纳米碳化钨的合成及其电催化活性研究

以钨酸和丙烯腈为原料,采用共沉淀法合成碳化钨（WC）前驱体,于H₂和Ar混合气氛中高温还原碳化制备纳米WC。采用傅立叶红外光谱、X射线衍射及扫描电镜等对试样进行表征,在酸性介质中采用循环伏安法测试Pt/WC电化学催化活性。结果表明,实验合成了较纯的纳米碳化钨,其颗粒形貌近似球形,粒径80 nm左右。Pt/WC的电化学表面积（ESA）较传统的Pt/C有较大提高,10%Pt/WC电流密度为51.2 mA·cm^-2。     

活性炭载碳化钨复合材料的制备及其对对硝基苯酚的电催化性能

以浓度为10%的偏钨酸铵溶液为前驱体、CH4/H2为还原碳化气氛,采用表面修饰技术和还原碳化技术制备了碳化钨(WC)/活性炭(C)复合材料。通过FT-IR、XRD、SEM等对制备的WC/C材料进行表征,结果表明,酸处理后的活性炭外表面大幅度增加了羟基和羰基,WC/C复合材料是由WC、W2C和C三相组成,碳化钨均匀地分散于活性炭表面,粒径约50～100nm。采用循环伏安法研究了碱性介质中WC/C-PME对对硝基苯酚的电还原行为,结果表明,该材料对对硝基苯酚的电催化活性优于WC和C,且WC/C材料在对硝基苯酚电还原过程中保持良好的化学稳定性。     

溶胶-凝胶法制备高表面积碳化钨

本文采用溶胶一凝胶法制备高表面积的碳化钨.CRD结果表明,该碳化钨为WC和β-W2C的混合物,其中β-W2C的含量很少.TEM观察显示,该碳化钨主要由无规则颗粒组成.N2吸附结果显示,碳化钨样品的表面积为150m2g-1,孔径分布主要集中在3-5nm范围内.     

WC/C制备条件对甲醇电氧化特性的影响研究

以钨酸铵为前躯体,采用程序升温控制还原法（TPR）制备了WC／C纳米颗粒,在碳载体存在的情况下,研究了钨源前躯体碳化过程中CH4与H2流量比对单-WC晶相以及Pt／WC／C电催化氧化甲醇性能的影响。XRD测试结果发现：仅在CH4：H2流量比为2时可获得单一WC多晶,其平均粒径为11．3nm。循环伏安实验结果证实：10wt％Pt-10wt％WC／C电催化氧化cH,OH的比质量活性达到875mA·mg^-1,远远高于10wt％Pt／C的658mA·mg^-1,且起始氧化电位负移80mV。计时电流法实验表明Pt／WC／C在酸性介值中稳定性高于Pt／C催化剂。     

WC/MMT纳米复合材料制备及其对PNP的电催化活性

以剥离后的蒙脱石(MMT)为载体,将浸渍法与原位还原技术相结合制备了碳化钨/蒙脱石(WC/MMT)纳米复合材料。采用X射线衍射、扫描电子显微镜和透射电子显微镜等手段对样品进行了表征。结果表明,剥离后蒙脱石的片层厚度为10～15 nm,层间距增大,边缘发生卷曲;复合材料由碳化钨(WC)、碳化二钨(W₂C)和蒙脱石组成,碳化钨颗粒均匀地分布于蒙脱石外表面。采用循环伏安法测试了样品对对硝基苯酚(PNP)的电化学还原性能,结果表明,WC/MMT纳米复合材料对对硝基苯酚具有良好的电催化活性,且具有较好的稳定性。蒙脱石是碳化钨基复合电催化材料良好的载体。     

场激活燃烧合成碳化钨和碳化钨钴反应机理

在场激活下燃烧合成碳化钨和碳化钨-钴复合材料，采用燃烧过程中切断电场的方法，得到了一系列不同相组成的燃烧产物，通过对样品从反应物端到产物端形貌和相组成的分析,研究了场激活下钨碳燃烧反应机制，WC的形成是通过钨碳之间的固-固反应进行的，首先生成W2C，然后再形成WC，W2C是反应的中间相。金属钴产生液相，促进了W2C的形成和W2C向WC的转化并与W和W2C作用形成WxCyCoz类化合物。     

碳化钨/碳纳米管纳米复合材料的制备及其对硝基苯的电催化活性

采用表面修饰技术和原位还原碳化技术制备了纳米碳化钨（WC）/碳纳米管（CNT）纳米复合材料,通过X射线衍射（XRD）、扫描电子显微镜（SEM）和热重-差热分析（TG-DTA）等手段对WC/CNT纳米复合材料的晶相组成、形态结构和热稳定性进行了表征,结果显示样品是由WC和CNT两相构成,纳米WC颗粒均匀地分散在碳纳米管上,粒径细小;在空气气氛中,WC/CNT纳米复合材料在470℃以下保持稳定。采用循环伏安法研究了WC/CNT纳米复合材料对硝基苯的电催化活性和电化学稳定性。结果表明,WC/CNT纳米复合材料对硝基苯的电催化活性优于纳米WC和CNT,且WC/CNT纳米复合材料在硝基苯电还原过程中保持良好的化学稳定性。     

