase composition, mechanical and thermal properties of samples after sintering were measured. It is found that the introduction of 0.3wt% SiO2 will make the YSZ grain size larger and the porosity decrease significantly. The hardness, Young's modulus and thermal conductivity of samples change faster due to the introduction of SiO2.

Abstract:Polymer-infiltrated-ceramic composites have already shown mechanical properties comparable to that of natural tooth. Composites with gradient mechanical properties as that of the natural tooth have seldom been fabricated. The aim of this work was to examine the gradient mechanical properties of natural tooth and fabricate polymer-infiltrated-ceramic to simulate simulate natural tooth and its mechanical behaviors. The elastic modulus and Vickers hardness of enamel and dentin were examined through nano indentation, which showed gradient characteristics. There were great differences in the mechanical properties of resin infiltrated partially sintered sodium aluminum silicate, alumina and zirconia. The gradient change of mechanical properties was realized through gradually changing the ceramic component. The one is nano glass phase aluminum silicate sodium-micron α alumina laminated composites. The sintering temperature of ceramic green body is 700 °C. The holding hours are 2, 4 and 6 hours respectively. Flexural strength, fracture toughness, elastic modulus and hardness of the composite were tested, which show that elastic modulus and hardness of the aluminum silicate sodium-alumina composite exhibited gradient characteristics. Another is 3Y-PZT-micron α alumina laminated composites. The sintering temperature of green body is 1150 °C and 1200 °C, with holding time of 2 hours. The results showed that both elastic modulus and hardness exhibited gradient characteristics. SEM observation shows that an interlocking grid structure was formed in transition zone. Different from those of ordinary homogeneous materials, composites prepared in this study have anisotropy. And therefore, the mechanical properties of the composites are more close to the primary teeth.

Abstract:High chromium white iron composites reinforced with TiC (TiC/HCWI) were prepared by hot pressing of TiC and high chromium white iron (HCWI) powders. The effects of TiC on microstructure, phase composition, mechanical properties and wear resistance of TiC/HCWI were studied. Results showed that the growth of M7C3(M = Fe, Cr) in HCWI was effectively inhibited by TiC grains, refining the microstructure of HCWI. Rockwell hardness, fracture toughness, flexural strength and wear resistance of the fabricated composites increased with increasing the content of TiC. X-ray diffraction analysis and scanning electron scope were used to characterize the phase composition and microstructure of composites. The reinforcing mechanism of TiC was analyzed.

Abstract:SiC/SiBCN composites were prepared by SiC fiber as the reinforcing phase and SiBCN composite ceramic precursor as the impregnating agent. The composition, morphology and mechanical behavior of SiC/SiBCN composites before and after oxidation were analyzed by SEM and mechanical properties tests. The results show that with the increase of PBN content in SiBCN composite ceramic precursors, The quality retention of precursor ceramics increases first and then decreases, and the retention of SiC/SiBCN composites under 1000 ℃ after 20h oxidation increases first and then decreases. This is mainly due to the increase of the PBN content in the SiBCN multiphase ceramic precursor, which is beneficial to the increase of the crosslinking degree of the precursor molecules, and easier to form a stable three-dimensional network structure. In addition, porosity and oxidation behavior of SiBCN multiphase ceramics also affect the oxidation stability of SiC/SiBCN composites.

Abstract:A thermal protecting coating was prepared at 1200 ℃ using TaSi₂, MoSi₂, borosilicate glass powders as the starting materials. Subsequently the thermal protecting coating was heated at 1650℃ for 2 min and cooled naturally to room temperature. The microstructures and composition of the thermal protecting coating before and after heated at 1650℃ were measured by XRD, SEM and EDS. It is found that the surface of the as-prepared thermal protecting coating contained Ta₂O₅ and small amount of TaSi₂. Lots of Ta₂O₅ sheets were formed in the heating center region of the coating surface after the heating of 1650℃. The section of the coating close to the surface became dense after heating at 1650℃, and the thickness of the dense section was about 23 μm. There is an even distribution for Ta and Mo elements in the element mapping of coating section, that is, the composition of the thermal protecting coating is uniformed.

