Search Results (246)

A systematic investigation was conducted into the effects of varying Al₂O₃ and SrO contents on the structure, sintering kinetics, crystallization patterns, and properties of the SrO-BaO-ZnO-MgO (RO)-B₂O₃-Al₂O₃-SiO₂ (RBAS) system. This glass-ceramic demonstrates effective applicability for low-temperature co-firing of alumina ceramics. Increasing Al₂O₃ content densified the glass network and reduced crystallinity, thereby promoting sintering densification. It led to improved acid resistance and a lower coefficient of thermal expansion (CTE). The composition with 17.50 mol% Al₂O₃ sintered at 800 °C exhibited optimal properties: a well-matched CTE of 7.45 × 10⁻⁶ K⁻¹, a high flexural strength of 130.58 MPa, and excellent chemical stability. Furthermore, it demonstrated excellent compatibility when co-sintered with an Al₂O₃ substrate. Full article

A transition metal-free synthesis of 1,2,5-trisubstituted 1H-indoles by a deprotonation–S_NAr cyclization sequence from 1-aryl-2-(2-fluoro-5-nitrophenyl)ethan-1-one (deoxy-benzoin) Schiff bases is reported. The starting deoxybenzoins were prepared by Friedel-Crafts acylation of activated aromatic compounds by 2-(2-fluoro-5-nitrophenyl)acetyl chloride with AlCl₃ or the corresponding acid with (CH₃SO₂)₂O. The Schiff bases were generated by slow distillation of toluene (18–24 h) from a heated solution of each deoxybenzoin (1 equiv) with a benzyl- or phenethylamine, a high-boiling aliphatic amine, or an aniline derivative (5 equiv). Subsequent addition of N,N-dimethylformamide, 2 equiv of anhydrous K₂CO₃, and heating at 90–95 °C for 18–24 h completed the synthesis. Benzyl-, phenethyl-, and high-boiling amines gave excellent yields while the heating requirements for the initial condensation made volatile aliphatic amines difficult to use and gave low yields. Aniline reactivities correlated with substituent-derived base strength, although modified conditions allowed some yields to be improved. Several anticipated competing processes had minimal impact on the outcome of the cyclizations. Full article

This study introduces a two-step treatment method for synthetic and real electric arc furnace dust (EAFD) wastewater, integrating sorption with Mg–Al layered double hydroxides (LDHs) and electrodialysis (ED). The hydrotalcite (LDH), mainly Mg₆Al₂(CO₃)OH₁₆·4H₂O (hydrotalcite-2H), was characterized by XRD, FTIR, SEM, and EDX, confirming its layered structure and ion-exchange capacity. Calcination at 550 °C was identified as optimal, enhancing sorption efficiency while retaining rehydration potential. Sorption tests demonstrated high effectiveness in removing multivalent ions, achieving over 99% elimination of Ca²⁺, SO₄²⁻, and Pb²⁺ ions and Cr from both synthetic and real wastewater. In contrast, monovalent ions such as Na⁺ and K⁺ were not effectively removed, except for partial removal of Cl⁻. To overcome this limitation, electrodialysis was applied in the second step, successfully targeting the remaining monovalent ions and achieving more than 95% conductivity reduction. A key challenge of ED, salt precipitation caused by calcium and sulphate in the concentrate, was effectively mitigated by the prior LDH treatment. The combined process minimized scaling risks, improved overall ion removal (above 97% for Na⁺ and K⁺), and produced low-salinity effluents (0.84 mS cm⁻¹), suitable for reuse in hydrometallurgical operations. These findings demonstrate that coupling LDH sorption with electrodialysis provides a sustainable and efficient strategy for treating high-salinity industrial wastewaters, particularly those originating from EAFD processes. Full article

