滑石质日用细瓷的显微结构及性质

叙述了日用滑石瓷结构中的各种物相比例,主晶相类型、粒径大小及其分布状态、性质,个绍了其具有晶体小、结构细微、光学性质相似,具有同质异构体的独特显微结构,探讨了显微结构与生产工艺、各项性能的相互依赖关系。     

烧结温度对放电等离子烧结氮化硅陶瓷显微结构和力学性能的影响

以亚微米级氮化硅为原料、Al_2O_3–Y_2O_3为烧结助剂,利用放电等离子烧结(spark plasma sintering,SPS)烧结技术制备氮化硅陶瓷。用X射线衍射和扫描电子显微镜对试样的物相组成和显微结构进行分析,研究了烧结温度对氮化硅陶瓷力学性能和显微结构的影响。结果表明,采用SPS烧结技术可在较低温度下获得致密度较高、综合力学性能较好的β相氮化硅陶瓷。随着烧结温度的提高,样品致密度、抗弯强度、断裂韧性均不断增大,在1 550℃时,其抗弯强度和断裂韧性分别达到973.74 MPa和8.23 MPa?m1/2。在1 550℃以下,陶瓷样品中β相氮化硅含量可达到98%,显微结构均匀,晶粒发育良好、呈长柱状,晶间紧密连接,晶间气孔较少。继续升高温度,部分晶粒发生异常长大,产生了更多的显微孔洞,抗弯强度急剧下降。     

Microstructure Development and Dielectric Properties of Potassium Strontium Niobate Ceramics

Sintering of a KSr₂Nb₅O₁₅ powder compact at 1350°C resulted in a duplex structure. Prefiring of the compact between 1200° and 1300°C inhibited the abnormal grain growth responsible for the duplex structure. The Curie temperature and dielectric constant were dependent on the microstructure.     

分散剂对PNN-PZT压电陶瓷组织与性能的影响

压电陶瓷作为能够将机械能和电能相互转换的功能陶瓷在国防领域以及民用领域得到了非常广泛的应用。当今为了追求更高性能的压电陶瓷材料,世界各国的研究人员都将注意力由压电陶瓷材料的研究转向了压电陶瓷的制作工艺。本课题研究的目的主要是在传统的压电陶瓷制备工艺的基础上,通过在球磨过程中加入分散剂制备出性能参数更高更为稳定的压电陶瓷材料。本次实验研究发现,柠檬酸铵的分散效果较为显著,当采用烧结温度1200℃,柠檬酸铵分散剂浓度15%时能得到一个综合性能都比较稳定的压电陶瓷材料,其压电常数为603pC/N,机电耦合系数为0.536,介电常数为5354,介电损耗为2.197%。     

Microstructure and Mechanical Properties of Silicon Nitride Ceramics with Controlled Porosity

Porous silicon nitride ceramic with a porosity from 0–0.3 was fabricated by partial hot-pressing of a powder mixture of α-Si₃N₄ and 5 wt% Yb₂O₃ as sintering additive. Irrespective of the porosity, the samples exhibited almost the same microstructural features including grain size, grain aspect ratio, and pore size. Porosity dependences of Young's modulus, flexural strength, and fracture toughness ( K _{I C} ) were investigated. All these properties decreased with increasing porosity. However, because of the fibrous microstructure, the decreases of flexural strength and fracture toughness were moderate compared with the much greater decrease of Young's modulus. Thus, the strain tolerance (fracture strength/Young's modulus) increased with increasing porosity. The critical energy release rate also increased slightly with an increasing volume fraction of porosity to 0.166 and remained at the same level with that of the dense sample when the porosity was 0.233. They decreased as porosity increased further.     

BNKT-xLaFeO3压电陶瓷的性能与微结构

采用传统固相法合成了(1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xLaFeO3无铅压电陶瓷.通过XRD分析,发现该三元体系压电陶瓷均能形成单相钙钛矿结构,并在x=0.005～0.01时范围内具有三方和四方共存结构,为该体系的准同型相界.并研究了该体系压电陶瓷的压电和介电性质.研究结果表明,在室温下该体系表...     

Formation, Microstructure, and Properties of Barium Zirconium Sulfide Ceramics

The preparation, microstructure, and properties of BaZrS₃ ceramics are described. The compound was prepared by heating either an equimolar mixture of BaS and ZrS₂ or BaZrO₃ alone in CS₂ gas. The reaction of the BaZrO₃−CS₂ system was extremely rapid, as would be expected in an autocatalytic reaction caused by very strong reduction by CS₂. Well-sintered bodies were obtained only by the BaZrO₃−CS₂ reaction. The time dependence of grain growth was affected considerably when reaction and sintering occurred above 1250° C. Non-uniform grain growth which occurs when an excess of Ba is present can be interpreted in terms of secondary recrystallization resulting from segregation of BaS at the grain boundary during sintering. The BaZrS₃ ceramic was stable in air up to 550°C and was oxidized above that temperature.     

