Hydrothermal synthesis and optical properties of Ni doped ZnO hexagonal nanodiscs

Single crystalline Ni-doped ZnO hexagonal nanodiscs are successfully synthesized. Zinc acetate, nickel nitrate, sodium hydroxide and poly (vinyl pyrrolidone) (PVP) were mixed together and transferred to a 100 ml Teflon-lined stainless steel autoclave which kept at 150 °C for 24 h. The morphology and microstructure were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. The investigation confirmed that the products were of the wurtzite structure of ZnO. The doped hexagonal nanodiscs have edge length 30 nm and thickness of 45 nm. EDX result showed that the amount of Ni in the product is about 12%. Photoluminescence of these doped hexagonal nanodiscs exhibits a blue shift and weak ultraviolet (UV) emission peak, compared with pure ZnO, which may be induced by the Ni-doping. The growth mechanism of the doped hexagonal nanodiscs was also discussed.     

A facile method to prepare MoS2 with nanolameller-like morphology

MoS₂ nanolamellers were synthesized by a one-step oxidation-reduction reaction in solution, in which the (NH₄)₂MoS₄ and H₂C₂O₄·2H₂O were used as reactants and then calcined at 800 °C under N₂ for 1 h. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The diameter and nanoplate thickness of the obtained MoS₂ nanolamellers were approximately 80 nm and 20-30 nm, respectively. These novel structures of nanolamellers had potential applications in solid lubricants.     

Ti-600合金蠕变性能及硅对其蠕变性能的影响

研究了Ti-600合金在3种温度(550、600、650℃)、5种应力(150、200、250、300、350 MPa)下的蠕变性能,并分析了硅化物对合金蠕变性能的影响。研究结果表明,Ti-600合金具有较小的稳态蠕变速率及较大的蠕变激活能,反映出该合金具有较好的蠕变抗力。当温度升高、应力增大时,Ti-600合金的稳态蠕变速率增大。600℃下,当蠕变应力高达350 MPa时,Ti-600合金的稳态蠕变速率低至3.72×10-7s-1。Ti-600合金的蠕变激活能最高可达574.6kJ·mol-1,最低为332.7 kJ·mol-1。在蠕变过程中,Ti-600合金内析出了S2型(TiZr)6Si3硅化物,能够钉扎位错、阻碍位错滑移,提高合金的蠕变抗力。     

Si含量对Fe-Cr-Si系合金组织与耐蚀性能的影响

利用电弧熔炼工艺制备了不同Si含量(6wt%、8wt%、10wt%、12wt%)的Fe-Cr-Si系合金,系统研究了Si含量对Fe-Cr-Si系合金组织和耐腐蚀性能的影响。结果表明,4种不同Si含量的Fe-Cr-Si合金均由初生树枝晶和枝晶间基体组成,Si含量的增加促进了合金中金属硅化物Fe₃Si的形成。Fe-Cr-Si系合金在10%HCl中均表现出良好的耐蚀性能,浸泡72 h后合金表面形成的SiO₂具有钝化作用,且Si含量的增加可以显著提高合金的耐蚀性能,当Si含量达到12%时,耐蚀能力为2Cr13不锈钢的26倍。     

Nb-Hf合金表面Si-Ti-Cr硅化物涂层在大气和真空中的高温热震性能

为了提高Nb-Hf合金的高温热震性能,采用浆料烧结和高温渗透法制备了Si-Ti-Cr硅化物涂层,对比分析了Si-Ti-Cr硅化物包覆的Nb-Hf合金样品在大气和真空条件下的高温热震性能。通过模拟在热冲击过程中涂层的温度场和热应力场分布,揭示了Si-Ti-Cr涂层在大气和真空条件下的热冲击失效机理。结果表明,在1300 ℃热震循环100次条件下,涂层的真空失重小于0.8 mg/cm²;在1600 ℃热震循环200次条件下,涂层的空气增重小于3 mg/cm²。硅化物涂层在1300 ℃真空环境下和1600 ℃空气环境下具有优异的抗热震性能。     

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti₅Si₃ was prepared by adding Si into MoNbTaTiV high-entropy alloy. The obvious oriented in situ Ti₅Si₃ phase formed eutectic phase with BCC phase in the inter-dendritic area, which leads to excellent properties of the composite. The alloy exhibits ultra-high yield stress of 718 MPa at 1200 °C and obvious compression plasticity. After reaching the maximum strength, dynamic recovery (DRV) and dynamic recrystallization (DRX) caused soften phenomena. The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction. The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms, while the Ti₅Si₃ phase has a geometric DRX mechanism in addition to the above two mechanisms. The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.     