High-temperature CaO-based CO₂ capture technology, energized by in situ coal combustion, exhibits substantial promise owing to its high energy efficiency, strong compatibility, and maturity. However, sorbent deactivation mechanisms under complex coal combustion conditions, particularly for industrially required pelletized sorbents, are unclear. Pelletized sorbents were co-fired with four representative coals (differing in Na-K, S, and Al-Si content) in this study. Key factors were decoupled, and two competing mechanisms were revealed: (1) High-temperature sintering deactivation: Single co-firing triggers localized overheating (>900 °C), causing severe sintering and pore collapse. This reduces the specific surface area by 29% and pore volume by 50%, occludes meso-/macropores, and leads to a significant drop in initial CO₂ capture capacity to 0.266–0.297 g/g. Coal types and minor residual surface impurities (<1.7%) are secondary factors. (2) Si-Al ash stabilization: During repeated co-firing (1–9 cycles), Si-Al ash components enrich on sorbents (0.1–7.6%), forming a thermally protective layer. After 20 adsorption–desorption cycles, the CO₂ capture capacity loss drops from 17.6% to 3.9%, improving cycle stability. These findings clarify these dual mechanisms, providing a theoretical basis for system optimization and highlighting precise control of the combustion temperature field as critical for industrial deployment. Full article

This research presents a novel methodology to classify copper tailings according to their potential as alkali-activated materials (AAMs) for construction applications. The methodology includes geochemical and mineralogical characterization via QEMSCAN and X-ray fluorescence, with mechanical performance evaluation through compressive strength test (UCS). A three-phase diagram based on Al₂O₃, Fe₂O₃, and CaO-MgO-K₂O is proposed for a fast screening of copper tailing potential to be used as a construction material. In this paper, three copper tailings were chosen to test the methodology, and a set of five samples for each tailing have been geopolymerized for testing. Copper tailing samples were mixed with 0, 2.5, 5, 7.5 and 10% by mass of Ordinary Portland Cement (OPC) to evaluate the effect on performance when a chemical co-activator is used to improve material reactivity. Compressive strength testing was applied on 2 cm³ cubes after 28 days of curing at 60 °C, yielding values from 6 to 26.1 MPa. The best performing sample featured a Si/Al ≅ 3 ratio and a mineralogy with significant presence of reactive species such as plagioclase and K-feldspar (≅42%). In contrast, high levels of Fe₂O₃ (≥12%), clay (≥7%), and pyrite (≥4%) were associated with reduced mechanical performance. Full article

Petrological knowledge on weathering processes controlling the mobility of chemical elements is still limited in the dry tropical zone of Cameroon. This study aims to investigate the mobility of major and trace elements during rhyolite weathering and soil formation in Mobono by understanding the mineralogical and elemental vertical variation. The studied soil was classified as Cambisols containing mainly quartz, K-feldspar, plagioclase, smectite, kaolinite, illite, calcite, lepidocrocite, goethite, sepiolite, and interstratified clay minerals. pH values ranging between 6.11 and 8.77 indicated that hydrolysis, superimposed on oxidation and carbonation, is the main process responsible for the formation of secondary minerals, leading to the formation of iron oxides and calcite. The bedrock was mainly constituted of SiO₂, Al₂O₃, Na₂O, Fe₂O₃, Ba, Zr, Sr, Y, Ga, and Rb. Ce and Eu anomalies, and chondrite-normalized La/Yb ratios were 0.98, 0.67, and 2.86, respectively. SiO₂, Al₂O₃, Fe₂O₃, Na₂O, and K₂O were major elements in soil horizons. Trace elements revealed high levels of Ba (385 to 1320 mg kg⁻¹), Zr (158 to 429 mg kg⁻¹), Zn (61 to 151 mg kg⁻¹), Sr (62 to 243 mg kg⁻¹), Y (55 to 81 mg kg⁻¹), Rb (1102 to 58 mg kg⁻¹), and Ga (17.70 to 35 mg kg⁻¹). LREEs were more abundant than HREEs, with LREE/HREE ratio ranging between 2.60 and 6.24. Ce and Eu anomalies ranged from 1.08 to 1.21 and 0.58 to 1.24 respectively. The rhyolite-normalized La/Yb ratios varied between 0.56 and 0.96. Mass balance revealed the depletion of Si, Ca, Na, Mn, Sr, Ta, W, U, La, Ce, Pr, Nd, Sm, Gd and Lu, and the accumulation of Al, Fe, K, Mg, P, Sc, V, Co, Ni, Cu, Zn, Ga, Ge, Rb, Y, Zr, Nb, Cs, Ba, Hf, Pb, Th, Eu, Tb, Dy, Ho, Er, Tm and Yb during weathering along the soil profile. Full article

