改性SiC料浆悬浮稳定性研究

选取丁二酸、乙二醇、对氨基苯磺酸和聚乙二醇（PEG4000）四种具有不同分子结构的有机物作为改性剂对SiC微粉进行表面包覆改性,研究了分子结构对料浆悬浮稳定性的影响及不同改性粉体在水中的分散机制。实验表明：丁二酸、乙二醇、对氨基苯磺酸改性的SiC微粉主要是静电稳定,其中对氨基苯磺酸改性粉体的Zeta电位绝对值最高,料浆的悬浮稳定性较前二者好;PEG400改性粉体主要是空间位阻稳定,但其悬浮稳定性最好。     

水基改性碳化硅陶瓷料浆流变性的研究

用有机硅偶联剂处理SiC粉体，在适合的上，经聚合反应再将有机的单体接枝于SiC颗粒表面上，在SiC颗粒表面上形成聚电解质包覆层，以改善SiC粒子在水介质中的分散性质。同时研究了改性SiC粉在水介质中的稳定条件，荷电性及在高固体含量下，用改性SiC粉所制备的陶瓷料浆的流变性。研究结果表明：改性后碳化硅粉在水中的分散稳定性能大大优于未改性碳化硅粉，所制备料浆体系的固体含量，分散稳定性能，粘度等参数有满足注浆成型工艺的要求。     

聚乙烯亚胺表面改性SiC粉体的流动特性

采用聚乙烯亚胺（PEI）作为表面活性剂对工业用SiC粉体进行表面改性处理,研究了改性前后SiC粉体的流动特性以及PEI加入量和pH值的影响.实验结果表明：PEI加入量为3%（质量分数）、pH值为6.5时,改性后的SiC粉体取得较好的流动特性和较高的饱和吸附量,颗粒分散较好,颗粒尺寸和形状较为均匀.     

油基纳米氧化锌分散浆的制备及其流变性能

选用硬脂酸钠对ZnO进行表面湿法改性,以环十五硅氧烷硅油为溶剂,PEG-10聚二甲基硅氧烷为分散剂,通过机械球磨法制备纳米ZnO分散浆.利用水接触角、热重、TEM和FTIR对纳米ZnO粉体进行表征.结果表明,硬脂酸钠改性后,粉体具有疏水性,且硬脂酸钠最佳包覆量为6％(以ZnO的质量计,下同).硬脂酸钠包覆量为6％的疏水性纳米ZnO粉体,包覆层厚度约为2 nm,此时水接触角最大为145.4°.模拟防晒乳液的防晒性能测试中,纳米ZnO分散浆的紫外屏蔽性能显著优于粉体.流变特性测试表明,分散浆为假塑性流体,流动曲线符合Ostwald-de Wale幂律方程,具有剪切稀化特性;分散浆具有黏度低、触变性小、储存稳定性高的特点;温度升高,分散浆黏度降低,配方生产中分散浆黏度对温度的敏感程度较小.     

高固体含量陶瓷料浆稳定机理及粉体表面改性方法

本文通过对高固体含量料浆的稳定机理的研究，总结了一些颇为有效的无机粉体表面改性方法，如酸洗工艺、疏水化处理、聚合物在粉体表面接枝、聚合物包覆等，最后展望了粉体表面改性方法的发展趋势。     

甘氨酸钠对SiC粉体的表面改性及其浆料流变性研究

以强电解质甘氨酸钠(SG)为改性剂,考察其在SiC粉体表面的吸附状况,制备高分散SiC粉体,同时研究其浆料流变性。结果表明,采用固相球磨和恒温处理工艺,0.15%甘氨酸钠改性后的SiC粉体Zeta电位绝对值明显高于改性前,pH值为10.0时,从38.9 mV增加到62.2 mV。TOC(总有机碳)对粉体洗涤液中有机物含量的测试表明,微量甘氨酸钠的平衡吸附可有效降低SiC浆料粘度,提高其固含量和稳定性。     

有机羧酸改性氮化铝粉体的抗水解性能

采用有机羧酸和PEG作为表面活性剂对工业AlN粉体进行表面改性处理,研究了改性前后AlN粉体的抗水解特性以及表面改性机制。研究结果表明,AlN表面与水分子发生化学反应,导致溶液的pH值迅速提高,表面包覆有机羧酸可有效地改善AlN粉体的抗水解性能;AlN粉体在水中浸泡48h后,氮含量基本保持不变,除了AlN晶相外,没有其他晶相出现,且改性粉体在高剪切应力的水基球磨介质中也保持较强的稳定性。     

