Viscoelastic properties of suspensions with weakly interacting particles

Rheological characterization of a model suspension containing hydroxyl-terminated polybutadiene and glass beads with filler concentration up to 30% by volume was performed by using a Haake parallel disk rheometer. The rheological tests conducted were the measurement of the storage modulus, G′, loss modulus, G′, and complex viscosity, η*, as functions of the frequency and the steady shear viscosity as a function of the shear rate. The linear viscoelastic region was determined to extend up to 50% strain by measuring G′, G′, and η* as functions of strain amplitude. By using multiple gap separations between the disks, it was found that the suspension did not exhibit slip at the walls of the rheometer. G′ and G′ were used to determine the relaxation times distribution, G_i(λ_i, ⊘) as functions of the relaxation time, λ_i, and the filler content, ⊘. The relaxation moduli, G_i(λ_i, ⊘), decreased with the relaxation time, but increased with the filler content. The Cox–Merz rule was also observed to be valid for these suspensions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 507–514, 1998     

The conductive properties of the electrorheological suspensions based on dihydroxypropyl chitosan particles

In this article, the electrorheological (ER) properties of the suspensions containing dihydroxypropyl chitosan particles in silicon oil with glycerin as activator are reported. In particular, the conductive property of these suspensions and its influencing factors, such as activator content, field strength, concentration, and shear rate, are investigated experimentally. The experimental results show that the suspension can display significant ER effects under the applied electric field strength. An optimum activator content exists, and the suspension's current density increases with particle concentration, activator content, and field strength, while it decreases with shear rate. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2077–2082, 1998     

Electrokinetic behaviour of coal particles suspensions

Measurements of the zeta potential of coal suspensions have been carried out by micro-electrophoresis. The influence of colloidal particles concentration, temperature, pH and ionic strength on two types of Spanish coals have been studied. Experimental results are discussed in terms of the adsorptive properties of coal surface and with regard to the formation of aggregates by coagulation.     

Electrorheological suspensions of two polarizable particles

Bi-disperse Electrorheological (ER) suspensions of two polarizable particles of the same size are investigated to understand the ER behavior of poly-disperse suspensions composed of various polarizable particles. The electrostatic polarization model is employed to describe ER suspensions, and solutions to the equation of motion are obtained by dynamic simulation. Even with the applied electric field, metastable structures and sheared configurations at a shear rate of 0.01 and 10 s^-1 show no inhomogeneous higher polarizable particle distributions (no higher polarizable particle cluster formation) regardless of the ratio of the two types of particles. The shear stress increases with the increase of the higher polarizable particle concentration both in the electrostatic force and hydrodynamic force dominant regions.     

The conductance of suspensions with conducting particles

The conductance of conductive ceramics, graphite and metal suspensions in aqueous KOH solutions was measured with the impedance technique using a four-electrode cell. The measurements were carried out for volume fractions up to high viscosities with particles of different sizes. A wide frequency range was used to investigate also the effect of particle-surface polarisation on the conductance. The results have been analysed in terms of the asymmetric and symmetric theories of Bruggeman and the GEM theory for a wide volume-fraction range of suspended particles. Depending on the suspended material, particle size and electrolyte properties, the suspensions reveal flocculation or chain formation. In case of chain formation, sometimes a decrease of the polarisation resistivity is found due to shortcircuiting by direct particle-particle contact. The conductivities of the particles phase, calculated from measured values, are orders lower than predicted from conductivity data of the pure materials. This is attributed to the occurrence of a constriction resistance and film resistance between the particles in the case of flocculation or chain formation as well as to poor wetting of the particles.     

Electro‐rheological properties of anhydrous ER suspensions based on phosphoric ester cellulose particles

The electro‐rheological (ER) behaviour of suspensions in silicone oil of phosphoric ester cellulose particles (average particle size 17.77 µm) was investigated at room temperature with electric fields up to 2.5 kV mm⁻¹ with the aim of developing anhydrous ER suspensions applicable over a wide temperature range. Anhydrous ER suspensions dispersing cellulose particles which were treated by phosphoric ester reaction of 2 mol phosphoric acid and 4 mol urea were measured; not only were the electrical characteristics such as dielectric constant, current density and electrical conductivity studied but also the rheological properties on the electric fields and volume fraction of dispersing particles. Anhydrous ER suspensions dispersing phosphoric ester cellulose particles showed very low current density, conductivity and very high performance of ER effect (τ_A/ τ₀ ≈ 1030) on the 2.5 kV mm⁻¹ electric field, and the yield stress (τ_y) had a quadratic dependence on electric fields. © 2000 Society of Chemical Industry     

The stabilisation of aqueous suspensions of coal particles

Dilute suspensions of coal particles having average diameters of 1 μm have been prepared from coals from the Shanxi Province, the People's Republic of China, and from the UK. The suspensions were stable only in the presence of surfactant repellants. Measurements of zeta potentials showed suspensions stabilised by non-ionic and ionic surfactants to behave very differently. The effects of the concentrations of repellant and of electrolyte, of the rank and maceral group composition of the coal and of the pH of the medium are contrasted for suspensions stabilised by a polyether, by CTAB and by a lignosulphonic acid. The non-ionic, polyether repellant which formed monolayers on the coal surface, each molecule being bound at more than one site, probably to oxygen groups, readily stabilised the colloidal system by pushing the zeta shear plane away from the coal surface. Larger concentrations of the ionic repellants were needed to confer stability, which they did by the formation of complex charged species on the coal surface.     

