高固相含量Si3N4浆料的研究（Ⅰ）——分散剂对Si3N4及助烧结剂胶体…

本工作以制备适用于直接凝固注模成型等胶态成型方法的高固相含量低粘度的浆料为目的，研究了氮化硅及助烧结剂的胶体特性。研究采用Ａｌ（ＯＨ）３溶胶及柠檬酸铵作为分散剂，分别改善氮化硅及助烧结剂氧化铝和氧化钇的胶体特性，使氮化硅，氧化铝及氧化钇在水中具有相似的胶体特性，并在适用于ＤＣＣ成型的ｐＨ值范围为９０１０具有最大ＥＳＡ值。     

丙烯酸聚合改性氮化硅粉体的研究

为制备高固相含量氮化硅悬浮液,研究了不同分散剂（柠檬酸铵、四甲基氢氧化铵、聚丙烯酸铵和丙烯酸）对氮化硅粉体的表面改性作用。结果发现,柠檬酸铵、四甲基氢氧化铵、聚丙烯酸铵不能有效吸附于氮化硅粉体表面而改变粉体的表面特性;而丙烯酸聚合过程中链自由基的较高活性使聚丙烯酸分子链吸附于氮化硅颗粒表面,氮化硅粉体的等电点从pH≈4．3降低到pH≈21,通过这种表面改性方法提高了氮化硅粉体在水中的分散特,制备出了固相体积分数为50％的氮化硅悬浮液。这种表面改性方法不改变氮化硅粉体的化学组成,有利于制备氮化硅基陶瓷时化学成分及相组成的准确控制。     

液体介质对氮化硅粉料表面基团和悬浮特性的影响

利用漫反射Fourier变换红外光谱（DRIFT）技术,研究了液体介质（水,乙醇和丙酮）对氮化硅粉料表面基团的改变和对其悬浮特性的影响。结果表明,氮化硅粉料在不同的液体介质中球磨中,粉料的表面基团和悬浮特性的变化各不相同,去离子水介质球磨的粉料,颗粒表面的Si-OH基团消失,Si-O-Si和Si-H基因数量减少,使粉料的悬浮特性有所提高,乙醇介质中处理的氮化硅粉料,颗粒表面生成稳定的Si-O-C-R表面官能团,使粉料的悬浮性能降低,丙酮介质中处理的氮化硅粉料,在颗粒表面生成Si…0＝C/(CH3)2基因,使粉料在水中的分散性大为下降,这种键合不稳定,在200℃干燥时大部分会断开消失,少量键合转变成稳定的Si-O-C-R形成;3种液体介质球磨改性的粉料,在600℃,6h煅烧之后,其DRIFT谱图基本相同,同时表现出几乎相同的流变特性。     

氮化硅轴承球表面层残余应力的形成机理及试验研究

本文论述了烧结热应力及研磨加工对氮化硅轴承球表面残余应力的影响机理.通过比容积测定,对氮化硅轴承球表面残余应力分布进行了分析计算,并就研磨加工对氮化硅轴承球表面残余应力的影响进行了试验研究.     

高固相含量Si3N4浆料的研究（Ⅱ）——浆料的流变特性

研究了分散剂对纯氮化硅及氮化硅和助烧结剂（氧化铝及氧化钇）多元粉料高固相含量浆料（大于５０％）流变性的影响。根据胶体特性的研究结果，选取Ａｌ（ＯＨ）３溶胶及柠檬酸铵改善高固相含量浆料的流变特性，得到适用于直接凝固注模成型的高固相体积分数、低粘度氮化硅浆料。此外，还研究了固相体积分数对浆料粘度及流变性的影响     

高固相含量Si3N4浆料的研究（II）——浆料的流变特性

研究了分散剂对纯氮化硅及氮化硅和助烧结剂（氧化铝及氧化钇）多元粉料高固相含量浆料（大于５０％）流变性的影响。根据胶体特性的研究结果，选取Ａｌ（ＯＨ）３溶胶及柠檬酸铵改善高固相含量浆料的流变特性，得到适用于直接凝固注模成型的高固相体积分数、低粘度氮化硅浆料。此外，还研究了固相体积分数对浆料粘度及流变性的影响。     

采用氮化硅超细粉制成的高密度材料

利用氮化硅等离子化学超细粉以活化烧结法制造了高密度材料。查明了成型压力对烧结氮化硅材料密度的影响。研究了在烧结时材料结构的形成过程。测定了主要的物理结构特性：密度、气孔率及固相颗粒的粒度。     

