Search Results (357)

The accumulation of copper smelting slags generated by non-ferrous metallurgy represents both an environmental challenge and a potential source of technogenic raw materials for value-added products. In this study, the feasibility of producing magnesia–quartz proppants from secondary copper smelting slag formed after the pyrometallurgical extraction of iron and zinc was investigated. The slag, primarily composed of oxides of the SiO₂–CaO–Al₂O₃–MgO system, was processed by centrifugal melt granulation to obtain spherical granules suitable for proppant applications. The initial granules exhibited an amorphous glassy structure and insufficient mechanical strength, with up to 70% of particles destroyed under a pressure of 34.5 MPa. Controlled heat treatment within the temperature range of 300–1000 °C induced crystallization of silicate and aluminosilicate phases, leading to a significant improvement in mechanical performance. Optimal properties were achieved after holding at 800 °C for 60 min, where the fraction of crushed granules decreased to 10%, meeting the requirements of GOST R 54571-2011. The influence of MgO content on microstructure and strength was also examined. Increasing the MgO concentration from 5 to 16 wt.% resulted in grain refinement and improved crushing resistance, reducing the fraction of destroyed granules to 3%. To enhance chemical durability, a phenol–formaldehyde protective coating was applied, decreasing proppant solubility in a hydrochloric–hydrofluoric acid mixture from 19% to 2%. These results demonstrate that secondary copper smelting slag can serve as a promising raw material for producing standard-compliant proppants while contributing to the efficient utilization of metallurgical waste. Full article

This work investigates the potential of wollastonite-based brushite cement (WBC) for the stabilization and solidification of radioactive waste contaminated by ⁹⁰Sr. This phosphate binder was formed by the reaction of wollastonite (CaSiO₃) with a phosphoric acid solution containing borax and metallic cations (Al³⁺, Zn²⁺). Two cement pastes were investigated: a commercial binder (WBC-C) and an optimized formulation (WBC-O), produced using a zinc-free mixing solution with a higher aluminum content than that of WBC-C. Mineralogical characterizations using XRD, TGA, XRF, SEM-EDX, and Raman spectroscopy showed that both materials mainly contained amorphous hydrated silica and calcium aluminophosphate, along with crystalline brushite, residual wollastonite, and quartz. The stability of WBC-C under γ-irradiation was evaluated up to a dose of 1 MGy. The only observable effect was water radiolysis, leading to dihydrogen production at yields comparable to Portland cement matrices and geopolymers. Strontium leaching, assessed using the ANSI/ANS-16.1-2003 (R2008) procedure, followed a two-stage release mechanism combining surface wash-off and diffusion. The apparent diffusion coefficient D_a of Sr in WBC-C was markedly lower than typical values reported for Portland cement matrices. WBC-O exhibited enhanced Sr retention, possibly due to its higher aluminum content, which refines mesopores and reduces diffusion pathways accessible to Sr. WBC binders therefore appear to be promising candidates for strontium immobilization. Full article

This study investigates the gel characteristics of alkali-activated materials (AAMs) synthesized using wood ash (WA), and metakaolin (MK) as solid precursors. The research explores the influence of precursor type and sodium hydroxide (NaOH) concentrations in the alkali activator solution on the resulting physicochemical, microstructural, mechanical, and radiological properties of gels. The alkaline activators were prepared by mixing sodium hydroxide solutions (6 M and 12 M) with a sodium silicate (water glass) solution at a volume ratio of 1.5. The physicochemical characteristics of raw materials and AAMs were thoroughly analyzed using X-ray fluorescence (XRF), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with EDS elemental mapping. FTIR analysis confirmed the formation of an amorphous gels geopolymer network. XRD revealed the presence of characteristic crystalline phases (quartz, calcite) within an amorphous matrix. Mechanical properties, such as compressive strength, depended on precursor type and alkali molarity: metakaolin (12 M) reached ~14 MPa, while wood ash showed ~4 MPa (6 M) and ~0.5 MPa (12 M) due to high CaO, low Si and Al, and unfavorable SiO₂/Al₂O₃ (5.71) and Na₂O/Al₂O₃ (3.19) ratios. Furthermore, this research estimates radiological doses by quantifying radionuclide content via gamma-spectrometry. Alkali activation significantly reduced radiological hazard parameters, with radium equivalent activity (Ra_eq) decreasing to 238.0 Bq/kg and the external hazard index (H_ex) to 0.643 for A₁₂MK, while the annual effective dose rate for A₁₂WA was only 0.265 nSv/y-all values remaining well below the recommended safety limit of 370 Bq/kg (≤1 mSv/y). The decrease in activity concentration index (I_γ), Ra_eq, and H_ex with increasing NaOH concentration indicates effective radionuclide immobilization within the geopolymer matrix, confirming the suitability of these alkali-activated materials for safe use in construction from a radiation protection perspective. Full article

