Hydride Complexes: The chemistry and current significance of covalent hydrogen compounds of transition metals are discussed

Hydride complexes of transition metals were virtually unknown 12 years ago, but they have now been found to lie at the root of many interesting catalytic chemical reactions, some of which were used in industry even before the unique properties of hydride complexes, which formed their basis, had been realized. This article surveys the history, preparations, important properties, and reactions of hydride complexes, surveys their part in important catalytic industrial processes, and speculates about their possible role in the biological fixation of nitrogen.     

The chemistry of deformation: how solutes soften pure metals

Solutes have been added to strengthen elemental metals, generating usable materials for millennia; in the 1960s, solutes were found to also soften metals. Despite the empirical correlation between the "electron number" of the solute and the change in strength of the material to which it is added, the mechanism responsible for softening is poorly understood. Using state-of-the-art quantum-mechanical methods, we studied the direct interaction of transition-metal solutes with dislocations in molybdenum. The interaction increases dramatically with increasing electron number and strongly influences the mechanisms responsible for plasticity in these materials. Our quantitative model explains solution softening of metals by using changes in energy and stress scales of plasticity from solutes.     

Electron-driven acid-base chemistry: proton transfer from hydrogen chloride to ammonia

In contrast to widely familiar acid-base behavior in solution, single molecules of NH3 and HCl do not react to form the ionic salt, NH+4Cl-, in isolation. We applied anion photoelectron spectroscopy and ab initio theory to investigate the interaction of an excess electron with the hydrogen-bonded complex NH3...HCl. Our results show that an excess electron induces this complex to form the ionic salt. We propose a mechanism that proceeds through a dipole-bound state to form the negative ion of ionic ammonium chloride, a species that can also be characterized as a deformed Rydberg radical, NH4, polarized by a chloride anion, Cl-.     

Hot hydrogen atoms: initiators of reactions of interest in interstellar chemistry and evolution

Photochemically generated hot hydrogen atoms initiate reactions with simple molecular substrates including methane to produce organic alcohols, amines, acids, amino acids, and other compounds. The typical quantum yields for the formation of amino acids are 2 x 10(-5) to 4 x 10(-5). Hot hydrogen atoms may be important initiators of reactions in interstellar space and in planetary atmospheres.     

In situ studies of chemistry and structure of materials in reactive environments

Most materials and devices typically operate under specific environmental conditions, many of them highly reactive. Heterogeneous catalysts, for example, work under high pressure of reactants or in acidic solutions. The relationship between surface structure and composition of materials during operation and their chemical properties needs to be established in order to understand the mechanisms at work and to enable the design of new and better materials. Although studies of the structure, composition, chemical state, and phase transformation under working conditions are challenging, progress has been made in recent years in the development of new techniques that operate under a variety of realistic environments. With them, new chemistry and new structures of materials that are only present under reaction conditions have been uncovered.     

不同重金属离子对异化铁(Ⅲ)还原过程的影响

以水稻土土壤浸提液作微生物接种液,人工合成的F e(OH)3为唯一电子受体,测定了厌氧培养过程中F e(Ⅱ)浓度的变化,探讨了添加Cu2+,Zn2+,Pb2+,Cd2+,Hg2+和A s5+对铁还原过程的影响及添加不同浓度Cu2+和Hg2+对F e(Ⅱ)浓度的影响,并以土壤中添加不同浓度的Cu2+试验作为对比。结果表明,不同重金属对异化铁还原影响不同,在同一浓度的几种重金属中,Cu2+和Hg2+对异化铁还原抑制最强;不同浓度Cu2+和Hg2+对异化铁还原有不同程度的抑制,主要表现在增加异化铁还原发生前的时间,减慢异化铁还原的速率,当Cu2+和Hg2+浓度增加到一定程度时异化铁还原几乎不发生;水稻土中含有大量铜时,铁还原也会被抑制;添加外源氧化铁可以减轻铜对水稻土铁还原的影响。     

