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1.
Aluminum nitride （AlN）/borosilicate glass composites were prepared by the tape casting process and hot-press sintered at 950 ℃ with AIN and SiO2-B203-ZnO-Al2O3-Li2O glass as starting materials. We characterized and analyzed the variation of the microstructure, bulk density, porosity, dielectric constant, thermal conductivity and thermal expansion coefficient （TEC） of the ceramic samples as a function of AIN content. Results show that AIN and SiO2-B2O3-ZnO-Al2O3-Li2O glass can be sintered at 950 ℃, and ZnAI204 and Zn2SiO4 phase precipitated to form glass-ceramic. The performance of the ceramic samples was determined by the composition and bulk density of the composites. Lower AlN content was found redounding to liquid phase sintering, and higher bulk density of composites can be accordingly obtained. With the increase of porosity, corresponding decreases were located in the dielectric constant, thermal conductivity and TEC of the ceramic samples. When the mass fraction of AlN was 40%, the ceramic samples possessed a low dielectric constant （4.5-5.0）, high thermal conductivity （11.6 W/（m.K）） and a proper TEC （3.0× 10^-6 K^-1 which matched that of silicon）. The excellent performance makes this kind of low temperature co-fired ceramic a promising candidate for application in the micro-electronics packaging industry. 相似文献
2.
《开放教育研究》2001,(1)
From the white book:Teaching and Learn-ing:Toward the learning Society by the EuropeanUnion in1 995and the report:Learning:the Trea-sure Within by the2 1 st Century Education Com-mittee of the UNESCO in 1 996,we can see the fu-ture society is definitely to be a learning society.The same idea is put forward in the green book:The learning Age:A Renaissance over New Britainin1 998in Britain.Because of this,the problemsofwhat role the universities are to play and what po-sition they shou… 相似文献
3.
《Reading and Writing(初中版)》2007,(10)
What is the best thing in life? In my view, the best thing consists1 of happiness, health, love and friendship. These are things important to one. Happiness is the good feeling one has to life and to work and study. If one is happy, that is the most desirable2 thing in the world. Health is equally3 important to us. One who is ill all the time can not be happy. With a healthy body, one can do things he likes. Love and friendship are the feelings one has towards parents, teachers and friends. One can not be happy unless one loves and is loved by people. 相似文献
4.
This paper presents the forward displacement analysis of an 8-PSS （prismatic-spherical-spherical） redundant parallel manipulator whose moving platform is linked to the base platform by eight kinemtic chains consisting of a PSS joint and a strut with fixed length. A general approximation algorithm is used to solve the problem. To avoid the extraction of root in the approximation process, the forward displacement analysis of the 8-PSS redundant parallel manipulator is transformed into another equivalent problem on the assumption that the strut is extensible while the slider is fixed. The problem is solved by a modified approximation algorithm which predicates that the manipulator will move along a pose vector to reduce the difference between the desired configuration and an instantaneous one, and the best movement should be with minimum norm and least quadratic sum. The characteristic of this modified algorithm is that its convergence domain is larger than that of the general approximation algorithm. Simulation results show that the modelified algorithm is general and can be used for the forward displacement analysis of the redundant parallel manipulator actuated by a revolute joint. 相似文献
5.
As the pace of life continues to increase,we are fast losing the art of relaxation.1you are in thehabit of rushing through life,being on the go from morningtill night,it is hard to2down.But relaxationis3for a healthy mind and body.Stress is a4part of everydaylife and there is no way to5it.Infact,it is not the bad thing that it is oftensupposed to be.A6amount of stressis important to provide motivation and give7to life.It is only when the stressgets out of control8it can lead topoor performanc… 相似文献
6.
《Reading and Writing(高中版)》2006,(12)
Just a single flake of snow, and soon the world around is transformed. Just a tiny drop of rain, but from those drops the rivers flow, and seas stretch from shore to shore. Just one tiny step and a journey is begun. Just one hand held out in friendly greeting, and a chain of warmth is started. Just a single voice raised in protest at injustice can be joined by many more and achieve results to change the face of history... So next time you are tempted to say, "Oh, my little efforts… 相似文献
7.
Image is not only an essential part,but also a major means to convey the implications in English poems.It is a literal and concrete representation of a sensory experience of an object.The rendering of images in English poems into Chinese can be guided by the dynamic equivalent translation theory put forward by Dr.Eugene A Nida.The theory emphasizes the roughly equivalent response of the target language receptors to the TL text to that of the source language receptors to the SL text.To achieve a Dynamic Equivalence,methods like Direct Translation,Addition,and Substitution can be employed in the translation of images in English poems. 相似文献
8.
