Reactive thermomechanical processing of intermetallic materials

Intermetallic materials have long attracted the serious attention of scientific and industrial organizations. This is primarily due to their attractive properties, which include high-temperature oxidation and corrosion resistance, low density, and high-temperature strength. Major drawbacks that have so far restricted the application of such materials include the high energy used in their synthesis and production in the final component shape. The thermomechanical processing of intermetallic materials often requires the heating of the work piece to temperatures in excess of 1000 °C. This paper presents results from recent research into new reactive thermomechanical approaches that can produce intermetallics at operating temperatures several hundred degrees lower than those currently used. The main findings suggest that these processes may provide benefits in terms of low energy, consolidation, microstructure refinement, and homogenization.     

The design and manufacturing of porous scaffolds for tissue engineering using rapid prototyping

This research paper addresses the issue of developing an efficient methodology to design and manufacture a complex scaffold structure of desired porosity required for tissue engineering applications using a novel approach based on fused deposition modelling (FDM) rapid prototyping (RP) technology. The scaffold provides a temporary biomechanical structure for cell growth and proliferation to produce the required body parts. Conventional techniques of scaffold fabrication (such as fibre bonding, solvent casting and melt moulding) generate scaffolds with unpredictable pore sizes due to their limitations in flexibility and control of pore volume and distribution. Moreover, such scaffolds have poor mechanical strength and structural stability. The paper describes an FDM pre-processor that ensures the fabrication of scaffolds of desired porosity and inter-connectivity on the FDM system.     

Micronization of polyethylene terephthalate via freezing of highly sheared emulsions of polyethylene terephthalate in saturated liquid tetrahydrofuran

A novel technique for micronizing polyethylene terephthalate (PET) resin (∼ 3 mm) with saturated liquid tetrahydrofuran (THF) has been developed. PET pellets were introduced to a high-pressure vessel filled halfway with THF at loadings up to ∼ 7 wt % PET. When the vessel was closed and heated, the PET pellets exhibited significant melting point depression at 190°C in saturated liquid THF at 17.1 bar. Although other organic solvents were also able to depress the melting point of PET, only THF was able to facilitate the formation of an emulsion of PET-rich liquid droplets in the saturated liquid solvent when the mixture was agitated. In an attempt to generate the smallest possible PET droplets, a high-speed (5000 rpm), close-clearance, radial flow impeller was used to shear and disperse the droplets at ∼ 200°C and 20.1 bar. Emulsion was rapidly cooled while mixing. The PET droplets froze at ∼ 190°C, and the vessel was then cooled to ambient temperature. The excess liquid THF was decanted, and the PET particles were dried in a vacuum oven to remove residual THF. The PET particle sizes ranged between 2 and 70 μm, with number, area, and volume average diameters of 6, 20, and 30 μm, respectively. A comparison between the PET resin and PET powder properties indicated that the micronization reduced the M_w from 32,700 to 22,800. DSC results suggest that the rapid quench leads to a morphology different from equilibrium, with small somewhat imperfect crystallites, a lower overall degree of crystallinity, and a suppressed ΔC_p at the glass transition. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

COMPUTATIONAL ANALYSIS OF TURBULENT GAS-PARTICLE FLOW IN TUBE BANKS USING A TWO-WAY COUPLING MODEL

It is important to investigate the influence of the presence of solid particles on gas flow, known as two-way coupling in gas-particle two-phase flow, because this influence may result in a considerable modification of the heat transfer performance in facilities such as tube bank heat exchangers. There is not yet available data with detailed information on two-way coupling interaction in tube bank systems Tor model validation. This paper presents a computational study of two-way coupling gas-particle flow in the tube bank system using a two-way coupling model previously developed by the present authors. Comparison of one-way coupling prediction for both gas and particulate phase in an in-line tube bank system is made with experimental data. Then, the effect or the presence of particles on the gas flow properties in this tube bank system is studied in terms of particle sizes and loadings. It is found that both the mean and turbulent How of the gas phase in the tube bank are modified significantly due to the presence of solid particles; and the modification depends to a great extent on the particle sizes and loadings.     

