Search Results (529)

During the process of oil and gas drilling, due to the existence of pores or micro-cracks, drilling fluid is prone to invade the formation. Under the action of hydration expansion of clay in the formation and liquid pressure, wellbore instability occurs. In order to reduce the wellbore instability caused by drilling fluid intrusion into the formation, this study proposed a method of forming a dynamic hydrogen bond cross-linked network weak gel structure with modified nano-silica and P(AM-AAC). The plugging performance of the drilling fluid and the performance of inhibiting the hydration of shale were evaluated through various experimental methods. The results show that the gel composite system (GCS) effectively optimizes the plugging performance of drilling fluid. The 1% GCS can reduce the linear expansion rate of cuttings to 14.8% and increase the recovery rate of cuttings to 96.7%, and its hydration inhibition effect is better than that of KCl and polyamines. The dynamic cross-linked network structure can significantly increase the viscosity of drilling fluid. Meanwhile, by taking advantage of the liquid-phase viscosity effect and the physical blocking effect, the loss of drilling fluid can be significantly reduced. Mechanism studies conducted using zeta potential measurement, SEM analysis, contact angle measurement and capillary force assessment have shown that modified nano-silica stabilizes the wellbore by physically blocking the nano-pores of shale and changing the wettability of the shale surface from hydrophilic to hydrophobic when the contact angle exceeds 60°, thereby reducing capillary force and surface free energy. Meanwhile, the dynamic cross-linked network can reduce the seepage of free water into the formation, thereby significantly lowering the fluid loss of the drilling fluid. This research provides new insights into improving the stability of the wellbore in drilling fluids. Full article

This study aimed to develop experimental filler-reinforced resin composites for vat-photopolymerization 3D printing and to evaluate the effects of filler addition on their mechanical, physicochemical, and bonding properties for dental restorative applications. Silanized nano- and/or micro-fillers were incorporated into acrylic resin monomers to formulate photocurable resins suitable for vat-photopolymerization. The rheological behavior of these liquid-state resins was assessed through viscosity measurements. Printed resin composites were fabricated and characterized for mechanical properties—including flexural strength, flexural modulus, and Vickers hardness—both before and after 8 weeks of water immersion. Physicochemical properties, such as water sorption, water solubility, and degree of conversion, were also evaluated. Additionally, shear bond strength to a resin-based luting agent was measured before and after artificial aging via thermocycling. A commercial dental CAD-CAM resin composite served as a reference material. Filler incorporation significantly improved the mechanical properties of the printed composites. The highest performance was observed in the composite containing 60 wt% micro-fillers, with a flexural strength of 168 ± 10 MPa, flexural modulus of 6.3 ± 0.4 GPa, and Vickers hardness of 63 ± 1 VHN, while the commercial CAD-CAM composite showed values of 152 ± 8 MPa, 7.9 ± 0.3 GPa, and 66 ± 2 VHN, respectively. Filler addition did not adversely affect the degree of conversion, although the relatively low conversion led to the elution of unpolymerized monomers and increased water solubility. The shear bond strength of the optimal printed composite remained stable after aging without silanization, demonstrating superior bonding performance compared with the CAD-CAM composite. These findings suggest that the developed 3D-printed resin composite is a promising candidate for dental restorative materials. Full article

The cement sheath is critical for ensuring the long-term safety and operational efficiency of oil and gas wells. However, complex geological conditions and operational stresses during production can induce cement sheath deterioration and cracking, leading to reduced zonal isolation, diminished hydrocarbon recovery, and elevated operational expenditures. This study investigates the development of a novel microbial self-healing well cement slurry system, employing fly ash as microbial carriers and sustained-release microcapsules encapsulating calcium sources and nutrients. Systematic evaluations were conducted, encompassing microbial viability, cement slurry rheology, fluid loss control, anti-channeling capability, and the mechanical strength, permeability, and microstructural characteristics of set cement stones. Results demonstrated that fly ash outperformed blast furnace slag and nano-silica as a carrier, exhibiting superior microbial loading capacity and viability. Optimal performance was observed with additions of 3% microorganisms and 3% microcapsules to the cement slurry. Microscopic analysis further revealed effective calcium carbonate precipitation within and around micro-pores, indicating a self-healing mechanism. These findings highlight the significant potential of the proposed system to enhance cement sheath integrity through localized self-healing, offering valuable insights for the development of advanced, durable well-cementing materials tailored for challenging downhole environments. Full article

