Silicon carbide fibre reinforced alumina compacts were formed by extrusion. The powder and fibre were pre-mixed and milled before high shear kneading to produce a homogeneous dispersion of up to 30 vol% chopped SiC fibre with high green density. The rheology of the paste was characterised using a physically based model. It is demonstrated that the pressure drop and constituent paste parameters are all systematically reduced with increasing fibre loadings for a given moisture content. It is suggested that particle packing theory in combination with fibre interactions within the paste and die system offers an explanation for the observed results.

Nitrate and acetate precursors to Ba2Cu3O7−x (123) are prepared using a molten salt technique. The viscosity and shear stress of the paste are controlled by evaporation of water from the paste. The pastes contain ˜20 - 80 volume percent solids. Rheometry over strain rates of 0 - 200 sec−1 shows both systems are shear-thinning. Both systems are thixotropic. The nitrate system may be described by a two-stage Bingham Plastic model, the acetate by a Hershel-Bulkley model. The existence of more than one region of flow behavior suggests that there are at least two mechanisms which contribute to flow. In the low strain rate region, flow resistance is due to the existence of flocs in the colloidal assembly. At higher strain rates, flow is probably controlled by interlaminar drag interactions. Precursors produced by both methods have been used to form fibers of YBa2Cu3O7−x, by ram extrusion.

Fresh concrete and mortar conform closely to the Bingham model, but the rheology of cement pastes is more complex and structural breakdown occurs. This can be explained by the existence of forces between the surfaces of individual particles which are less significant in the coarser grained materials. The requirements of apparatus to determine the rheology of these materials are described and typical results reported. The behaviour of the materials in practical applications such as pumping, vibration and trowelling can be explained by the rheological parameters so obtained, and a consistent view of the performance of cement based materials may be developed.

Characteristics of aqueous cement suspensions and the packing nature during setting were investigated as keys controlling the microstructure and density of a cement paste. The theological properties of the paste were studied as functions of hydration and setting; these properties are influenced by a variety of external factors, which are discussed. The objective of this paper is to sketch a new atomistic approach to a group of rheological phenomena which are as interesting from a scientific viewpoint as they are important for technology. The experiments were carried out by a HAAKE rheometer and an acoustic ultrasonic system. At different flow state, the acoustic emission signal generated from micro-structure is transformed due to wave propagation and due to the transducer response. The scientific information obtained through this study is expected to contribute the establishment of concept of setting processing. The measurements of flow properties relating to flocculation and coagulation were evaluated with respect to the effects of processing conditions on structure development in cement paste.

The most important property of cements and concretes after strength is the workability, which is controlled by the rheological characteristics of the mix. Theoretical modeling having proved complicated and in some cases mathematically untractable, cement specialists have concentrated on empirical based models for the last two decades. The major theoretical contributions to date on the properties of colloidal and concentrated suspensions are summarized and a general framework for theoretical modeling of cement viscosity is established. The empirical modeling and the experimental investigation of the rheological properties of fresh cements are reviewed and discussed. A semi-empirical model is proposed and its validity tested in the interpretation of some published experimental results.

The Krieger-Dougherty equation allows calculation of viscosity as a function of volume fraction for suspensions of noninteracting particles. For model suspensions (of spherical, monosized particles), it has been shown to provide excellent agreement between calculated and measured viscosities. In the present study, this equation was applied to portland cement pastes, also with good correlations between calculated and measured viscosities. Because cement has a broad particle size distribution and its particles are angular and elongated, the two constants in this equation (the maximum volume fraction and the intrinsic viscosity) were estimated using nonlinear optimization techniques. The equation provides an excellent fit to measured viscosity data. However, the nature of the equation makes the estimation somewhat difficult, and the solutions are not well-defined.

The response of a freshly mixed oil-field cement slurry to an imposed shear strain has been experimentally studied using a method based upon concentric cylinders rheometry. At various stages of the reaction of cement with water, the slurry was deformed at quasi-static rates and the resultant shear stresses calculated. In an attempt to reduce errors due to wall slip, porous coated bobs which allow some infiltration of the slurry have been used. Stress-strain curves for the cement have been produced and the variation of yield stress with time after mixing evaluated. The experimentally determined stress-strain curves exhibited three characteristic regions. Firstly, a region of negligible stress increase at very low strain. A region of rapid linear increase in stress with strain, and finally, a post-yield strain softening region. The low strain (<0.01) response of cement slurries has been compared to that of suspensions of polyethylene beads in water with similar solids volume fraction and mean particle size. A number of similarities in the stress versus strain curves of these two granular suspensions have been observed.