Spherical porous carbon particles derived from suspensions and sediments of resorcinol-formaldehyde particles

The goal of this study is the completion of the parameter field of resorcinol-formaldehyde solutions towards the regime of non-monolithic phases. For low sodium carbonate concentration and low mass content of resorcinol and formaldehyde in the starting solution the formation of spherical particles rather than monolithic gels is observed. The organic precursors were converted into carbon powders by pyrolysis. The resulting carbon particles were characterized by scanning electron microscopy (SEM), nitrogen sorption and small-angle X-ray scattering (SAXS). The study shows that carbonization of the organic particles results in spherical carbon particles with a micropore volume of about 0.28 cm³/g. The composition of the starting solution, however, strongly affects the external surface area as determined from sorption data for the organic as well as for the corresponding carbon particles; the values derived can be converted into average diameters of spherical particles ranging from 30 nm to 5 μm. Complementary SEM and SAXS measurements confirm these findings. A diameter of 5 μm appears to be the upper size limit in particle size forming, while 30 nm spheres develop near the formation of a continuous gel at relatively high sodium carbonate concentrations.     

Cellular ceramics from emulsified suspensions of mixed particles

In this work concentrated alumina suspensions have been emulsified with decane using silica nanoparticles of a range of hydrophobicities as stabiliser giving rise to novel porous ceramic materials. The materials are characterized by open porosities between 49 and 61% and average cell sizes between 18 and 25???m. Comparison with surfactant-stabilized emulsified suspensions is given. In particular, high temperature strength is a key property of the particle-stabilized materials.     

Simulation studies of nearest-neighbor distribution functions and related structural properties for hard-sphere systems

Molecular dynamics simulations have been carried out to investigate nearest-neighbor distribution functions and closely related quantities for the system of hard-spheres. The nearest-neighbor distribution function and the exclusion probability function were computed to examine the density dependence on the structural ‘void’ and ‘particle’ properties. Simulation results were used to access the applicabilities of various theoretical predictions based on the scaled-particle theory, the Percus-Yevick equation, and the Carnahan-Starling approximation. For lower density systems the three different approximations give the nearest-neighbor distribution functions which are very close to one another and also to the resulting simulation data. Among those theoretical predictions, the Carnahan-Starling approximation gives remarkably good agreement with the simulation data even for higher density systems. Also calculated is the nth moment of the nearest-neighbor distribution functions, in which the corresponding length scale is directly related to the measurement of the characteristic pore-size distribution.     

气化炉通用水动力计算软件的研发及应用

为了核对气化炉水汽系统的水动力安全或优化水汽系统的操作参数,分析了干煤粉气流床气化炉水汽系统,推导了压降-流量关系式及更新流量关系式,设计了循环系统校核计算迭代流程图,开发了适用于干煤粉气化系统的通用水动力计算软件。以神华宁煤GSP干煤粉气化的水动力系统为算列,结果表明:烧嘴支撑水路水量工业运行值为15 080.9 kg/h,软件计算值为15 190.5 kg/h。水冷壁水路流量计算值与监测值的最大偏差为3.3%,最小偏差0.17%。排渣口水路流量计算值和监测值偏差为1.83%。排渣口水路的出口温度计算值高于监测值1.5℃,其他水路出口温度计算值和监测值相差小于0.1℃。循环水罐、汽包和泵相关参数的模拟值与工业实际运行数值一致。     

Electrorheological properties of chitin suspensions

Electrorheological suspensions are suspensins of solid particles whose rheological behavior can be strongly modified by the application of an electric field, In this article, the electrorheological properties of suspensions containing chitin particles (and its derivative— carboxylmethyl chitosan particles) in silicone oil are reported for a range of suspension weight concentrations, applied field strengths, shear rates, etc. In these suspensions, glycerin was used as an activator. The adsorbed amount of glycerin, one of the electrorheological parameters, was also studied experimentally. The ER effect of the chitin suspension reaches the maximum at about 11% of weight concentration. The dependence of the experimentally determined dynamic yield stress on particle concentration and field strength is found to be similar to that reported for other systems. The dynamic yield stress is found to increase with the particle concentration and the applied electric field strength. © 1996 John Wiley & Sons, Inc.     