Enhanced Geothermal Systems (EGS) require thermochemically stable proppant materials capable of sustaining fracture conductivity under harsh subsurface conditions. This study systematically investigates the response of commercial proppants to coupled thermo-hydro-chemical (THC) effects, focusing on chemical stability and microstructural evolution. Four proppant types were evaluated: an ultra-low-density ceramic (ULD), a resin-coated sand (RCS), and two quartz-based silica sands. Experiments were conducted under simulated EGS conditions at 130 °C with daily thermal cycling over a 25-day period, using diluted site-specific Utah FORGE geothermal fluids. Static batch reactions were followed by comprehensive multi-modal characterization, including scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and micro-computed tomography (micro-CT). Proppants were tested in both granular and powdered forms to evaluate surface area effects and potential long-term reactivity. Results indicate that ULD proppants experienced notable resin degradation and secondary mineral precipitation within internal pore networks, evidenced by a 30.4% reduction in intragranular porosity (from CT analysis) and diminished amorphous peaks in the XRD spectra. RCS proppants exhibited a significant loss of surface carbon content from 72.98% to 53.05%, consistent with resin breakdown observed via SEM imaging. While the quartz-based sand proppants remained morphologically intact at the macro-scale, SEM-EDS revealed localized surface alteration and mineral precipitation. The brown sand proppant, in particular, showed the most extensive surface precipitation, with a 15.2% increase in newly detected mineral phases. These findings advance understanding of proppant–fluid interactions under low-temperature EGS conditions and underscore the importance of selecting proppants based on thermo-chemical compatibility. The results also highlight the need for continued development of chemically resilient proppant formulations tailored for long-term geothermal applications. Full article

The superhydrophobic coatings for outdoor use need to be exposed to sunlight for a long time; therefore, their UV-aging resistances are crucial in practical applications. In this study, the primary product of titanium dioxide (P-TiO₂) was used as the raw material. Nano-silica (SiO₂) was coated onto the surface of P-TiO₂ by the acid precipitation method to prepare P-TiO₂-SiO₂ composite particles. Then, they were modified and sprayed simply to obtain a superhydrophobic P-TiO₂-SiO₂/HDTMS coating. The results indicated that amorphous nano-SiO₂ was coated on the P-TiO₂ surface, forming a micro–nano binary structure, which was the essential structure to form superhydrophobic coatings. Additionally, the UV-aging property of P-TiO₂ was significantly enhanced after being coated with SiO₂. After continuous UV irradiation for 30 days, the color difference (ΔE*) and yellowing index (Δb*) values of the coating prepared with P-TiO₂-SiO₂ increased from 0 to 0.75 and 0.23, respectively. In contrast, the ΔE* and Δb* of the coating prepared with P-TiO₂ increased from 0 to 1.68 and 0.74, respectively. It was clear that the yellowing degree of the P-TiO₂-SiO₂ coating was lower than that of P-TiO₂, and its UV-aging resistance was significantly improved. After modification with HDTMS, the P-TiO₂-SiO₂ coating formed a superhydrophobic P-TiO₂-SiO₂/HDTMS coating. The water contact angle (WCA) and water slide angle (WSA) on the surface of the coating were 154.9° and 1.3°, respectively. Furthermore, the coating demonstrated excellent UV-aging resistance. After continuous UV irradiation for 45 days, the WCA on the coating surface remained above 150°. Under the same conditions, the WCAs of the P-TiO₂/HDTMS coating decreased from more than 150° to 15.3°. This indicated that the retention of surface hydrophobicity of the P-TiO₂-SiO₂/HDTMS coating was longer than that of P-TiO₂/HDTMS, and the P-TiO₂-SiO₂/HDTMS coating’s UV-aging resistance was greater. The superhydrophobic P-TiO₂-SiO₂/HDTMS self-cleaning coating reported in this study exhibited outstanding UV-aging resistance, and it had the potential for long-term outdoor use. Full article

