Key Engineering Materials Vol. 1015

Abstract: The suppression of superconductivity (T_c) in electron-doped superconducting materials Eu_1.81Ce_0.19Cu_1-yZn_yO_4+α-δ (ECCZO) heavily overdoped regimes by nonmagnetic impurity Zn with concentration of y = 0, 0.01, 0.02, and 0.03 has been successfully investigated by using XRD and SQUID measurements. All samples were synthesized using the solid-state reaction method. The crystal structure obtained from XRD measurements has a tetragonal T° structure, which matches the crystal structure of electron-doped superconductors in general. The addition of Zn impurity shows no change in the crystal structure, but there is a decrease in the α-lattice and an increase in the c-lattice, unit cell volume, and Cu-O bond length. This causes the distance between the charge reservoir and the conduction layer to increase and affects the disappearance of T_c. Magnetic susceptibility measurements using SQUID were carried out under FC (Field Cooling) conditions with temperatures between 2 - 30 K with a field of 5 Oe. The sample with y = 0 has diamagnetic properties with a superconductivity value (T_c) of about 11 K. The addition of Zn impurities succeeded in suppressing superconductivity as indicated by the disappearance of T_c, so that the sample is in the ground state. The Curie constant and the effective magnetic moment decrease with increasing Zn concentration. This is probably due to the decrease in Cu²⁺ when the non-magnetic Zn²⁺ atoms were added, therefore the overall value of the µ_eff decreases when Zn²⁺ substitutes some Cu²⁺. This result is different from that described by Abrikosov-Gor’kov theory in the hole-doped high-T_c cuprates.

Abstract: Tetragonal zirconia (t-ZrO₂) has broad applications for structural ceramics, such as solid oxide fuel cells, electrolysis materials, membranes, and biomedical applications. However, its electronics and magnetics properties are rarely well studied. We carried out spin-polarized calculations to understand the vacancy characteristics in t-ZrO₂. We apply neutral single Zr vacancy (V_Zr) and O vacancy (V_O) for supercell calculations up to 108 atoms. The calculated band gap of t-ZrO₂ is 3.81 eV, which becomes a narrowing band gap by V_Zr. We find that both vacancies systems induce outward relaxations of atoms near vacancies, creating lower symmetry from pristine D_4h to D_2d and C_2v for V_Zr and V_O cases, respectively. The calculated magnetic moment V_Zr is 4 mB due to four electrons of the valence band being occupied in the majority state. Four oxygen electrons of p-orbitals dominate the spin densities near V_Zr. In contrast, the magnetic moment in the case of V_O is 0 µB. Thus, since they have a high magnetic moment in the case of V_Zr, t-ZrO₂ is potentially used as material for diluted magnetic semiconductors.

Abstract: Density-functional-theory calculations have been performed to investigate the magnetism induced in silicene and germanene by hydrogen terminations. We varied the H-terminated structures from monomers to pentamers. Silicene and germanene exhibit magnetic properties after H termination, as indicated by the appearance of magnetic moments. The greater the magnetic moment, the more H atoms are added in the same direction. Conversely, H atoms added in the opposite direction reduce the magnetic moment. We calculated the adsorption energy for each variation of H-terminated silicene and germanene. The results show that both have negative adsorption energies. H-terminated silicene has a more negative adsorption energy than H-terminated germanene. For example, pentamer silicene has an adsorption energy of -10.37 eV, while pentamer germanene has an adsorption energy of -7.39 eV. This indicates that H is more easily adsorbed on silicene. Thus, H-terminated silicene and germanene are suitable for magnetic material device applications.

Abstract: We investigated a Rashba-type spin-orbit coupling in a density functional approach based on a grand-canonical force theorem (GCFT). In the investigation, we introduced an averaged effective Rashba parameter estimated at each layer in several realistic magnetic slabs. This parameter may be used to characterize an intrinsic effective electric field imposed on the atomic layer. In particular, the interface between magnetic and non-magnetic materials enhances the parameters of the magnetic layer, such as interfaces of spintronics applications.

