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.     

应用于钼靶材的大粒度钼粉制备技术

研究了在两阶段氢气还原法生产钼粉的过程中还原温度、料层厚度等已达到设备极限的情况下,通过提高一段还原氢气露点以继续提高钼粉粒度的可行性。结果表明,露点从-20℃提高到20℃后,钼粉颗粒的微观形貌仍基本呈近球形,且团聚程度更低,小颗粒更少;激光粒度分布与费氏粒度结果均显示钼粉的粒度有明显提高。     

仲钨酸铵循环氧化还原法制备亚微米球形钨粉

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紫钨,紫钨在纯度为99.99%,露点小于–40℃的氢气中进行还原,紫钨还原的钨粉在空气中被氧化为三氧化钨,三氧化钨再在氢气中还原,然后利用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2次氧化和3次还原,制备出粒度分布在0.1～1.0μm之间占95.73%,比表面积为1.082m2/g的球形亚微米球形钨粉。     

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。     

喷雾干燥法制备钼合金微粉的研究

钼合金的制备过程广泛采用原料粉末混匀、坯料压制、烧结成型的粉末冶金方法,因此原料粉末混合的均匀程度、纯度、粉末粒径和形貌对钼合金制品的性能有重要影响。本文采用溶液喷雾干燥法制备前驱体粉末,再将前驱体粉末在氢气气氛下进行高温还原制备钼钨合金粉和钼钌镍复合粉,研究了喷雾干燥工艺参数（溶液浓度、进料速度、干燥温度等）和还原热处理工艺参数（还原气氛、温度、时间等）对钼合金微粉粒径、成分和形貌的影响,此外还分析了钼钨合金化和钼钌镍复合粉钎焊性能。结果表明,采用溶液喷雾干燥结合还原热处理工艺,可获得粒径0.5~3μm的球形钼钨固溶体合金粉和0.5~2μm的球形钼钌镍复合粉,且钼钌镍复合粉在钼板上钎焊时具有优异的润湿性。     

超细钼粉制备钼板过程中O含量影响因素研究

研究了超细钼粉的还原和烧结过程中O含量的影响因素,以及O含量对钼板性能的影响。结果表明,还原温度和氢气流量以及水汽平衡对钼粉影响很大,超细钼粉经过预烧+低温烧结可使钼板的O含量达到80×10~(-4)%,且0.5 mm钼板的力学性能与常规钼板性能接近。     

钨钼粉末还原中稳定氢气质量几个要素的探讨

对国内外一些生产厂家的氢气再生装置进行比较,找出国内氢气再生在设计、工艺、操作和设施方面存在的问题,氢气再生系统没有有效的稳压措施,造成氢气流量的波动;用冷冻水方法冷凝氢中含水弊端很多,特别是在炎热的夏天会造成氢气露点的波动;干燥塔使用多的自动阀,难免会出现故障,造成各种不同后果。建议采用钟罩式气柜、氢气再生系统增压和改进新鲜氢气补充方式等办法,解决氢气流量波动和安全问题;建议直接采用冷干机冷冻氢气进行脱水,采用四通阀替代自动阀,从而解决氢气露点和故障多发问题。     

转炉和平四管炉生产二氧化钼板结成因分析及控制方法研究

二氧化钼的板结不仅降低后续钼粉的成品率而且影响钼粉的质量。为了消除二氧化钼板结提高钼粉的品质，本文对比分析了转炉和平四管还原炉生产二氧化钼过程中板结成因及控制方法。结果发现，三氧化钼钾含量越低，粒度越小，细小颗粒越多，二氧化钼板结越严重；转炉和平四管还原炉工艺温度越高，二氧化钼越容易板结；氢气流量分别为40和6 m³/h时转炉和平四管炉生产的二氧化钼松散无板结。因此，可以通过简单的设备改造减缓反应速率，优化还原工艺及原料优化选择来控制二氧化钼板结。     

钨的还原机理(述评Ⅰ)

目前,用氢还原三氧化钨制取钨粉是一种公认的工业生产方法。凭生产经验可以通过改变还原参数生产出0.5～15μm的任何平均粒度钨粉。在可以改变的还原参数中,最重要的是温度,时间,氢气流量,氧化物料     

小粒度钼粉氧含量的影响因素研究

研究了钼粉氢还原生产过程中的还原方式、混料方式、保存方式对钼粉粒度及氧含量的影响。结果表明,通过对MoO3进行合理的三段还原,能在较低的温度下,有效降低钼粉氧含量,并控制钼粉的粒度。随着钼粉粒度的变小,钼粉中氧含量容易受环境温度的影响而急剧增加。通过真空混料、抽真空保存等方式,能有效减缓钼粉合批、保存过程中氧含量的增加。     