油基纳米氧化锌分散浆的制备及其流变特性

选用硬脂酸钠对ZnO进行表面湿法改性，以环十五硅氧烷硅油为溶剂，PEG-10聚二甲基硅氧烷为分散剂，通过机械球磨法制备了纳米ZnO分散浆。利用水接触角、热重、TEM和FTIR对纳米ZnO粉体进行表征。结果表明，硬脂酸钠改性后，粉体具有疏水性，且硬脂酸钠最佳包覆量为6%（以ZnO的质量计，下同）。硬脂酸钠包覆量为6%的疏水性纳米ZnO粉体，包覆层厚度约为2 nm，此时水接触角最大为145.4°。模拟防晒乳液的防晒性能测试中，纳米氧化锌分散浆的紫外屏蔽性能显著优于粉体。流变特性测试表明，分散浆为假塑性流体，流动曲线符合Ostwald-de Wale幂律方程，具有剪切稀化特性；分散浆的黏度低，触变性小，储存稳定性高；温度升高，黏度降低，配方生产中对温度的敏感程度较小 。     

工艺参数对凝胶注模成型ZrO_2料浆性能的影响

以亚微米级ZrO2粉体为原料,采用丙烯酰胺(AM)/N,N-亚甲基双丙烯酰胺(MBAM)凝胶体系,通过凝胶注模成型工艺制备低粘度、高固相含量的ZrO2料浆。探讨了分散剂用量、料浆pH值、固相含量及研磨时间等工艺参数对ZrO2料浆性能的影响。用Zeta电位仪、粘度计和流变仪分别对料浆的Zeta电位、粘度值和流变学特性曲线进行测定。结果表明,A型分散剂(聚丙烯酸盐)用量为ZrO2体积的2%~2.5%时,对超细ZrO2粉体分散效果最佳,其料浆pH值以10~11为宜,研磨时间控制在12~15h,料浆固相体积分数可达50%~54%。     

化学镀法制备SiC/Cu金属陶瓷复合粉体工艺的研究

为改善SiC与其他金属的结合性能，采用化学镀法在SiC粉体上镀Cu，制备包覆型陶瓷颗粒。通过精选、粗化、敏化、活化表面镀前处理，用硫酸铜镀液成功地得到在SiC上均匀镀Cu的包覆粉体，利用Olympus显微镜观察到包覆程度可达95％，通过详细讨论镀液的配方、pH值、镀液与SiC粉体的配比与对包覆效果的影响，最终得到硫酸铜用量控制在10—15g／l能得到我们所控制的沉积反应速度；包覆反应过程中pH值控制在11—13之间较为合适。     

Adsorption of anionic polyelectrolyte on an SiC surface and effects on dispersion stability

Aluminum nitrate (Al(NO₃)₃) and sodium polystyrene sulfonate (PSS) were used to improve the dispersion of fine silicon carbide (SiC) powders. Effects of modification parameters on the viscosity of modified SiC slurry were studied by orthogonal experiments. Modified SiC slurry with the solid loading of 50 vol% reached the lowest viscosity of 34 MPa s. The adsorption processes of PSS on the as-received and Al(NO₃)₃ premodified SiC surface were investigated. The results indicated that the adsorption between PSS and premodified SiC surfaces was a high affinity type and was mainly controlled by active sites on an SiC surface. The Langmuir model and the pseudo-second-order model could better fit the adsorption isotherm and kinetics data, respectively. The contact angle decreased from 32.8 to 15.2° and the wettability was improved by modification. The isoelectric point of modified SiC powder shifted to the acidic region and the maximum zeta potential was obtained at pH 11. Sedimentation results also showed that a stable dispersed suspension of modified SiC was achieved at pH 11. Density–pressure curves demonstrated that the flowability and formability of SiC powder were improved by modification. The dispersion effect of PSS on SiC and Al₂O₃ composite powder was verified by viscosity and sedimentation results.     

Surface modification of superfine SiC powders by ternary modifiers-KH560/sodium humate/SDS and its mechanism

SiC is a promising functional ceramic material with many great properties. High concentrated SiC slurry with excellent rheology and stability is required in some processes of ceramic forming. In this work, the dispersion of SiC powders was obviously improved by ternary modifiers: γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560), sodium humate and sodium dodecyl sulfate (SDS). Modified SiC slurry showed the lowest viscosity of 0.168 Pa s at a solid content of 50 vol%. The maximum absolute value of zeta potential of SiC increased from 47.3 to 61.6 mV by modification. Sedimentation experiments showed that a highly stable suspension of modified SiC was obtained at pH 10. SiC green body with high density of 2.643 g/cm³ was prepared with modified powders by slip casting. X-ray photoelectron spectra (XPS) and thermogravimetry (TG) measurements indicated the adsorption of modifiers on SiC surface. Therefore, modified SiC powders could stably disperse in aqueous media due to the increase of electrosteric repulsion between particles. The novel strategy used in this study could further improve the dispersion of SiC powders.     

