Flocculation of suspensions of calcined finely milled alumina

Conclusions It is shown that for corundum suspensions in an acid medium the best flocculants are polyacrylamide types. The control parameters for accelerated settling of corundum slips are: concentration of suspension, pH of medium, and amount of PAA and the time taken to introduce it.Flocculation of such slips carried out in semiindustrial conditions accelerates the washing of corundum to remove the tramp iron by more than 4 times. These powders can be used to press and slip cast in plaster molds articles with outstanding properties.Translated from Ogneupory, No. 2, pp. 30–35, February, 1982.     

zeta电位与菌悬液絮凝活性

通过克雷伯杆菌、有机高分子絮凝剂表面zeta电位分析和絮凝实验,初步研究了有机高分子絮凝剂对克雷伯杆菌的絮凝特性和絮凝机理。zeta电位测定表明克雷伯杆菌的等电点大致为2.2,阳离子聚丙烯酰胺（cPAM）表面的零电点约为8.0,非离子聚丙烯酰胺（nPAM）和阴离子聚丙烯酰胺（aPAM）表面均带有少量负电荷。pH<8,cPAM带正电,能与带负电的菌体电中和,显示良好的絮凝效果,最佳絮凝条件为pH7,絮凝率（FR）达94.5%。加入无机电解质后,nPAM絮凝效果变化最明显,pH4时絮凝率达95.1%,结果表明,克雷伯杆菌发酵液絮凝除菌过程是以电性中和为主,吸附架桥为辅。     

Cake filtration of suspensions in viscoelastic fluids

The fundamental framework for cake filtration of suspensions in viscoelastic media is extended to include the effects of polymer retention, including adsorption in the filter cake, polymer retention and elongational flow in the filter medium, which also undergoes compaction, and evaluation of polymer degradation in the filter cake and medium. Experimental data obtained in constant pressure filtration of starch suspensions in dilute aqueous polyacrylamide solutions confirmed the prediction of an enhanced apparent medium resistance R_ma and a reduced cake resistance α_R. Evaluations are presented of the contributions to the pressure drop due to enhanced normal stresses in elongational flow and to polymer retention (adsorption), and of the ratio of the particle size with and without adsorbed polymer in the cake. The analysis of the data points to high levels of polymer degradation during the flow of the polymer solution through the filter cake and medium.     

Flocculation properties and adsorption kinetics of cationic starches in kaolin suspensions

The flocculation characteristics of cationic starches with degree of substitution (DS 0.32–0.63) have been evaluated in 1.0 wt % kaolin suspension by spectrophotometry and colloid titration. Cationic starch is found to be an effective flocculant for removal of anionic suspension particles. Changes in the electrokinetics of kaolin as a function of pH were investigated in the absence of flocculant. The results show that kaolin in water exhibits a negative surface charge at pH > 2.5. The negative hydrophilic surface sites of kaolin are responsible for the adsorption of cationic starch molecules. The experimental data of the adsorption of cationic starch (DS 0.51) follow a Langmuir isotherm with maximum adsorption capacities of 16.89 mg/g. For the adsorption of cationic starch, chemical reaction seems significant in the rate‐controlling step and the pseudosecond‐order chemical reaction kinetics provides the best correlation for the experimental data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A new linear viscoelastic model for emulsions and suspensions

A new modified form of the Palierne model is proposed to describe the linear viscoelastic behavior of concentrated emulsions and suspensions. The proposed model takes into consideration the crowding effect and packing limit of particles. The model is verified using two sets of experimental data on the storage and loss moduli of emulsions and suspensions. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Flocculation behavior of some cationic polyelectrolytes

The settling rates and adsorption isotherms produced by a variety of suites of cationic polyelectrolytes in 3% kaolin suspensions were measured. Settling rates increased with molar mass even for low-mass, high-charge polymers. The very high settling rates produced by cationic copolymers of acrylamide decreased as the charge density of the polymer used increased. Hydrolysis of unbuffered polymers occurred over time and produced large changes in the effectiveness of the polymers. This is attributed to conformational changes. © 1994 John Wiley & Sons, Inc.     

Flocculation behavior of mallow and okra mucilage in treating wastewater

In this study, the flocculant behavior of Malva sylvestris (mallow) and Hibiscus esculentus (okra) mucilages was assessed for the removal of turbidity from synthetic and biologically-treated effluent. A series of flocculation experiments were conducted to assess the optimal concentration of each species. Aluminum salts were used as coagulants. The results showed that mallow and okra mucilage have significant flocculation properties. It was determined that okra was as efficient as mallow in removing turbidity, at much lower doses. However, at higher dosages the DOC of both synthetic wastewater and effluent increased, probably due to the organic substances present in the okra and mallow mucilage.     

