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.     

纳米陶瓷烧结技术研究进展与展望

纳米化被认为是解决陶瓷脆性的有效途径之一。纳米陶瓷的特殊显微结构决定了其独特的性能,如高强度、高断裂韧性、低温超塑性等。此外,纳米效应还可赋予材料特殊的光、电、磁等功能特性。烧结是纳米陶瓷制备的关键环节,初始颗粒在高温烧结过程中极易长大,因此,合理的烧结技术和工艺是促进陶瓷致密化并控制晶粒长大的重要保证。按照是否存在外场辅助条件及辅助条件类型,本工作将纳米陶瓷烧结技术分为无压烧结、压力辅助烧结、电磁辅助烧结3大类,并结合研究实例讨论其烧结机理。通过对不同烧结技术的特点对比,提出目前纳米陶瓷烧结技术存在的主要挑战并进行展望。     

纳米陶瓷复合材料的制备方法

纳米陶瓷复合材料具有良好的力学性能和优越的高温性能等特性，是当今材料科学研究的重要课题。本文综合国内相关资料对纳米陶瓷昨合材料的制备方法作一简要评述，主要介绍纳米陶瓷复合粉体的制备方法和固体纳米陶瓷复合材料的烧结。     

纳米陶瓷及其进展

综述了国内外纳米陶瓷研究动态,介绍了从纳米粉末制备、表征到纳米粉末的烧结及纳米陶瓷性能的发展过程,同时,指出了存在的问题。从近年来纳米陶瓷研究的成功实例,探讨了纳米陶瓷的研究作为当前国际陶瓷研究前沿课题的理论和实际依据。最后,分析了纳米陶瓷的发展前景及对传统陶瓷学、陶瓷工艺的新挑战。     

影响纳米陶瓷性能因素分析

本介绍了纳米陶瓷的性能，详细分析了纳米陶瓷的微结构和纳米粉体的制备技术、团聚、成型方法以及纳米陶瓷的烧结技术等因素对纳米陶瓷性能的影响。     

Al2O3/SiC纳米复合陶瓷的制备及性能

在Al2O3陶瓷基体中引入第2相纳米SiC颗粒,可以改善力学性能、耐磨损性能,是陶瓷领域研究的热点之一。纳米颗粒的均匀分散和适当的成型烧结决定了其性能。本文就目前存在的Al2O3/SiC纳米复合陶瓷粉体制备方法与烧结工艺进行了详细阐述。     

纳米陶瓷的烧结方法

纳米陶瓷被认为是解决陶瓷脆性的战略途径。本文主要综述了纳米陶瓷的几种常见的烧结方法。     

纳米TiO2添加量对95氧化铝陶瓷材料性能的影响

笔者采用CaO-MgO-SiO2-TiO2为烧结助剂,讨论了纳米TiO2添加量对95氧化铝陶瓷烧结性能、力学性能、化学性能、电性能的影响,通过扫描电镜对氧化铝陶瓷的微观形貌进行了观察.结果表明:TiO2添加量为1.0％,氧化铝陶瓷微观结构均匀,烧结性能和力学性能最佳,收缩率和体积密度达到最大值18.98％和3.72 g...     

纳米TiO2添加剂对Al2O3陶瓷微观结构与烧结性能的影响

用微米级和纳米级两种不同的TiO2作为烧结助剂,研究其对Al2O3陶瓷微观结构和烧结性能的影响.结果表明:纳米TiO2能更好的提高Al2O3陶瓷的烧结活性,降低烧结温度.当TiO2含量为2%时,在1 580℃烧结试样的显气孔率为0.54%;在1 650℃烧结试样的显气孔率为0.16%.纳米TiO2的加入改变了Al2O3陶瓷的微观结构,更有利于Al2O3陶瓷的烧结.     

纳米介电陶瓷的晶粒尺寸效应及低温烧结技术

微电子技术对纳米陶瓷材料的需求催生了各种新型纳米陶瓷材料制备与烧结技术的开发与研究。结合纳米晶介电陶瓷的晶粒尺寸效应（即晶粒尺寸与陶瓷介电特性、烧结特性之间的依赖关系）,系统介绍了制备纳米晶介电陶瓷材料的低温烧结技术,包括液相烧结、两步烧结、水热压烧结和放电等离子体烧结,重点阐述了各种低温烧结技术的基本原理、使用设备、实验参数,比较了其优、缺点和应用领域,综述了近年来国内外相关领域的研究进展,并对这些技术目前存在的问题和今后的研究方向进行了分析和展望。     

Densification and grain growth of Gd2Zr2O7 nanoceramics during pressureless sintering

Gd₂Zr₂O₇ nanoceramics were fabricated using pressureless sintering method, in which the nanopowders were synthesized via solvothermal approach. The effects of starting powders on grain growth and densification during sintering of ceramics were revealed. Two distinct pressureless sintering methods were investigated, including conventional and two-step sintering. The sample grain size increases abruptly as sintering temperature increases during conventional sintering. In contrast, in two-step sintering, abnormal or discontinuous grain growth was suppressed in the second step, leading to Gd₂Zr₂O₇ nanoceramics formation (average grain size 83 nm, relative density ∼93%). Such distinct behaviors may originate from the interplay between kinetic factors such as grain boundary migration and diffusion. Moreover, suppression of grain growth and promotion of densification in the two-step sintering are mainly due to dominant role of grain boundary diffusion during the second-step sintering process.     

