关键词： Mo复合粉末   氧化铝   氧化镧   溶胶-凝胶   氢还原  

摘要： Al_(2)O_(3)协同La_(2)O_(3)强韧化的钼及钼合金具有优越的综合力学性能,通过粉末冶金方法制备钼及钼合金的关键在于获得超细或纳米Mo-Al_(2)O_(3)-La_(2)O_(3)粉末。本文以仲钼酸铵、硝酸铝、硝酸镧和柠檬酸为原料,采用溶胶-凝胶-煅烧-高温氢还原工艺制备Mo-Al_(2)O_(3)-La_(2)O_(3)复合粉末,利用XRD、SEM、EDS和TEM等分析手段对粉末的微观组织结构进行表征。结果表明:当水浴温度为85℃、pH=1、柠檬酸与钼酸铵的质量比为1.7时,形成了网状结构大分子交联的络合物前驱体,这有利于在后续高温还原过程中制备超细或纳米Mo复合粉末。前驱体粉体在550℃煅烧3 h后,粉末主要由MoO_(3)和Al_2(MoO_(4))_(3)组成。采用一步高温氢还原时,还原3 h后MoO_(3)全部转化成Mo,其最低还原温度为650℃。在650℃以下通过氢还原得到了微米尺寸Mo-Al_(2)O_(3)-La_(2)O_(3)复合粉末,而在750℃通过氢还原得到了由纳米颗粒聚集而成的近球形絮状粉末,在850℃通过氢还原得到的粉末内部出现烧结颈,其颗粒尺寸略有增大。

关键词： WC−Ni硬质合金   化学共沉淀法   高温氢还原法   Ni含量   显微组织   冲击韧性   耐腐蚀性  

摘要： 采用化学共沉淀−高温氢还原工艺制备纳米Ni均匀包覆的WC复合粉体(简称CM-WCN),在1450℃下真空烧结1 h,获得WC−Ni硬质合金,并对其组织及性能进行研究。结果表明,CM-WCN硬质合金中WC的平均晶粒度为3.0~3.8μm,仅观察到少量孔隙。CM-WCN−10%Ni(质量分数)的相对密度、硬度及抗弯强度分别为99.63%、HRA 86.5及1860 MPa,CM-WCN−12%Ni(质量分数)的最高冲击韧性为6.17 J/cm^(2),优于本文中手混法制备的WC−Ni(HM-WCN)硬质合金及文献报道同类合金的性能。由于结构均匀性及低孔隙率,CM-WCN硬质合金具有优异的力学性能,其主要断裂模式为穿晶断裂,并伴随黏结相塑性形变。此外,当Ni含量为6%~12%(质量分数)时,CM-WCN比HM-WCN硬质合金的耐腐蚀性能更好。

关键词： Mo-ZrO_(2)(Y_(2)O_(3))   纳米粉末   溶胶凝胶   高温还原  

摘要： 纳米Mo-ZrO_(2)(Y_(2)O_(3))复合粉末是一种很有发展前景的粉末冶金材料。采用溶胶凝胶法制备前驱体复合粉末,并对得到的前驱体复合粉末采用高温氢还原工艺制备Mo-ZrO_(2)(Y_(2)O_(3))复合粉末。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和能谱分析(EDS)等分析检测技术对前驱体复合粉末的物相组成和微观结构进行表征,并分析不同的还原时间和温度对高温氢还原后Mo-ZrO_(2)(Y_(2)O_(3))复合粉末的物相组成及微观组织结构的影响。结果表明,在400-650℃下煅烧后的前驱体粉末物相均由MoO3组成;随着煅烧温度的升高,粉末形貌按照薄片状-片层状-长棒状规律演变;在保温3 h条件下,MoO3还原成Mo的起始温度为550℃;如果采用一步还原的方法,煅烧产物MoO3完全转换为Mo的还原温度必须高于650℃;溶胶凝胶结合高温氢还原能够制备纳米级别且纯度较高的Mo-ZrO_(2)(Y_(2)O_(3))复合粉末,团聚的复合粉末由80-100 nm细小颗粒组成,ZrO_(2)(Y_(2)O_(3))均匀地分布在Mo基体粉末中。

关键词： 镍钴锰酸锂   三元正极材料   报废   氢气还原   回收   机理  

摘要： 通过高温氢还原和湿法冶金联用的方法回收报废动力电池镍钴锰酸锂三元正极材料中的镍、钴、锰以及锂金属,并对其回收机理及工艺进行研究。结果表明:报废三元正极材料经过高温氢气还原后,在层状镍钴锰酸锂结构中的锂迁移到表面,变成LiOH、LiOH∙H2O和少量的Li2CO3;镍钴锰由之前的Co^2+、Ni^3+和Mn^4+分别还原成了Co0、Ni0和MnO,其在还原水洗后物料的表面相分别为Ni(OH)2和Co(OH)2及MnO;还原后的LiOH、LiOH∙H2O和少量的Li2CO3经过水浸、酸洗、沉淀后,可得纯度为99.5%的Li2CO3,实现了锂与镍、钴、锰的分离;还原后的镍、钴和MnO经过硫酸酸浸后,镍、钴和锰浸出率分别为96.88%、97.23%和99.78%。浸出后溶液经氧化沉淀及萃取分离,锰沉淀分离率为98.46%,萃取分离后氯化钴和氯化镍溶液杂质含量低于10 mg/L。

