气体静压轴承用多孔SiC陶瓷的制备及静态性能

以α-SiC和β-SiC粉末为原料,羧甲基纤维素为造孔剂,制备了多孔SiC陶瓷.探讨了烧结温度、成型压力和造孔剂含量对SiC陶瓷的气孔率、显气孔率以及弯曲强度的影响,研究了用不同渗透率的多孔SiC陶瓷制备气体静压轴承的承载能力和静态刚度.结果表明:在高温下,β-SiC转变为α-SiC,同时,通过α-SiC的蒸发-凝聚过程实现了SiC陶瓷的烧结,并形成无收缩自结合结构;试样的气孔率和显气孔率随烧结温度和成型压力的增加而略有降低,但弯曲强度却增大;造孔剂含量越高,试样的气孔率和显气孔率越大,弯曲强度越低.添加质量分数为10%的造孔剂,经250MPa冷等静压成型,在2 400℃下制备的试样气孔率和显气孔率分别为28.91%和24.03%,渗透率为7.74×10-13 m2,弯曲强度为63.8MPa.因此,多孔SiC陶瓷的渗透率越低,利用它制备的气体静压轴承的承载能力越低,静态刚度就越高.     

多孔SiC陶瓷的两种制备方法

采用两种不同的方法制备多孔SiC陶瓷,讨论了其显微组织对性能的影响,探索了由天然木材经炭化、渗硅处理制造多孔SiC陶瓷的新方法。研究结果表明,半干压法制得的SiC陶瓷的气孔率随SiC粒度的增大而降低,且强度升高。由天然木材制得的多孔SiC陶瓷的新方法。研究结果表明,半干压法制得的SiC陶瓷的气孔率随SiC粒度的增大而降低,且强度升高。由天然木材制得的多孔SiC陶瓷的气孔形状较规则,且分布均匀,其表观气孔率可达40％以上,是制备高气孔率SiC陶瓷的一种可行技术。     

艺术陶瓷材料的制备与性能研究

研究了成型压力、SiC微粉添加量和造孔剂含量对多孔陶瓷体积密度、显气孔率、常温和高温折弯强度的影响。结果表明,多孔陶瓷适宜的成型压力为100MPa,此时,陶瓷材料具有较高的折弯强度和体积密度以及低的显气孔率;随着SiC微粉加入量的增加,陶瓷试样的常温和高温抗折强度都呈现出先增加后减小,然后又逐渐增加的特征,当SiC微粉加入量为40%时,陶瓷试样具有较高的常温和高温折弯强度,且此时的体积密度较高、显气孔率较低。随着造孔剂加入量的增加,陶瓷试样的体积密度逐渐减小,而显气孔率逐渐增加,陶瓷试样的常温和高温抗折强度都呈现逐渐减小的特征;加入相同量的造孔剂的情况下,陶瓷试样的高温抗折强度高于常温抗折强度。     

炭泡沫中Si含量对碳化硅多孔陶瓷 组织和性能的影响

研究炭泡沫预制体中Si添加量的变化对碳化硅多孔陶瓷的组织及性能的影响. 以中间相沥青添加一定质量分数的Si粉为原料,经发泡工艺制备含Si的炭泡沫预制体并结合反应烧结工艺制得碳化硅多孔陶瓷. 对碳化硅多孔陶瓷的微观形貌、相组成、孔隙率、孔筋密度和抗弯强度进行分析与测试. 结果表明:随着炭泡沫预制体中Si量的增加,碳化硅多孔陶瓷的孔隙率下降,孔筋密度增加,抗弯强度提高. 当Si的质量分数为50%时,多孔陶瓷孔筋完全由SiC相组成,孔筋密度为3.14g/cm3,多孔陶瓷的抗弯强度达到23.9MPa,对应孔隙率为55%.     

