高性能陶瓷创新工艺--陶瓷胶态注射成型技术

成型工艺作为制备高性能陶瓷材料及部件的关键技术,介绍黄勇教授创新提出的把胶态成型和注射成型结合的“陶瓷胶态注射成型新工艺”。     

陶瓷材料的胶态原位成型技术

生产成本高、稳定性低和可重现性差一直都是特种陶瓷材料商业化的主要障碍 ,理想的解决方法就是净尺寸成形技术 ,在成形大型复杂零件的同时仍能保证高的产品质量。近十年来 ,新发展起来的胶态原位成形技术因工艺设备简单 ,成本低廉 ,制品组分均匀 ,缺陷少 ,强度高 ,且易于成形复杂形状零件等优点 ,得到了国内外人士的关注 ,并已得到了大量的实际应用。[1～ 3 ] 它们是 :注射成形、直接凝固注模成形和注凝成形亦称凝胶注模成形。1　陶瓷的注射成形技术1.1　技术简介注射成形是将陶瓷粉料与热塑性树脂等有机物混练后得到混合料 ,在注射机上于…     

陶瓷基复合材料胶态成型工艺研究进展

重点介绍了几种主要陶瓷基复合材料胶态成型工艺,包括注浆成型、注射成型、凝胶注模成型、直接凝固注模成型、温度诱导絮凝成型、水解辅助固化成型、电泳浇注成型和溶胶-凝胶法成型.对上述工艺的原理、工艺过程及特点进行了比较,并提出了陶瓷成型工艺的关键问题.     

陶瓷材料成型工艺研究新进展

陶瓷制造经历数千年历史，当前阻碍陶瓷材料进一步发展的关键之一是成型工艺技术没有突破。本文介绍了胶态成型，固体无模成型工艺及气态成型，对上述工艺的原理、工艺过程及特点进行比较，提出了陶瓷成型工艺的关键问题。并介绍了水基非塑性浆料的注射成型新工艺。     

陶瓷成型加工技术新进展

陶瓷材料以其优异的耐高温?高强度?耐磨损?耐腐蚀等性能和优点被广泛应用在各个领域中。文中介绍了陶瓷成型加工技术的新方式?新特点和新进展。     

陶瓷材料成型工艺研究新进展

陶瓷制造经历数千年历史,当前阻碍陶瓷材料进一步发文介绍了胶态成型、固体无模成型工艺及气态成型,对上述工艺的原理、工艺过程及特点进行比较,提出了陶瓷成型工艺的关键问题.并介绍了水基非塑性浆料的注射成型新工艺.     

陶瓷成型技术的新进展

提高成型技术是提高陶瓷产品可靠性的关键步骤。本文介绍了陶瓷胶态成型技术方面的最新发展情况，并对它们的应用情况做了简要的分析。     

先进陶瓷胶态成型新工艺的研究进展

总结了先进陶瓷胶态成型新工艺在清华大学的研究进展.简要介绍了几种高固相含量的浓悬浮体和高质量坯体的制备新技术,提出胶态成型新工艺固化机制的新见解.采用新工艺去除坯体中缺陷,实现高可靠性、复杂形状高性能陶瓷部件低成本的自动化、批量化制备,为先进陶瓷产业化铺平了道路.     

陶瓷直接凝固注模（DCC）成型

直接凝固注模式型（ＤＣＣ）是一种陶瓷净尺寸胶态成型方法，ＤＣＣ成型的坯体具有成型密度高，密度及组分分布均匀，不含或只含少量有机物等特点，本文了ＤＣＣ成型的原理、成型过程及特点。     

陶瓷材料成形工艺研究新进展

陶瓷制造经历了数千年的历史，当前阻碍陶瓷材料进一步发展的关键之一是成形工艺技术没有突破。笔者介绍了胶态成形、固体无模成形工艺及气态成形，对上述工艺的原理、工艺过程及特点进行比较，提出了陶瓷成形工艺的关键问题。并介绍了水基非塑性浆料的注射成形新工艺。     

Aqueous colloidal processing of PLZT ceramics near the morphotropic phase boundary