The preparation of calcium phosphate (CP) coating on alumina ceramics using electric pulse stimulating method has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid ( SBF), and a square pulse potential with frequency of 1 Hz and voltage of 110 V was applied between the inner and outer surfaces of the alumina cup. Surface morphology of CP coatings during different deposition periods was observed by a Philips XL-30 scanning electron microscope (SEM). Compositional analysis was examined by EDAX. The mechanism of nucleation and growth of CP coating was discussed. SEM result indicates that the coating comprises of a large number of tiny needle-like grains and has a porous microstructure. There is a strong bond between the deposited layer and Al2O3 substrate, which may be due to the gentle growth of the biomimetic method. The EDAX analysis indicates that main composition of the coating is calcium and phosphor. The formation of CP coating may be contributed to the stimulation of electric pulse and the high ions concentration which is 1.5 times of the concentration of SBF solution ( 1.5SBF solution). Such surface functionalization method by electric pulse potential can be used to prepare CP coating on various electric-insulating bioinert materials for improving their bioactive character. 相似文献
9.
According to the theory that rotation transformation from the basecoordinate to an arbitrary one can be described by a single equivalent rotation about agiven rotational axis,it is proposed that the orientation of robot can be described by usingthe vector of equivalent angular displacement.And the concept of pose motor and itsPlücker linear coordinate are established and used to describe the position and orientationof robot.Based on the fact that there is a one-to-one correspondence between the ori-ented straight lines in three-dimensional dual space,the interpolation plannings corre-sponding to the pose motors are developed in dual space.A new algorithm of robot CPmotion trajectory planning is presented.The correctness of the theory and derivation isconformed by an example. 相似文献
10.
Using agarose as a gel agent to prepare ceramics is a suitable non-toxic gel-casting method. The effects of agarose concentration and addition amount on gel-cast 3Y-ZrO_2 green and sintered bodies were investigated. Green bodies were prepared by gel-casting using an agarose solution of a different agarose mass fraction including 3.0%, 3.5%, 4.0%, 4.5%, 5.0% and 5.5%with an added amount of agarose in the green body at a mass fraction of 0.7%, and using the agarose solution of a mass fraction of4.5% with a different amount of added agarose including 0.6%, 0.7%, 0.8%, 0.9%, and 1.0% in terms of mass fraction. The green bodies were sintered at 1 600 °C for 4 h. The relative density, linear shrinkage, and bending strength of the green bodies, and the density, microstructure, bending strength, and fracture toughness of sintered samples were characterized and analyzed. Results show that comprehensive properties of green bodies made with 4.5%(in terms of mass fraction) agarose solution added to an mass fraction of agarose in the slurry at 0.6% were the best, of which the bending strength was 3.14 MPa, the linear shrinkage was below 4.3%, and the relative density is 57.3%. For sintered bodies, the best fracture toughness was 5.63 MPa m~(1/2), and the optimal density was 5.88 g cm~(-3). 相似文献
11.
以α Al2O3,TiO2,ZrO2 为主要原料,以MgO SiO2 或MgO Fe2O3 为稳定剂,经1 500 ℃×2 h烧成可制得低热膨胀系数的Al2TiO5 ZrO2 复相材料。试验发现:随试样中ZrO2 含量的提高或ZrO2 稳定程度的提高,Al2TiO5 ZrO2 材料的RT~1 000 ℃热膨胀系数逐步降低,这与陶瓷复合体热膨胀系数的常规相背。ATZ 5试样的抗折强度为39.15 MPa,吸水率为3.28%,热膨胀系数为4.46×10-6/℃,其抗热震性能优良,可承受的热震温差是P ZrO2 试样的1.6倍。 相似文献
12.
Thermodynamic assessment in the ternary systems ZrO2 -CeO2 -Y2 O3, ZrO2 -CeO2 -Ce2 03 and the limiting binaries ZrO2 -Y2 O3, ZrO2 -CeO2, CeO2 -Y2 03, ZrO2 -Ce2O3, CeO2 -Ce2O3 as well as the modeling for oxides are reviewed comprehensively. Based on the recent estimations on the YO1.5-CeO2, ZrO2-CeO2 and ZrO2 -YO1.6 systems, isothermal sections at 1273 and 1 973 K of the ternary CeO2- ZrO2-YO1.5system are calculated. In the system of ZrO2-CeO2-Ce2O3, the complex relation between the nonstoichiometry （y） in CeO2-x, the composition of the ZrO2 -CeO2 solid solution and the oxygen partial pressure （Po2 ） for different ZrO2 containing solid solutions CexZr1-xO2-x. are evaluated from 1 473 to 1 773 K. The relation between the degree of Ce^＋4 reduction to Ce.3 under different Po2 in the fluorite CeO2-xy and CexZr1-xOz-x solid solutions at different temperatures can be used as a guide in the development of functional ceramics. 相似文献
13.