铁矿废弃地复垦土壤重金属来源解析研究

为探明铁矿废弃地复垦土壤重金属含量特征及其主要来源,以铁矿废弃地复垦土壤为研究对象,采用多元统计分析和地统计学方法,对复垦土壤重金属(As、Cd、Cr、Cu、Hg、Zn)的主要来源、各来源的贡献量及其贡献量的空间分布特征进行研究。结果表明:研究区6种重金属变异系数在31%～67%,均属中等程度变异。对比当地背景值,除Cr外,其他5种元素均呈现富集现象,且以As、Cu累积明显。由相关性分析、主成分分析及聚类分析结果推测复垦土壤重金属主要有3个来源,PC1(As、Hg、Cu)为矿业活动源,PC2(Cd、Zn)为交通和农业活动源,PC3(Cr)为成土母质自然源。由主成分分析/绝对主成分分数(PCA/APCS受体模型)和地统计分析可知,几种元素受3种源共同作用,其中源1对As、Hg、Cu的贡献率分别为67.10%、46.30%、89.82%,源2对Cd、Zn的贡献率为86.05%、62.26%,而源3对Cr的贡献率为90.56%。Cu、Cd、Cr元素空间分布规律和其最大源贡献量空间分布格局较为一致。     

In situ determination of the nanoscale chemistry and behavior of solid-liquid systems

Many fundamental questions in crystal-growth behavior remain unanswered because of the difficulties encountered in simultaneously observing phases and determining elemental concentrations and redistributions while crystals nucleate and grow at the nanoscale. We show that these obstacles can be overcome by performing energy-dispersive x-ray spectroscopy on partially molten Al-Si-Cu-Mg alloy particles during in situ heating in a transmission electron microscope. Using this technique, we were able to (i) determine that the aluminum and silicon concentrations change in a complementary and symmetric manner about the solid-liquid interface as a function of temperature; (ii) directly measure the solid- and liquid-phase compositions at equilibrium and in highly undercooled conditions for quantitative comparison with thermodynamic calculations of the liquidus and solidus phase boundaries; and (iii) provide direct evidence for homogeneous nucleation of the aluminum-rich solid.     

High-pressure polymorphism in sodium chloride: a reinvestigation

X-ray studies of sodium chloride near 20 kilobars were made in an attempt to verify the reported highpressure-stable, cesium chloride-type structure. Experiments employing extreme shear forces, elevated temperature, and various moisture contents have shown no indication of a second phase. A reexaminatino of the original x-ray evidence suggests that the data may be explained by lithium found in the apparatus.     

DGT法原位测量水体中金属有效态组分及动力学研究

根据不同厚度扩散膜DGT(梯度扩散薄膜)对金属络合易解离态解离能力差异性这一原理,提出了一套计算金属解离动力学及有效态组分方法,并将其应用于水体Zn、Ni、Cu、Fe、Mn、Cd、Pb等金属形态及运移动力学特征差异性计算中。结果表明,研究提出的计算方法,克服了原有方法过拟合的缺点,可以不借助第三方金属形态分析软件一次性计算出金属有效态含量、组分构成及K-1值,且计算结果更好地体现出有效态中络合易解离部分的贡献,计算公式假设参数少,避免了金属价态、有机质组分构成差异性等因素对有效态含量计算的影响。     