Rheological behavior of two- and three-phase fiber suspensions

The rheology of two polyamide 6.6 systems filled with long glass fibers, as well as at of a three-phase polyamide 6.6-glass fiber-gas bubble system, was studied using capillary rheometry, To investigate the influence of fiber concentration, the shear and extensional viscosities were determined for both 30 and 40 vol% fiber filled suspensions as well as for the base polymer. Comparison revealed a modest increase in both the shear and extensional viscosities with increased fiber fraction. The shear viscosities, η_s, of both suspensions are shown to be close to one order of magnitude greater than the base matrix fluid viscosity, η. However, the extensional viscosities, η_E, of the suspensions are determined to be approximately four orders of magnitude greater than the shear viscosity of the matrix fluid for strain rates from 10⁰ s⁻¹ to 10² s⁻¹. The addition of a gas bubble phase to the neat polymer and polymer-fiber suspensions was accomplished through the decomposition of various percentages of an azodicarbonamide blowing agent. The presence gas bubbles resulted in reduced shear and extensional viscosities for both the neat and fiber-filled polyamide with greater reductions observed for the neat polyamide. Greater viscosity reductions were observed as the blowing agent centration was increased.     

Universal aspects of composite viscoelastic behavior

The viscoelastic behavior of a series of vinyl ester resins and E-glass fiber-reinforced composites is discussed. It is shown that the temperature shift factors for these systems, and others, suggests a universal behavior. A similar observation is made for the aging shift rate. On the other hand, the temperature dependence of compliance components per se appear to differ from system to system. Finally, it is shown that the retardation spectra for the vinyl ester resin and composites systems are the same to within a multiplicative constant in the glassy and in the short time transition regions. This shows that the presence of fibers has no influence on the distribution of retardation times in those regions.     

Flocculation of clay suspensions with water-insoluble starch grafting acrylamide/sodium allylsulfonated copolymer powder

Use of water-soluble and -insoluble starch grafting acrylamide/sodium allylsulfonated copolymers as flocculants to flocculate the clay suspension was investigated. The composition of acrylamide (AM), sodium allylsulfonated (SAS), and starch (St) repeating units in the water-soluble and -insoluble starch-grafted copolymer is about 0.718, 0.022, and 0.260 and 0.439, 0.014, and 0.547, respectively. For the water-soluble starch-grafted copolymer, the fast initial A_r decreasing rate and the lowest final A_r value occur at pH 2, 80 mg/L water-soluble starch-grafted copolymer and 100 mg/L clay suspension. As the suspension contains 1000 mg/L Na⁺ ion, the flocculating capability would be increased. For the water-insoluble starch-grafted copolymer, the initial A_r decreasing rate and the final A_r value are 1.6 times and 0.4 times, respectively, that of the water-soluble starch-grafted copolymer at the same test suspension. © 1995 John Wiley & Sons, Inc.     

The nonlinear behavior of surfactant-activated electrorheological suspensions

The nonlinear electrorheological (ER) behavior of nonionic surfactant-activated ER suspensions is investigated. The influence of three nonionic surfactants (Brij®30, GMO, and GTO) on the electrorheological (ER) response of various alumina/silicone oil suspensions shows similar behavior. The prevalent feature common to all formulations is that the yield stress, τ₀, initially increases with surfactant concentration, passes through a maximum, then decreases with surfactant concentration. The nonlinear behavior observed at large surfactant concentrations (i.e., τ₀≈Eⁿ;, where n>2) arises from field-induced phase separation of a surfactant-rich phase as opposed to field-dependent conductivity of a homogeneous continuous phase.     

Viscoelastic behavior of ceramic suspensions with carrageenan

Aqueous gelcasting of ceramic suspensions with carrageenan is one of the novel ceramic shaping techniques that have received considerable attention during the last few years. The ability of carrageenans to form cold-setting reversible gels in aqueous media is responsible for the body formation step. In this work the rheology and viscoelastic behavior of these systems is studied. Zirconia (TZ-3YE) suspensions with a solids loading of 67 wt.% (i.e. approximately 25 vol.%) and three different carrageenan concentrations (0.7, 1.0 and 1.3 wt.%, related to the free water content in the suspension) were prepared. The temperature dependence of the dynamic storage and loss moduli is determined by oscillatory shear rheometry. The concentration dependence of melting and cooling cycles (ranges 50–63 and 29–37 °C, respectively) is considered and analyzed. The results are interpreted in terms of linear viscoelasticity and the gelation step is discussed in relation to the mechanism of body formation.     

