Theoretical study of elastic electron scattering off stable and exotic nuclei
X. Roca-Maza,∗ M. Centelles, F. Salvat, and X. Vi˜ nas
Departament d’Estructura i Constituents de la Mat` eria and Institut de Ci` encies del Cosmos, Facultat de F´ ısica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain Results for elastic electron scattering by nuclei, calculated with charge densities of Skyrme forces and covariant effective Lagrangians that accurately describe nuclear ground states, are compared against experiment in stable isotopes. Dirac partial-wave calculations are performed with an adapted version of the elsepa package. Motivated by the fact that studies of electron scattering off exotic nuclei are intended in future facilities in the commissioned GSI and RIKEN upgrades, we survey the theoretical predictions from neutron-deficient to neutron-rich isotopes in the tin and calcium isotopic chains. The charge densities of a covariant interaction are used to this end as an illustrating example. Since the experimental analysis of scattering data commonly involves parameterized charge densities, as a surrogate exercise for the yet unexplored exotic nuclei, we fit our calculated mean field densities with Helm model distributions. This procedure turns out to be helpful to study the neutron-number variation of the scattering observables and allows us to identify correlations of potential interest among some of these observables within the isotopic chains.
PACS numbers: 21.10.Ft, 25.30.Bf, 13.40.Gp, 21.60.-n
arXiv:0808.1252v1 [nucl-th] 8 Aug 2008
I.
INTRODUCTION
Elastic electron-nucleus scattering has been for many years a very useful tool to investigate the size and shape of stable nuclei [1, 2, 3, 4, 5]. Electrons interact with nuclei basically through the electromagnetic force. If the energy of the electrons is high enough, they become a relatively clean probe to explore precisely the internal structure of nuclei, insensitive to strong interaction effects. In particular, the analysis of electron scattering data provides most valuable information about the charge distribution in atomic nuclei [6, 7, 8]. Developments in accelerator technology and detection techniques nowadays allow experimentation with nuclei beyond the limits of β -stability. The number of nuclei whose masses have been measured keeps growing [9] and this tendency is expected to continue with the use of radioactive isotope beams (RIB) [10, 11, 12]. A new generation of electron-RIB colliders using storage rings is now under construction in RIKEN (Japan) [13, 14] and GSI (Germany) [15, 16]. These facilities will offer unprecedented opportunities to study the structure of exotic unstable nuclei through electron scattering in the ELISe experiment at FAIR in Germany [17] and the SCRIT project in Japan [18, 19]. Therefore, the theoretical investigation of exotic nuclei with models of purported reliability in stable isotopes is a timely and challenging problem. Such effort will test the ability of the established nuclear theory in the domain of exotic nuclei, and may as well provide valuable references for future experiments. Several theoretical studies of elastic electron-nucleus scattering in exotic nuclei have been recently reported in
the literature [20, 21, 22, 23, 24, 25]. Part of these works is concerned with analyzing electron scattering in light neutron-halo nuclei, such as 6,8 He [20] and 11 Li [20, 22], and in light exotic proton-rich nuclei, such as 8 B [22], 12 O and 28 S [23]. Other works study the variation of the charge form factors along some isotopic [20, 21, 24] and isotonic [25] chains of medium and heavy nuclei. It has been found that when the number of neutrons (protons) in these isotopic (isotonic) chains increases, the squared modulus of the charge form factor and the position of its minima show, respectively, an upward trend and a significant inward shifting in the momentum transfer. To investigate the internal structure of nuclear charge densities, the de Broglie wavelength of the probe has to be of the order of 1 fm. This means that the energy of the electron beam has to be of the order of several hundred MeV. Therefore, for accurate theoretical calculations of differential cross sections (DCS) and electric charge form factors, one needs to solve the elastic scattering of Dirac particles in the scalar potential pertaining to the nuclear charge distribution. The simplest approach is the plane-wave Born approximation (PWBA), where one assumes that the initial and final states of the electronபைடு நூலகம்can be described by plane waves. Although the PWBA is able to account for important features of scattering, it is not enough accurate for quantitative calculations of the electric charge form factor. A more elaborate method is supplied by the Glauber theory using a relativistic eikonal approximation of the Dirac equation [26]. It has been successfully applied to a systematic study in elastic electron-nucleus scattering [23, 24, 25]. The most sophisticated calculations of electron-nucleus scattering employ the exact phase-shift analysis of the Dirac equation. This method corresponds to the so-called distorted wave Born approximation (DWBA) [27] and was employed e.g. in Refs. [20, 21]. In the present work we apply a modified version of the recently published code elsepa [28] to the
金属材料英文词汇
物料科学Material Science物料科学定义Material Science Definition加工性能Machinability强度Strength抗腐蚀及耐用Corrosionresistance durability金属特性Special metallic features抗敏感及环境保护Allergic，recyclingenvironmental protection化学元素Chemical element元素的原子序数Atom of Elements原子及固体物质Atom and solid material原子的组成、大小、体积和单位图表The size，mass，charge of an atom，and is particles (Pronton，Nentron and Electron) 原子的组织图Atom Constitutes周期表Periodic Table原子键结Atom Bonding金属与合金Metal and Alloy铁及非铁金属FerrousNon Ferrous Metal金属的特性Features of Metal晶体结构Crystal Pattern晶体结构，定向格子及单位晶格Crystal structure，Space latticeUnit cellX线结晶分析法X – ray crystal analyics method金属结晶格子Metal space lattice格子常数Lattice constant米勒指数Mills Index金相及相律Metal Phase and Phase Rule固熔体Solid solution置换型固熔体Substitutional type solid solution插入型固熔体Interstital solid solution金属间化物Intermetallic compound金属变态Transformation变态点Transformation Point磁性变态Magnetic Transformation同素变态Allotropic Transformation合金平衡状态Thermal Equilibrium相律Phase Rule自由度Degree of freedom临界温度Critical temperture共晶Eutectic包晶温度Peritectic Temperature包晶反应Peritectic Reaction包晶合金Peritectic Alloy亚共晶体Hypoeutetic Alloy过共晶体Hyperectectic Alloy金属的相融、相融温度、晶体反应及合金在共晶合金、固熔孻共晶合金及偏晶反应的比较Equilibrium Comparision金属塑性Plastic Deformation滑动面Slip Plan畸变Distortion硬化Work Hardening退火Annealing回复柔软Crystal Recovery再结晶Recrystallization金属材料的性能及试验Propertiestesting of metal化学性能Chemical Properties物理性能Physical Properties颜色Colour磁性Magnetisum比电阻Specific resistivityspecific resistance比重Specific gravityspecific density比热Specific Heat热膨胀系数Coefficient of thermal expansion导热度Heat conductivity机械性能Mechanical properties屈服强度(降伏强度) (Y ield strangth)弹性限度、阳氏弹性系数及屈服点elastic limit，Y eungs module of elasticity to yield point 伸长度Elongation断面缩率Reduction of area金属材料的试验方法The Method of Metal inspection不破坏检验Non – destructive inspections渗透探伤法Penetrate inspection磁粉探伤法Magnetic particle inspection放射线探伤法Radiographic inspection超声波探伤法Ultrasonic inspection显微观察法Microscopic inspection破坏的检验Destructive Inspection冲击测试Impact Test疲劳测试Fatigue Test潜变测试Creep Test潜变强度Creeps Strength第壹潜变期Primary Creep第二潜变期Secondary Creep第三潜变期Tertiary Creep主要金属元素之物理性质Physical properties of major Metal Elements工业标准及规格–铁及非铁金属Industrial Standard – FerrousNon – ferrous Metal磁力Magnetic简介General软磁Soft Magnetic硬磁Hard Magnetic磁场Magnetic Field磁性感应Magnetic Induction透磁度Magnetic Permeability磁化率Magnetic Susceptibility (Xm)磁力(Magnetic Force)及磁场(Magnetic Field)是因物料里的电子(Electron)活动而产生抗磁体、顺磁体、铁磁体、反铁磁体及亚铁磁体Diamagnetism，Paramagnetic，Ferromagnetism，AntiferromagnetismFerrimagnetism 抗磁体Diamagnetism磁偶极子Dipole负磁力效应Negative effect顺磁体Paramagnetic正磁化率Positive magnetic susceptibility铁磁体Ferromagnetism转变元素Transition element交换能量Positive energy exchange外价电子Outer valence electrons化学结合Chemical bond自发上磁Spontaneous