碳化钨/碳气凝胶纳米复合材料增强Pt电催化甲醇性能的研究

以间苯二酚和甲醛为原料,采用溶胶-凝胶法原位合成WC纳米颗粒制备了碳化钨/碳气凝胶(WC/CAs);以WC/CAs为载体,利用微波加热乙二醇还原法制备了Pt/WC/CAs催化剂。运用循环伏安法(CV)、线性扫描(LSV)、计时电流法(CA)、能谱(EDS)、透射电子显微镜(TEM)和X射线衍射(XRD)等技术分析Pt/WC/CAs催化剂的组成、结构及其对甲醇的电催化氧化活性的影响。实验结果表明,载体中WC纳米颗粒的加入促进Pt贵金属颗粒对甲醇的电催化氧化活性,正扫电流峰ip与扫描速率的平方根v1/2线性相关,Pt/WC/C催化氧化甲醇的过程受扩散控制;且电催化活性比Pt/C要好。     

沉淀-水解法制备ZrO2纳米微晶及其表征

运用沉淀-水解法在高温、高压条件下制备ZrO2纳米微晶,所制得的ZrO2纳米微晶利用X-射线衍射（XRD）测得为四方晶系,利用扫描电子显微镜（SEM）测定其粒径为100 nm左右。     

一种纳米级碳化钨粉的制备方法

本发明公开了一种纳米级碳化钨粉[粒度≤0．2μm、w（化合碳）≥6．10％]的制备方法，它是以纳米（粒度≤0．2μm）钨粉、纳米炭黑为原料，将纳米钨粉与纳米炭黑放入容器，并向容器内通入惰性气体，在惰性气体保护状态下将纳米钨粉与纳米炭黑进行搅拌混合，混合过程中加入0．5％～3％的有机活性材料，待混合均匀后，在500～1500kg／cm^2压力下压制成块，煅烧压块（W＋C），使纳米钨粉、纳米炭黑化合形成碳化钨（WC），待碳化钨形成后，采用气流研磨方式将碳化钨研磨、打散形成纳米级碳化钨粉。该方法具有工艺流程短、投资少、产量大、产品质量及稳定性均可得到大幅度提高的特点，是一种环保型的制备方法。     

火柴棒状纳米碳管的制备及其生长机理

以钨酸钠为钨源,氯化钠为诱导剂,通过水热法制备了三氧化钨(WO₃)纳米棒,再以葡萄糖为碳源,经再次水热反应对WO₃表面进行碳包覆,然后在氢气和甲烷混合气氛中反应一段时间获得了具有火柴棒状结构的纳米碳管。采用X射线衍射分析、场发射扫描电子显微镜、透射电子显微镜和X射线能量散射谱等手段对样品的晶型、形貌、微结构和表面化学元素进行了表征与分析。结果表明,样品由纳米碳管和碳化钨(WC)构成。其中,纳米碳管为火柴棒状,长度0.5～1.0 μm,直径100 nm左右;WC颗粒位于纳米碳管内部,其大小决定了火柴棒状纳米碳管的内径。这充分说明WC在碳管的生长过程中充当催化剂的作用。     

Pt/WC催化剂的制备及其在气体扩散电极上的氧还原性能

以喷雾干燥处理的偏钨酸铵为前驱体,采用CO/CO₂为还原碳化气氛,利用程序升温气固反应法制备了分散性良好的空心球状WC粉体,并分别以WC和Vulcan XC-72R碳粉为载体,采用液相沉积还原法制备了Pt/WC及Pt/C催化剂。XRD和SEM测试结果表明, 所制备催化剂中Pt/WC的Pt粒子粒径要大于Pt/C。酸性条件下氧电极极化曲线测试结果表明, Pt/WC的氧还原催化性能要优于Pt/C,这主要表现在同一电位下较高的电流密度及还原起始电位正移约28 mV。讨论了Pt/WC催化性能提高的可能原因及催化机理,并对控制条件下Pt/WC氧气扩散电极的交流阻抗谱进行了研究。     

