High Solid Suspensions Research Articles

Applicability of UV-Curable Binders in High Solid Suspensions for Direct-Ink-Write 3D Printing in Extremely Cold Temperatures.

Leveraging material extrusion 3D printing of high solid suspensions for rapid manufacturing in future space missions requires materials compatible with the unique environments found on the Lunar surface. However, there is currently a lack of selection criteria for materials processable in the harsh environmental conditions on the Moon without significantly altering the 3D printers. Here, we provide valuable insights into the behavior of high solid suspensions at low temperatures to guide informed decision-making for manufacturing in subzero environments. We investigate the effects of direct-ink-write (DIW) printing at -30 °C on the structure-property relationships of UV-curable high solid inks of glass microspheres. We analyze the inks based on extrudability and curability at subzero temperatures to verify extrusion, shape retention, and sufficient solidification, culminating in successful printing at -30 °C. Preferential polymerization among monomers is observed at -30 °C and results in a lower cross-linking density in the final print, with a reduced tensile modulus. However, lower ratios of highly mobile monomers result in the retention of mechanical properties, demonstrating the selection criteria for binder design. Through this work, we highlight the importance of binder formulations used for 3D printing in uncommon environmental conditions that are emerging as tomorrow's manufacturing challenge.

Direct ink write 3D printing of high solids loading bimodal distributions of particles

AbstractAs additive manufacturing (AM) expands as a processing technology for structurally customizable materials, there is increasing interest in printing with high particle contents. For suspensions with particle contents of over 50 vol%, there are significant formulation and processing challenges due to increased interparticle friction and suspension complexity. We focus on suspensions with bimodal particle distributions and two common binder systems, a high molecular weight polymer in a solvent that solidifies via solvent evaporation and a monomer mixture that cures via ultraviolet irradiation. We examine the interplay between formulation and processing and show that the formulation effects are particularly important at optimal printing parameters, but that they are overcome by processing‐related defects at sub‐optimal parameters. By understanding the processing and formulation effects specific to direct ink write AM of high solids suspensions, new customized inks can be designed for a wide range of applications, including construction, energetics, and ceramics.

Extending thermal stability of calcium carbonate pills using sepiolite drilling fluid

Abstract The aim is to investigate the plugging ability of sepiolite clay water base drilling fluids over a wide range of high permeable zones at high temperature and high pressure conditions. The special emphasis of this study is to extend the usage of loss preventer material (LPM) as a component of fresh water sepiolite base mud that has never been investigated for this purpose before. The rheology and loss tests at 27−204 °C and 2070 or 6895 kPa revealed that the sepiolite drilling mud shows good rheology and high solid suspension capability at all temperatures except 149 °C, and low loss circulation at high temperature and high pressure. The Permeability Plugging Apparatus (PPA) experiment, in which the 10−90 µm permeable ceramic plate was simulated as formation, showed that the sepiolite drilling mud without CaCO 3 can not plug the pores, while the sepiolite drilling mud with CaCO 3 can plug the pores quickly and keep the CaCO 3 particles suspended even at high temperature (up to 193 °C). The PPA experiment results were proved by the analysis using SEM and ideal packing theory.

Rheology of cellulose nanofibers suspensions: Boundary driven flow

Cellulose nanofibers (CNFs) are an exciting new renewable material produced from wood fibers. Even at low solids content, CNF-water suspensions have a complex rheology that includes extreme shear-thinning as well as viscoelastic properties and a yield stress similar to other suspensions of nanoscale particles. When characterizing the rheology of CNF suspensions, the measurement method may influence the results due to a water layer expected at the boundary, but it is unclear how the behavior near walls influences the measurement method. Parallel-plate, Couette, and vane geometries were used to compare yielding and flow of CNF suspensions obtained by steady-state shear and oscillatory rheological measurements. Five different techniques were compared as methods to obtain a yield stress. Cone and plate geometries were found to lead to sample ejection at low shear rates: Floc-floc interactions can explain this ejection. The suspensions violated the Cox-Merz rule by a significant amount; this behavior has been explained in the past as weak gel structures that break down in shear, but for this material it seems that the acting mechanism involves the formation of a water-rich layer near the solid boundaries in steady shear, while for oscillatory tests, these layers do not form. For suspensions lower than 3% solids, the yield stress measured by different procedures was within 20% of each other, but for high solids suspensions, differences between the methods could be as large as 100%; the water-rich layer formation likely is the cause of these results. Oscillatory methods are suggested as a method to obtain yield stress values for this type of material. The Couette geometry data were below the power-law lines fitted to the parallel-plate geometry data from steady-shear measurements perhaps again attributable to different water-rich layers that form in these different geometries.

