机械合金化合成的新材料(二)——弥散强化合金、磁性材料、超导合金、金属间化合物及机械化学效应

本文介绍了由机械合金化方法合成的各种新材料——弥散强化材料、磁性材料、超导材料、金属间化合物及机械化学效应的工艺、材料结构、性能特点、机制以及应用状况。认为由机械合金化技术可以获得一些用常规方法难以制备的新型合金及难以获得的独特性能,因而是一项值得大力研究开发的新技术。     

纳米WC的合成及Pt/WC电催化性能的研究

以钨粉为钨源, 酚醛树脂(PF)为碳源, 采用溶胶?凝胶法合成纳米碳化钨(WC). 以甲醛(HCHO)为还原剂, 在含有纳米WC的氯铂酸(H₂PtCl₆·6H₂O)悬浮液中还原氯铂酸制备纳米WC负载纳米Pt的复合粒子, 再采用Nafion溶液制备质子交换膜燃料电池工作电极. 运用傅立叶红外光谱(FTIR)、X射线衍射(XRD)、扫描电镜(SEM)及透射电镜(TEM)等对前驱体及试样进行表征, 并在酸性介质中采用循环伏安法测试工作电极的电化学催化活性. 结果表明: 采用溶胶?凝胶工艺制备的WC沿(100)晶面择优取向, 其晶面间距为0.25nm, Pt主要沿(111)晶面择优取向, 其晶面间距为0.23nm. 10wt% Pt/WC在0.5mol/L H₂SO₄中的催化电流密度达到28.5mA/cm², 并发现纳米WC与Pt之间存在协同催化作用.     

难互溶体系中合金的机械合金化合成

本文用x-ray衍射,电子探针和金相分析方法,系统地研究了因熔点和比重相差较大,难以用常规冶炼方法互溶的Ti-Pb和Ti-Al两个二元系.在球磨过程中的组织、结构变化。发现在普通熔炼条件下完全不互溶的Pb-Al二元系,在适当的条件下,能够形成固溶度很高的以Pb为溶剂的固溶体。而Ti-Pb二元系在球磨过程中则经过形成过饱和固溶体和非晶化2个阶段,最终形成相图上的PbTi_4金属间化合物。实现了在难互溶体系中,合金的机械合金化合成。     

碱液中镍电极的析氢机理

研究镍电极在碱液中的析氢机理对开发二次清洁能源有指导意义,过去对其研究不够.通过Tafel曲线和电化学阻抗谱对镍电极在KOH溶液中的析氢机理进行了研究.结果表明,过电位低于600 mV时,析氢服从复合脱附机理,反应历程为电化学步骤+复合脱附步骤;过电位高于600 mV时,析氢服从迟缓放电机理或电化学脱附机理,反应历程为电化学步骤+电化学脱附步骤.     

石墨化介孔碳包裹WC纳米粒子的构建及其氧还原性能研究

采用模板复型辅助的化学气相沉积法(CVD)成功制备出一种非贵金属的氧还原反应(ORR)催化剂材料—包裹碳化钨纳米粒子的石墨化介孔碳(WC/MG)复合物。制备的介孔结构WC/MG复合材料不仅具有高氧还原反应电化学催化活性, 还表现出良好的电化学稳定性。在O₂饱和的0.1 mol/L KOH电解质溶液中, 900℃制备的样品WC/ MG-900其半波电势(E_1/2)和极限电流密度仅比商用贵金属催化剂Pt/C分别低50 mV 和 0.2 mA/cm²。Koutecky- Levich曲线和旋转环盘电极实验均表明, 该介孔结构的WC/MG复合材料表现出近似4电子的ORR反应途径, 具有可与Pt/C催化剂相比拟的ORR催化活性, 以及比Pt/C更优越的电化学稳定性和耐甲醇性能, 使得该介孔结构WC/MG复合物在氧还原电极材料中表现出良好的应用前景。     

改性骨胶合成工艺的效应面优化分析

为了优化接枝共聚法改性骨胶的工艺,采用效应面分析了pH值等因素对于改性骨胶品质(拉伸强度、凝固点)的影响,并建立了相应的回归模型.方差分析的结果表明:pH值等对于改性骨胶品质都有着极为显著的影响.优化所得的较优工艺参数为:pH值为6.5,交联剂质量分数为2.4%,交联温度为40℃.对应的拉伸强度、凝固点的预测值分别为:10.20MPa和4.0℃.TGA与DSC结果表明说明了改性后骨胶分子结构与改性前有所不同.     

富勒烯生物分子衍生物的合成与生物学效应研究

富勒烯具有独特的物理化学性质,是药物设计的理想基体.将富勒烯与各种生物分子进行连接,能改善富勒烯在极性溶剂中的溶解度,得到的新化合物具有富勒烯与生物分子的双重特性,因而具备生物分子的原有功能或产生一些新的生物活性,近年来引起越来越多的关注.综述了富勒烯与氨基酸、肽、寡糖、卟啉等生物分子的最新合成及生物学方面的研究进展.展望了富勒烯生物分子的研究方向和应用前景.     