Recycled wood fiber (RWF) obtained through the multi-stage processing of waste wood serves as an eco-friendly green construction material, exhibiting lightweight, porous, and high toughness characteristics that demonstrate significant potential as a cementitious reinforcement, offering strategic advantages for environmental protection and resource recycling. In this study, high-performance sulfoaluminate cement (SAC)-RWF composites prepared by modifying RWFs with nano-silica (NS) and a silane coupling agent (KH560) were developed and their effects on mechanical properties, shrinkage behavior, hydration characteristics, and microstructure of SAC-RWF composites were systematically investigated. Optimal performance was achieved at water–cement ratio of 0.5 with 20% RWF content, where the KH560-modified samples showed superior improvement, with 8.5% and 14.3% increases in 28 d flexural and compressive strength, respectively, compared to the control groups, outperforming the NS-modified samples (3.6% and 8.6% enhancements). Both modifiers improved durability, reducing water absorption by 6.72% (NS) and 7.1% (KH560) while decreasing drying shrinkage by 4.3% and 27.2%, respectively. The modified SAC composites maintained favorable thermal properties, with NS reducing thermal conductivity by 6.8% through density optimization, whereas the KH560-treated specimens retained low conductivity despite slight density increases. Micro-structural tests revealed accelerated hydration without new hydration product formation, with both modifiers enhancing cementitious matrix hydration product generation by distinct mechanisms—with NS acting through physical pore-filling, while KH560 established Si-O-C chemical bonds at paste interfaces. Although both modifications improved mechanical properties and durability, the KH560-modified SAC composite group demonstrated superior overall performance than the NS-modified group, providing a technical pathway for developing sustainable, high-performance recycled wood fiber cement-based materials with balanced functional properties for low-carbon construction applications. Full article

The regulatory mechanism of vinyl acetate-ethylene (VAE) in the interfacial properties of silicate cement–silica fume repair mortar was investigated by examining the effects of varying VAE contents (0 wt.% to 10.0 wt.%) on mortar fluidity, mechanical strength, and interfacial bonding strength. The interface microstructure was also examined to reveal its evolution. Results indicate that VAE enhances mortar fluidity through micro-filling and interfacial activity. At 10% VAE content, fluidity reached 265 mm, a 14.97% increase. However, VAE introduction reduced compressive and flexural strength due to pore induction at low dosages and polymer network interference at high dosages. By improving interfacial stress transfer and refining calcium sulfoaluminate (AFt) and C-S-H crystals in the interfacial transition zone, VAE increased the tensile bonding strength of the repaired mortar to 2.1 MPa at 28 days, a 133.3% increase, according to microscopic analysis. Based on performance analysis, 5.0 wt.% VAE is optimal, increasing interfacial bonding strength by 133.3% while limiting compressive strength loss to 9.4%, thus achieving interfacial collaborative optimization of the repaired mortar. Full article

