ZrO_2_-3Al_2O_3-2Sio_2/SiC_n纳-微米复相陶瓷的反应烧结技术

概述复相陶瓷和纳米陶瓷的主要内容和机理,介绍反应烧结ＺｒＯ２－３Ａｌ２Ｏ３·２ＳｉＯ２－Ａｌ２Ｏ３／ＳｉＣｎ纳米复相陶瓷技术的研究内容、技术路线、工艺原理和发展前景。     

工业用高温热电偶瓷管材料烧结行为的研究

为制备工业用高温热电偶瓷管,本实验依据原位反应的原理,配制了不同Ａｌ２Ｏ３含量的试样,主要研究了以Ａｌ２Ｏ３作为第二相增韧增强的ｍｕｌｌｉｔｅ基复相陶瓷材料的烧结行为。     

A1N陶瓷的晶界缺陷

本文研究以Ｙ２Ｏ３为烧结助剂的无压烧结Ａ１Ｎ陶瓷中，晶界第二相和气孔等晶界缺陷对热导率的影响。结果表明，Ａ１Ｎ陶瓷晶界第二相的组成主要取决于配料中的Ｙ２Ｏ３／Ａｌ２Ｏ３比值，同时也受工艺因素影响，随着Ｙ２Ｏ３加入量增多，晶界第二相含量线性增加，其分布也从三晶连接外延伸到所有晶界。     

激光熔覆Al2O3+TiO2复合陶瓷涂层的微观结构

研究了４５＃钢表面Ａｌ２Ｏ３＋ＴｉＯ２复合陶瓷激光熔覆层的微观组织和相结构、Ａｌ２Ｏ３＋ＴｉＯ２复合陶瓷激光熔覆涂层由α－Ａｌ２Ｏ３,ＴｉＯ２,γ－ＴｉＯ２,γ－Ａｌ２Ｏ３及Ａｌ２ＴｉＯ５相组成,消除了等离子喷涂层的层状组织特征,形成了大致方向的柱状晶,晶内为溶入了Ｔｉ及少量底层元素的α－Ａｌ２Ｏ３;晶界为由ＴｉＯ２和Ａｌ２Ｏ３形成的Ａｌ２ＴｉＯ５相,溶有少量的Ｃｒ,Ｆｅ,Ｙ取代了Ａｌ２ＴｉＯ５     

添加剂对AIN陶瓷力学性能及抗氧化性能的影响

本文研究了Ａｌ２Ｏ３、Ｙ２Ｏ３、Ｌａ２Ｏ３、Ｙ２Ｏ３＋ＳｉＯ２几种类型的添加剂对ＡＩＮ陶瓷力学性能和高温抗氧化性能的影响。结果表明：Ｙ２Ｏ３＋ＳｉＯ２为一种较好的ＡＩＮ陶瓷添加剂，材料在烧结过程中由于２Ｈ＾５Ｓｉａｌｏｎ及８Ｈ－Ｓｉａｌｏｎ等纤维状的Ｓｉａｌｏｎ相形成，对材料起到一种自补强作用，ＳｉＯ２的存在使用ＡＩＮ陶瓷在氧化工程中形成Ｍｕｌｌｉｔｅ保护层，故使ＡＩＮ陶瓷肯有良好的力学性能及高温     

锂质耐热陶瓷的研究

研究了ＬｉＯ２－ＳｉＬ２－Ａｌ２Ｏ３系锂质陶瓷的原料,生产配方,制作工艺及其性能,介绍了锂质耐热陶瓷的晶相结构。     

中温烧结MgO—TiO2—ZnO系陶瓷结构和性能的研究

本文在研究中温烧结ＭｇＯ－ＴｉＯ－ＺｎＯ系陶瓷基础上，获得了温度系数接近于零的瓷料（ＮＰＯ）。ＸＲＤ证明其主晶相为正钛酸镁（２ＭｇＯ．ＴｉＯ２）还有正钛酸锌（２ＺｎＯ．ＴｉＯ２）和ＣａＴｉＯ３附加晶相，同时研究了各组分的不同含量对介电性能的影响。     

A1N陶瓷的晶界缺陷

本文研究以Ｙ２Ｏ３为烧结助剂的无压烧结Ａ１Ｎ陶瓷中，晶界第二相和气孔等晶界缺陷对热导率的影响，结果表明Ａ１Ｎ陶瓷晶界第二相的组成主要取决于配料中的Ｙ２Ｏ３／Ａｌｋ２Ｏ３比值，同时也受工艺因素的影响。     