烧结助剂对氮化硅陶瓷显微结构和性能的影响

氮化硅中氮原子和硅原子的自扩散系数很低，致密化所必需的扩散速度和烧结驱动力都很小，在烧结过程中需采用烧结助剂。烧结助剂是影响氮化硅陶瓷的显微结构和性能的关键因素之一。有效的烧结助剂不但可以改善氮化硅陶瓷的显微结构，而且可以提高氮化硅陶瓷的高温性能和抗氧化性能。     

Effects of Zirconia on Microstructure and Dielectric Properties of Barium Titanate Ceramics

Dielectric properties and structural characteristics of BaTiO₃ ceramics are significantly influenced by small addition (2 wt%) of ZrO₂. SEM and TEM observations revealed enhanced microstructural uniformity and retarded grain growth depending on sintering temperature. Above 1320°C, Zr diffusion into the BaTiO₃ lattice resulted in a chemical modification of the tetragonal structure and the development of core–shell grains. Below 1320°C, TEM analysis showed ZrO₂ at the grain boundaries as discrete particles (∼0.03μm). X-ray diffraction analysis revealed a decrease in the axial (c/a) ratio with decreasing grain size. A corresponding decrease in the spontaneous polarization, and twinned domain structures, were also observed in the fine-grained ceramics. These samples also showed a flattened permittivity response with temperature and significantly lower losses.     

富氧烧成陶瓷的物相结构与性能研究

利用不同O2浓度的模拟富氧气氛烧成陶瓷试样,采用TG/DSC、XRD、SEM、三点弯曲及阿基米德原理进行了烧成气氛中O2浓度及组分-SiO2/Al2O3变化对陶瓷试样的结构及机械强度影响研究.结果表明:富氧气氛中O2浓度的增加及组分中SiO2/Al2O3的增加对于陶瓷试样的结构改善、机械强度提高均具有促进作用.与普通空气烧成相比,富氧技术的应用能适当的缩短烧成周期,给陶瓷工业带来一定能源节约.     

反应烧结工艺对碳化硅陶瓷微结构及性能的影响

研究了脱胶温度、加硅量、升温速率及重烧次数对反应烧结碳化硅陶瓷金相组织、体积密度、力学性能和微观结构的影响.结果表明:经800℃脱胶,硅与碳化硅生坯的质量比为0.9∶1,升温速率为1.0 ℃/min时,反应烧结碳化硅陶瓷产品的性能最好,体积密度为3.09 g/cm3,维氏硬度为26.82 GPa,弯曲强度为388 MPa,断裂韧性为4.49MPa·m1/2.对渗硅不充分的不合格品进行重烧可以有效提高产品的致密度和力学性能,但是,重烧次数过多会引起晶粒粗化,从而导致力学性能下降.     

Cellular Anorthite Glass–Ceramics: Synthesis, Microstructure and Properties

Highly permeable cellular anorthite glass ceramics with porosity of ∼95% were obtained by a simple replication technique using near-stoichiometric glass powders and a polymeric foam as sacrificial template material. Impacts of sintering conditions and additions of minor constituents, respectively, on microstructural evolution and resulting macroscopic properties of the derived foams were investigated by X-ray diffraction, scanning electron microscopy (SEM), differential thermal analysis and X-ray microcomputer tomography. Apparent activation energies of crystallization and the Avrami coefficient were estimated from nonisothermal crystallization experiments to evaluate the impact of titania and zirconia, respectively, as potential nucleation agents. Consistent with SEM analyses, it was found that crystal growth occurs in two dimensions. While TiO₂ primarily acts on the viscosity of the precursor glass and, thus, on the process of sintering by viscous flow, ZrO₂ is found to exhibit at least some nucleation efficiency. As compared with sintering of ceramic powders and solid-state reactions in general, the glass ceramic route enables significant reduction in sintering time and temperature.     

Microstructure and Optical Properties of Hot Isostatically Pressed Nd:YAG Ceramics

Neodymium-doped transparent yttrium-aluminum garnet (Y₃Al₅O₁₂, YAG) (Nd:YAG) ceramics for solid-state laser material were fabricated by a solid-state reaction method using high-purity powders (Al₂O₃, Y₂O₃, and Nd₂O₃) as starting materials and capsule-free hot isostatic pressing (HIP). The mixed powder compacts were presintered at 1600°C for 3 h under vacuum, hot isostatically pressed at 1500°–1700°C for 3 h under 9.8 or 196 MPa of argon gas pressure, and then sintered again at 1750°C for 20 h under vacuum. Although the presintered specimen approached full density after HIP, its optical transmittance was quite low (∼5% at 1000 nm) because of lack of grain growth. Grain growth was observed in the specimens that were hot isostatically pressed and vacuum sintered at 1750°C for 20 h, but numerous pores occurred around the surface of these specimens. Consequently, the optical transmittance of Nd:YAG ceramics that were treated by HIP was inferior to that of the same ceramics that were sintered under vacuum only because of light scattering that was caused by the pores (at the grain boundaries) that were produced during the HIP treatment.     

