中空Ta2O5/TiO2复合光催化剂的可控氧化制备及性能

以钛粉、钽粉为原料,炭黑作为反应性模板,通过熔盐法在炭黑表面原位生长了TaTiC₂纳米碳化物涂层,并以所得TaTiC₂/C复合物为碳化物前驱体,再经可控氧化制备出中空Ta₂O₅/TiO₂复合光催化剂。采用X射线粉末衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、紫外-可见（UV-Vis）漫反射（DRS）及N₂物理吸附等手段对所制备的光催化剂进行形貌、显微结构及孔结构表征。以高压汞灯为紫外光源,以亚甲基蓝为目标降解物,通过光催化降解实验评价中空Ta₂O₅/TiO₂复合光催化剂的光催化活性。结果表明,熔盐法生长碳化物涂层厚度均匀（20~30 nm）,碳化物主要以TaTiC₂晶相存在且具有纳米级的颗粒尺寸。中空Ta₂O₅/TiO₂复合光催化剂同时具有200 nm左右的中空大孔结构及壳层10 nm左右的介孔结构。中空大孔和介孔的存在提高了所制备催化剂对亚甲基蓝的吸附能力。此外,TiO₂与Ta₂O₅通过电子能带结构的耦合,有效提高了光生电子和空穴的分离效率,从而显著提高了光催化活性。n_Ti∶n_Ta=2.5∶1.5时,相应的中空Ta₂O₅/TiO₂复合光催化剂表现出最佳的光催化活性,对亚甲基蓝的紫外光催化降解率高达97%。     

沉淀铁催化剂在F-T合成反应过程中的物相变化

 采用元素分析、X射线衍射和穆斯堡尔谱等手段研究了喷雾干燥沉淀Fe-Cu-K/SiO2催化剂在F-T合成反应过程中的物相变化. 结果表明,新鲜催化剂样品主要由α-Fe2O3组成,且81.1%的α-Fe2O3粒径小于13.5 nm. 随着反应时间的延长,催化剂表面碳沉积物的含量逐渐增多,不饱和度逐渐增大; χ-Fe5C2的含量逐渐增多,Fe3O4的含量逐渐减少并趋于稳定. 超顺磁Fe3+的含量呈先增加后减少的变化趋势. 由于碳沉积物是由CO生成的,而χ-Fe5C2是由α-Fe2O3经Fe3O4生成的,故催化剂表面碳沉积物的生成先于χ-Fe5C2的生成.     

SiC/环氧树脂复合材料冲蚀磨损性能的研究

采用环氧树脂为粘接剂制备了SiC/环氧树脂复合材料,在自制的射流式冲蚀磨损试验机上研究了SiC/环氧树脂的冲蚀磨损性能.结果表明:大尺寸SiC颗粒制备的复合材料较小尺寸SiC颗粒制备的复合材料具有更好的冲蚀磨损性能,且大尺寸SiC颗粒复合材料的冲蚀磨损性能优于Q235钢,而小尺寸SiC颗粒复合材料则低于Q235钢.随着冲蚀角度的变化,其平行材料表面的切削分量和垂直材料表面的冲击分量将会发生变化,低角度冲蚀磨损机理以显微切削和碾压造成环氧树脂及SiC颗粒的层片状脱落为主转变为高角度冲蚀磨损以SiC颗粒碎裂造成环氧树脂疲劳脱落为主.     

Ohmic contacts of 4H-SiC on ion-implantation layers

The ohmic contacts of 4H-SiC are fabricated on nitrogen ion implanted layers made by performing box-like-profile implantation three and four times. Implantation parameters such as the standard deviation σ and the projection range R_p are calculated by the Monte Carlo simulator TRIM. Ni/Cr ohmic contacts on Si-face 4H-SiC implantation layers are measured by transfer length methods (TLMs). The results show that the values of sheet resistance R_sh are 30~kΩ /□ and 4.9~kΩ/□ and the values of specific contact resistance ρ_c of ohmic contacts are 7.1× 10^-4Ω.cm² and 9.5× 10^-5Ω.cm² for the implanted layers with implantation performed three and four times respectively.     

