高性能陶瓷成型工艺进展

本文论述了高性能陶瓷成型工艺的和重要性，重点介绍了陶瓷胶态成型工艺的研究进展及陶瓷成型工艺的最新动向，提出了瓷成型工艺研究中必须重视和加强的若干研究领域。     

精密陶瓷原位凝固制备技术的研究

七十年代末，世界范围内伴随着陶瓷热机部件的热潮，精密陶瓷受到了各国政府、研究部门及产业界的充分重视。进入九十年代后，精密陶瓷的发展遇到了许多问题，其中形状复杂结构部件的成型工艺是制造高性能陶瓷材料最为关键的环节之一。本文综合分析了近年来精密陶瓷成型工艺的研究进展，着重强调指出砂位凝固成型技术是保证坯体均匀性和解决高性能陶瓷可靠性的重要环节，同时，指出成型工艺今后需要加强和解决的几个关键技术。     

高可靠性层状复合陶瓷的制备

层状复合陶瓷具有显著的增韧增强效果，其成型工艺具有许多独特的工艺特性，是整个制备技术的关键。本文着重评述了层状复合陶瓷的成型制备技术。     

陶瓷现代成型技术的研究进展

分析了成型工艺在陶瓷制备中的重要作用和高质量的陶瓷坯体对成型工艺的基本要求，评述了国内外陶瓷现代成型技术，着重介绍了离心沉积成型、电泳沉积成型、离心注浆成型、注射成型、胶态成型和快速自动成型等新工艺，讨论了上述成型方法的基本原理和特点，指出了陶瓷成型技术的发展思路。     

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。     

多孔超高温陶瓷:制备、结构及性能EI北大核心CSCD

综述了近年来国内外在多孔超高温陶瓷制备工艺、结构表征及性能评价的研究进展。基于制备多孔超高温陶瓷材料使用的陶瓷原料和助剂的差异,可以大致将多孔超高温陶瓷的制备方法分为干法成型、胶态成型、前驱溶液成型,不同制备工艺获得的多孔超高温陶瓷的在微观结构上差异化明显。最后,我们对多孔超高温陶瓷的发展趋势作了展望。     

镁铝质泡沫陶瓷过滤器的研制

研究了镁铝质泡陶瓷过滤器的成分，成型工艺，烧结工艺，性能及应用效果。实验结果表明，镁铝质泡沫陶瓷过滤器具有良好的应用前景。     

陶瓷的注射成型技术

陶瓷注射成型技术可解复杂形状的高性能陶瓷元件的大批量生产难题,并且产品尺寸精度高,表面条件好,论述了瓷注射成型工艺中粘结剂选取,注射成型,脱脂等步骤,并提出了将来的研究方向。     

高性能陶瓷原位凝固成型技术的研究进展

综述了高性能陶瓷原位凝固成型工艺的特点;重点介绍了近年来的四种陶瓷原位凝固成型方法,即注凝成型,直接凝固成型,温度诱导絮凝成型和胶态振动注模成型,并简要介绍了国内陶瓷原位凝固成型技术研究取得的新成果。     

陶瓷壶体一次注浆成型工艺的研究

本文论述了陶瓷壶体一次注浆成型工艺，并且介绍了陶瓷壶体一次注浆成型的技术关键以及在生产中的实际应用。     

Gelcasting of alumina suspension using gellan gum as gelling agent

As one of the excellent colloidal ceramic forming methods for fabricating complex shaped ceramic components, gelcasting has been extensively investigated in the past two decades. In this article, a novel nontoxic system for gelcasting of ceramics was investigated using gellan gum as gelling agent. The rheological and gelling properties of gellan gum solutions with different types of cations and different concentrations of divalent magnesium ions were studied. Influences of concentration of gellan gum and solid loading of alumina suspension on the rheological properties and gelling properties of alumina suspension were investigated. The rheological properties of concentrated alumina suspension mixing with gellan gum and magnesium chloride were evaluated. Dense ceramics prepared by gellan gum gelation showed homogeneous microstructure and good mechanical properties.     