Nanofluids are an innovative working medium in solar hot water installations (DHWs), thanks to their increased thermal conductivity and heat transfer coefficient. The aim of this work was to assess the effect of Al₂O₃ nanofluids in a water–ethylene glycol base (40:60%) and with the addition of Tween 80 surfactant (0.2 wt%) on thermal efficiency (ε) and exergy (η_ex) in a plate heat exchanger at DHW flows of 3 and 12 L/min. The numerical NTU–ε model was used with dynamic updating of thermophysical properties of nanofluids and the solution of the ODE system using the ode45 method, and the validation was carried out against the literature data. The results showed that the nanofluids achieved ε ≈ 0.85 (vs. ε ≈ 0.87 for the base fluid) and η_ex ≈ 0.72 (vs. η_ex ≈ 0.74), with higher entropy generation. The addition of Tween 80 reduced the viscosity by about 10–15%, resulting in a slight increase of Re and h-factor; however, the impact on ε and η_ex was marginal. The environmental analysis with an annual demand of Q = 3000 kWh/year and an emission factor of 0.2 kg CO₂/kWh showed that for ε < 0.87 the nanofluids increased the emissions by ≈16 kg CO₂/year, while at ε ≈ 0.92, a reduction of ≈5% was possible. This paper highlights the need to optimize nanofluid viscosity and exchanger geometry to maximize energy and environmental benefits. Nowadays, due to the growing problems of global warming, the analysis of energy efficiency and carbon footprint related to the functioning of a building seems to be crucial. Full article

The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly identified Late Carboniferous adakitic granodiorite from the South Tianshan, incorporating geochronological, zircon U-Pb and Lu-Hf isotopic, whole-rock geochemical, and Sr-Nd isotopic data. Zircon U-Pb analysis indicates that the granite was emplaced at 310 ± 2.5 Ma. Based on major element compositions, the granodiorite belongs to medium-K calc-alkaline weakly peraluminous series (A/CNK = 0.95–1.09). The samples exhibit typical high-silica adakitic affinity, as evidenced by the elevated contents of SiO₂ (67.75–69.27 wt.%), Al₂O₃ (15.29–15.90 wt.%), Sr (479–530 ppm), and Ba (860–910 ppm); low concentrations of Yb (0.43–0.47 ppm) and Y (7.12–7.44 ppm); high Sr/Y ratios (67–72); and slight Eu anomalies (δEu = 0.89–1.03). The sodium-rich composition (K₂O/Na₂O = 0.48–0.71) is comparable to adakitic rocks from slab-derived melts. Elevated concentrations of Ni (22.12–24.25 ppm), Cr (33.20–37.86 ppm), Co (6.32–6.75 ppm), and V (30.33–32.48 ppm), along with high Mg# values (55–57), suggest melt–mantle interaction during magma ascent. The slightly enriched isotopic signatures, characterized by higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.706086–0.706205) and lower ε_Nd(t) (−3.09 to –2.47) and ε_Hf(t) (−3.11 to +7.66) values, point to notable sedimentary contributions, potentially through source contamination and/or shallow-level crustal contamination. By integrating the new results with previously published data, we consider that the adakitic granodiorite was generated by partial melting of the subducted oceanic crust, triggered by asthenospheric upwelling associated with the southward rollback of the north-dipping South Tianshan oceanic lithosphere. Our data provide new insights into Late Carboniferous retreating subduction along the southern active margin of the Yili-Central Tianshan and the accretionary architecture of the southern Altaids. Full article