AIN陶瓷中的晶界第二相

晶界第二相是ＡＩＮ陶瓷显微结构的重要组成部分，对ＡＩＮ陶瓷的热导率有重大影响。本工作研究了以Ｙ２Ｏ３为烧结助剂的无压烧结ＡＩＮ陶瓷中，晶界第二相的组成、含量及其分布。结果表明：晶界第二相的组成主要决于配料中的Ｙ２Ｏ３／Ａｌ２Ｏ３比值，同时也受工艺因素影响；随着Ｙ２Ｏ３加入量增多，晶界第二相含量呈线性增加，其分布也变成从三个晶粒连接处延伸到所有晶界，还讨论了晶界第二相对热导率的影响，认为只要ＡＩＮ晶     

富Al2O3区域CaO行为的研究

本应用Ｄ／Ｍａｘ－３ＢＸ－射线衍射，热分析等方法研究了赋存于α－Ａｌ（ＯＨ）３粉体中的含钙矿物于１００℃至１６００℃煅烧过程中的行为。在α－Ａｌ（ＯＨ）３煅烧过程中，伴随着含钙矿物的热转化及固相反应，历经１２ＣａＯ·７Ａｌ２Ｏ３，ＣａＯ·Ａｌ２Ｏ３，ＣａＯ·２Ａｌ２Ｏ３，ＣａＯ·６Ａｌ２Ｏ３，最终ＣａＯ·６Ａｌ２Ｏ３与α－Ａｌ２Ｏ３共存，本并提供了ＣａＯ·６Ａｌ２Ｏ３的Ｘ射线粉末衍射数据。研究     

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.     

Inter-particle interactions of alumina powders in UV-curable suspensions for DLP stereolithography and its effect on rheology,solid loading,and self-leveling behavior

For the UV-curable alumina suspensions used in digital light processing (DLP) stereolithography, optimizing the dispersant type is important for achieving low viscosity, high solid loading, and remarkable self-leveling behavior. However, the inter-particle interactions in UV-curable alumina suspensions dispersed using different dispersants are overlooked. Herein, the effect of inter-particle interactions on rheology, solid loading, and self-leveling behavior of UV-curable alumina suspensions was systematically investigated. Three different commercial dispersants were used: oleic acid (OA), alkane-acrylic phosphate ester (PM1590), and copolymer dispersant (BYK111). After dispersing, BYK111 endowed alumina powders with thicker adsorption polymer layer to provide stronger steric repulsion force and facilitated better wetting of alumina powers in the photocurable resin, resulting in a reduced network structure degree, which decreased the viscosity (1.04 Pa s at 30 s^?1); homogeneous packing of alumina powders, which enhanced the maximum solid loading (55 vol%); and inhibition of particle flocculation, which facilitated the spontaneous spreading of suspension.     

氧化锆、不锈钢复合粉体浆料流变性的研究

初步探索金属-陶瓷复合粉体浆料的粘度与浆料的pH值、分散剂含量、固体含量之间的关系,制备出高固体含量(体积分数为40%)、低粘度(0.32Pa·s)的氧化锆、不锈钢复合粉体浆料.     

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.     

Dispersion and properties of zirconia suspensions for stereolithography

Stereolithography is an attractive technique for the fabrication of complex-shaped ceramic components with high dimensional accuracy. One of the challenges in this technology is the development of high solid loading, low viscosity photosensitive ceramic suspension. In this study, the dispersion of zirconia in photocurable resin and the slurry properties were intensively investigated. Rheological measurements showed that DISPERBYK-103 proved to be an effective dispersant. 42 vol% ZrO₂ suspension was successfully prepared using 3.5 wt% DISPERBYK-103 as the dispersant, with a suitable viscosity (4.88 Pa·s) below the maximum allowable viscosity value (5 Pa·s) for stereolithography applications. The adsorption behavior of DISPERBYK-103 on the surface of zirconia powders was characterized by TG and FT-IR, confirming the dispersion effect of dispersant. Contact angle measurements were also conducted to show that the adsorption of DISPERBYK-103 could help to improve the wettability between powder and photocurable resin. Results showed that DISPERBYK-103 was effective for the preparation of suitable slurries for the development of ZrO₂ ceramics through stereolithography.     

The influence of solid loading in suspensions of a submicrometric alumina powder on green and sintered pressure filtrated samples

The present work deals with preparation of stable suspensions of a submicrometre alumina powder with different contents of solid for pressure filtration. The optimum dispersant content (2.2 wt.% of Darvan C-N) was determined by sedimentation tests and viscosity measurements. By modification of the solid loading and dispersant content two kinds of aggregation were observed. One type of aggregates is related to the use of excessive solid loading in suspension. In samples prepared from these suspensions only minor effect on sintered microstructure was observed, which increased with increasing volume fraction of hard aggregates. In case of excess dispersant addition weak aggregates formed as the result of depletion flocculation. Weak aggregates had stronger negative effect on green microstructure, with consequent negative impact on sinterability.     