Recent developments in gelcasting of ceramics

Gelcasting is a well-established colloidal processing method with a short forming time, high yields, high green capacity and low-cost machining, and has been used to prepare high-quality and complex-shaped dense/porous ceramic parts. In this article, we reviewed recent developments in gelcasting technology for ceramic preparation. For environmental pollution reduction during ceramic preparation by gelcasting, the development of low-toxic and nontoxic gelcasting systems is discussed. The occurrence and control of inner stress and surface-exfoliation in ceramic green bodies prepared by gelcasting are analyzed, and then some methods to control and eliminate the inner stress and surface-exfoliation in ceramic gelcast green bodies, especially for colloidal injection molding of ceramics (CIMC) are proposed. Finally, the applications of gelcasting for the fabrication of porous ceramics and complex-shaped ceramics (e.g., microbeads, rutile capacitor, thin-wall rutile tube, refractory nozzle) are summarized.     

A Synergistic Low-Toxicity Gelcasting System by Using HEMA and PVP

A new low-toxicity gelcasting system with a 2-hydroxyethyl methacrylate (HEMA) monomer was applied for casting of alumina ceramics. Polyvinyl pyrrolidone (PVP) was adopted for modifying the homogeneity of the PHEMA (poly-HEMA) gel. The rheological properties of alumina suspension in the HEMA–PVP premix solution were studied. After preparation of a concentrated alumina suspension, homogenous alumina green body with a relatively high strength of about 19 MPa could be formed through the PVP-modified HEMA system. Dense complex-shaped ceramic parts can be successfully produced through the system. Besides, the surface exfoliation phenomenon that seems inherent to the acrylamide gelcasting system could also be eliminated by using the PVP-modified HEMA system. Analysis of the interaction of HEMA and PVP suggested that the improved microstructure and strength homogeneity, as well as the elimination of surface exfoliation in the new system, should be attributed to the intermolecular hydrogen bonding formed between PHEMA and PVP molecules.     

Producing Large Complex‐Shaped Ceramic Particle Stabilized Foams

Highly porous ceramic foams can be produced by combining particle stabilized foams and gelcasting concepts. Sulfonate‐type surfactants are selected to weakly hydrophobize the alumina surface and stabilize air bubbles in suspensions containing gelcasting additives, polyvinyl alcohol (PVA), and 2,5‐dimethoxy‐2,5‐dihydrofurane (DHF). The aim of this work was to prepare large complex‐shaped ceramic foam objects with homogeneous microstructure and high porosity. A key to avoiding drying cracks is to strengthen the wet green body via gelcasting. The influence of the amount of gelcasting additives on the mechanical strength of the ceramic foam green bodies is investigated as well as the effect of using cross‐linking agent versus the addition of just a binder. The presence of a cross‐linked polymeric network within the green body increases its mechanical strength and minimizes crack formation during drying.     

Gelcasting of a rutile mixture applied to extrusion forming

To improve sintering and forming behaviors, many additives are normally included in the rutile powder during extrusion forming. Hence, this complex rutile mixture is difficult to be dispersed into an aqueous solution of acrylamide monomers for gelcasting. In this work, with the aid of a dispersant, the mixture is easy to be dispersed by calcining at high temperature and then ball-milling, and a concentrated rutile suspension with low viscosity was successfully obtained. The suspension can be used to form in-situ a ceramic green body. After sintering the green body, the microstructure and performance of the product are both improved. For example, breakdown strength improved from 12.6 kV/mm to more than 23.6 kV/mm.     

2-carboxyethyl acrylate as a new monomer preventing negative effect of oxygen inhibition in gelcasting of alumina

The paper presents the application of 2-carboxyethyl acrylate as a new monomer in gelcasting of alumina. The research showed that the use of 2-carboxyethyl has a positive influence on the properties of green bodies, limiting the negative effect of oxygen inhibition. Oxygen inhibition which hampers polymerization reaction is a well known negative phenomenon in gelcasting but still not fully overcome for samples formed in air atmosphere. As a reference monomer 2-hydroxyethyl acrylate was used in the research. Rheological behavior of alumina suspensions containing both monomers has been studied, as well as the properties of green and sintered bodies obtained by gelcasting have been measured. The differences in the rheological properties and thus ceramic-monomer interactions in the slurries has been analyzed. The high values of densities and mechanical strength, accompanied with the pictures of microstructures of sintered ceramic parts have been presented, as a result of a successfully completed gelcasting process of alumina powder.     