SiC epitaxial layers grown by chemical vapour deposition and the fabrication of Schottky barrier diodes

This paper presents the results of unintentionally doped 4H-SiC epilayers grown on n-type Si-faced 4H-SiC substrates with 8° off-axis toward the [11\overline 2 0] direction by low pressure horizontal hot-wall chemical vapour deposition. Growth temperature and pressure are 1580~°C and 10⁴~Pa, respectively. Good surface morphology of the sample is observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize epitaxial layer thickness and the structural quality of the films respectively. The carrier concentration in the unintentional 4H-SiC homoepitaxial layer is about 6.4×10¹⁴~cm^-3 obtained by c--V measurements. Schottky barrier diodes (SBDs) are fabricated on the epitaxial wafer in order to verify the quality of the wafer and to obtain information about the correlation between background impurity and electrical properties of the devices. Ni and Ti/4H-SiC Schottky barrier diodes with very good performances were obtained and their ideality factors are 1.10 and 1.05 respectively.     

不同压力下硬质合金表面微波等离子体化学气相沉积SiC涂层规律性的研究

以氢气和四甲基硅烷作为先驱气体,采用微波等离子体化学气相沉积法,不同沉积压力条件下、在YG6硬质合金表面制备了的SiC涂层.利用SEM、EDS、XRD、划痕测试法对SiC涂层的表面形貌、相组成和附着力进行了分析.实验结果表明,在较低的压力下,SiC涂层为胞状的纳米团聚物,且胞团的尺度随压力的升高而变小;随着压力的升高,胞状SiC开始并最终全部转变为片层状SiC,并在此过程中伴随着颗粒状Co2Si的形成与长大;随着压力的继续升高,片层状SiC开始转变为须状SiC.胞状SiC向片层状SiC的转变会使涂层致密度提高,而涂层对硬质合金衬底的附着力也会随之增强;Co催化作用的上升引起的片层状SiC向须状SiC的转变会导致SiC涂层的附着力明显降低.以具有片层状特征的SiC作为过渡层,可在未经去Co酸蚀预处理的硬质合金衬底上制备出具有较好附着力的金刚石涂层.     

类石墨烯结构二维层状碳化硅的非线性二次谐波特性的第一性原理研究

二维层状碳化硅（two-dimensional layered silicon carbide,2d-SiC）是一种类石墨烯结构的半导体,在非线性光学频率转换上具有潜在的应用.本文基于第一性原理高精度全电子势线性缀加平面波结合态求和方法研究了层叠和拉伸下类石墨烯2d-SiC结构的非线性二次谐波系数.非线性过程物理源分析表明,三带项构成的单粒子跃迁过程是2d-SiC结构的二次谐波过程的主要微观跃迁机制,电子的带间运动显著受到带内运动的调谐,π电子离域带对非线性过程有重要贡献.理论上给出了2d-SiC结构的二次谐波系数的角度依赖,为实验研究提供理论参考.拉伸可导致不同频率的二次谐波增强.     

Development and Application of WC-Based Alloys Bonded with Alternative Binder Phase

WC–Co alloys have enjoyed great practical significance owing to their excellent properties during the past decades. Despite the advantages, however, recently there have been concerns about the challenges associated with the use of Co, i.e. price instability (the major incentive for alternative binder development), toxicity and properties degeneration. Thus, the current study applies towards summarize the current knowledge of the impacts of different binders partial or total substitution of the traditional cobalt binder highlighting the influences of metal, intermetallic compound, ceramics (metal oxide) binders on the sintering behavior as well as mechanical properties of WC-based alloys, so as to provide reference for those who would like to enhance the performance of cemented carbides with better reliability advancing them to further wide applications and prepare the alloys in a way that is environment friendly, harmless to human health and low in production cost. It is concluded that the alternative for cobalt in tungsten carbide cemented carbide is economically and technically feasible. Strict control of the chemical composition of the binder coupled with taking into careful account the effects of sintering process and subsequent treatments is of great importance to improve the sintering behavior and tailor mechanical properties of tungsten carbide-based hardmetals.     

