氧化钨相成分对超细钨粉均匀性的影响

研究了通过传统氢还原工艺制备超细钨粉末过程中氧化钨原料相组成对超细钨粉均匀性的影响。结果表明：单一相组成的氧化钨能制得超细而均匀的钨粉,多种相组成的氧化钨,由于其在还原过程中存在不同的还原路径和还原速度,制得的钨粉虽细但不均匀。     

蓝钨与紫钨氢还原法生产超细钨粉的比较

在相同的工艺条件下,比较了蓝钨与紫钨氢还原法生产的钨粉的性能差别.结果表明:与蓝钨相比,紫钨生产的钨粉粒度更细更均匀,并且钨粉粒度受装舟量和氢气流量的影响较小.并从原料的微观结构和氢还原机理两方面分析了造成不同原料生产的钨粉粒度和均匀性差别的原因.     

液—固混料法制取钨—稀土氧化物包覆粉的研究

进行了以氧化钨为原料，稀土氧化物为掺杂相，用液－固混料法将掺杂与氧化钨混合，再经过盐类分解，氧化钨还原等工艺，制取不同掺杂相和掺杂量的钨－稀土氧化物包覆粉的研究，着重探讨了原料类型，还原温度及掺杂相对还原程度的影响。结果表明，以ＷＯ２．９为原料的包覆粉，综合性能好；随还原温度升高，粉末还原程度提高，掺杂相含量高的比含量低的难还原，三元系粉末比二元系粉末难还原，用液－固法制备钨－稀土氧化物包覆粉，其     

Preparation of ultrafine tungsten powders by in-situ hydrogen reduction of nano-needle violet tungsten oxide

Ultrafine tungsten powders with a grain size below 0.5 μm are key raw materials for fabricating ultrafine cemented carbides. Conventional hydrogen reduction technique has been utilized to prepare the ultrafine tungsten powders. In the present work, highly pure nano-needles of violet tungsten oxide (WO_2.72) were reduced by dry hydrogen. Nucleation and growth of the metallic tungsten in the early stage of hydrogen reduction have been studied by XRD, FESEM and HRTEM. Mechanism of formation of nano-size tungsten powders is proposed and a concept of in-situ hydrogen of the nano-needle WO_2.72 is presented. Empirical relations between an average diameter of nano-needle WO_2.72 and an average particle size of the resultant tungsten powders in both stage of nucleation and industrial conduction have been established. These empirical relations could be a reasonable guidance for suitably choosing the raw materials of nano-needle WO_2.72 to prepare ultrafine tungsten powders. It has been determined that the BET special surface areas of the in-situ hydrogen-reduced tungsten powders with the average particle size of 0.2 μm and 0.3 μm, which were produced from the raw nano-needle WO_2.72 powders with the average diameter of 60 nm and 80 nm, are 6.03 m²/g and 4.65 m²/g, and the oxygen contents are 0.35% and 0.29%, respectively.     

氧化钨的形貌结构对纳米WC粉末均匀性的影响

研究了在传统氢还原工艺制备纳米碳化钨粉末过程中不同氧化钨的形貌结构对纳米W/WC粉末均匀性的影响,并对粉末及其WC-Co烧结体的性能进行了表征。结果表明,用具有疏松、多孔形貌结构的细小氧化钨颗粒更容易制备出结构较疏松、分散性较好的纳米W粉和WC粉。晶粒聚集和异常粗大颗粒的产生,主要与碳化过程中团聚纳米钨粉颗粒因烧结合并增粗有关。     

Effect of process parameters on induction plasma reactive deposition of tungsten carbide from tungsten metal powder

1　ＩＮＴＲＯＤＵＴＩＯＮＴｕｎｇｓｔｅｎｃａｒｂｉｄｅｉｓｗｉｄｅｌｙｕｓｅｄａｓｃｕｔｔｉｎｇｔｏｏｌｉｎｓｅｒｔａｎｄｗｅａｒ ｒｅｓｉｓｔａｎｔｃｏａｔｉｎｇｍａｔｅｒｉａｌｂｅｃａｕｓｅｏｆｉｔｓｈｉｇｈｈａｒｄｎｅｓｓａｎｄｇｏｏｄｔｈｅｒｍａｌｓｈｏｃｋｒｅｓｉｓｔａｎｃｅ .Ｔｒａｄｉｔｉｏｎａｌｌｙ ,ｔｕｎｇｓｔｅｎｃａｒｂｉｄｅｉｓｐｒｏｄｕｃｅｄｔｈｒｏｕｇｈｔｈｅｃａｒｂｕｒｉｚａｔｉｏｎｒｅａｃｔｉｏｎｂｅｔｗｅｅｎｔｕｎｇｓｔｅｎｍｅｔａｌａｎｄｃａｒｂｏｎａｔｈｉｇｈｔ…     

Synthesis of high-purity ultrafine tungsten and tungsten carbide powders

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO_2.9 and the following deep reduction with H₂ or carbonization with CH₄+H₂ mixed gases. The effects of C/WO_2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO_2.9 ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO₂. With changing C/WO_2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO_2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively.     

