Characterization of concentrated colloidal ceramics suspension: a new approach

The dispersion behavior of a concentrated ceramic suspension (Al(2)O(3)) has been investigated in terms of capillary suction time (CST) with varying solids concentration both in the absence as well as in the presence of dispersant (APC). The CST value is found to be the lowest at the pH(iep) whereas it increases as the pH is changed either to the acid side or alkaline side due to the repulsive forces acting among the neighboring particles keeping them in more dispersed state. It has been further observed that the CST value increases with increasing concentration of solids in the suspension. The dispersability of the suspension has been quantified in terms of dispersion ratio (DR). The higher the dispersion ratio of a particular system above unity, the better is the dispersability and vice versa. Further, quantification of dispersion stability by the CST technique is found to be useful and practical for optimization of different parameters concerning suspension stability. A correlation is found among the CST, zeta potential, colloidal stability, and maximum solids loading. It has been finally concluded that the CST method could be potentially employed as a quantitative and diagnostic technique for characterizing concentrated ceramic suspension.     

高分子分散剂在陶瓷浓悬浮体制备中的应用

良好分散的陶瓷浓悬浮体是胶态成型实现的前提和关键。本文阐述了高分子分散剂的分散稳定作用及其在多种单相复相陶瓷浓悬浮体制备中的研究和应用,进而从高分子分散剂自身特性,陶瓷分散相和分散介质的物理化学性质以及陶瓷胶态成型工艺操作等方面,分析了各因素对高分子分散剂分散效果的影响,最后指出了能够优化陶瓷浓悬浮体性能的高分子分散剂的研究趋势。     

Selection and Optimization of Dispersant in Ceramic Slurry Processing by Different Techniques: Comparison,Correlation, and Standardization

This article describes the selection and optimization of dispersant dosage in colloidal processing of ceramic slurry by techniques such as particle charge detector (PCD), capillary suction time (CST), rheological measurement, and wet point and flow point techniques. In general, experimental results are found to be in good agreement with each other with some degree of variation. PCD, CST, and rheological techniques are related by a simple linear function. The experimental and calculated values are well matching within an error limit of 10%. Attempt has been made to develop formula for correlating results of optimization from one technique to those obtained from another technique. The region where the suspension is well dispersed, CST is linearly correlated with PCD. The advantages and limitations of each technique have been described and discussed.     

Optimization of LiFePO4 nanoparticle suspensions with polyethyleneimine for aqueous processing

Addition of dispersants to aqueous based lithium-ion battery electrode formulations containing LiFePO(4) is critical to obtaining a stable suspension. The resulting colloidal suspensions enable dramatically improved coating deposition when processing electrodes. This research examines the colloidal chemistry modifications based on polyethyleneimine (PEI) addition and dispersion characterization required to produce high quality electrode formulations and coatings for LiFePO(4) active cathode material. The isoelectric point, a key parameter in characterizing colloidal dispersion stability, of LiFePO(4) and super P C45 were determined to be pH = 4.3 and 3.4, respectively. PEI, a cationic surfactant, was found to be an effective dispersant. It is demonstrated that 1.0 wt % and 0.5 wt % PEI were required to stabilize the LiFePO(4) and super P C45 suspension, respectively. LiFePO(4) cathode suspensions with 1.5 wt % PEI demonstrated the best dispersibility of all components, as evidenced by viscosity and agglomerate size of the suspensions and elemental distribution within dry cathodes. The addition of PEI significantly improved the LiFePO(4) performance.     

