“五一”小长假终究还是过去了，电量不足的小伙伴们，带上你的小马达，跟我一起充充“电”吧！ 第一站：电池诞生记 1 ） 1746 年：莱顿瓶 莱顿大学的马森布罗克用一支枪管悬在空中，用起电机与枪管连着，另用一根铜线从枪管中引出，浸入一个盛有水的玻璃瓶中，一个助手一只手握着玻璃瓶，马森布罗克在一旁使劲摇动起电机。这时他的助手不小心将另一只手与枪管碰上， 随后 猛然感到一次强烈的电击，喊了起来。马森布罗克由此得出结论：把带电体放在玻璃瓶内可以把电保存下来 ， 后来人们就把这个蓄电的瓶子称作“ 莱顿瓶 ” ，这个实验称为 “ 莱顿瓶实验 ” 。 2 ） 1786 年：“生物电” 意大利 解剖学家伽伐尼在做青蛙解剖时，两手分别拿着不同的金属器械，无意中同时碰在青蛙的大腿上，青蛙腿部的肌肉立刻抽搐了一下，仿佛受到电流的刺激，而只用一种金属器械去触动 青蛙 ，却并无此种反应。伽伐尼认为，出现这种现象是因为动物躯体内部产生的一种电，他称之为“ 生物电 ” 。 3 ） 1799 年：伏特电堆 意大利物理学家伏特把一块锌板和一块银板浸在 盐水 里，发现连接两块金属的导 线中有电流通过。于是，他就把许多锌片与银片之间垫上浸透盐水的绒布或纸片，平叠起来。用手触摸两端时，会感到强烈的电流刺激。伏特用这种方法成功的制成了世界上第一个电池──“ 伏特电堆 ” 。 4 ） 1836 年：丹尼尔电池 英国的 丹尼尔 对“ 伏特电堆 ” 进行了改良。他使用 稀硫酸 作电解液，解决了电池极化问题，制造出第一个不极化，能保持 平衡 电流的锌─ 铜电池，又称 “ 丹尼尔电池 ” 。 5 ） 1860 年：蓄电池 法国的普朗泰发明出用铅做电极的电池。当电池使用一段使电压下降时，可以给它通以反向电流，使电池电压回升。因为这种电池能充电，可以反复使用，所以称它为“ 蓄电池 ” 。 电池已经诞生了 200多年，现在仍然在前进。无论是过去还是现在，电池的目标都没有改变：随时随地让人享受电能的巨大恩惠。 如何预测电池的剩余电量？如何提高电池性能？英国学者为你解惑 ~ 第二站：好文推荐 VRLA 电池系统中分析孔隙几何形状及识别方块效应的高级预测机制 An Advanced Prediction Mechanism to Analyse Pore Geometry Shapes and Identification of Blocking Effect in VRLA Battery System Alessandro Mariani 1 , Kary Thanapalan 1 , Peter Stevenson 2 , Jonathan Williams 1 1. Faculty of Computing, Engineering and Science , University of South Wales , Pontypridd , UK 2. Yuasa Battery (UK) Ltd , Rassau Industrial Estate , Ebbw Vale , UK 收录信息： Alessandro Mariani, Kary Thanapalan, Peter Stevenson etc. An Advanced Prediction Mechanism to Analyse Pore Geometry Shapes and Identification of Blocking Effect in VRLA Battery System . International Journal of Automation and Computing , 2017,14(1): 21-32. 全文链接： 1） Springer Link: https://link.springer.com/article/10.1007/s11633-016-1040-0 2） IJAC 官网： http://www.ijac.net/EN/abstract/abstract1855.shtml 文章概要： 本文提出一种高级预测机制，用于 阀控密封铅酸（ VRLA ）电池 系统中的孔隙几何形状分析以及方块效应识别。本研究首先构建了一个数学模型来识别 VRLA 电池的剩余电量，而后通过电化学阻抗技术得出实验数据，用以验证该模型。最后，基于数据分析，得出低性能电池中发生扩散限制的原因。通过本研究可知，电极大小及孔分布将影响电池在充电及放电时的电化及电解过程。 关键词 ： Positive active material, crystal structure, valve regulated lead acid (VRLA) batteries, modelling, estimation and recovery techniques. 作者简介 ： Alessandro Mariani received the B. Eng. degree from University of Glamorgan, UK in 2010. He is currently a Ph.D. degree candidate at University of South Wales, UK. His research interests include lead acid battery technology and electrochemical performance analysis. ORCID iD: 0000-0001-5810-2681 Kary Thanapalan received the B.Eng. degree in control engineering from City University London, UK. Later he received the Ph.D. degree in aerospace control systems from the University of Liverpool, UK . He is currently working as a senior researcher in the faculty of computing, engineering and sciences, University of South Wales, UK, and a leading researcher in the fields of energy and renewable energy and control and automation engineering. His research interests include control system design, renewable energy and optimization analysis. ORCID iD: 0000-0001-6398-4340 Peter Stevenson received the M. Sc. degree in chemistry from the University of Cambridge, UK in 1979. He is currently working as senior technical co-ordinator at the Yuasa Battery (Europe) Ltd. His research interests include lead acid and lithium battery technology. ORCID iD: 0000-0003-3894-2207 Jonathan Williams received the M. Eng. degree in mechatronic engineering and has since worked with numerous industrial companies and specialist materials companies at the University of South Wales, UK . He is currently working as a CAPSE director at the University of South Wales, UK, and a leading researcher in the development of new innovative energy storage system and solutions. His research interests include power system engineering and lithium based energy storage. 部分内容整理自网络，参见： http://tech.qq.com/a/20090524/000025.htm http://baike.so.com/doc/1207846-1277666.html IJAC International Journal of Automation and Computing IJAC的出版服务不会止于论文发表。在论文发表后，IJAC也在积极地通过多种方式帮助作者提升研究成果的影响力，“IJAC推文”是其中一种方式，即通过互联网，以研究简介、实验视频等内容和形式，来帮助作者推广出版作品。 IJAC官方微信平台带您开启一场不一样的学术之旅，这里有最新会议资讯、研究成果、科普常识、美图美文，还有热情活泼而又不失严肃认真的阳光小编！ IJAC官方网站： 1) http://link.springer.com/journal/11633 2) http://www.ijac.net 新浪微博：IJAC-国际自动化与计算杂志 官方微信：IJAC Twitter: IJAC_Journal Linked in(领英): Int. J. of Automation and Computing