This article focuses on the synthesis and characterization of an amorphous carbon derived from spent coffee grounds converted into a porous amorphous carbon (Cp₁) by carbonization up to 900 °C and subsequently combined with aluminum via mechanochemical treatment to obtain the composite Al@Cp₁. Powder X-Ray diffraction, Raman spectroscopy, and X-Ray photoelectron spectroscopy indicate turbostratic carbon domains (ID/IG ≈ 1.04) and an Al–O/Al–OH surface layer (Al₂O₃/Al(OH)₃) with a minor metallic Al contribution. Electrochemical performance in Li half-cells was evaluated by cyclic voltammetry, galvanostatic cycling, rate capability tests, and electrochemical impedance spectroscopy. At 0.02 A g⁻¹, Al@Cp₁ delivers 212.1 mAh g⁻¹, compared with 83.0 mAh g⁻¹ for Cp₁, with an initial coulombic efficiency of ~44%. Across increasing current densities, Al@Cp₁ retains higher reversible capacities than Cp₁ and shows stable cycling over extended tests (>160 cycles). Impedance analysis indicates a reduced interfacial/charge transfer resistance after electrode conditioning, consistent with interfacial stabilization by the Al-containing surface layer. These results demonstrate a simple, scalable route to upgrade coffee waste carbon into a higher-performance lithium-ion battery anode through mechanochemical interfacial engineering. Full article

This work examines the micromechanical response of Al₂O₃/IF-WS₂ (IF-inorganic fullerene-like) composite coatings formed on the EN AW 5251 aluminium alloy by anodic oxidation. The resulting amorphous oxide layer contains a nanopores system that can be filled with IF-WS₂ particles, provided the modifier is properly dispersed. Because commercial IF-WS₂ powders exhibit strong agglomeration, a high-intensity ultrasonic treatment was applied to enhance particle separation before incorporation. The influence of newly established incorporation parameters was assessed using a two-level experimental design. As part of the research, analyses of the microstructure, micromechanical, and sclerometric properties were performed. Cross-sectional SEM observations confirmed the presence of IF-WS₂ within the oxide structure and revealed differences in particle distribution, depending on the incorporation technique used. The results indicate that although microhardness and Young’s modulus are largely insensitive to the nanopowder incorporation method, the interaction between the anodising current density and the incorporation technique significantly influences the strain energy components and tribological response of the coatings. These findings suggest that appropriately selected processing parameters can be used to tailor the mechanical and tribological properties of Al₂O₃/IF-WS₂ coatings to specific loading conditions and functional requirements, rather than striving for a single, universal, optimal processing configuration. Full article

Valorizing construction and demolition waste (CDW) via alkaline activation enables low-carbon binders. This study assesses binary geopolymers formulated with recycled brick powder (PLR) and recycled concrete powder (PCR) in seven precursor ratios (0–100% PCR), activated with a ternary NaOH/Na₂SiO₃/KOH solution (silicate modulus M_s ≈ 3.2) at L/B = 0.15, and cured for 7, 14, and 28 days. Compressive strength (fc), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) were used to link microstructure–phases–properties. A local maximum in fc at ~30% PCR (16.2 MPa at 28 d) was observed versus 0% PCR (14.2 MPa) and ≥50% PCR (13.8 → 10.1 MPa at 28 d). XRD indicated a reduction in inherited crystalline phases and an increased amorphous fraction at ~30% PCR; FTIR (normalized peak position and FWHM of the T–O–Si band, not absolute intensity) suggested higher network extension; SEM-EDS (local/semiquantitative) showed a moderate rise in Ca that supports C-A-S-H domains bridging the N-A-S-H network. At a high PCR, excess Ca simplified mineralogy (quartz/portlandite dominance), promoted competitive routes (C-S-H/carbonation), reintroduced microdefects, and reduced fc. A theoretical oxide balance per mix identified a compositional window where Ca/(Si + Al) ≈ 0.35–0.45 coincides with the mechanical optimum and with XRD/FTIR tracers. Overall, a ~30% PCR window maximizes co-reticulation of N-A-S-H/C-A-S-H and densification without compromising aluminosilicate continuity, providing transferrable design and process-control criteria for CDW-based geopolymer binders. Full article

