Radu Stefanoiu

Agri-food waste contains fermentable carbon, nutrients and functional compounds, yet its variable composition prevents a universal technology choice. This structured critical narrative review evaluates how cascading recovery can combine high-value compound extraction, biological conversion and thermochemical processing to retain the highest feasible value from unavoidable residues. The review links feedstock characteristics and logistics to configuration choices, positions biohydrogen as a complementary energy pathway, and examines the role of life cycle assessment (LCA) and artificial intelligence (AI) in system design. Wet carbohydrate-rich streams can be routed after selective extraction to fermentation or anaerobic digestion, whereas drier and recalcitrant fractions are more suited to pyrolysis or gasification when drying and gas-cleaning requirements are justified. Wet digestate and other moisture-rich residuals may support nutrient recovery and hydrothermal carbonisation. Dark fermentation is most valuable when its residual effluent is further valorised, for example, through anaerobic digestion. Life cycle outcomes depend on the functional unit, system boundary, co-product treatment, transport, energy demand and direct emissions. AI can improve adaptation to feedstock variability only when the underlying data, models and environmental assumptions are transparent and validated.

Background: Tile C1.2 pelvic ring injuries are characterized by combined rotational and vertical instability and require reliable posterior stabilization. The aim of this exploratory biomechanical study was to compare the construct-level mechanical behavior of three posterior pelvic ring fixation strategies in a standardized Tile C1.2 injury model while maintaining identical anterior symphyseal fixation in all specimens. Methods: Nine fourth-generation composite pelvic specimens with a simulated Tile C1.2 injury pattern were allocated to three groups (n = 3 per group) according to posterior fixation method: anterior sacroiliac plating, sacroiliac screw fixation, and ilioiliac plate fixation. All specimens received the same anterior symphyseal plate. Mechanical testing was performed under monotonic axial compression using a universal testing machine and a custom acetabular support designed to ensure reproducible load transmission. A preload of 50 N was applied before data acquisition, after which displacement was zeroed. Loading was then continued up to a predefined maximum load of 1.9 kN. Axial displacement was obtained from actuator travel, and apparent axial secant stiffness was evaluated at predefined load levels. Results: Across the tested loading range, sacroiliac screw fixation demonstrated the lowest axial displacement and the highest apparent axial secant stiffness, whereas ilioiliac plate fixation showed the greatest displacement and the lowest stiffness values. Anterior sacroiliac plate fixation showed intermediate mechanical behavior. No structural failure occurred within the tested load range. Conclusions: Within the limits of this small synthetic biomechanical study, the investigated posterior fixation strategies showed different construct-level displacement and stiffness profiles under monotonic axial compression when anterior fixation was kept constant. Among the tested posterior constructs, sacroiliac screw fixation was associated with lower displacement and higher apparent stiffness within this experimental model.

Regenerative medicine based on Mg alloy implants is considered a modern approach to address bone defects. It represents a promising alternative to traditional grafting strategies (auto-, allo-, and xenografts) by potentially mitigating complications such as donor-site morbidity and limited supply, which are discussed in this paper. In line with this global topic, attention is devoted to an innovative manufacturing route for Mg-Nd and Mg-Zn implants for the treatment of small bone defects. First, the proposed manufacturing method is described in detail, including the materials used and the manufacturing steps, and then a comparison between the reference (cast alloys) and implant samples is performed. The mechanical properties, weight loss in simulated body fluid (SBF), surface analysis (contact angle and roughness measurements), and cytotoxicity were evaluated to determine whether the developed implants are suitable for consideration as future bone implants. The main conclusions of the study were that both Mg-based implants exhibited mechanical properties (compressive strength and Young’s modulus) with values very close to those of the human bone, reduced mass loss (a fact that is in a direct relationship with an increase in corrosion resistance due to MgF₂ conversion coating, which is a secondary result of the proposed manufacturing route), and finally, a good biocompatibility sustained by cell culture and cytotoxicity assessment, as well as by apoptosis and necrosis analysis on a human patella-derived osteoblastic cell line.

The paper presents a comparative experimental study of heat-transfer behavior in three alloys considered candidate materials for nuclear reactors: the austenitic stainless steel 316L, Zircaloy-4 (currently used in CANDU reactors), and an ODS alloy with a ferritic matrix. The investigation was conducted across five temperature intervals, each sample being subjected to a thermal shock through short-term overheating to the upper limit of its respective interval. The variation of thermal diffusivity in the three alloys was determined as a function of both measurement temperature and applied thermal shock, and trends in heat-transfer behavior were compared across the five temperature ranges. The experimental results show that up to 400 °C, Zircaloy-4 exhibits the highest thermal diffusivity, followed by the ODS alloy, with the lowest values measured for 316L steel. At approximately 450 °C, the ratio between 316L and the ODS alloy reverses. Beyond this point, increasing the temperature up to 900 °C is accompanied by a continuous rise in thermal diffusivity for both 316L stainless steel and Zircaloy-4. In contrast, for the ODS steel, increasing temperature leads to a continuous decrease in thermal diffusivity, reaching a minimum near the Curie point. The novelty of the study lies in the comparative assessment of the influence of temperature on the heat-transfer process in three alloys relevant to nuclear energy, covering the operating temperature ranges of CANDU and ALFRED reactors, as well as potential accidental overheating up to 900 °C. A particular feature of the work is the prior application of a short-duration overheating step produced using solar energy. The results are relevant not only for nuclear reactors but also for other high-temperature applications in corrosive environments.

