Search Results (215)

The sintering of coal gangue ceramsites (CGCs) using belt roasting technology involves the recirculation of flue gases and variations in oxygen concentrations. This study investigates the effects of temperature and pyrolysis atmosphere on the pore structure of CGCs at three temperature levels: 600 °C, 950 °C, and 1160 °C. The results revealed that apparent porosity is primarily influenced by O₂-promoted weight loss and the densification process, while closed porosity is affected by pyrolysis reactions and crystal phase transformations. Below 950 °C, enhancing the oxidative atmosphere facilitates the preparation of porous CGCs, whereas above 950 °C, reducing the oxidative atmosphere favors the preparation of high-strength CGCs. These findings provide valuable insights for the industrial production of CGCs, offering a basis for optimizing sintering parameters to achieve the desired material properties. The latest production equipment, furnished with adjustable atmospheres (such as belt sintering roasters), can better regulate the mechanical properties of the products. Full article

Ammonia (NH₃) is one of the characteristic gases used to detect food spoilage. In this study, the 10 wt% Ag-NiFe₂O₄ nanocomposite was synthesized via the hydrothermal method. Characterization results from SEM, XRD, and XPS analyzed the microstructure, elemental composition, and crystal lattice features of the composite, confirming its successful fabrication. Under the optimal working temperature of 280 °C, the composite exhibited excellent gas-sensing properties towards NH₃. The 10 wt% Ag-NiFe₂O₄ sensor demonstrates rapid response and recovery, as well as high sensitivity, towards 30 ppm NH₃, with response and recovery times of merely 3 s and 9 s, respectively, and a response value of 4.59. The detection limit is as low as 0.1 ppm, meeting the standards for food safety detection. Additionally, the sensor exhibits good short-term repeatability and long-term stability. Additionally, density functional theory (DFT) simulations were conducted to investigate the gas-sensing advantages of the Ag-NiFe₂O₄ composite by analyzing the electron density and density of states, thereby providing theoretical guidance for experimental testing. This study facilitates the rapid detection of food spoilage and promotes the development of portable food safety detection devices. Full article

The rise of two-dimensional (2D) materials has transformed gas sensing, with Nb₂CT_x MXene drawing significant interest due to its distinct physicochemical behaviors. As part of the MXene family, Nb₂CT_x MXene demonstrates a remarkable combination of high electrical conductivity, adjustable surface chemistry, and exceptional mechanical flexibility, positioning it as a promising candidate for next-generation gas sensors. This review explores the synthesis techniques for Nb₂CT_x MXene, highlighting etching methods and post-synthesis adjustments to achieve the tailored surface terminations and structural qualities essential for gas detection. A comprehensive examination of the crystal structure, morphology, and electronic characteristics of Nb₂CT_x MXene is presented to clarify its outstanding sensing capabilities. The application of Nb₂CT_x MXene for detecting gases, including NH₃, humidity, NO₂, and volatile organic compounds (VOCs), is assessed, showcasing its sensitivity, selectivity, and low detection limits across various environmental settings. Furthermore, the integration of Nb₂CT_x MXene with other nanostructures in sensor platforms is reviewed. Lastly, challenges related to scalability, stability, and long-term performance are addressed, along with future prospects for Nb₂CT_x MXene-based gas sensors. This review offers significant insights into the potential of Nb₂CT_x MXene as a pioneering material for enhancing gas sensing technologies. Full article