Dispersion of Colloidal Alumina using a Rhamnolipid Biosurfactant

Dispersability of colloidal alumina in water has been studied using a rhamnolipid containing biosurfactant. Zeta potential measurements revealed that the surface charge of alumina was altered due to adsorption of the biosurfactant and the iso‐electric‐point of alumina shifted from pH 9 to 6.3. Sedimentation tests indicated that the alumina suspension was completely dispersed for 3–5 hours in the presence of biosurfactant after which some settling was observed. Stability of the suspension in the time period studied was found to be independent of pH. Capillary suction time measurements showed that the alumina suspension was dispersed in the presence of the biosurfactant and varied with pH. Maximum dispersion is obtained in the pH range of 3.5–5 and 7–11 while a minimum is obtained around pH 6. This behavior is consistent with the changes in zeta potential in the presence of the biosurfactant and thus capillary suction time measurements appeared to be more reliable than the sedimentation tests. Optimization studies showed that about 60 mg/g of biosurfactant was necessary for best dispersion and dispersion could be done up to 40% solids. The application of a natural biosurfactant for dispersing colloidal alumina has been demonstrated.     

Dispersibility of Barium Titanate Suspension in the Presence of Polyelectrolytes: A Review

Dispersibility of colloidal barium titanate suspensions is reviewed with an emphasis on the use of various polyelectrolytes as dispersants. The fundamentals of colloidal stability are discussed followed by the colloidal properties of barium titanate powder. Dispersion behavior of BaTiO₃ in both nonaqueous and aqueous media has been reviewed. Several studies on the stabilization of micron and nano‐sized barium titanate using various polymeric dispersants and a rhamnolipid biosurfactant are presented and discussed. The article attempts to provide a comprehensive review of the current state‐of‐the‐art in the area of colloidal processing of barium titanate.     

NOVEL DISPERSANTS OF SILICON CARBIDE AND ALUMINUM NITRIDE

Recent advances in ceramics processing indicate that significant materials improvements can be attained by control of dispersion and colloid theology. New results are presented, where natural and synthetic lipopeptide surfactants were discovered to be excellent dispersants of ceramic powders in toluene. Relatively low concentrations of the lipopeptides promoted rapid dispersion of colloidal 0-silicon carbide (SiC) and aluminum nitride (AlN) at slurry concentrations of up to 40 wt% solids. Gravity settling produced up to 5 fold densification improvement over common industrial agents. The new dispersants may find application in a variety of ceramic, pharmaceutical and colloidal processes where superior control of dispersion, slurry rheology and product density are required.     

Effect of dispersants on dispersion stability of collophane and quartz fines in aqueous suspensions

A stable dispersion of fine mineral particles in an aqueous system facilitated by dispersants is an essential prerequisite for their successful separation. We investigated the dispersion stability and mechanism of suspensions of aqueous collophane and quartz fines (10?µm) in the presence of sodium hexametaphosphate (SHMP), sodium silicate or sodium carbonate using the sedimentation balance method, zeta potential measurements, contact angle measurements, micro-flotation tests and theoretical calculation of Extended-DLVO (Derjaguin-Landau-Verwey-Overbeek). The results showed that three dispersants significantly enhanced the dispersion stability of collophane in the following descending order SHMP?>?sodium silicate?>?sodium carbonate. This is because they increased the zeta potential of collophane in the same order; meanwhile, the SHMP made the collophane more hydrophilic compared to two other dispersants. These results illustrated that the dispersion stability was attributed to electrostatic repulsion and hydration repulsion and that the hydration repulsion had a greater influence on the stability than electrostatic repulsion based on the calculation of Extended-DLVO. However, the quartz suspension always maintained a stable dispersion in the absence or presence of dispersants, since there was a higher zeta potential and stronger hydrophilicity for natural quartz. These provide a theoretical direction for the dispersion of fine-disseminated siliceous phosphorites and phosphate slimes in separations.     