Simulation of viscoelastic behavior of glassy polymers

The frequency master curves of thermoset and thermoplastic glassy polymers were determined by dynamic mechanical analysis, and the results were simulated by sinusoidal response of the standard viscoelastic model. The elastic and viscous elements of the model were determined and correlated with structure of glassy polymers. The advantage of this viscoelastic approach in toughening studies of polymers was discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 971–982, 1997     

Rheology and gelation behavior of gel-cast cordierite-based glass suspensions

A cordierite-based glass suspension was shaped by gel-casting method. Effects of various parameters like pH, volume fraction of glass particles, gelling agents and dispersant on the rheology of the prepared slurries were investigated. The results demonstrated that using sodium tripolyphosphate (STPP) dispersant brings about a suspension of minimum viscosity. The bending strength of the dried gels was increased with the gelling agents. In addition, the utilization of cross linkers at a fixed concentration of monomer led to the gradual enhancement of the bending strength of the dried bodies. A bending strength of ∼11 MPa was obtained for the most promising dried gel cast bodies.     

Preparation and freezing behavior of TiO2 nanoparticle suspensions

Freeze casting can prepare porous materials with high porosity, directional pores, and complex shapes. However, due to the difficulty of obtaining nanoparticle suspensions with high solids loading, the formed bodies usually experience large shrinkage and have low strength in the process of vacuum drying and heat treatment. To address these problems, we studied the zeta potential, agglomeration, and rheological property of commercial P25 TiO₂ nanoparticle suspensions by adjusting the pH value and the sodium hexametaphosphate additive amount of the suspensions. Suspensions with up to 30 vol% solids loading were prepared. The water freezing process and the directional arrangement of the pores are influenced by freezing temperature gradient, and porous TiO₂ samples with directional laminar structures are obtained.     

Dispersion and gelation behavior of alumina suspensions with Isobam

As a copolymer of isobutylene and maleic anhydride, Isobam, a newly-developed gelling agent, plays a significant role in ceramic forming process. However, dispersion and gelation behavior of Isobam has not been discussed in detail yet. To investigate the influence of other dispersants, pH and electrolytes on dispersion and gelation behavior of Isobam, zeta potential, viscosity and modulus curves during gelation were measured from 50?vol% alumina suspensions with 0.1–0.7?wt% Isobam. A two-step bridging mechanism is proposed to explain the gelation behavior of Isobam, providing guidance on usage of Isobam in combination of other additives to achieve suspensions with high solids loading and adjustable gelation characteristic.     

Microstructure and phase behavior of concentrated silica particle suspensions

Dispersion stability and microstructural transition of colloidal silica suspensions were examined by rheological measurements under either steady simple shear or oscillatory flow. Monodisperse silica particles were prepared by the so-called modified Stöber method and were stabilized by either steric or electrostatic repulsive force. Depending upon the methods of stabilization, the suspension showed hard-sphere or soft-sphere response. In particular, silica suspensions exhibited hard-sphere response when the silica spheres coated with 3-(trimethoxysilyl)propyl methacrylate (MPTS; (CH₃O)₃Si(CH₂)₃OCOC(CH₃)=CH₂) were dispersed in a refractive-index matching solvent, tetrahydrofurfuryl alcohol. On the other hand, silica particles in aqueous media behaved like soft spheres with long-range electrostatic repulsive interactions when they were coated with steric layer of aminosilane coupling agent, N-[3-(trimethoxysilyl)propyl]ethylenediamine ((CH₃O)₃Si(CH₂)₃NHCH₂CH₂NH₂). In this case, the electrostatic repulsion or equivalently the softness of the silica spheres was controlled by the ionic strength using a symmetric salt KCl. Both the hard-sphere and soft-sphere suspensions showed stable shear-thinning behavior without experiencing shear-induced flocculation. Moreover, the oscillatory shear rheology showed that the electrostatically stabilized soft-sphere suspensions underwent a microstructural transition from liquid-like to solid-like structure when either the particle loading increased or the ionic strength was reduced.