多管炉工作状况下的温度分布

本文以钨、钼粉末制备常用十五管还原炉为对象,采用特制的加长型热电偶,分别对每根炉管和各炉管的10个截面在通氢状况下的温度进行测定,比较两种炉子的截面温差和沿炉管方向温度分布。结果表明:天然气炉的截面温差最大达到134℃,而电炉最大为65℃;沿炉管方向的温度分布曲线电炉也更加平滑,即电炉的温度分布更均匀一致。从炉子传热过程和结构方式入手初步探讨了影响炉子温度分布和均匀性的原因,天然气炉因对流传热受到气体流速、压力和操作等多因素的影响而难以控制炉子的温度分布,电炉则相对简单和稳定。比较了两种设备生产细颗粒钨粉的粒度分布,结果表明天然气炉的钨粉粗颗粒含量高,粉末不均匀,在细颗粒生产上电炉质量更优。     

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.     

INDUCTION PLASMA REACTIVE DEPOSITION OF TUNGSTENCARBIDE FROM TUNGSTEN METAL POWDER

1. IntroductionIt was reported by Smith et al.[1] and S.ith[2] that tungsten carbide and titaniumcarbide can be formed in d.c. plasma via the reactions of tungsten powder and titaniumpowder with methane, respectively Due to the characteristics of small plasma volume,short particle residence time, and lateral injection of the powders into the d.c. plasma,only a fraction of the fed-in powders were carburized. Actually the deposits are mixturesof WC and W and the composite of TiC and Ti, respe…     

Induction plasma spheroidization of tungsten and molybdenum powders

The melting, evaporation and oxidation behaviors as well as the solidification phenomena of tungsten and molybdenum in induction plasma were studied. Scanning electron microscopy was used to examine the morphology and the cross section of plasma-processed powders. X-ray diffraction was used to analyze the oxides formed on the particle surface of these two metals. The influence of spray chamber pressure on the spheroidization and oxidation phenomena was discussed. The results show that fewer Mo particles than W particles are spheroidized at the same powder feed rate under the same plasma spray condition although molybdenum has a lower melting point. A small fraction of tungsten is evaporized and condensed either on the surface of tungsten particles nearby or on the wall of spray chamber. Tungsten oxides were found in tungsten powder processed under soft vacuum condition. Extremely large grains form inside some spheroidized particles of tungsten powder.     

Effect of Nitrides of Refractory Metals on the Properties of Sintered Molybdenum and Tungsten

The effect of additives of titanium, zirconium, hafnium, and niobium in an amount of 2% on the technological and mechanical properties of sintered molybdenum and tungsten is considered. The changes in the chemical and phase compositions of pressed specimens after sintering in a flow of hydrogen are described. The temperature ranges of the effective hardening of molybdenum and tungsten by nitride additives are established. The composition with the best parameters of ductility and strength in tensile tests is determined.     

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

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The Corrosion of metals in an oxidizing-chloridizing environment at high temperature

An investigation has been undertaken into the behaviour of metals which form the basis of high-temperature alloys in an argon ?5.5% oxygen ?0.96% hydrogen chloride ?0.86% sulphur dioxide gas mixture at 900°C. The intention has been to ascertain the reaction products, with particular emphasis on the formation of volatile species which can cause considerable degradation of commercial alloys in this environment. From consideration of the thermodynamics of the gas system, the potentials of the reactive species can be determined and correlated with the possible reaction products. In this gas mixture, the oxides of nickel, iron, cobalt, chromium, molybdenum and tungsten are the stable phases with respect to the corresponding metals. Indeed, on exposure of the metals to the environment, the appropriate oxide scales are developed. However, the reactions are complicated by formation of volatile corrosion products, particularly for nickel, cobalt and molybdenum. Although a Cr₂O₃ scale is established on chromium, there is evidence for penetration of chlorine-containing species to the scale/alloy interface. The oxide scale on tungsten is not very protective and thickens rapidly while that on molybdenum is volatile, resulting in rapid consumption of the specimen.     

Electrochemical Properties of Pulse Plating Amorphous Ni-Mo-W Alloy Coating in Alkaline Medium

采用脉冲电镀技术获得了高活性Ni-Mo-W析氢合金阴极。以析氢反应过电位为考察指标,确定了脉冲镀Ni-Mo-W合金的最佳电镀条件,如Na2WO4·2H2O浓度、平均电流密度和占空比等。同时,系统研究了Mo和W含量对Ni-Mo-W合金镀层成分和组成的影响规律。结果表明,在二元合金中添加W能有效提高电极的析氢反应活性(η200＝80 mV);非晶态Ni-Mo-W合金的组织结构主要取决于Mo含量;与非晶态Ni-Mo合金镀层相比,Ni-Mo-W合金析氢阴极的电化学稳定性得到一定程度的提高。     

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。