Abstract

Abstract

Single phase PLZT powder was fabricated using the mixed oxide approach, with a composition (6/60/40) lying on the rhombohedral-tetragonal (morphotropic) phase boundary. Aqueous suspensions showed an IEP of pH?9·7 in the absence of a polyelectrolyte surfactant. Inductively coupled plasma optical emission spectrometry analysis demonstrated considerable leaching of Pb²⁺ and La³⁺ ions under acidic conditions. The addition of an ammonium salt of poly(methacrylate), or PMA-NH₄, decreased the IEP to pH?5-6. Suspensions were readily stabilised at basic pH using low PMA-NH₄ concentration (<0·1?wt-% of solids). Concentrated suspensions exhibited shear thinning behaviour under low shear rates, with a transition to shear thickening at modest rates (i.e. 100?s^?1). Excessive shear thickening imposed a maximum solids loading of 46?vol.-% on concentrated suspensions, which related to the somewhat ‘flake-like’ particle morphology. Slip casting resulted in green and sintered (1250°C for 30?min) densities of 56±1% and 98·3±0·6% of theoretical, respectively.     

Yttria nettings by colloidal processing

Porous ceramic burners have been shown as a promising technology to produce heat and lighting by burning low calorific fuels like modern biomass. Among ceramics, yttria (Y₂O₃) presents considerable luminescent proprieties for gas burner technology. By colloidal processing of yttria, this work aims to produce luminescence ceramic nettings with potential to be used as gas burners. Processing parameters such as mean particle size, zeta potential and flow behavior were evaluated in order to prepare suitable suspensions for replica method. Yttria nanoparticles presented light emission with λ = 550 nm when being thermal stimulated at 150 °C. Besides, the nano sized powders d₅₀ = 113.8 nm and specific surface area of 13.6 m² g⁻¹ could be highly stabilized at pH 10.5. Suspensions with 30 vol% of solids, pH 10.5, 1 wt% of dispersant and 0.3 wt% of binder presented shear thinning behavior and thixotropy suitable for replica method. As a result, samples sintered at 1600 °C/1 h showed homogeneous morphology of struts and porous microstructure desirable for gas recirculation and burning process.     

The transformation mechanism from suspension to green body and the development of colloidal forming

Colloidal forming is a novel wet-processing way to prepare complex shaped ceramic parts with high reliability at low cost. In this article, the transformation mechanisms from suspension to green body and the development of colloidal forming are reviewed. The transformation from suspension to green body in colloidal forming is mainly dependent on the characteristics of suspension, and solidification is the key link in colloidal forming. Various colloidal forming methods are developed to produce ceramic parts, and these methods include slip casting, tape casting, direct coagulation casting, injection molding, gel-casting and so on. The study of defects during colloidal forming should be focused on the defects formation, inheritance and evolution during drying, de-binding and sintering processes. External free controllable technology of colloidal forming is an effective way to achieve ceramic fabrication industrialization, and stress-free colloidal forming is important for the future development of ceramic fabrication.     

Direct foaming of macroporous ceramics containing colloidal alumina

Liquid foams containing Al₂O₃ nanoparticles were obtained after direct foaming of a colloidal alumina suspension with ammonium stearate. These systems were stable for at least 24 h and were comprised by small cells (<35 μm). Up to 10 wt% of these foams were added to an ultrastable Al₂O₃-stabilised one and resulted in macroporous samples with high total porosity (>70%). Their green mechanical strength was proportional to the amount of colloidal alumina added, but lower than a composition with calcium aluminate cement. When compared with compositions prepared with colloidal alumina suspension, the colloidal foams resulted in samples with a higher number of small pores (<30 μm) and lower linear shrinkage after firing at 1600 °C for 5 h (~9%). Thus, colloidal alumina foams can be used for processing macroporous refractory ceramics with smaller pores, lower dimensional changes after firing and higher porosity.     

