Defect and Diffusion Forum Vol. 445

Abstract: The impact of cooling rates on the microstructural evolution of an Al-Sr eutectic alloy was investigated. Two distinct cooling rates, 0.02 and 57.12 °C/s, were employed during the solidification process. To elucidate the characteristics of phase transformations and microstructural evolution during solidification, thermal analyses were conducted on the recorded cooling curves. Both the first and second derivatives of these curves were examined. At the slower cooling rate, the microstructure predominantly consisted of the eutectic Al phase and the eutectic Al-Sr phase, as identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Conversely, at the higher cooling rate of 57.12 °C/s, primary Al phases were observed, indicating a significant departure from equilibrium solidification conditions. Additionally, a substantial quantity of nanosized eutectic Al-Sr particles was detected, resulting in a markedly refined microstructure.

Abstract: Titanium and its alloys are commonly used for biomedical implants and therefore should have good biocompatibility, suitable levels of strength, fracture toughness, fatigue resistance, and low elastic modulus. Alloying Ti with β-stabilizing elements (Ta, Mo, Nb and V) allows obtaining alloys with elastic modulus closer to that of bone (10-30 GPa), thus minimizing the tendency for stress shielding and bone resorption. A combinatorial method, based on variable composition laser-assisted deposition, has been used for synthesizing Ti-Ta alloys. The alloys were characterized in composition and microstructure by XRD, SEM, and EDS, and mechanical properties were assessed using depth-sensing ultramicroindentation tests. As the Ta content increases from 3 wt% to 36 wt%, the elastic modulus of the alloys decreases from 120 GPa to about 45 Gpa, corresponding to a region formed of the predominant α” (orthorhombic) phase. The lowest value of elastic modulus (45 GPa) was obtained for the Ti-36Ta (wt%) alloy, which is considerably lower than those of commercial Ti alloys currently used (above 110 GPa). Based on these results, volumetric samples of Ti-40Ta alloy were produced by laser deposition, presenting the predominance of the α” (orthorhombic) phase, elastic modulus as (80±12) GPa, and nanohardness as (4.2±0.6) GPa with H_it/E_it equal to 0.052±0.015, which reinforces the viability of using this composition with potential application as a biomaterial.

Abstract: Conventional physical sunscreens are formulated with titanium oxide (TiO₂), which reflects and scatters the UVA and UVB radiation, making them suitable for sensitive skin. However, its high refractive index can result in an undesirable white cast and potentially limit their cosmetic acceptability and effectiveness. Therefore, this study focuses on the formation of titanium oxide nanotubes (TNTs) as an alternative, since their nanoscale size minimizes light scattering and allows for a more transparent appearance when applied to the skin. TNTs were formed by anodic oxidation using an electrolyte based on ethylene glycol (EG), ammonium fluoride (NH₄F), and distilled water. Anodization was conducted at a constant voltage of 60 V for 1 h. TNTs were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), which confirmed the presence of Ti₂O and an inner diameter of 53 ± 4 nm. Biocompatibility was assessed using 3D spheroid cultures of hFOB 1.19 osteoblasts, and results showed that TNTs at concentrations of 0.2 mg/mL and 0.02 mg/mL were non-cytotoxic. The 0.2 mg/mL concentration exhibited a superior photoprotective effect, maintaining approximately 75% cell viability under UVB radiation conditions. These findings highlight the potential of TNTs as transparent, biocompatible UV filters for next-generation sunscreens.

Abstract: Enhanced Oil Recovery (EOR) techniques have evolved significantly to meet the demands of maximizing crude oil extraction from complex reservoirs. This study investigates the application of manganese dioxide (MnO₂) nanofluids in EOR, emphasizing the synergistic effects of electrochemical potentials and electromagnetic fields. MnO₂ nanoparticles were synthesized using a hydrothermal method at 160°C, yielding uniform spherical nanostructures approximately 50 nm in size. These nanofluids demonstrated promising properties including improved surface reactivity, wettability alteration, and interfacial tension reduction between oil and water phases. Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Analysis (EDAX) confirmed the structural and elemental purity of the nanoparticles. The experimental findings reveal that MnO₂ nanofluids can effectively mobilize trapped oil, especially under the influence of electromagnetic fields, which enhance nanoparticle dispersion and oil displacement. Pressure drop analysis during core flooding tests further confirmed increased recovery efficiency at optimal nanofluid concentrations, with 0.3% MnO₂ showing the highest performance. This research presents a viable approach to improving EOR outcomes through nanotechnology, offering a scalable and efficient method to recover residual oil in challenging reservoir conditions.

Abstract: Enhanced Oil Recovery (EOR) methods are increasingly essential as traditional extraction techniques face declining efficiency and mounting environmental concerns. Nanotechnology offers a promising approach by integrating engineered nanomaterials such as carbon nanotubes (CNTs), graphene oxide, and metal oxide nanoparticles to improve oil displacement. This study evaluates the role of nanomaterials in modifying wettability, reducing interfacial tension, and enhancing mobility control in reservoirs. Experimental results show that optimized CNT concentrations increase oil recovery by up to 18%, while graphene oxide achieves a 22% enhancement. Additionally, the integration of artificial intelligence (AI) with nanoEOR enables real-time optimization of nanofluid deployment. Despite notable progress, challenges such as nanoparticle stability, economic feasibility, and environmental impact remain. Addressing these challenges through advanced synthesis methods, scalable nanofluid production, and AI-driven predictive modeling will accelerate the commercialization of nanoEOR technologies, facilitating more sustainable and efficient oil extraction.