magnetization磁畴Magnetic domain相反旋Opposite span比较抗磁体、顺磁体及铁磁体Comparison of Diamagnetism，ParamagneticFerromagnetism反铁磁体Antiferromagnetism亚铁磁体Ferrimagnetism磁矩magnetic moment净磁矩Net magnetic moment钢铁的主要成份The major element of steel钢铁用"碳"之含量来分类Classification of Steel according to Carbon contents铁相Steel Phases钢铁的名称Name of steel纯铁体Ferrite渗碳体Cementitle奥氏体Austenite珠光体及共释钢Pearlite Eutectoid奥氏体碳钢Austenite Carbon Steel单相金属Single Phase Metal共释变态Eutectoid Transformation珠光体Pearlite亚铁释体HyppoEutectoid初释纯铁体Proentectoid ferrite过共释钢Hypeeutectoid珠光体Pearlite粗珠光体Coarse pearlite中珠光体Medium pearlite幼珠光体Fine pearlite磁性变态点Magnetic Transformation钢铁的制造Manufacturing of Steel连续铸造法Continuous casting process电炉Electric furnace均热炉Soaking pit全静钢Killed steel半静钢Semikilled steel沸腾钢(未净钢) Rimmed steel钢铁生产流程Steel Production Flow Chart钢材的熔铸、锻造、挤压及延轧The Casting，Fogging，Extrusion，RollingSteel 熔铸Casting锻造Fogging挤压Extrusion延轧Rolling冲剪Drawingstamping特殊钢Special Steel简介General特殊钢以原素分类Classification of Special Steel according to Element特殊钢以用途来分类Classification of Special Steel according to End Usage易车(快削)不锈钢Free Cutting Stainless Steel含铅易车钢Leaded Free Cutting Steel含硫易车钢Sulphuric Free Cutting Steel硬化性能Hardenability钢的脆性Brittleness of Steel低温脆性Cold brittleness回火脆性Temper brittleness日工标准下的特殊钢材Specail Steel according to JIS Standard铬钢–日工标准JIS G4104Chrome steel to JIS G4104铬钼钢钢材–日工标准G4105 62Chrome Molybdenum steel to JIS G4105镍铬–日工标准G4102 63Chrome Nickel steel to JIS G4102镍铬钼钢–日工标准G4103 64Nickel，ChromeMolybdenum Steel to JIS G4103高锰钢铸–日工标准High manganese steel to JIS standard片及板材Chapter FourStrip，SteelPlate冷辘低碳钢片(双单光片)(日工标准JIS G3141) 73 95Cold Rolled (Low carbon) Steel Strip (to JIS G 3141)简介General美材试标准的冷辘低碳钢片Cold Rolled Steel Strip American Standard – American Society for testing and materials (ASTM) 日工标准JIS G3141冷辘低碳钢片(双单光片)的编号浅释Decoding of cold rolled(Low carbon)steel strip JIS G3141材料的加工性能Drawing abillity硬度Hardness表面处理Surface finish冷辘钢捆片及张片制作流程图表Production flow chart cold rolled steel coil sheet冷辘钢捆片及张片的电镀和印刷方法Cold rolled steel coilsheet electroplatingpainting method冷辘(低碳)钢片的分类用、途、工业标准、品质、加热状态及硬度表End usages，industrial standard，quality，condition and hardness of cold rolled steel strip硬度及拉力HardnessTensile strength test拉伸测试(顺纹测试)Elongation test杯突测试(厚度: 0.4公厘至1.6公厘，准确至0.1公厘3个试片平均数)Erichsen test (Thickness: 0.4mm to 1.6mm，figure round up to 0.1mm)曲面(假曲率)Camber厚度及阔度公差Tolerance on ThicknessWidth平坦度(阔度大于500公厘，标准回火)Flatness (width500mm，temper: standard)弯度Camber冷辘钢片储存与处理提示General advice on handlingstorage of cold rolled steel coilsheet防止生锈Rust Protection生锈速度表Speed of rusting焊接Welding气焊Gas Welding埋弧焊Submergedarc Welding电阻焊Resistance Welding冷辘钢片(拉力: 3032公斤/平方米)在没有表面处理状态下的焊接状况Spot welding conditions for bared (free from paint，oxides etc) Cold rolled mild steel sheets(T/S:3032 Kgf/ μ m2)时间效应(老化)及拉伸应变AgingStretcher Strains日工标准(JIS G3141)冷辘钢片化学成份Chemical composition – cold rolled steel sheet to JIS G3141冷辘钢片的"理论重量"计算方程式Cold Rolled Steel Sheet – Theoretical mass日工标准(JIS G3141)冷辘钢片重量列表Mass of ColdRolled Steel Sheet to JIS G3141冷辘钢片订货需知Ordering of cold rolled steel strip/sheet其它日工标准冷轧钢片(用途及编号)JIS standardapplication of other cold Rolled Special Steel电镀锌钢片或电解钢片Electrogalvanized Steel Sheet/Electrolytic Zinc Coated Steel Sheet简介General电解/电镀锌大大增强钢片的防锈能力Galvanic Action improving WeatherCorrosion Resistance of the Base Steel Sheet上漆能力Paint Adhesion电镀锌钢片的焊接Welding of Electrogalvanized steel sheet点焊Spot welding滚焊Seam welding电镀锌(电解)钢片Electrogalvanized Steel Sheet生产流程Production Flow Chart常用的镀锌钢片(电解片)的基层金属、用途、日工标准、美材标准及一般厚度Base metal，application，JISASTM standard，and Normal thickness of galvanized steel sheet 锌镀层质量Zinc Coating Mass表面处理Surface Treatment冷轧钢片ColdRolled Steel Sheet/Strip热轧钢片HotRolled Sheet/Strip电解冷轧钢片厚度公差Thickness Tolerance of Electrolytic Coldrolled sheet热轧钢片厚度公差Thickness Tolerance of Hotrolled sheet冷轧或热轧钢片阔度公差Width Tolerance of Cold or Hotrolled sheet长度公差Length Tolerance理论质量Theoretical Mass锌镀层质量(两个相同锌镀层厚度)Mass Calculation of coating (For equal coating)/MM锌镀层质量(两个不同锌镀层厚度)Mass Calculation of coating (For differential coating)/MM镀锡薄铁片(白铁皮/马口铁) (日工标准JIS G3303)简介General镀锡薄铁片的构造Construction of Electrolytic Tinplate镀锡薄钢片(白铁皮/马日铁)制造过程Production Process of Electrolytic Tinplate锡层质量Mass of Tin Coating (JIS G3*******)两面均等锡层Both Side Equally Coated Mass两面不均等锡层Both Side Different Thickness Coated Mass级别、电镀方法、镀层质量及常用称号Grade，Plating type，Designation of Coating MassCommon Coating Mass镀层质量标记MarkingsDesignations of Differential Coatings硬度Hardness单相轧压镀锡薄铁片(白铁皮/马口铁)SingleReduced Tinplate双相辗压镀锡薄钢片(马口铁/白铁皮)DualReduction Tinplate钢的种类Type of Steel表面处理Surface Finish常用尺寸Commonly Used Size电器用硅[硅] 钢片Electrical Steel Sheet简介General软磁材料Soft Magnetic Material滞后回线Narrow Hystersis矫顽磁力Coercive Force硬磁材料Hard Magnetic Material最大能量积Maximum Energy Product硅含量对电器用的低碳钢片的最大好处The Advantage of Using Silicon low Carbon Steel晶粒取向(GrainOriented)及非晶粒取向(NonOriented)Grain OrientedNonOriented电器用硅[硅] 钢片的最终用途及规格End Usage and Designations of Electrical Steel Strip电器用的硅[硅] 钢片之分类Classification of Silicon Steel Sheet for Electrical Use电器用钢片的绝缘涂层Performance of Surface Insulation of Electrical Steel Sheets晶粒取向电器用硅钢片主要工业标准International Standard – GrainOriented Electrical Steel Silicon Steel Sheet for Electrical Use晶粒取向电器用硅钢片GrainOriented Electrical Steel晶粒取向，定取向芯钢片及高硼定取向芯钢片之磁力性能及夹层系数(日工标准及美材标准)Magnetic Properties and Lamination Factor of SIORIENTCORE SIORIENTCOREHI B Electrical Steel Strip (JIS and AISI Standard)退火Annealing电器用钢片用家需自行应力退火原因Annealing of the Electrical Steel Sheet退火时注意事项Annealing Precautionary碳污染Prevent Carbon Contamination热力应先从工件边缘透入Heat from the Laminated Stacks Edges提防过份氧化No Excessive Oxidation应力退火温度Stress –relieving Annealing Temperature晶粒取向电器用硅[硅] 钢片–高硼(HIB)定取向芯钢片及定取向芯钢片之机械性能及夹层系数Mechanical Properties and Lamination Factors of SIORIENTCOREHIB and SIORIENTCORE Grain Orient Electrical Steel Sheets晶粒取向电器用硅[硅] 钢;片–高硼低硫(LS)定取向钢片之磁力及电力性能Magnetic and Electrical Properties of SIORIENTCOREHIBLS晶粒取向电器用硅[硅] 钢片–高硼低硫(LS) 定取向钢片之机械性能及夹层系数Mechanical Properties and Lamination Factors of SIORIENTCOREHIBLS晶粒取向电器用硅(硅)钢片高硼(HIB)定取向芯钢片，定取向芯钢片及高硼低硫(LS)定取向芯钢片之厚度及阔度公差Physical Tolerance of SIORIENTCOREHIB，SIORIENTCORE，SICOREHIBLS GrainOriented Electrical Steel Sheets晶粒取向电器用硅(硅)钢片–高硼(HIB)定取向芯钢片，定取向芯钢片及高硼低硫(LS)定取向芯钢片之标准尺寸及包装Standard Forms and Size of SIORIENTCOREHIB，SICORE，SIORIENTCOREHIBLS GrainOriented Electrical Steel Sheets绝缘表面Surface Insulation非晶粒取向电力用钢片的电力、磁力、机械性能及夹层系数Lamination Factors of Electrical，MagneticMechanical NonGrain Oriented Electrical电器及家电外壳用镀层冷辘[低碳] 钢片Coated (Low Carbon) Steel Sheets for Casing，ElectricalsHome Appliances镀铝硅钢片Aluminized Silicon Alloy Steel Sheet简介General镀铝硅合金钢片的特色Feature of Aluminized Silicon Alloy Steel Sheet用途End Usages抗化学品能力Chemical Resistance镀铝(硅)钢片–日工标准(JIS G3314)Hotaluminumcoated sheets and coils to JIS G 3314镀铝(硅)钢片–美材试标准(ASTM A46377)35.7 JIS G3314镀热浸铝片的机械性能Mechanical Properties of JIS G 3314 HotDip Aluminumcoated Sheets and Coils公差Size Tolerance镀铝(硅)钢片及其它种类钢片的抗腐蚀性能比较Comparsion of various resistance of aluminized steelother kinds of steel镀铝(硅)钢片生产流程Aluminum Steel Sheet，Production Flow Chart焊接能力Weldability镀铝钢片的焊接状态(比较冷辘钢片)Tips on welding of Aluminized sheet in comparasion with cold rolled steel strip钢板Steel Plate钢板用途分类及各国钢板的工业标准包括日工标准及美材试标准Type of steel PlateRelated JIS，ASTM and Other Major Industrial Standards钢板生产流程Production Flow Chart钢板订货需知Ordering of Steel Plate不锈钢Stainless Steel不锈钢的定义Definition of Stainless Steel不锈钢之分类，耐腐蚀性及耐热性Classification，Corrosion ResistantHeat Resistance of Stainless Steel铁铬系不锈钢片Chrome Stainless Steel马氏体不锈钢Martensite Stainless Steel低碳马氏体不锈钢Low Carbon Martensite Stainless Steel含铁体不锈钢Ferrite Stainless Steel镍铬系不锈钢Nickel Chrome Stainless Steel释出硬化不锈钢Precipitation Hardening Stainless Steel铁锰铝不锈钢Fe / Mn / Al / Stainless Steel不锈钢的磁性Magnetic PropertyStainless Steel不锈钢箔、卷片、片及板之厚度分类Classification of Foil，Strip，SheetPlate by Thickness表面保护胶纸Surface protection film不锈钢片材常用代号Designation of SUS Steel Special Use Stainless表面处理Surface finish薄卷片及薄片(0.3至2.9mm厚之片)机械性能Mechanical Properties of Thin Stainless Steel(Thickness from 0.3mm to 2.9mm) – strip/sheet不锈钢片机械性能(301，304，631，CSP)Mechanical Properties of