B_4C陶瓷材料的无压烧结与性能

以碳化硼微粉作为原料,选用SiC和C为烧结助剂,研究了SiC和C对无压烧结B4C材料的体积密度、硬度、抗折强度和断裂韧性等性能的影响.结果表明,最佳烧结温度为1975℃,保温时间是30min.SiC和C的质量分数对材料密度、硬度和抗折强度的影响都是先增大后减小.烧结助剂SiC和C的最佳添加量分别为6%和5%(质量分数)时,得到相应的无压烧结B4C陶瓷材料的最佳力学性能:体积密度为2.45g/cm3,维氏硬度为35GPa,抗折强度为240MPa,断裂韧性为3.0MPa.m1/2     

热压烧结C-SiC-B_4C复合材料组织与性能(Ⅰ)

以Cfg,SiC,B4C,TiO2为原料,热压工艺为1750~1 900℃×30 min,25 MPa,制备了C-SiC-B4C复合材料,并研究了材料的组织与性能.结果表明随热压温度升高,复合材料的体积密度、抗折强度、断裂韧性均升高;相同热压温度下随Cfg含量增加,其抗折强度降低、断裂韧性升高.在1 900℃热压,原料质量配比(质量分数,%)为Cfg20,SiC 61.7,B4C 12.3和TiO26时,复合材料的综合力学性能最佳,抗折强度为142.5MPa,断裂韧性为4.8 MPa.m21.复合材料的主晶相为层状结构的Cfg,在Cfg层间为SiC,B4C和原位生成的TiB2颗粒.复合材料的增...     

两步包埋法制备C/C复合材料SiC/Cr-Al-Si涂层研究

采用两步包埋法在碳/碳复合材料表面制备了SiC/Cr-Al-Si涂层.采用XRD、SEM和EDS分析了涂层的物相组成、微观结构及断面元素分布,测试了双涂层碳/碳复合材料试样在1 500℃静态空气中的抗氧化性能.结果表明:SiC/Cr-Al-Si涂层主要由SiC、AlCr2Si及Al4Si2C三相组成,厚度约为120μm,无穿透性裂纹;与一步包埋法所得SiC涂层相比,SiC/Cr-Al-Si涂层碳/碳复合材料试样的抗氧化性能有所提高,该涂层试样氧化12 h后的失重不超过5%.两步包埋法所得SiC/Cr-Al-Si涂层表面存在微裂纹,并且包埋过程易于使Cr-Al-Si合金成分扩散到SiC涂层内部,从而无法形成内SiC涂层、外Cr-Al-Si涂层的双层涂层结构,降低了Cr-Al-Si合金涂层对C/C复合材料基体的高温氧化保护效果.     

Si3N4／[SiC＋B4C]复合陶瓷的制备与性能研究

采用高分散、高稳定混合水悬浮液方法制备Si3N4／[SiC B4C]复合陶瓷，研究了亚微米B4c含量对Si3N4／[SiC B4C]复合陶瓷性能的影响以及断裂相变量与性能的关系，讨论了B4C应力诱导相变增韧机制与微米粒子强韧化机制迭加的可能性．     

聚碳硅烷热解产物抗氧化性能的研究

在流动氩气中将聚碳硅烷(PCS)于不同温度下进行热解处理制得热解产物,对其进行抗氧化实验,并采用XRD、EDX对PCS热解产物及其氧化产物的物相和成分组成进行表征.结果表明,PCS于1000℃的热解产物主要为无定形的SiC、SiO2和C;随着温度的升高,SiC晶体尺寸逐渐增大,1560℃的热解产物仍由立方SiC、无定形C和SiO2组成;PCS热解产物中的SiO2含量以及SiC的晶化度对其起始氧化温度有一定影响;热解产物中SiO2、SiC氧化形成的SiO2使得PCS热解产物在高温下具有良好的抗氧化性能.     