Introduction to MagnetochemistryDavid Young Cytoclonal Pharmaceutics Inc. Introduction Magnetochemistry is the study of the magnetic properties of materials. By magnetic properties we mean not only whether a material will make a good bar magnet, but whether it will be attracted or repelled by a magnet. This includes synthesis, analysis and understanding. This short description is meant to give a basic understanding before you delve into a more complex treatment. Magnetism arises from moving charges, such as an electric current in a coil of wire. In a material which does not have a current present, there are still magnetic interactions. Atoms are made of charged particles (protons and electrons) which are moving constantly. The processes which create magnetic fields in an atom are Nuclear spin. Some nuclei, such as a hydrogen atom, have a net spin which creates a magnetic field. Electron spin. An electron has two intrinsic spin states (similar to a top spinning) which we call up and down or alpha and beta. Electron orbital motion. There is a magnetic field due to the electron moving around the nucleus. Each of these magnetic fields interact with one another and with external magnetic fields. However, some of these interactions are strong and others are negligible. Measurement of interactions with nuclear spins are used to analyze compounds in nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy. In most other situations, interaction with nuclear spins is a very minor effect. Interactions between the intrinsic spin of one electron and the intrinsic spin of another electron are strongest for very heavy elements such as the actinides. This is called spin-spin coupling. For these elements this coupling can shift the electron orbital energy levels. The interaction between an electron's intrinsic spin and it's orbital motion is called spin-orbit coupling. Spin-orbit coupling has a significant effect on the energy levels of the orbitals in many inorganic compounds. Macroscopic effects, such as the attraction of a piece of iron to a bar magnet are primarily due to the number of unpaired electrons in the compound and their arrangement. The various possible cases are called magnetic states of matter. Magnetic States of Matter Diamagnetic - A diamagnetic compound has all of it's electron spins paired giving a net spin of zero. Diamagnetic compounds are weakly repelled by a magnet. Paramagnet - A paramagnetic compound will have some electrons with unpaired spins. Paramagnetic compounds are attracted by a magnet. Ferromagnet - In a ferromagnetic substance there are unpaired electron spins, which are held in alignment by a process known as ferromagnetic coupling. Ferromagnetic compounds, such as iron, are strongly attracted to magnets. Ferrimagnet - Ferrimagnetic compounds have unpaired electron spins, which are held in an pattern with some up and some down. This is known as ferrimagnetic coupling. In a ferrimagnetic compound, there are more spins held in one direction, so the compound is attracted to a magnet. Antiferromagnetic - When unpaired electrons are held in an alignment with an equal number of spins in each direction, the substance is strongly repelled by a magnet. This is referred to as an antiferromagnet. Superconductor - Superconductors are repelled by magnetic fields because the magnetic field is excluded from passing through them. This property of superconductors, called the Meissner effect, is used to test for the presence of a superconducting state. The underlying theory of how superconductivity arises is still a matter of much research and debate at the time of this writing. It does appear that the mechanism behind the magnetic properties of superconductors is significantly different from the other classes of compounds discussed here. For these reasons, superconductors will not be discussed further here. Interaction with an External Magnetic Field A magnetic field is given the symbol H which is a vector since the field has both a direction and a magnitude. For this discussion we will consider only interactions in one dimension making H and many other quantities we will define scalars. This gives us results for a homogeneous magnetic field and is a very good approximation for the way that most magnetic property measurements are performed. The magnitude of the magnetic field is usually given in units of gauss (G) or tesla (T) where 1 tesla = 10000 gauss. When a material is placed in a magnetic field, the magnetic field inside the material will be the sum of the external magnetic field and the magnetic field generated by the material itself. The magnetic field in a material is called the magnetic induction and given the symbol B. The formula for this is B = H + 4 Pi M where B = magnetic induction H = external magnetic field Pi = 3.14159 M = magnetization ( a property of the material ) For mathematical and experimental convenience this equation if often written as B = 1 + 4 Pi M = 1 + 4 Pi Xv - ------ H H where Xv = M/H = volume magnetic susceptibility The volume magnetic susceptibility is so named because B, H and M are defined per unit volume. However this results in Xv being unitless. It is convenient to use the magnetic susceptibility instead of the magnetization because the magnetic susceptibility is independent of the magnitude of the external magnetic