In this article, we consider the roles of transcrustal magma- and fluid-conducting faults (TCMFCFs) in the formation of mineral deposits, showing the importance of deep sources of heat and hydrothermal solutions in the genesis and history of deposit formation. As a result of the impact on the lithosphere of mantle plumes rising along TCMFCFs, intense block deformations and tectonic movements are generated; rift systems, and volcanic–plutonic belts spatially combined with them, are formed; and intrusive bodies are introduced. These processes cause epithermal ore formation as a consequence of the impact of mantle plumes rising along TCMFCF to the lithosphere. At hydrocarbon fields, they play extremely important roles in conductive and convective heat, as well as in mass transfer to the area of hydrocarbon generation, determining the relationship between the processes of lithogenesis and tectogenesis, and activating the generation of hydrocarbons from oil and gas source rock. Detection of TCMFCFs was carried out using MMSS (the method of microseismic sounding) and MTSM (the magnetotelluric sounding method), in combination with other geological and geophysical data. Practical examples are provided for mineral deposits where subvertical transcrustal columns of increased permeability, traced to considerable depths, have been found; the nature of these unique structures is related to faults of pre-Paleozoic emplacement, which determined the fragmentation of the sub-crystalline structure of the Earth and later, while developing, inherited the conditions of volumetric fluid dynamics, where the residual forms of functioning of fluid-conducting thermohydrocolumns are granitoid batholiths and other magmatic bodies. Experimental modeling of deep processes allowed us to identify the quantum character of crystal structure interactions of minerals with “inert” gases under elevated thermobaric conditions. The roles of helium, nitrogen, and hydrogen in changing the physical properties of rocks, in accordance with their intrastructural diffusion, has been clarified; as a result of low-energy impact, stress fields are formed in the solid rock skeleton, the structures and textures of rocks are rearranged, and general porosity develops. As the pressure increases, energetic interactions intensify, leading to deformations, phase transitions, and the formation of chemical bonds under the conditions of an unstable geological environment, instability which grows with increasing gas saturation, pressure, and temperature. The processes of heat and mass transfer through TCMFCFs to the Earth’s surface occur in stages, accompanied by a release of energy that can manifest as explosions on the surface, in coal and ore mines, and during earthquakes and volcanic eruptions. Full article

In recent years, climate change has attracted the attention of the scientific community. These changes are attributed to human action, which is responsible for the emission of polluting gases, mainly through the burning of fossil fuels, deforestation, and industrial processes that are responsible for the greenhouse effect. Post-combustion CO₂ capture using solid adsorbents is a technology that is currently gaining prominence as an alternative and viable form of capture to other industrial processes used. Zeolites are adsorbents capable of capturing CO₂ selectively due to their properties such as textural properties, high surface area, and active sites. In this context, this work developed materials with a zeolite structure with an alternative low-cost silica source from beach sand, called MPI silica, to make the process eco-friendly. Crystallization time studies were carried out for materials containing MFI-type zeolites with MPI silica with a time of 15 h (ZM 15 h) and 3 days (SM 3 d), with relative crystallinities of 92.90% and 111.90%, respectively. The synthesized materials were characterized by several techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), the textural analysis of N₂ adsorption/desorption isotherms, absorption spectroscopy in the infrared region with Fourier transform (FTIR), scanning electron microscopy (SEM), and thermal analysis. The evaluation of the experimental adsorption isotherms showed that the best results were for the zeolites synthesized in the basic medium, namely ZMP 3 d, ZM 10.5 h, and ZM 15 h, with capacities of 3.72, 3.10, and 3.22 mmol/g of CO₂, respectively, and in the hydrofluoric medium, namely SP 9 d, SM 3 d, and SM 6 d, with capacities of 3.94, 3.78, and 3.60 mmol/g of CO₂, respectively. The evaluation of the mathematical models indicated that the zeolites in the basic medium best fitted the Freündlich model, namely ZMP 3 d, ZM 10.5 h, and ZM 15 h, with capacities of 2.56, 1.68, and 1.87 mmol/g of CO₂, respectively. The zeolites in the hydrofluoric medium are adjusted to the Langmuir model (SP 9 d and SM 3 d) and Temkin model (SM 6 d), with capacities of 3.79, 2.23, and 2.11 mmol/g of CO₂, respectively. Full article

The Junqueira massif is a syn- to late-kinematic Variscan batholith intruded into Ediacaran-Cambrian metasedimentary rocks of the Douro-Beiras Supergroup (DBSG) in the Central Iberian Zone. The batholith occupies the axial zone of the Porto-Viseu antiform, a large NW-SE trending megascopic domal structure formed during the last Variscan ductile deformation event. Field and petrographic evidence reveals that the Junqueira batholith comprises several units of leucocratic granites distinguished by variations in grain size and relative proportions of the main rock-forming minerals. This work provides new petrographical, geochemical, Sr–Nd isotope data and ID-TIMS U–Pb ages for the Junqueira batholith. U–Pb dating of zircon and monazite by ID-TIMS gives a crystallization age of ca. 312–309 Ma for this batholith. Combined geochemical and Sr–Nd isotopic data for the different granite units (ASI > 1.1; high SiO₂ and K₂O contents, low CaO, MgO, Ba, Sr, moderately fractionated REE patterns, Eu negative anomalies, ⁸⁷Sr/⁸⁶Sr_i > 0.713, εNd₃₁₀ = −3.5 to −5.9; T_DM = 1.1–1.4 Ga) support a provenance by fluid-absent melting processes of exclusively supracrustal sources (mainly metapelites), similar to the adjoining country rocks of the Beiras Group of the DBSG. Full article

