陶瓷材料微波烧结工艺与机理研究现状

微波烧结作为一种新型材料烧结技术,在陶瓷材料制备领域受到越来越多的关注.与传统烧结技术相比,微波烧结具有快速高效、节能环保以及改善材料微观结构,提高材料性能的优点.本文介绍了传统烧结和微波烧结的特点,对比了传统烧结和微波烧结陶瓷材料的烧结工艺和力学性能;列举了运用微波烧结法制备的典型结构陶瓷的烧结工艺及其力学性能;全面综述了陶瓷材料微波烧结机理;最后提出了微波烧结在未来发展中亟待解决的问题.     

细晶钛酸钡陶瓷的烧结方法

本文用两步法、两段法、高压成型常压烧结、高压烧结和掺杂烧结等特殊方法烧结得到了细晶钛酸钡陶瓷,它们的烧结温度低于常规烧结的温度.用扫描电子显微镜观测了陶瓷的显微结构.结果表明:用这些特殊方法烧结得到的陶瓷的晶粒尺寸远小于常规法烧结得到的钛酸钡陶瓷的尺寸.此外,对它们的烧结机理进行了简单的解释.     

微米级α-Al2O3陶瓷恒速无压主烧结曲线的建立

主烧结曲线对于预测陶瓷的烧结行为非常有用,以主烧结曲线理论为基础,对微米级α-Al2O3,的恒速无压烧结行为进行了研究.根据Hansen提出的全期烧结模型,结合低升温速率条件下热膨胀仪记录的烧结数据建立了α-Al2O3(平均粒径为2.5μm)的主烧结曲线,并由此得到其烧结过程中的表观激活能为1148kJ/mol.为验证所建主烧结曲线的正确性,对同批次坯体样品进行不同路径的烧结,用Archimedes法实测烧结体密度,所测结果与主烧结曲线预测的结果相一致,从而证明了所建主烧结曲线的正确性.因此微米级α-Al2O3主烧结曲线对烧结路径不敏感,烧结体的相对密度仅是时间和温度的函数,可以预测烧结收缩率和最终相对密度,反之,可以根据目标相对密度制定相应的烧结制度.     

无烧结助剂SiC陶瓷的高压烧结研究

以纳米SiC为原料,用两面顶压机在不同工艺条件下(1100-1300℃,4.0-4.5GPa,20-35min)实现了无烧结助剂添加的SiC陶瓷体的烧结.研究了烧结工艺对SiC陶瓷性能的影响.用XRD、SEM、显微硬度测试仪等对SiC高压烧结体进行了表征.结果表明:采用超高压工艺可实现无烧结助剂SiC陶瓷高致密化烧结;烧结体晶粒长大得到抑制,维持在纳米级,晶格常数收缩发生了收缩;烧结体显微硬度和密度随烧结温度、烧结压力、保温时间的升高或延长而提高.在4.5GPa/1250℃/35min的超高压烧结条件下烧结的无烧结助剂SiC致密度达到96%,且显微硬度达到Hv1.96 3850.     

利用主烧结曲线预测TiO2陶瓷无压烧结显微组织演变

纳米金红石TiO2粉末在高温热膨胀仪中进行恒速无压烧结,升温速率为2℃/min和5℃/min,热膨胀仪自动记录烧结收缩量,根据全期烧结模型,建立TiO2主烧结曲线;利用阿基米德法测量烧结体的相对密度,利用扫描电镜观察烧结体在不同温度的显微组织演变.结果表明:利用主烧结曲线得到的相对密度和Archimedes法实测的密度吻合,证明了主烧结曲线对烧结路径不敏感,烧结体的相对密度仅是时间和温度的函数.烧结体的显微组织是烧结温度和时间的函数,烧结体的相对密度和显微组织有关联,主烧结曲线理论可以用来预测和控制烧结体的相对密度、显微组织和陶瓷性能.     

微波烧结SiC-Cu/Al复合材料的工艺及机理

用微波烧结工艺成功制备了铜包裹碳化硅颗粒增强铝基(SiC-Cu/Al)复合材料,利用扫描电镜和X射线衍射分析仪对烧结样品进行表征,并讨论了烧结过程及机理.研究表明:采用多晶莫来石纤维棉、硅碳棒和氧化铝坩锅组合设计的保温结构能很好地促进烧结.烧结温度为720℃时,SiC-Cu/Al复合材料的密度取得最大值为2.53g/cm3.SiC-Cu/Al复合材料的硬度随烧结温度的升高的变化成马鞍状.烧结温度对样品显微结构的影响较大,随着烧结温度的升高,相分布的均匀性降低,在较高的烧结温度下会出现SiC颗粒的偏聚.涡流损耗和界面极化损耗是促进微波烧结的主要动力.     