The article considers issues related to improving the surface characteristics of titanium Gr2 using one of the lightest, cheapest and most ecological methods—electrospark deposition with low pulse energy and with ultradisperse electrodes TiB₂-TiAl with nanosized additives of NbC and ZrO₂. Using profilometric, metallographic, XRD, SEM and EDS methods, the change in the geometric characteristics, composition, structure, micro and nanohardness of the coatings as a function of the electrical parameters of the ESD regime has been studied. The results show that the use of TiB₂-TiAl electrodes and low pulse energy allows the formation of dense, continuous and uniform coatings that demonstrate a significant reduction in roughness, inherent irregularities and structural defects of electrospark coatings. Coatings with minimal defects, with crystalline–amorphous structures, with newly formed intermetallic and wear-resistant double and triple phases of the type AlTi₃, TiAl₃, TiB, TiN_0.3, Al₂O₃, AlB₂, TiC_0.3N_0.7, Ti_3.2B_1.6N_2.4, Al_2.86O_3.45N_0.55 have been obtained. Possibilities have been found for controlling and obtaining specific values for the roughness and thickness of coatings in the ranges Ra = 1.5–3.2 µm and δ = 8–19.5 µm, respectively. The electrical parameters of the modes ensure the production of coatings with previously known thickness and roughness, with increased microhardness up to 13 GPa, with the maximum possible content of deliberately synthesized high-hard phases and with ultra-fine-grained structures have been defined. Full article

Background: gemcitabine is a cytidine analog and major anticancer drug functioning as an antimetabolite. However, its administration by systemic route is accompanied by “burst” and side effects. To limit this, drugs are encapsulated in matrices; metal–organic frameworks (MOFs) are coordination polymers with strong potential for drug encapsulation and delayed release. Methods: mechano-chemical synthesis of solid-state binary complex lag(CYCU-3)(Gem) is described from aluminum MOF (Al-MOF) CYCU-3 and gemcitabine free base (Gem). Synthesis is conducted by liquid-assisted grinding (LAG) with dimethyl sulfoxide (DMSO) followed by its outgassing. The alternative “dry” synthesis results in dry(CYCU-3)(Gem). Materials were characterized by FTIR spectroscopy and XRD, and delayed Gem release was tested to phosphate buffered saline (PBS) at 37 °C. The in vitro toxicity to pancreatic cancer PANC−1 and healthy cells hTERT−HPNE E6/E7/K−RasG12D was assessed by fluorometric assay. Results: in lag(CYCU-3)(Gem) interactions MOF-drug are via non-covalent bonds at O-H and COO⁻ groups of CYCU-3 as found by FTIR marker peak shifts and crystal structure is retained, while dry(CYCU-3)(Gem) shows significant amorphization and loss of functional groups. The lag(CYCU-3)(Gem) but not dry(CYCU-3)(Gem) shows delayed Gem release for 6000 min. The suppression of PANC−1 cells by lag(CYCU-3)(Gem) is time-dependent and it correlates with delayed Gem release. For the first time, a concept of ternary stoichiometric complex lag(CYCU-3)₁(Gem)₁(CIT)₂ is tested that also contains natural organic compound citronellol (CIT), and its structure, bonding and release of Gem are compared to those of binary complex. Bonding is at the O-H groups of CYCU-3 and this complex shows delayed Gem release. Conclusions: binary and ternary complexes of Gem with CYCU-3 yield delayed release and cytotoxicity. LAG is promising for synthesis of solid-state complexes of gemcitabine for delayed release and time-dependent suppression of cancer cells. Full article

To evaluate the stability of fiber-reinforced cemented foamed backfill (FCFB) in complex underground mining environments, this study investigates the synergistic effects of fiber content and modified coal gangue (MCG) under acidic and high-temperature conditions. Through a systematic analysis of hydration processes, compressive strength, and deformation characteristics, the research identifies critical mechanisms for optimizing backfill performance. Calcination of MCG at 700 °C enhances gelling activity via amorphous phase formation, while modified aluminum dross (MAD) treated at 950 °C develops dense α-Al₂O₃ and spinel phases, significantly improving chemical stability. In acidic environments, the suppression of calcium silicate hydrate (C-S-H) is offset by the development of Al³⁺-driven C-A-S-H gels. These gels adopt a tobermorite-like structure, substantially increasing acid resistance. Mechanical testing reveals that while 1% fiber reinforcement promotes nucleation and densification, a 2% concentration hinders hydration. Compressive strength at 28 days shows constrained growth due to pore inhibition, and failure modes transition from multi-crack parallel failure (3-day) to single-crack tensile-shear failure. Under acidic conditions, strain concentration in the upper sample highlights a competitive mechanism between Al³⁺ migration and fiber anchorage. Ultimately, the coordinated regulation of MCG/MAD and fiber content provides a robust solution for roof support in challenging thermo-chemical mining environments. Full article