YAG ceramic processed by slip casting via aqueous slurries

Stable YAG (Y₃Al₅O₁₂) aqueous slurry with ammonium polyacrylate (NH₄PAA) polyelectrolytes as dispersant was prepared by ball mill method. The effects of polyelectrolyte concentration and pH value on the stability of the suspension is described here, and the stability maps are constructed at different pH value and polymer concentration. The rheological behavior of YAG slips of different solid loading (60–70%) has been studied by measuring their viscosity and shear stress as a function of shear rate and pH of the slurry. An optimal amount of dispersant and pH value for the suspension was found. YAG suspension displays a maximum in zeta potential values and a minimum viscosity in pH range of 9–11. Slips behaved as near Newtonian at the pH value up to a solid loading of 60 wt% and as non-Newtonian with thixotropic behaviors above this solid loading value. The density and the green as well as sintered microstructure of the cast products bear a direct relationship to the state of this slips induced by the alternation in the pH and the concentration of the dispersant as well as solid loading.     

UV Curable Systems for Tape Casting

The substitution of solvents by photopolymerizable binders in the tape casting process allows to achieve high ceramic loading and to eliminate the drying stage which is a critical step of the tape casting process. After the rapid UV polymerization of the resin, the high strength green tapes can be debinded and sintered. Ceramic suspensions containing alumina or zirconia powder, dispersant, UV curable binder and photoinitiator have been prepared. The use of a low viscosity organic vehicle allows to prepare low viscosity ceramic suspensions, containing about 50 vol% powder, which have a shear thinning behaviour. Because of the rapid attenuation of the incident light in UV curing systems containing ceramic particles it is important to estimate the thickness of the tape that can be treated. The effect of incident energy, of photoinitiator concentration and of powder volume fraction was studied. There is an optimal photoinitiator concentration which maximizes the cured depth and which depends on the volume fraction of solid. A theoretical model based on the Beer–Lambert’s law enables the prediction of cured depth for any volume fraction of solid. To prove the ability to manufacture ceramic sheets by tape casting, some suspensions were tape cast.     

Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria-stabilized zirconia sediments

In the present work, particle arrangement and their packing in the sediment layer of zirconia suspension were studied. To evaluate the particle settling, aqueous suspensions of zirconia nanoparticles were prepared in different dispersion states. In one state, Dolapix CE64 was used as a dispersant to provide electrosteric mechanism. In another state, pH of the suspension was adjusted at 4 to provide electrostatic mechanism. The other state was the combination of dispersant and pH adjustment which resulted in the most stable suspension. First of all, the stability of all dispersion states was evaluated by zeta potential, sediment volume (SV) and height, viscosity, and packing density (PD). Then, the sediment layers of all suspensions were characterized. Incorporation of electrostatic mechanism was resulted in a main decrease in viscosity with high surface charges, while electrosteric mechanism caused lower sedimentation of particles. Fall velocities of particles/agglomerates were estimated, and the influences of dispersion states on the particles fall velocities were characterized. The microstructural observation revealed homogeneous packing of particles in the sediment layer of the stable suspension demonstrating the proper dispersion of particles. Dolapix CE64 and pH adjustment resulted in a uniform arrangement of particles without agglomeration and spherical and regular granules with a uniform shape.     

Mullite coatings on ceramic substrates: Stabilisation of Al2O3–SiO2 suspensions for spray drying of composite granules suitable for reactive plasma spraying

The present work deals with the preparation of stable alumina + silica suspensions with high solid loading for the production of spray-dried composite powders. These composite powders are to be used for reactive plasma spraying whereby the formation of mullite and the coating on a ceramic substrate are achieved in a single step process. Electrostatic stabilisation of alumina and silica suspensions has been studied as a function of pH. Silica suspensions are most stable at basic pH whereas alumina suspensions are stable at acidic pH. The addition of ammonium polymethacrylate (APMA) makes it possible to stabilise alumina and prepare a stable 50 wt% alumina + silica suspension at pH 10. The optimum amounts of dispersant and binder have been determined by zeta potential, viscosity and sedimentation measurements. Spray drying of the suspension yields composite powders whose morphology, size distribution and flowability have been characterized before realizing reactive plasma spraying tests.