陶瓷材料的微波连续化烧结系统研究

陶瓷材料烧结通常需要整体在窑炉内烧结,以保证材料性能.本文利用微波烧结的特性,研究了混合场的模型,设计了微波连续化烧结系统,并在该系统上成功地实现了Φ40×2400mm的陶瓷辊棒的微波连续化烧结.结果表明,微波烧结陶瓷辊棒的抗热震性能及抗弯强度均有较大幅度提高.本研究对微波烧结的实用化具有较大的推动作用.     

纳米陶瓷的特性和烧结方法研究进展

本文综述了纳米陶瓷在超塑性、铁电性能、力学性能和增韧等方面的特殊性能,介绍了纳米陶瓷的两步法烧结、放电等离子烧结、超高压烧结和微波烧结等成功的烧结方法并阐述了这些特殊烧结方法的烧结机理.此外,对纳米复相陶瓷的特性也进行了介绍.     

AlN陶瓷烧结技术研究进展

氮化铝(AlN)因其具有高热导率,作为基片材料在电子元器件中得到日益重视.本文主要论述了氮化铝陶瓷制备过程中各种烧结参数,包括烧结助剂、烧结气氛、保温时间、常压烧结、热压烧结、微波烧结和等离子烧结等对氮化铝陶瓷性能的影响.并指出可通过合适的AlN粉体制备技术,结合快速烧结方法可得到具有晶粒细小、结构均匀、高致密度和高导热率的AlN陶瓷.     

无压烧结碳化硅研究进展

碳化硅具有良好的高温性能以及化学稳定性,已广泛应用于许多领域.综述了无压烧结碳化硅烧结助剂体系的研究进展,综述了碳化硅原料种类、烧结助剂种类及用量、成形工艺、烧结工艺对无压烧结碳化硅性能的影响.     

Preparation of transparent Bi2O3-ZnO-B2O3 glass by conventional sintering at low temperatures

Glass components fabricated by the sintering route have wide-ranging applications. However, one issue is that the crystallization tendency of glass powders often leads to residual pore-glass interfaces and crystal-glass interfaces, thereby causing strong light scattering and rendering the sintered glass opaque. This issue is particularly pronounced in glasses with a low glass transition temperature (T_g) due to their weak bonding and thus high crystallization tendency. In the present study, a Bi₂O₃-ZnO-B₂O₃ glass with a low T_g of 364°C was fabricated using the conventional sintering method to explore whether transparent glass materials can be obtained. The temperature range of crystallization of the glass powders was analyzed using differential scanning calorimetry. X-ray diffraction was employed to analyze the crystalline phases formed in the sintered glasses. The microstructure of the sintered glasses was examined using scanning electron microscopy. The optical transmittance of the sintered glasses was measured using ultraviolet-visible spectroscopy. The results show that transparent sintered glasses with the highest transmittance of 54% at the wavelength of 650 nm can be obtained by using a coarser initial particle size, lower forming pressure, and an appropriate sintering temperature/time (430°C/30 min). It is suggested that this combination of processing parameters can suppress glass crystallization while maintaining a low glass viscosity during sintering.     

Rapid manufacturing of silica glass parts with complex structures through stereolithography and pressureless spark plasma sintering

This paper reports a method for preparing silica glass by pressureless spark plasma sintering (PL-SPS), which can rapidly manufacture silica glass parts with complex structures by coupling with stereolithography 3D printing technology. The rapid sintering process and microstructure evolution of silica glass prepared by PL-SPS were mainly investigated. The experimental results showed that the sintering temperature and dwelling time were the main factors affecting the PL-SPS of silica glass. The microstructure evolution indicated that the densification rate of the sample was very fast from 1250 °C to 1300 °C, and the interlayer defects caused by the printed layer thickness could be healed in the final stage of densification. Like conventional pressureless sintering, silica glass with a relative density of more than 99% and a visible-light transmittance of more than 90% could also be obtained through PL-SPS, but the entire working time was shortened from 22.53 h to 0.49 h.     

反应析晶烧结法制备硅灰石玻璃陶瓷

本文提出了一种直接利用废玻璃制备硅灰石玻璃陶瓷的新工艺:反应析晶烧结法。将高岭土和碳酸钙为主要原料合成的析晶促进剂加入到废玻璃粉末中烧结,通过两者间的反应析出硅灰石。研究了析晶促进剂含量和烧结温度对硅灰石玻璃陶瓷的组织、烧结和性能的影响,结果表明:随着析晶促进剂含量的增加,玻璃陶瓷的体密度和开孔隙率增加,强度先增后降。提高烧结温度促进反应析晶,并导致玻璃陶瓷的体密度、开孔隙率和强度降低。析晶促进剂含量为15%,烧结温度为850℃时,制得的硅灰石玻璃陶瓷的力学性能最佳。     

Sintering and reactive crystal growth of diopside-albite glass-ceramics from waste glass

Diopside-albite glass-ceramics were fabricated by sintering the powder mixtures of crystallization promoters and waste glass. Two kinds of promoters were synthesized using kaolin clay, talc and chemical reagents. The crystalline phases were formed by a reactive crystallization between promoters and glass during sintering. The effect of promoter components, additions and sintering temperatures on the crystallizing and densifying behavior, microstructures and mechanical properties of glass-ceramics was investigated. The results showed that the higher densities and better mechanical properties were obtained for the glass-ceramics with 12-15% crystallization promoters sintered at 950 °C for 2 h.     

