添加纳米微粒的溴化锂溶液稳定性及烧结特性研究

通过在58%浓度工业用溴化锂水溶液中添加纳米微粒及其相应的分散剂,对纳米溴化锂溶液的稳定性及其在高温温度下的烧结特性进行研究。研究结果表明,在纳米溴化锂溶液中分散剂浓度从0.3%变化到0.6%,具有最佳组分值,即:最佳稳定性能值。纳米溶液在160℃温度下,分散剂组分由0.1%增至1.0%,加热过程的24h中,烧结物粒径增长率较大,48h后,所有组分的粒径增长趋于缓慢;在纳米溶液分散剂组分不改变,加热温度由50℃增加到160℃期间,12h过程中,粒径增长速率较快,48h后纳米粒径增长趋势平稳。烧结粒径微观分析可知,分散剂组分从0.1%增加至1.0%,烧结体粒径变小,这说明分散剂组分越浓,烧结体粒径越小,烧结层越密实。因此,需要在改变纳米溴化锂溶液的稳定性和烧结现象之间进行优化组合,并选择耐高温的分散剂。     

Surface modification and characterization for dispersion stability of inorganic nanometer-scaled particles in liquid media

Abstract

Inorganic nanoparticles are indispensable for science and technology as materials, pigments and cosmetics products. Improving the dispersion stability of nanoparticles in various liquids is essential for those applications. In this review, we discuss why it is difficult to control the stability of nanoparticles in liquids. We also overview the role of surface interaction between nanoparticles in their dispersion and characterization, e.g. by colloid probe atomic force microscopy (CP-AFM). Two types of surface modification concepts, post-synthesis and in situ modification, were investigated in many previous studies. Here, we focus on post-synthesis modification using adsorption of various kinds of polymer dispersants and surfactants on the particle surface, as well as surface chemical reactions of silane coupling agents. We discuss CP-AFM as a technique to analyze the surface interaction between nanoparticles and the effect of surface modification on the nanoparticle dispersion in liquids.     

利用Turbiscan Lab稳定性分析仪研究水焦浆的稳定性

采用静置观察法与Turbiscan Lab稳定性分析仪相结合研究了粒度分布、分散剂和黏土矿物对水焦浆〖JP〗(PCWS)稳定性的影响。结果表明,PCWS中焦粉粒度越大,沉降末速越大,稳定性越差,但成浆浓度较高。木质素系分散剂能够使得复合焦粒通过氢键作用形成三维网络结构,有效地阻止焦粒间的聚结,显著提高水焦浆的稳定性;蒙脱石在水中易于细分散并吸水膨胀,使焦粒的密度逐渐接近于水的密度,阻碍焦粒的沉降,进而提高水焦浆的稳定性。选择平均粒度为4147 μm的石油焦粉,采用木质素系分散剂配以少量蒙脱石作为添加剂,制备的水焦浆浓度可达6660%,静置15 d内既不产生沉淀,又不发生析水分层,TSI值仅为01左右,具有良好的静态稳定性,有利于水焦浆的大规模工业化应用。     

Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts

The slurry-based Three Dimensional Printing (3DP^TM) process requires the production of an easily redispersible powder bed from a well-dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle–particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle–particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low-molecular-weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.     

Lead Zirconate Titanate Particle Dispersion in Thick-Film Ink Formulations

Diverse device applications for lead zirconate titanate (PZT) ceramics in thick-film form are currently in active development. In the present study, the particle dispersion properties of thick-film ink formulations containing PZT powder have been determined using rheological measurements. Although all of the eight commercially available dispersants tested are more effective than the terpineol solvent alone in decreasing attractive interparticle forces in suspensions, the best dispersant identified for hard and soft PZT powders is a phosphate ester oligomer. This dispersant is extremely efficient, and its use in thick-film ink formulations results in viscosity decreases of 50% at low shear rates (10 s⁻¹) and 30% at high shear rates (100 s⁻¹) compared with current ink formulations containing no dispersant. The effects upon rheology of the order of addition of components in the processing of inks have been studied, with the most effective processing route using a fugitive solvent that probably facilitates uniform coverage of the particle surfaces by the dispersant molecules. Modeling of the rheological profiles of inks indicates that the use of a dispersant decreases the depth of the primary minimum in the interparticle potential by a factor of 3. Demonstrated advantages of the use of a dispersant in PZT thick-film inks include improved microstructural homogeneity in the green body and the ability to formulate printable inks with higher solids loadings. No adverse effects of the dispersant upon the dielectric and piezoelectric properties of bulk PZT samples are found following burnout and sintering.     