原位析出片晶韧化相的SiBON玻璃陶瓷的结构与力学性能

本文对非晶态SiBON纳米粉末热压烧结研究，发现SiBON材料在1400℃时开始致密化同时开始析晶，析出晶体为h—BN，其余成分以非晶态存在。h—BN析出量随着烧结温度的升高而增多。在1400℃、1600℃和1700℃时，材料中BN形态分别为近等轴颗粒、大片晶和小片晶。这种从玻璃基体中析出的BN比通常所见的BN粉末有更完整的层片状晶体结构。这种原位析出片晶韧化相的SiBON玻璃陶瓷具有很高的力学性能。分析认为较高的强度主要归因于BN析出相对玻璃基体产生的压应力，而较高的断裂韧性来自于BN晶片所产生的裂纹偏转、桥接和晶片拔出增韧机制。     

掺杂三氧化二锑的钛酸铋钠钾陶瓷的显微结构和电学性能

采用固相合成工艺制备了（1–x）[0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3]–xSb2O3（BNKT–xSb）压电陶瓷,研究了Sb2O3掺杂对BNKT陶瓷的显微结构和电学性能的影响规律。研究表明：Sb2O3掺杂量x小于0.020时,不改变基体的钙钛矿结构,且Sb具有可变化合价,能形成＂施主＂和＂受主＂2种掺杂而起到＂软化＂或＂硬化＂的作用。当Sb2O3掺杂量x≤0.005时,其压电系数d33随Sb2O3掺杂量的增加而增大,此时Sb2O3表现出了＂软化＂的特征;当Sb2O3掺杂量x〉0.005时,d33降低,从而又表现出了＂硬化＂的特性;当Sb2O3掺杂≥0.010时,诱使陶瓷室温下反铁电微畴的形成,导致铁电性和压电性的骤减。     

Influence of Rare-Earth Dopants on Barium Titanate Ceramics Microstructure and Corresponding Electrical Properties

In this article, ytterbium and erbium oxides are used as doping materials for barium titanate (BaTiO₃) materials. The amphoteric behavior of these rare-earth ions leads to the increase of dielectric permittivity and decrease of dielectric losses. BaTiO₃ ceramics doped with 0.01–0.5 wt% of Yb₂O₃ and Er₂O₃ were prepared by conventional solid-state procedure and sintered at 1320°C for 4 h. In BaTiO₃ doped with a low content of rare-earth ions (0.01 wt%) the grain size ranged between 10 and 25 μm. With the higher dopant concentration of 0.5 wt%, the abnormal grain growth is inhibited and the grain size ranged between 2 and 10 μm. The measurements of capacitance and dielectric losses as a function of frequency and temperature have been carried out in order to correlate the microstructure and dielectric properties of doped BaTiO₃ ceramics. The temperature dependence of the dielectric constant as a function of dopant amount has been investigated.     

放电等离子低温烧结h-BN-SiC复相陶瓷的结构与力学性能

以纳米h-BN和Si C粉为原料、B2O3为烧结助剂,利用放电等离子烧结(SPS)制备h-BN-Si C复相陶瓷,研究了烧结压力(20~50 MPa)对h-BN-Si C复相陶瓷结构与力学性能的影响。结果表明:在不同烧结压力下,h-BN-Si C复相陶瓷中h-BN晶粒的c轴倾向于平行压力方向,增大烧结压力能够提高复相陶瓷的致密化和力学性能,但较大的烧结压力(40 MPa)降低了c轴倾向于平行压力方向的取向度和断裂韧性。在40 MPa烧结压力时获得了较佳的综合性能,复相陶瓷的相对密度、抗弯强度和断裂韧性分别达到98%、289.2 MPa和3.45 MPa·m1/2,比同条件制备的纯h-BN陶瓷的抗弯强度和断裂韧性分别提高了约138.4%和64.3%。复相陶瓷断裂为典型的沿晶断裂模式,微裂纹及裂纹偏转提高了复相陶瓷的断裂韧性。     

Influence of Microstructure on the Electrical Properties of Iron-Substituted Calcium Titanate Ceramics

CaTi_0.8Fe_0.2O_3–δ ceramics with grain sizes that varied from 2 to 10 μm were obtained and studied using SEM, TEM, Mössbauer spectroscopy, impedance spectroscopy, and electrochemical oxygen permeability measurements. Smaller grains developed a core–shell microstructure that consisted of a pure CaTiO₃ core and an iron-rich microdomain structure at the shell. The effect of grain size on electronic conductivity was negligible. The ionic conductivity was higher for the ceramics with core–shell grains, which suggested that fast oxygen transport along microdomain walls may have occurred. For the homogeneous ceramics, the ionic conductivity decreased with decreased grain size, in which case the grain boundary represented an additional resistance, probably because of the depletion of oxygen vacancies.