Spring use Stainless Steel不锈钢–种类，工业标准，化学成份，特点及主要用途Stainless Steel – Type，Industrial Standard，Chemical Composition，Characteristicend usage of the most commonly used Stainless Steel不锈钢薄片用途例End Usage of Thinner Gauge不锈钢片、板用途例Examples of End Usages of Strip，SheetPlate不锈钢应力退火卷片常用规格名词图解General Specification of Tension Annealed Stainless Steel Strips耐热不锈钢HeatResistance Stainless Steel镍铬系耐热不锈钢特性、化学成份、及操作温度HeatResistance Stainless Steel铬系耐热钢Chrome Heat Resistance Steel镍铬耐热钢Ni Cr Heat Resistance Steel超耐热钢Special Heat Resistance Steel抗热超级合金Heat Resistance Super Alloy耐热不锈钢比重表Specific Gravity of Heat – resistance steel plates and sheets stainless steel不锈钢材及耐热钢材标准对照表Stainless and HeatResisting Steels发条片Power Spring Strip发条的分类及材料Power Spring Strip Classification and Materials上链发条Windup Spring倒后擦发条Pull Back Power Spring圆面("卜竹")发条Convex Spring Strip拉尺发条Measure Tape魔术手环Magic Tape魔术手环尺寸图Drawing of Magic Tap定型发条Constant Torque Spring定型发条及上炼发条的驱动力Spring Force of Constant Torque Spring and Wingup Spring定型发条的形状及翻动过程Shape and Spring Back of Constant Torque Spring定型发条驱动力公式及代号The Formula and Symbol of Constant Torque Spring边缘处理Edge Finish硬度Hardness高碳钢化学成份及用途High Carbon Tool Steel，Chemical Composition and Usage每公斤发条的长度简易公式The Length of 1 Kg of Spring Steel StripSK5AISI301 每公斤长的重量/公斤(阔100200公厘) Weight per one meter long (kg) (Width 100200mm)SK5AISI301 每公斤之长度(阔100200公厘) Length per one kg (Width 100200mm)SK5AISI301 每公尺长的重量/公斤(阔2.010公厘)Weight per one meter long (kg) (Width 2.010mm)SK5AISI301 每公斤之长度(阔2.010公厘)Length per one kg (Width 2.010mm)高碳钢片High Carbon Steel Strip分类Classification用组织结构分类Classification According to Grain Structure用含碳量分类–即低碳钢、中碳钢及高碳钢Classification According to Carbon Contains弹簧用碳钢片CarbonSteel Strip For Spring Use冷轧状态Cold Rolled Strip回火状态Annealed Strip淬火及回火状态HardenedTempered Strip/ Precision – Quenched Steel Strip 贝氏体钢片Bainite Steel Strip弹簧用碳钢片材之边缘处理Edge Finished淬火剂Quenching Media碳钢回火Tempering回火有低温回火及高温回火LowHigh Temperature Tempering高温回火High Temperature Tempering退火Annealing完全退火Full Annealing扩散退火Diffusion Annealing低温退火Low Temperature Annealing中途退火Process Annealing球化退火Spheroidizing Annealing光辉退火Bright Annealing淬火Quenching时间淬火Time Quenching奥氏铁孻回火Austempering马氏铁体淬火Marquenching高碳钢片用途End Usage of High Carbon Steel Strip冷轧高碳钢–日本工业标准ColdRolled (Special Steel) Carbon Steel Strip to JIS G3311 电镀金属钢片Plate Metal Strip简介General电镀金属捆片的优点Advantage of Using Plate Metal Strip金属捆片电镀层Plated Layer of Plated Metal Strip镀镍Nickel Plated镀铬Chrome Plated镀黄铜Brass Plated基层金属Base Metal of Plated Metal Strip低碳钢或铁基层金属IronLow Carbon as Base Metal不锈钢基层金属Stainless Steel as Base Metal铜基层金属Copper as Base Metal黄铜基层金属Brass as Base Metal轴承合金Bearing Alloy简介General轴承合金–日工标准JIS H 5401Bearing Alloy to JIS H 5401锡基、铅基及锌基轴承合金比较表Comparison of Tin base，Lead base and Zinc base alloy for Bearing purpose易溶合金Fusible Alloy焊接合金Soldering and Brazing Alloy软焊Soldering Alloy软焊合金–日本标准JIS H 4341Soldering Alloy to JIS H 4341硬焊Brazing Alloy其它焊接材料请参阅日工标准目录Other Soldering Material细线材、枝材、棒材Chapter Five Wire，RodBar线材/枝材材质分类及制成品Classification and End Products of Wire/Rod铁线(低碳钢线)日工标准JIS G 3532Low Carbon Steel Wires ( Iron Wire ) to JIS G 3532光线(低碳钢线)，火线(退火低碳钢线)，铅水线(镀锌低碳钢线)及制造钉用低碳钢线之代号、公差及备注Ordinary Low Carbon Steel Wire，Annealed Low Carbon Steel Wire，Galvanized low Carbon Steel WireLow Carbon Steel Wire for nail manufacturing classification，Symbol of Grade，Tolerance and Remarks.机械性能Mechanical Properites锌包层之重量，铜硫酸盐试验之酸洗次数及测试用卷筒直径Weight of ZincCoating，Number of Dippings in Cupric Sulphate Test and Diameters of Mandrel Used for Coiling Test冷冲及冷锻用碳钢线枝Carbon Steel Wire Rods for Cold HeadingCold Forging (to JIS G3507)级别，代号及化学成份Classification，Symbol of Grade and Chemical Composition直径公差，偏圆度及脱碳层的平均深度Diameter Tolerance，Ovality and A verage Decarburized Layer Depth冷拉钢枝材Cold Drawn Carbon Steel Shafting Bar枝材之美工标准，日工标准，用途及化学成份AISI，JIS End Usage and Chemical Composition of Cold Drawn Carbon Steel Shafting Bar冷拉钢板重量表Cold Drawn Steel Bar Weight Table高碳钢线枝High Carbon Steel Wire Rod (to JIS G3506)冷拉高碳钢线Hard Drawn High Carbon Steel Wire(to JIS G3521，ISO8458012)化学成份分析表Chemical Analysis of Wire Rod线径、公差及机械性能(日本工业标准G 3521)Mechanical Properties (JIS G 3521)琴线(日本标准G3522)Piano Wires ( to G3522)级别，代号，扭曲特性及可用之线材直径Classes，symbols，twisting characteristic and applied Wire Diameters直径，公差及拉力强度Diameter，Tolerance and Tensile Strength裂纹之容许深度及脱碳层Permissible depth of flaw and decarburized layer常用的弹簧不锈钢线编号，特性，表面处理及化学成份StainlessSpring Wire –National Standard number，Charateristic，Surface finishChemical composition弹簧不锈钢线，线径及拉力列表Stainless Spring Steel，Wire diameter and Tensile strength of Spring Wire处理及表面状况FinishSurface各种不锈钢线在不同处理拉力比较表Tensile Strength of various kinds of Stainless Steel Wire under Different Finish圆径及偏圆度之公差Tolerance of Wire DiametersOvality铬镍不锈钢及抗热钢弹簧线材–美国材验学会ASTM A313 – 1987Chromium – Nickel Stainless and Heatresisting Steel Spring Wire – ASTM A313 – 1987化学成份Chemical Composition机械性能Mechanical Properties305，316，321及347之拉力表Tensile Strength Requirements for Types 305，316，321 and 347A1S1302 贰级线材之拉力表Tensile Strength of A1S1302 Wire日本工业标准–不锈钢的化学成份(先数字后字母排列)JIS – Chemical Composition of Stainless Steel (in order of numberalphabet)美国工业标准–不锈钢及防热钢材的化学成份(先数字后字母排列)AISI – Chemical Composition of Stainless SteelHeatResistant Steel(in order of numberalphabet)易车碳钢Free Cutting Carbon Steels (to JIS G4804 )化学成份Chemical composition圆钢枝，方钢枝及六角钢枝之形状及尺寸之公差Tolerance on Shape and Dimensions for Round Steel Bar，Square Steel Bar，Hexagonal Steel Bar易车(快削)不锈钢Free Cutting Stainless Steel易车(快削)不锈钢种类Type of steel易车(快削)不锈钢拉力表Tensile Strength of Free Cutting Wires枝/棒无芯磨公差表(μ) (μ = 1/100 mm)Rod/Bar Centreless Grind Tolerance易车不锈钢及易车钢之不同尺寸及硬度比较Hardness of Different TypesSize of Free Cutting Steel扁线、半圆线及异形线Flat Wire，Half Round Wire，Shaped Wire and Precision Shaped Fine Wire加工方法Manufacturing Method应用材料Material Used特点Characteristic用途End Usages不锈钢扁线及半圆线常用材料Commonly used materials for Stainless Flat WireHalf Round Wire扁线公差Flat Wire Tolerance方线公差Square Wire Tolerance。
CoxBy合金力学性能、热学性质及电子性质的第一性原理研究
第 4 期第 192-199 页材料工程Vol.52Apr. 2024Journal of Materials EngineeringNo.4pp.192-199第 52 卷2024 年 4 月Co x B y 合金力学性能、热学性质及电子性质的第一性原理研究Mechanical ，thermal and electronic properties of Co x B y alloys ：a first -principles study金格1，吴尉1，李姗玲1，陈璐1，史俊勤1，2*，贺一轩1，2*，范晓丽1，2（1 西北工业大学 材料学院 先进润滑与密封材料研究中心，西安 710049；2 凝固技术国家重点实验室，西安 710072）JIN Ge 1，WU Wei 1，LI Shanling 1，CHEN Lu 1，SHI Junqin 1，2*，HE Yixuan 1，2*，FAN Xiaoli 1，2（1 Center of Advanced Lubrication and Seal Materials ，School of Materials Science and Engineering ，Northwestern PolytechnicalUniversity ，Xi ’an 710049，China ；2 State Key Laboratoryof Solidification Processing ，Xi ’an 710072，China ）摘要：Co x B y 合金是一种具有高硬度和高熔点的材料，因其稳定的化学性质、高强度以及良好的热稳定性，在诸多领域具有广泛的应用前景。
基于第一性原理方法研究了CoB ，Co 2B ，Co 3B ，Co 23B 6，Co 5B 16 5种Co x B y 合金的热力学性质和电子性质。
采用能量-应变方法计算了二元合金的弹性常数和相关力学特性，基于准简谐德拜模型计算了有限温度内的德拜温度ΘD 和热膨胀系数α等热力学特性。
国际流行化学软件介绍
北京宏剑公司
2007.07
材料模拟
80年代中期以来，一些新材料非预期地被发现出来，包括高 Tc铜氧化物超导体、富勒烯及其衍生物、纳米材料、超硬材料、 人工低维量子结构材料等。应当看到，计算和理论对于阐明这些 新材料的性能起了重要作用。一些事实表明，理论和方法的进步 已能对实际材料性能进行理论预测。现在，研究者已处在通过理 论计算来“设计”材料的初期阶段。
ChemDraw - 化学结构绘图软件， 是各论文期刊指定的格式。 Chem3D - 提供工作站级的3D分子轮廓图及分 子轨道特性分析，并和数种量子化学软件结合 在一起。
WIEN2K 2007
用密度泛函理论计算固体的电子结构。它基于键结构计算 最准确的方案-完全势（线性）缀加平面波(L)APW + 局域轨道(lo)方法。在密度泛函中可以使用局域（自旋） 密度近似(LDA)或广义梯度近似(GGA)。WIEN 2K使用全电 子方案，包含相对论影响。
MedeA-VASP
Materials Explorer 4.0
专业的材料分子模拟多功能分子动力学软件包-结合应用领域研究材料工程的有力工具 计算能力 分子动力学 Crystal Builder 无机固体及分子晶体系统 Solution Modeler 轻松建立随机多组分液相或气相系统 Layer Cell Model 研究异相系统(气-固界面,固体颗粒边界等 NEV NTV NPH NTP 系宗的模拟 周期边界条件 评估界面势能的高级算法 外部电子场的应用 分析能力 对X射线和中子衍射的干涉函数; 对无定型固体进行表征; 显示时间与温度,压力,内部能量等性质的二维图象； 显示系统的快照，轨迹和动画； 计算Voronoi多面体的数量和表面数
基于赫兹接触模型的发动机封严涂层碰磨力计算与优化
表面技术第53卷第5期热喷涂与冷喷涂技术基于赫兹接触模型的发动机封严涂层碰磨力计算与优化丁坤英，裴祥忠，刘子剑，王梦潇，贾治豪（中国民航大学 天津市民用航空器适航与维修重点试验室，天津 300300）摘要：目的提高航空发动机的推进效率，在压气机机匣上喷涂可以减少叶尖径向间隙的封严涂层。
叶尖与涂层之间的碰磨力会导致涂层脱落，且会击伤叶片，需要对碰磨力进行分析。
方法采用大气等离子喷涂技术制备4种不同硬度的AlSi-PHB（聚苯酯）封严涂层，通过表面硬度测试、弹性模量测试和高速碰磨试验，分别评价封严涂层的硬度、弹性模量，以及在高速碰磨过程中不同工况下涂层受到的碰磨力；基于赫兹接触模型对叶尖与涂层之间的碰磨力进行计算，通过激光共聚焦显微镜和扫描电子显微镜对碰磨后的涂层和叶尖进行分析，同时根据接触面形态特征和温度特征对赫兹模型进行优化。
结果碰磨力与涂层的硬度、叶尖转速、叶尖切入速率有关，复杂的接触表面形貌和摩擦升温会导致理论计算值与实验值之间出现偏差。
