先驱体转化法制备多孔陶瓷的研究现状

多孔陶瓷作为重要的陶瓷材料,广泛应用于冶金、化工等众多领域,其制备工艺的改进一直是研究重点。先驱体转化法是20世纪末提出的制备多孔陶瓷新型工艺,利用陶瓷先驱体高温裂解产生气体的特性,可将其作为粘结剂、骨料、发泡剂制备多孔陶瓷,具有成型工艺简单,烧成温度低等特点,拥有广泛的应用前景。本文主要从以上几个方面简要介绍先驱体转化法制备多孔陶瓷的工艺、结构和性能的研究现状。     

氮化硅反应烧结的研究进展

氮化硅作为高温功能陶瓷性能优越，但将其制备成陶瓷零件比较困难，目前一般用反应烧结法制备氮化硅陶瓷零件。此外，反应烧结制备氮化硅陶瓷还具有成本低、烧结温度低、产品成型好、陶瓷高温性能好等优点。综述了氮化硅陶瓷反应烧结工艺流程和工艺的优缺点，着重介绍了氮化硅反应烧结在成型工艺、烧结工艺、原材料影响、后处理和陶瓷增韧等方面所取得的进展。     

陶瓷先驱体催化裂解研究进展

有机聚合物衍生陶瓷技术具有聚合物分子可设计性强、成型容易和制备温度低等优点,已经成为陶瓷及其复合材料的主要制备技术之一。裂解是陶瓷先驱体实现从有机到无机转化的关键步骤,对目标陶瓷的组成、结构和性能有着决定性的影响。在陶瓷先驱体中添加过渡金属进行催化裂解,可以改变其裂解行为,进而调控和拓展裂解产物的结构和性能。本文从不同过渡金属对陶瓷先驱体的催化裂解作用入手,总结了陶瓷先驱体催化裂解的研究现状,探讨了催化机理,并就后续深化研究与应用提出了发展建议。     

模拟放射性废物泥浆陶瓷固化的烧结试验研究

采用钾长石、粘土、煅烧氧化铝为原料,对模拟放射性废物泥浆的陶瓷固化进行了研究。结果表明:该放射性废物泥浆陶瓷固化的最佳成型工艺为压制成型;烧结温度在1100℃以上的固化体抗渗性良好;本实验所选取的3个实验配方的最佳烧结温度范围均为1100-1150℃;K ,Na 在干燥过程中或烧结低温阶段的迁移扩散以及Na2SO4在 1200℃左右的分解,对固化体的致密烧结会产生不利的影响。     

先进结构陶瓷研究进展评述

评述了先进结构陶瓷的研究现状和发展趋势,重点介绍了近几年来先进结构陶瓷在超细粉体的制备、低成本复杂形状部件的成型新工艺、烧结技术、强化韧化机理以及新材料的研制等方面的最新研究进展.     

Y_2O_3透明陶瓷的研究进展

Y2O3透明陶瓷具有优异的光学和热学性能,是一种有较高应用价值的功能材料,现已成为单晶的可替代材料。介绍了Y2O3透明陶瓷的研究进展,阐述了Y2O3透明陶瓷的粉体合成、坯体成型、高温烧结和机械加工的制备工艺,并分析了成型时坯体开裂的原因。     

先驱体转化法制备泡沫陶瓷的发展现状

泡沫陶瓷由于具有一系列优异的性能,使得其应用范围越来越广泛,其制备方法也在不断地发展.先驱体转化法制备泡沫陶瓷是20世纪末才出现的一种新型工艺.它具有制备温度低、陶瓷组成和结构町设计、容易成型复杂构件等优点,成为目前泡沫陶瓷制备方法中的一个研究热点.根据泡沫陶瓷制备过程中成孔原理的不同,先驱体转化法制备泡沫陶瓷大致町以分为三类:(1)直接发泡法;(2)有机泡沫浸渍法;(3)添加造孔剂法.本文详细地介绍了由这三类先驱体转化法制备泡沫陶瓷的研究现状,并分析了其优缺点以及亟待解决的问题.     

Y2O3透明陶瓷的研究进展

Y2O3透明陶瓷具有优异的光学和热学性能,是一种有较高应用价值的功能材料,现已成为单晶的可替代材料.介绍了Y2O3透明陶瓷的研究进展,阐述了Y2O3透明陶瓷的粉体合成、坯体成型、高温烧结和机械加工的制备工艺,并分析了成型时坯体开裂的原因.     

