陶瓷料浆稳定分散进展

本文综述了影响陶瓷料浆稳定分散的胶态理论进展,同时指出配制稳定分散陶瓷料浆的控制因素及调控措施。     

表面活性剂在陶瓷工业中的应用

详细介绍了表面活性剂在防止纳米陶瓷粒子的团聚、提高分散效率、降低能耗及提高陶瓷品质等方面的应用;同时概述了表面活性剂在粒子表面的吸附和对制品的消泡等作用原理及在其他方面的应用;最后展望了新型表面活性剂在陶瓷工业中的应用前景。     

海泡石陶瓷料浆稳定性的研究

通过Zeta电位、沉降实验、粘度等测试表征不同分散剂对海泡石陶瓷料浆稳定性的影响。研究表明:阴离子活性剂十六烷基苯磺酸钠对固相浓度增大、粒径小的海泡石料浆的分散稳定性效果较好,且在pH=11,浓度为0.8wt%时达到最佳,其分散稳定作用的实质是增强了微粒间的静电排斥作用和空间位阻排斥作用,并减弱了范德华吸引作用。海泡石对SDBS的吸附曲线是Langmuir单分子层吸附模型。     

分散剂在铁氧体软磁材料制备中的应用

分散剂是一种同时具有亲油性和亲水性两种相反性质的表面活性剂。笔者综合论述了分散剂的分类及其作用机理。着重介绍了分散剂在铁氧体材料制备中的作用．并分析了分散剂的选用、分散剂的最佳用量、分散剂的PH值等因素对铁氧体料浆分散效果的影响。     

以聚硅氧烷乳液/聚丙烯酸铵为复合分散剂制备高性能氮化硅料浆

以聚硅氧烷乳液(S-17)/聚丙烯酸铵[poly(acrylic acid)ammonium,PAA-NH4]为复合分散剂制备了高浓度且稳定的Si3N4凝胶注模料浆,用电泳仪分析了料浆中颗粒表面zeta电位,用转子黏度计测量了料浆的黏度,用沉降法表征了Si3N4粉体的分散稳定性,用黏度法获得颗粒对聚硅氧烷分子的吸附等温线.研究了PAA-NH4分散剂和聚硅氧烷表面活性剂对高固相含量、低黏度料浆的稳定性影响机制.结果表明:单独使用PAA-NH4不能达到较好的稳定效果,采用聚硅氧烷乳液/PAA-NH4复合分散剂,聚硅氧烷乳液用量为0.4%(质量分数,下同),PAA-NH4为0.8%时,可制备固相体积含量为50%,黏度低于1.0 Pa·s,稳定性较高的料浆.该料浆适于凝胶注模操作.根据静电作用原理,结合颗粒对聚硅氧烷分子的吸附特性,提出通过降低液相表面张力来降低料浆黏度及提高稳定性,探讨了高固相含量料浆分散的理论机理.     

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。     

氮化硅泡沫陶瓷浆料性能的研究

系统地研究了料浆pH值、分散剂及固相含量等因素对陶瓷料浆电势和流变性的影响,制备出了有良好稳定性和流动性的氮化硅料浆。研究表明,静电空间位阻稳定机制是陶瓷料浆稳定性的根本原因。料浆pH值、分散剂和固相含量等因素对陶瓷料浆的分散稳定性及流变性均有一定的影响。料浆的pH值为10-11、分散剂PAA-NH4用量为1 wt.%以及固相含量为50 wt.%时,可获得具有良好性能的氮化硅料浆浓悬浮体。     

表面活性剂对料浆法重钙水溶磷影响的实验研究

为了提高重钙产品水溶磷含量,模拟料浆法重钙生产工艺,在实验过程中添加表面活性剂,研究其对重钙产品水溶磷的影响。从21种单一及其复配型中筛选出了可以有效提高重钙水溶磷的6种表面活性剂。实验表明,通过添加表面活性剂,改善料浆反应状况,提高重钙水溶磷含量是可行的。     

卵磷脂改善瘠性料浆悬浮性的研究

注浆成型是一种应用广泛的陶瓷成型工艺 ,但要浇注出密度高、微观结构均匀的坯体 ,配制稳定性好的浆料悬浮液是关键之一。瘠性料浆由于不具亲水性 ,通常较难获得稳定的浆料 ,而卵磷脂是天然的两性表面活性剂 ,既存在极性基 ,又存在非极性基 ,固体颗粒可以通过卵磷脂的吸附、表面改性使料浆悬浮。本文以氧化铝浆料为例进行了添加卵磷脂改善与提高瘠性料浆的悬浮性的研究 ,并获得了良好的效果     