Abstract: In this paper, we analyze the thermal performance of a Latent Thermal Energy Storage (LTES) system prototype, consisting of a finned-tube heat exchanger immersed in the paraffinic Phase Change Material (PCM) RT50. With the aim of demonstrating the influence of the fin density on the system thermal performance, experimental tests were conducted by varying the fin pitch while maintaining constant the Heat Transfer Fluid (HTF) operating conditions (i.e., mass flow rate and inlet temperature). The experimental findings indicate that increasing the fin density significantly reduces the charging and discharging process durations up to approximately 5-10 times, consequently improving the average heat transfer rate between the HTF and the PCM.

Abstract: Diffusion Absorption Refrigeration (DAR) systems are renowned for their lack of moving parts and for being driven by heat energy. Traditionally, these systems have relied on ammonia water or water-lithium bromide solutions. However, recent advancements in refrigerant technology have introduced Hydrofluoroolefins (HFOs) as promising alternatives. Compared to ammonia, HFOs offer the advantage of reduced toxicity, while compared to water, they can achieve lower temperatures suitable for refrigeration. These refrigerants are chemically stable, non-corrosive, and miscible across a wide temperature range. Despite their potential, literature on HFO-based DAR systems is scarce.The present study aims to consider R-1233zd(E) (HFO refrigerant), DMAC as an absorbent, and helium as an auxiliary gas. First, thermodynamic properties of the binary solution in thermodynamical equilibrium were obtained experimentally. The binary solution was inserted into a specially designed reactor. The results enabled the authors to find the pressure-temperature and concentration relations and get the mixture's enthalpy. Once the properties were acquired, they were integrated with a theoretical model. The model results enabled the authors to determine the range of generation temperatures for various solution concentrations and the coefficient of performance (COP). The analysis indicates that the generation temperatures range from. The rich solution concentration was 0.25 to 0.3, and the optimal poor solution concentration was 0.1.

Abstract: This study presents an in-depth analysis of heat loss mechanisms in a rotary kiln system used for biomass torrefaction, with briquetted biomass fuel serving as the primary thermal energy source. The study evaluates five principal heat loss pathways: wall heat loss, exhaust gas heat loss, hydrogen-related heat loss, moisture evaporation, and heat loss due to incomplete combustion. Experimental tests were conducted at three torrefaction temperatures (230°C, 250°C, and 270°C), and thermal energy losses were quantified through temperature measurements, energy balance equations, and gas composition analysis. Results indicate that while absolute heat loss values increased with higher torrefaction temperatures due to elevated energy input and system load, the percentage of heat loss relative to total input decreased, improving net thermal efficiency. Wall heat loss was the dominant component across all conditions but declined in percentage terms from 80.5% to 30.9% as temperature increased. The reuse of exhaust gas for drying briquetted biomass was also investigated, demonstrating that waste heat recovery significantly reduces drying time—from 19 hours at 230°C to 13 hours at 270°C—without compromising fuel integrity. These findings confirm that integrating exhaust gas utilization into the torrefaction process enhances energy efficiency, supports continuous operation, and reduces external energy demand, offering a viable strategy for sustainable biomass fuel processing at an industrial scale. The findings provide design guidance for integrating heat recovery into industrial-scale biomass torrefaction systems.

Abstract: Fire-clay blocks were prepared using clay-size sediments from Phong River sieved through mesh number 200 (74 μm) mixed with Rice Husk Ash (RHA) at various ratios of 1:1, 1:2, and 1:3. The clay blocks were cast in a cylindrical mold and fired at 900, 1,000, 1,100, and 1,200°C. A uniaxial compressive test was carried out for all types of specimens acquired from different firing temperatures. In addition, imaging characteristics of the samples were also analyzed using various spectroscopy techniques. Results showed that the compressive strength, and elastic modulus of fired-clay blocks present a linear relationship when compared between two firing temperatures of 900 and 1,200°C but dramatically fluctuates at firing temperatures between 1,000 and 1,100°C. The primary conclusion is that the strength of the fired-clay blocks is governed by the quartz-tridymite-cristobalite phase transformation. It was found that cristobalite transforms from tridymite at temperatures as low as 1,100°C which strongly disagrees with the theoretical temperature of 1,470°C. This can be explained from the presence of RHA in the composite. When sintered, organic carbon in RHA changes into carbon dioxide gas and volatile matters leaving interstitial voids that allow the vibrating atoms of the silica to realign into more open cubic crystal lattices of the cristobalite form. Only when the firing temperature reaches 1,200°C where cristobalite transformation is complete does the strength relationship become more linear with firing temperature.

Abstract: An inverse problem involves determining unknown physical quantities denoted as u = (u₁, ..., u_np), which cannot be directly measured but need to be evaluated based on accessible measurements, represented as y = M(u), where M is a mathematical model. Solving such problems often requires mathematical techniques like differential equations or optimization methods such as least squares. Inverse problems can be well-posed (stable, unique solutions) or ill-posed (unstable or non-unique), with ill-posedness often resulting from poor experimental setups or measurement errors. This study addresses the identification of thermophysical parameters - specifically thermal conductivity and heat transfer coefficients—in a 2D steady-state diffusive medium. The proposed method uses a boundary element approach and an iterative descent algorithm to minimize a functional and identify the unknown parameters, validated through simulated thermograms. As a result, the use of sensitivity functions to weight the functional to be minimized makes it possible to avoid selection of the sensors according to the parameter to be identified.