Torque rheometry and rheological analysis of powder–polymer mixture for aluminum powder injection molding

Selection of desired powder–polymer mixture (feedstock) formulation is a key factor in manufacturing perfect parts via powder injection molding. In the present study, feedstock characteristics of an aluminum-based powder were investigated by torque rheometry and rheological analyses. Several binders containing various amounts of polypropylene (PP), paraffin wax (PW), and stearic acid (SA) were selected for torque mixing and viscosity evaluation. Then, feedstocks consisting of 54, 58, 62, and 66 vol. % solid contents were prepared with modified binder. Feedstock flow behaviors were investigated regarding the rheological parameters such as mixing torque, viscosity, flow behavior index, flow activation energy and moldability index. It was found that increasing solid loading from 54 to 62 vol. % led to improved rheological behavior. This improvement was not observed in high solid contents, i.e., 66 vol. %. Based on experimental results, the optimized binder composition (60PW,35PP,5SA vol. %) and the optimum powder loading (62 vol. %) were selected as the best formulations for injection of aluminum powder. These values are supported by critical powder volume concentration measurements deduced from the oil absorption method. The resulting aluminum molded green parts with no defects exhibited the straightforward injection molding process of selected feedstock.     

A simplified model to predict the current–voltage relationship of an electro-chlorination cell

A simplified model is described to predict the Current–Voltage (I–V) relationship of a parallel plate electro-chlorination cell containing aqueous NaCl solution as electrolyte. The simplifications allowed obtaining an analytical solution without recourse to computationally intensive numerical solutions like finite element method. The anodic and cathodic exchange current densities and symmetry factors for the model were obtained using linear sweep voltammetry experiments for two different electrodes, viz. graphite and mixed metal oxide coated titanium. Using them, anodic and cathodic overpotential values (for a particular device current I) were predicted using the Butler–Volmer equation. The solution potential drop for the same device current was determined using a modified Nernst–Plank equation. The predicted device voltage (for the device current I), which is the sum of equilibrium electrode potentials, electrode overpotentials and solution potential drop, was compared with experimental (I–V) data for the two electrochemical cells as mentioned above. Results showed that the simplified model could predict the I–V data well, when the electrode surface area was assumed to be twice the superficial area.     

Quantification of powder holdups in the presence of a cavity with lateral gas–powder injection in a packed bed

The lateral flow of gas–powder through a packed bed in a cold model is studied to understand the flow and holdup behaviour of powder in the presence of a cavity, nozzle (tuyere) protrusion, and decreasing gas condition, a system used in the ironmaking blast furnace. Experiments conducted in the current study included a two-dimensional (2D) slot-type packed bed. A previously published mass balance and elutriation velocity concept formed the basis for accurately quantifying the static and dynamic powder holdups. Experiments conducted under different conditions such as powder size and flux, gas flow rate, and packed particle density and size resulted in quantifying the powder holdups. The pressure drop in both horizontal and vertical directions is studied in all two-phase flow experiments. The formation of the static holdup with time in the packed bed is studied. The reproducibility of the experiments was confirmed. The static holdup inside the packed bed at various locations along the vertical direction (i.e., height) is also quantified. The static holdup correlation developed based on experimental data resulted in a 95% confidence interval. Static powder holdup increases with a decrease in the superficial gas velocity, an increase in the size of the powder particle, and powder flux. Dynamic holdup also showed a similar trend.     

An extended chemical index model to predict the fly ash dosage necessary for mitigating alkali–silica reaction in concrete

Currently, the concrete prism test per ASTM C1293 or RILEM AAR-3 is considered the most reliable accelerated test to determine the dosage of pozzolans to suppress alkali–silica reaction (ASR) in concrete. However, the test takes 2 years, which makes it impractical as a mixture design tool for new concrete construction. In the present work, a multiple nonlinear regression model is developed for predicting the fly ash dosage necessary to mitigate ASR per CPT. The model uses the oxide compositions of Portland cement and fly ash as well as the reactivity of the aggregates. Seventy-six experimental data points on CPT expansion results for plain Portland cement and fly ash-blended concrete mixtures were used to develop and evaluate the model. The model successfully predicts the fly ash required to mitigate ASR for different aggregates, cement, and fly ash combinations. The prediction errors in most cases meet ASTM C1293 multi-laboratory precision criterion.     