The use of dielectric spectroscopy for the characterization of polymer-induced flocculation of polystyrene particles

The flocculation of colloidal suspensions is an important unit operation in many industries, as it greatly improves the performance of solid separation processes. The number of available techniques for evaluating flocculation processes on line is limited, and most of these are only functional in dilute suspensions. Thus, techniques usable for flocculation characterization in high-solids suspensions are desirable. This study investigates the use of dielectric spectroscopy to monitor the flocculation of polystyrene particles with a cationic polymer. The frequency-dependent permittivity is modeled and the model parameters are used to describe the particle aggregation. The results show a peak in the modeled time constants of the dielectric relaxation at the onset of flocculation. Further, the adsorption of polymeric flocculant onto the particle surface results in a reduction in particle charge, evident as a decrease in the magnitude of the dielectric dispersion. The use of dielectric spectroscopy is found to be valuable for assessing flocculation processes in high-solids suspensions, as changes in parameters such as floc size and charge can be detected.

Effect of blend ratio on rheological properties of aqueous SiC suspensions

The relationship between blend ratio and rheological properties of concentrated suspensions is of great importance since it is the key to get high solid suspensions. The rheological properties of bidisperse aqueous suspensions made of two SiC powders with different particle size [ d (0.5)=1.63 and 18.43 μm, respectively] has been studied as a function of blend ratio ξ (the volume fraction of larger particle size). The results showed that the value of critical blend ratio ξ, at which the viscosity is minimized, is in close relation to the shear rate applied. At shear rates below 10 S −1, the critical ξ was greater than 70%. But at shear rates from 10 to 500 S −1, ξ turned to be 50%. The change of shear region from shear-thinning behavior to shear-thickening behavior may be used to account for the variation of critical ξ. Dynamic oscillatory tests showed that the moduli and the linear viscoelastic region of suspensions with higher ξ are smaller than those with low ξ and the increment of blend ratio ξ leads to the change of suspension from nearly an elastic response to a liquid like response.

Temperature Induced Bridge Flocculation of Aqueous Zirconia Suspensions in the Presence of Polyacrylic Acid.

Temperature-induced bridge flocculation of aqueous zirconia suspensions in the presence of polyacrylic acid (PAA) has been studied. The viscosity (20 vol%) of zirconia suspensions with different concentrations of PAA as a function of temperature was measured. The results showed that the viscosity of the suspension in the absence of PAA suddenly increased with increasing temperature above 35°C due to the depletion of zirconium and yttrium cations. In contrast, heating the suspension over 45°C in the presence of PAA led to a sudden increase in viscosity, which can be rationalized by considering the increase in the ionic strength of the suspension as a result of leaching of both yttrium and zirconium cations and also the extent of adsorption of the PAA on the suspension particles. To confirm the bridge flocculation or gelation of the zirconia suspensions in the presence of PAA, viscoelastic measurements in terms of complex, storage and loss moduli (G* and G' and G, respectively) as a function of temperature were studied. Preliminary tests on temperature-induced bridge flocculation of high solid suspension (40 vol%) in the presence of PAA were also carried out. It was found that with increasing the temperature up to 85°C, the height stability of the samples reached to an optimum level and no deformation was detected. To reach the optimum stability for the samples at lower temperatures, the polymer dosage must be increased. G*, G' and G of high solid suspensions (40 vol%) were measured to evaluate the gel formation. The abrupt changes of G* and G' values from < 50 kPa to about 300 kPa, where G was approximately constant at <50 kPa at ∼55°C, can be taken to indicate the formation of gel-like stable solids.

Investigation of three dimensional interstitial velocity, solids motion, and orientation in solid–liquid flow using particle tracking velocimetry

In this study, the advancement of Particle Tracking Velocimetry (PTV) techniques to study flows of coarse solid–liquid mixtures is reported. The method has been adapted successfully to high solid concentrations (30% and 50%) by matching the index of refraction of clear solid pieces and the carrier fluid. Digital image processing of tracer and solid piece motion recorded on stereoscopic motion picture films were used to identify solids and tracers, and obtain data on location and velocity. These studies reveal local slip velocity between phases that is dependent on solid piece shape and aspect ratio. However, the complexity of the flow necessitates the use of unprocessed velocity vector information, rather than a flow field interpolated onto a regular grid. The PTV technique may be further modified to determine solid motions and orientation distribution of high solids suspensions, by determination of Euler angles. Our results demonstrate that objects of non-unity aspect ratio tend to align along the flow, within the constraints set by solids concentration, and that such solids also demonstrate decreased rotational motion in comparison with non-elongated solids. It is noted that elongated solids may rotate till an equilibrium position is achieved, whereupon no further rotation occurs. The results also show that, as expected, increasing solids size and concentration decreases the incidence of rotation.

Viscosity improvement of an Argentine kaolin by ionic treatment

Although kaolins from the provinces of Chubut and Santa Cruz (in Argentina's Patagonia) exhibited some promising characteristics for their use as paper-coating pigments, the rheological properties of their high solids suspensions preclude their industrial utilization. Verwey-Overbeek's theory provides the information necessary to improve the flow properties of suspensions by means of ionic treatment. Saturation with a monovalent ion — such as Na + — generates an energy barrier which prevents flocculation and significantly improves the viscosity of suspensions so that they compare favorably with coating clays from Georgia in the U.S.A.