微波合成Ca_3Co_4O_9热电材料的微观结构和性能

利用微波技术合成了Ca3Co4O9化合物,考察了微波加热时间对产物纯度和微观结构的影响;再利用微波及常规烧结技术制备了Ca3Co4O9热电陶瓷片,考察了烧结时间、烧结方式对材料微观结构和热电性能的影响.结果表明:二次微波烧结30 min制备的热电陶瓷片在所测试温度范围内具有低电阻率、高塞贝克系数及最佳功率因子,其中966 K时微波产物的最大功率因子为0.141 m W/m K2,而常规高温烧结产物的功率因子为0.120 m W/m K2.     

微波烧结陶瓷装备的研制

微波烧结陶瓷装备关键技术是微波加热,其原理是物质在微波作用下发生界面极化、偶极转向极化、电子极化、原子极化等方式,将微波的电磁能转化为热能,使原料在微波场中整体加热至烧结温度而实现烧结的过程.     

现场岩土热物性参数的影响因素分析

对邢台市一试验井分别进行3d和2d的热响应试验,研究加热功率、测试时长、土壤初始温度对岩土热物性参数的影响。结果表明,同一测试孔在不同的加热功率下的岩土热物性参数存在差异;测试时长为48~64 h时测得的岩土热物性参数比较稳定;土壤初始温度越高,岩土热扩散系数越小。     

圆柱形微波多模烧结腔烧结Al_2O_3陶瓷的性能

应用微波加热技术进行高纯Al2O3陶瓷烧结是一种理想的选择.本文使用一种新型的圆柱形微波多模烧结腔体进行了Al2O3陶瓷的烧结研究,该设备可在短时间内达到较高的烧结温度,并能实现坯体的整体烧结.分别对纯Al2O3粉体和Al2O3/MgO混合粉体进行了烧结实验,结果表明,添加MgO作为助烧剂烧结得到的陶瓷试样的相对密度高于纯Al2O3粉体烧结得到的陶瓷试样,在1 700℃下保温40 min,其相对密度可以达到理论密度的97.8%,维氏硬度达22.3 HV/GPa.从SEM图中可观察到试样微观结构良好,晶粒大小均匀,致密化程度高.     

圆柱形微波多模烧结腔烧结Al2O3陶瓷的性能

应用微波加热技术进行高纯Al2O3陶瓷烧结是一种理想的选择.本文使用一种新型的圆柱形微波多模烧结腔体进行了Al2O3陶瓷的烧结研究,该设备可在短时间内达到较高的烧结温度,并能实现坯体的整体烧结.分别对纯Al2O3粉体和Al2O3/MgO混合粉体进行了烧结实验,结果表明,添加MgO作为助烧剂烧结得到的陶瓷试样的相对密度高于纯Al2O3粉体烧结得到的陶瓷试样,在1 700℃下保温40 min,其相对密度可以达到理论密度的97.8%,维氏硬度达22.3 HV/GPa.从SEM图中可观察到试样微观结构良好,晶粒大小均匀,致密化程度高.     

微波混合加热中SiC预加热体工艺参数对升温特性的影响

微波混合加热是利用微波烧结低介电损耗陶瓷材料的一种有效方法,SiC是一种典型的预加热体材料。本文利用自制的微波烧结系统,通过实验研究了SiC的用量、粒径、成型温度等参数对其微波场中升温特性的影响,对微波场中SiC预加热体的应用具有重要意义。     

微波混合加热中SiC预加热体工艺参数对升温特性的影响

微波混合加热是利用微波烧结低介电损耗陶瓷材料的一种有效方法,SiC是一种典型的预加热体材料.本文利用自制的微波烧结系统,通过实验研究了SiC的用量、粒径、成型温度等参数对其微波场中升温特性的影响,对微波场中SiC预加热体的应用具有重要意义.     