不同种类氮化硅粉在Al_2O_3-SiC-C铁沟料中的作用比较

为进一步提高出铁沟的高温使用性能,以棕刚玉颗粒、板状烧结刚玉细颗粒、白刚玉粉、碳化硅颗粒和细粉、活性氧化铝粉、硅微粉、铝酸钙水泥、抗氧化剂、单质硅粉、球沥青、氮化硅粉制备了Al_2O_3-SiC-C浇注料。比较了三种不同种类的氮化硅粉(氮化硅-氧氮化硅复合粉、氮化硅铁粉、高纯氮化硅粉)在铁沟料中的作用,结果发现:1)三种氮化硅粉的引入,降低了浇注料的流动值,对线变化率影响不大,但增强了致密度,改善了抗氧化性,提高了高温抗折强度。2)氮化硅-氧氮化硅复合粉对铁沟料高温抗折强度和抗渣性均有显著提高,且与高纯氮化硅粉综合作用相当;氮化硅铁粉的引入提高了铁沟料的致密度,并改善其在1 100、1 450℃时的抗氧化性,但也降低了材料的强度及抗渣性能。3)将氮化硅-氧氮化硅复合粉与氮化硅铁粉共同加入铁沟料中时,相对于仅加氮化硅-氧氮化硅复合粉有更好的流动性,又抑制了氮化硅铁粉对强度和抗渣性能的劣化,具有良好的综合性能,可望在铁沟料中得以应用与发展。     

好氧颗粒污泥形成机理

介绍了好氧颗粒污泥的基本特性,并对目前主流的好氧颗粒形成机理如晶核假说、选择压驱动假说、细胞表面疏水性假说、胞外多聚物假说、自凝聚原理、丝状菌假说和阶段形成假说等进行了综述,结果表明,虽然目前还没有统一的机理,但水力剪切力、胞外多聚物、微生物的自固定等的联合作用对好氧颗粒污泥的形成起了关键作用。     

烧结工艺对β-氮化硅陶瓷的影响

以β-Si3N4粉末为原料,以YAG（钇铝石榴石）为烧结助剂,通过气氛压力烧结（GPS）制备出致密的β-氮化硅陶瓷材料,形成大小均匀的柱状颗粒和小球状颗粒复合显微结构,研究了烧结助剂质量分数、烧结温度以及保温时间对β-氮化硅陶瓷致密化程度及力学性能的影响.     

Evaluation of oxygen content on silicon nitride powder surface from the measurement of the isoelectric point

The oxygen content associated to the surface of silicon nitride powder particles was characterized using a method which is based on the measurement of the specific surface area and the isoelectric point in aqueous solution. From the dissociation model of hydrolyzed surface groups a linear dependence between the fraction of silanol groups (SiOH) and the pH of the isoelectric point is predicted, which was confirmed by electrophoretic measurements of various commercial silicon nitride powders. The proposed method provides rapid information on the particle surface composition, which is of particular relevance for colloidal processing of silicon nitride powders.     

Charging Behavior at the Alumina–Water Interface and Implications for Ceramic Processing

The interaction of water and the alumina surface is comprehensively reviewed. Water can be incorporated in the alumina crystal structure resulting in the formation of aluminum hydroxides such as gibbsite. Alumina dissolves into water to an extent that depends primarily upon the solution pH and temperature. The soluble Al (III)_aq species (hydrolysis products) likewise depend upon the solution pH, temperature, aluminum, and other salt concentrations. The development of charge on the surface of alumina is controlled by amphoteric surface ionization reactions. The charging behavior of both alumina powders and single crystal faces is compared. The differences can be explained by the reactivities of different types of surface hydroxyl groups. The substantial difference in surface charging behavior of single crystal sapphire and alumina powders indicates that experiments and modeling conducted on single crystals is of limited use in predicting suspension behavior. The atomic scale structure of the hydroxylated sapphire (0001) basal plane is nearly identical to the gibbsite (001) basal plane. The observed surface structures are consistent with the charging behavior of the surfaces. The role of surface charge on the adsorption of processing additives is briefly discussed. How surface charge and processing additives at the alumina aqueous solution interface influence surface forces between particles is reviewed. The influence of these forces on suspension properties such as rheological behavior is outlined. The importance of controlling these behaviors to improve colloidal ceramic powder processing is stressed.     

Preparation of aluminum nitride green sheets by aqueous tape casting

Aluminum nitride green sheets were prepared by aqueous tape casting. The characteristics of a treated AlN were studied in aqueous ball-milling media. The oxygen content picked up with the increase of ball-milling time. It was noted that the oxygen content of AlN powder with the dispersant DP270 was lower than that of AlN powder without the dispersant DP270. The isoelectric points of the treated AlN with and without DP270 were, respectively, at pH 3.35 and pH 3.90. The dispersant DP270 not only efficiently dispersed AlN powder in water to form a stable suspension, but also formed a coat onto AlN surface to limit hydrolysis of the AlN powder. The tape casting slurry exhibited a typical shear-thinning behavior. Aqueous AlN green tape had a smooth surface and a narrow pore size distribution. Its relative density was 52.6%. No other crystalline phase was detected by XRD except for AlN and sintering aid yttria in AlN green sheet.     