Plasma-assisted rapid sintering of nanotitania powders

In this work, Plasma-Assisted Rapid Sintering (PARS), a pulsed DC plasma system in a hollow cathode regime, is presented as a novel technology to sinter nanoceramics. Nano-TiO₂ powders are used as proof of concept and submitted to thermal treatment using several PARS conditions and sintering schedules. PARS heating process induced solely by the hollow cathode effect is consistent and affordable, providing a homogeneous temperature distribution to the compact. Furthermore, the heating rate and the maximum temperature are easily tunable by the discharge current applied in the plasma source and can go safely from room to maximum temperature in a matter of seconds with heating speed comparable with other reported rapid sintering techniques. Using 1-min of non-isothermal PARS cycles up to 1000 °C, porous nanostructured samples were obtained; reaching 80 % relative density while the grains remained at the nanoscale. Adding dwell times, the relative density was increased up to 96 % using a temperature plateau for up to 10 min, but the TiO₂ grains grow intensively when temperatures exceeded 1000 °C. The results indicate that the developed process is a promising new alternative technology for sintering nanoceramics.     

Development of Nanocrystalline Wear-Resistant Y-TZP Ceramics

The present contribution reports some interesting and new results obtained while developing yttria-stabilized tetragonal zirconia (Y-TZP) using spark plasma sintering (SPS). The experimental results clearly showed that ZrO₂-nanoceramics with high hardness(∼14.5 GPa) can be processed at a lower sintering temperature of 1200°C in a short time (5 min). Another important result is that the newly developed Y-TZP nanoceramics, compared with the conventional sintered TZP, exhibit better fretting wear resistance against bearing steel. The intergranular fracture and the grain pullout were observed as the major wear mechanisms of the zirconia nanoceramics.     

Microstructure and fracture behavior of β-Si3N4 based nanoceramics

Fully dense β-Si₃N₄ based nanoceramics were consolidated by spark plasma sintering (SPS). A commercially available β-Si₃N₄ nano-powder was used as starting material. The sintering bulks were fabricated with a heating rate of 90 °C/min by varying SPS temperature from 1550 °C to 1700 °C, and the linear shrinkage was used to evaluate the sintering behavior of the nano-powder. The microstructures of the developed Si₃N₄ based ceramics were achieved, and the grain length, grain width, and aspect ratio for these sintering bulks were found to increase gradually with elevating sintering temperature. The hardness and fracture toughness are associated with the microstructural characteristics. The crack propagation and fracture behavior for these β-Si₃N₄ based nanoceramics have been observed for the specimens sintered at different sintering temperatures. Crack deflection is found to be one of the toughening mechanisms for these β-Si₃N₄ based nanoceramics.     

Liquid phase assisted high pressure sintering of dense TiC nanoceramics

To address the difficulty of achieving high density while effectively suppressing grain growth in the fabricating of nanoceramics, this paper demonstrates a novel integrated approach, consisting of a solid-liquid reaction, high pressure and low temperature sintering, to prepare dense nanocrystalline TiC ceramics. Using Si as the additive, a low-viscosity Si liquid phase is formed under the sintering condition of 1200?°C/4.5?GPa. It is shown that both of the sintering aid and high pressure are crucial in achieving high density nanostructured TiC ceramics and controlling their microstructure and thus their mechanical properties. The pure TiC can be sintered to reach 95.3% of its theory density and, with the assistance of liquid Si additive, it can be sintered to full densification without grain growth by high pressure technique.     

Liquid-phase assisted spark-plasma sintering of SiC nanoceramics and their nanocomposites with carbon nanotubes

The appropriate conditions for liquid-phase assisted spark-plasma sintering (SPS) were identified for the fabrication of both SiC nanoceramics and their nanocomposites with carbon nanotubes (CNTs). A parametric study of the nanoceramics and nanocomposites with a given type of CNTs showed that the SPS temperature (as measured by the radial optical pyrometer) optimizing their densification, nanograin size, and mechanical properties is 1700 °C (soaking for a few minutes), below which there is incomplete densification, and above which there is obvious grain growth with no benefit in hardness or toughness in the case of the nanoceramics, and prejudicial to both properties in the case of the nanocomposites due to the CNT degradation. It was also shown that the nanocomposites have smaller nanograins than their nanoceramic counterparts, and are softer but tougher. Extension to nanocomposites with different types of CNTs confirmed these trends, and showed that the CNT features do not condition the densification, microstructure or mechanical properties of these nanocomposites.     

Grain boundary region and local piezoelectric response of BiScO3–PbTiO3 nanoceramics prepared by combination of SPS and two-step sintering

Highly dense 0.37BiScO₃–0.63PbTiO₃ (BS–PT) nanoceramics with average grain sizes of 23, 33 and 70 nm were prepared by a combination of spark plasma sintering and two-step sintering methods. The microstructure, phase and piezoelectric behaviours of BS–PT nanoceramics were investigated. High-resolution transmission electron microscopy revealed that the samples had dense and thin grain boundaries. Experimental evidence demonstrated that the polarisations of the BS–PT nanoceramics were switchable and that their ferroelectricity was retained with grain sizes as fine as 23 nm. However, the local piezoelectric response showed a large fluctuation over different regions. Moreover, a significant difference between local and macro piezoelectric coefficients was observed. The properties of the grain boundary regions are the key factor to understanding the ferroelectric behaviours of BS–PT nanoceramics.     

Densification as an exothermic process revealed by rapid high temperature consolidation of BaTiO3 nanopowder

Abstract

Densification is an exothermic process according to the classical sintering theories; however, it has never been explored experimentally. In the present work, such heat release was successfully detected from nanosized BaTiO₃ nanopowder compact, which was rapidly consolidated by spark plasma sintering. A reduction of total power consumption was observed immediately when rapid densification occurred. The effects of the deviation of overall electric resistance on total power consumption were analysed. The temperature at which a falling inflection point of the power supply was observed can be used as an indicator of the minimum temperature required for densification. This would be of help for defining the ‘kinetic window’ for processing of nanoceramics in sintering practice.