结论通过优化叶尖和涂层的接触系数，同时考虑摩擦升温对涂层弹性模量的影响，可将不同工况下碰磨力计算值与测量值之间的偏差控制在1%~11%，这项研究对于指导航空发动机封严涂层的设计具有重要意义。
关键词：封严涂层；大气等离子喷涂；高速碰磨；赫兹模型；摩擦升温；优化系数中图分类号：TG174.4 文献标志码：A 文章编号：1001-3660(2024)05-0184-10DOI：10.16490/ki.issn.1001-3660.2024.05.019Calculation and Optimization of Impact and Wear Forces ofEngine Sealing Coatings Based on Hertz Contact ModelDING Kunying, PEI Xiangzhong, LIU Zijian, WANG Mengxiao, JIA Zhihao(Tianjin Key Laboratory of Civil Aircraft Airworthiness and Maintenance,Civil Aviation University of China, Tianjin 300300, China)ABSTRACT: The aircraft engine sealant coating can effectively improve the air tightness of the aircraft engine and improve the fuel utilization efficiency. However, due to the existence of friction between the blades and the coating, the coating often peels off and causes damage to the blades, resulting in economic losses. Therefore, it is necessary to analyze the friction between the blade and the coating.In this paper, four kinds of aluminum-silicon polyphenylene ester sealed coatings with different polyphenylene ester contents were prepared by atmospheric plasma spraying (APS). The hardness and elastic modulus of the coatings were obtained by a hardness test and an elastic modulus test, and the cross-sectional microstructures of the four coatings were observed with a scanning electron microscopy (SEM). It was found that the hardness of the coatings was related to the non-metallic phase收稿日期：2023-05-25；修订日期：2023-11-15Received：2023-05-25；Revised：2023-11-15基金项目：中央高校基本科研业务经费项目（3122019189）Fund：Basic Research Funds for Central Universities (3122019189)引文格式：丁坤英, 裴祥忠, 刘子剑, 等. 基于赫兹接触模型的发动机封严涂层碰磨力计算与优化[J]. 表面技术, 2024, 53(5): 184-193. DING Kunying, PEI Xiangzhong, LIU Zijian, et al. Calculation and Optimization of Impact and Wear Forces of Engine Sealing Coatings Based第53卷第5期丁坤英，等：基于赫兹接触模型的发动机封严涂层碰磨力计算与优化·185·content of the coatings. More pores, cracks and polyphenylene ester content resulted in smaller coating hardness, and the elastic modulus of the coatings increased with the increase of coating hardness.A high-speed bruising test machine was used to analyze the bruising force between the blade and the coating, and fourbruising conditions were designed to conduct high-speed bruising tests on four coatings and the maximum normal bruising force during the bruising process was recorded; the maximum normal contact load on the coating during the bruising process was calculated based on the Hertzian contact model. The test values of the high speed contact test were compared with the theoretical calculated values, and it was found that the calculated values of the Hertzian contact model were always larger than the test values. In order to make the Hertzian contact model more accurate for the calculation of the contact force between the blade and the coating, the coefficients of the contact coefficient in the Hertzian contact model were optimized. The coefficients Δ" and β of the Hertzian contact model were optimized according to the adhesion of the blade tip and the average line roughness of the coating surface after the grinding test by means of a laser confocal microscope and a scanning electron microscope. The elasticity coefficients E* in the Hertzian model were optimized by the effect of temperature change on the elastic modulus of the coating material during the bruising process.The optimized coefficients were substituted into the Hertzian contact model to recalculate the maximum normal contact load on the coating during the high speed bruising process, and the results of the optimized Hertzian contact model, the results of the Hertzian contact model before the optimized coefficients and the high speed bruising test values were compared. The results show that the actual contact between the blade and different coatings and the thermal aggregation effect caused by high blade speed are the main reasons for the deviation between the calculated results before the optimized factor and the test values. The Hertzian model after the optimization factor is closer to the experimental test value than the Hertzian model before the optimization factor, and the deviation from the test value is within 1%-11%. The reason for the deviation may be related to the coupling effect between the tangential force and the normal force.KEY WORDS: sealing coating; atmospheric plasma spraying; high speed impact and wear; hertz model; friction heating;optimization coefficient随着航空工业的迅速发展，对于飞机发动机提出了越来越高的要求，更大的推力、更高的效率和更低的油耗是发动机研制和设计的目标[1-2]。
“一题两课”案例式教学方法研究
“一题两课”案例式教学方法研究作者：曹金凤王志文刘鹏撒占友李策来源：《教育教学论坛》2022年第16期[摘要] “彈性力学与有限元”“有限元分析软件及应用”两门课程是各大高校理工科硕士研究生的学位课和专业课，占据十分重要的地位。
“弹性力学与有限元”课程公式多，推导过程烦琐，学习难度大，而“有限元分析软件及应用”课程则重点关注工程应用，却又离不开“弹性力学与有限元”课程的理论支撑，二者既有联系，又有差异。
为了提高研究生对两门课程的学习效果和学习效率，达到学以致用、研以致用的目的，对“一题两课”案例式教学模式进行探索，选取“弹性力学与有限元”课程中的课后练习题，通过理论分析和有限元仿真分析结果进行比较，找出两门课程学习过程中的重点、难点、差别，帮助学生更加生动形象地理解“弹性力学与有限元”的知识，更有助于将理论方法与工程实践结合，实现举一反三、触类旁通的学习效果。
该教学模式已成功应用于5届研究生的教学过程中，效果良好，值得推广使用。
[关键词] 弹性力学与有限元;有限元分析软件及应用;案例式教学;教学模式;课程改革[基金项目] 2020年度山东省教育厅山东省专业学位研究生教学案例库项目“‘有限元分析软件Abaqus及应用’案例库建设”（SDYAL20112）[作者简介] 曹金凤（1978—），女，山东青岛人，博士，青岛理工大学机械与汽车工程学院副教授，主要从事计算力学与Abaqus软件数值模拟研究;王志文（1995—），男，山东临沂人，硕士，青岛理工大学机械与汽车工程学院2020级机械专业硕士研究生，研究方向为Abaqus有限元仿真与轮胎的设计仿真一体化;刘鹏（1990—），男，山东青岛人，博士，青岛理工大学机械与汽车工程学院副教授（通信作者），主要从事故障诊断与可靠性分析、海洋工程装备研究。
[中图分类号] O343.1 [文献标识码] A [文章编号] 1674-9324（2022）16-0157-04 [收稿日期] 2021-07-28引言“弹性力学与有限元”课程主要研究变形体在外来因素作用下的位移、应变和应力的分布规律，是机械工程、土木工程、力学相关专业的研究生必修课程[1]。
弹力纤维在肺腺癌组织中的分布量与患者临床特征和预后的关系
弹力纤维在肺腺癌组织中的分布量与患者临床特征和预后的关系王玉蓉;孟刚【摘要】目的探讨弹力纤维在肺腺癌组织中的分布量与患者临床特征和预后的相关性.方法收集安徽医科大学第一附属医院2012年1月至2014年8月术后病理诊断为肺腺癌的标本123例.所有病理标本行苏木精-伊红、弹力纤维染色,观察弹力纤维在肺腺癌中的分布量,同时依据弹力纤维在癌组织中量的多少,将弹力纤维量的表达分为I级、II级、III级3个等级,术后随访5～66个月,分析弹力纤维3个等级与肺腺癌的临床特征和预后的关系.结果 123例肺腺癌中,弹力纤维I级60例(48.78％),II级23例(18.70％),III级40例(32.52％);单因素分析显示,3组弹力纤维分级患者一般资料比较显示,年龄、性别,差异无统计学意义(P均>0.05),肿瘤直径、淋巴结分期和病理类型,差异有统计学意义(P均<0.05).随访结果显示,123例肺腺癌中,弹力纤维I级、II级、III级患者的总生存率分别为60.00％、79.30％、95.00％,弹力纤维III级患者的总生存率高于I级、II级,差异有统计学意义(P<0.05).COX多因素分析显示,肿瘤直径、淋巴结分期是影响肺腺癌预后的独立危险因素(P均<0.05),弹力纤维分级与患者预后无关(P>0.05).结论弹力纤维明显增生的肺腺癌患者预后较好,但弹力纤维增生不是影响肺腺癌预后的独立危险因素.【期刊名称】《安徽医学》【年(卷),期】2018(039)008【总页数】4页(P932-935)【关键词】弹力纤维;肺腺癌;预后【作者】王玉蓉;孟刚【作者单位】230032 合肥安徽医科大学病理学教研室;230032 合肥安徽医科大学病理学教研室【正文语种】中文弹力纤维存在于各种组织中，如皮肤、血管壁、肺等，由微原纤维和均质状物两种成分构成，这样独特的化学结构维持了纤维的弹性[1-3]。
钙钛矿结构BaTiO3的热物理性能的第一原理研究
钙钛矿结构BaTiO3的热物理性能的第一原理研究翟娟;李兰英;欧阳义芳【摘要】运用基于密度泛函的第一原理方法对具有钙钛矿结构BaTiO3的热物理性能进行了计算，得到了BaTiO3的晶格常数、弹性性能和热物理性能，并对电子结构特性进行分析。
计算结果表明：计算所得的晶格常数和实验值符合的很好，计算了钙钛矿结构的BaTiO3的单晶弹性常数，并利用Viogt—Reuss—Hill方法获得了多晶的体积模量、剪切模量、杨氏模量、泊松比以及弹性各向异性比。
由B／G的比值可知，钙钛矿结构的BaTiO3呈脆性性质。
能带结构和电子态密度的计算表明，钙钛矿结构的BaTi03是一个具有1．59eV能隙的间隙半导体。
利用准谐德拜模型．计算了该化合物的热熔和热膨胀系数随温度和压强的变化关系。
%The lattice constant, elastic constants and thermophysical properties for proverskite BaTiO3 have been investigated hy the density function theory. The calculation indicates that BaTiO3 with proverskite is brittle according to the value of B/G. The calculated band structure indicates that it is indirect semiconductor with a band gap 1.59eV. The heat specify and thermal expansion which vary with temperature and pressure are also discussed based on a qusiharmonie Debye model.【期刊名称】《广西民族师范学院学报》【年(卷),期】2012(029)003【总页数】3页(P39-41)【关键词】钙钛矿结构;热物理性质;弹性;电子结构【作者】翟娟;李兰英;欧阳义芳【作者单位】广西大学物理科学与工程技术学院,广西南宁530004 广西民族师范学院物理与电子工程系,广西崇左532200;广西大学物理科学与工程技术学院,广西南宁530004 广西民族师范学院物理与电子工程系,广西崇左532200;广西大学物理科学与工程技术学院,广西南宁530004【正文语种】中文【中图分类】TN914.3BaTiO3是一种典型的铁电材料，由于其具有优良的铁电性质和高的介电常数而备受关注［1］157-165。
单层GaTe电子结构特性及其场效应管的第一性原理研究
摘要随着电子工业的快速发展，硅基电子元器件的特征长度将趋于物理极限。
为了促进器件的发展，微电子器件特征尺寸已进入纳米量级，器件的性能得到很大的提升，但同时也面临着严重的挑战，如短沟道效应引起亚阈值斜率和隧穿电流的增加，衬底高掺杂而导致载流子迁移率的退化等。
为了解决这些问题并进一步提高小尺寸器件的性能，需要寻找合适带隙、高迁移率和表面无悬挂键的超薄沟道材料。
III-VI族二维镓族材料GaTe由于其独特的光电特性有望成为未来超高速、低功耗器件的理想沟道材料。
本文基于第一性原理计算分析了基底和应力对结构转变后单层GaTe的几何结构、电子结构以及稳定性的影响，在此基础上，进一步仿真模拟了单层GaTe双栅金属-氧化物-半导体场效应晶体管的电学性能。
主要内容如下：(1) 系统研究了单层GaTe在H-Si(111)、H-Ge(111)以及Cu(111)、Ag(111)、Au(111)等五种基底上的生长情况。
通过电子结构、成键方式以及稳定性的研究，发现单层GaTe在H-Si(111)上的生长并不稳定，但在其余四种基底上可以稳定生长。
单层GaTe与H-Ge(111)结合形成的体系仍为半导体，而与金属物质相接触时体系呈现出金属性质。
单层GaTe与基底间的结合方式为范德瓦耳斯力，且体系的能带主要由基底决定。
(2) 在应力调控的研究中，探讨了不同方向不同程度的应力对单层GaTe能带结构、弹性常数、形变势、有效质量和载流子迁移率的影响。