Abstract:Y2O3-MgO nanocomposite powders have been prepared by ball mill using the commercial Y2O3, MgO powders. The crystal structure, morphology, uniformity of the Y2O3-MgO nanocomposite powder have been characterized by XRD, SEM, EDS respectively. And then the hot-pressing has been used to densify of the Y2O3-MgO nanocomposite ceramic. The FTIR and Vickers hardness tester have been used to reveal the optical and mechanical properties of Y2O3-MgO nanocomposite ceramic with different preparation parameter. The transmittance and hardness reach to 80% (6μm) and 12.3 GPa respectively with optimal conditions.

Abstract:SnO2 nanomaterial was synthesized by a simple one-step hydrothermal method and the structure and morphology of the material was characterized by XRD, SEM, TEM and nitrogen adsorption-desorption. The results showed that the prepared SnO2 nanomaterial was composed of hollow nanospheres with a diameter of 150-200 nm and had a large specific surface area (82.6 m2/g). The SnO2 gas sensitive paste was applied to the interdigital electrode by screen printing technology to form thick film gas sensing elements, and the gas sensing properties of the elements toward hydrogen were studied. The results showed that SnO2 hollow nanospheres had high response value and fast response speed to hydrogen ranging from 5 to 200 ppm at a low temperature (200 oC). This is attributed to the hollow structure and large specific surface area of the prepared SnO2 material, which facilitates the adsorption and diffusion of hydrogen gas.

Abstract:Pt/NiO nanofibers were prepared by electrospinning followed by calcination. The crystal structure, morphology and electrical conductivity of the nanofibers were investigated by XRD, SEM, TEM and semiconductor analyzer, respectively. The results show that rough, continuous and uniform nanofibers were successfully fabricated with full removal of inner cores. Adding NiO to Pt nanofibers is beneficial for the sake of maintaining the continuous structure and avoid the bead formation. The prepared Pt/NiO nanofibers have a conductivity of 5.95×10_² S/cm, strongly indicating Pt nanoparticles formed continuous networks in the composite structure.

Abstract:Zirconium nitride (ZrN) nanopowders were prepared by carbothermic nitriding of precursor in flowing nitrogen. The precursor was mixture of zirconia gel and carbon black which was obtained by using internal gelation process. The heat treatment behavior of the precursor material, phase composition, morphology and microstructure of powder products were characterized by simultaneous thermogravimetric analysis and differential scanning calorimetric analysis (TGA/DSC), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). With increase in temperature, nitriding level increased. Pure ZrN phase was achieved at 1400°C and the particle size of the powder product was in nanometers. Carbon plays an important role of reductant in nitridation process and the carbon to zirconium mole ratio should be properly controlled to ~2 such that desired ZrN products could be prepared.

Abstract:The porous SiC ceramics / Zr-based amorphous alloy composites were prepared by the pressure - infiltration casting method. The influence of pressure - infiltration casting holding time and the properities of porous SiC ceramics on the dynamic compression performance were investigated with the split Hopkinson pressure bar (SHPB) and the S-4800 scanning electronic microscope (SEM). The results showed that The dynamic compressive strength of porous SiC ceramic /Zr based amorphous alloy composites was significantly affected by the holding time and the properties of porous SiC ceramic. The composited exhibited the highest dynamic compressive strength which was1757MPa with the porosity and Average aperture size were 23.77 and 26.72um, respectively, under the condition of the pressure - infiltration casting temperature and time were 860℃ and 6.0min, respectively. The fracture mode of the composite shows the brittle fracture under the dynamic compress load. The fracture morphology characteristics included the cleavage steps appear in ceramic with different characteristics and Different patterns of veins in Zr-base amorphous alloy kept in relatively intact. The Zr-based amorphous alloy can effectively hinder cracks expansion with the surrounding silicon carbide broke up and movement with amorphous alloys, which would improve the dynamic compressive strength of porous SiC ceramic / Zr-based amorphous composites.

Abstract:The preparation of large hexagonal boron nitride (h-BN) nanosheets with high crystallinity has always been a challenging topic. In this paper, a method for preparing high crystallinity h-BN nanoparticles by microwave-assisted hydrothermal is presented. By means of XRD, SEM, TEM, AFM, Raman and other characterization methods, the validity of the method was proved, and the properties of the nanosheets were characterized. Based on the results of characterization analysis, the mechanism of microwave hydrothermal to prepare boron nitride nanosheets was proposed, which laid a foundation for the preparation of other two-dimensional materials.