Direct solid-state synthesis of tungsten carbide nanoparticles from mechanically activated tungsten oxide and graphite

Solid-state carbothermic reduction of tungsten oxide (WO₃) to nano-sized tungsten carbide (WC) particles was achieved by calcining mechanically activated mixtures of WO₃ and graphite at 1215 °C under vacuum condition. By experiments and thermodynamic calculations, the intermediate phases, WO_2.72, WO₂ and metallic tungsten (W), were observed at 741 °C, which decomposed to synthesize the final product (WC). Homogeneity increase and associated decrease in the diffusion path by mechanical milling and formation of these intermediates are mainly responsible for the successful production of WC. The process indicates that solid-state synthesis of WC nanoparticles directly from as-milled mixtures of tungsten oxide and graphite powder is possible.     

Scandia doped tungsten matrix for impregnated cathode

As a matrix for Sc-type impregnated cathode,scandia doped tungsten with a uniform ldistribution of SC2O3 was obtained by powder metallurgy combined with the liquid-solid doping method.The microstructure and composition of the powder and the anti-ion bombardment behavior of scandium in the matrix were studied by means of SEM,EDS,XRD,and in-situ AES methods.Tungsten powder covered with scandium oxide,an ideal scandium oxide-doped tungsten powder for the preparation of Sc-type impregnated cathode,was obtained using the liquid-solid doping method.Compared with the matrix prepared with the mechanically mixed powder of tungsten and scandium oxide,SC2O3-W matrix prepared with this kind of powder had smaller grain size and uniform distribution of scandium.Sc on the surface of Sc2O3 doped tungsten mauix had good high temperature stability and good anti-ion bombardment capability.     

On the reduction of tungsten blue oxide in a stream of hydrogen

To overcome the slow reaction rate during the commonly practiced hydrogen reduction of tungsten blue oxide in a push-type furnace, a new more time-efficient method for producing metallic tungsten powder was developed. By injecting tungsten blue oxide particles in a stream of hydrogen at temperatures above 1000 °C, the reduction was completed in a couple of seconds. The influence of temperature on the overall reduction, which is chemically controlled at the reaction interface of a single blue oxide particle, is discussed. The results show that the reduction does not proceed via a CVT-mechanism. It is due to a different reaction mechanism in contrast to the industrial reduction in a powder bed. An activation energy of 126 kJ mol⁻¹ was determined for the overall reduction of tungsten blue oxide particles in a stream of hydrogen.     

Preparation and electrocatalytic properties of tungsten carbide electrocatalysts

1　ＩＮＴＲＯＤＵＣＴＩＯＮ ｉｎ 1 5 0℃ .Ｍａａｓ[1 0 ] ａｌｓｏｍａｎｕｆａｃｔｕｒｅｄｔｈｅＨ2 Ｏ2 ｆｕｅｌｃｅｌｌｓｔａｃｋｓｗｉｔｈｔｈｅｏｕｔｐｕｔｐｏｗｅｒｕｐｔｏ 1ｋＷ ,ａｎｄｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅａｓ ｐｒｅｐａｒｅｄｆｕｅｌ     

强流脉冲离子束作用下超细晶钨的抗瞬态热负荷性能评价(英文)

采用高能球磨和放电等离子体烧结技术制备纯钨、氧化物弥散强化钨和碳化物弥散强化钨。为了评价钨在瞬态热冲击下的性能,采用强流脉冲离子束,在热流密度高达160MW/(m2·s-1/2)的条件下对4种不同晶粒尺寸的钨进行抗热冲击试验。与商品钨相比,弥散强化钨在瞬态高热流作用下显现出不同的行为。氧化物弥散强化钨显现出较差的抗热冲击性能,这主要是由于低熔点的第二相Ti和Y2O3的引入,从而使得钨的表面发生熔融、起泡和开裂。而碳化物弥散强化钨合金则显现出较好的抗热冲击性能。     

纳米材料在硬质合金中的应用

WC晶粒不断细化是硬质合金发展的一个重要特征。从硬质合金的纳米原料、纳米硬质合金、纳米材料助长或增强超粗晶硬质合金以及硬质合金的纳米涂层材料等4个方面论述了纳米材料在硬质合金中的应用,着重报道了中国在这些方面的优势。纳米粒径原料的制备是首要难题,1997年发明的“紫钨原位还原”技术利用传统工艺制备纳米、超细碳化钨粉末,碳化钨粉的粒径可小于20 nm。纳米硬质合金技术利用低压热等静压或热等静压,克服了烧结过程中 WC异常长大的难题,制备100～200 nm纳米硬质合金,抗弯强度在5000 MPa以上,使用性能优于亚微或超细晶硬质合金,已用于生产。利用“纳米颗粒溶解法”制备的超粗晶硬质合金晶粒度可达12μm;而含有纳米Co2 W4 C增强相的超粗晶硬质合金产品,使用寿命比普通合金产品提高了2～3倍。涂层材料纳米化,是硬质合金工具的一个发展方向,在耐磨性、硬度和抗裂纹扩展方面有明显优势,加工工件表面质量更好,工具使用寿命更长。     

Influence of tungsten oxides’ characteristics on fineness, homogeneity and looseness of reduced ultrafine tungsten powder

This paper deals with the influence of the characteristics of tungsten oxides on fineness, homogeneity and looseness of tungsten powder by conventional hydrogen reduction techniques.     