低温低膨胀系数高硬度无铅电子玻璃粉

叙述了低温低膨胀系数无铅电子玻璃粉研制过程。当Bi2O3的质量分数在60%,B2O3在10.7%,ZnO在21.3%,SiO2在5%,其它成分在3%时,可获得膨胀系数为(55～62)×10-7/℃,软化点为380～385℃,玻化温度在450±10℃,附着力优良的无铅玻璃粉。     

Constrained Densification Kinetics of Alumina/Borosilicate Glass + Alumina/Alumina Sandwich Structure

The densification kinetics and mechanism of a low-temperature cofirable borosilicate glass (BSG) + alumina during the constrained sintering of a sandwich structure of alumina/(BSG + alumina)/alumina has been studied. The densification kinetics becomes slower when the BSG + alumina tape is constrained during firing. However, a viscous flow-controlling mechanism of the BSG also is still operative during free and constrained sintering. The densification behavior of constrained sintering can be mathematically described by free sintering, using the viscous analogy for the constitutive equations of a porous sintering glass.     

Suppression of phosphor‐glass reactions in YAG:Ce phosphor‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass (BiG) by sintering route. A high‐T_g silicate glass (SiG) was also used for comparison. Dense (porosity<2%) phosphor‐glass composites were obtained after sintered at 800°C (for SiG) and 325°C (for BiG). XRD quantitative analysis indicates that the loss of phosphor content is in the range of 2.5%‐22%, caused by partial dissolution of phosphor particles into the glass matrix during sintering. The element distribution across the interface and within the reaction zone between phosphor and glass was analyzed by TEM/SEM‐EDS. The intrinsic emission characteristic of YAG:Ce is nearly not altered, possibly resulted from the slight modification of the YAG phase during sintering. Thus the final emission intensity of the sintered body is mainly determined by the residual amount of the YAG:Ce phase. Replace the high‐T_g SiG glass by the low‐T_g BiG glass, prenitridize the YAG:Ce phosphor, and change the sintering atmosphere from air to N₂ suppress the loss of phosphor during sintering. Therefore, the resulting loss of emission intensity of the phosphor‐embedded glass material can be reduced to only about 1.8%.     

Bi2O3-ZnO-B2O3低熔点封接玻璃的烧结特性

利用X射线衍射、扫描电子显微镜对Bi2O3-ZnO-B2O3系统低熔点玻璃的烧结性能、结晶特性以及烧结后玻璃试样的结构进行了研究.结果表明:随着B2O3含量的增加,玻璃的转变温度与软化温度都随之提高,影响了玻璃的烧结.Bi2O3-ZnO-B2O3系统低熔点玻璃粉末的烧结有黏性液相参与,使得玻璃试样的致密化更加有效,效率更高.当B2O3含量为5.24%(以质量计)时,玻璃的析晶倾向增大,试样中析出了Bi2482O39晶相.当温度继续升高时,试样的烧结收缩出现了"滞缓",有大量的液相出现,且在表面张力的作用F出现了流散.     

单体中添加玻璃粉后的光固化研究

本文研究了在多元醇丙烯酸酯光敏体系中添加超细玻璃粉和有机载体,通过丝网印刷于玻璃基片上,研究其紫外光固化反应和烧结后的性能。     

A multiscale model for quantifying helium diffusion in porous unsintered glass

Helium‐aided sintering of porous unsintered glass is a complex multiscale process, characterised by three different timescales, namely, that of helium diffusion, heat conduction, and radial shrinkage of the glass core. This work presents a multiscale model for quantifying heat and helium diffusion in a shrinking core system by decoupling the timescales based on their orders of magnitude. We obtain analytical solutions of our model, which allow us to quantify the spatio‐temporal profiles of temperature and helium concentration in the glass during the sintering process. Our results show that the introduction of helium increases the sintering rate of glass, and we conclude that pre‐sintering heating followed by helium‐aided sintering is better than simultaneous heating and helium diffusion. We also show that the pre‐sintering heating process for a standard glass sample should not be longer than an hour for the sake of heat economy, following which we may switch to the helium‐aided sintering process, where the sintering should occur under isothermal conditions for approximately 6 h. We perform dynamic simulations using glass porosity as a parameter, and find the sintering rate to be directly proportional to the initial porosity of the glass sample.