Improved Aqueous Dispersion of Silicon Nitride with Aminosilanes

The addition of a standard fiberglass surfactant, 3-aminopropyltriethoxysilane (APS), improves whisker and powder dispersion of silicon nitride aqueous suspensions. Aqueous suspensions of APS-coated silicon nitride have lower viscosities, increased consolidation, and higher dried green-body densities compared to uncoated silicon nitride in suspensions with pH values ≤8. The APS coating shifts the isoelectric point (IEP) of silicon nitride to a more basic value, dependent on the concentration of APS coating. Suspension pH measurements indicate that APS extracts one hydrogen ion for each APS molecule either chemisorbed on the particle surface or dissolved in the solution. Optical microscopy reveals that dilute suspensions coated with APS at pH 10 are qualitatively more dispersed than uncoated silicon nitride at pH 7. Our results show increased dispersion of APS-coated silicon nitride in acidic environments, with a 12% increase in green density under identical wetpressing conditions.     

Photocatalytic causticization of sodium oxalate using commercial TiO2 particles

Oxidative photocatalytic degradation has proven to be an effective method for the removal of toxic sodium oxalate, a major impurity in the Bayer liquor obtained during alumina processing. The proposed route also simultaneously converts the oxalate to causticizable solution. The reaction was carried out in an annular multiphase photoreactor with commercial TiO₂ powder (99% anatase) as the catalyst. There was a strong influence of both catalyst content and initial pH of the reaction mixture. Conversion generally decreased with increased pH. Complete mineralization of the oxalate to caustic solution was achieved within a very short period of 2 h at 303 K, 0.5 g l⁻¹ catalyst loading and an initial solution pH of 2. We believe that the reaction proceeds via a homogeneous-heterogeneous mechanism involving interaction between adsorbed oxalate ions (generated from liquid phase dissociation of sodium oxalate) on the titania surface (holes) and hydroxyl species to give adsorbed hydrogen carbonate ions which later desorb to form the caustic NaHCO₃ solution.     

Comparison of the Surface Charge Behavior of Commercial Silicon Nitride and Silicon Carbide Powders

The adsorption and desorption of protons from aqueous solution onto the surfaces of a variety of commercial silicon carbide and silicon nitride powders has been examined using a surface titration methodology. This method provides information on some colloidal characteristics, such as the point of zero charge (pzc) and the variation of proton adsorption with dispersion pH, useful for the prediction of optimal ceramic-processing conditions. Qualitatively, the magnitude of the proton adsorption from solution reveals small differences among all of the materials studied. However, the results show that the pzc for the various silicon nitride powders is affected by the powder synthesis route. Complementary investigations have shown that milling can also act to shift the pzc exhibited by silicon nitride powder. Also, studies of the role of the electrolyte in the development of surface charge have indicated no evidence of specific adsorption of ammonium ion on either silicon nitride or silicon carbide powders.     

Chemical mechanical planarization of copper in alkaline slurry with uric acid as inhibitor

Chemical mechanical planarization of copper disks in hydrogen peroxide and l-arginine based alkaline slurry was investigated. Various commonly proposed inhibitors were screened by static etch rate experiments and only BTA and uric acid were found to be effective in the alkaline pH range, while potassium sorbate was moderately effective. The combination of arginine, hydrogen peroxide and uric acid leads to a more robust polish rate than can be achieved with glycine, hydrogen peroxide and BTA based slurries. The dissolution in presence of uric acid was further studied by potentiodynamic and cyclic polarization experiments which indicate formation of a passivation layer on the copper surface. Silicon dioxide wafers were polished to determine the Cu/silicon dioxide polish rate selectivity in alkaline pH range and a high selectivity (>100) was observed. These results indicate that it is possible to conduct a robust copper CMP with alkaline slurries while maintaining an excellent Cu/silicon dioxide polish rate selectivity.     

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.     

Metal-organic Surfactants as Sintering Aids for Silicon Nitride in an Aqueous Medium

Interaction between two commercial silicon nitride powders and various metal-organic surfactants was investigated in an aqueous medium to obtain a homogeneous distribution of sintering aid. Conditions under which the silicon nitride particles could be coated with metal oxide sintering aids were identified. Acoustophoresis, XPS, TEM, and FTIR were used to characterize the interaction between the metalorganic and the silicon nitride powder. From these data, the mechanism of attachment of the coatings was proposed. The surface area and surface chemistry of the powder, the pH of the solution, the structure of the surfactant, and the surface charge behavior of the powder and the coating were found to be the crucial parameters. The control of these parameters offered a simple and reproducible method to homogeneously distribute various metal oxides. Multicomponent coatings were also possible. The coated powders containing 0.5–4 wt% sintering aid could be compacted to 72% green density.     