Rheological properties of glaze suspensions

Glass and Ceramics -     

Magnetically driven hydrodynamic interactions of magnetic and non-magnetic particles

The influence of magnetic forces on (i) the motion of magnetisable particles in a non-magnetisable fluid and (ii) the motion of non-magnetisable particles in a magnetisable fluid was investigated. A non-uniform magnetic field was used to induce a strong magnetic field gradient. The study was conducted at low particle Reynolds numbers allowing independent evaluation of the hydrodynamic forces along the tangential and normal directions, which in turn were used to deduce the strength and variation of the magnetic forces. Two iron spheres placed in a non-magnetisable fluid showed strong mutual attraction in the normal direction, consistent with an inverse distance to the power four law. The velocity of each sphere in the tangential direction prior to aggregation was constant. Upon aggregation, the velocity of the dumbbell in the tangential direction was approximately two times higher. This sudden increase in velocity was attributed to an increase in the magnetisation following aggregation of the two spheres. It was concluded that a dumbbell has a larger concentration of matter along the direction of the magnetic field and hence, with respect to motion in the tangential direction, a higher magnetisation. For the two acrylic spheres in a magnetised fluid the attractive force was found to be negligible, most probably because of the low magnetisation of the paramagnetic salt solution used. The two spheres did migrate towards each other because of the local field gradients that develop in the normal direction. Interestingly, the spheres developed a constant velocity prior to aggregation, which was also maintained after aggregation. Two acrylic spheres glued together also travelled in the tangential direction at the velocity observed for the individual spheres. It was concluded that there was no change in the magnetisation of the fluid following the aggregation of the spheres.     

Viscoelastic behavior of suspensions of particles in polymer solutions

Suspensions, consisting of glass beads about 1 μm in diameter and a 20 wt percent polystyrene solution in diethyl phthalate, were prepared at concentrations up to 13 vol percent. The viscoelastic properties were measured by means of a conventional dynamic method and by the raised cosine pulse method. The relaxation intensity and relaxation times of suspensions increased with increasing particle concentration. However, at concentrations > 13 vol percent, the stress against the raised cosine pulse strain did not approach zero. It was found that concentrated suspensions were complicated by a combination of viscous, elastic, and plastic effects. The experimental results have been qualitatively explained on the base of the network structure of particles.     

Flow properties of PLZTN aqueous suspensions for tape casting

Several aqueous suspensions of lead zirconate titanate powder doped with lanthanum and niobium (PLZTN) were prepared, tape cast and characterized by rheological measurements in steady shear flow. Experimental data were fitted by some viscous models available on literature and the model parameters compared in order to obtain information about the effects of the composition on suspension viscosity. Such approach represents a necessary step in the desirable optimization of tape casting process, which includes also the analysis by flow simulations. Five viscous models have been considered: from the classic plastic models of Bingham and Herschel–Bulkley, to the modified plastic model of Papanastasiou, up to the pseudoplastic models of Cross and Roberts–Barnes–Carew. The parameter-based comparison was carried on with the latter, resulting, with its eight parameters, the best-fit model, while for flow simulation purposes the ones with few parameters, as the Cross and Herschel–Bulkley models, resulted the more appropriate from some simple considerations.     

Initiation of detonation in vacuum suspensions of RDX particles

The initiation of detonation in a vacuum suspension of volatile secondary explosives is studied numerically. A mathematical model of a two-phase, two-velocity medium takes into account the nonuniform temperature inside the particles as the gas flows around them. The formation dynamics of the reaction zone of a nonstationary detonation wave with a collisionless structure in a vacuum suspension of RDX particles is discussed. The critical size of the initiation region and of the energies for excitation of plane, cylindrical, and spherical detonations are determined as functions of the initial mass concentration and diameter of the particles. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 65–71, July–August 1998.     

Rheological properties of re-melted paraffin-wax suspensions used for LPIM

The influence of re-melting of suspensions of ceramic powder and paraffin-wax used for LPIM on the yield stress and the flow behaviour was investigated. As a model system we used alumina powder and paraffin-wax, which has a liquid/solid phase transition at around 58 °C. The only parameter that was changed during this study was the number of particles per unit volume and, consequently, the number of attractive, interparticle interactions in the suspensions per unit volume.During cooling the particles took up closer interparticle distances than in the prepared suspension due to the huge shrinkage associated with paraffin-wax, which occurs below the liquid–solid phase transition. This resulted in an increased, attractive interparticle interaction (and so an increased yield stress) and an increase in the strength of attractive particle network formed after re-melting, which can be destroyed by homogenization, as was shown during the flow-curve measurements, and the initial flow properties of the paraffin-wax suspensions can be regained.