Mixed emulsifying agents

Summary Attempt has been made to correlate emulsification and wetting of the mixed agents. This has been achieved by measuring sedimentation values of various substances used as mixed emulsifying agents. Addition of natural colloids in traces (gum acacia and gelatin)to aluminium hydroxide, bentonite and inorganic insecticides like copper and aluminium arsenates, increases the initial specific area and stability. The wettability or dispersability of these systems was found to be greatly increased. So there is a correlation between specific area and stability exists with the wettability of the system. Addition of sodium oleate to copper arsenate suspension decreases the wettability and so the emulsion formed of such a suspension has a lower value of initial specific area and stability. But in the case of aluminium arsenate addition of sodium oleate enhances the property of emulsification. The initial specific area and stability is increased. The wettability of this system was found to be increased. This shows a direct relationship between initial specific area, stability and wettability of the system. In general the percentage of sediment decreases in colloidal suspensions of gums, gelatin and sodium oleate in water, thereby showing that these solid agents acquire greater dispersibility or wettability. Increasing the concentration of these colloidal ingredients the wettability or dispersibility is also further increased. The correlation of the extent of sedimentation and initial specific area however is only qualitative, because although extent of flocculation of settling may be a simple function of the wettability of the powder by the liquid, there are several other factors which cannot be ignored. For example electrical relation (Zeta potential) at the solid liquid interface and the energy of adhesion and cohesion may be involved. With 2 tables     

Dispersant adsorption and viscoelasticity of alumina suspensions measured by quartz crystal microbalance with dissipation monitoring and in situ dynamic rheology

Adsorption behavior and water content of adsorbed layers of four dispersants for aqueous ceramic processing were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) on alumina surfaces. The dispersants were a poly(acrylic acid), a lignosulfonate, and two hydrophilic comb copolymers with nonionic polyoxyethylene chains of different molecular weights. A Voigt model was applied to analyze the viscoelastic behavior of the adsorbed dispersant layers. The results from QCM-D were compared with viscoelastic properties determined by in situ dynamic rheology measurements of highly concentrated alumina suspensions during slip casting. The QCM-D results showed that both the poly(acrylic acid) and the lignosulfonate adsorbed in low amounts and in a flat conformation, which generated thin, highly rigid layers less than 1 nm thick. The water content of these layers was found to be around 30% for the lignosulfonate and 35% for the poly(acrylic acid). High casting rate and strength in terms of storage modulus were observed in the final consolidate of the suspensions with the two polyelectrolytes. In contrast, the high molecular weight comb copolymer adsorbed in a less elastic layer with a thickness of about 6 nm, which is enough to provide steric stabilization. The viscous behavior of this layer was attributed to high water content, which was calculated to be around 90%. Such a water-rich layer gives a lubrication effect, which allows for reorientation of particles during the consolidation process, resulting in a high final strength of the ceramic material. During consolidation, the suspension showed a slow casting rate, most likely due to rearrangement facilitated by the lubricating layer. The short-chain comb copolymer adsorbed in a 1.5 nm thick, rigid layer and gave low final strength to the consolidated suspension. It is likely that the poor consolidation behavior is caused by flocculation due to insufficient stabilization of the dispersion.     

Rheology and UV protection properties of suspensions of fine titanium dioxides in a silicone oil

Ultrafine particles of titanium dioxide (TiO2) are very attractive as a UV protection ingredient in cosmetic products. The UV-scattering behavior of TiO2 suspensions in a silicone oil are studied in relation to rheological properties. To control the dispersion stability of suspensions, two types of polyether-modified silicones are used as dispersants. When the suspensions are prepared with branch-type dispersants in which the polyether groups are incorporated as side chains along the backbone, the flow is shear-thinning even at low shear rates. The appearance of plateaus in the frequency-dependence curves of storage modulus implies the solidlike responses. On the other hand, the suspensions prepared with linear conformation dispersants, in which the silicone group and polyether group are alternately repeated in one long chain, are Newtonian at low shear rates. The suspensions are regarded as liquids, because the storage modulus decreases rapidly in the low-frequency region. The suspension rheology is strongly associated with flocculated structures that are primarily controlled by the interparticle attractions. The differences in rheological behavior can be explained by the differences in the adsorbed conformation of dispersant silicones. From optical measurements, it is confirmed that UV scattering increases with decreasing flocculation degree. Therefore, good agreement is established between rheological properties and UV protection ability.     

