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Using Ti3AlC2 as the precursor, a new MAX phase Ti3ZnC2 was synthesized via an A-elemental substitution reaction in a molten salts bath. Composition and crystal structure of Ti3ZnC2 were confirmed ...

Au nanorods (Au NRs) with good monodispersity and uniform aspect ratio were prepared via seed-meditated method. Au/Pd nano-dumbbells (Au/Pd NDs) were synthesized by using H2PdCl4\ as precursor, hexadecyl trimethyl ammonium chloride (CTAC) as soft template, Ag+ as structure-directing agent and ascorbic acid as reduction agent to modify Au NRs. Structure and morphology of the samples were characterized by transmission electron microscope (TEM), energy dispersive spectrometer (EDS) and ultraviolet-visible-near infrared spectrophotometry (UV-Vis-NIR). The formation mechanism of Au/Pd NDs were discussed. The results of Au/Pd NDs samples demonstrated that lots of poly-crystalline Pd particles were deposited onto two ends of Au nanorods selectively to form dumbbell-like structure. The dumbbell size can be continuously tuned by adjusting the molar ratio of AA and H2PdCl4. The experiments of reduction of p-nitrophenol by NaBH4 to p-aminophenol indicate that the sample with good dispersibility and large number of total catalytic active sites of Pd nanoparticles has high catalytic performance. Adding 0.04 mg/mL Au/Pd NDs with suitable Pd particles size (20.7 nm) show excellent catalytic activity (rate constant 0.44 min(-1)), indicating it is useful for reducing p-nitrophenol.

探究HfO 2 薄膜的激光损伤特性以进一步提高激光损伤阈值(Laser Induced Damage Threshold, 简称LIDT), 对其在高功率激光系统中的广泛应用具有重要的意义。在不同的离子源偏压下, 采用等离子体辅助电子束蒸发金属铪(Hf)并充氧(O 2 )进行反应沉积法制备了中心波长为1064 nm, 光学厚度为4H的HfO 2 薄膜样品。测试了薄膜组分和残余应力; 根据透射谱拟合了薄膜的折射率; 通过XRD谱图和SEM表面形貌图分析了薄膜的微观结构; 对激光损伤阈值、损伤特性和机理进行了论述。结果表明: 偏压100 V时制备的薄膜具有最佳O/Hf配比; 薄膜压应力和折射率均随偏压降低而减小。薄膜内存在结晶, 激光能量在晶界缺陷处被强烈聚集和吸收, 加速了膜层的破坏, 形成由几百纳米的烧灼坑聚集而成的海绵状损伤结构。随着偏压降低, 膜结晶取向由()晶面向(002)晶面转变, 界面能降低; 晶粒减小, 结构更均匀, 缓解了激光能量在晶界处的局部聚集与吸收, 表现出较大的激光损伤阈值。

SiC with d0 ferromagnetism is thought to be one of the most important materials in the spintronics field, and it has received widespread attention. In this paper, Al: SiC magnetic powder is fabricated by high temperature calcination method with the protection of Ar gas. X-ray diffraction results show that the obtained powder is of 6H-SiC phase, and Al is proposed to enter into the 6H-SiC crystalline. Raman results show that Ar gas plays a crucial role in impeding the SiC from decomposing at high temperature. With the protection of Ar gas, it maintains round shape after calcination about 2200℃, no any other peakis detected in the Raman spectrum. Without the protection of Ar gas, SiC particle would decompose into graphite, and the instinct peak of graphite is detected in the Raman spectrum. Energy dispersive spectrometer results show that there is 0.96 at% Al in the powder. The obtained powder shows magnificent magnetic hysteresis loop and large coercive force. Its saturation magnetic moment reaches 0.07 emu/g after calcination at 1800℃. Its coercive force reaches a maximum after calcination at 2000℃, while the saturation magnetic moment is 0.012 emu/g. With the rise of calcination temperature, the magnetism of the powder changes from diamagnetism to ferromagnetism. But when the calcination temperature rises to 2200℃ or more, it would change back to diamagnetism. The phenomenon of ferromagnetism disappearing is similar to that in ZnO as reported. The total quantity of magnetic impurities(Fe, Co, Ni) is evaluated to be less than 5 ppm. Saturation magnetic moments arising from these impurities can be calculated to be less than 10-5 emu/g according to the reported results, which is impossible to affect the accuracy in the experiment. Thus it is proposed that the ferromagnetism originates from the doping of Al in SiC powder. To understand the origin of the observed magnetism, we carry out first principles calculations based on spin polarized density functional theory. All the calculations are performed by using the generalized gradient approximation in the form of the Perdew-Burke-Ernzerhof function, which is implemented in the Viemma ab initio simulation package. A supercell consisting of 331 unit cells of 6H-SiC containing one AlSi-VSi, corresponding to a defect concentration of 0.93 at%, is built for calculations. The origin of its ferromagnetism is studied, and its spin situation in the space is mapped. The results show that the combination of Al and vacancy leads to a local magnetic moment of 1.0 B, and magnetic coupling is steady in the c axis direction. It is found that the p electron of carbon is the origin of the net spin.