工艺条件对低温烧结90氧化铝陶瓷显微结构及性能的影响

本文使用CaO-MgO-BaO-SiO2-ZrO2作为90氧化铝陶瓷的烧结助剂,在1420℃烧结得到了密度达3.77g/cm3的90氧化铝陶瓷。探讨了氧化铝粉末的活性、原料细度、成型工艺、烧结温度和保温时间等工艺条件对氧化铝陶瓷的烧结密度及其显微结构的影响。结果表明:活性高细度小的氧化铝粉末可显著降低氧化铝陶瓷的烧结温度,提高烧结体的密度;等静压成型与模压成型试样的烧结密度相近,但前者的强度则比后者提高了60~80%;其它工艺条件对氧化铝陶瓷的结构及性能的影响不显著。     

专利信息

硼氮陶瓷纤维先驱体的制备方法;高频低损耗铁电移相器复相陶瓷材料及其制备;一种低温烧结的高介电常数电介质陶瓷及其制备方法;一种制备高温陶瓷耐磨衬体的浇注料;一种激光透明陶瓷及其制备方法;固体废物陶瓷生态砖。     

Plastic forming of preceramic polymers

The method of plastic forming for the preparation of green bodies from different polymeric precursors is discussed. Experiments on the influence of the pressure, the temperature and the grain size of the powders were carried out with different precursors of the system Si–C–N and the system Si–B–C–N. Optimised conditions led to lower porosities in the pyrolysed ceramic for the specimen prepared by plastic forming (PF) than for the specimen prepared by cold isostatic pressing (CIP) of the preceramic polymer. It was also possible to form dense green bodies from polymers which could not be shaped by CIP. Furthermore, the mechanism of the plastic forming behaviour of the preceramic polymers is shown for the first time.     

Novel application of ceramic precursors for the fabrication of composites

Preceramic polymers are enabling the development of a variety of advanced shaping methods which, in turn, make possible new and cost-effective approaches for the fabrication of composite materials. This opens new perspectives for the mass production of composites which might, for example, be used in cost-sensitive areas of application in the machine and automobile industries. In two examples it will be shown how preceramic polymers can be used to obtain both metal matrix composites (MMC) and ceramic matrix composites (CMC). Their properties will be discussed in particular with respect to the usage of a preceramic polymer.The first example shows an approach to manufacturing short-fibre-reinforced CMCs by means of a plastic forming technique which involves mixing of either carbon or SiC fibres, ceramic fillers and a viscous ceramic precursor. The precursor permits a fibre-reinforced ceramic with a low porosity to be obtained. The role of the precursor in the whole process and the resulting material properties will be discussed.The second example shows a method for fabricating porous SiC ceramic preforms which are subsequently infiltrated with aluminium to form a MMC. By using the precursor route, a machinable preform with tailored porosity can be produced. Correlations between precursor, preform and MMC properties will be drawn.     

Ceramic Microtubes from Preceramic Polymers

A novel process for the production of ceramic microtubes involving the microextrusion of preceramic polymers was studied. Microtubes with a wide range of inner and outer diameters and several centimeters long were produced from two silicone resins. A coextrusion approach was also used to extend the forming capability of the technique. The addition of carbon black resulted in electrically conductive silicon oxycarbide (SiOC) ceramic microtubes. SiOC microtubes possessed a high bending strength, ranging from ∼30–1100 MPa.     

Fabrication of Microcellular Ceramics Using Gaseous Carbon Dioxide

A microcellular ceramic with cell densities >10⁹ cells/cm³ and cells <10 μm was made with a preceramic mixture of polycarbosilane and polysiloxane. The preceramic compact was saturated with gaseous CO₂, a large number of cells were nucleated and grown by using a thermodynamic instability induced by a rapid pressure drop, and the microcellular preceramic was transformed into a microcellular ceramic by pyrolysis.     