蒸汽吞吐水平井加热半径计算新模型

基于水平段热物性参数计算模型,利用非活塞式水驱油理论和保角变换理论将油藏内渗流与水平段管流进行耦合,建立了蒸汽吞吐水平井加热半径模型。研究了热物性参数、加热半径沿水平段的分布规律和不同影响因素对蒸汽干度、加热半径分布的影响。研究表明:加热半径沿水平段分布呈"U"型;注汽速度增加,热损失降低,加热半径基本不变;周期注汽量增加,热损失不变,加热半径增加;水平段长度增加,蒸汽干度沿程降低变缓,但指端蒸汽干度降低。该模型对阐明注蒸汽油藏内渗流规律,优化注汽参数具有重要意义。     

陶瓷材料的微波烧结特性及应用

介绍了微波烧结陶瓷材料的应用历史、基本原理，分析了陶瓷材料的微波烧结特性和微波烧结在氧化物陶瓷、非氧化物陶瓷及透明陶瓷方面的应用，指出了应用中存在的一些待解决的问题，展望了微波烧结陶瓷材料的应用前景。     

微波烧结BaTiO3陶瓷的微结构

本文报道了微波烧结ＢａＴｉＯ３陶瓷的初步研究结果。利用微波烧结的ＢａＴｉＯ３陶瓷、与常规烧结相比,其轴向收缩率显著地不同。采用ＳＥＭ观察其微观结构也与常规烧结有显著的差异。ＸＲＤ分析其结构为四方晶系,初步推断此现象与ＢａＴｉＯ３陶瓷在微波场中的取向生长有关。     

Numerical modeling dynamic process of multi-feed microwave heating of industrial solution media

The exothermic efficiency of microwave heating an electrolyte/water solution is remarkably high due to the dielectric heating by orientation polarization of water and resistance heating by the Joule process occurred simultaneously compared with pure water.A three-dimensional finite element numerical model of multi-feed microwave heating industrial liquids continuously flowing in a meter-scale circular tube is presented.The temperature field inside the applicator tube in the cavity is solved by COMSOL Multiphysics and professional programming to describe the momentum,energy and Maxwell's equations.The evaluations of the electromagnetic field,the temperature distribution and the velocity field are simulated for the fluids dynamically heated by singleand multi-feed microwave system,respectively.Both the pilot experimental investigations and numerical results of microwave with single-feed heating for fluids with different effective permittivity and flow rates show that the presented numerical modeling makes it possible to analyze dynamic process of multi-feed microwave heating the industrial liquid.The study aids in enhancing the understanding and optimizing of dynamic process in the use of multi-feed microwave heating industrial continuous flow for a variety of material properties and technical parameters.     

FINITE ELEMENT COMPUTER MODEL OF MICROWAVE HEATED CERAMICS

At present,the concerned papers appeared in special maga-zines abcout discussing or introducing finite element method for calcu-lating temperature distribution in ceramic body during microwave sin-tering,are not a good many,but it seems that finite element method ismore convenient than finite difference method in dealing with specialor complex geometry of ceramic body.In this paper,we describe a 3D finite element model simulatingthe heating pattern of ceramic microwave sintering in TE_(10N)single-mode rectangular cavity in which the microwave energy deposition pat-tern in the samples can be expressed as an analysis function of space,and present a series of transient temperature distributions and heatingrates of ceramic cylinders and cuboids under variable thermal conduc-tivities,dieletric loss factors,power consumer levels,etc.These digitalsolutions may provide a better understanding of eliminating thermalrunaway and improving temperature homogeneity.     

Analysis and control of the thermal runaway of ceramic slab under microwave heating

Thermal runaway is a special macroscopic phenomenon of the dielectrics during microwave heating, in which there is a big jump of the steady state temperature while the applied microwave power varies slightly. It hinders the applications of microwave heating technique in industry. A simulation based on the finite difference time domain (FDTD) method to solve Maxwell’s equations coupled with the finite difference (FD) method to solve a heat transfer equation (HTE) is presented, and the temperature variation in a ceramic slab during microwave heating is obtained. The temperature variation in the ceramic slab during microwave heating is simulated with various ceramic parameters and applied microwave powers so as to analyze the condition under which thermal runaway is introduced. Moreover, a microwave power control method, based on a single temperature threshold and dual applied microwave powers, is presented, which improves microwave heating efficiency and controls thermal runaway. The relation between the final applied microwave power and the monitored temperature threshold is presented as well. This method can be applied in many fields related with microwave heating techniques. Supported by the National Natural Science Foundation of China (Grant Nos. 60301004 and 60411140521), Korea Science and Engineering Foundation (Grant Nos. F01-2004-000-10263-0, R14-2003-019-01000-0 and KRF-2006-070-C00014)     

Numerical simulation of the temperature field of titania-bearing BF slag heated in a microwave oven

Considering the characteristic of selective heating of microwave and the treatment of titania-bearing BF slag, a mathematical model for the heating of a slag specimen is developed. The temperature distribution in the specimen is studied by numerical simulation. The temperature in the center of the cylindrical slag specimen is the highest and the temperature decreases when the radius increases rapidly. In this case, the temperature rising rate decreases with heating time rapidly, and it tends to zero when the heating time is up to 150 s.     