Effect of Dispersant on the Colloidal Stability of Nano‐sized CuO Suspension

The stabilization of nano‐sized CuO suspensions was examined to look for the primary mechanism of dispersion. The dispersion stability of suspension was characterized by sedimentation tests, Zeta potential, granularity tests, and infrared spectroscopy (IR). Influence factors such as pH and the concentration of the dispersant on the colloidal stability of the suspension were investigated. The results showed that sodium polyacrylate was fit to stabilize the suspension of CuO nanoparticles through electrosteric repulsion. Also, smaller viscosity and better dispersion effects were achieved when sodium polyacrylate mass fraction was 0.4%～0.8% (based on the powder), pH was 10.     

A new model system for diffusion NMR studies of concentrated monodisperse and bidisperse colloids

A method to prepare monodisperse and simultaneously NMR-visible and fluorescent colloidal particles is described, and a systematic approach to obtain spectrally resolved diffusion coefficient for every component in a monodisperse colloidal suspension is presented. We also prepared bidisperse colloidal suspensions, where each colloid component has a distinct NMR spectral signature, and obtained the diffusion coefficients of both colloid species simultaneously in concentrated colloidal suspensions, with volume fractions between 20 and 50%. The colloidal model system developed in this work enables the study of colloidal phase behavior in binary mixtures for different number and size ratios.     

Model of aggregation of colloidal fine particles in the presence of supersized polymer

A simple model of the process of stabilization and destabilization of fine colloidal suspensions induced by supersized linear polymers has been tested by the direct simulation method. In the model, a single polymer molecule may bind a number of colloidal particles and thus form an aggregate. It is assumed that a simultaneous attachment of a few fine particles to one macromolecule does not necessarily destabilize the suspension. The destabilization of the system (occurring if aggregate sedimentation dominates its diffusion ability) takes place only when the number of the attached particles per macromolecule exceeds the critical value which depends on the polymer coil dimension in the dispersion medium. The model permits interpretation of several experimental observations of the behavior of colloidal sols upon introduction of very high molecularweight polymers. The simulation results have been compared with the experimental data on the effect of polyacrylamide on the stability of AgI sol.     

Advantages and limitations of the synchrotron based transmission X-ray microscopy in the study of the clay aggregate structure in aqueous suspensions

This paper reports new application of new transmission X-ray microscopy powered by a synchrotron source for the study of aqueous based clay suspensions. This paper delineates the advantages and limitations of this method. The tested transmission X-ray microscopy (TXM) technique has shown good agreement with the cryo-stage SEM technique. The spacial resolution of this TXM technique is 60 nm and clay particles with diameter below 500 nm are clearly visible and their pseudohexagonal symmetry is recognizable in detail. It is clearly demonstrated the methodology of implementing TXM to study aqueous based clay suspensions that are close to approximately 60 nm tomographic resolution. The technique enables us to study discrete structure of clay suspensions in water and within aggregates. This has never been previously possible. Larger crystals, more compact aggregates and less colloidal fraction present in kaolinite from Georgia has impact on faster settling and gelling in denser suspension than for Birdwood kaolinite in which colloidal particles create gel-like networking in less dense aqueous suspension.     

Dispersion Characterization of Short Slag Fiber in Aqueous Solution

Slag fiber with desirable properties is a promising candidate for applications as fillers or reinforced materials. Its poor dispersion in bulk materials, however, becomes the major challenge. Some aspects of its physicochemical properties were focused upon in the present article. The effect of three kinds of dispersants, viz., sodium carboxymethyl cellulose (CMC), anionic polyacrylamide (APAM), and cationic polyacrylamide (CPAM), as well as their combinations on the dispersion of slag fiber in aqueous solution was investigated. The viscosities of fiber suspensions were measured and the results were correlated with the dispersion of suspensions. It was shown that the slag fiber appeared amorphous, smooth surface with high length/diameter (L/d) ratio and negatively charged in water. The dispersion of slag fiber in aqueous solution directly depended on the dispersants. The optimal uniform and stable fiber suspension could be achieved under the dispersant concentration of the combination of 2 wt% CMC and 0.25 wt% APAM. In this case, the fiber concentration was as large as 25 g/L. In addition, the plausible dispersion mechanism of slag fiber in aqueous solutions was elucidated based on the electrostatic steric stabilization.     

