Oleksiy V. Khavryuchenko
,
Volodymyr D. Khavryuchenko
,
苏党生
催化学报
doi:10.1016/S1872-2067(15)60948-2
当初始态和过渡态之间存在能量差时，通常会考虑用催化的方法来增加反应速率，即经由能量更低过渡态的反应路径，或增加反应物初始态能量，如改变溶剂或在特殊表面吸附分子。然而，对于某些类型的反应，如H2和O2反应生成水， NO的氧化等，仅仅采用这些方法还不够，因为反应物和产物具有不同的自旋态，而自旋守恒定律一般会禁止该过程的发生。即使克服了能垒，该体系也不能转化成稳定的产物，且不改变其电子自旋多重态。但在特殊的非热力学条件下，该类反应仍可发生。这通常指自旋不守恒的过程。改变体系电子自旋最直接的方法是与原子核自旋有作用的电子自旋翻转。它可由自旋-轨道耦合来实现，因此，其实现的几率取决于元素的原子数。从3d金属开始，发生这种情况的可能性甚至更大。这是由于与d轨道耦合的效率更高所致，所以采用自旋交叉就能方便地解释自旋禁止反应发生的原因。然而，轻原子发生自旋翻转的可能性很低，因此，当面对无金属化学时，我们应该考虑自旋禁止反应发生的第二个方法—自旋催化。通过帮助克服自旋禁止的物质以促进化学反应，或通过顺磁催化剂诱导自旋解耦以降低活化能垒，这类现象就可定义为自旋催化。简而言之，为了得到想要的和热力学更有利的自旋态，一个反应粒子可以与自旋催化剂交换磁矩；该自旋催化剂需有拟自旋-简并基态或低激发态。因此，体系整个的自旋仍守恒，但可发生反应。值得强调的是，自旋“催化剂”指的是分子状态和固体状态，通常后者应用于工业中则方便得多。自旋催化是作为自旋化学的范例来研究的，或在外磁场中化学诱导动态核极化和反应，主要是指采用EPR光谱研究以液相为主的过程。本文简略介绍了自旋催化的理论。实际上，自旋催化与常规催化之间并不相互抵触—相同的材料既可作为自旋催化剂，也可用作常规催化剂，都起着降低反应能垒和提供自旋交换的自由基中心的作用。另外，许多现代材料包含着常规催化剂和自旋催化剂的特性。有些发生在多核磁性金属中心上的过程可能本身就包含着常规催化(活化底物)、自旋交叉(与d金属相互作用)和自旋催化(金属-氧簇合物中低能的铁磁-反铁磁转化)效应。气相自旋催化在实际应用中产生的主要问题是在稀释的体系中三粒子碰撞几率低，常规催化在这方面则有很多优势。我们首先列出固体成为自旋催化剂的条件：(1)活性中心中至少2个自旋态的能量差要小于反应温度下热运动的能量，这样无需额外的能量活化催化剂；(2)较大的比表面积以提供更多的自旋中心用于相互作用；(3)最好能够自旋导电，在此情况下反应无需三粒子碰撞即可发生。这是因为自由基可通过催化剂的电子系统交换自旋，使得自旋-自旋相互作用的几率迅速增加，从而有利于自旋催化反应的进行。另外，如果固体或载体具有自旋导电性，则无需外加电场或磁场，即有可能遥控催化中心的电荷和自旋态，从而避免使用外电场或磁场。实际上，许多反应过程本身就包含着自旋催化，它还可使反应过程的许多不足变成优势，如对于不需要的链式自由基反应；通过引入自旋捕获剂使得自旋禁止反应成为有用的自旋催化；磁性粒子的浓度以及外加磁场和电场均可导致自旋催化/禁止反应。由于均相自旋催化的研究较早，在此不再赘述。本文详细介绍了多相体系中的自旋催化的应用，如燃烧、温和氧化、环化、开环、非极性小分子的活化和不稳定自由基的耦合等。可能用作自旋催化剂的材料有：含有不同顺磁性的金属离子的磁性氧化物或多核磁性簇合物；嫁接在一些载体上的多核络合物或过渡金属(低温催化)；带有非整数氧化价态的导电金属；各种具有半金属性和导电性的碳材料。研究自旋催化反应的一个突出问题就是这些过程大部分是自由基式的，趋于非线性区域，因而很难预测，也没有一个便利的工具用以描述，甚至预测自旋催化反应，但也许这些研究的特点就是不可预测性。自旋催化除了可调变反应的进行，我们还可从中获得一个独特的调节手段：通过外加磁场或电场触发基元过程，在非热力学上控制反应的进行。该手段在控制化学反应方面具有明显优势，因为现在大都是通过调节温度、压力和流量等参数来实现对化学反应的控制，且滞后严重。同时，通过添加外加磁场可立刻改变反应速率。另外，通过降温可精细控制基元反应，从而开辟了一种抑制副反应的方法，因而也使得反应的随机性降低。
关键词:
催化
,
自旋化学
,
化学键均裂
,
氧化过程
,
自由基耦合
Physics and Chemistry of Liquids
In earlier work, Ma [S.K. MA, Phys. Rev. Lett., 29, 1311 (1972)] has studied the critical exponents and for charged and neutral Bose gases. Here we use the result of Ma, valid for general dimensionality d but only to O(m-1), where m is the number of components of the Bose field, to write a relation between (d) and (d) to O(m-1). This then motivates, but now for the Ising model, a relationship between the critical exponents and , via the dimensionality d. We finally demonstrate a connection between the two renormalisation group eigenvalues yt and yh, via the critical exponent with a dimensional dependence.
