【作者】 陈利祥；

【导师】 尹衍升； 刘英才；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2011， 博士

【摘要】 结构陶瓷具有耐高温、耐氧化、耐腐蚀、耐磨耗等优点,因此,在非常严苛的环境或工程应用条件下,所展现的高稳定性与优异的机械性能,使其在材料工业上倍受瞩目,其市场潜力巨大。结构陶瓷的微波烧结/焊接技术是一种利用微波加热对材料进行烧结/焊接。它是利用微波具有的特殊波段与材料的基本细微结构耦合而产生热量,使其材料整体加热至烧结/焊接温度而实现致密化的方法,是制备新型高性能结构陶瓷材料和产品的重要技术手段。本论文研究的目的是借助先进的电磁仿真软件研究烧结/焊接腔空腔和加载试样时电磁场的分布规律,通过精确的图形显示和色彩对比来表征微波电磁场的分布,对试样的几何尺寸与微波参数对电磁场分布的影响进行分析与探讨。掌握单模/多模微波烧结/焊接腔内电磁场的分布以及如何控制其均匀范围的方法,可确定实际工艺过程中试样的大小和放置位置,提高试样烧结/焊接的成功率,制备出尺寸较大且形状复杂的结构陶瓷零件,对微波烧结/焊接工艺都具有重要的指导意义,对改进和研发新的先进实验或生产设备具有非常重要的应用价值。利用HFSS软件,对单模烧结腔的谐振特性和电磁场的分布规律进行数值模拟,分析其建模仿真中的影响因素,并且借助实验进行验证。模拟其加载试样后的电场分布,探讨试样的几何尺寸对烧结腔和试样内部电场分布的影响。单模烧结腔在加载圆柱状试样后,腔内电场的三个均匀区域都有不同程度的缩小,两边的均匀区域缩小程度相对较小,中间的均匀区域由于试样吸收微波能量受到较大影响,均匀区域的场强密度和稳定性都大大降低。试样不同的几何尺寸对烧结腔和试样内部电场分布的影响:当表面半径R较小时,试样的电场分布从里到外逐渐增强,R的增大使试样中心和左右两端出现较高电场,腔内中间的均匀区域受到破坏,两边的受到“挤压”。轴向高度H不同都会使试样内部出现完全相反的电场分布,当H处于发生变化的分界点时,试样内部的场强趋于一致。H的增大使径向表面退极化场的减少幅度大于轴向表面的增加幅度,也使腔内中间的均匀区域的场稳定性逐渐升高。模拟单模微波焊接腔空载和加载试样后的电场分布,探讨试样的放置方向对烧结腔和试样内部电场分布的影响。研究结果表明:沿Z轴方向摆放时,负载的接触面上电磁场的分布强度较强且相对均匀。对微波多模谐振腔内不同尺寸的烧结试样时,腔内和试样内部电场分布的进行了模拟并讨论,当试样高度不变时,随着直径的减小,多模烧结腔内的电场均匀性呈现上升趋势,同时烧结腔内的电场强度E也逐渐升高,试样尺寸为d=80mm,h=100mm时,试样内部电场分布较为均匀。当试样直径不变时,随着高度的减小,多模烧结腔内的电场均匀性也是呈现上升趋势,但此时腔体内的电场强度呈现下降趋势,当试样尺寸为d=40mm,h=80mm时,试样内部电场分布同样比较均匀。后者试样内部的电场强度较前者要强很多。多模腔内焊接试样的摆放方向对电磁场分布影响较小,而试样的大小对焊接过程中的试样接触面上的电磁场分布有较大的影响,研究表明,焊接面场强分布均匀的范围为半径r小于40mm高度h小于50mm。更多还原