Developing resource-efficient technologies for producing ceramic materials with specific properties and performance characteristics is one of the most important tasks in modern materials science. As natural resources face depletion, the use of anthropogenic wastes, including fly ash from coal combustion, for the development of new compositions and the production of ceramics with an improved microstructure is of particular significance. The use of PM₁₀ fly ash microspheres in ceramic production will help to reduce particulate matter emissions. In this study, fine narrow fractions of PM₁₀ microspheres were successfully separated from coal fly ash using aerodynamic and magnetic separation. Glass–ceramic materials with a homogeneous microstructure, an open porosity of 0.4–37%, a compressive strength of 5–159 MPa, and acid resistance of up to 99.9% were obtained using narrow fractions. The materials obtained are promising for application as highly porous ceramics, effective microfiltration membranes, and fine-structured technical ceramics, which can be used in installations operating in aggressive media and/or at high temperatures. The ceramic membranes were characterised by high liquid permeability values up to 1194 L·m⁻²·h⁻¹·bar⁻¹. Filtration tests showed that the retention coefficient for dispersed microsilica particles with d_av = 1.9 μm is 0.99. Full article

In this study, composites were developed using a biopolyamide matrix modified with microsilica at varying concentrations (0.5–2% by weight). These composites underwent water absorption analysis, and diffusion velocity was assessed. Based on the findings, hybrid composites incorporating aramid, basalt, and carbon fibers, further modified with 2% microsilica by weight, were fabricated. Investigations into fundamental mechanical properties, microstructure analysis, and accelerated fatigue tests were conducted. The results demonstrate that microsilica positively influences the enhancement of fatigue strength and mechanical properties of the composites. Specifically, microsilica is found to increase the approximate fatigue strength by 15% for the base material modified with 2 wt.% microsilica, by approximately 5% for composites with aramid fiber, and by between 10 and 15% for composites with basalt and carbon fiber. Furthermore, the incorporation of microsilica reduces water absorption in polymer composites, potentially enhancing their durability in humid environments and increasing resistance to degradation. Full article

This study evaluated the effects of print orientation and thermal aging on the flexural strength (FS) and flexural modulus (FM) of novel permanent three-dimensional (3D)-printed polymethyl methacrylate (PMMA) resins reinforced with nano-zirconia and nano-silica. Bar-shaped specimens (25 × 2 × 2 mm) were fabricated using a digital light processing (DLP) 3D printer (Asiga Max UV, Asiga Inc., Australia) in two orientations (0° and 90°). Specimens underwent three-point bending tests at 24 h and after artificial thermal aging (10,000 and 30,000 cycles) to simulate one and three years of intraoral conditions. Scanning electron microscopy (SEM) was used to analyze fracture patterns. Print orientation did not significantly affect FS or FM (p > 0.05). However, artificial aging significantly reduced FS and FM after 10,000 cycles (p < 0.001), with further deterioration after 30,000 cycles. The micro hybrid resin composite exhibited higher FS than the 3D-printed materials throughout aging. SEM analysis revealed distinct fracture patterns, with 3D-printed resins displaying radial fractures and the micro hybrid composite exhibiting horizontal fractures. These findings indicate that aging plays a more critical role in the long-term mechanical performance of 3D-printed restorative resins than print orientation. This study provides original data on the effects of print orientation and prolonged thermal aging on the mechanical behavior of permanent three-dimensional (3D)-printed dental resins. Furthermore, the comparative evaluation of aging protocols simulating one and three years of intraoral service represents a novel contribution to the existing literature. Further studies are required to optimize the mechanical durability of 3D-printed dental restorations. Full article