Atomic layer deposition (ALD) was employed to fabricate single-layer Al₂O₃, single-layer ZrO₂, and Al₂O₃/ZrO₂ nanolaminate coatings on SUS304 to enhance corrosion protection in chloride-containing environments. All coatings were deposited at 250 °C using optimized self-limiting ALD processes, and the total film thickness was controlled at approximately 54 nm for a fair comparison. Structural characterization revealed that Al₂O₃ films remained amorphous, whereas ZrO₂ films exhibited a thickness-dependent transition from amorphous to crystalline phases. In the nanolaminate structures, thinner ZrO₂ sublayers (<9 nm) retained amorphous or locally nanocrystalline characteristics, while thicker ZrO₂ sublayers (15 nm) developed polycrystalline features with increased grain boundary density. Electrochemical corrosion tests conducted in 3.5 wt% NaCl solution demonstrated that the Al₂O₃/ZrO₂ nanolaminate coatings exhibited significantly lower corrosion current densities and delayed pitting corrosion compared to single-layer coatings. Among all samples, the [Al₂O₃ (15 nm)/ZrO₂ (3 nm)] × 3 nanolaminate showed the best corrosion resistance, with the lowest corrosion current density (I_corr = 6.20 nA/cm²) and the highest protective efficiency (98.34%). These results highlight the critical role of nanolaminate architecture and sublayer crystallinity in suppressing ionic diffusion and provide an effective strategy for designing ultrathin, high-performance corrosion barrier coatings for stainless steel. Full article

Al-rich NH₄-ZSM-5 with highly oriented crystals was directly synthesized through a one-pot hydrothermal technique, using ammonium nitrate as a metal-free mineralizer. The samples were characterized by XRD, N₂ adsorption–desorption, SEM, FTIR, Py-FTIR, ²⁷Al MAS NMR, ²⁹Si MAS NMR, ¹H MAS NMR, and TGA techniques. The impact of aluminum source, ammonium source, and H₂O/SiO₂ molar ratio was studied. XRD results showed that the ZSM-5 catalyst with a low Si/Al ratio (13) was successfully synthesized without any amorphous phase, including a microporous/mesoporous structure. A low H₂O/SiO₂ molar ratio (75) resulted in coffin-shape surface morphology, large b-axis-oriented particles (ca. 19 µm), and high specific surface area (>300 m² g⁻¹), providing a large portion of straight channels (90.5%). The catalytic activity of the catalysts was evaluated in the CO₂ hydrogenation reaction in tandem configuration with a Na/Fe₂O₃ catalyst. The results confirmed that highly b-oriented crystals improved the product shape selectivity to p-xylene by affecting the diffusion resistance. Therefore, the developed catalyst provided high CO₂ conversion (45%) and high aromatic selectivity (77%), with p-xylene accounting for 82% of the produced xylene compounds, over a long-term time on stream (17 h). These results demonstrate the effectiveness of the direct synthesis strategy in producing Al-rich ZSM-5 catalysts with tailored textural and acidic properties for tandem and shape-selective catalysis. Full article

This study assesses two Brazilian Type F fly ash samples (FA-A and FA-B), collected from the same thermoelectric complex in different years, to investigate their influence on the production of alkali-activated materials (AAMs). FA-A exhibited a slightly higher SiO₂/Al₂O₃ ratio (3.52 vs. 3.34) and a finer average particle size (D₅₀ = 19.7 μm vs. 30.8 μm) than FA-B. X-ray diffraction revealed that FA-A presented a broad amorphous halo between 15° and 35° (2θ), indicative of phases with low atomic ordering, which are more susceptible to dissolution and capable of supplying Si- and Al-rich species for the formation of alkali activation products. These differences directly affected reactivity and mechanical performance. After 1 day of curing, FA-A-based matrices achieved 88.5 MPa in compressive strength—approximately 100% higher than FA-B (44.2 MPa). However, FA-A suffered a 19.6% strength reduction after 28 days of curing, whereas FA-B showed only a 3.8% decrease over the same period, reflecting better long-term stability. FTIR confirmed Na₂CO₃ formation in FA-A, associated with excess sodium (Na/Al = 2.07 after 28 days), while SEM revealed unreacted spheres persisting in FA-B, consistent with its lower dissolution rate. Water absorption was also significantly different, with FA-B matrices reaching values up to 52% lower than FA-A after 7 days of curing. These results demonstrate that even slight variations in chemical composition and atomic ordering, even for ashes from the same plant, strongly influence the reactivity, microstructure, and mechanical performance of alkali-activated binders. Full article

