Rheological Behavior Of Slurries Research Articles

Additive manufacturing of oriented chopped carbon fiber reinforced mullite refractory via extrusion-based technique- Effects of slurry rheological behavior and 3D printing parameters

This study investigated the fabrication of oriented chopped carbon fiber-reinforced mullite-based refractory using extrusion-based 3D printing technology. Dispersants were incorporated into the printing paste to optimize its rheological properties. The effects of carbon fiber content on paste rheology and castable flowability were also evaluated. At dispersant and carbon fiber contents of 0.2 wt% and 0.3 wt%, respectively, the paste exhibited pronounced shear thinning behavior and notable structural recovery, significantly enhancing its printability. Furthermore, precise adjustments in air pressure and layer height, along with an analysis of shear rate distribution during printing, contributed to improved structural accuracy of the printed bodies. Post-printing, the chopped carbon fibers were oriented in the mullite matrix. Following sintering, the flexural strength of the 3D-printed specimens increased from 6.1 MPa to 6.7 MPa, with concurrent improvements in fracture toughness compared to carbon fiber-reinforced mullite refractory specimens produced by casting.

Quantitative correlation analysis between particle liquefaction and saccharification through dynamic changes of slurry rheological behavior and particle characteristics during high-solid enzymatic hydrolysis of sugarcane bagasse

This study identified the intrinsic relationships among slurry rheology, particle characteristics, and lignocellulosic liquefaction/saccharification based on correlation analysis and principal component analysis during the hydrolysis of sugarcane bagasse pretreated by deep eutectic solvents (DES) and mechanical milling (MM). The DES-MM pretreated lignocellulosic slurry (20% solids) exhibited high apparent viscosity of 1.4 × 104 Pa·s and shear stress of 929.0 Pa under steady state. Glucose production had a negative linear correlation with slurry viscosity (R2, 0.69–0.97), whereas its correlation with yield stress (R2, 0.85–0.98) depended on the particle liquefaction rate. The availability of free water provided a major contribution to improving slurry rheology. However, the size reduction of submillimeter particles and the changes in particle hydrophilicity during liquefaction were not significantly correlated with rheological changes. Various interrelated particle characteristics and rheological changes were integrated into two simple principal variables to predict glucose production with a high R2 of 0.96.

Study of phosphoric acid slurry rheological behavior in the attack reactor and development of a model to control its viscosity using artificial intelligence

This work aims to determine the rheological properties of the industrial phosphoric acid slurry and its behavior under the operating conditions of the phosphoric acid production process. For that, several experimental tests on the slurry were carried out, using a Rheometer (Anton Paar), which testing the effect of temperature and solid content. The results show that, for a fixed solids rate, the viscosity of the slurry decreases with temperatures from 75°C to 82°C and increases for temperatures above 82°C considered as the maximum temperature required by the process. This phenomenon is due to the morphological change of the gypsum which corresponds to the range of calcium sulfate hemihydrate formation. For a fixed temperature, the viscosity increases with increasing slurry solid content (31% to 37%). The viscosity increases with the shear gradient. Increasing the solid charge in the slurry increases its resistance to flow and movement. Thus, the slurry has a higher tendency to settle. A comparative study of four rheological models, Casson, Bingham, Ostwald and Herschel-Buckley, led to the selection of the Herschel-Bulkley model. This predicts the behavior of the phosphate slurry with a correlation coefficient of 99.9% and a MAE less than 4%. Overall, the results show that the threshold flow of the slurry is negligible, and its behavior is nonlinear. Thus, the slurry is a non-Newtonian fluid, with a dilatant rheological behavior. The various tests carried out enabled us to measure the viscosity of the phosphoric acid suspension for different solids contents and at different temperatures. The results obtained enabled us to study the rheological behavior and develop an artificial neural network model to control the viscosity of the slurry at the phosphoric acid attack tank.