Although chemical reactions in cement slurries are very slow during the first few hours (induction period), the viscosity increases continuously. Relationships between various mixing methods, structure, and rhcology of cement paste throughout the induction period are being investigated, and some results are reported in this paper.

Modem concrete technology projections indicate a great expansion in low-cost and time efficient construction. Mixture designers will likely be more concerned with the developments in concrete making materials. Among those is the effective use of chemical admixtures and superplasticizers which will lower the water to cement ratio but will still give a dense workable concrete. An investigation of the workability of fresh concrete and the effect of superplasticizers should, therefore, constitute an essential part of modem concrete durability studies.

In this paper we report part of the work on rheological properties of fresh concrete. Various concrete samples covering a range of compositions that are commonly used for highway pavements are prepared. The proportioning parameters are: cement content, aggregate size, gradation and sphericity-roundness, and water and superplasticizer contents. The individual solid ingredients were characterized and the fresh concrete properties were assessed by the slump, two-point workability (Tattersall's) apparatus, air pressure and unit weight methods. The effects of superplasticizer on the apparent viscosity and yield stress of concrete are discussed and the relevance of the findings for field applications (handling of fresh concrete) are discussed. Also discussed are the implications for microstructural development.

Research has been done on the interaction of two types of polymer dispersions, a styrene acrylate (SA) and a polyvinylidene chloride (PVDLC), with portland cement by means of a COULTER particle size analyzer and a filtration technique. It was found that over 50% of the polymer SA particles were adsorbed onto the cement surface, the others did not adhere to cement grains and remained dispersed in the mixing water. However, the polymer dispersion PVDLC caused a quick flocculation and coagulation of cement grains and stiffening of the paste. Hardly any free polymer particles of this polymer were found in the liquid phase.

This paper describes part of recent studies (Briscoe, et al., Proc. 11th Inter. Congs. on Rheology, 588–590, Aug. 1992, Brussels; Briscoe, et al., The properties of drilling fluids at high pressures and high temperatures', submitted to Proc. Roy. Soc.,1992) of the rheology of concentrated clay dispersions (weight fraction from 7%–12%) under the conditions which commonly occur during oil-well drilling operations. The experimental data, which are reported in terms of the Bingham yield stress and the plastic viscosity, show that the application of high pressures modifies the Bingham characteristic parameters in a way which is both temperature and gelation-time (or shear history) dependent. The extent of this shearhistory effect may be described in terms of a “time-dependent gel strength”. The experimental results obtained with controlled shear-history measurements, using a high pressure and high temperature rolling-ball rheometer, support an extended induced volume change model, which presumes an equilibrium state for the system. The data also indicate that long time constants are associated with the gelation process at ambient temperatures of ca 20 °C. The time constants for the gelation process decrease as the temperature is increased indicating that the gelation is a thermally activated process.

The constitutive flow behavior of semi-solid metal alloy slurries has been modeled using an internal variable framework. The formulation represents the primary flow response of these materials: history dependence (thizotvopy), steady state shear rate thinning (pseudoplasticity) and constant internal structure shear rate thickening (dilatancy). The flow response at any given structure has been decoupled from structure-dependent response in carefully controlled rapid transient experiments done on a computer-controlled, high temperature, Couette geometry rheomneter. The data for Sn-15wt%Pb correlates well with the model.

The focus of this work is to determine the type of interparticle forces that are primarily responsible for the rheology control of high solids solvent borne coatings containing polymer microgels. Rheological behavior is an important consideration when formulating high solids coatings due to the relatively low viscosities required for sufficient atomization during spray application and the difficulty of preventing the film from sagging during the bake cycle. Rheology control agents such as microgels are used to modify rheological properties where solvent evaporation is insufficient during the bake cycle to prevent sagging.

In this paper that describes the first phase of our work, we have characterized several microgel dispersions used as rheology control agents in high solids automotive topcoats using scanning electron microscopy (SEM) and steady shear viscosity measurements. The steady shear viscosity versus microgel volume fraction data was compared with the expected behavior of ideal hard sphere dispersions. One of the microgel dispersions showed very nearly ideal behavior while others deviated from the expected behavior at higher volume fractions. We have also investigated the steady shear behavior of increasing concentrations of microgel dispersions added to low molecular weight acrylic polymer, typical of resins used in high solids automotive coatings. These microgel dispersions induce a yield stress in the Newtonian resin that shows a strong dependence on microgel particle concentration.