The objective of this study is the fabrication of sensors which can detect modifications in CO₂ concentrations at room temperature, thus indicating the quality or microbial spoilage of food products when incorporated into food packaging. ZnO nanostructures are known for their ability to detect organic gases; however, their effectiveness is limited to high temperatures (greater than 200 °C). To overcome this limitation, sodium (Na) doping is investigated as a way to enhance the sensing properties of ZnO films and lower the working temperature. In this study, undoped and Na-doped ZnO thin films were developed via the sol-gel method with different Na percentages (2.5, 5 and 7.5%) and were deposited via spin coating. The crystal structure, the morphology, and the surface topography of the developed films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), respectively. Furthermore, the response to CO₂ was measured by varying its concentration up to 500 ppm at room temperature. All the developed films presented the characteristic diffraction peaks of the ZnO wurtzite hexagonal crystal structure. SEM revealed that the films consisted of densely packed grains, with an average particle size of 58 nm. Na doping increased the film thickness but reduced the surface roughness. Finally, the developed sensors demonstrated very good CO₂ sensing properties, with the 2.5% Na-doped sensor having an enhanced sensing performance concerning sensitivity, response, and recovery times. This leads to the conclusion that Na-doped ZnO sensors could be used for the detection of microbial spoilage in food products at room temperature, making them suitable for smart food packaging applications. Full article

Taranakite is a mineral consisting of a hydrated layered aluminum phosphate, with the formula K₃Al₅(PO₃OH)₆(PO₄)₂·18H₂O; its structure belongs to the R-3C group. If the mineral grows in an environment rich in bat and bird guano, the high nitrogen guano content induces the intercalation of NH₄⁺ into the structure, replacing the potassium ion. The thermal decomposition of guano-derived taranakite releases water and ammonia. The aim of this work is to confirm the presence of ammonium in the guano-derived taranakite. Thermogravimetric analysis (TGA) was performed on taranakite collected in Pollera Cave (Liguria), and the gases evolved during its decomposition were analyzed by Fourier-transform infrared (FT-IR) spectroscopy. All the samples were characterized before and after thermal analysis by means of powder X-ray diffractometry (PXRD) and scanning electron microscopy (SEM). The release of crystallization water occurs at a temperature below 200 °C; further ammonia can be detected above 200 °C. Full article

Using the Bridgman technique, GaSe single crystals were obtained which were mechanically split into plane-parallel plates with a wide range of thicknesses. By heat treatment in air at 820 °C and 900 °C, for 30 min and 6 h, micro- and nanocomposite layers of Ga₂Se₃–Ga₂O₃ and β–Ga₂O₃ (native oxide) with surfaces made of nanowires/nanoribbons were obtained. The obtained composite Ga₂Se₃–Ga₂O₃ and nanostructured β–Ga₂O₃ are semiconductor materials with band gaps of 2.21 eV and 4.60 eV (gallium oxide) and photosensitivity bands in the green–red and ultraviolet-C regions that peaked at 590 nm and 262 nm. For an applied voltage of 50 V, the dark current in the photodetector based on the nanostructured β–Ga₂O₃ layer was of 8.0 × 10⁻¹³ A and increased to 9.5 × 10⁻⁸ A upon 200 s excitation with 254 nm-wavelength radiation with a power density of 15 mW/cm². The increase and decrease in the photocurrent are described by an exponential function with time constants of τ_1r = 0.92 s, τ_2r = 14.0 s, τ_1d = 2.18 s, τ_2d = 24 s, τ_1r = 0.88 s, τ_2r = 12.2 s, τ_1d = 1.69 s, and τ_2d = 16.3 s, respectively, for the photodetector based on the Ga₂Se₃–Ga₂S₃–GaSe composite. Photoresistors based on the obtained Ga₂Se₃–Ga₂O₃ composite and nanostructured β–Ga₂O₃ layers show photosensitivity bands in the spectral range of electronic absorption bands of ozone in the same green–red and ultraviolet-C regions, and can serve as ozone sensors (detectors). Full article