炭质原料对C-SiC-B4C复合材料性能和微观 结构的影响

分别采用鳞片石墨、生石油焦和煅后沥青焦为基体炭质原料,以酚醛树脂作为粘结剂,掺入定量SiC,B4C陶瓷相,通过模压成型(140MPa 1min)制备弥散型C-SiC-B4C复合材料.研究了原料种类及含量对C-SiC-B4C复合材料性能和显微结构的影响.研究表明:C-SiC-B4C复合材料的性能和显微结构与基体炭质原料的种类和含量有关,生焦的微观结构以流线型为主,以生石油焦为原料制备的复合材料抗压强度最高,达到226MPa;煅后沥青焦的显微结构以镶嵌型居多,制备的样品导电性较差,抗氧化能力最弱;以晶态鳞片石墨为原料制备的复合材料显示出了较低的电阻率和较好的抗氧化性能.     

热压烧结C-SiC-B4C复合材料组织与性能(Ⅰ)

以Cfg,SiC,B4C,TiO2为原料,热压工艺为1750~1 900℃×30 min,25 MPa,制备了C-SiC-B4C复合材料,并研究了材料的组织与性能.结果表明随热压温度升高,复合材料的体积密度、抗折强度、断裂韧性均升高;相同热压温度下随Cfg含量增加,其抗折强度降低、断裂韧性升高.在1 900℃热压,原料质量配比(质量分数,%)为Cfg20,SiC 61.7,B4C 12.3和TiO26时,复合材料的综合力学性能最佳,抗折强度为142.5MPa,断裂韧性为4.8 MPa.m21.复合材料的主晶相为层状结构的Cfg,在Cfg层间为SiC,B4C和原位生成的TiB2颗粒.复合材料的增韧机制主要为Cfg与陶瓷相的热膨胀不匹配产生的热应力导致的弱界面分层诱导韧化作用.     

一种高性能烧结摩擦材料摩擦剂的选择

合理选择摩擦组元对改善高性能金属基烧结摩擦材料的性能至关重要.采用粉末冶金工艺制备了以SiO2,SiC,B4C等为摩擦剂的金属基烧结摩擦材料,研究了该摩擦组元对材料的机械性能特别是摩擦磨损性能的影响,探讨了其作用机理.研究结果表明同时添加SiO2,SiC,B4C作摩擦剂的材料比单独添加SiO2,SiC或SiO2+SiC的材料综合性能优异得多.这是由于除了SiO2,SiC作为摩擦组元具有一些优良性能外,B4C与铁在烧结温度下反应生成了一种高硬度的金属间化合物Fe2B,其综合作用结果使该材料的摩擦因数比其他3种材料高出30%～40%,摩擦因数稳定度高出20%～60%,且磨损小,是一种理想的、可广泛应用于各种高能重载工况下工作的高性能摩擦材料.     

SiCp/Cu复合材料高温抗氧化性能研究

采用粉末冶金方法制备了SiCp/Cu复合材料,研究了复合材料在恒温氧化和循环氧化条件下的抗氧化性能。结果表明：在400—700℃时,SiCp/Cu复合材料具有比纯铜优良的抗氧化性能;在温度一定的条件下,SiC体积分数为20%时,复合材料的抗氧化性能最好;在循环氧化条件下,随着氧化时间延长,复合材料氧化增重率逐渐增大,而且呈现近抛物线变化规律;对相同SiC颗粒含量的SiCp/Cu复合材料,SiC颗粒越细,试样的抗氧化性能越好。     

炼镁还原罐用SiC外衬材料烧结性能和抗氧化性能的研究

为了延长炼镁还原罐的使用寿命,拟在离心法铸造还原罐时引入SiC质外衬材料保护层.采用SiC和亚白刚玉为主要原料,酚醛树脂粉为结合剂,添加适量外加剂,经混合、成型、固化后在1 400 ℃保温3 h烧成,研究外加剂的种类、加入量对烧结性能和抗氧化性能的影响.结果表明,加入硼砂或萤石均能提高材料的烧结性能、常温物理性能和抗氧化性能,而加入萤石的试样,其抗氧化能力明显优于加入硼砂的试样;加入质量分数为2%的萤石时,材料的烧结性能和抗氧化性能均较优.     

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。     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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     

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