This study evaluates the wear and corrosion resistance of the Cu-50Ni-5Al alloy reinforced with CeO₂ nanoparticles for potential use as anodes in molten carbonate fuel cells (MCFCs). Cu–50Ni–5Al alloys were synthesized, with and without the incorporation of 1% CeO₂ nanoparticles, by the mechanical alloying method and spark plasma sintering (SPS). The samples were evaluated using a single scratch test with a cone-spherical diamond indenter under progressive normal loading conditions. A non-contact 3D surface profiler characterized the scratched surfaces to support the analysis. Progressive loading tests indicated a reduction of up to 50% in COF with 1% NPs, with specific values drop-ping from 0.48 in the unreinforced alloy to 0.25 in the CeO₂-doped composite at 15 N of applied load. Furthermore, the introduction of CeO₂ decreased scratch depths by 25%, indicating enhanced wear resistance. The electrochemical behavior of the samples was evaluated by electrochemical impedance spectroscopy (EIS) in a molten carbonate medium under a H₂/N₂ atmosphere at 550 °C for 120 h. Subsequently, the corrosion products were characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the CeO₂-reinforced alloy exhibits superior electro-chemical stability in molten carbonate environments (Li₂CO₃-K₂CO₃) under an H₂/N₂ atmosphere at 550 °C for 120 h. A marked reduction in polarization resistance and a pronounced re-passivation effect were observed, suggesting enhanced anodic protection. This effect is attributed to the formation of aluminum and copper oxides in both compositions, together with the appearance of NiO as the predominant phase in the materials reinforced with nanoparticles in a hydrogen-reducing atmosphere. The addition of CeO₂ nanoparticles significantly improves wear resistance and corrosion performance. Recognizing this effect is vital for creating strategies to enhance the material’s durability in challenging environments like MCFC. Full article

5-aminotetrazole (5AT)-based gas generators, particularly the 5AT/NaIO₄ system, have garnered interest for their high gas production and energy potential. This study investigates the impact of various metal oxides (MnO₂, Al₂O₃, TiO₂, CuO, Fe₂O₃, MgO, ZnO, and MoO₃) on the thermal decomposition and combustion performance of 5AT/NaIO₄. The REAL calculation program was used to infer reaction products, which indicated that the gas products are almost all harmless, with negligibly low percentages of NO and CO. Thermogravimetric analysis revealed that metal oxides, especially MoO₃, significantly advance the decomposition process above 400 °C, reducing the activation energy by 130 kJ/mol and lowering critical ignition and thermal explosion temperatures. Combustion performance tests and closed bomb tests confirmed MoO₃’s positive effect, accelerating reaction rates and enhancing decomposition efficiency. The system’s high Gibbs free energy indicates non-spontaneous reactions. These findings provide valuable insights for designing environmentally friendly gas generators, highlighting MoO₃’s potential as an effective catalyst. Full article

The solution combustion method is widely used because of its simple operation and ability to produce porous structures. The chemical composition and morphological structure of the material can be regulated by different oxidiser-to-fuel ratios (φ). In this work, AlCo₂O₄ derived “Al” catalytic materials were successfully synthesised by adjusting the fuel-to-oxidiser ratio using a one-step solution combustion method. On the one hand, the aluminium nanoparticles act as a part of the metal fuel in the composite solid propellant and, at the same time, serve as a catalytic material. In contrast, the thermal decomposition performance of AP was significantly improved by the synergistic catalysis of AlCo₂O₄. Among the samples prepared under different fuel ratios, considering all aspects (high-temperature decomposition temperature, activation energy, and decomposition heat) comprehensively, the AlCo₂O₄ prepared with φ = 0.5 had a more excellent catalytic effect on AP thermal decomposition, and the T_HTD of AP was reduced to 285.4 °C, which is 188.08 °C lower. The activation energy of the thermal decomposition of AP was also significantly reduced (from 296.14 kJ/mol to 211.67 kJ/mol). In addition, the ignition delay time of AlCo₂O₄-AP/HTPB was drastically shortened to 9 ms from 28 ms after the addition of 7% AlCo₂O₄ derived “Al” catalytic materials. Composite solid propellants have shown great potential for application. Full article

Five requeijão samples, classified as Brazilian cream cheeses, were developed: one control (without guabiroba pulp (Campomanesia xanthocarpa O. Berg) and four with 5, 10, 15, and 20% (m/m) guabiroba pulp. They were evaluated for pH, water activity (aw), color, texture, multi-mineral composition, carotenoid content, and microstructure. The addition of guabiroba pulp reduced pH and maintained Aw. The samples with 5%, 10%, 15%, and 20% guabiroba pulp presented a yellow–reddish coloration. The formulation with 5% had the lowest values of firmness, resilience, texture, and spreadability. From 10% onwards, an increase in cohesiveness and a reduction in creaminess were observed. The sample with 15% presented better spreadability, while the 20% sample had adhesiveness similar to the control. No traces of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Pb, or Se were detected. The detected elements, in descending order, were Na, Ca, P, S, K, Mg, Sr, and Zn. β-carotene was predominant, with guabiroba pulp enhancing α-carotene, β-carotene, β-cryptoxanthin, and λ-carotene levels, especially at 20% pulp. Microstructure analysis by scanning electron microscopy (SEM) showed no significant differences. These findings highlight the potential of guabiroba pulp as a functional ingredient in requeijão, enhancing its carotenoid profile while maintaining desirable textural and physicochemical properties. Full article