Al_2O_3/SiC纳米陶瓷复合材料的制备及力学性能

采用一次粒径分别为10nm和15nm的αAl2O3和SiC粉体为原料,制备了Al2O3/SiC纳米陶瓷复合材料·纳米SiC颗粒明显抑制Al2O3基体晶粒的长大,SiC体积分数超过4%时,材料的断裂方式由沿晶断裂变为穿晶断裂·随SiC含量的增加,Al2O3/SiC纳米复合材料的硬度增大·材料的弯曲强度和断裂韧性在SiC体积分数为5%时达到最大值·最大三点弯曲强度和断裂韧性分别为641MPa和47MPam1/2,明显高于热压单相Al2O3陶瓷(344MPa和31MPam1/2)·复合材料的强化主要来源于内晶颗粒残余应力强化和晶粒细化...     

以木材为模板制备Al2O3多孔陶瓷的工艺

利用Al2O3和木屑混料,分别采用直接烧结和分步炭化烧结的方法制备了一种具有木材管胞组织结构的多孔Al2O3陶瓷.利用X射线衍射对物相进行分析,采用扫描电镜对多孔Al2O3陶瓷的形貌进行观察,测定了其密度、显气孔率和抗弯强度.试验结果表明:分步炭化烧结法更加适合得到性能较好的Al2O3多孔陶瓷,木材的显微管胞组织结构在多孔Al2O3陶瓷中保留很好.利用分步烧结法可以有效地防止开裂和严重变形,且制备得到的多孔陶瓷具有低密度高显气孔率的性质,说明孔洞大部分已连通并呈网络状分布,其抗弯强度明显提高.     

SiC-WC复相陶瓷的力学性能与显微结构

在α-SiC和β-SiC超细粉末中,以Al、B、C为烧结助剂,分别添加0～24vol%WC,研究了SiC—WC复相陶瓷的力学性能和显微结构,获得了一种室温弯曲强度和断裂韧性分别达700MPa和8.6MPa·m(1/2)的SiC-WC复相陶瓷.     

聚氮硅烷催化裂解原位合成碳纳米管增强SiC/Si3N4复相陶瓷

以聚氮硅烷为前驱体,通过催化裂解原位生成SiC/Si3N4复相陶瓷,同时原位生成碳纳米管增韧相;研究热解温度、掺杂催化剂种类对SiC/Si3N4复相陶瓷微观结构及形态的影响,运用扫描电镜、高分辨率透射电镜、X射线衍射、综合热分析进行结构分析和表征.结果表明,催化裂解可有效增强陶瓷基体的强度和实现基体与纳米相的复合和分散,并降低SiC/Si3N4复相陶瓷晶化温度 .     

CVD SiC涂层的C/SiC复合材料的弯曲性能

以针刺整体毡为预制体制备C／SiC复合材料,在材料表面制备CVD SiC涂层,研究涂层试样氧化前、后的微观结构和室温弯曲性能。研究结果表明：CVD SiC涂层由球形颗粒熔聚体、裸露裂纹和附着裂纹组成,于1400℃氧化时附着裂纹发生愈合;C／SiC试样的弯曲强度为119．9MPa,涂层试样及其分别经1000,1200和1400℃连续氧化5h后,弯曲强度分别为188．5,41．0,60．7和104．5MPa;随氧化温度的升高,SiC涂层的保护作用增强是残留弯曲强度提高的根本原因：C／SiC试样、涂层试样和经1200和1400℃氧化的试样均表现为分层断裂,纤维束边缘区域炭的适度氧化弱化了纤维／热解炭界面,使氧化试样表现出明显的假塑性;经1000℃氧化的涂层试样,由于纤维束的严重氧化,表现为脆性断裂特征。     

ZrO_2对堇青石多孔陶瓷吸水率和显气孔率的影响

采用活性炭和淀粉作造孔剂,ZrO2作添加剂,经湿混、干燥、造粒、成型和烧成制备堇青石多孔陶瓷.通过X射线衍射和陶瓷吸水率测定仪对堇青石多孔陶瓷的物相组成、吸水率和显气孔率进行了表征.实验结果表明:用10%活性炭和5%可溶性淀粉作造孔剂,添加1.0%的ZrO2,在1250℃下制得的堇青石多孔陶瓷的吸水率和显气孔率最高,分别为49.96%和39.89%。     

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

正~~