Improving the properties of TiC steel bonded cemented carbides by optimizing the slurry rheology, printing path and shape design of 3D gel printing

TiC steel bonded cemented carbide was modeled by an extrusion-based 3D gel printing(3DGP) method. The rheological behavior of slurry was studied to control the slurry extrusion and modeling. The effects of printing parameters, printing path and modeling complexity were researched to get a printed sample without defects. The results indicated that the slurry with a solid loading of 50 vol% (85 wt%) was prepared, and its viscosity change is very little during 24 h in case of a higher shear rate like a nozzle. The viscosity of the slurry decreases with increasing the extrusion pressure and nozzle diameter. The skewed pattern of filaments eliminated pores in printed samples in comparison with the rectangular pattern under the condition of straight lines of the printing path. Pores at the corners of a model can be eliminated by changing the printing path from concentric lines to zigzag lines or two sets of slanted parallel lines. The modeling complexity without a support structure can be revealed by printing tilt cylinders with different angles, and the local parts on a model with a tilt angle of <45° can be printed accurately without designing a support structure. Improving the 3DGP procedure based on these experiences, the TiC steel bonded cemented carbide samples had properties similar to those prepared by conventional powder metallurgy methods.

Fabrication and characterization of ZrO2(3Y)/Al2O3 micro-ceramic gears with high performance by vat photopolymerization 3D printing

To date, overcoming the trade-off between high solid loading and print accuracy and strength, achieving high-performance and fine ZrO2 micro-ceramic components through vat photopolymerization 3D printing remains challenging. In this study, the effects of dispersant, particle size and solid content on the dispersion, rheological behavior and stability of ZrO2 ceramic slurry were systematically studied, and complex, fine and high-performance ZrO2 micro-ceramic gears were successfully prepared. Then, the microstructure, mechanical properties, tribological properties and surface quality were evaluated. The results show that the rheological behavior of the slurry is the best when the optimal dispersant content is 3.5 wt%. With the increase of solid content, the sintering shrinkage of ZrO2(3Y)/Al2O3 ceramics decreased, while the relative density, compressive strength, flexural strength, fracture toughness and hardness increased. The prepared micro-ceramic gears not only have fine structure, but also have dense microstructure and good mechanical properties. The relative density, compressive strength, flexural strength, fracture toughness and hardness strength of ZrO2(3Y)/Al2O3 ceramics can reach 98.53 %, 1900 MPa, 648 MPa, 6.4 MPa × m1/2 and 13.40 GPa, respectively. In particular, this study couples the printing accuracy and strength with the solid load. By adjusting the relationship between the fixed load and the shrinkage rate, the printing of samples with different sizes is realized, which breaks through the accuracy limit of the printing equipment and provides a new idea for the preparation of micro-ceramic gears.

Fabrication of novel BPO4 ceramic foams using the combination of the direct foaming method and freeze‐drying techniques

AbstractIn this study, ammonium phosphate monobasic and boric acid were used as the primary starting materials to produce BPO4 powder by solid‐state reaction. Using BPO4 powders as the main raw material, BPO4 ceramic foams were prepared for the first time using the direct foaming method and freeze‐drying techniques. The effects of the additive content and solid loading on the slurry's rheological behavior were investigated, and the microstructures and properties of the as‐prepared BPO4 ceramic foams were examined. The results reveal that the porosity of the BPO4 ceramic foams synthesized at 1223 K ranged from 84.2% to 90.4%, the compressive strength ranged from .12 MPa to .72 MPa, and the thermal conductivity ranged from .32 W/(m·K) to .74 W/(m·K) (298 K). The findings of this study have great significance for the development of new thermal insulation ceramic materials.

A Brief Review of Micro-Particle Slurry Rheological Behavior in Grinding and Flotation for Enhancing Fine Mineral Processing Efficiency

Recent years have witnessed growing research interest in applying rheology in grinding and flotation treatment of finely disseminated ores. Slurry rheology has long been identified as the comprehensive effect of inter-particle interactions, including their aggregation and dispersion states in slurry, which are more impactive under the fine-particle effect. In this regard, rheology has the potential to play a significant role in interpreting the flowing and deforming phenomena of inter-particle aggregates, particle-bubble aggregates, and flotation froth. Though much attention has been paid to the rheological effect in industrial suspension, this has not been the case for mineral grinding and flotation for fine particles. The influential mechanism of rheology on the sub-processes of mineral processing has not been systemically determined nor revealed thoroughly, thus the underpinning mechanism for enhancing the processing efficiency has been difficult to discover. This paper reviews the current application and importance of rheology in fine mineral processing, and the potential research direction in the field is proposed.