A microstructural approach to the chemical reactions during the spark plasma sintering of novel TiC–BN ceramics

In this work, the monolithic TiC and h-BN doped ceramics were spark plasma sintered at 1900 °C for 10 min under 40 MPa pressure. The sinterability and physical-mechanical qualifications of as-produced specimens were studied to assess the impacts of the h-BN additive on TiC-based composites. Adding h-BN did not have any evident effect on the relative density so that both series of specimens achieved the same values around 95%. The X-ray diffraction (XRD) and microstructural evaluations proved the in-situ generation of TiB, TiB₂, TiC and C phases. Although the monolithic TiC samples reached an average hardness of 3128 HV_{100 g}, this value decreased by ~7% when h-BN was added to TiC. Finally, the monolithic sample showed a higher flexural strength (504 MPa) compared with the doped sample (429 MPa).     

Effect of co-agents on adhesion between peroxide cured ethylene–propylene–diene monomer and thermoplastics in two-component injection molding

Two-component (2K) injection-molded products combining ethylene–propylene–diene monomer (EPDM) with polar or nonpolar thermoplastics require strong interfacial bonding. To optimize the adhesion, co-agents trimethylolpropane trimethacrylate (TMPT) and triallyl cyanurate (TAC) are compared and concentrations were varied between 0 and 12 parts per hundred rubber (phr). Changes in material compatibility were characterized by contact angle measurements at high temperature, the adhesion was evaluated by tensile testing, and physicomechanical properties of the EPDM bulk were analyzed. Results show that with polypropylene, the adhesion increases to an optimum (3 phr TAC or 6 phr TMPT) independent of the co-agent type, while for polyethylene only TAC (1.5 phr) effectively boosts adhesion. It is surmised that these optimal concentrations promote crosslinking reactions at the interface. For polycarbonate and acrylonitrile–butadiene–styrene, increasing TAC concentration causes higher adhesion due to improved compatibility. Furthermore, physicomechanical bulk properties change significantly with co-agent concentrations, making the optimal curing composition application dependent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48414.     

A novel route to obtain B4C nano powder via sol–gel method

Boron carbide nanopowders and nanowhiskers were synthesized using phenolic resin and boron alkoxide as precursors through sol–gel process in water–solvent–catalyst–dispersant system. The effects of soaking time on free carbon content and synthesized B₄C particles morphology were evaluated at 1270 °C. The synthesis process of B₄C nanopowders was completed at 1270 °C after 1 h while B₄C nanowhiskers were heterogeneously nucleated and grown from obtained nanopowders after 3 h.     

Segregation and agglomeration of Type C powders from homogeneously aerated Type A–C powder mixtures during fluidization

Impressive segregation and agglomeration of fine powders (Type C powders) were found during fluidization. Agglomerates precipitated from a homogeneous emulsion phase of Type A-C powder mixtures. These phenomena provide various hints and insights concerning the mixing mechanism of fine powders in aerated conditions in relation to the powder packing structure.     

An extension of the hard-sphere particle–particle collision model to study agglomeration

When performing Eulerian–Lagrangian simulations of particle–fluid flows collisions between the particles need to be accounted for. One of the methods used for this is the hard-sphere model. This model, however, does not take into account cohesive forces between the particles, and for this reason it is not able to simulate many aspects of real flows, such as the formation of agglomerates. There have been some attempts in literature to treat cohesive forces in simulations of particulate flows but none of these methods were actually implemented directly into the hard-sphere model but rather have been solved separately as a part of the numerical scheme. In this paper we show how the standard hard-sphere model may be extended to include these important interactions in an efficient and proper way. The extended model is presented in detail and some numerical results are shown.     

On the enhancement of the spark-plasma sintering kinetics of ZrB2–SiC powder mixtures subjected to high-energy co-ball-milling

The spark-plasma sintering (SPS) kinetics of ZrB₂–SiC powder mixtures was investigated as a function of the degree of high-energy co-ball-milling and of the SiC content (5, 17.5, or 30 vol%). As in ZrB₂ without SiC, it was found that the crystal size refinement induced by the continued milling progressively enhances the SPS kinetics of ZrB₂–SiC, again only moderately if the refinement is to the ultra-fine range, but very marked if the refinement is to the nanoscale. It was also found that the SiC addition further enhances the SPS kinetics of ZrB₂, although the improvement did not scale directly with the SiC content, and became less relevant with the refinement of the ZrB₂ crystal sizes to the nanoscale. The improved kinetics induced by the SiC addition was identified as being due to the formation of amorphous borosilicate from the oxide passivating layers on the ZrB₂ and SiC particles. This not only speeds up the interparticle diffusion, but also it is segregated under the application of pressure into the multi-grain joints, filling pores. The enhanced kinetics induced by the progressive milling is due to the continuous reduction of the diffusion distances and to the development of a greater density of grain boundaries available as faster diffusion paths, together with the greater formation of amorphous borosilicate. Implications of interest for the ultra-high-temperature ceramics community are discussed.     