Fabrication of ceramic particles from preceramic polymers using stop flow lithography

Stop flow lithography (SFL) combines aspects of microfluidic and photolithography to continuously fabricate particles with uniform planar shapes as dictated by a mask. In this work we aim to expand the palette of materials suitable for SFL processing by investigating the use of UV-crosslinkable preceramic polymers to make ceramic particles. A commercially available methacrylated-polysiloxane was used as the preceramic polymer and was mixed with 2.5 wt% Irgacure 651 photoinitiator. A simple SFL system was assembled to continuously fabricate UV-crosslinked preceramic polymer particles in the shape of hexagons, triangles, and gears with diameters ranging from 100 to 200 μm and thicknesses of 74 μm +/- 4 μm. Particles were harvested from the excess preceramic solution, cleaned and then pyrolyzed at 1000 °C to transform them into silicon oxycarbide ceramic particles. Particle shape was maintained during pyrolysis despite a ～80 % linear shrinkage due to the removal of acryl and methyl side groups, as confirmed via FTIR. After pyrolysis the outer diameters of the SiOC particles ranged from 20 to 40 μm with thicknesses of 10 μm–12 μm. Pyrolyzed particles were successfully recovered and dispersed in water. This work demonstrates a robust path for the fabrication of ceramic particles with specific shapes from preceramic polymers via SFL.     

Modeling the pyrolysis of preceramic polymers: A kinetic study of the polycarbosilane SMP-10

A material model was developed to predict changes in mass, density and thus volume of cured preceramic polymers for CMC matrices as they pyrolyze into ceramics. Because part warpage and delaminations are most likely to occur when matrix strain rates and strain rate gradients are the highest, the ability to accurately predict changes in a matrix material’s volume is essential to determining the processing conditions that will efficiently minimize composite scrap rates. Experimental and model analysis of the SiC forming polycarbosilane, SMP-10, revealed that volume shrinkage is initially driven by mass loss, is quickly dominated by density’s contribution, and has both temperature and time at temperature dependencies, where density is not a simple function of mass yield. While material density is rarely reported in the open literature, the ability to predict changes in density is essential to accurately predicting the volume yield of preceramic polymers used in ceramic matrix composites.     

Preparation of ultra-high temperature SiC–TiB2 nanocomposites from a single-source polymer precursor

SiC–TiB₂ ceramic nanocomposites are valuable ultra-high temperature materials, which are rarely prepared from preceramic polymers. In this work, we synthesized SiC–TiB₂ nanocomposites from a new preceramic polymer called titanium- and boron-modified polycarbosilane (TB–PCS). The polymer structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The structure, composition, and morphology of the resulting ceramic products were investigated by FT-IR, X-ray diffraction, and transmission electron microscopy. The elements of titanium and boron were incorporated into the preceramic polymer, and nanoscale TiB₂ and β-SiC grains generated in situ were detected in the pyrolyzed ceramic products at temperatures higher than 1400 °C. The new preceramic polymer presents a novel approach to preparing SiC–TiB₂ nanocomposites.     

Fabrication of Porous SiC Ceramics with Special Morphologies by Sacrificing Template Method

Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.     

3D printing of SiC ceramic: Direct ink writing with a solution of preceramic polymers

3D structured SiC ceramics with varying feature sizes (100–400?μm) were achieved by direct ink writing of polycarbosilane (PCS)/n-hexane solution. The rheological properties of the PCS solution and printing parameters were tailored for optimum writing behaviour. The integrity and clear surface of the filaments indicated the printing ability of forming the self-supporting features along with the rapid evaporation of solvent. As-printed 3D structured PCS was processed by oxidative crosslinking and pyrolysis and converted to SiC ceramic. Although strong shrinkage occurred during the pyrolysis, SiC ceramic maintained the original 3D structure. Both proper viscoelasticity of printable solutions and the homogeneous shrinkage in the pyrolysis determine the integrity and feature characteristic of 3D structured SiC using direct ink writing preceramic polymer.     

Multifunctional advanced ceramics from preceramic polymers and nano-sized active fillers

In this paper, the introduction of nano-sized active fillers into preceramic polymers for the realization of multifunctional ceramic components is discussed. Several silicate and oxynitride systems have been produced, by heat treatment in air or nitrogen, greatly widening the compositional range of ceramics made from preceramic polymers. Phase pure ceramics were obtained with very favorable reaction kinetics, and therefore at low temperature and for short heating times. Shaping of the components was carried out using several plastic forming technologies, such as warm pressing, extrusion, injection molding, foaming, machining, fused deposition and 3D printing. Some significant examples of this new methodology are described, ranging from relatively simple oxide systems (mullite, zircon, cordierite, fosterite, yttrium-silicates) to more complex oxynitride ceramics (SiAlONs, YSiONs). Some results concerning the potential application of these components, ranging from structural or thermo-structural functions (bulk components and environmental barrier coatings) to more functional purposes (bioactive ceramics and inorganic phosphors), are also reported.