Effects of Grain Morphology on Flow Behavior of Semi-Solid Slurries

The flow behavior of semi-solid slurry determines the quality of the castings produced by the semi-solid forming process. Many studies have done to investigate the flow behavior of slurry under different conditions, and results show that the rheological behavior of slurry with dendritic structure is inappropriate for semi-solid forming. In this study, slurries with varying morphologies of grain for the same alloy with the same fraction solid have tested using a partial filling method. The SEED process was employed, and the pouring temperature adjusted to prepare semi-solid slurries with different grain morphologies. The flow pattern, entrapped air during the filling process, and also microstructure of the samples were examined to characterize the macro and micro flow behavior. The results show that a turbulent macro-flow, leading to entrapped air, and severe segregation appeared in the sample using slurry of Tpour ≥ 660 °C . For the slurry of Tpour &lt; 660 °C, none of the three phenomena found in the sample. This investigation further showed that the detriment of dendrite on the semi-solid forming process, and implied that large size dendrite in semi-solid slurry must avoided.

Construction of CL‐20 Surface Layer with Different Wetting Properties and its Effect on Slurry Rheological Behavior and Mechanical Sensitivities

AbstractTo have a deep understanding of the effects of surface wettability on the mechanical sensitivity and rheological characteristics of PBX slurry, CL‐20 particles with hydrophilic property was prepared through a polymerization process of dopamine, and CL‐20 particles with hydrophobic property were prepared through a condensation polymerization process of hexadecyltrimethoxylsilane. The morphology, surface element content and surface wettability of CL‐20 crystals before and after modification were characterized by scanning electronic microscope (SEM), X‐ray photoelectron spectroscopy (XPS), and contact angle test. The rheological characteristics of CL‐20 based PBX slurry showed that the interaction between explosive particles and binder was changed with different surface wettability of CL‐20. The weaker interaction between CL‐20@hydrophobic and binder lead to weaker solid‐liquid friction, resulted in lower apparent viscosities of CL‐20@hydrophobic based PBX slurry at high shear rate. The mechanical sensitivity of wax coated CL‐20 with different surface wettability was tested. CL‐20@hydrophobic‐wax exhibited better mechanical stability compared to CL‐20‐wax and CL‐20@hydrophilic‐wax, probably owning to the weaker interaction between CL‐20@hydrophobic surface and wax.

Experimental and Numerical analysis of Flow characteristics of sand water slurry in a horizontal pipe

The transportation of the solid material using hydraulic transportation method is economically the best method. The head loss occurs during transportation of slurry through horizontal pipelines usually depends on the rheological behavior of slurry, slurry concentration, particle size, and influx velocity. An experimental investigation has been performed using sand-water slurry flowing through the horizontal pipe section of a pilot plant test loop. The head loss obtained from the experimental results was validated through CFD simulation using FLUENT. The solid concentration of sand-water slurry and influx velocity used during both experiments and numerical simulation were in the range of 10-40% (by weight) and 1 to 4 m/s respectively. The numerical simulations were performed using five different turbulence models and the results obtained using SST k-omega model was in close agreement with experimental results. It is observed from both the experiment and numerical analysis that the pressure loss, granular pressure, volume fraction and skin fraction coefficient during transportation of slurry through a horizontal pipe is a function of solid concentration and influx velocity. The present study observed that as the flow velocity increases four times, the pressure loss is increasing more than 10 times. Uniform volume fraction at middle zone of outlet of the pipe is observed as both the slurry concentration and velocity of flow increases.