研究结果表明：在a方向施加应力时，其带隙类型仍为间接带隙，但带隙值随着应力的增大而减小；在b方向施加3%的压应变时，带隙转变为直接带隙并且其值减少为1.31 eV，沿b方向电子迁移率达到824 cm2/(V·s)，空穴迁移率为493 cm2/(V·s)；在a-b方向施加2%的压应变时，沿b方向的电子迁移率可达到91798 cm2/(V·s)。
(3) 利用ATK(Atomistix ToolKit)软件对单层GaTe双栅金属-氧化物-半导体场效应晶体管电学特性进行了模拟仿真。
狗股动脉弹性纤维的构筑
狗股动脉弹性纤维的构筑狗股动脉弹性纤维的构筑第29卷第2期1998年4月解剖ACTAANAT0MICASINICAVO1.29,No.2Apr.1998/动脉弹性纤维的构筑*星红陈尔瑜,-'.'————-———一.二———————-(第三军医大学解剖学教研室,重庆1~322,/zf余汇洋李振强糜建红400038;,第二军医大学解剖学教研室,上海)摘要为研究正常动脉的弹性纤维,用甲酸消化法制取动脉的弹性网,在扫描电镜下观察了8例健康狗股动脉弹性纤维的构筑.可见内弹性膜有光滑的腔面并有许多窗孔,中膜互相吻合的弹性纤维组成复杂的网状,外膜含有由大的纵行纤维及纤细的横行纤维组成的7,8层不完全的弹性膜.3层膜里所有的弹性纤维互相连接,形成连续的弹性网.关键词塑一馕弹性纤维是动脉壁的主要成分之一,它与动脉的静态及动态力学性质有关.对动脉弹性纤维知识的熟悉有助于了解在动脉移植或血管疾病过程中,血管弹性纤维的适应性改变,故作此研究.材料和方法'成年健康杂种狗8条,麻醉下取股动脉段,生理盐水冲洗,2.5戊二醛磷酸缓冲液固定24h,然后分别切成宽约2ram的动脉环及长约5ram,宽约2ram的动脉条,蒸馏水清洗后入88甲酸中于45?下消化96h,取出浸入双蒸水中5min,然后用0.O02mol/LHC1清洗,梯度酒清脱水,醋酸异戊酯置换,CO临界点干燥,金属喷镀,JSM—T3OO扫描电镜观察. 结果和讨论狗的股动脉由内,中,外3层膜组成,各层中均含有弹性纤维.内膜中的弹性纤维以内弹性膜的方式出现,它是一层连续的较致密的膜状结构,与中膜相隔,一般为1层(图1).内弹性膜上有许多大小不一的窗孔,有的窗孔上面有纤维跨过,将其分成若干小孔(图2),内弹性膜腔面光滑,膜的外表面有纤维与中膜的弹性组织相连.内弹性膜除了能将管腔内完整的内弹性膜还是防止可导致动脉粥样硬化的大分压力均匀地传递给中膜外, 子(如低密度脂蛋白)通过的屏障J.中膜弹性纤维不呈膜状,而是由粗细不一的纤维组成(图3),有的纤维较宽大成膜状.这些纤维互相吻合,朝各个方向排列,形成连续的网样结构.而不是象弹性动脉那样,其中膜弹性组织形成明显的同心圆层?.股动脉中膜弹性纤维网能将管腔内传递来的以及中膜平滑肌主动收缩产生的力均匀地向四周传递.狗股动脉外膜是弹性纤维集中之处口],它们以不完整的膜状形式出现,呈同5-圆排列成7,8层(图4),其中紧靠中膜的是外弹性膜,它与中膜弹性网有较细的弹性纤维相连.这种呈同5-圆排列的弹性纤维层主要由宽大的纵行纤维组成,通常有几条大纤维合并成宽而扁的条带,然后再分叉,再吻合,大的纵行纤维之间有细的横纤维相连(图5),在同心圆排列的弹性纤维层之间,也有纤细的纤维连接(图6).由于外膜是肌性动脉的弹性纤维集中之处,所以对维持血管的弹性起重要作用.又由于它以宽大的纵行纤维为主,所以外膜弹性纤维主要传递纵向张力. 狗股动脉3层膜中的弹性纤维无论其以何种方式出现,每个部位的纤维均与相邻部位的纤维连*国家自然科学基金资助课题(No.39270378)2期朱星红等.狗股动脉弹性纤维的构筑?223?接,从而形成一个连续的弹性"套袖",此"套袖"均匀地将力传递到整个管壁,以适应血压的波动.一些血管疾病常累及弹性纤维,使它产生某些变化.如动脉粥样硬化患者内弹性膜多有复制,从内弹性膜的光滑腔面,形成一些纤维分叉伸出腔面,同时窗孔变大乜],大分子物质易进入中膜.这样,一方面使动脉弹性下降,另一方面又进一步加重动脉粥样硬化的形成.外膜弹性组织中则是较细的横行纤维易受损.由于某种病变,如动脉瘤形成前期,首先累及这种细的横行纤维,最终引起管壁延长,扩张,血管回弹力减低[4.5].这些血管病变破坏了血管弹性网的正常结构,从而改变了管壁的力学特性及生理机能.另外,在血管移植时,应尽量选择与受体血管弹性纤维构筑相似的移植物,以保证两者的力学性质大致相近,从而提高血管移植的成功率.收稿1996—11修回1997—08本文图1,6见插图第20页参考文献[1]WasanoK,YamamotoT.Tridimensionalarchitectureofelastictissueinther ataortaandfemoralartery——Ascanningelec—tronmicroscopestudy.JElectronMicrosc,1983,32(1):33[2]NakatakeJ,WasanoK,YamamotoT.Three—dimensionalarchitectureofelastictissueinearlyatheroscleroticlesionso ftherat aorta.Atherosclerosis,1985,57(2):199[3]陈尔瑜,朱星红,糜建红等.狗股动脉断面形态和结构成分的测量.见《生物力学研究与应用'.广州:华南理工大学出版社,1990:245,249[4]HassKS,PhillipsSJ,ComerotaAJ,eta1.Thearchitectureofadventitialela stininthecanineinfrarenalaorta.AnatRec,1991,230(1):86FS]CoxRH.Passivemechanicsandconnectivetissuecompositionofcaninearter ies.AmJPhysiol,1978,234(3):H533ARCHITECTUREoFELASTICFIBERSINCANINEFEMoRALARTERYZhuXinghong,ChenEryu?,YuHuiyang,LiZhengqiang,MiJianhong(DepartmentofAnatomy,TheThirdMilitaryMedicalUniversity,Chongqingf ?D epartmentofAnatomy,TheSecondMilitaryMedicalUniversity,Shanghai) Inordertostudytheelasticfibersofnormalartery.thearchitectureofelastictis sueinthefemoralarteriesfrom8healthydogswasobservedunderscanningelectronmicroscop ewiththemethodofhot—formicacidextraction.Itwasfoundthattheinternalelasticlaminahadflsmoo thluminalsurfacewithnumerousfenestrae.Thetunicamediacontainedflcomplexnetw orkofanas—tomosingelasticfibers.Thetunicaadventitiacontained7-8incompletelaminaeoflargelongitudi—nallyorientedfibersandfinetransversefibers.Alltheelasticfibersinthre etunicaewereconnect—edeachotherandformedflsuccessiveelasticnetwork.KEYWORDSElasticfiber;Femoralarteryd3og?DepartmentofAnatomy,TheSecondMilitaryMedicalUniversity,Shanghai20043 3,China},。
材材料科学与工程专业英语
2.6 semiconductorFollowing the discussion of intrinsic ,elemental semiconductors we note that the fermi function indicates that the number of charge carriers increases exponentially with temperature. This effect so dominates the conductivity of semiconductors that conductivity also follows an exponential increase with temperature(an example of an arrhenius equation ).This increase is in sharp contrast to the behavior of metals.We consider the effect of impurities in extrinsic,elemental semiconductors.Doping a group IV a material(such as Si) with a group V a impurity (such as P)produces an n-type semiconductor in which negative charge carriers(conduction electrons)dominate.The “extea”electron from the group V A addition produces a donor level in the energy band structure of the semiconductor.As with instrinsic semiconductors,extrinsic semiconduction exhibits arrhenius behavior.in n-type material, the temperature span between the regions of extrinsic and insrinsic behavior is called the exhaustion range .A p-type semiconductor is produced by doping a group IV a material with a group III a impurity(such as Al).The group III A element has a “missing” electron producing anacceptor level in the band stucture and leading to formation of positive charge carriers (electron holes). The region between extrinsic and instrinsic behavior for p-type semiconductors is called the saturation range . Hall effect measurements can distinguish between n-type and p-type conduction.Compound semiconductors usually have an MX composition with an average of four valence electrons per atom .The III-V and II-VI compounds are the common examples .amorphous semiconductors are the non-crystalline materials with semiconducting behavior.Elemental and compound material are both found in this category .To appreciate the applications of semiconductors,we review a few decades.the solid state rectifier (or diode) contains a single p-n junction .Current flows readily when this junction is forward biased but is almost completely choked off when reverse biased.the transistor is a device consisting of a pair of nearby pn junctions.The net result is a solid state amplifier. Replacing vacuum tubes with solid state elements such as these produced substantial miniaturization of electrical circuits.Further miniaturization has resulted by the production of microcircuis consisting of precise parrerns of n-type and p-type regions ona single crystal chip.The major electrical properties needed to specify an intrinsic semiconductor are band gap,electron mobility,hole mobility,and conduction electron density (=electron hole density ) at room temperature.For extrinsic semiconductors,one needs to specify either the donor level (for n-type material) or the acceptor level (for p-type material).2.7 compositesOne category of structural engineering material is that of composites .These materials involve some combination of two or more components from the “fundamental” materal types .A key philosophy in selecting composite materials is that they provide the “best of both worlds”that is ,attrative properties from each component. A classic example is fiberglass.The strength of small diameter glass fibers is combined with the ductility of the polymetric matrix.The combination of these two components provides a product superior to either component alone .Many composites,such as fiberglass,involve combinations that cross over the boundaries of different kinds of materials. Others,such as concrete,involve different component from within a single material type.In general,we shall use a fairly narrowdefinition of composites.We shall consider only thode material thata combine different components on the microscopic(rather than macroscopic )scale .We shall noot include multiphase alloys and ceramics ,which are the result of routine processing.Similarly,the microcircuits be discussed later are not include because each component retains its distinctive character in these material systems. In spite of these restrictions,we shall find this category to include a tremendously diverse collection of materials,from the common to some of most sophisticated.We shall consider three categories of composites mateials. Conveninently ,these categories are demonstrated by three of our most common structural material ,fiberglass ,wood,and concrete .Fiberglass(or glass fiber reinforced polymer ) is an excellent example of a human made fiber reinforced composite.The glass-polymer system is just one of many important example .The fiber reinforcement is generally found in one of three primary configutations: aligned in a single direction ,randomly chopped,or woven