分散剂用量对碳化硅浆料流变性能的影响

使用四甲基氢氧化铵(TMAH)作为分散剂,研究了分散剂用量对SiC浆料流变性能的影响,并分析了其原因。结果表明：TMAH能够显著提高SiC粉体的zeta电位,降低浆料粘度,从而显著优化浆料的流变性能。在pH为10左右,加入质量分数为0．3％和o．6％NTMAH后zeta电位分别提高了11.7mV和21mV。实验中,在不同体积分数SiC浆料中,加入0．6%TMAH时能够达到最优性能,浆料粘度都达到最低。过量的分散剂则会增加浆料中的离子浓度而导致双电层厚度减小,从而恶化浆料的流变性。     

Electrostatic and electrosteric stabilization of aqueous slips of 3Y–ZrO2 powder

Yttria-doped zirconia powder (3Y-ZrO₂) was characterized and dispersed in distilled water. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the slip. Zeta potential, apparent viscosity and the mean particle size as a function of pH indicated the pH range of electrostatic stabilization. These results showed that electrostatic stabilization of the slip can be accomplished in low acidic and high basic range of pH. Dissolution of yttria from the powder surface in acidic pH was found to be high and fast, risky to the stability of the slip as well as the microstructure of the sintered body. Electrosteric stabilisation by addition of an anionic polyelectrolyte (PMAA-NH₃) shifted the isoelectric point (IEP) to lower pH. The state of dispersion was further investigated by particle size measurements of the solid phase in the slip. The optimum amount of dispersant is discussed in terms of zeta potential and viscosity. The adsorption of polyelectrolyte is considered at pH 4, native pH of suspension and at pH 10, below and above the IEP of powder and correlated with the dissociation rate of polymer and the net surface charge of particles at given pH. Higher adsorption of dissociated polymer to the positively charged surfaces justifies the higher optimum amount of polyelectrolyte at pH 4.     

Surface modification of SiC powders by hydrolysed aluminium coating

SiC powders are surface modified to behave like alumina in aqueous suspensions by coating the powders with in situ generated hydrolyzed aluminium from dilute aqueous aluminum nitrate solutions in a pH range of 3–4.5 using hexa-methylene-tetramine as the base generator at ambient temperature. By examining the zeta potential and rheological properties of aqueous suspensions of the powder with different Al-coverage, it was observed that the coated powder begins to show alumina-like surface properties at an Al-coverage of 0.1 mg/m², in contrast to 0.5 mg/m² that was the minimum value reported earlier for observing the effect. This is explained by proposing a coating mechanism which proceeds through adsorption of a layer of cationic hydrolysed aluminum molecules, such as [Al(OH)(H₂O)₅]²⁺ and [Al₂(OH)₂(H₂O)₈]⁴⁺, during which the particles attain alumina-like surface charge properties. The modified powder retained alumina-like surface characteristics when stored under moist conditions and in acidic suspensions. The low value of Al-coverage and the resulting low increase (<10%) of powder surface area are advantageous for preparation of concentrated SiC and SiC–Al₂O₃ composite suspensions in acidic aqueous medium with rheological properties similar to that of their counterparts containing alumina only.     

Influence of Surface Cleaning and Calcination on Rheological Properties of Silicon Carbide Aqueous Suspensions

The influence of surface cleaning, including deionized water, acid, and base cleaning, on the rheological properties of silicon carbide (SiC) aqueous suspensions was investigated. The SiC powders were well dispersed irrespective of the surface treatment. However, the viscosity was affected by the surface cleaning. The experimental results indicated that base cleaning caused a lower viscosity. The reason of the cleaning influence on viscosity was discussed. The influence of SiC oxidative thermal treatment was determined for SiC suspensions. Calcination of SiC powders at 550°C is observed to evidently reduce the viscosity of the SiC slurry. But further increase of the calcination temperature will be deleterious to the rheologic properties. The hydration of amorphous SiO₂ on the SiC surface is used to clarify the phenomenon.     

ZrO_2表面改性及凝胶注模研究

凝胶注模成型工艺能够制备出高强度,高致密性,且形状复杂的氧化锆陶瓷。粉体团聚对凝胶注模成型工艺存在不良影响,粉体团聚导致陶瓷内部产生缺陷,导致致密性、均匀性变差,力学性能降低。本文通过对氧化锆粉体表面改性,改善粉体团聚,将改性粉体用于凝胶注模成型,制备出低粘度浆料。通过SEM、粘度仪、显微镜等仪器,对强度、粘度及粉体分散情况进行表征。结论 :当钛酸酯偶联剂加入量为0.4 wt%时,粉体团聚情况以及粘度达到最佳,当固相含量为50%时,粘度达到557.6 mPa·s,抗弯强度达到710.08 MPa,洛氏硬度达到92 HRB;断面观察,改性后陶瓷内部颗粒间结合较为紧密,结构均匀。     

Dispersion properties of alumina powders in silica sol

The dispersion of alumina powders in silica sol has been investigated by zeta potential, sedimentation, and rheological measurements. Zeta potential of alumina in silica sol changes significantly in comparison with that of alumina in deionized water. This is caused by the absorption of silica colloidal particles with negative charge on the surface of alumina particles. Sol-dispersed alumina slurry shows a minimum in sedimentation volume and viscosity around pH 10. The viscosity depends strongly on the silica sol concentration and reaches a minimum in 10–15 wt.% silica sols. It is proposed that the dispersion and stabilization of alumina particles in silica sol are attributed to the electrostatic and steric effects of the colloidal particles absorption. Effects of pH, solids content and silica sol concentration on the rheological behavior of sol-dispersed alumina slurries are discussed in detail.