Alumina–copper joining by the sintered metal powder process

Sintered metal powder process (SMPP) is one of the high technology methods in ceramic–metal joining domain. The present study examines the effect of temperature and time of metalized layer sintering on the thickness and homogeneity of the joining layer, the leakage rate in alumina–copper joining zone, and also identifies the different phases formed during sintering. The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Microstructure studies indicate that sintering the metalized layer with a holding time of 90 min at the temperature of 1530 °C, and with an applied layer thickness of 50 μm with proper plating and brazing stages lead to a completely homogeneous joining zone with an adequate thickness (about 33 μm). The results of leak tests on alumina–copper specimen in this condition was less than 10^?9 Pa l s^?1.     

A novel arterial Wick for gas–liquid phase separation

Gas–liquid phase separation under microgravity conditions or in small-scale fluidic systems represents a challenge for two-phase liquid-continuous systems. In this study, capillary channels formed by 3-mm diameter stretched stainless-steel springs coated with a commercial superhydrophobic coating are used to remove air bubbles from water. A single channel is capable of absorbing a stream of 3.7-mm diameter bubbles impinging on a small area of the channel at a rate of over 50 bubbles/s. High-permeability walls lead to fast individual absorption events (4 ms for 2.5-mm bubbles) where bubble collapse time is limited by the inertia of the surrounding liquid. A horizontal three-channel array has been shown capable of absorbing impinging bubbles from a sparger at superficial gas velocities of 0.03 m/s. The ultimate capacity of the 3-mm diameter channel is predicted to be much higher than what could be measured with the existing apparatus. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1340–1354, 2019     

Synthetic scheme to increase the abrasion resistance of waterborne polyurethane–urea by controlling micro-phase separation

As an environmental-friendly coating material in industry, waterborne polyurethane–urea (WPU) is still not comparable with solvent-based polyurethane (SPU) in mechanical properties, due to the hydrophilic chain-extender. Herein, a synthetic scheme to increase the abrasion resistance of WPU with ether diol, and conventional hydrophilic chain-extender (DMBA, 2,2-bis[hydroxymethyl]butanoic acid) is revealed. This study discuss the degree of micro-phase separation (DPS) with toughness, elongation, abrasion resistance, and compared with the WPU contain various types of diol, such as esters, ether and carbonates, and the ether-based SPU. From the results, the major factor that affect to the abrasion properties of WPU is DPS, which is highly depend on the chemical structure of diol, and hard segment content. WPU film achieve higher toughness with ether-based diol with higher DPS, and better abrasion resistance than SPU. This study demonstrate a strategy for the composition designing, and the synthesis of high-abrasion resistance WPU by controlling the micro-phase separation, and content of DMBA without any inorganic fillers.     

A thermodynamic and kinetic model for paste–aggregate interactions and the alkali–silica reaction

A new conceptual model is developed for ASR formation based on geochemical principles tied to aqueous speciation, silica solubility, kinetically controlled mineral dissolution, and diffusion. ASR development is driven largely by pH and silica gradients that establish geochemical microenvironments between paste and aggregate, with gradients the strongest within the aggregate adjacent to the paste boundary (i.e., where ASR initially forms). Super-saturation of magadiite and okenite (crystalline ASR surrogates) occurs in the zone defined by gradients in pH, dissolved silica, Na⁺, and Ca^2 +. This model provides a thermodynamic rather than kinetic explanation of why quartz generally behaves differently from amorphous silica: quartz solubility does not produce sufficiently high concentrations of H₄SiO₄ to super-saturate magadiite, whereas amorphous silica does. The model also explains why pozzolans do not generate ASR: their fine-grained character precludes formation of chemical gradients. Finally, these gradients have interesting implications beyond the development of ASR, creating unique biogeochemical environments.     

