Key Engineering Materials Vol. 918

Abstract: Recently degradable Mg matrix composites as a promising candidate for degradable downhole tools application have aroused extensive interest. In the present work, the effects of heat treatment (solution treatment and artificial aging) on the microstructure, mechanical properties and degradation behaviors of the newly developed hollow glass microsphere reinforced Mg-Al₁₅-Zn₆-Cu_1.5 composites were investigated. The results show that the solution treatment causes the β-Mg₁₇Al₁₂ phase and Mg₃₂(Al,Zn)₄₉ phase to dissolve into the α-Mg matrix and the coarse eutectic τ-Al₂CuMg phase to translate into blocky morphology. Aging treatment causes the β phase to precipitate at the grain boundaries or the edge of the residual second phases in lamellar and blocky morphology. After solution treatment, the ductility of the composites was significantly increased, while the following aging treatment could significantly increase the ultimate compressive strength (UCS), hardness and degradation rate. The composites solution treated at 420 °C for 20 h and aged at 200 °C for 24 h shows the higher degradation rate of 6.5 mg·cm^-2·h^-1 in 3 wt.% KCl at ambient temperature, with UCS of 471 MPa, Brinell hardness of 115 HB and fracture strain of 8.7 %, this outstanding comprehensive performance is more suitable for degradable downhole tools application.

Abstract: Reinforcement of both fibrous and particulate materials can improve composite properties for various applications, such as biomedical applications. The alkali-treated kenaf fibers and (SiO2, bentonite, and CaCO3) microparticles 400 mesh in size reinforce the epoxy matrix for hybrid composites. The bending and impact properties of hybrid composites, as well as their water absorption, are compared. The hybrid composites were prepared in a compression mold using a hand lay-up technique at 100°C for 20 – 50 minutes consisting of 28 vol.% of short kenaf fibers ~5 mm in length, 2 vol.% of each type of microparticle, and 70 vol.% the epoxy resin. The flexural and impact properties of kenaf/silica/epoxy composite indicated the highest flexural strength (58.37±3.9 MPa), flexural modulus (4.68 ± 0.17 MPa), and impact strength (7.49 kJ/m²⁾. The addition of the microparticles reduced water absorption in the composites. The water absorption of kenaf/silica/epoxy composite appeared to be stable for immersion time near 216 hours. Other microparticle-filled composites did not show this pattern. The incorporation of silica microparticles to the kenaf/epoxy composite potentially enhanced the mechanical properties of the composite, with the expectation of using it to be developed for biomedical composite material.

Abstract: This paper examines the mechanical properties of reinforced thermoplastic pipes (RTP) under the influence of external pressure. We used the three-dimensional (3D) thick-walled cylinder theory, combined the 3D Hashin failure criterion with the theory of the evolution of damage in composite materials, considered their nonlinear mechanical behaviors, and introduced changes in the winding angle caused by deformation to formulate a model for the progressive failure analysis of RTP. The model was used to examine the failure sequence and external pressure capacity of RTP, and its correctness was verified by a finite element model. The results show that increasing the winding angle of RTP within a certain range can improve its external pressure capacity. When the winding angle exceeded ±50°, the failure of the RTP under external pressure mainly depended on the fiber fracture of the reinforced layer. With an increase in the ply number of the reinforced layer, the external pressure capacity of the RTP increased nonlinearly and its rate of growth gradually decreased.

Abstract: In this paper, near unity broadband absorption of Van der Waals semiconductors on a metallic substrate, and their photovoltaic performances in the visible spectrum are simulated. Ultrathin layered semiconductors such as Molybdenum disulfide (MoS₂), Tungsten disulfide (WS₂), Molybdenum di-selenide (MoSe₂), Tungsten di-selenide (WSe₂), Molybdenum ditelluride (MoTe₂), and Tungsten ditelluride (WTe₂) can create strong interference by damping optical mode in their multilayer form and increase light absorption at their heterojunctions with noble metals. From our simulation, it is observed that this absorbance can reach up to 94% when the semiconductors are placed on a gold substrate. The optimum thickness of these semiconductors in their heterostructures with gold is analyzed to create resonant absorption to generate the maximum amount of current density. The power conversion efficiency of the designed Schottky junction solar cells is calculated from their current density vs bias voltage characteristics that ranges from 1.57% to 6.80%. Moreover, the absorption coefficient, dark current characteristic, electric field intensity distribution in the device, and carrier generation rate during light illumination are presented with a view to characterizing and comparing among the parameters of TMDC based nanoscale solar cell.

Abstract: Biodiesel production from waste-or by-product oils having high free fatty acid (FFA) contents is required oil pretreatment. Esterification has been used to reduce FFA contents of crude oils prior to transesterification. In this present work, palm empty fruit bunch (EFB) oil which is a by-product from the palm oil industry was used as feedstock for biodiesel production. The EFB oil has very high FFA contents. Thus, esterification of the oil was carried out. The esterification was enhanced by dual frequency ultrasound waves (28 kHz + 40 kHz). Zeolite was used as a heterogenous acid catalyst. Methanol to oil (M:O) molar ratio, catalyst loading, and reaction were main factors affecting on the process and were investigated using central composite design (CCD) of experiment. Response surface methodology (RSM) was used to optimise these parameters. The results showed that at the optimised condition of 12:1 M:O molar ratio, 11.36 %wt catalyst loading and 60 min of reaction time, the FFA conversion was highest at 91.69% compared with the predicted value of 93.56% which was only 1.99% difference between tested and predicted values.

Abstract: Carbon-based materials are widely used in various fields such as wastewater treatment, gas sensing, and energy storage applications. In this study, waste peanut shell (PSH), available in Egypt, were transformed into useful materials by physical, chemical, and thermal treatments. The physical properties of materials from the different processing combinations were investigated. The activated (APSH), carbonized (CPSH), and activated/carbonized (A/CPSH) forms were successfully prepared. The prepared solids were characterized by SEM, FTIR, XRD, and nitrogen gas adsorption. Ball milling at 5 runs for 45 min resulted in 84 wt% of the ground PSH passing through the 212 μm mesh. Accordingly, the activation, carbonization, and activation/carbonization increased the surface areas of resulting solids by 6, 34, and 580 times, respectively. Among the materials prepared, the activated/carbonized PSH had a mean pore diameter of 1.9 nm, mesoporous material, and the highest electrical conductivity of 0.0042 Ω^-1cm^-1. This PSH is available as adsorbent in water treatment and materials for gas sensing and energy storage.

Abstract: Building gypsum has the disadvantage of short setting time and fast hardening characteristics. Based on the systematic experiments, a combined retarding system of phosphoric acid modified steel slag (3%, gypsum-based) and protein-based material (Sika 200P 0.005%, gypsum-based) is proposed. The initial setting time of gypsum is prolonged to 206 min and the final setting time is 221 min. The retarding effect for desulfurization building gypsum is significantly better than Sika 200P, and the cost is greatly reduced.