Gelcasting and Pressureless Sintering of Translucent Alumina Ceramics

Gelcasting is a very useful technique for producing ceramic parts with complex shapes. In this work, gelcasting in air and pressureless sintering in hydrogen were applied to manufacture translucent alumina ceramics. A stable suspension with 75 wt% solids was prepared by ball milling. Trapped bubbles were removed completely before casting to obtain homogeneous green bodies. Final sintering was carried out in a hydrogen furnace at 1850°C for 3 h. Homogeneous microstructures of both calcined and sintered bodies were obtained. The in-line transmission of the sample with a thickness of 0.5 mm increased gently from 9% to 10% in the wavelength range of 190–1100 nm.     

Mechanical and electrical properties of lithium stabilized sodium beta alumina solid electrolyte shaping by non-aqueous gelcasting

A novel non-aqueous gelcasting system based on the polymerization of 2-hydroxyethyl methacrylate (HEMA) with low toxicity is applied to the fabrication of lithium stabilized beta alumina solid electrolyte (Li-BASE). Triethanolamine and polyethylene glycol (MW. 1000) are used as dispersant and plasticizer, respectively. Effects of dispersant concentration, solids loading and plasticizer concentration on the rheological behavior of the suspensions are investigated and optimized. Cracking and warpage phenomena in the gelcast green body during drying process are discussed. Green body gelcast from the optimized suspension shows homogeneous microstructure with a relative density of 59.4 % and a bending strength of 17 MPa. Properties, including the relative density, phase composition, microstructure, bending strength and ionic conductivity, of Li-BASEs sintered from green body formed by gelcasting and cold isostatic press are evaluated. Results show that gelcasting forming technique performs well in preparing BASE ceramics with high Weibull modulus and ionic conductivity.     

Preparation of alumina by aqueous gelcasting

The alumina ceramic was prepared by aqueous gelcasting. The effects of zeta potentials, solid loading, dispersant content and milling time on the alumina suspension were studied systematically. The dispersant content has remarkable effects on the viscosity of the suspension. The appropriate dispersant concentration for alumina aqueous slurry with the solid loading of 55 vol.% is 0.6 wt.%. It can be seen that all suspensions (50–56 vol.% solid loading) exhibited a shear-thinning behavior and relatively low viscosity, which was suitable for casting. The degree of shear thinning and the viscosity at high shear rates increased with increasing volume fraction of solid. As the milling time prolongs, viscosity of the suspension decreases first, then the plateau appears and the average diameter keeps changeless. When the milling time was shorter than 20 h, the viscosity of slurries decreased gradually as the time of milling increased. After 20 h milling, the viscosity of the slurry tended to be consistent. Therefore, the ball milling time should be equal to or more than 20 h to obtain a stable suspension at equilibrium. The time available for casting the slurry (idle time) can be controlled by the amounts of initiator and catalyst added to the slurry as well as by the processing temperature. Micrograph of the gelcast green body was homogeneous.     

Alumina gelcasting by using HEMA system

A low-toxicity gel system based on the polymerization of low-toxicity 2-hydroxyethyl methacrylate (HEMA) was successfully developed. In order to obtain high solid loading ceramic slurry with low viscosities, a polyelectrolyte dispersant was selected. The results based on alumina suggested that the polyelectrolyte dispersant was more effective for the new HEMA system than tri-ammonium citrate (TAC), which was widely used for dispersing alumina powders. The green alumina bodies derived through the HEMA exhibited a mechanical strength as high as 18 MPa. SEM photos revealed that the green body also had a high homogeneity. Dense complex-shaped ceramic parts were produced through the new gelcasting system.