等离子喷雾法制取球形钨粉工艺探讨

由于等离子喷雾技术具有特殊优势 ,该技术广泛应用到高性能材料研究与生产中。如 :等离子技术已在制备球形金属粉末、生产超细粉末等领域获得了很大的发展。本文尝试了用等离子喷雾技术制取球形钨粉。     

蓝钨物理性能对钨粉和碳化钨粉性能的影响

仲钨酸铵(APT)对蓝钨性能影响较大,而蓝钨物理性能对钨粉和碳化钨粉的性能影响也较大,通过对APT煅烧前或煅烧后进行特殊处理优选蓝钨原料,可以制取优质碳化钨粉。     

铸造碳化钨粉末物性对激光熔覆陶瓷颗粒增强Fe基复合材料耐磨性能的影响

为研究铸造碳化钨粉末物性对激光熔覆陶瓷颗粒增强Fe基复合材料耐磨性能的影响,将不同制备方法和粒径的铸造碳化钨粉末添加到Fe基合金粉中,在45号钢表面进行激光熔覆以获得高硬度和高耐磨的合金化层。利用金相显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、硬度计分别分析了合金化层的显微组织、物相组成以及显微硬度。利用轮式磨损试验机测试了其常温下的耐磨性能,并进行了比较。结果表明:熔覆层主要由莱氏体组成,碳化钨粉末的制备方法和粒径差异对复合材料的耐磨性能具有重要影响。等离子旋转电极雾化法制备的碳化钨粉末能起到最好的增强耐磨作用,粒径细的碳化钨粉末比粒径粗的粉末增强耐磨效果要好。     

蓝钨循环氧化还原对钨粉末粒度分布的影响

以特纯仲钨酸铵为原料,通过特纯仲钨酸铵在氩气中煅烧获得蓝钨,此蓝钨在纯度为99.99%、露点小于-40℃的氢气中进行还原,蓝钨还原的钨粉在空气中被氧化为三氧化钨,对此三氧化钨再在氢气中还原,然后利用扫描电子显微镜和激光粒度分析仪对试样进行分析,结果表明:经过循环一次氧化和两次还原,制备出了粒径分布在3～10μm之间占83.86%、比表面积为0.180m2/g的中颗粒钨粉。     

A novel approach to synthesis of scandia-doped tungsten nano-particles for high-current-density cathode applications

A novel synthesis approach for scandia-doped tungsten nano-powder using a sol–gel method is developed. It involves dissolving tungsten oxide at 300 °C in the presence of a mixture of nitric acid, citric acid and ammonia. The dissolved tungsten oxide reacts with an aqueous solution of scandium nitrate in the liquid–liquid phase, which results in the homogeneous mixing of tungsten and scandium particles. A spherical shape particle was obtained due to the dissolving of tungsten oxide in the solution. Citric acid enhances the mixing of ions at the atomic scale, which affects the hydrolysis reactions and leads to the formation of the phase pure nano-particle. The synthesized nano-powder was characterized by SEM (Scanning Electron Microscopy), EDS (Energy-dispersive X-ray spectroscopy), TEM (Transmission Electron Microscopy), and XRD (X-ray Diffraction) analyses. The spherical morphology was observed via a SEM analysis and a narrow particle size distribution was noted by means of a TEM analysis. The XRD analysis of the powder showed the complete formation of the phase pure nano-particle with an average diameter of 50 nm without any contamination by other materials.     

The effects of ball-milling treatment on the densification behavior of ultra-fine tungsten powder

Ultra-fine tungsten powder with a BET particle size of 210 nm was synthesized by sol spray drying, calcination and subsequent hydrogen reduction process. Then this powder was treated by ball-milling, the characteristic changes of this powder before and after milling were investigated. Then the sintering densification behavior of these powders with different ball-milling time (0 h, 5 h, 10 h) were also studied. The results show that ball-milling treatment greatly activates the sintering process of ultra-fine tungsten powder. The relative density of the powder ball-milled for 10 h could reach 97.3% of theoretical density (TD) when sintered at 1900 °C for 2 h, which is 600 °C lower than the required temperature of the traditional micro-scaled powder sintered for the same density. At the same time, ball-milling treatment could substantially reduce the onset temperature of sintering as well as recrystallization, and bulk tungsten materials with more uniform and finer microstructure and much better mechanical properties (hardness) could be obtained.