PbTiO3纳米粉体的制备与X射线衍射分析

以醋酸铅和钛酸丁酯为原料,甲醇为溶剂,冰醋酸为催化剂,采用溶胶-凝胶法制备出PbT iO3干凝胶粉体,在高于450℃的不同温度下空气气氛中焙烧,得到PbT iO3纳米粉体.用X射线粉末衍射仪对粉体的晶态进行了表征,计算了不同焙烧温度下PbT iO3纳米晶的晶格常数和平均晶粒大小.分析表明:焙烧温度高于600℃时可形成单一四方相钙钛矿结构的PbT iO3纳米粉体,并且随热处理温度的升高,晶粒度增加.在450℃~800℃区间时,平均晶粒大小在35 nm~50 nm左右.     

BaTiO3纳米粉体及其陶瓷的制备和介电性能

采用溶胶-凝胶(Sol-gel)法制备BaTiO3纳米粉体及其陶瓷.通过XRD、SEM和TEM对BaTiO3粉体及其陶瓷进行了表征,并测试了陶瓷的介电性能.研究了预烧温度和烧结温度对BaTiO3粉体及其陶瓷微观结构和介电性能的影响.结果表明:950℃预烧2 h的BaTiO3粉体主要为四方相,其尺寸为60 nm左右,经1 300℃烧结2 h的BaTiO3陶瓷具有高的介电常数(10 820)和小的介电损耗(0.01).     

掺镍钛酸钡纳米粉体及其陶瓷的溶胶-凝胶制备

目的研究焙烧温度和烧结温度对由溶胶-凝胶法制备的掺镍钛酸钡样品微结构及介电性能的影响。方法采用溶胶-凝胶法制备了掺镍钛酸钡粉体及其陶瓷,通过FT-IR,XRD,SEM和TEM对干凝胶粉体、预烧粉体以及陶瓷进行了表征,并测定陶瓷的介电性能。结果采用溶胶-凝胶法可制备纳米级(30~80 nm)掺镍钛酸钡粉体及其细晶陶瓷(1~3μm);较高的焙烧温度有利于四方相钛酸钡的形成和晶粒的长大,但降低了陶瓷的介电常数;较高的烧结温度有利于陶瓷居里点介电常数的提高,合适的焙烧温度及烧结温度分别为800℃和1 300℃。结论溶胶-凝胶法可制得组成均匀、性能优异的介电材料,是制备多组分掺杂钛酸钡陶瓷的理想方法。     

柠檬酸用量对溶胶—凝胶法制备ZnNb_2O_6陶瓷粉体工艺的影响

将Nb2O5溶于HF酸获得Nb5 的可溶性盐溶液,并以此为原料,采用溶胶-凝胶法合成了ZnNb2O6陶瓷粉体.利用XRD、TG和SEM等测试手段对所合成粉体的晶体结构、显微形貌和干凝胶的分解过程进行了系统研究.TG和XRD分析结果显示,干凝胶经700℃煅烧2h时可以获得单相铌铁矿相结构纳米ZnNb2O6粉体.SEM分析结果显示,柠檬酸与Nb5 比例对所合成粉体晶粒尺寸有明显影响.     

Dy2O3掺杂对BaTiO3陶瓷结构与性能的影响

对水热法合成的BaTiO3粉体进行稀土氧化物Dy2O3掺杂改性,利用扫描电镜、X射线衍射及电气性能测试等手段,分析了离子取代行为和晶格参数与固溶度之间的关系,重点研究了Dy2O3掺杂量对BaTiO3陶瓷的晶粒尺寸、介电性能的影响规律.结果表明,Dy2O3在陶瓷的烧结过程中可抑制晶粒生长,使晶粒尺寸变小,提高了陶瓷的致密度.当掺杂量w(Dy2O3)为0.6%时,陶瓷晶粒的晶格常数达到最大值,此时晶粒内部缺位浓度最低,常温介电常数提高到4100,在-15～100℃范围内,介电常数随温度变化率为±10%,交流击穿场强为3 2kV/mm.     