Pressure drop calculation for fly ash slurry using rheological model

Purpose This paper aims to the transportation of high concentration slurry through pipelines that will require thorough understanding of physical and rheological properties of slurry, as well as its hydraulic flow behavior. In spite of several contributions by the previous researchers, there is still a need to enrich the current understanding of hydraulic conveying through pipeline at various flow parameters. The pilot plant loop tests, particularly at high concentrations, are tedious, time-consuming and complex in nature. Therefore, in the current research the prediction methodology for slurry pipeline design based on rheological model of the slurry is used for calculation of pressure drop and other design parameters. Design/methodology/approach It has been established that slurry rheology plays important role in the prediction of pressure drop for laminar and turbulent flow of commercial slurries through pipeline. In the current research fly ash slurry at high concentration is chosen for rheological analysis. The effect of particle size and solid concentration is experimentally tested over the rheological behavior of slurry and based on the rheological data a correlation is developed for calculation of pressure drop in slurry pipeline. Findings The present study strongly supports the analytical approach of pressure drop prediction based on the rheological parameters obtained from the bench scale tests. The rheological properties are strongly influenced by particle size distribution (PSD), shear rate and solid mass concentration of the slurry samples. Pressure drop along the pipeline is highly influenced by flow velocity and solid concentration. The presence of coarser particles in the slurry samples also leads to high pressure drop along the pipeline. As the concentration of solid increase the shear stress and shear viscosity increase cause higher pressure drop. Research limitations/implications The transportation of slurry in the pipeline is very complex as there are lot of factors that affect the flow behavior of slurry in pipelines. From the vast study of literature it is found that flow behavior of slurry changes with the change in parameters such as solids concentration, flow velocity, PSD, chemical additives and so on. Therefore, the accurate prediction of hydraulic parameter is very difficult. Different slurry samples behave differently depending upon their physical and rheological characteristics. So it is required to study each slurry samples individually that is time-consuming and costly. Practical implications Nowadays in the world, long distance slurry pipelines are used for the transportation of highly concentration slurries. Many researchers have carried out an experiment in the design aspects of hydraulic transportation system. Rheological characteristics of slurry also play crucial role in determining important parameters of hydraulic conveying such as head loss in commercial slurry pipeline. The current research is useful for the prediction of pressure drop based on rheological behavior of fly ash slurry at various solid concentrations. The current research is helpful for finding the effect of solid concentration and flow velocity on the flow behavior of slurry. Social implications Slurry pipeline transportation has advantages over rail and road transportation because of low energy consumption, economical, less maintenance and eco-friendly nature. Presently majority of the thermal power plants in India and other parts of the world dispose of coal ash at low concentration (20 per cent by weight) to ash ponds using the slurry pipeline. Transporting solids in slurry pipelines at higher concentrations will require a thorough knowledge of pressure drop. In the current research a rheological model is proposed for prediction of pressure drop in the slurry pipeline, which is useful for optimization of flow parameters. Originality/value All the experimental work is done on fly ash slurry samples collect from the Jharli thermal power plant from Haryana State of India. Bench scale tests are performed in the water resource laboratory of IIT Delhi for physical and rheological analysis of slurry. It has been shown in the results that up to solid concentration of 50 per cent by mass all the samples behave as non-Newtonian and follows a Herschel–Bulkley model with shear thickening behavior. In the present research all the result outcomes are unique and original and does not copied from anywhere.

The Improved Thermal Conductivity of a Potting Material for High-Power Fast Warm-Up Cathodes

With higher power, frequency and longer life of microwave tubes, cathode heater assembly is being modified to enhance the warm-up performance and reliability, which are governed by ceramics thermal conductivity, electrical resistivity and shrinkage. In present work, a potting material with a high thermal conductivity of 22.14 W/(m K) and low linear shrinkage of 5.5% was prepared using two kinds of alumina powders with different size and morphology. Aqueous slurries were produced for centrifugal casting. The highest solid loading slurries with 70 vol.% were obtained. Green body with relative density above 70% was easily made from slurries using centrifugal casting. Relative sintered density reached 86.75% maximum without any sintering aids. Rheological behavior of slurries, potting microstructure, sintering shrinkage and thermal conductivity were analyzed. Continuous particle distribution, series and parallel models were used to guide the powders proportion and explain the thermal conductivity. The potting material thermal conductivity experimental data agreed with the series and parallel models when the weight parameter ξ was between 0.3 and 0.5.

