Search Results (5)

In this work, a sustainable approach to reclaiming high-value anatase/rutile TiO₂ nanoparticles from deactivated or used selective catalytic reduction (SCR) catalysts is demonstrated using a composite flux (NaOH/Na₂CO₃) through an efficient sintering and subsequent leaching methodology. This method directly addresses the urgent need for circular economy strategies in industrial waste management. Sintering experiments revealed that while NaOH enhanced the separation efficiency of V₂O₅ and SiO₂, it led to agglomerated products, hindering TiO₂ recovery. In contrast, Na₂CO₃ enabled the production of powdery sintered residues, facilitating the complete separation of anatase/rutile TiO₂ nanoparticles, as confirmed by XRD. By optimizing the sintering-leaching conditions, this method achieves near-total recovery of TiO₂ with retained photocatalytic performance, ensuring its suitability for reuse in applications such as air/water purification or renewable energy systems. This study advances sustainability by repurposing industrial waste into high-performance materials, reducing the energy and resource demands associated with conventional TiO₂ synthesis, and preventing hazardous material leakage into ecosystems. The scalable, low-complexity process aligns with global sustainability goals, including responsible consumption (SDG 12), climate action (SDG 13), and industrial innovation (SDG 9), offering a blueprint for transforming waste streams into valuable resources for a greener economy. Full article

Reduction–oxidation (redox) cycling of a solid oxide fuel cell (SOFC) due to leakage of a fuel or standby and shutdown cycling is an issue that has attracted the attention of many research groups for a long time. The researchers mainly note the harmful effects of redox cycling on the microstructure of SOFC constituents and search for ways to mitigate or diminish them. The purpose of this study was to use reduction and oxidation stages in an appropriate mode as a positive preconditioning to improve redox cycling stability of Ni-containing SOFC anode materials. The redox treatment was applied to YSZ–NiO(Ni) anode substrate specimens at 600 °C and 800 °C. The mechanical tests (flexural strength, microhardness, and fracture toughness) were performed on these specimens and the results were compared to those for as-sintered and one-time reduced specimens. Microstructure and fracture surface morphology of material in corresponding modes were analyzed. The main findings were summarized as follows: (i) Redox treatment at 600 °C provides an increase in flexural strength and electrical conductivity of YSZ–NiO(Ni) anode cermets; (ii) the treatment at 800 °C causes formation of a gradient microstructure with lateral cracks that result in a significant decrease in flexural strength; (iii) the mode of redox treatment at 600 °C for 4 h in Ar–5% H₂/air atmosphere provides an increase in flexural strength of YSZ–NiO(Ni) anode cermets (up to 127 ± 4 MPa), while electrical conductivity was provided at a comparatively high level (7 × 10⁵ S/m). Full article

This article reviews the progress in developing ZnO-V₂O₅-based metal oxide varistors (MOVs) using powder metallurgy (PM) techniques. The aim is to create new, advanced ceramic materials for MOVs with comparable or superior functional properties to ZnO-Bi₂O₃ varistors using fewer dopants. The survey emphasizes the importance of a homogeneous microstructure and desirable varistor properties, such as high nonlinearity (α), low leakage current density (J_L), high energy absorption capability, reduced power loss, and stability for reliable MOVs. This study investigates the effect of V₂O₅ and MO additives on the microstructure, electrical and dielectric properties, and aging behavior of ZnO-based varistors. The findings show that MOVs with 0.25–2 mol.% V₂O₅ and MO additives sintered in air over 800 °C contain a primary phase of ZnO with a hexagonal wurtzite structure and several secondary phases that impact the MOV performance. The MO additives, such as Bi₂O₃, In₂O₃, Sb₂O₃, transition element oxides, and rare earth oxides, act as ZnO grain growth inhibitors and enhance the density, microstructure homogeneity, and nonlinearity. Refinement of the microstructure of MOVs and consolidation under appropriate PM conditions improve their electrical properties (J_L ≤ 0.2 mA/cm², α of 22–153) and stability. The review recommends further developing and investigating large-sized MOVs from the ZnO-V₂O₅ systems using these techniques. Full article

The air leakage in sintering machines affects the technological and economic indexes of the sintering process. It is of great significance to monitor and estimate the key areas. Mathematical models of sintering air leakage through holes in the steady-state process are given based on the fluid mechanics to predict the flow rate and effect on the key area. It was found that the hole model is the application of constant orifice outflow in the computation of sintering air leakage. The counter-flow bed model is suitable for predicting the flow rate through a complete break in sintering wind boxes. Furthermore, This paper proposes a new hole–bed generalized model to cover all the possible hole diameters for further high-precision application. The model connects the leakage hole diameter with the sintering process for the first time and establishes their coupling relationship. The pressure state in the sintering system depends on the ratio of the leakage hole area to the sintering bed area. The proposed fast estimation models are a step forward in developing more precise and powerful calculation tools to foresee the effects and consequences of sintering air leakage. It has a good prospect for reducing and replacing complex manual measurement and bringing some insight into the state of the art that could be improved in the future. Full article

K_0.5Na_0.5NbO₃-based ceramics, a promising group of lead-free piezoelectrics, are challenging to sinter dense while avoiding alkali evaporation. This work explores hybrid atmosphere processing, a new approach where reducing atmospheres is used during heating to avoid coarsening from alkali carbonates and hydroxides, and oxidizing atmospheres is used during sintering to avoid alkali evaporation. Discs of Li_0.06(K_0.52Na_0.48)_0.94Nb_0.71Ta_0.29O₃ with 0.25 mol% Mn (KNNLTM) were sintered in air, N₂, 9% H₂ in N₂, or 9% H₂ in N₂ during heating and air during sintering (hybrid atmosphere processing). The highest density was obtained by sintering in 9% H₂ in N₂, but resulted in high alkali loss and decomposition of the surface, followed by low piezoelectric response. However, with the hybrid H₂/air processing it was possible to both avoid surface decomposition and leakage currently associated with alkali evaporation during sintering in H₂, and to obtain a denser, more phase-pure and small-grained KNNLTM ceramic with a higher piezoelectric response than obtained by sintering in air or N₂. Full article