Aggregation behavior of single-walled carbon nanotubes in dilute aqueous suspension

The aggregation behavior of colloidal single-walled carbon nanotubes (SWNT) in dilute aqueous suspensions was investigated using a novel light scattering measurement technique. The aggregation of SWNT in three suspensions was examined: (1) nanotubes after acid treatment; (2) as-received nanotubes stabilized by a nonionic surfactant; and (3) acid-treated nanotubes with nonionic surfactant. Continuous light scattering measurements of the SWNT suspensions (probing the 38-436 nm length scale) made over two weeks showed that the nanotubes in each sample formed networks with fractal-like structures. The as-received nanotubes were stable over the measurement period, while the acid-treated nanotube suspension showed greater dispersion variability over time, yielding looser structures at large length scales and more compact structures at smaller length scales. The addition of surfactant to the acid-treated suspension significantly enhanced nanotube dispersion.     

Suppression of Multiple Scattering in a Depolarized Light-Scattering Experiment Using the One-Beam Setup

We have performed depolarized dynamic light-scattering measurements of suspensions of colloidal spherical particles made of tetrafluoroethylene copolymerized with perfluoromethylvinylether (MFA). Measurements on highly concentrated turbid suspensions of 17 wt% MFA in water show that the one-beam cross-correlation technique successfully suppresses the multiple scattering contributions. This is the first time that a cross-correlation technique has been used in a depolarized scattering experiment.     

Purification and dispersibility of multi-walled carbon nanotubes in aqueous solution

In this paper, the pristine multi-walled carbon nanotubes (P-MWCNTs) were purified either by the high temperature treatment (HT-MWCNTs) or by concentrated acid treatment (CA-MWCNTs). The HT-MWCNTs were prepared by heating at 500°C, while the CA-MWCNTs were treated by the mixture of concentrated nitric and sulfuric acids taken in a volume ratio of 3: 1. Ultrasonic processing and surfactants were utilized to achieve homogenous MWCNTs suspensions. The HT-MWCNTs and CA-MWCNTs were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). Among these three MWCNTs, the prepared homogeneously dispersed MWCNTs suspensions were characterized by UV–Vis absorbency and transmission electron microscopy (TEM). Finally, the dispersion mechanism was discussed. The results showed that both high temperature treatment and concentrated acid treatment can be used for purification of the P-MWCNTs, removing the amorphous carbon and other impurities. In these suspensions, the purified MWCNTs showed a better dispersibility in aqueous solution. The high temperature treatment was a kind of physical purification treatment method and it just burned the amorphous carbon away and strengthened the structure of MWCNTs, while the concentrated acid treatment was a chemical purification treatment method and this chemical treatment method grafted more effective groups to improve the dispersibility of MWCNTs.     

Capillary suspensions: Particle networks formed through the capillary force

The addition of small amounts of a secondary fluid to a suspension can, through the attractive capillary force, lead to particle bridging and network formation. The capillary bridging phenomenon can be used to stabilize particle suspensions and precisely tune their rheological properties. This effect can even occur when the secondary fluid wets the particles less well than the bulk fluid. These materials, so-called capillary suspensions, have been the subject of recent research studying the mechanism for network formation, the properties of these suspensions, and how the material properties can be modified. Recent work in colloidal clusters is summarized and the relationship to capillary suspensions is discussed. Capillary suspensions can also be used as a pathway for new material design and some of these applications are highlighted. Results obtained to date are summarized and central questions that remain to be answered are proposed in this review.