Aqueous colloidal processing of submicrometric SiC plus Y3Al5O12 with diamond nanoparticles

Aqueous colloidal processing was used for the environmentally friendly preparation of well-dispersed concentrated suspensions and powder mixtures of submicrometric SiC powders with submicrometric Y₃Al₅O₁₂ as sintering additive plus diamond nanoparticles as reinforcing phase. It is shown that the addition of nano-diamond markedly increases the viscosity and thixotropy of the SiC + Y₃Al₅O₁₂ suspensions, and also that, by adjusting the pH, deflocculant content, and sonication time it is possible to co-disperse these three rheologically different ceramic phases (i.e., non-oxide, oxide, and hydrophobic compounds) in aqueous media, thereby avoiding the otherwise irremediable severe hetero-aggregation. Moreover, the microstructural characterization of the powder mixtures obtained by freeze-drying the suspensions confirmed the homogeneous dispersion of the diamond nanoparticles among the submicrometric SiC and Y₃Al₅O₁₂ particles in the form of isolated or adhered nanoclusters and nanodeposits. Implications for engineering the microstructure of non-oxide ceramics with diamond nanodispersoids are discussed.     

Colloidal processing and sintering of WC-based ceramics with low Ni content as sintering aid

To soften the extreme sintering conditions of Tungsten Carbide (WC), a 3 wt.% of metallic nickel (Ni) was added to the starting powders. To ensure a fair distribution of the second phase and an intimate mixture of the phases, the colloidal process was adopted. A commercial Ni and a in-house synthesised nanosized nickel were used as sintering aids. Rheological studies allowed a high dispersion of the nickel in the final composite powders. Sintering studies by Hot-Pressing route (HP) proved the great benefices of Ni as a sintering aid, decreasing the maximum temperature necessary to achieve full densification, from 1900 to 1450 °C and dwell times from 20 to 7 min. Among all the materials obtained, the best results in terms of density, microstructure and properties were obtained for WC-nNi, which achieved hardness of 14.8 GPa and toughness comparable to conventional cermets with much higher content of metallic phase.     

Creep behaviour of alumina–mullite–zirconia nanocomposites obtained by a colloidal processing route

The high-temperature creep behaviour of high-purity alumina (A) and an alumina–mullite–zirconia nanocomposite (AZS) has been studied. The alumina–mullite–zirconia nanocomposite was prepared by using a colloidal processing route (powder–alkoxide mixtures). Creep tests were carried out in air in a 4-point-bending-fixture from 1200 to 1400 °C under constant stresses ranging from 30 to 220 MPa. Creep parameters (stress exponent n and activation energy Q) were correlated with microstructural features in order to determine the dominant creep mechanisms for both materials. The slow crack growth region (SCG), given by pairs of critical stress and the corresponding critical strain rate at the temperatures 1200, 1300 and 1400 °C of both materials was studied.

It was found that the creep rate of AZS was two orders of magnitude lower than the creep rate of undoped alumina A. The dominant creep mechanism of A is assumed to be a combination of grain boundary and lattice diffusion controlled creep. The creep mechanism for AZS is different and depends on the temperature. It is supposed that lattice diffusion controlled creep (Nabarro–Herring) is the dominant creep mechanism at 1200 °C, whereas at 1300 °C it is supposed to be grain boundary sliding accommodated by grain boundary diffusion. Comparing the slow crack growth region of both materials, a dramatic improvement was observed. The slow crack growth region of alumina is shifted nearly twice concerning the applied stresses for AZS at the temperatures 1200, 1300 and 1400 °C.     

A novel colloidal processing route to alumina ceramics

The fabrication of complex-shaped alumina ceramics following a new near-net shape technique based on hydrolysis induced aqueous gelcasting (GCHAS) is reported in this paper. Aqueous suspension containing 50 vol.% solids loading was prepared by dispersing alumina in an aqueous solution of methacrylamide and methlynebisacrylamide (17 wt.% in 6:1) using polycarboxylic acid as dispersing agent. Consolidation was accomplished by adding a polymerization initiator, a catalyst and AlN powder (4 wt.%). For comparison purposes, alumina ceramics were also consolidated by aqueous gelcasting (GC) and by hydrolysis assisted solidification (HAS) from the same concentrated suspensions, and by conventional dry pressing (DP) from freeze dried granules prepared from the same suspensions by freeze granulation. Among the four shaping techniques used, GCHAS was found to be best for consolidating near-net shape alumina components like thin wall radomes with the highest green strength ever reported for alumina ceramics. Green samples were sintered for 2 h at 1600 °C and then characterized for microstructure and mechanical properties.