Peroxo-oxalate Preparation of Doped Barium Titanate

The peroxo-oxalate complexation method is a method that can be used for the preparation of doped barium titanate. In this paper we focus on BaTi_0.91Zr_0.09O₃, which can be used for discharge capacitors in lamp starters. The preparation method described here is based on the complexation and subsequent precipitation in basic environment of Ba, Ti, and Zr ions with hydrogen peroxide and oxalate. The influence of several process parameters, like precipitation temperature and pH, on powder properties is described. A single-phase perovskite crystal structure is obtained after calcination starting from a chloride precursor solution using a precipitation temperature of 40°C and a pH of 9. Because the peroxo-oxalate process starts with inexpensive chlorides and is performed in air, the peroxo-oxalate process is suitable for the commercial production of doped barium titanate.     

Aqueous Processing of Sintered Reaction-Bonded Silicon Nitride: I, Dispersion Properties of Silicon Powder

An aqueous-based system (Si-Al₂O₃-Y₂O₃-Fe₂O₃) for processing sintered reaction-bonded silicon nitride (SRBSN) was investigated with an emphasis on chemical control of suspension component interactions. Chemical stability and dispersion properties of a commercial silicon powder were characterized using electroacoustic, adsorption isotherm, and rheological measurements. The interactions of silicon with nitriding agent, sintering aids, dispersants, and binder were considered. The effects of pH, electrolyte, aging, particle size, and solids loading were examined. The suspension properties of the silicon powder were influenced by the native oxide film and powder treatment history. The silicon-oxide composite particles exhibit dispersion behavior similar to silica, characterized by a negative surface potential above pH 2. A method to improve the dispersion and homogeneity of suspension components based on the use of quaternary amine dispersants is proposed.     

Nitridation Kinetics and Thermodynamics of Silicon Powder Compacts

The nitridation kinetics of Si powder compacts were studied by measuring the flow rate dependence of N₂ and N₂–H₂ gas mixtures during slow heating of Si compacts while simultaneously monitoring the oxygen partial pressure of the egress gas. The reaction was found to occur in two distinct stages. In pure nitrogen the initial stage was interpreted in terms of devitrification of the native silica layer, catalyzed by Fe impurities, and the exposure of the underlying Si. The reaction sequence at that point has been unequivocally shown to be followed by the formation of oxynitride according to as evidenced by a large increase in the oxygen partial pressure simultaneously with the onset of the initial stage. In the absence of hydrogen, both reactions are rapidly suppressed as the oxygen liberated competes with the nitrogen for the exposed silicon surface and reoxidizes it. However, in the presence of hydrogen, the oxygen liberated reacts with the hydrogen and prevents the reoxidation of the Si. The net reaction in this case is and/or with the second reaction being thermodynamically favored. The main nitridation reaction occurring between 1300° and 1400°C appears to be diffusion controlled and depends on the nature of the passivating layer that forms during the initial stage.     

沉钒废水除硅制备冶金级氢氧化铬研究

研究了以石灰为脱硅剂,采用石灰+片碱（氢氧化钠）沉淀法脱除沉钒废水中的硅,以除硅液为原料制备冶金级氢氧化铬。结果表明,先用石灰调节pH为7.5~8.0,再用片碱调节pH为9.5以上,除硅温度为55~65 ℃,除硅时间为20~30 min,在此条件下除硅率达到67.9%。沉钒废水用石灰除硅后制备的氢氧化铬硅含量低,以二氧化硅质量分数计达到4.2%,可用于冶炼焊剂用、铝剂用金属铬的原料。     

溶剂萃取法准确测定硫酸镍溶液中的微量硅

探索出了用异戊醇萃取硫酸镍溶液中形成的硅钼蓝、然后用弱碱性溶液进行反萃、最后用分光光度法对反萃液进行测定的一种新方法. 实验结果显示,在硅浓度为1~20 μg/mL的范围内符合比尔定律,所测的吸收光度值与硫酸镍溶液中的硅含量有很好的线性关系,相对误差3.6%,测量结果准确、迅速、可靠. 此方法还可以推广应用于其他有色溶液中微量硅的测定.     

流化床生产多晶硅的研究

在流态化CVD法生产多晶硅的过程中发生了无数的均相反应和异相反应,均相反应十分的复杂,生成的无定形硅粉中含有氢键,是硅粉发生爆炸的关键因素。主要介绍了均相反应和异相反应的反应机理和主要影响因素(反应温度、入口硅烷浓度、进料气速、颗粒的平均直径、反应压力、床层高度等)对多晶硅和硅粉的影响规律。     

铁与硅粉及硅铁粉复合电镀工艺的研究

通过复合电镀铁与硅粉及铁与硅铁粉的方法在普通硅钢板表面增硅。研究了复合电镀工艺及粉末颗粒对复合层增硅量的影响。结果表明,随电流密度的增加,镀速加快,但复合镀层中的硅含量逐渐降低。同时,细化复合颗粒及增加镀液中的颗粒含量对提高复合镀层中的硅含量有显著效果。     

Kinetics of CeO2 Surface Area Reduction in a Mixture of HCI, H2O, and O2

Surface area reduction of a cerium dioxide powder is studied at 900 K in a HCI, H₂O, and O₂ atmosphere. The rate of surface area decrease is determined as a function of the surface chloride content and of the partial pressure of hydrogen chloride. It is shown that particle growth occurs due to the surface diffusion of cerium and hydroxyl ions, which results from hydrogen chloride adsorption. Adsorbed chloride ions react to give gaseous chlorine. The rate-determining step of the process of initial coarsening is hydrogen chloride fixation at the surface of cerium dioxide particles.     