煤油水三元料浆流变特性的研究

对煤油水三元料浆的流变特性进行了实验研究。实验结果表明,由煤粉、水、油组成的三元料浆是一种复杂的固－液分散体系,其属于非牛顿流体中假塑性流体。体系中加入适宜的表面活性剂可改变其粘滞性,特别是非离子型复合添加剂TW－SP的使用,可显著改善体系的流动性。此外采取湿磨成浆,可提高煤浆浓度和流动性。     

天然鳞片石墨在水中的分散性研究

利用ζ电位、润湿性、沉降性、流变学测试研究了表面活性剂、表面包覆Al(OH)3对天然鳞片石墨在水中分散性的影响。结果表明：经过表面活性剂处理和Al(OH)3表面包覆能使石墨在水中的分散性能得以改善，石墨在水中的分散性取决于石墨与水的润湿性。     

Coal slurries in mixed liquid fuels: rheology and ignition characteristics

In the presence of surfactant, coal/No.2 oil+ethanol, slurries containing water exhibited dramatic reduction in Bingham yield stress and plastic viscosity. The observed rheological behavior was explained in terms of coal particle network formation by water bridging mechanism. Lowering of interfacial tension between water and suspension medium in the presence of surfactant was attributed to be responsible for the reduced yield stress and plastic viscosity. In the low heating rate experiments, ignition behavior of slurries containing up to 20 wt.% of water was not appreciably altered. It appears that water vaporizes prior to the ignition/combustion stage, thereby not influencing the overall ignition behavior.     

Effect of Zwitterionic Surfactants on Interparticle Forces, Rheology, and Particle Packing of Silicon Nitride Slurries

Phosphocholine (PC) zwitterionic surfactants, with different hydrocarbon chain lengths (C₆C₆PC to C₉C₉PC), were absorbed on the surface of silicon nitride near the isoelectric point (pH 6). Adsorption of the surfactants changed the lateral and normal surface forces, the rheology, and the consolidation behavior of the particles. The normal force between two silicon nitride surfaces as a function of separation and the lateral (friction) forces were measured using an atomic force microscope (AFM). These measurements indicated that surfactant adsorption reduced the magnitude of the long-range attractive van der Waals force and produced a repulsive short-range force. Although the adsorbed layers provided a barrier to particle contact, they could be ejected with a critical force that increased with the hydrocarbon chain length. The effect of an adsorbed layer on the viscosity and consolidation of slurries was also measured. The viscosity of all slurries decreased with increasing shear rate, indicative of attractive particle networks. The highest viscosity was observed for slurries formulated at the isoelectric point without added surfactant. Much lower viscosities were observed when the surfactant concentration was greater than the critical micelle concentration (cmc). A relative density of 0.46 was obtained via pressure filtration at 4 MPa without a surfactant, and between 0.46 to 0.59 (C₆C₆PC to C₉C₉PC, respectively) for surfactant concentrations greater than the cmc. Comparing force measurements with rheology and packing density provides a basis for discussing the role of interparticle forces in ceramic powder processing via colloidal routes.     

Pipe diameter effect on flow and heat transfer characteristics of ammonia alum hydrate slurries with additives

In this study, pipe diameter effect on flow and heat transfer characteristics of ammonia aluminium sulfate dodecahydrate (ammonia alum hydrate: AlNH₄(SO₄)₂·12H₂O) slurries with drag reducing surfactants and poly(vinyl alcohol) was investigated. Pressure loss and heat-transfer coefficients of ammonia alum hydrate solutions and slurries were measured with double-pipe heat exchangers with different inner tube diameters. Measurement results indicated that pseudo-laminarization by the surfactant caused drag-reduction effect and its saturated magnitude was affected by inner tube diameters. Pseudo-laminarization also produced heat transfer reduction effect and its magnitude was not affected by inner tube diameters. Calculation results of Colburn's j-factor divided by friction factors indicated that heat transportation efficiency of the hydrate solutions/slurries with additives was increased due to the contribution of drag-reduction effect.     

Defect and microstructural evolution during drying of soapnut-based alumina foams

The present study demonstrates the use of soapnut, a naturally occurring surfactant for producing alumina ceramic foams. A range of slurry compositions with soapnut amounts ranging from 2 to 20 wt% in water, alumina loading of 35–55 vol% were studied. Though all slurry compositions foamed when subjected to mechanical agitation the formation of green ceramic foams free of macroscopic defects was found to be strongly dependent on conditions during drying of foamed slurries. Addition of guar gum to the slurries was shown to enhance foam stability and thus produce defect-free foams from compositions that otherwise either collapsed or resulted in other macroscopic defects during drying. Drying conditions also had a strong effect on microstructural parameters such as cell size and cell connectivity. Soapnut-based foams appear to have a greater connectivity between cells than foams produced by other comparable processes.     