盐封后碳化钼电催化剂的制备及其氢析出性能

Molybdenum carbide is regarded as an excellent substitute for Pt-based catalysts in the hydrogen evolution reaction (HER), owing to its low cost, superior catalytic performance, and long-term stability. In this work, salt-sealed molybdenum carbide was prepared using sodium molybdate and 2, 6-diaminopyridine as the reactive raw materials, followed by continuous salt sealing and calcination of the precursor under an inert atmosphere. The morphology, composition and structure of salt-sealed molybdenum carbide were determined by scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicate that salt-sealed molybdenum carbide has irregular morphology and includes nanoparticles and nanorods. A comparison of the TEM images of Mo₂C with salt sealing (Mo₂C/SS) and Mo₂C without salt sealing (Mo₂C) indicates that Mo₂C/SS exhibits a smaller particle size. This suggests that salt sealing can efficiently avoid particle aggregation. The Brunauer-Emmett- Teller (BET) specific surface area of the catalysts was obtained from nitrogen adsorption/desorption isotherms. The increase in BET surface area from 2.55 to 8.14 m²·g⁻¹ after salt sealing provides evidence for the formation of pores in the product. The results of XRD, EDS and XPS analyses show that Mo₂C/SS has an orthorhombic crystal structure with molybdenum oxides on the surface, which may originate from surface oxidation. Considering the results of XPS and the turnover frequency (TOF) calculation, we can conclude that the formation of pores via salt sealing contributes to the exposure of more active sites, while simultaneously enlarging the contact area with oxygen. Therefore, higher molybdenum oxide content is generated on the surface, resulting in a lower proportion of active centers (molybdenum carbides) on the catalyst surface. Furthermore, the pseudocapacitance generated by the faradaic reaction of molybdenum oxides is superimposed on the double-layer capacitance of Mo₂C catalysts, which increases the double layer capacitance. Since the effect of pseudo-capacitance on Mo₂C/SS is more significant, the TOF number declines after salt sealing. Compared with Mo₂C, Mo₂C/SS exhibits three features that promote HER mass activity: (1) the generation of large quantities of pores via salt sealing leads to an increase in the BET surface area and exposure of more active sites, which is beneficial for improving HER performance; (2) the porous structure and enlarged surface area pave the way for effective mass and charge transfer; (3) the decrease of the Tafel slope from 145 to 88 mV·dec⁻¹. In summary, salt-sealed Mo₂C exhibited enhanced HER activity with an overpotential of 175 mV to achieve a current density of 10 mA·cm⁻². The Tafel slope for HER on salt-sealed Mo₂C is 88 mV·dec⁻¹. This can be considered as the proof of the Volmer-Heyrovsky mechanism with electrochemical desorption as the rate-determining step.     

直接以碳化钙为炔源合成有机化合物

以往利用碳化钙作为原料制备有机化学品时, 首先须将碳化钙转化成乙炔气体, 再由乙炔气体进一步制备有机化合物, 而乙炔气体易燃易爆, 反应条件苛刻, 应用受到一定限制。碳化钙可以由可再生的生物炭在较低的温度下快速制备, 是一种绿色经济的化工原料。因此, 直接利用碳化钙作为绿色炔源代替乙炔气体、乙炔试剂制备各种重要有机化学品将是一条简洁的绿色化学途径。本文综述了直接以碳化钙为炔源合成有机化合物的反应类型、反应机理以及研究现状, 展望了碳化钙作为固体炔源构建有机化合物的发展趋势。