直接法合成DDS过程中催化剂的分散及其影响

引　言有机硅材料是半无机、半有机结构的一类高分子化合物 ,具有优良的耐温特性、介电性、生理惰性和低表面张力等性能 ,因此被广泛地应用在航空航天、军事技术、电子电气工业、纺织造纸、建筑工业、化学工业、金属和油漆工业、医药医疗等领域 .甲基氯硅烷是制造有机硅材料的重要原料 ,而二甲基二氯硅烷 (DDS)则是其中需求量最大的一种[1] .目前普遍采用由美国通用电气公司的罗乔(RochowEG)和康宁玻璃厂的海德 (HydeJF)发明的“直接法”生产有机硅单体 ,其主反应为[2 ]Si+2CH3Cl Cu(CH3) 2 SiCl2 ( 1)此过程的主要副反应是[2 ]Si+C…     

表面处理对碳化硅浆料流变性的影响

本文通过对SiC粉体洗涤、表面氧化和聚乙二醇(PEG)包覆等处理后制得的SiC浆料的zeta电位和粘度的测试,研究了表面处理对SiC粉体流变性能的影响.研究表明:通过用酸碱洗涤过后再经过在780℃氧化处理或经PEG包覆所得的SiC粉体,都可以使其浆料的zeta电位的等电点向酸性方向偏移,从而使在pH值为11.8时的电位差大幅度增加,改善了浆料的流变性能.而且用PEG包覆过的SiC粉体浆料的电位差增幅达20左右,使其流变性改善的效果更佳.     

嗜酸氧化亚铁硫杆菌在沥青铀矿石浸出中的作用

为了研究沥青铀矿石的细菌浸出机理,设计了有菌有铁、有菌无铁及无菌无铁3种矿粉浸出试验及有菌无铁、无菌无铁两种试块浸出试验,检测了矿粉浸出体系中细菌的浓度、pH值、Eh、亚铁离子浓度、总铁离子浓度及铀浓度的变化,分析了浸出尾渣中O、Mg、K、P、S、Fe、U等元素的含量,观测了浸出前后试块表面形貌的变化。结果表明,在沥青铀矿石浸出过程中,嗜酸氧化亚铁硫杆菌可以高效氧化浸出体系中的亚铁、还原态硫及元素硫,使得浸出体系中的Eh升高和pH值降低;有菌有铁浸出体系中,高浓度的细菌、高浓度的铁、低pH值和高Eh可加速铀矿石的浸出和提高铀矿石的浸出率;有菌无铁浸出体系中,即使总铁离子浓度很低,但由于有细菌的存在,同样可以加速铀矿石的浸出和提高铀矿石的浸出率。有菌无铁的试块浸出中,试块表面出现了许多溶蚀坑,这表明细菌对铀矿石具有直接氧化作用。     

四氯化硅固定床冷氢化工艺的研究

对四氯化硅固定床加氢工艺进行了研究,考察了反应温度、压力、n(氢气)/n(四氯化硅)、m(催化剂)/m(硅)等因素对四氯化硅转化率的影响。该工艺克服了流化床中粉末状物质会严重堵塞反应装置以及催化剂大量流失的缺点,可以指导生产并为企业带来可观效益。经探讨,最适宜工艺条件为：温度500 ℃;压力35 MPa;n(氢气)/n(四氯化硅)为50;m(催化剂)/m(硅)为0100。     

Effect of surface silanisation on the dry pressing behaviour of silicon nitride powder

The influence of surface modification of silicon nitride powders with alkylsilanes on their compaction behaviour was studied with an instrumented compacting tool. The powder–powder interactions were investigated by viscosity measurements additionally. All silanes, even those with short alkyl chains, reduce interparticular interactions (e.g. hydrogen bridging) and therefore improve the compaction behaviour of ceramic granules in general.     

Dispersing Behavior of Hydroxyapatite Powders Produced by Wet-Chemical Synthesis

Three hydroxyapatite powders with different surface properties were produced by wet-chemical synthesis and characterized. The electrokinetic properties of powders dispersed in water were investigated by electroacoustic spectroscopy measurements. The different surface reactivity (pH_iep and ζ potential versus pH curves) was related to the interplay of dissolution and adsorption of Ca²⁺ ions. With a view toward the preparation of porous bodies by sponge impregnation, the behavior of powder suspensions was studied. Four deflocculants were tested, and the optimum dispersing conditions for each powder were found. Anionic polyelectrolytes resulted in the best effective dispersing agent, with different optimum amounts added to the suspensions.