As a major contributor to industrial energy consumption and carbon emissions, the kiln industry faces increasing pressure to adopt cleaner energy sources. This study investigated the combustion characteristics, redox processes in celadon firing, product quality, and pollutant emissions for an industry furnace with methanol and liquefied petroleum gas (LPG) as kiln fuels. Methanol combustion reduced firing time by 17.4% due to the faster temperature rise during oxidation and holding phases and provided a more uniform and stable flame, compared with LPG cases. Significant reductions in emissions were observed when methanol is used as fuel. For example, NO concentration is reduced by 70.89%, 37.43% for SO₂, 93.67% for CO, 45.07% for CO₂, and 85.89% for CH₄. The methanol-fired celadon exhibited better quality in terms of the appearance and threshold stress–strain value. The chemical analysis results show that K/O element ratio increased from 8.439% to 11.706%, Fe/O decreased from 4.793% to 3.735%, Al/O decreased from 33.445% to 31.696%, and Si/O increased from 76.169% to 89.825%. These findings demonstrate the potential of methanol as a sustainable kiln fuel, offering enhanced combustion efficiency, reduced emissions, and improved ceramic quality. Full article

The main purpose of this work is to suppress the rate of thermal and oxidative corrosion of copper substrates using double-ceramic-layer thermal barrier coatings (TBCs). Herein, the orthogonal spray experiment was employed to optimize the spraying parameters for TBCs consisting of Cu/NiCoCrAlY/8YSZ/(Y_0.5Gd_0.5)TaO₄. The thermal cycling and average mass loss rate of TBCs prepared by atmospheric plasma spraying (APS) with optimum spraying parameters correspond to 20 cycles and 0.56‰, respectively. The thermal conductivity (0.39 W·m⁻¹·K⁻¹ at 900 °C) of (Y_0.5Gd_0.5)TaO₄ is 71.68% and 52.7% lower than that of (Y_0.5Gd_0.5)TaO₄ bulk and 8YSZ, respectively. Meanwhile, the bond strength increased from 8.86 MPa to 14.03 MPa as the heat treatment time increased from 0 h to 24 h, benefiting from the heat treatment to release the residual stresses inside the coating. Additionally, the hardness increased from 5.88 ± 0.56 GPa to 7.9 ± 0.64 GPa as the heat treatment temperature increased from room temperature to 1000 °C, resulting from the healing of pores and increased densification. Lastly, crack growth driven by thermal stress mismatch accumulated during thermal cycling is the main cause of coating failure. The above results demonstrated that 8YSZ/(Y_0.5Gd_0.5)TaO₄ can increase the service span of copper substrate. Full article

Understanding the impact of CO₂ on cobalt-based Fischer–Tropsch synthesis catalysts is critical for optimizing system efficiency, particularly in scenarios employing solid oxide electrolysis cells for syngas production, given the inevitable incorporation of CO₂ into syngas during the SOEC co-electrolysis process. In this study, we conducted comparative experiments using a Co-Re/γ-Al₂O₃ catalyst in a fixed-bed reactor under industrial conditions (2 MPa, 493 K, GHSV = 6000–8000 Ncm³/g_cat/h), varying the feed gas compositions of H₂, CO, CO₂, and Ar. At an H₂/CO ratio of 2, the addition of CO₂ led to a progressive decline in catalyst performance, attributed to carbon deposition and cobalt carbide formation, as confirmed by Raman spectroscopy, XRD analyses, and TPH. Furthermore, DFT calculations combined with ab initio atomistic thermodynamics (AIAT) were performed to gain molecular insights into the loss of catalyst activity arising from multiple factors, including (sub)surface carbon derived from CO or CO₂, polymeric carbon, and carbide formation. Full article