The construction sector faces pressure to decarbonise while addressing rising resource demands and agricultural waste. Ordinary Portland cement (OPC) is a major CO₂ emitter, yet biomass residues are often open-burned or landfilled. This study explores corncob ash (CCA) as a sustainable supplementary cementitious material (SCM), examining how calcination conditions influence pozzolanic potential and support circular economy and climate goals, which have not been adequately explored in literature. Ten CCA samples were produced via open-air burning (2–3.5 h) and electric-furnace calcination (400–1000 °C, 2 h), alongside a reference OPC. Mass yield, colour, XRD, XRF, LOI, and LOD were analysed within a process–structure–property–performance–sustainability framework. CCA produced in a 400–700 °C furnace window consistently achieved high amorphous contents (typically ≥80%) and combined pozzolanic oxides (SiO₂ + Al₂O₃ + Fe₂O₃) above the 70% ASTM C618 threshold, with 700 °C for 2 h emerging as an optimal condition. At 1000 °C, extensive crystallisation reduced the expected reactivity despite high total silica. Extended open-air burning (3–3.5 h) yielded chemically acceptable but more variable ashes, with lower amorphous content and higher alkalis than furnace-processed CCA. Simple industrial ecology calculations indicate that valorising a fraction of global CC residues and deploying optimally processed CCA at only 20% OPC replacement could displace 180 million tonnes CC waste and clinker avoidance on the order of 5–6 Mt CO₂ per year, while reducing uncontrolled residue burning and primary raw material extraction. The study provides an experimentally validated calcination window and quality indicators for producing reactive CCA, alongside a clear link from laboratory processing to clinker substitution, circular resource use, and alignment with SDGs 9, 12, and 13. The findings establish a materials science foundation for standardised CCA production protocols and future life cycle and performance evaluations of low-carbon CCA binders. Full article

Three processes for the production of ceramics close to stoichiometric MgAl₂O₄ are benchmarked against each other. The traditional ceramic route is based on mostly crystalline starting powder, which is converted into ceramic via shaping and heat treatment (IKTS). The other two processes are based on glasses. Partial or complete crystallization without pressure (ISC) or complete crystallization with pressure (CAU) leads to (glass) ceramics. Spinel powder is mixed with various dopants (BaO, TiO₂, CaO and SrO), with the aim to reduce the grain size (IKTS). The doping results in a second, partly interfering phase, and the transmission decreases strongly due to absorption with increasing content of the added oxide. For the glass route without pressure (ISC), it is shown that a network-forming oxide (B₂O₃, TiO₂) is needed to produce the glasses. Compared to the starting glasses, the resultant glass ceramics suffer loss of transparency due to crystallization. Using the levitation furnace, it is possible to produce amorphous glass beads from MgAl₂O₄ enriched with 25 wt% SiO₂ without a container. The nanocrystalline ceramics synthesized from these glasses and the ISC glasses via the high-pressure route (CAU) are moderately transparent to translucent. Full article

Coal gangue, a major industrial solid waste from coal mining and processing, requires efficient alumina and silica separation for high-value utilization. This study focused on mineral reaction mechanisms and characteristics of coal gangue during calcination and alkaline leaching. Results showed calcination at 900–1200 °C altered its phase composition, affecting silica separation efficiency, with the optimal calcination range being 960–1120 °C. Poorly crystallized mullite and Al₂O₃ in calcined gangue were insoluble under low-alkaline and low-temperature conditions. On the contrary, amorphous silica is soluble and forms a sodium silicate solution in the proper alkaline conditions. This characteristic facilitates the efficient separation of alumina and silica. It was determined that the suitable conditions for silica removal from coal gangue are as follows: 1080 °C calcination for 90 min, leaching at 75 °C with 200 g/L NaOH (solid–liquid ratio of 1:4) for 4 h. Under these selected conditions, the silica leaching efficiency was 77.31%, the alumina leaching efficiency was 12.21%, the Na₂O content in the leached residue was 1.94%, and the mass ratio of alumina to silica (A/S) in the leached residue increased from 0.88 to 3.42. A potential desilication mechanism was also analyzed. Full article