关键词： 铌膜   氧化物去除   机械磨抛   高温氢还原   渗透率  

摘要： 难熔金属铌具有机械强度好、选择渗氢速率高、成本低等优点,被认为是可以取代金属钯的渗氢分离材料。有效去除铌表面氧化层是获得快速渗氢性能的关键。采用机械磨抛和高温氢还原方法去除铌膜表面氧化物,并对处理后的铌膜进行了渗氢、渗氘实验。结果表明:机械磨抛和高温氢还原相结合能有效去除铌膜表面氧化物;600~800℃范围内氢、氘在铌膜中的渗透率(Φ)分别为ΦH=4.98×10-6exp(-6 406.9/T)mol·m-1·s-1·Pa-0.5和ΦD=3.51×10-6exp(-6 418.8/T)mol·m-1·s-1·Pa-0.5,相同温度下,铌中氢同位素渗透率高于CLAM钢,而低于Pd8.5Y0.19Ru合金,这归因于表面残余氧化物对氢同位素的渗透有一定阻滞作用。

关键词： 锂离子电池   石墨烯   纳米硅粉   高温氢还原法   电池容量  

摘要： 将Hummers法制备的氧化石墨烯(graphene oxide,GO)与纳米硅粉进行超声复合和高温氢还原,制备锂离子电池用纳米硅/石墨烯(Si/G)复合材料。利用扫描电镜、透射电镜、X射线衍射和Raman光谱分析,对Si/G复合材料的形貌与结构进行分析与表征,并测试其电化学性能。结果表明,通过高温氢还原,氧化石墨烯全部还原为石墨烯,无其它杂质相生成。石墨烯包覆在纳米硅颗粒表面,形成层状复合结构;与纯纳米硅粉相比,Si/G复合材料的电化学性能明显提高,在300 m A/g电流密度下,首次放电比容量为2 915.0(m A·h)/g,首次充电比容量为1 080.5(m A·h)/g,20次循环后比容量稳定在969.6(m A·h)/g,库伦效率为99.8%;而纯纳米硅粉的首次放电比容量和首次充电比容量分别为932.7和349.4(m A·h)/g,20次循环后比容量仅为6.4(m A·h)/g。

关键词： VO2薄膜   金属绝缘体转变   氢退火  

摘要： 过渡金属氧化物二氧化钒(VO2)在温度340 K附近会发生金属绝缘体的转变(metal-insulator transition,MIT).基于金属绝缘体的转变性质,VO2薄膜材料具有很好的应用前景.本文首先采用脉冲激光沉积制备了高质量的V2O5薄膜,再通过高温氢退火还原V2O5薄膜制备出VO2多晶薄膜.研究了不同的退火温度、退火时间、退火气氛对VO2薄膜制备的影响,采用X射线衍射、X射线光电子能谱、变温电阻特性测量等手段对样品进行分析,发现在H2(5%)/Ar退火气氛下,在一定的退火温度范围内(500—525 C),退火3 h,得到了B相和M相共存的VO2薄膜,具有M相的VO2的MIT特性,而相同退火温度下退火时间达到4.5 h,薄膜完全变成B相的VO2.通过纯Ar气氛下对B相VO2再退火,得到了转变温度为350 K,电阻突变接近4个数量级的M相的VO2薄膜.实现了VO2的B相和M相的相互转变.

关键词： ESCHERICHIA-COLI   THERMOTOGA-MARITIMA   HYDRIDE TRANSFER   ENZYME MECHANISMS   CATALYSIS   MOTIONS   SPECTROSCOPY   FLEXIBILITY   PROTONATION   STABILITY  

摘要： We report here solvent kinetic isotope effects for two dihydrofolate reductases, namely the monomeric, mesophilic enzyme from E. coli (EcDHFR) and the dimeric, thermophilic enzyme from Thermotoga maritima (TmDHFR). Multiple isotope effects reveal mechanistic differences between the two enzymes. EcDHFR follows a stepwise mechanism in which proton transfer precedes hydride transfer, whereas the two steps are concerted in TmDHFR. At elevated pH, EcDHFR also follows a concerted reaction pathway. TmDHFR at pH 7 behaves more like EcDHFR at elevated pH suggesting that the restricted motions of TmDHFR resulting from dimerization preclude it from modulating the pK(a) of its substrate as efficiently as EcDHFR. The reduced reaction rates of TmDHFR therefore appear to be a consequence of its quaternary structure, which is required for increased thermostability but which also prevents active modulation of the reactivity of the active site bound substrate observed in EcDHFR.

关键词： CONFORMATIONAL FLEXIBILITY   SIMULATION ANALYSIS   HYDRATION   POWDER  

摘要： The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two.

关键词： ION CHROMATOGRAPHY  

摘要： A quick, sensitive, and accurate method, high-temperature hydrogen reduction gas chromatography (GC) (1,2), for measuring arsenic (As), phosphorus (P), and sulfur (S) in the waste gases and water emitted from semiconductor processes is proposed in this paper. A high-temperature hydrogen reduction system that changes As, P, S, and their compounds into hydrides by atomic hydrogen has been designed. It is convenient to detect these elements in solid, liquid, and gaseous samples by high-temperature hydrogen reduction GC without pretreating samples. The lower detection limits of As, P, and S by this method are 0.01, 0.003, 0.02 mg/L, respectively, and the values of relative standard deviation are 6.2%, 8.6%, and 0.3%, respectively. Results determined by high-temperature hydrogen reduction GC are primarily accordant to those by conventional methods such as colorimetry and ion chromatography. The error statistics of this analysis method also show that high-temperature hydrogen reduction GC can be successfully used to determine trace As, P, and S in waste gases and wastewater emitted from semiconductor processes.