field, H, for diamagnetic and paramagnetic materials. Many studies are done using Xg, magnetic susceptibility per gram, which is Xv divided by the density. This gives units of cm cubed per gram. Another useful form is Xm, molar magnetic susceptibility, which is Xg times the molecular weight. This gives units of cm cubed per mole. Another measure of magnetic interaction that is often used is an effective magnetic moment, mu, where mu = 2.828 ( Xm T ) 1/2 where mu = effective magnetic moment Xm = molar magnetic susceptibility T = temperature The numeric factor puts mu in units of Bohr magnetons (BM). Where one BM equals 9.274 x 10^-24 joules per tesla. The effective magnetic moment is a convenient measure of a material's magnetic properties because it is independent of temperature as well as external field strength for diamagnetic and paramagnetic materials. This said, we would now like to examine how the magnetization, magnetic susceptibility and effective magnetic moment depend on molecular structure. Diamagnetism Diamagnetism can be described by electrons forming circular currents, orbiting the nucleus, in the presence of a magnetic field. As such, a diamagnetic contribution can be calculated for any atom. However, the magnitude of the diamagnetic contribution is so much smaller than the magnitude of paramagnetic and other effects that it is usually ignored for any other type of materials. In this orbital model, the diamagnetic susceptibility from a given electron is proportional to the square of it's mean distance from the nucleus. Thus larger atoms are expected to have a larger diamagnetic interaction than smaller atoms. Often, the contributions for common atoms are tabulated along with corrections for multiple bonds. Thus a magnetic susceptibility can be predicted merely by adding together the contributions from all of the atoms and bonds in the molecule. For an example of these scheme, see Drago. For a more complete treatment, see Selwood. Paramagnetism The structural feature most prominent in determining paramagnetic behavior is the number of unpaired electrons in the compound. A spin only formula for the magnetic moment of a paramagnetic compound is mu = g { S ( S + 1 ) } 1/2 where mu = effective magnetic moment g = 2.0023 S = 1/2 for one unpaired electron 1 for two unpaired electrons 3/2 for three unpaired electrons, etc. This equation is sometimes written with g=2. This does not introduce a significant error since this simple spin only treatment is a decent approximation but is often not accurate even to two significant digits. An equation which takes into account both spin and orbital motion of the electrons is mu = { 4 S ( S + 1 ) + L ( L + 1 ) } 1/2 where mu = effective magnetic moment S = 1/2 for one unpaired electron, 1 for two, etc. L = total orbital angular momentum This equation is derived for atoms. It is applicable only to molecules with very high symmetry where the energies of the orbitals containing unpaired electrons are degenerate. A discussion of the calculation of L can be found in any introductory quantum mechanics text or in the chapter on quantum mechanics in many physical chemistry texts. If the splitting of orbital energy levels is large relative to k T ( k is the Boltzman constant ) then the applicable formula is mu = g { J ( J + 1 ) } 1/2 where g = 1 + S ( S + 1 ) - L ( L + 1 ) + J ( J + 1 ) --------------------------------------- 2 J ( J + 1 ) where J = S + L This formula is usually used for the lanthanide and actinide elements. For more accurate treatment of these elements, a diamagnetic contribution can be added to this as described by Selwood. If the splitting of orbital energy levels is comparable in magnitude to k T then the expression for magnetic properties must incorporate a Boltzman distribution. This is often the case with high spin transition metal complexes. The worst case, where this procedure is absolutely imperative, is the description of spin cross overs such as exhibited by some iron coordination compounds. Examples of this type of treatment are given in both the Drago and Selwood texts. For all of the cases of paramagnetic behavior the spin only formula is often used as a first rough approximation. If the only purpose for measuring the magnetic susceptibility is to determine the number of unpaired electrons this is often all that is done. Ferromagnetism, Antiferromagnetism and Ferrimagnetism The advantage of using effective magnetic moments for describing paramagnetic behavior is that it is a measure of the materials magnetic behavior which is not dependent upon either the temperature or the magnitude of the external field. It is not possible to set up such a convention for ferromagnetic, antiferromagnetic and ferrimagnetic materials. All