ODS镍基超合金的研究进展

γ'和Y2O3强化的镍基超合金高于1000℃仍有优异的蠕变性能,可用作涡轮喷气发动机中的叶片.本文介绍了氧化物弥散强化(ODS)镍基超合金的制备和三阶段热处理获得柱状晶粒,重点分析了其独特的二次再结晶行为,同时阐述了预退火、区域退火速率以及γ'和Y2O3的含量对二次再结晶的影响.讨论了γ'溶解诱发二次再结晶、弥散相粗化诱发二次再结晶和晶界形核三种理论,解释了二次再结晶温度高和活化能高的原因.最后讨论了细晶粒态和粗晶粒态在不同应变速率和不同取向上性能的差异.     

机械合金化合成的新材料(一)——非晶、准晶及纳米晶亚稳态材料

本文介绍了由机械合金化方法合成的各种亚稳态新材料——非晶、准晶及纳米晶材料的各类体系,形成的热力学与动力学条件,结构及性质等方面的最新进展。认为由机械合金化合成的亚稳态新材料的技术有着广阔的前景。     

Failure of Tungsten Carbide Rolls from a Wire and Rod Mill

The paper presents the failure analysis of tungsten carbide rolls for the Wire and Rod Mill (WRM) and establishes the failure reasons and the corrective and preventive actions taken to improve roll performance. A sharp continuous increase in failure rate and decrease in average time between failure (ATBF) was observed during 2001 to 2004. The increase in premature failure of these rolls (16 rolls in 2003 and 38 rolls in 2004) raised the cost of operations. Due to unscheduled stoppage of the mill after roll failures, the unplanned mill delays also increased, causing production losses. The analysis revealed significant increase in premature failure of rolls in the finishing stands 19, 22, 23, and 24 and prefinishing stand 14. The primary causes of such failures were faulty roll cooling and roll mounting and accumulation of cobbles. Implementation of modified cooling headers, a calibrated gage to monitor hydraulic pressure during roll mounting, and eddy current inspection resulted in decreasing the trend in roll failure and increasing the trend in ATBF.     

高能球磨制备碳化钨过程中的结构转变

高能球磨W粉和石墨粉的混合物，并对球磨产物进行退火处理。球磨4小时后在1173K退火，就得到WC和W2C；球磨28h后退火，得到了安全的h.c.p.WC。对球磨过程的分析发现W50C50混合粉末先形成固溶体，随后产生非晶化转变。在此实验条件下，球磨直接产物中没有检测到WC。另外，球磨时间和退火温度影响了相的组成与结构。     

Preparation and Electrocatalytic Activity of Tungsten Carbide Nanorod Arrays

High density tungsten carbide nanorod arrays have been prepared by magnetron sputtering （MS） using the aluminum lattice membrane （ALM） as template. Electrocatalytic properties of nitromethane electroreduction on the tungsten carbide nanorod arrays electrode were investigated by electrochemical method, and their electrocatalytic activity is approached to that of the Pt foil electrode.     

Plasma Enhanced Chemical Vapor Deposition Nanocrystalline Tungsten Carbide Thin Film and Its Electro-catalytic Activity

Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition (PECVD) at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS), respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V (vs SCE).     

Synthesis and characterization of nanostructured silicon carbide

Equiatomic nanostructured silicon carbide was successfully prepared by milling elemental Si and C powders, using a planetary ball mill. The synthesis of this carbide proceeded at milling conditions corresponding to 5.19 W/g shock power. The reaction was gradual and completed after 15 h. After 20 h of alloying duration and towards the end of the process, the SiC diffraction crystallite size (DCS) reached a critical value of 4 nm. At this same alloying duration, SEM characterization revealed that the powders exhibit homogeneous distribution of the particles with 0.3 µm in size.     

Template‐Free Pseudomorphic Synthesis of Tungsten Carbide Nanorods

A unique nanorod‐structured tungsten carbide material with high specific surface area of 198 m² g^?1 is successfully synthesized for the first time by pseudomorphic transformation of chemically synthesized WO₃ nanorods through a high‐temperature method. An electrocatalyst composed of Pt nanoparticles supported on WC nanorods demonstrates higher electrocatalytic activity for methanol electro‐oxidation, better tolerance to CO poisoning, and superior performance for cathodic electrocatalytic hydrogen evolution than a Pt/C catalyst. This work provides a novel method to synthesize high‐surface‐area nanorod‐structured WC materials by preparing oxide precursors with the desired external morphology, thus offering great potential for a broad range of applications of these materials in related reaction systems.     

超细碳化钨介质球磨工艺的研究

对介质球磨法制取超细碳化钨粉末进行了研究。实验探讨了不同线速度、磨球尺寸、分散剂的添加对初始粒径约1μm的碳化钨粉末的介质球磨工艺的影响。根据W=P·t,在保持能耗不变的情况下得到了粒度与线速度之间的关系,从而在一定粒度范围内选择最有效的线速度。同时,采取分阶段球磨的球磨效率要高于单一线速度球磨,可实现用更少的成本达到相同粒度。此外,球磨时添加羧甲基纤维素钠分散剂,粉末粒度越小时分散效果越明显,实验中在输出功率不变时,与不添加分散剂对比,其时间效率提高了13%,最终的粉末也呈现很好的分散性。最后,磨球尺寸的大小可决定最终粒度的大小。因此,根据目标粒度采用合适的磨球尺寸和球磨工艺才能达到最高的球磨效率。