【Abstract】 Structural ceramics have tremendous market potential profit for the highstability and good mechanical properties in very harsh environment or engineeringapplication conditions, such as high-temperature resistance, oxidation resistance,corrosion resistance and wear resistance. Microwave sintering/welding technologyis achieved by using the microwave absorption property of the materials. The heatgenerated to high temperature by coupling of the special band of the microwaveand the basical material microstructure. The materials can be overall heated forsintering/weldingdensification.This technologyis important for preparingthe newhigh performance materials and products of structural ceramics.By using the simulation software to simulate the electromagnetic fielddistribution inside the specimen and the cavities, the research work of this thesisprovides the technical support in improving the microwave sintering/weldingprocess and design the new advanced R&D microwave heating equipment, Thetechnique is also can be used to analyze the influence of the microwave parametersand sample dimension on electromagnetic field distribution.The accurate graphic display and color contrast were used to characterizemicrowave electromagnetic field distribution rule of the geometric size of samples.The simulation is achieved by using high frequency structure simulator(HFSS) based on the finite element method. The accuracy and reliability of HFSSapplications to model and simulate the microwave sintering are proved by thenumerical simulation and experimental results of field contour distribution. Theimproved cavity design with an extended distribution range of homogenous fieldbased on the simulation is also studied, which can be used for sintering larger sizesamples.Three uniform region of the electromagnetic field decreases to different levels when the cylindrical samples are loaded on single-mode sintering cavity.The smaller reduction can be obtained on the evenly area of both-side. The largerreduction can be obtained on the middle uniformity region due to the largermicrowave energy absorption. The uniform field density and stability of thisregion is greatly reduced. Improved single-mode sintering cavity can furtherextendthe uniform field space range, uniform field volume is doubled.The electricfield distribution of the sinteringcavityand the effects of the sample geometrysizeand microwave parameters are studied as follow: firstly, the electric field of thesample increases graduallyfrom inside to outside when the surface radius R is verysmall; secondly, the higher electric field appears in the center and both sides of thesample with increases of the radius R. The completely opposite electric fielddistribution is obtained when the axial height (H) and the relative dielectricconstantεr is different. The internal electric field of the sample becomes uniformwhen the axial height (H) and the relative dielectric constantεr at the point of thechanging boundary. The reduction scale of the radial surfacedepolarization field islarger than the increased scale of the axial surface depolarization field when theaxial height H is increased. The stability of the middle uniform region inner thecavity increases gradually. The depolarization field of the sample is increased dueto the increases of the relative dielectric constantεr..The stability of the middleuniform region inner the cavity decreases gradually. The inner electric field of thesample is increased gradually from inside to outside while the inner electric fieldof the cavity is not be changed when the tangent of dielectric lose angle (tgδ) isdifferent. The depolarization field increases with the increasing of the tangent ofdielectric lose angle (tgδ)The electric field distributions of the single-mode microwave welded cavityand the loaded sample are simulated. The influences orientation of the sample onthe inner electric field of the cavityand the loaded samples are also discussed. Theresults show that the contact surface electromagnetic field intensity is muchstronger and relatively uniform when the orientation of the sample is along the Zaxis. The uniformity of the inner electric field distribution of the different sizedsintered sample in the microwave multimode resonant cavity is also simulated anddiscussed. If the height is not changed, the inner electric field intensity anduniformity in the microwave multimode resonant cavity increase with thedecreasing of the diameter. The inner electric field distributions of the sample isuniform with the sample size of d = 80mm, h = 100mm. If the diameter is notchanged, the inner electric field uniformity increases while the electric fieldintensity decreased in the microwave multimode resonant cavity with thedecreasing of the height. The inner electric field distributions of the sample isuniform with the sample size of d = 40mm, h = 80mm. The internal electricintensityof the latter sample is much stronger than that of the former one.For the multi-mold cavity welding sample, the influence of the loadingdirection on the electromagnetic field distribution is small, while the influence ofthe sample dimension on sample contact surface electromagnetic fields distributionin the welding process is much higher. The results show that the uniformelectromagneticfields distribution area is in theregion of radius R less than 40mmand height less than 50 mm.In conclusion, the technical is very important to improve the microwavesintering/welding process and design the new advanced R&D microwave heatingequipment by simulating the electromagnetic field specimen and distributionsimulation in the single and multi mode sintering/welding cavities and the loadedsamples. The sample dimension and loading direcution can be controlled in thesintering/weding process to improve the success ratio of the microwavesintering/weding. The larger size and complex structural ceramics can be easilyfabricated.更多还原