Assessing the performance of an industrial SBCR for Fischer–Tropsch synthesis: Experimental and modeling

The main objective of this study is to predict the performance of an industrial‐scale (ID = 5.8 m) slurry bubble column reactor (SBCR) operating with iron‐based catalyst for Fischer–Tropsch (FT) synthesis, with emphasis on catalyst deactivation. To achieve this objective, a comprehensive reactor model, incorporating the hydrodynamic and mass‐transfer parameters (gas holdup, ε_G, Sauter‐mean diameter of gas bubbles, d₃₂, and volumetric liquid‐side mass‐transfer coefficients, k_La), and FT as well as water gas shift reaction kinetics, was developed. The hydrodynamic and mass‐transfer parameters for He/N₂ gaseous mixtures, as surrogates for H₂/CO, were obtained in an actual molten FT reactor wax produced from the same reactor. The data were measured in a pilot‐scale (0.29 m) SBCR under different pressures (4–31 bar), temperatures (380–500 K), superficial gas velocities (0.1–0.3 m/s), and iron‐based catalyst concentrations (0–45 wt %). The data were modeled and predictive correlations were incorporated into the reactor model. The reactor model was then used to study the effects of catalyst concentration and reactor length‐to‐diameter ratio (L/D) on the water partial pressure, which is mainly responsible for iron catalyst deactivation, the H₂ and CO conversions and the C₅₊ product yields. The modeling results of the industrial SBCR investigated in this study showed that (1) the water partial pressure should be maintained under 3 bars to minimize deactivation of the iron‐based catalyst used; (2) the catalyst concentration has much more impact on the gas holdup and reactor performance than the reactor height; and (3) the reactor should be operated in the kinetically controlled regime with an L/D of 4.48 and a catalyst concentration of 22 wt % to maximize C₅₊ products yield, while minimizing the iron catalyst deactivation. Under such conditions, the H₂ and CO conversions were 49.4% and 69.3%, respectively, and the C₅₊ products yield was 435.6 ton/day. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3838–3857, 2015     

The Inhibition of the Iron Corrosion in aqueous solutions containing oxygen

The corrosion behaviour of iron and steel in aerated aqueous 0.5 M Na₂SO₄ solutions in the range 7 ≤ pH ≤ 9 was studied on rotating disc electrodes. The polarization curves measured cyclic voltammetrically or under steady-state potentiostatic conditions show a membrane inhibition effect caused by the time-dependent formation of three-dimensional porous oxide layers on the electrode surface. In presence of the inhibitors hexane (1, 6) biphosphonic acid, sodium-dihydrogenphosphate, Preventol VP OC 2003 and Aktiphos the inhibition effect is markedly enhanced leading to more homogeneous and compact protecting layers.     

Preparation and characterization of sulfonated polystyrene/magnetite nanocomposites for organic dye adsorption

Magnetite nanoparticles (MNPs) were prepared by co-precipitation method and were found to have average size of 5 nm with spherical shape crystalline structure with super-magnetic properties. Commercial polystyrene (PS) was sulfonated through the reaction with freshly prepared acetyl sulfate. Three different degrees of sulfonation, based on the ratio of the acetyl sulfate to polystyrene, were prepared (1:1, 1:3 and 1:5). Nanocomposites of the prepared magnetite nanoparticles 1:3 sulfonated polystyrene were prepared at different magnetite content (1, 5 and 10%). The produced materials were characterized by dynamic light scattering (DLS), transmittance electron microscope (TEM) X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). PS, MNPs and the prepared nanocomposites were investigated as adsorbents for Congo Red (CR). The variables influencing the adsorption capacity, such as solution pH, contact time and the initial dye concentration were systematically investigated. The adsorption for CR by the previous adsorbents show maximum experimental uptake capacity of 26.78, 33.15, 53.35, 64.73, and 76.29 mg/g for PS, MNPs, SPS/MNPs 1%, SPS/MNPs 5% and SPS/MNPs 10%, respectively. The adsorption process was found to follow the pseudo second order kinetic model and fit quite well with Langmuir adsorption isotherm.