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals measured at temperatures in the range from 9.5 to 300 K were analyzed. The absorption spectra with features caused by Ga vacancies in two charge states and direct interband transitions were fitted by a model equation. Temperature dependencies of the defect concentrations and optical transition energies, as well as of the GaSe band gap, were determined. Current- and capacitance-voltage characteristics and DLTS spectra were measured for as-grown and electron-irradiated GaSe slabs with Sc (barrier) and Pt (ohmic) contacts. An experimental Sc/GaSe Schottky barrier height of 1.12 eV was determined in close agreement with a theoretical estimate. The activation energy and the hole capture cross-section deduced from the DLTS data are 0.23 (0.66) eV and 1.5 × 10⁻¹⁹ (2.3 × 10⁻¹⁵) cm⁻² for the supposed $V_{\mathrm{Ga}}^{-1}$ ($V_{\mathrm{Ga}}^{-2}$) defect. For the electron-irradiated GaSe crystals, the found activation energies are close to the values inferred from the optical measurements. Full article

This contribution provides a petrographic and Raman investigation of fluid inclusions found in chromitites collected in the ophiolites of Santa Elena (Costa Rica), Bracco (Italy), Otrhys and Vourinos (Greece), and Troodos (Cyprus). Most of the analyzed chromites are classified as high-Cr, with the exception of those from Bracco and some of the Othrys complexes that are high-Al. Although the investigation of fluid inclusions in chromitites is very challenging due to the poor transparency of the host chromite, the studied samples contain numerous fluid inclusions. The fluid inclusions look to be more abundant in the high-Cr chromitites, related to a subduction zone environment, compared to the high-Al chromitites generated in a mid-ocean ridge. This is in agreement with the petrogenetic model for the formation of podiform chromitites that implies the presence of a metasomatic event caused by hydrous fluids that reacted pervasively with variable depleted mantle tectonites, especially in the subduction zone setting. The fluid inclusions, between 1 and 15 µm in size, show negative crystal or irregular angular shapes. They occur when enclosed in chromite crystals that have not been affected by low-temperature processes. The fluid inclusions consist of liquid (L), vapour(V~30–50 area%) and L + V (V~40–60 area% rarely 10–80 area%). The fluid inclusions may contain only vapour and a vapour and a solid phase, too. The Raman spectra reveal the presence of CH₄ in certain fluid inclusions. Considering the high number of fluid inclusions that potentially contain CH₄, we suggest that the fluid inclusions in the chromite crystals and their leaching can be a possible source in order to explain the high amount of CH₄ detected in some podiform chromitites, previously attributed to the Sabatier reaction. The mode of the occurrences of the studied CH₄ bearing fluid inclusions, i.e., entrapped in unaltered chromite crystals formed at a magmatic temperature, suggest their abiotic origin from mantle-derived fluids, rather than those related to the low-temperature serpentinization processes. The investigation of fluid inclusions, although it is difficult and challenging or even impossible when the chromite is too opaque, can be applicable to other chromitites worldwide to verify the presence of H₂O, CH₄ or other gases. This information will greatly improve our understanding of the nature of the fluid phases during the formation of podiform chromitites. Full article

Emissions caused by polluting gases, such as carbon dioxide, are one of the main contributors to the generation of the greenhouse effect that leads to global warming, responsible for climate change. An alternative to mitigating these emissions is the use of adsorbents capable of capturing CO₂. Zeolites are considered one of the most effective adsorbents in gas adsorption and separation technologies due to their high specific area and pore size and, consequently, greater adsorption capacity when compared to other commonly used materials. Despite this, reagents used in syntheses as the source of silica often make obtaining these materials more expensive. Seeking to overcome this limitation, in this work, materials (for CO₂ capture) were developed with a zeolitic structure using a low-cost alternative source of silica from beach sand called MPI silica to make the synthesis process eco-friendly. The crystallization time of the materials was studied, obtaining an LTA zeolite with MPI silica in a period of 1 h (ZAM 1 h), with a relative crystallinity of 74.26%. The materials obtained were characterized using the techniques of X-ray diffraction (XRD), X-ray fluorescence (XRF), absorption spectroscopy in the infrared region with Fourier transform (FTIR), scanning electron microscopy (SEM), and thermal analysis. The evaluation of the experimental adsorption isotherms showed that the zeolite LTA Aerosil^®200 (standard zeolite) and MP had adsorption capacities of 5.25 mmol/g and 4.83 mmol/g of CO₂, respectively. The evaluation of mathematical models indicated that the LTA zeolites fit the Temkin model best and had the same trend, with calculated adsorption capacities of 3.97 mmol/g and 3.75 mmol/g, respectively. Full article