High pressure surface enhanced Raman (SERS) spectra are reported for a highly dense silver colloidal suspension, termed a MEtal Liquid-Like Film or MELLF. Comparison is made with the SERS spectrum of a dilute organosol. Raman signals due to adsorbed molecules and the solvent dichloromethane reveal appreciable frequency shifts as the colloidal environment is influenced by temperature, pressure, and packing. The C-Cl stretch of neat dichloromethane near 705 cm−1 shifts 1.7 cm −1 blue in a MELLF. Raman signals due to the adsorbed anisic acid in MELLFs blue shift about 2 cm −1 as 4 kilobars of pressure are applied; the solvent peaks shift blue only about 1 cm −1. Temperature influences the MELLF in two ways: desorption of anisic acid and formation of agglomerated particles.

The reinforcement of plastics with fibers has been practiced for many years. Only recently have long discontinuous fibers been compounded with thermoplastics by the method of pultrusion which preserves fiber length while promoting wetting of each fiber by the matrix polymer. Reinforcement of linear polymers with high strength fibers enhances physical properties and creates formable thermoplastic composites. Conventional compounding of fiber and polymer in a pelletizing extruder creates pellets. These are typically cylindrical, about 3 × 3 mm; containing fibers with a length distribution averaging 0.3 mm (but always > 3 mm). In distinction to such “short fiber” (SF) materials, greater fiber length can be achieved by the process of pultrusion. In this technology, continuous tows of fiber are wetted by molten polymer, “pultruded” through a die; and chopped to any desired length. The resulting pellets are typically 3 mm diameter, 12 mm long, and contain 30 to 60 weight percent of fibers with l/d ≥ 700. These long fiber (LF) pellets can be processed e.g. by injection molding, to give parts with net shape and good dimensional tolerances, high stiffness, tensile, and impact strength.1−3

In order to understand the distribution of discontinuous fibers in molded parts, and to comprehend the flow behavior of these non-Newtonian fiber-filled suspensions,4−8 we have examined the melt rheology of short and long fiber reinforced thermoplastics.

Many functional fluids, such as cement slurries or drilling muds, contain high-density solids, typically grains of 10–100 micron in diameter, suspended in a liquid of much lower density. Coaxial cylinder rheometers, conventionally used for oilwell fluids and dense suspensions generally, are shown to give large errors owing to gravitational or centrifugal migration of the high-density solids. Further errors can arise from slippage between the fluid and the smooth walls of the rheometer.

A modification is described to a coaxial cylinder rheometer, in which the fluid is circulated, using an external pump, through the sample cup and around the rotor/stator assembly. This circulation mixes and homogenises the fluid, prevents solids build-up in both the annular gap and the cup bottom, and provides an independently-controllable shear history. Thus stable and accurate data can be obtained for fluids which give measurement problems using standard rheometers.

Results are given for various power-law/yield stress granular fluids.

Previous work involving the squeeze-film flow of a model paste substance, a mixture of clay particles and mineral oil commonly known as ‘Plasticine’, has suggested that it behaves as a simple Herschel-Bulkley fluid which exhibits little strain history. However, tensile measurements, which are naturally limited to small strains by the onset of necking, indicate that this material shows strain hardening. A two roll-mill is employed here to investigate the influence of larger extensional strains. The data are analysed using an available first order engineering plasticity solution. The results confirm that this material exhibits both extensional strain and strain rate hardening. This observed strain hardening effect, which is not observed in the squeeze-film experiments, is attributed, in part, to the more homogeneous deformation fields induced during rolling and tensile extension.

Many advanced ceramics are formed by colloidal consolidation using techniques such as sedimentation, centrifugation, or pressure filtration. In all these, the minimization of density variations of various colloidally-consolidated cakes has not been examined systematically until recently. Schilling et al. used γ-ray densitometry to study the density variations in a sedimented cake and showed that the sediment of a flocculated alumina suspension exhibited significant density variations within the cake whereas the sediment of a dispersed alumina suspension showed a constant density profile. Auzerais et al. used a medical X-ray computer tomography (CT) to study the settling of dispersed and flocculated silica suspensions and obtained similar results: The sedimented cake of a dispersed silica suspension was fairly uniform whereas those of flocculated silica suspensions exhibited significant density variations. However, Shih et al. examined pressure-filtered cakes of flocculated alumina suspensions with γ-ray densitometry and showed that the density profiles of pressure-filtered cakes of flocculated alumina suspensions were uniform, in contrast to their sedimentation counterparts which showed significant density variations. These studies illustrate that how the local density varies within a consolidated cake depends not only on the suspension conditions but also on how the suspensions are consolidated, e.g., the consolidation pressure.