Abstract: The effects of heat treatment in different ambient pressures or oxygen concentration on the wettability of the titanium (Ti) surface were examined. Polished titanium plates were heat-treated at various temperatures and periods in the pressure-controlled or oxygen concentration-controlled atmospheres. The wettability was evaluated by water contact angle measurement. The X-ray photoelectron spectroscopy was performed on the heat-treated and stored Ti surface to analyze adsorbates and surface products. The heat-treated Ti in the atmospheric air became hydrophilic due to the desorption of hydrocarbons on the surface. Then, the adsorption of hydrocarbons during storage in the atmospheric air returned its wettability to that before heating. On the other hand, the heat-treated Ti in a vacuum (low ambient pressures) or low oxygen concentration became hydrophobic due to an increase in the CH/OH (hydrocarbon/hydroxyl group) ratio on the surface. The wettability of hydrophobized Ti retained its wettability during storage in the atmospheric air.

Abstract: Ti-6Al-7Nb is commonly used as orthopedic implant, especially for total hip arthroplasty application, due to its excellency in biocompatibility and surface feature. This study investigates the effects of varying solution treatment temperatures on the mechanical properties and corrosion resistance of the biomedical Ti-6Al-7Nb alloy fabricated using centrifugal investment casting. Solution treatment was performed at 850°C, 970°C, and 1050°C, and the results were evaluated through tensile tests, hardness measurements, microstructural observations, and potentiodynamic polarization tests. The treatment at 970°C produced the optimal combination of mechanical strength and corrosion resistance, achieving a tensile strength of 690 MPa and the lowest corrosion rate of 0.00826 mmpy. The superior performance at 970°C is attributed to the formation of fine α precipitates in the microstructure. These findings highlight the effectiveness of suitable solution treatment temperature in enhancing Ti-6Al-7Nb’s properties for potential use in biomedical applications.

Abstract: The present research proposes the comparison of chitosan zinc nanocomposites in the form of membranes and hydrogels. Three concentrations (0.2, 0.4, and 0.6 wt%) of zinc (Zn) nanoparticle inclusion were used to create the chitosan nanocomposites for enhanced biological applications. Statistical analysis was performed with sample size N=16, an alpha error of 0.5, 95% confidence interval (CI), and G-power at 80%, The nanocomposite variations were analyzed for their improved capabilities against chitosan for its antibacterial activity (mm), water uptake (%), and other visual parameters including SEM and FTIR. Independent T-test through SPSS software revealed that both nanocomposites were statistically significant with (p = 0.01, p<0.05) and (p=0.026, (p>0.05)). The current study proposes novel chitosan with zinc nanocomposites with enhanced biological activity and offers a future scope for improved biomedical applications.

Abstract: Bioadhesives provide a good alternative to traditional wound treatment for developing liquid bandages or self-adhesive wound dressings. In this study, a bioadhesive is developed by blending locally available gum arabic (Gum) and citric acid (CA), and the Gum-CA blending formulation is optimized based on different properties: drying rate, swelling capacity, and hydrophilicity. A regression model based on the desirability function approach was derived from the obtained experimental data to determine the optimum blend ratio, which is then used to synthesize a Gum-CA blend to validate the model. Results show that the optimal Gum-CA blend fraction ratio is 0.5131/0.4869 with an ideal drying rate of 0.0051 g/min, a swelling capacity of 101.53%, and a water contact angle of 54.76°. It was also observed that the blending ratio is directly proportional to the drying rate and swelling capacity and inversely proportional to the water contact angle. Moreover, the regression model validation shows that all the models overestimate the data sets for the parametric analysis and validation experiments.

Abstract: Conventional drug delivery systems face challenges like low bioavailability, rapid degradation and limited effectiveness in drug delivery, especially for persistent infections. Our research focus to develop nanofiber drug delivery systems (NDDSs) using biopolymers like starch and gelatine. In this study, nanofilm was produced using polylactic acid (PLA), Nanocrystalline Cellulose (NCC), gelatine/starch, and paracetamol (acetaminophen) as the drug at different ratios. From SEM, the best ratio for gelatine-based nanofilm was 6% PLA: 0.5% gelatine : 0.15% NCC : 0.02% drug while starch-based nanofilm the best ratio was 8% PLA: 0.2% starch: 0.15% NCC: 0.02% drug. In drug release kinetics study, the results were compared using mathematical models such as zero order, first order, and Higuchi models for both types of bio-based nanofilm. The drug release kinetics results indicate that the starch-based nanofilm was superior to the gelatin-based nanofilm in drug delivery, fitting both the Higuchi and Zero-order models.