Crystallization behavior of polymer derived silicon carbide sintered through microwave heating technique

A self-crosslinkable liquid highly branched polycarbosilane(LHBPCS) with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.     

烧结温度对BN陶瓷材料强度的影响

采用热压烧结(HP)法制备纯BN陶瓷和B2O3-BN陶瓷复合材料．利用三点弯曲方法测定了这两种材料的抗弯强度、弹性模量等力学性能，通过扫描电镜对两种材料的断口进行了分析。结果表明：纯BN陶瓷烧结温度达到1800℃时相对质量密度和强度较低；添加B2O3烧结温度超过900℃时可以形成液相，改善了BN的烧结性能，提高了B2O3-BN复合陶瓷的相对质量密度，从而提高了材料的强度。     

助烧剂对(Zr_(0.8)S_(0.2))TiO_4晶相与介电性能的影响

采用传统的固相反应法制备(Zr0.8S0.2)TiO4陶瓷样品,研究不同含量ZnO、Fe2O3、NiO对(Zr0.8S0.2)TiO4材料的晶相、显微结构与介电性能的影响。结果表明:上述添加剂可以降低(Zr0.8S0.2)TiO4陶瓷的烧结温度,当助烧剂ZnO、Fe2O3、NiO的质量分数分别为0.5%、0.5%、0.2%时,烧结温度为1 350℃时已烧结成瓷,没有气孔,致密性好,具有α-PbO2型结构(Zr0.8Sn0.2)TiO4相;随着烧结温度的升高,陶瓷样品出现过烧,介电常数εr由1 300℃的39.833 4下降到1 400℃的26.298 4,介质损耗tanδ在10-3数量级。     

基于超声背向散射积分的微波热疗无损测温

旨在探索一种基于超声背向散射积分的微波热疗无损测温方法,利用水浴加热实验系统,以新鲜离体猪肝组织为研究对象,通过采集不同温度下的超声原始射频信号,分析各温度下组织的背向散射积分,建立背向散射积分与温度相关性模型用于微波加热实验过程中温度的检测.所建相关性模型为:超声背向散射积分值为0.062×t+3.591;该模型在低温段(≤70℃)测温误差较小(<5℃),在高温段(>70℃)测温误差较大(>10℃).研究结果表明:超声背向散射积分可用于常规热疗无损测温;微波热疗温度分布不均使得检测较为困难;利用正常与热凝固组织背向散射积分的差异进行热凝固区检测具有一定优势.     

微波烧结Nd：YAG透明陶瓷及工艺研究

采用溶胶凝胶法和微波烧结工艺制备掺杂钕离子浓度为1.0%（分子百分数）的Nd：YAG透明陶瓷。研究前驱粉体煅烧制度对粉体的纯度、粒度和晶相生成的影响,同时探索微波烧结法制备Nd：YAG陶瓷的工艺方法。结果表明,溶胶凝胶法制得的Nd：YAG粉体晶相转换温度低于固相合成法,900℃煅烧温度可完全形成YAG晶相。煅烧温度和升...     

低温燃烧法制备YAG透明陶瓷纳米粉体

透明YAG陶瓷具有较好的化学稳定性、光学性能和高温性能,是单晶激光材料的有力替代品,纳米YAG粉体的合成有利于制备性能优异的YAG透明陶瓷．采用低温燃烧法,以Y2O3、Al（NO3）3·9H2O、柠檬酸、乙二醇为原料,采用TG／DSC,XRD和SEM等测试手段对YAG前驱体进行表征,对YAG前驱体在不同温度下进行煅烧．结果发现,在900℃左右已完全转变成YAG相,最终获得单分散、无团聚、形状规则的YAG纳米粉体．