关键词:
critical exponents;Ising model;dimensionality
赵国华
,
齐砚勇
,
潘玉峰
硅酸盐通报
对YNLL水泥厂2500 t/d生产线进行热工标定并分析,系统烧成热耗为3889 kJ/kg.cl,高于全国平均水平.高温风机拉风偏大,一级筒出口温度为370℃,偏高.篦式冷却机效果欠佳,AQC抽风量偏高,直接影响了熟料质量和余热发电量,热回收效率偏低.经过改进和优化,熟料产能提高为2600 t/d.该生产线系统还有比较大的潜力,熟料产量还有可能进一步提高,热耗及电耗均可能明显下降.
关键词:
热工标定
,
新型干法水泥
,
篦冷机
曹华夏
,
毕金栋
,
李昌勇
硅酸盐通报
对LNZL水泥厂2500 t/d生产线进行热工标定并分析,该厂熟料产量超过设计产量28.96％,达到3224.1t/d.系统烧成热耗为3302.6kJ/kg熟料,低于全国平均水平,一级筒出口温度为334℃,稍有些偏高;系统的分离效率为91.49％,出预热器飞灰量偏高,还有明显的改善空间.篦式冷却机效果欠佳,直接影响了熟料质量和余热发电量,热回收效率也偏低.该生产线系统还有比较大的潜力,如经过改进和优化,熟料产能还有可能进一步提高,热耗及电耗均可明显下降.
关键词:
热工检测
,
水泥生产线
,
运行情况
Physical Review B
In the investigation of the optical and magnetic properties of the semiconductors containing transition-metal ions, the one-electron orbital cannot be treated with a pure d orbital because of a strong covalence. This paper presents the energy matrix of the d*(8) and d*(2) (d* means a modified d function) system, in which the covalence is described by two covalent factors. The differences between the matrix diagonal elements of the t(2)(m)e(n) term of the d*(8) system and the t(2)(6-m)e(4-n) term of the d*(2) system vary with m and n. The d(N) electron system can be explained with the d(10-N) hole system because the difference between the energy matrix of the d(N) and d(10-N) systems has a fixed value. However, this kind of simple relation does not exist for the d*(N) and d*(10-N) systems when the covalence is considered. A numerical calculation shows that the variation of the energy levels with the covalence for Ni2+ in the d*(8) electron system is larger than that in the d*(2) hole system. The calculated energy levels obtained from the d*(8) matrix are in good agreement with the experimental data of the Ni2+ ion for ZnS:Ni and ZnSe:Ni. This suggests that the d*(8) electron system instead of the d*(2) hole system should be used in the investigation of optical and magnetic properties of semiconductor containing Ni2+ ions.
关键词:
zns-ni;absorption;vanadium;impurities;spectra;ions
Materials Chemistry and Physics
In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91 D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES). The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5gl(-1) corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1-5 gl(-1) are integrated and uniform. However, those formed in 20-50 gl(-1) have some micro-cracks on the (x phase. The coating formed in 5 gl(-1) has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1-20 gl(-1) can all improve the corrosion resistance of AZ91 D. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.
关键词:
concentration;magnesium alloys;phytic acid;conversion coatings;corrosion-resistance;chromatography;behavior;copper;mg
张兴
,
郑成武
,
李宁
,
周兴丹
,
李正强
,
华瑞茂
液晶与显示
doi:10.3788/YJYXS20122704.0448
介绍了3D显示的基本原理,重点介绍了目前3D显示的主流技术类型,包含了眼镜式3D技术以及裸眼式3D技术,其中眼镜式3D技术包含色差式3D技术、偏光式3D技术和主动快门式3D技术;裸眼式3D技术包含视差屏障式3D技术、柱状透镜式3D技术、指向光源式3D技术和多层显示式3D技术.阐述了各种3D显示技术的基本实现原理和应用领域、并对涉及液晶显示的几种3D技术的优缺点进行了对比.结合液晶材料的特点与3D液晶显示的实际要求,阐述了3D液晶面板对液晶材料快速响应方面的要求,以及液晶透镜对液晶材料光学各向异性参数的要求.
关键词:
3D显示
,
眼镜式3D显示
,
裸眼式3D显示
,
液晶材料
D.Han
,
S.R.Qiao
,
M.Li
,
J.T.Hou
,
X.J.Wu
金属学报(英文版)
The differences of tension-tension fatigue and tensile creep characters of 2D-C/SiC and 3D-C/SiC composites have been scrutinized to meet the engineering needs. Experiments of tension-tension fatigue and tensile creep are carried out under vacuum high temperature condition. All of the high temperature fatigue curves are flat; the fatigue curves of the 2D-C/SiC are flatter and even parallel to the horizontal axis. While the tension-tension fatigue limit of the 3D-C/SiC is higher than that of the 2D-C/SiC, the fiber pullout length of the fatigue fracture surface of the 3D-C/SiC is longer than that of the 2D-C/SiC, and fracture morphology of the 3D-C/SiC is rougher, and pullout length of the fiber tows is longer. At the same time the 3D-C/SiC has higher tensile creep resistance. The tensile curve and the tensile creep curve of both materials consist of a series of flat step. These phenomena can be explained by the non-continuity of the damage.
关键词:
2D-C/SiC
,
null
,
null