A novel surface modification method for C-f/SiC composites is proposed with aqueous slurry painting together with reaction bonding. Stable slurries were obtained by dispersing SiC to carbon black in aqueous solution, under centain binder content and solid loading conditions. The results show that porous carbonaceous C/SiC tape with porosity of 49% could be obtained by aqueous slurry painting. Si/SiC coating with high density and strong bonding onto the substrate is realized by infiltrating liquid silicon into the as-prepared tape. A reaction layer of similar to 15 um in thickness is formed between the coating and the substrate. This Si/SiC coating exhibits excellent mechanical properties, with HV hardness of (14.19 +/- 0.46) GPa and fracture toughness of (3.02 +/- 0.30) MPa.m(1/2). The coating is achieved fine surface of 2.97 nm RMS in roughness after precision grinding and polishing.

The solid state sintered SiC (SSiC) ceramics are mainly used for structural materials, but they are rarely used for electronic devices and resistance components. In this work, the electrical properties of the SSiC ceramics with different carbon additives were investigated, including V-I characteristic, the relationship between current and resistance, as well as the relationship between temperature and resistance. These results show that the SSiC ceramics present obvious nonlinear electrical behavior and their resistance decreases with the current increase. When the electrical field intensity is over 15.8 V/mm for the SSiC ceramics with 3wt% carbon additives, as well as 70.7 V/mm for the SSiC ceramics with 6wt% carbon additives, the boundary barrier is breakdown and the resistance becomes very low, due to the resistance being only controlled by the grain size. The resistance of the SSiC ceramics decreases with the temperature increase at the electrical field intensity of 1 V/mm, indicating thermo-sensitive characteristic of SSiC ceramics of which the resistance is changed from 10(6) Omega.cm at 25 degrees C to 5 Omega.cm at 400 degrees C.

The effect of density and surface roughness on the optical properties of silicon carbide optical components is investigated. The density is the major factor of the total reflectance while the surface roughness is the major factor of the diffuse reflectance. The specular reflectance of silicon carbide optical components can be improved by increasing the density and decreasing the surface roughness, in the form of reducing bulk absorption and surface-related scattering, respectively. The contribution of the surface roughness to the specular reflectance is much greater than that of the density. When the rms surface roughness decreases to 2.228 nm, the specular reflectance decreases to less than 0.7% accordingly.

为制备高性能SiC-ZrB 2 网眼多孔陶瓷, 对SiC-ZrB 2 复合浆料的流动性质进行了初步研究。分析SiC和ZrB 2 粉体在水溶液中的流动性质, 并对分散剂硅溶胶和粘结剂羧甲基纤维素(CMC)的添加量进行优化。基于以上优化结果, 重点探索了固含量和ZrB 2 添加量对浆料流动性质的影响. 固含量为65wt%的浆料可作为有机泡沫浸渍过程的最有条件, 而ZrB 2 添加量不可超过25wt%。

The densification process of liquid phase sintered SiC ceramics with Al2O3 and Y2O3 as sintering additives was investigated by in situ measurement apparatus combined with conventional methods. The shrinkage curve, mor- phology of the sample and liquid phase formation process simulation were observed by high temperature in-situ ob- servation furnace. The relative density, flexural strength and microstructure evolution were characterized by analysis of samples sintered at temperatures ranging from 1640℃ to 1920℃ at 40℃ interval. The obvious temperature that liquid phase began to function was confirmed between 1640℃ to 1680℃. The classical liquid phase sintering theory was testified. Highly-densified SiC ceramics were obtained by being sintered at 1880℃, of which the relative density was (99.46 ± 0.37)%, and the flexural strength was (650 ± 26) MPa.