in a fabric that is laminated with the matrix.Wood is a stuctural analog of fiberglass ,that is ,a natural fiber reinforced composite.The fibers of wood are elongated,biological cells. The matrixcorresponds to lignin and hemicellulose deposits.concrete is our best example of an aggregate composite, in which particles rather than fibers reinforce amatrix common concrete is rock and sand in a calcium aluminosilicate (cement)matrix.While concrete has been a construction material for centuries ,these are numerous c composites developed in recent decades that use a similar particulate reinforcement concept.The concept of property averaging is central to understanding the utility of composite material.an important example is the elastic modulus of a composite .The modulus is a sensitive function of the gemetry of the reinforcing component.similarly important is the srength of the interface betweeen the reinforcing component and the matrix .We sahll concentrate on these mechanical properties of composites in regard for their wide use as structural materials.So caaled “advanced”composites have provided some unusually attractive features,such as high strrenth to weight ratios.Some care is required in citing these properties,as they can be highly directional in nature.2.6there are numerous uses of piezoelectrics. for instance, plates cut from a single crystal can exhibit a specific natural resonance frequency(i.e., the frequency of an electromagneticwave that causes it to vibrate mechanically at the same frequency); these can be used as a frequency standard in highly stable crystal controlled clocks and in fixed frequency communications devices. other resonant applications include selective wave filters and transducers(e.g., for ultrasonic cleaning and drilling) and non-resonant devices(e.g., accelerometers, pressure gauges, microphone pickups) are dominated by ceramic piezoelectrics.2.7.3 fiberglass was a convenient and familiar example of fiber reinforced composites. Similarly ,concrete is an excellent example of an aggregate composite. As with wood,this common construction material is used in staggering quantities. The weight of concrete used annually exceeds that of all metals combined.For concrete, the term “aggregate” refers to a combination of sand(fine aggregate) and gravel(coarse aggregate). This component of concrete is a “natual” material in the same sense as wood. Ordinarily ,these materials are chosen for their relatively high density and strength. A table of aggregate compositions would be complex and largely meaningless. In general, aggregate materials are geological silicates chosen from locally available deposits. As such, these materials arecomplex and relatively impure examples of the crystalline silicates. Igneous rocks are common examples. “igneous” means solidified from a molten state. For quickly cooled igneous rocks ,some fraction of the resulting material may be non-crystalline, corresponding to the glassy silicates. The relative particle sizes of sand and gravel are measured(and controlled) by passing these materials through standard screens(or sieves). The reason for a combination of fine and coarse aggregate in a given concrete mix is that the space is more efficiently filled by a range of particle sizes. The combination of fine and coarse aggregate accounts for 60 to 75 percent of the total volume of the final concrete.Modern concrete uses portland cement,which is a calcium aluminosilicate. There are five common types of portland cement. They vary in the relative concentrations of four calcium containing minerals. The matrix is formed by the addition of water to the appropriate cement powder. The particle sizes for the cement powers are relatively small compared to the finest of the aggregates. Variation in cement particle size can strongly affect the rate at which the cement hydrates. As one might expect from inspecting the complex compositions of portland cement, the chemistry of the hydration process isequally complex.In ploymer technology, we noted several “additives” which provided certain desirable features to the end product. In cement technology , there are a numble of admixtures,which are additions providing certain features. Any component of concrete other than aggregate,cement,or water is, by definition ,an admixture. One of the admixtures is an “air entrainer” which reminds us that air can be thought of as a fourth component of concrete. The air entrainer admixture increases the concentration of entrapped air bubbles, usually for the purpose of workability(during forming) and increased resistance to freeze thaw cycles.Why concrete is an important engineering material, a large numble of other composite systems are based on particle reinforcement. Particulate composites refer specifically to systems with relatively large size dispersed particles(at least several micrometers in diameter),and the particles are in relatively high concentration(greater than 25 and frequently between 60 and 90) of small diameter oxide particles. The oxide particles strengthen the metal by serving as obstacles to dislocation motion.2.7.2 like so many accomplishments of human beings, those fiberreinforced composites imitate nature. Common wood is such a composite, which serves as an excellent structural material. In fact, the weight of wood used each year in the Uited Sates exceeds the combined total for steel and concrete. We find two categories , softwoods and hardwoods. These are relative terms, although softwoods generally have lower strengths. The fundamental difference between the categories is their seasonal nature. Softwoods are “evergreens” with needlelike leaves and exposed seeds. Hardwoods are deciduous( i.e., lose their leaves annually)with covered seeds( i.e.,nuts)The microstructure of wood illustrates its commonality with the human-made composites. The dominant feature of the microstructure is the large number of tubelike cells oriented vertically. These longgitudinal cells are aligned with the vertical axis of the tree. There are some radial cells perpendicular to the longitudinal ones. As the name implies, the radial cells extend from the center of the tree trunk out radically toward the surface. The longitudinal cells carry sap and other fluids critical to the growth process. Early seaon cells are of larger diameter than later season cells. This growth pattern leads to the characteristic “ring structure”which indicates the tree’s age. The radial cells store foodfor the growing tree. The cell walls are composed of cellulose. The strength of the cells in the longitudinal direction is a function of fiber alignment in that direction. The cells are held together by a matrix of lignin and hemicellulose. Lignin is a phenol propane network ploymer, and hemicellulose is ploymeric cellulose with a relatively low degree of ploymerization.Related to this ,the dimensions as well as the proper ties of wood vary significantly with atmospheric moisture levels. Care will be required in specifying the atmospheric conditions for which mechanical property data apply.2.7.1 let us begin by concentrating on fiberglass, or glass fiber reinforced ploymer. This is a classic example of a modern composite system. A typical fracture surface of a composite shows fibers embedded in the ploymeric matrix, such fibers may have different composition since each is the result of substantial development that has led to optimal suitability for specific applications. For example, the most generally used glass fiber composition is E glass, in which E stands for its especially low electrical conductivity and its attractiveness as a dielectric. Its popularity in structural composites is related to the chemical durability of the borosilicatecomposition. We should note that optimal strengh is achieved by the aligned, continuous fiber reinforcement. In other words, the strength is highly anisotropic.The fiber reinforced composites include some of the most sophisticated materials developed by man for some of the most demanding engineering