Effect of Processing Parameters on Gelcasting Process for Mo/Cu Powders

Abstract A non-aqueous gelcasting system of 2-hydroxyethyl methacrylate (HEMA)-1,6-hexanediol diacrylate (HDDA) was adopted to prepare concentrated slurry of Mo/Cu powders. The effects of dispersant dosage, monomer content and solid loading on rheological behavior of slurry were studied. The effects of processing parameters such as monomer content, monomer/cross-linker ratio, initiator dosage, and temperature on the gelation behavior and green bodies' flexural strength were studied. The results show that solid loading influences the viscosity of slurry the most, followed by dispersant dosage and monomer content. The flexural strength of green bodies is increased with the increasing of monomer content and the decreasing of monomer/cross-linker ratio, while the initiator dosage has a slightly effect. On the basis of them, the optimum processing parameters for Mo/Cu non-aqueous gelcasting are as follows: HEMA content is 25 vol%∼30 vol%, monomer/cross-linker ratio is 10:1∼15:1, initiator dosage is 1.5 vol%∼2.5 vol%, and gelation temperature is 60∼80 °C.

Jets of three-phase power-law fluids and foam jet mixing in gypsum slurry

Gypsum wallboard is one of the major components of lightweight construction throughout the world. There have been significant efforts in manufacturing lightweight wallboard. One of the key elements of the manufacturing process is mixing foam in gypsum slurry. However, the dynamics of foam mixing in gypsum slurry is not fully explored and understood, which results in a trial-and-error based approach in the process optimization. In the present work, we study foam jet injection into gypsum slurry at rest and in cross-flow. The experimental part of the works reveals the foam/gypsum slurry rheological behavior. Namely, the foam-gypsum slurry mixtures are power-law fluids with the consistency and behavior indexes strongly depending on the local foam content. The submerged jet-like flows of foam/gypsum slurry mixtures belong to the class of the boundary layer problems of strongly non-linear power-law fluids of three-phase media (gypsum stucco, water and air), which is insufficiently studied in the framework of the non-Newtonian fluid mechanics. Moreover, jet propagation in cross-flow is studied here for the first time. Accordingly, a novel numerical approach to this class of problems is proposed and implemented in the theoretical part of the work, and the effect of several governing parameters [e.g., water-to-stucco ratio by mass (WSR), the Schmidt number, etc.] on the flow structure and the mixing rate is evaluated. The theoretical framework described here has a broader importance for multiple technologies related to material processing, and in particular, to formation of gypsum wallboard, since it allows one to predict the effective penetration depth of a jet, and thus, the foam/slurry mixing efficiency and the apparatus size.

Low cost foam-gelcasting preparation and characterization of porous magnesium aluminate spinel (MgAl2O4) ceramics

Porous MgAl2O4 ceramics were prepared via a low cost foam-gelcasting route using MgAl2O4 powders as the main raw material, ammonium polyacrylate as a dispersant, a small amount of modified carboxymethyl cellulose as a gelling agent, and TH-IV polymer as a foaming agent. The effects of additive's content, solid loading and gelling temperature on slurry's rheological behavior were investigated, and microstructures and properties of as-prepared porous MgAl2O4 ceramics examined. Based on the results, the roles played by the foaming agent in the cases of porosity, pore structure, pore size, mechanical properties and thermal conductivity were clarified. Porosity and pore sizes of as-prepared porous MgAl2O4 ceramics increased with increasing the foaming agent from 0.05 to 0.6vol%. Porous MgAl2O4 ceramics with porosity of 75.1% and average pore size of 266µm exhibited a compressive strength as high as 12.5±0.8MPa and thermal conductivity as low as 0.24W/(mK) (at 473K).

Ni/CeO2-thin ceramic layer depositions on ceramic monoliths for syngas production by Oxy Steam Reforming of biogas

Ni-CeO2 catalysts (metals load equal to 7.5wt.%) as thin oxide layers on ceramic monoliths have been obtained by support dip-coating into acid-free stable catalyst dispersion. Ni-based catalysts were prepared by precipitation-dry-impregnation method or solution combustion synthesis and characterized by XRD, BET, CO-Chemisorption, TPR, TEM and SEM-EDX techniques.Coating load (15–20wt.%) was controlled by multiple depositions on the basis of the slurry rheological behavior. Procedure goodness was evaluated in terms of coating load and adhesion performance. Homogeneous and well adherent layers of ca. 10–20μm were found. The performance of final structured systems was evaluated towards biogas oxy-steam reforming (OSR) reaction, highlighting the influence of morphological and structural properties of synthesized Ni-based powders on the catalytic activity. Catalytic tests demonstrated superior performances of solution combustion synthesized Ni/CeO2 catalyst washcoated on monolith, especially at high space velocity.