碳化钨纳米晶薄膜电极在对硝基苯酚电化学还原中的催化性能

采用磁控溅射物理气相沉积和等离子体增强化学气相沉积技术,在金属镍基体上制备具有纳米晶结构的碳化钨薄膜;采用循环伏安、准稳态极化和恒电位阶跃等电化学方法研究了对硝基苯酚(PNP)在碳化钨纳米晶薄膜电极上电化学还原的特性和机理.研究表明,采用磁控溅射物理气相沉积技术制备得到的薄膜是由直径为20nm的WC1-X构成,在这种薄膜电极上,PNP电化学还原在电位为(0.95V(Vs. SCE)时,出现一个电流密度为6.0mA(cm(2还原峰,还原反应的表观活化能为12.0kJ(mol(1;而采用等离子体增强化学气相沉积技术制备得到的薄膜是由直径为35nm的纯相WC构成,PNP在该薄膜电极上电化学还原峰电位为(1.05 V(Vs. SCE),还原电流达10.0 mA(cm(2,表观活化能为10.9 kJ(mol(1. PNP在这两种碳化钨薄膜电极上都经过两步不可逆的电化学反应还原成对氨基苯酚,控制步骤为电极反应的电荷传递过程.     

Reaction Sintering of HfC/W Cermets with High Strength and Toughness

Hafnium carbide/tungsten (HfC/W) cermets were prepared by an in situ reaction sintering process, using hafnium oxide (HfO₂) and tungsten carbide (WC) as the raw materials. The reaction path, densification behavior, microstructure development, and mechanical properties of the cermets were comprehensively investigated. It was found that WC decomposed to tungsten semicarbide (W₂C) and tungsten (W) in sequence, and meanwhile HfC was formed by carbothermal reduction between HfO₂ and as‐released carbon from the dissociation of WC. The solid solution formation between HfC and W during sintering was also studied. The obtained cermets (>98% TD) have a Vickers' hardness of 8.16 GPa, a fracture toughness of 14.45 MPa m^1/2, and a high flexural strength of 1211 MPa.     

Precursor synthesis and properties of nanodispersed tungsten carbide and nanocomposites WC:nC

Nanoscale tungsten carbide (WC) and WC:nC nanocomposites have been synthesized by the precursor method. The precursor, obtained in the form of a glassy mass by thermal treatment of a mixture of (NH₄)₁₀W₁₂O₄₁∙7H₂O and glycerol, was heated in inert gaseous atmosphere up to 1050–1100 °C. The concentration of chemically active carbon in the precursor and nanocomposites depends on the W/C ratio in the initial mixture. At W/C=1/3 pure tungsten carbide is formed; at W/C>1/3 composites of WC and free carbon (WC:nC) are formed. Heating of the precursor with W/C=1/6 up to 1100 °C in helium atmosphere results in the formation of carbon-encapsulated tungsten carbide nanoparticles. An increase in the precursor-heating rate leads to the formation of chain-like structures. Each chain consists of hexagonal WC grains with unit cell parameters a=2.93 Å and c=2.83 Å. Free carbon in WC:nC composites forms agglomerates of carbon “nano-onions” of spherical or multi-layered tubular shapes.     

Plasma Synthesis of Tungsten Carbide Nanopowder from Ammonium Paratungstate

A thermal plasma process has been applied to the synthesis of nanosized tungsten carbide powder with ammonium paratungstate (APT) as the precursor. The reduction and carburization of vaporized APT produced nanosized tungsten carbide (WC_{1− x} ) powder, which sometimes contained a small amount of W₂C phase. The effects of reactant gas composition, plasma torch power, the flow rate of plasma gas, and the addition of secondary plasma gas (H₂) on the product composition and particle size were investigated. The produced tungsten carbide (WC_{1− x} ) powder was <20 nm in particle size. The synthesized powders were also subjected to a hydrogen heat treatment to fully carburize the WC_{1− x} and W₂C phases to the WC phase as well as to remove excess carbon. Finally, WC powder of particle size <100 nm was obtained.     

Molten salt synthesis of continuous tungsten carbide coatings on graphite flakes

Continuous tungsten carbide (WC) coatings were prepared on graphite flakes (G_f) by molten salt synthesis (MSS) technique using NaCl and KCl as reaction medium. The effect of reaction temperature, dwelling times and WO₃/G_f molar ratio on the compositions and morphologies of resultant samples was investigated, and the related formation mechanism for the coatings was also discussed. The results show that continuous WC coatings can be prepared at 1100 °C for 60 min with a WO₃/G_f molar ratio ranging from 1/15 to 1/5. These coatings exhibit homogeneous and crack free features, and their thickness increases with the increase of molar ratio. With the WO₃/G_f molar ratio below or beyond the above range, discontinuous WC coatings or W/W₂C/WC flake-like particles without graphite are obtained, respectively. The varied compositions of the samples obtained with different WO₃/G_f molar ratio can be related to the detailed chemical reaction process between WO₃ and G_f in the molten salts. A “template-growth” mechanism is proposed to explain the formation of WC coatings in the MSS process.