three of these classes of materials can be considered a special case of paramagnetic behavior. The description of paramagnetic behavior is based on the assumption that every molecule behaves independently. The materials discussed here result from a situation in which the direction of the magnetic field produced by one molecule is affected by the direction of the magnetic field produced by an adjacent molecule, in other words their behavior is coupled. If this occurs in a way in which the magnetic fields all tend to align in the same direction, a ferromagnetic material results and the phenomenon is called ferromagnetic coupling. Antiferromagnetic coupling gives an equal number of magnetic fields in opposite directions. Ferrimagnetic coupling gives magnetic fields in two opposite orientations with more in one direction than in the other. With a few exceptions, the magnetic moments are not aligned through out the entire material. Typically regions, called domains, will form with different orientations. The existence of domains of coupled molecules gives rise to a number of types of behavior as described in the following paragraphs. The tendency of molecules to align themselves to one another enhances the magnetization of the material due to the presence of an external magnetic field. This is why ferromagnetic and ferrimagnetic materials can have magnetic susceptibilities several orders of magnitude large than paramagnetic materials. This also gives rise to the fact that the magnetic susceptibility of these materials is not independent of the magnitude of the external magnetic field as was the case for diamagnetic and paramagnetic materials. For a ferromagnetic material, the actual field acting on a given magnetic dipole ( unpaired electron ) is designated Ht and given by an equation similar to the equation for magnetic induction given above. Ht = H + Nw M where Ht = magnetic field felt by an electron H = external magnetic field Nw = molecular field constant, approximately 10000 M = magnetization This equation is used because it allows a mathematical treatment of a ferromagnetic substance similar to that used for paramagnetic substances. In this form the molecular field constant, Nw, is typically defined empirically in order to take the ferromagnetic coupling into account. To obtain the molecular field constant in a rigorous way would require a quantum mechanical calculation that takes into account the elements, their arrangement in the solid, kinetic energy of the electrons, coulombic attraction of electrons to the nucleus and repulsion with other electrons as well as spin interactions. What is most often done is a computer simulation using the Ising model, which is not truly rigorous but is based on quantum mechanics. This is a spin only quantum mechanical treatment assuming that the values of neighboring spins can be replaced by their average over time. For more explanation, see Morrish. Vibrational motion of the molecules, which increases with temperature, can disrupt the domain structure. Thus the magnetic properties of all three of these types of materials are strongest at low temperatures. At sufficiently high temperatures, no domain structure is able to form so all of these materials become paramagnetic at high temperatures. The temperature at which paramagnetic behavior is seen called the Curie temperature for ferromagnetic and ferrimagnetic materials and called the Neel temperature for antiferromagnetic materials. This is why a temperature independent effective magnetic moment cannot be defined for these materials. The alignment of the magnetic moments of the domains may give the material a net magnetic moment even in the absence of an external field. This gives a permanent magnet, such as a bar magnet. A material with no net moment prior to being exposed to an external magnetic field may retain a net moment after being exposed to an external magnetic field. This is how cassette and video tapes and computer disks store information. The magnitude of this memory effect can be quantified by plotting magnetization vs field strength as the external field intensity is varied from one polarity to the other and back again. A strong memory effect will be indicated by a wide hysteresis loop. Over a period of time magnetic domains tend to return to a random orientation. This makes the kinetics of this relaxation process another factor in the magnetic behavior of these materials. This is also responsible for the limited life span of magnetically stored music, video and computer data. Variation with Temperature The source of variation of magnetic properties with temperature is the disruption of the alignment of molecular magnetic moments due to the thermal motion of the atoms. As such, it