Elimination of Surface Spallation of Alumina Green Bodies Prepared by Acrylamide-Based Gelcasting via Poly(vinylpyrrolidone)

Surface spallation of gelcast alumina green bodies due to the exposure of the surface to air during gelation was successfully eliminated by adding a proper amount of poly(vinylpyrrolidone) (PVP) in aqueous acrylamide premix solution. The influences of PVP on the colloidal characteristics of alumina powder in aqueous solutions, the rheological properties of alumina slurries, the gelation process, and the properties and microstructures of the gelcast green bodies and the sintered samples were systematically investigated. Even though the addition of PVP to premix solution has slightly negative effects on the viscosity of alumina slurries, gelation and strength of green bodies, it has no obvious influence on the final structure and properties of alumina ceramics. Thus, PVP was considered an effective polymer to resolve the problem of the inhibition of gelation due to the presence of oxygen, which usually occurs in gelcasting during the formation of polymer network gel by in situ polymerization of monomers in air. The mechanism of PVP in eliminating the surface spallation problems of green bodies is also discussed.     

Particle size and zeta potential of carbon black in liquid media

Zeta potential is a parameter that can be used for studying and predicting colloid stability and surface morphology. Even though zeta potential measurements have been applied to both aqueous and non-aqueous suspensions, theories for colloidal behavior and zeta potential in non-aqueous media are not as well-established as those in aqueous environments. There are few reports on systematic studies of zeta potential of colloids in liquid media. In the present study, zeta potential and particle size measurements of two carbon black powder samples in various media were performed. Combined with particle size characterization, the experimental zeta potential values were used to discuss charge transfer and colloid stability of carbon black in suspension.     

Surface modification of ultrafine silicon nitride powders by calcination

Calcination was used for surface modification of ultrafine silicon nitride powders, which improved the flowability and dispersion stability of their slurries. Surface characteristics of the powder were investigated by X-ray photoelectron spectroscopy, which showed the generation of an oxide layer and partial elimination of amine groups on the particle surfaces. Ion analysis results suggested a drop in both ion conductivity and supernatant concentration after calcination. For the as-received powder, poor flowability and dispersion stability was caused by high-valence cations, which were detrimental to colloidal processing according to the Schulze–Hardy rule, and surface amine groups were also present; both of these were partly removed by calcination. The oxide layer formed on the particle surfaces hydrolyzes into silanol groups when the powder is dispersed in aqueous solutions, which was favorable for surface charging and formation of higher diffuse layer potential on the particles. These factors contributed to the improved flowability and dispersion stability of the slurries.     

高固相、低粘度熔石英陶瓷料浆特性的研究

制备高固相、低粘度、高分散性和稳定性的料浆是原位凝固成型高性能熔石英陶瓷的基础.本文通过研究熔石英颗粒在液相介质中的某些胶体特性,分别讨论了pH值对料浆稳定性和流动性的影响;乳酸对熔石英、水系统的稀释和分散机理;分散剂的用量对胶体性质的调节作用.     

Corrosion of ZrB2 Powder During Wet Processing – Analysis and Control

Corrosion behavior of ZrB₂ powder during wet processing in water or ethyl alcohol was studied both with and without an organic additive. Incorporation of oxygen and pH change did not intensively occur during static aging of aqueous slurries, but corrosion was enhanced when stirring the slurries. The oxygen content of the powder increased rather rapidly with milling time in ethyl alcohol. The molecular weight of polyethylenimine effected the pH change and oxygen content of ZrB₂ powder, after corrosion in water for 18 months. X-ray photoelectron spectroscopy analysis informed that the surface of both the pristine and corroded powders was mainly covered with ZrOH, but a certain amount of Zr–B bonding remained at the powder surface after the wet processing.     

Dispersion of Oleate-Modified CuO Nanoparticles in a Nonpolar Solvent

Two nanosized cupric oxide powders, which are synthesized by a vapor-phase reaction and aqueous precipitation, are surface modified with oleic acid to form cupric oleate on the surface. This enhances the dispersibility of cupric oxide powders in a nonpolar solvent of octane. The cupric oxide powder prepared by aqueous precipitation exhibits much better dispersion in octane than that synthesized by vapor-phase reaction. This is attributed to the presence of larger amounts of hydroxyl group on the particle surface, forming more cupric oleate and thus enhancing the colloidal stability of the resulting organic suspension.     

The Role of Material Chemistry in Processing BaTiO3 in Aqueous Suspensions

The application of material chemistry concepts to processing powder suspensions including solution thermodynamics will be demonstrated on several material systems, notably the complex metal oxide, barium titanate, in aqueous environments. After a discussion of the relevant thermodynamic and kinetic issues for fine particles in liquids, various characterization approaches to understand and control the behavior of powders in liquids will be discussed. Various colloidal characterization techniques, high-resolution TEM, and chemical analyses of both the solution and solid exposed to solution have been used to study the nature of the chemical reactions and subsequent altered surface layers in the barium titanate–water system. The key factor in developing an effective aqueous processing scheme for any water sensitive material (and all metal oxides are water sensitive) in aqueous suspension, is recognition that deleterious surface hydrolysis reactions must be prevented. It is shown that local chemical inhomogeneities play a role in abnormal grain growth in the barium titanate system exposed to aqueous environments, but can be controlled with appropriate chemical passivation approaches. The success of a passivation–dispersion approach in the aqueous processing of these materials will be discussed as well as the implementation of the general concept of material chemistry approaches to the aqueous processing of other water sensitive materials.