applications. Important examples include boron reinforced aluminum, graphite epoxy, and al reinforced aluminum. Metal fibers are frequently small diameter wires. Especially high strength reinforcement come from “whiskers” which are small, single crystal fibers that can be grown with a nearly perfect crystalline structure. Unfortunately , whiskers cannot be grown as continuous filaments in the manner of glass fibers or metal wires.2.5polymerpolymers are chemical compounds that consist of long,chainlike molecules made up of multiple repeatinf units.The term polyner was coined in 1832 by the Swedish chemist Jins Jacob Berzelius from the Greek pols,or "many" and meros,or "parts."Polymers are also referred to as macromolecules,or "gaint molecules"-a term introduced by the German chemist Hermann Staudinger in 1992.Some gaint molecules occur maturally.Proteins ,for example ,are natural polymers of amino acids that make up muchof the structural material of animals;and the polymers deoxyribonucleic acid(DNA) and ribonucleic acid(RNA) are liner strands of nucleotides that define the genetic make up of living organisms.Other examples of natural polmers are silk ,wool.natural rubber,cellulose ,and shellac.There materials have been known and exploited since ancient times.Indeed,people in what is now Switzerland cultivates flax,a source of polymeric cellulose fibres,during the Neolithic Period,or New Stone Age,some 10 000 years ,while other ancients collected proteinaceous wool fibers from sheep and silk fibers from silkworms.About five millennia ago,tanners produced leather through the cross linking of proteins by gallic acid forming the basis of the oldest industry in continuous production.Even embalming,the art for which ancient Egypt is famous is based on the condensation and cross linking of proteins with form aldehyde.Early developments in polymer technology,taking place in the 19th century,involved the conversion of natural polymers to more useful products-for example,the conversion of cellulose,obtained from cotton or wood,into celluloid,one of the first plastic.Before the 1930s only a small number of synthetically produced polymers were availablecommercially,but after that period and especially after World War II,synthetic compounds came to dominance.Derived principally from the refining of petroleum and natural gas,synthetic polymers are made into the plastics,rubbers,man-made fibres,adhesives,and surface coatings that have become so ubiquitous in modern life.As an important materials,the polymers are available in a wide variety of commercial forms:fibers,thin films and sheets,foams and in bulk.A common synonym for polymers is "plastic",a name derived from the deformability associated with the fabrication of most polymeric products.To some critics,"plastic" is a synonym for modern culture.Accurate or not,it represents the impact that this complex family of engineering materials has had on our society.Polymers are distinguished from our previous types of materials by chemistry.Metal,ceramics.and glasses are inorganic materials.The polymers discussed here are organic.The student should not be concerned about a lack of background in organic chenistry.This passage is intended to provide any of the fundamentals of organic chemistry needed to appreciate the unique nature of polymeric materials.We begin our discussion of polymers by investigating polymerization,theprocess by which long chain or network molecules are made from relatively small organic molecules.The structural features of the resulting polymers are rather unique compared to the inorganic materials.Ingeneral,the ,elting point and rigidity of polymers increase with the extent of plymerization and with the complexity of the molecular structure.We shall find that polymers fall into one of two main categories.Thermoplastic polymers are materials that become less rigid upon heating,and thermosetting polymers become more rigid upon heating.For both categories,it is important to appreciate the roles played by additives,which provide important features such as color and resistance to combustion.As with ceramics and glasses,we shall discuss important mechanical and optical properties of polymers.Mechanically,polymers exhibit behavior associated with their long chain molecular structure.Examples include viscoelastic and elastomeric deformation .Optical properties such as transparency and color,so important in ceramic technology,are also significant in the selection of polymers.2.5.1 PolymerizationThe term polymer simply means "many mers" where mer is thebuilding block of the long chain or network molecule.There are two distinct ways in which a poly merization reaction can take place.Chain growth(also known as addition polymerization)involves a rapid "chain reaction" of chemically activated monomers.Step growth(also known as condensation polymerization)involves individual chemical reactions between pairs of reactive monomers and is a much slower process.In either case,the critical feature of a monomer,which permits it to join with similar molecules and form a polymer,is the presence of reactive sites,that is double bonds(chain growth) or reactive functional groups (step geowth).Each covalent bond is a pair of electrins shared between adjacent atoms.The double bond is two such pairs.The chain growth reaction converts the double bond in the monomer to a single bond in the mer.The remaining two electrons become parts of the single bonds joining adjacent mers.2.5.2 Thermal Plastic PolymersThermoplastic polymers become soft and deformable upon heating.This is characteristic of linear polymeric molecules.The high temperature plasticity is due to the ability of the molecules to slide past one another.This is anotherexample of a thermally activated,or Arrhenius process.In this sence ,thermoplastic materials are similar to metals that gain ductility at high temperatures.The key distinction between thermoplastics and metals is what we mean by "high" temperatures.The secondary bonding,which must be overcome to deform thermoplastics,may allow substantial deformation around 100,whereas metallic bonding generally restricts creep deformation to temperature closer to 1000 in typical alloys.It should be noted that,as with metals,the ductility of thermoplastic polymers is lost upon cooling.2.5.3 Thermal Setting PolymersThermosetting polymers are the opposite of the thermoplastics.They become hard and rigid upon heating.Unlike thermoplastic polymers,this phenomenon is not lost upon cooling.This is characteristic of network molecular structures formed by the step growth mechanism.The chemical reaction "steps" are enhanced by higher temperatures and are irreversible,that is,the polymerization remains upon cooling.In fabricating thermosetting products,they can be removed from the mold at the fabrication temperature (typically 200 to 300).By contrast,thermoplastics must be cooled in themokd to prevent distortion.It might also be noted that network copolymers can be formed similar to be the block and graft copolymers.The network copolymer will result from polymerization of a combination of more than one species of polyfunctional monomers.2.5.4 AdditivesCopolymers and blends were discussed above as analogs of metallic alloys.There are aeveral other alloylike additives that traditionally have been used in polymer technology to provide specific characteristics to the polymers .A plasticizer is added to soften a polymer.This addition is essentially blending with a low molecular weight (approximately 300 amu) polymer.A filler ,on the other hand .is added to strengthen a polymer primarily by restricting chain mobility.it also provides dimensional stability and reduced cost.Relatively inert materials are used.Examples include shortchanger cellulose (and organic filler) and asbestos (and inorganic filler).Roughly one third of the typical automobile tire is a filler (i.e.,carbon black).Reinforcements such as glass fibers are also categorized as additives but produce suchfundamentally different