To address the issue of air pollution caused by automobile exhaust in China, a titanium dioxide/graphite carbon nitride (TiO₂/g-C₃N₄) composite photocatalyst capable of degrading automobile exhaust was prepared in this study. It was used as an additive to modify styrene–-butadiene latex (SBR) emulsified asphalt. The basic properties of modified emulsified asphalt before and after aging were analyzed, and the dosage range of TiO₂/g-C₃N₄ (TCN) was determined. The environmentally friendly micro-surfacing of degradable automobile exhaust was prepared. Based on 1 h and 6 d wet wheel wear test, rutting deformation test, surface structure depth test, and pendulum friction coefficient test, the road performance of TCN environmentally friendly micro-surfacing mixture with different contents was analyzed and evaluated, and the effect of environmentally friendly degradation of automobile exhaust was studied by a self-made degradation device. The results show that when the mass ratio of TiO₂ and melamine was 1:4, the TCN composite photocatalyst had strong photocatalytic activity. The crystal structure of TiO₂ and g-C₃N₄ was not damaged during the synthesis process. The g-C₃N₄ inhibited the agglomeration of TiO₂. The introduction of N-Ti bond changed the electronic structure of TiO₂, narrowed the band gap and broadened the visible light response range. When the TCN content was in the range of 1~7%, the softening point of SBR- modified emulsified asphalt increased with the increase in TCN content, the penetration decreased, the ductility decreased gradually, and the storage stability increased gradually. The penetration ratio and ductility ratio of the composite-modified emulsified asphalt after aging increased with the increase in TCN content, and the increment of the softening point decreased. This shows that the TCN content is beneficial to the high-temperature performance and anti-aging performance of SBR-modified emulsified asphalt, and has an adverse effect on low temperature performance and storage stability. The addition of TCN can improve the wear resistance and rutting resistance of the micro-surfacing mixture, and has no effect on the water damage resistance and skid resistance. The environment-friendly micro-surfacing asphalt mixture had a significant degradation effect on NO, CO, and HC. With the increase in TCN content, the degradation efficiency of the three gases was on the rise. When the content was 5%, the degradation rates of NO, CO, and HC were 37.16%, 25.72%, and 20.44%, respectively, which are 2.34 times, 2.47, times and 2.30 times that of the 1% content, and the degradation effect was significantly improved. Full article

Conditions of high-temperature volcano-related mineral formation are a source of the new and rare minerals and their associations; they are rather fragmentarily described for volcanic systems as a whole, except for several objects characterized in this regard. The study aim is to present the first results of the mineralogical study of atypical suprasubduction zone neoformation encountered from the Taketomi flank eruption (1933–1934) of the Alaid volcano (Kuril Islands), which has been studied through electron microprobe analyses and powder and single-crystal X-ray diffraction. The following mineral paragenesis is described: diopside, andradite, anorthite, wollastonite, esseneite, wadalite, rhönite-like mineral, fluorite, calcite, apatite, and atacamite. The parageneses of calcium silicates found in volcanic systems are usually interpreted as reworked crustal xenoliths and commonly associated with volcanoes that have a carbonate basement. However, carbonates have not been previously described at the base of the Alaid volcano. Even though the skarn nature of such a mineral paragenesis is possible, we suggest the important role of high-temperature volcanic gases along with the pyrometamorphic effect in the mineral-forming process at depth or in near-surface conditions (fumarole-like type in the form of a system of cracks and burrows). The described mineral paragenesis has not been previously documented, at least for the North Kuril Islands. A detailed mineralogical study of such formations is one of the important steps in understanding the functioning of magmatic systems, the circulation and transformation of natural matter, and mineral-forming processes. Full article