should come as no surprise that diamagnetic behavior shows no variation with temperature. Paramagnetism As temperature increases, the magnetic susceptibility of a paramagnetic substance decreases. In some paramagnetic compounds the magnetic susceptibility is inversely proportional to the temperature. These are called normal paramagnets and have magnetic properties arising primarily due to the presence of permanent magnetic dipoles. This is referred to as the Curie Law and is expressed in mathematical form as X = C / T where C = Na g 2 b 2 ------- 4 k where X = magnetic susceptibility C = the Curie constant T = temperature Na = Avogadro's number g = the electron g factor b = the Bohr magneton k = the Boltzman constant In most paramagnetic compounds, an inverse relationship is observed, but the extrapolation to zero temperature does not obey the Curie Law. These compounds obey the Curie-Weiss Law which is X = C --------- T - theta where theta is a constant referred to as the Weiss constant. The Weiss constant can have a large range of values from -70 K to 3000 K. Most often it is positive. Ferromagnetism ferrimagnetism Ferromagnetic and ferrimagnetic compounds also show a decrease in magnetic susceptibility with increasing temperature. However, a plot of magnetic susceptibility vs. temperature shows a different line shape for these compounds than for paramagnetic compounds. This plot would have a positive curvature for paramagnetic compounds and a negative curvature for ferromagnetic compounds. A rough sketch of the shapes of these curves is as follows When a critical temperature ( called the Curie temperature ) is reached, the curvature of the plot changes. At the Curie temperature, ferromagnetic and ferrimagnetic compounds become paramagnetic. Curie temperatures range from 16 C for Gd to 1131 C for Co. For ferromagnetic substances a universal temperature curve can be constructed, meaning that all substances with the same total spin follow the same curve. This is done by plotting M(T)/M(0) vs T/Tc where M(T) is the magnetization at a given temperature, M(0) is the magnetization at absolute zero, T is the temperature and Tc is the Curie temperature. For more information, see Morrish. Antiferromagnetism Antiferromagnetic compounds show an increase in magnetic susceptibility until their critical temperature, called the Neel temperature, is reached. Above the Neel temperature these compounds also become paramagnetic. Neel temperature range from 1.66 K for MnCl 2 *4H 2 O to 953 K for alpha-Fe 2 O 3 . As with ferromagnetic substances, a universal temperature curve can be constructed that all substances with the same number of unpaired electrons follow. This is done by plotting X(T)/X(Tn) vs T/Tn where X(T) is the magnetic susceptibility at a given temperature, X(Tn) is the magnetic susceptibility at the Neel temperature, T is the temperature and Tn is the Neel temperature. For more information, see Morrish. Further Information Magnetochemistry is most often the realm of inorganic chemists so there should be a short discussion in any basic inorganic text. An old but good book on many aspects of magnetochemistry is P. W. Selwood Magnetochemistry Interscience (1956) Another good text is A. H. Morrish The Physical Principles of Magnetism John Wiley Sons (1965) There are chapters on magnetochemistry in R. S. Drago Physical Methods For Chemists Saunders College and Harcourt Brace Jovanovich (1992) L. Solymar, D. Walsh Lectures on the Electrical Properties of Materials Oxford (1993) A mathematical treatment can be found in D. L. Goodstein States of Matter Dover (1985) Solid state properties are covered in A. R. West Solid State Chemistry and its Applications John Wiley Sons (1992) A book describing more sophisticated simulation techniques is M. H. Krieger Constitutions of Matter University of Chicago Press (1996)
Analysis of the GaAs GaAsBi material system for heterojunction bipolar transistors 共6页。 摘要： This paper reports on the simulation of a double heterojunction bipolar transistor using the novel GaAs/GaAsBi material system. Published material parameters were used to simulate the device performance using an analytic drift-diffusion device model. DC and RF parameters were calculated as a function of emitter current density, base thickness and doping, and emitter stripe width and doping. Current gain is predicted to be between 102 and 103 at a current density of 105 A/cm2 and a bismuth concentration of 1.5%–3%. RF performance was calculated to range from10 to 30GHz for fT and from100 to 120 GHz for fmax at a current density of 105 A/cm2, base thickness of 100–200 nm, and emitter stripe width of 0.1–1 μm. 下载地址： http://www.pipipan.com/file/22096698
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