Enhancement of piezoelectric properties of BF–BT ceramics by using ZrO2 powder bed during the sintering process

ZrO₂ powders of various particle sizes (0.15, 0.7, 500 µm) were used to simulate loose powder bed sintering to prepare BF–BT piezoelectric ceramics. The phase structure, dielectric properties, ferroelectric properties, and piezoelectric properties were compared with the samples sintered by the conventional powder bed method (i.e., powder of the same composition as the sample). Results showed that the use of loose ZrO₂ powder bed could improve the heat conduction rate and the sintering quality of bulk BF–BT piezoelectric ceramics. The XPS results showed that the samples sintered with 500 µm ZrO₂ powder beds had the lowest concentration of Fe²⁺, exhibited the largest piezoelectric coefficients (d₃₃ = 201 pC/N). In contrast, the sample sintered with a conventional powder bed under the same sintering conditions had a piezoelectric coefficient d₃₃ of 156 pC/N.     

A solution strategy for the film model for non-isothermal gas–liquid reactions

A general solution strategy for the film model for gas–liquid reaction has been proposed using the boundary element method (BEM) of discretization over subintervals in gas–liquid films. Non-isothermal effects in the film are included and the associated temperature changes near the gas–liquid interface are computed. The accuracy of the solution procedure is first established using some simple isothermal and non-isothermal benchmark problems and with semi-analytical solutions. Then illustrative results are presented for a non-isothermal series reaction system to illustrate effects of various parameters such as Arrhenius number, solubility changes with temperature, effect of volatility of the liquid phase reactant, etc. The proposed solution method provides fast and accurate values for interfacial fluxes and fluxes into the bulk liquid in addition to concentration profiles. Hence the method is extremely useful for coupling local effects of the film model with global effects based on CFD coupled compartmental model for gas–liquid reactors.     

A numerical study of capillary pressure–saturation relationship for supercritical carbon dioxide (CO2) injection in deep saline aquifer

Carbon capture and sequestration (CCS) is expected to play a major role in reducing greenhouse gas in the atmosphere. It is applied using different methods including geological, oceanic and mineral sequestration. Geological sequestration refers to storing of CO₂ in underground geological formations including deep saline aquifers (DSAs). This process induces multiphase fluid flow and solute transport behaviour besides some geochemical reactions between the fluids and minerals in the geological formation. In this work, a series of numerical simulations are carried out to investigate the injection and transport behaviour of supercritical CO₂ in DSAs as a two-phase flow in porous media in addition to studying the influence of different parameters such as time scale, temperature, pressure, permeability and geochemical condition on the supercritical CO₂ injection in underground domains. In contrast to most works which are focussed on determining mass fraction of CO₂, this paper focuses on determining CO₂ gas saturation (i.e., volume fraction) at various time scales, temperatures and pressure conditions taking into consideration the effects of porosity/permeability, heterogeneity and capillarity for CO₂–water system. A series of numerical simulations is carried out to illustrate how the saturation, capillary pressure and the amount of dissolved CO₂ change with the change of injection process, hydrostatic pressure and geothermal gradient. For example, the obtained results are used to correlate how increase in the mean permeability of the geological formation allows greater injectivity and mobility of CO₂ which should lead to increase in CO₂ dissolution into the resident brine in the subsurface.     

Application of microwave heating to pervaporation: A case study for separation of ethanol–water mixtures

Membrane pervaporation experiments for dewatering of water–ethanol mixtures were conducted, using a polymeric hydrophilic membrane, under microwave and conventional heating in a multimode microwave oven and a convection oven, respectively. Three feed temperatures (33.5, 45.5 and 51.5 °C) and two feed compositions (5.5 wt% and 20 wt% water in the feed) were considered. At 20 wt% water content, higher water fluxes through the membrane were obtained in the convection oven. At lower water content in the feed (5.5 wt%), the opposite effect was observed; the water fluxes were higher under microwave heating over the considered temperature range. These differences may arise from the different dielectric properties and consequently thermal behaviour of the feed mixtures under microwave heating. Microwave coupling with ethanol is stronger than with water. Moreover, unlike water, the dielectric loss factor of ethanol increases with temperature, which makes microwave dissipation preponderant in hot areas. Hence, high ethanol concentrations in the feed can easily induce thermal gradients.     

A facile method to functionalize engineering solid membrane supports for rapid and efficient oil–water separation

A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oil–water separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid–liquid separation, showing high affinity to water but not to oils as an ideal membrane for oil–water separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m³/(m²·h) and retentate at the flux of 1.95 m³/(m²·h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.