1IntroductionZrO2-containing ceramics receive extensive attentionbecause of their great i mportance in science and tech-nology[1,2].Zirconia doped with divalent or trivalentoxides has been proved to be an i mportant solid elec-trolyte,finding wide usage in oxygen sensors and fuelcells.It is also well known that Y2O3-stabilized tetra-gonal ZrO2polycrystals(Y-TZP)possess excellent me-chanical properties at roomtemperature,combining astrength higher than1000MPa and a toughness be-tween6MPa·… 相似文献
14.
王少辉 《绵阳师范学院学报》2010,29(2):39-43
首次采用高温快速合成方法成功地将比例适当的Eu2O3和WO3粉末合成了形貌良好的Eu2（WO4）,材料,并对该材料使用了多种分析手段进行分析。拉曼光谱分析说明在合适工艺参数下高温快速烧结可避免原料挥发,使原料完全参与反应。X射线衍射（XRD）分析表明合成物主要是Eu2（WO4）3材料,属空间群C12／cl,具有单斜结构,不可能具有负热膨胀特性。扫描电镜（SEM）发现合成物晶粒呈不规则的多边形、排列致密,少有气孔、大小在10～100μm之间不等。能量散射光谱（EDS）分析显示合成物内部成分分布均匀。 相似文献
15.
首次采用高温快速合成方法成功地将比例适当的Sc2O3和WO3粉末合成了形貌良好的Sc2（WO4）3材料,并对该材料使用了多种手段进行分析。拉曼光谱分析说明在合适工艺参数下高温快速烧结可避免原料挥发,使原料完全参与反应。X射线衍射（XRD）分析表明合成物主要是Sc2（WO4）3材料,属空间群Pnca,具有正交结构,可以呈现负热膨胀特性。扫描电镜（SEM）发现合成物晶粒分散性好,呈链状并互相纠缠在一起。能量散射光谱（EDS）分析显示合成物内部成分分布均匀。 相似文献
16.
设计了Ti(C,N)基超细金属陶瓷制备及表征综合实验。以Ti(C,N)-Mo2C-WC-Ni/Co系为研究对象,改变化学成分、湿磨工艺、生坯密度、烧结工艺,并研究上述因素对超细金属陶瓷微观组织和孔隙度、密度、硬度和强度等性能的影响。研究结果表明:WC和Mo2C的添加都会导致环形相的形成,微观形貌随添加量变化;球料比、研磨时间和球磨机转速对研磨效率的影响是一致的,但这些参数的过度增大会引起杂质的产生和设备的磨损;高的生坯密度有利于减小烧结后的孔隙度;烧结温度和时间对金属陶瓷的致密化和晶粒长大都有重要的影响。 相似文献
17.
通过对康庄磷化厂生产线钢结构工房3#厂房副跨改造难点进行分析,在与原有钢柱的连接问题上采用一小牛腿与原钢柱等强度焊接,再用高强度螺栓把牛腿与钢梁连接;在屋面彩板的搭接及防水问题采用将固定支架上部的彩板割开,然后将要搭接的彩板和原来的彩板在支架上部处内搭接,再在接口处用密封条封闭的方案;在柱距为16m处的柱间及屋面板衔接问题上采用矩管平面桁架。 相似文献
18.
首次采用高温快速合成方法成功地将比例适当的Sc2O3和WO3粉末合成了形貌良好的Sc2（WO4）3材料,并利用多种分析手段对该材料进行分析．拉曼光谱分析说明在合适工艺参数下高温快速烧结可避免原料挥发,使原料完全参与反应．X射线衍射（XRD）分析表明合成物主要是Sc2（WO4）3材料,属空间群Pnca,具有正交结构,可以呈现负热膨胀特性．扫描电镜（SEM）发现合成物晶粒分散性好,呈链状并互相纠缠在一起．能量散射光谱（EDS）分析显示合成物内部成分分布均匀． 相似文献
19.
简要介绍了ZrO_2/SO_4~(2-)类固体超强酸的制备及其改性;综述了近年来此类催化剂以其独特的不溶性、酸性、活性、选择性在有机合成反应中的广泛应用. 相似文献