Tailoring the microstructure of high porosity Si3N4 foams by direct foaming with mixed surfactants

The mixed surfactants were successfully applied to fabricate the highly porous Si₃N₄ ceramic foams by the direct foaming method. The oppositely charged surfactants mixed in slurries could combined into catanionic surfactant by the electrostatic attraction and facilitate the formation of ultra-stable foams. The microstructure of the Si₃N₄ ceramic foams, including pore structure, mean pore size, pore size distribution and porosity were tailored by varying the mixing ratio of surfactant, mixed surfactants concentration and solid content of the initial slurries. Si₃N₄ ceramic foams with porosity of 92%-97%, mean pore size of 140-240 µm and compressive strength of 0.85-5.38 MPa were obtained by adjusting mixed surfactants between 0.1 and 0.4 wt% and solid content between 22 and 30 vol%. The compressive strength of Si₃N₄ ceramic foams in current work was much higher than most reported results.     

Interaction force measurements using atomic force microscopy for characterization and control of adhesion,dispersion and lubrication in particulate systems

Atomic force microscopy is used as a vital tool in understanding the fundamental mechanisms of particulate processes in dry, humid and aqueous systems. Adhesion forces in both dry and humid systems were studied between surfaces of varying roughness, taking into account the capillary forces at high humidity conditions. Colloidal stability in aqueous systems due to non-DLVO forces and steric effects of surfactant aggregates formed on particle surfaces at varying pH and ionic strength conditions were investigated. The force–distance curves obtained by atomic force microscopy were used to determine the mechanical and thermodynamic properties of the self-assembled surfactant structures formed on the surface. Besides determining the repulsive force barrier provided by the surfactant aggregates in dispersion of slurries, the frictional interactions between surfactant adsorbed surfaces were measured using lateral force microscopy, providing valuable insights into the role of dispersants acting as lubricants. The range of interaction forces that can be explored using the Atomic Force Microscopy (AFM) can be utilized to predict, optimize and design a variety of industrially relevant processes such as chemical mechanical polishing (CMP), powder flow and handling and nano-dispersions, just to name a few.     

RHEOLOGY OF VERY CONCENTRATED COAL SUSPENSIONS

Non-Newtonian viscosity curves of coal slurries were measured over a 3-5 decade shear rate range with a Weissenberg Rheogoniometer, for coal volume fractions up to 0.6 and particle sizes under 62 fim. Suspending media were Aroclor 1254 (a chlorinated biphenyl), glycerin, and glycerin with surfactant; these have densities very close to that of coal, so no settling occurred. Viscosity magnitudes generally exceeded predictions of correlations and theory established for spherical particles; explanations are sought in terms of particle aggregation, shape irregularity, and surface effects.     

RHEOLOGY OF VERY CONCENTRATED COAL SUSPENSIONS

Non-Newtonian viscosity curves of coal slurries were measured over a 3-5 decade shear rate range with a Weissenberg Rheogoniometer, for coal volume fractions up to 0.6 and particle sizes under 62 fim. Suspending media were Aroclor 1254 (a chlorinated biphenyl), glycerin, and glycerin with surfactant; these have densities very close to that of coal, so no settling occurred. Viscosity magnitudes generally exceeded predictions of correlations and theory established for spherical particles; explanations are sought in terms of particle aggregation, shape irregularity, and surface effects.     

石油磺酸盐表面活性剂在水煤浆制备中的应用

提出利用廉价易得的石油磺酸盐表面活性剂制备水煤浆。通过FTIR光谱分析了5种不同工艺的石油磺酸盐产品的结构,并考察了各种石油磺酸盐所成浆体的流变性、静态稳定性等因素。研究发现,原料馏分油中芳香类物质含量越多、对其磺化程度越高,所得的石油磺酸盐产品分散降黏性能越好,更适合作为水煤浆分散剂。结果表明,F#石油磺酸盐的成浆性能最好,当w(F#)=1 5%时,水煤浆中w(煤粉)可达65%,在25℃下剪切速率为100s-1时浆体的表观黏度为620mPa·s,可稳定贮存20d以上,达到了工业上对水煤浆性能的要求。