铁尾矿库区白茅对重金属的吸收与富集特征

【目的】分析白茅对重金属Cu、Mn、Zn、Ni和Cd的吸收富集作用,探索受重金属污染的尾矿库区的生态修复方法。【方法】以陕西略阳米箭沟铁尾矿库区内的白茅为研究对象,野外采集白茅植株和相关土样,室内对样品重金属含量进行检测与分析。【结果】白茅植株不同部位对重金属Cu、Mn、Zn、Ni和Cd的吸收与分布表现出一定的差异。重金属Cu和Mn在白茅根部含量最高,分别达到70.27和125.19mg/kg,叶部含量最低,分别为1.15和4.54mg/kg;Zn和Ni在白茅茎部含量最高,分别为92.28和105.44mg/kg,而在根部含量最低,分别为12.76和22.16mg/kg;Cd在茎部含量最高,为86.32μg/kg,叶部含量最低,仅为29.18μg/kg。白茅对不同重金属总富集系数的大小顺序为ZnCuNiMnCd,对各重金属转移能力的大小顺序ZnNiCdMnCu。【结论】白茅对Cu、Mn、Zn、Ni和Cd 5种金属的富集能力不强,但可在贫瘠的铁尾矿砂中生长而不受这些重金属的影响,并能改变尾砂的土壤理化性质,因此白茅可用于重金属污染尾矿库区的生态修复,尤其是Mn、Ni和Cd含量较高的矿区。     

Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride, and ice: release of active chlorine

The reaction rate between atmospheric hydrogen chloride (HCl) and chlorine nitrate (ClONO(2)) is greatly enhanced in the presence of ice particles; HCl dissolves readily into ice, and the collisional reaction probability for ClONO(2) on the surface of ice with HCl in the mole fraction range from approximately 0.003 to 0.010 is in the range from approximately 0.05 to 0.1 for temperatures near 200 K. Chlorine (Cl(2)) is released into the gas phase on a time scale of at most a few milliseconds, whereas nitric acid (HNO(3)), the other product, remains in the condensed phase. This reaction could play an important role in explaining the observed depletion of ozone over Antarctica; it releases photolytically active chlorine from its most abundant reservoir species, and it promotes the formation of HNO(3) and thus removes nitrogen dioxide (NO(2)) from the gas phase. Hence it establishes the necessary conditions for the efficient catalytic destruction of ozone by halogenated free radicals. In the absence of HCl, ClONO(2) also reacts irreversibly with ice with a collision efficiency of approximately 0.02 at 200 K; the product hypochlorous acid (HOCI) is released to the gas phase on a time scale of minutes.     

Hydrogen Embrittlement of Metals: Atomic hydrogen from a variety of sources reduces the ductility of many metals

Hydrogen interacts with many metals to reduce their ductility (2) and frequently their strength also. It enters metals in the atomic form, diffusing very rapidly even at normal temperatures. During melting and fabrication, as well as during use, there are various ways in which metals come in contact with hydrogen and absorb it. The absorbed hydrogen may react irreversibly with oxides or carbides in some metals to produce a permanently degraded structure. It may also recombine at internal surfaces of defects of various types to form gaseous molecular hydrogen under pressures sufficiently high to form metal blisters when the recombination occurs near the outer surface. In other metals, brittle hydrides that lower the mechanical properties of the metal are formed. Another type of embrittlement is reversible, depending on the presence of hydrogen in the metal lattice during deformation for its occurrence. Under some conditions the failure may be delayed for long periods. A number of different mechanisms have been postulated to explain reversible embrittlement. According to some theories hydrogen interferes with the processes of plastic deformation in metals, while according to others it enhances the tendency for cracking.     

高压水射流在高压气管内表面清洗中的应用

储运高压气的高压气管使用中因其内表面残留氧化皮脱落造成出口阀路堵塞,导致高压气管失效。介绍了高压水射流清洗技术的特点和水射流效应的机理,阐述了该设备的工作过程、系统组成和基本参数,并作了经济分析和效果评价。     

橙汁的高压处理:果胶甲酯酶失活的动力学

进行了橙汁中果胶甲酯酶(PME)失活的动力学研究.橙汁样品在不同时间内联合使用高压(400MPa,500MPa,600 MPa)和热(25℃,37.5℃,50℃)处理.PME的失活遵循一级动力学模型,保留有耐压酶的残留活性.计算得到的D值分别为600 MPa/50℃和400MPa/25℃下的4.6 min和117.5 min.压力超过500MPa产生足够快的失活速率,从而使本工艺经济可行.