materials (e.g.,fiberglass) that they are properly discussed later on composites.Stabilizers are additives used to reduce polymer degradtion.They represent a complex set of materials because of the large variety of degradation mechanisms(oxidation,thermal,and ultraviolet).As an example,polyisoprene can absorb up to 15% oxygen at room temperature with its elastic properties being destoryed by the first 1%.Natural rubber latex contains complex phenol groups that retard the room temperature oxidation reactions.However,these naturally occurring antioxidants are not effective at elevated temperatures.Therefore ,additional stabilizers(e.g.,other phenols,amines,sulphur compounds,etc.)are added to rubber intended for tire applications.Flame retardant are added to reduce the inherent combustibility of certain polymers such as bustion is simply the reaction of a hydrocarbon with oxygen accompanied by substantial heat evolution.Many polymeric hydrocarbons exhibit combustibility.Others,such as polyvinylchloride(PVC),donot.The resistance of PVC to combustion appears to come from the evolution of the chlorine atoms from the polymeric chaim.These halogens hinder the process of combustion by terminating free radical chain reactions.Additives that provide this function for halogen free polymers include chlorine,bromine,and phosphorus containing reactants.Colorant are additions to provide color to a polymer where appearance is a factor in materials selection.Two types of colorants are used,pigments and dyes.A pigment is an insoluble,colored material added in powered form.Typical examples are crystalline ceramics such as titanium oxide and aluminum silicate,although organic pigments are availble.Dyes are soluble,organic colorants that can provide transparent colors.2.5.5 Viscoelastic DeformationAt relatively low temperature,polymers are rigid solids and deform elastically.At relatively high temperatures,they are liquidlike and deform viscously.The boundary between elastic and viscous behavior is again known as the glass transition temperature,Tg.However,the variation in polymer deformation with temperature is not demonstrated in the sameway.For glassws,the variation in viscosity was plotted against temperature.For polymers,the modulus of elasticity is plotted instead of viscosity.There is a drastic and complicated drop in modulis with temperature for a typical,commercial thermoplastic with approxinately 50% crystallinity.THe magnitude of the drop is illustrated by the use of a logarithmic scale for modulus.At "low" temperatures (well below Tg),a rigid modulus occurs corresponding to mechanical behavior reminiscent of metals and ceramics.However,the substantial component of secondary bonding in the polymers cause the modulus for these materials to be substantially lower than the ones found for metals and ceramics,which were fully bonded by primary chemical bonds (metallic,ionic,and covalent).In the glass transition temperature (Tg) range,the modulus drops precipitously and the mechanical behavior is leathery.The polymer can be extensively deformed and slowly returns to itTys original shape upon stress removal.Just above Tg,a rubbery plateau is observed.In this region,extensive deformation is possible with rapid spring back to the original shape when stress is removed.These last two regions(leathery and rubbery) extend our understanding of elastic deformation.Sometimes the elastic deformation meant a relatively small strain directlyproporyional to applied stress.For polymers,extensive,non-linear deformationcan be fully recovered and is ,by definition,elastic.This concept will be explored shortly when we discuss elastomers,those polymers with predominant rubbery region.2.5.6 ElastomersTypical linear polymers exhibits a rubbery deformation region.For certain polymers known as elastomers,the rubbery plateau is pronounced and establishes the normal room temperature behavior of these materials.(For these materials,the glass transition temperature is below room temperture.)This subgroup of thermoplastic polymers includes the natural and synthetic rubbers (such as polyisoprene).These materials provide a dramatic example of the uncoiling of a linear polymer.As a practical matter,the complete uncoiling of the molecule is not achieved,but huge elastic strains do occur.The stress-strain curve for the elastic deformation of an elastomer shows dramatic contrast to the stress-strain curve for a common metal.In that case,the elastic modulus was constant throughout the elastic region (stress was directly proportional to strain).While the clastic modulus (slope of thestress-strain curve) increases with increasing strain.For low strains,the modulus is low corresponding to the small forces needed to overcome secondary bonding and to uncoil the molecules.For high strains,the modulus rises sharply,indicating the greater force needed to stretch the primary bonds along themolecular "backbone".In both region,however,there is a significant componrnt of secondary bonding involved in the deformation mechanism,and the moduli are much lower than those for common metals and ceramics.Tabulated values of moduli for elastomers are generally for the low strain region in which the materials are primarily used.Finally,it is important to emphasize that we are talking about elastic or temporary deformation.The uncoiled polymer molecules of an elastomer recoil to their original length upon removal of stress.2.5.7 Stress RelaxationFor metals and ceramics,we found creep deformation to be an important phenomenon at high temperatures (greater than one half the absolute melting point).A similar phenomenon,termed stress relaxation,occurs in polymers.This is perhaps moresignificant to polymers.Because of their loe melting points,stress relaxation can occur at room temperature.A familar example is the rubber band,understress for a long period of time,which does not snap back to its original size upon stress removal.2.4（88）Chemical substitutions in the BaTio3 structure can alter a number of ferro electric properties.For example,BaTio3 exhibits a large peak in dielectric constant near the Curie point-a property that is undesirable for stable capactior applications.This problem may be addressed by the substitution of lead (**) for (**),which increases the Curie point;by the substitutionof strontium,which lowers the Curie point;or by substituting Ba with calcium,which broadens the temperature range at which the peak occurs.Barium titanate can be produced by mixing and firing barium carbonate and titanium dioxide,but liquid-mix techniques are increasingly used in order to achieve better mixing,precise control of the barium titanium ratio,high purity,and submicrometre particle size.Processing of the resulting powder varies according to whether the capacitor isto be of the disk or multilayer type.Disks are dry pressed or punched from tape and then fired at temperatures between 1250 and 1350.Silver-paste screen printed electrodes are bonded to the surfaces at 750.Leads are soldered to the electrodes,and the disks are epoxy coated or wax impregnated for encapsulation.The capacitance of cermic disk capacitors can be increased by using thinner capacitors;unfortunately,fragility result.Multilayer capacitors overcome this problem by interleaving dielectric and electrode layers.The electrode layers are usually palladium or a palladium-silver alloy.These metals have a melting point that is higher than the sintering temperature of the ceramic,allowing the two materials to be cofired.By connecting alternate layers in paralled,large capacitance can be realized with the MLC.The dielectric layers are processed by tape casting or doctor blading and then yer thickness as small as 5 micrometres have been achieved.Finished "build" of dielectric and electrode layers are then diced into cubes and cofired.MLCs have the advantages of small size,low cost ,and good mounting on circuit boards.They are increasingly used in palce of disk capacitors in most electronic circuitry.Where monolithic units are still。