Metal silicide/poly-Si Schottky diodes for uncooled microbolometers

Nickel silicide Schottky diodes formed on polycrystalline Si 〈P〉 films are proposed as temperature sensors of monolithic uncooled microbolometer infrared focal plane arrays. The structure and composition of nickel silicide/polycrystalline silicon films synthesized in a low-temperature process are examined by means of transmission electron microscopy. The Ni silicide is identified as a multi-phase compound composed of 20% to 40% of Ni₃Si, 30% to 60% of Ni₂Si, and 10% to 30% of NiSi with probable minor content of NiSi₂ at the silicide/poly-Si interface. Rectification ratios of the Schottky diodes vary from about 100 to about 20 for the temperature increasing from 22℃ to 70℃; they exceed 1,000 at 80 K. A barrier of around 0.95 eV is found to control the photovoltage spectra at room temperature. A set of barriers is observed in photo-electromotive force spectra at 80 K and attributed to the Ni silicide/poly-Si interface. Absolute values of temperature coefficients of voltage and current are found to vary from 0.3%℃ to 0.6%/℃ for forward bias and around 2.5%/℃ for reverse bias of the diodes.     

Structure and oxidation behavior of Si-Y co-deposition coatings on an Nb silicide based ultrahigh temperature alloy prepared by pack cementation technique

In order to improve the oxidation resistance of silicide coatings on Nb silicide based alloys, Y-modified silicide coatings were prepared by co-depositing Si and Y at 1050, 1150 and 1250 °C for 5-20 h, respectively. It has been found that the coatings prepared by co-depositing Si and Y at 1050 and 1150 °C for 5-20 h as well as at 1250 °C for 5 h were composed of a thick (Nb,X)Si₂ (X represents Ti, Cr and Hf elements) outer layer and a thin (Nb,X)₅Si₃ inner layer, while the coatings prepared by co-depositing Si and Y at 1250 °C for 10-20 h possessed a thin outer layer composed of (Ti,Nb)₅Si₃ and Ti-based solid solution, a thick (Nb,X)Si₂ intermediate layer and a thin (Nb,X)₅Si₃ inner layer. EDS analyses revealed that the content of Y in the (Nb,X)Si₂ layers of all the coatings was about 0.34-0.58 at.% while that in the outer layers of the coatings prepared by co-depositing Si and Y at 1250 °C for 10-20 h was about 1.39-1.88 at.%. The specimens treated by co-depositing Si and Y at 1250 °C for 10 h were selected for oxidation test. The oxidation behavior of the coating specimens at 1250 °C indicated that the Si-Y co-deposition coating had better oxidation resistance than the simple siliconized coating because the oxidation rate constant of the Si-Y co-deposition coating was lower than that of the simple siliconized coating by about 31%. The scale developing on the Si-Y co-deposition coating consisted of a thicker outer layer composed of SiO₂ and TiO₂ and a thinner SiO₂ inner layer.     

Properties of mechanically alloyed P/M composites of Al–Mg2Si–oxide systems

With a purpose of obtaining light-weight materials of high strength, mixture of aluminum powder and Mg₂Si powder at the composition of Al–20mass%Mg₂Si₂ was mechanically alloyed with addition of oxide (Cr₂O₃, Fe₂O₃, MnO₂) powders. Mechanical alloying was conducted by using an Attritor-type ball mill under argon atmosphere. The mechanically alloyed powders were consolidated to the P/M materials by vacuum hot pressing and hot extrusion. Solid-state reactions during mechanical alloying and subsequent thermomechanical processing were studied. Their structures and mechanical properties were examined and compared with hyper-eutectic Al–Si based P/M materials. All added oxides were decomposed and aluminide compounds were formed during heating of the extruded P/M materials. Mg₂Si was only partially decomposed after heating P/M materials. All the P/M materials of Al–Mg₂Si–oxide showed high compressive strength above 900 MPa. Among them, the highest strength of 1090 MPa was obtained for Al–Mg₂Si–Fe₂O₃. Even the P/M material of Al–Mg₂Si without oxide addition showed compressive strength of 795 MPa. The Al–Mg₂Si based P/M materials showed higher compressive strength and higher ductility than hyper-eutectic Al–Si based P/M materials.