特殊液相沉淀法制备纳米Al2O3粉体

采用特殊液相沉淀法制备氧化铝前驱体,经不同温度焙烧,通过TEM表征,给出了焙烧温度与粉体粒径的曲线.可以看出,在500 ℃至1 100 ℃范围内,随焙烧烧温度的升高,粉体粒径有增大的趋势,但不明显;当温度继续升高,粉体粒径明显增大,当温度升至1 250 ℃时平均粒径达到50nm.XRD检测表明,经1 250 ℃焙烧,可得到α相纳米氧化铝粉体.对反应过程中沉淀产物的过滤性进行比较,发现Al 2(SO 4) 3为反应物较AlCl 3为反应物的过滤性好.     

尿素-硝酸盐低温燃烧法制备Ce_(0.8)Gd_(0.2)O_(1.9)纳米粉体

以尿素为还原剂,硝酸盐为氧化剂,利用低温燃烧合成法制备了Ce0.8Gd0.2O1.9纳米粉体。分析了凝胶的热分解行为、合成粉体的物相结构及微观形貌,以及尿素与硝酸盐摩尔比(nU/nN)对凝胶的燃烧特性及合成粉体性能的影响。结果表明:尿素-硝酸盐干凝胶的点火温度约为279.0℃;制得的粉体经600℃焙烧后即形成了单相立方萤石结构的纳米级固溶体;当尿素与硝酸盐摩尔比(nU/nN)为7∶1时,制得的粉体比表面积最大、晶粒尺寸最小,分别为105.71m2/g和20.15nm。     

纳米TiO2粉末的溶胶-凝胶法制备及结构分析

采用溶肢-凝肢法制备了纳米晶TiO2粉末.TiO2粉末的X射线衍射结果表明,所制样品的平均晶粒粒径随焙烧温度的升高而增大,在400℃以下焙烧的样品晶粒大小为4.7-1 0.6nm,500℃以上晶粒很快长大,600℃基本完成了从锐钛矿型向金红石型的转变.透射电镜结果显示400℃处理后晶粒尺寸为7-8nm;700℃处理后的晶粒尺寸达150nm.运用相变理论计算了晶粒长大激活能,结合晶界结构弛豫解释了粒径随热处理温度变化关系.     

掺杂锆钇氮硫硼p-n结型光催化剂的制备及其催化降解甲基橙的研究

本文以钛酸四丁酯为原料,采用溶胶-凝胶法制备掺杂N-Zr-Y-S的n型、B-Zr-Y的p型以及p-n型干凝胶,将各种干凝胶在不同温度下焙烧制得纳米光催化剂,以甲基橙为目标降解物,考察它们的光催化活性.实验结果表明a:、相同温度、相同时间焙烧的p型TiO2光催化剂的光催化活性大于n型;b、以未焙烧的p型干凝胶制备出来的p-n型催化剂的催化效率比p型干凝胶在不同温度下焙烧后制备的p-n结型光催化剂高c;、在可见光条件下,未焙烧的p型制备出来干凝胶在250℃下焙烧所得p-n型催化剂的催化效率是最高的.     

溶胶-凝胶法制备钙钛矿型复合氧化物La1-xCaxCoO3纳米晶

采用溶胶—凝胶法合成了 La1-x Cax Co O3 (X=0 .1 ,0 .3 ,0 .5 ,0 .7)纳米晶 ,采用 TGA技术确定干凝胶焙烧温度 ;XRD技术证明所合成粉体为钙钛矿型复合氧化物 La1-x Cax Co O3 ,其粒径为 2 0 nm左右 .实验表明 ,脱水温度 70— 80℃左右 ,p H值小于 5时较合适 .同时也考察了柠檬酸用量对溶胶、凝胶形成的影响 .     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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