Influence of Particle-Size Distribution and Temperature on Rheological Behavior of Coal Slurry

The rheological behavior of coal-water slurry of Indian coal is studied using rheometer. The effect of particle size, solid concentration, and temperature on the rheology of the coal-water slurry has been investigated. The settlement analysis of various size ranges of coal particles has been carried out. A particle size less than 75 µm is used for analysis of rheological behavior of coal slurry and it is found that the increase in solid concentration caused the increase in apparent viscosity of the coal-water mixture. Also, it is observed that as the solid concentration increases the coal-water mixture converts to a non-Newtonian fluid. The rheological behavior of the slurry is also analyzed by blending the coal samples with mixture of coarse and fine particles, hence making a bimodal particle-size distribution. The slurry having the bimodal particle-size distribution is prepared by blending the fine particles of 53–75 µm with the coarse particles of 106–150 µm or 150–250 µm with various proportions. The optimum fraction obtained in bimodal slurry sample is 30% at which point the apparent viscosity is minimum. The change in the flow behavior of coal slurries are fitted to rheological models and the model parameters are calculated.

Rheological Behavior of Al-7Si-0.3Mg Alloy at Mushy State

In recent years, semisolid manufacturing has emerged as an attractive option for near net shape forming of components with aluminum alloys. In this class of processes, the key to success lies mainly in the understanding of rheological behavior of the semi-solid slurry in the temperature range between liquidus and solidus. The present study focuses on the non-Newtonian flow behavior of the pseudo plastic slurry of Al-7Si-0.3Mg alloy for a wide shear range using a high-temperature Searle-type rheometer. The rheological behavior of the slurry is studied with respect to relevant process variables and microstructural features such as shear rate, shear duration, temperature history, primary particle size, shape, and their distribution. The experiments performed are isothermal tests, continuous cooling tests, shear jump tests, and shear time tests. The continuous cooling experiments are aimed toward studying the viscosity and shear stress evolution within the slurry matrix with increasing solid fraction at a constant shear rate. Three different cooling rates are considered and their effect on flow behavior of the slurry was studied under iso-shear condition. Descending shear jump experiments are performed to understand the viscous instability of the slurry.

Thickness control and interface quality as functions of slurry formulation and casting speed in side-by-side tape casting

A novel method of co-casting called side-by-side tape casting was developed aiming to form thin functionally graded films with varying properties within a single plane. The standard organic-based recipe was optimized to co-cast slurries into thick graded tapes. Performed numerical simulations identified the stable flow beneath the blade with a shear rate profile independent of slurry viscosity as long as the slurry load in the casting tank was low. Thickness and interface shape could be well predicted if the rheological behaviour of slurries is known and the processing parameters are well-controlled. A well-defined steep interface was obtained by co-casting slurries with similar viscosities above 4000 mPas at a speed of 40 cm/min. The elastic properties of green tapes were proven to be defined by the binder concentration in the recipe formulation. The interfaces in graded tapes were shown to withstand high stresses identifying a good adhesion between side-by-side cast materials.

Review on Microencapsulated Phase Change Materials (MPCM) Slurries: Materials, Rheological Behavior and Applications

Microencapsulated phase change materials (MPCM) slurries with high heat transfer and great latent heat can serve as both the heat transfer fluids and energy storage medias. Studies showed that the effective specific heat and heat transfer rate increased by 28.1% and 23.6% respectively as using MPCM slurries. The rheological behavior of slurries do not change as adding MPCM with low concentration, can be characterized by Newtonian fluid feature with mass fraction &lt;0.25. MPCM particles have flow drag reduction effect under turbulent situation, which was applied to building energy efficiency and refrigeration, obtained remarkable energy conservation effect.