The Inconel 718 alloy is a nickel-based superalloy that can be strengthened through precipitation hardening. Due to its exceptional mechanical properties, high corrosion resistance, and good workability, it is particularly suitable for applications where components operate in corrosive environments at temperatures up to 600 °C. Under these conditions, overheating frequently occurs, leading to structural transformations and changes in mechanical properties. This experimental study examined the effect of repeated overheating on the alloy’s structure, the formation of oxide layers, and hardness. The cyclic overheating process was simulated using thermal shocks induced by solar energy, with temperatures exceeding the recommended range, between 700 and 1000 °C. Morphological characterization, elemental chemical analysis, qualitative phase analysis, and microhardness measurements highlighted the transformations induced by cyclic thermal stress at high temperatures.

The increasing demand for sustainable energy solutions has prompted a significant interest in non-conventional energy sources, leading to the development of innovative materials that can enhance energy conversion and storage efficiency. This review paper explores the pivotal role of zirconium dioxide (ZrO₂) in industrial applications related to non-conventional energy technologies, highlighting its contributions to the circular economy. We discuss various synthesis methods for ZrO₂, including top-down and bottom-up approaches, elucidating how these techniques influence the material’s properties and applicability. Furthermore, we examine the unique characteristics of nano-ZrO₂ and its transformative potential in energy conversion and storage systems. By synthesizing current research findings, this review underscores the significance of ZrO₂ in promoting sustainable energy practices and its role in advancing the circular economy through material reuse and recycling strategies. The insights provided herein aim to inform future research directions and industrial applications, ultimately fostering a more sustainable energy landscape.

The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity powders in a planetary ball mill, achieving a good homogenization and a high alloying degree, followed by spark plasma sintering consolidation. The electrodes for electrospark deposition were cut and machined from the bulk material. Stainless steel specimens were coated and electrochemically tested for corrosion resistance in a 3.5% NaCl saline solution.

Due to worldwide regulations on electric motor manufacturing, the energy efficiency of these devices has to be constantly improved. A solution may reside in the fact that high quality materials and adequate cutting technologies should be carefully chosen. The magnetic properties of non-oriented electrical steels are affected by the cutting methods, through induced plastic, and thermal stresses. There is also an important correlation between chemical composition and different magnetic properties. In this paper, we analyze different industrial grades of non-oriented electrical steels, used in electrical machines’ core manufacturing as M800-65A, M800-50A, M400-65A, M400-50A, M300-35A, and NO20. The influence of the cutting methods on the normal magnetization curve, total energy loss and its components, and relative magnetic permeability is investigated in alternating currents using a laboratory single sheet tester. The chemical composition and grain size influence are analyzed and correlated with the magnetic properties. Special attention is devoted to the influence of the increased cutting perimeter on the energy losses and to the way it relates to each chemical alloy constituent. The final decision in what concerns the choice of the proper magnetic material and the specific cutting technology for the motor magnetic cores is imposed by the desired efficiency class and the specific industrial applications.

In this work, a CoCrFeNiMo high-entropy alloy (HEA) material was prepared by the vacuum arc melting (VAM) method and used for electro-spark deposition (ESD). The purpose of this study was to investigate the phase evolution and microstructure of the CoCrFeNiMo HEA as as-cast and electro-spark-deposited (ESD) coating to assess its suitability for corrosvie environments encountered in geothermal energy production. The composition, morphology, and structure of the bulk material and the coating were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness of the bulk material was measured to access the mechanical properties when preselecting the composition to be pursued for the ESD coating technique. For the same purpose, electrochemical corrosion tests were performed in a 3.5 wt.% NaCl solution on the bulk material. The results showed the VAM CoCrFeNiMo HEA material had high hardness (593 HV) and low corrosion rates (0.0072 mm/year), which is promising for the high wear and corrosion resistance needed in the harsh geothermal environment. The results from the phase evolution, chemical composition, and microstructural analysis showed an adherent and dense coating with the ESD technique, but with some variance in the distribution of elements in the coating. The crystal structure of the as-cast electrode CoCrFeNiMo material was identified as face centered cubic with XRD, but additional BCC and potentially σ phase was formed for the CoCrFeNiMo coating.

The development of novel Ti-based amorphous or β-phase nanostructured metallic materials could have significant benefits for implant applications, due to improved corrosion and mechanical characteristics (lower Young’s modulus, better wear performance, improved fracture toughness) in comparison to the standardized α+β titanium alloys. Moreover, the devitrification phenomenon, occurring during heating, could contribute to lower input power during additive manufacturing technologies. Ti-based alloy ribbons were obtained by melt-spinning, considering the ultra-fast cooling rates this method can provide. The titanium alloys contain in various proportions Zr, Nb, and Si (Ti₆₀Zr₁₀Si₁₅Nb₁₅, Ti₆₄Zr₁₀Si₁₅Nb₁₁, Ti₅₆Zr₁₀Si₁₅Nb₁₉) in various proportions. These elements were chosen due to their reported biological safety, as in the case of Zr and Nb, and the metallic glass-forming ability and biocompatibility of Si. The morphology and chemical composition were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the structural features (crystallinity, phase attribution after devitrification (after heat treatment)) were assessed by X-ray diffraction. Some of the mechanical properties (hardness, Young’s modulus) were assessed by instrumented indentation. The thermal stability and crystallization temperatures were measured by differential thermal analysis. High-intensity exothermal peaks were observed during heating of melt-spun ribbons. The corrosion behavior was assessed by electrocorrosion tests. The results show the potential of these alloys to be used as materials for biomedical applications.