Dispersants for silicon carbide in water—A comparative study

The present work describes a comparative study on a pool of 12 dispersants for the de-agglomeration and stabilization of silicon carbide in aqueous suspensions with solids loading relevant for dip coating applications. As silicon carbide slurries may include sintering aids, different functional groups, molecular weight, and stabilization mechanisms were considered for the dispersants to be able to stabilize both slurry components. Additionally, pH effect, toxicity, additive compatibility, and foaming properties were considered, giving all the necessary information for developing new aqueous formulation of SiC suspensions, including advantages and disadvantages of the different candidates. Different de-agglomeration procedures, powder surface area, and calcination temperature were also considered to study the effect of the SiC surface properties. The outcome is that slurry stabilization provided by an alkaline environment at pH larger than 8‒9 is significantly more effective than slurry stabilization by any of the tested dispersants. Alkaline environments facilitate a negative surface charge on SiC particles and provide a stable electrostatic stabilization mechanism not observed in neutral or acidic environments. One among the dispersant candidates (FA 4404) seems to broaden slightly the range of stability toward the acidic regime. Anionic surfactants or block co-polymers tested exhibited no significant interaction with the SiC particles.     

不同分散剂对提高钛白粉生产过程中分散效果的研究

针对钛白粉生产过程中粗品分散问题进行了研究,主要添加分散剂硅酸钠和六偏磷酸钠比较分散的情况。试验表明,当分散剂加入量为钛白粉质量的0.5%时,硅酸钠对几种钛白粉的分散性比较好,矿浆黏度比较低;六偏磷酸钠的分散性比较弱,矿浆黏度下降很少。分析表明是因为分散剂在水中水解成阴离子吸附在颗粒表面,使颗粒表面带电,阻止了颗粒之间的团聚。     

Group transfer polymerization and its use in water based pigment dispersants and emulsion stabilizers

Group transfer polymerization (GTP) can be used to make AB diblock acrylic polymers. It provides excellent control of the structure of these polymers. With a hydrophilic B block, these polymers have been used to prepare water based emulsions, pigment dispersions, and slurries. These systems have property advantages over emulsions and dispersions made with conventional stabilizers. These advantages include increased stability, smaller particle sizes, lower viscosities, and less moisture sensitivity. The structure of the AB diblock polymer affects the properties of both the pigment dispersion and the emulsion particle. The composition, size and ratio of each block affect the overall quality. For aqueous systems, a balance of hydrophobic ‘A’ blocks and very hydrophilic ‘B’ blocks is needed for optimum properties. The hydrophobic ‘A’ blocks, which are homo or copolymers of methacrylate monomers (such as butyl or ethylhexyl methacrylate), are surface active and can associate with either pigment or emulsion polymer surfaces. The hydrophilic ‘B’ blocks, which are neutralized acid or amine containing copolymers, provide both ionic as well as steric stabilization in water-borne systems.     

Additive-Enhanced Redispersion of Ceramic Agglomerates

Deagglomeration of ceramic powders is usually accomplished by immersion of powders in a surfactant-containing liquid vehicle, followed by milling. We seek alternative mechanisms to the classical milling approach by generating a chemical pressure to break up the agglomerate. This study explores the enhanced redispersion of TiO₂ ceramic compacts that contain a nonionic water-soluble polymer, poly(ethylene glycol) (PEG). PEG forms a polymer solution within the agglomerated structure during redispersion. The resulting osmotic pressure gradient forces water into the porous structure and creates a tensile stress on the particle network with magnitudes as high as 0.6 MPa. Thus, the principle to achieving redispersion is to develop osmotic pressures that exceed the cohesive strength of the agglomerated structure. A critical PEG concentration of 2.0 vol% PEG 400 with respect to titania has been determined, below which redispersion is minimal.     

Demonstrating Improved Fuel Economy Using Subsystem Specific Lubricants on a Modified Diesel Engine

Fuel economy performance in modern internal combustion engines is of increasing importance to lubricant formulators due to regulations targeting global greenhouse gas emissions. Engines typically employ a single lubricant, with a common sump, to service all components. As a result, base oil and additive selection for fuel economy performance is a compromise among competing demands for different engine subsystems. Opportunities for significant fuel economy improvement through targeted formulation of lubricants for specific engine subsystems are presented, with specific emphasis on segregating the lubricant supplies for the valve train and the power cylinder subsystems. A working prototype was developed in a lab environment by modifying a commercially available twin-cylinder diesel engine. Motored valve train and whole-engine fired test results were obtained and compared to model data. Fuel economy benefits were demonstrated using market representative heavy-duty diesel lubricants, including mineral oil and polyalphaolefin (PAO) blends. The fuel economy benefits of a dual-loop lubricant system are demonstrated through significant viscosity reduction in the power cylinder subsystem, achieving overall engine friction reductions of up to 8% for the investigated operating condition. Results suggest that additional gains may be realized through targeted base oil and additive formulation. Implications for incorporation in larger diesel engines are also considered.