The “yellow-skinned” Nanhong agate represents a unique variety of Nanhong agate found in northeastern Yunnan, China, and it is highly valued for its distinctive yellow exterior and clear red–yellow interface. Owing to the limited research on this variety, the present study provides the first comprehensive analysis. Field surveys and various laboratory techniques—including polarizing microscopy, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectrometry, ultraviolet–visible (UV-VIS) absorption spectrometry, Raman spectroscopy, micro X-ray diffraction (µ-XRD) with Rietveld refinement, electron microprobe analysis (EPMA), and laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS)—were utilized to investigate its gemological, microtextural, spectroscopic, and geochemical characteristics. Field surveys identified the occurrence states of the “yellow-skinned” Nanhong agate. The laboratory results indicate that the agate primarily consists of α-quartz, with minor amounts of moganite, goethite, and hematite. The coloring mechanism observed in this study is consistent with the findings of previous studies: the external yellow coloration is due to goethite, while the internal red hue is attributed to hematite. Its unique pseudo-granular silica (Type III) structure provides a foundational basis for the later formation of the “yellow-skinned” agate variety, and geochemical data reveal the distribution patterns of elements. Based on geological surveys and experimental data, the formation of the “yellow-skinned” Nanhong agate in northeastern Yunnan can be divided into two stages: first, hydrothermal fluids filled the vesicles in the Permian Emeishan Basalt Formation (P₂β), leading to the formation of primary Nanhong agate. Subsequently, the Type III primary agate underwent weathering, erosion, transport, and deposition in the red–brown sandy mudstone of the Lower Triassic Feixianguan Formation (T₁f). The sedimentary environment in the second stage facilitated the conversion of outer hematite into goethite, resulting in the distinct “yellow-skinned” appearance with a clear red–yellow boundary. Based on the occurrence and stratigraphic relations, this study constrains the formation age of the “yellow-skinned” Nanhong agate to approximately 261.6 Ma. Full article

This study investigates the impact of widely used mineral fillers in self-compacting concrete compositions applied in vibration-free reinforced concrete production technology, as a means of enhancing rheological characteristics and cost-effectiveness. Three distinct types of mineral fillers, including the well-studied fillers microsilica and metakaolin, as well as the lesser-explored filler Kazakhstani natural opal-chalcedony opoka, are examined in this research. In addition to the evaluation of conventional rheological and performance properties of concretes containing these fillers, the internal processes within the cement–filler matrix are analyzed. This includes X-ray phase analysis and microstructural examination of cement hydration products in combination with a superplasticizer and each of the three minerals. The findings confirm the potential for optimizing the rheological parameters of the concrete mixture by substituting up to 15% of the cement with mineral fillers, achieving optimal viscosity and workability. It is established that compositions with the addition of microsilica and metakaolin have a more homogeneous structure, mainly represented by low-basicity calcium hydrosilicates of the CSH(B) type, along with an increase in compressive strength of up to 10%. The addition of these mineral fillers to C30/35 strength class self-compacting concrete resulted in improved frost resistance up to F300, a reduction in volumetric water absorption by up to 30%, and a decrease in shrinkage deformations by 32%. The developed SCC compositions have successfully passed production testing and are recommended for implementation in the operational processes of reinforced concrete product manufacturing plants. Full article

Fair-faced concrete has garnered substantial attention in recent years owing to its aesthetic appeal and eco-friendly attributes. However, as a construction material, its long-term performance is highly dependent on its service environment, particularly ultraviolet (UV) radiation. This research focuses on examining the influence of UV exposure and managing the admixtures employed in concrete and investigating the effects of UV radiation on the appearance quality, pore distribution, and micro-composition of fair-faced concrete. Results indicate that UV radiation enhances moisture evaporation, increases surface and bulk porosity, and accelerates carbonation and early hydration reactions, forming more calcite on the surface. These factors degrade the appearance quality of fair-faced concrete. To mitigate UV-aging damage, two common anti-UV admixtures, nano-silica (NS) and water-based fluorocarbon paint (FC), were evaluated. Results show that both admixtures effectively improve the UV-resistance of fair-faced concrete, particularly when combined. The FC+NS group reduced the surface glossiness loss rate from 28.63% to 12.95% after 28 days of UV exposure, with surface porosity and maximum pore diameter recorded at 0.157% and 3.66 mm, respectively, indicating excellent appearance quality. These findings underscore the potential of these admixtures, both individually and in combination, to enhance the UV resistance of fair-faced concrete, sustaining its durability under prolonged UV exposure. Full article

The dynamic evolution of alkalinity during hydration/carbonation of CO₂-conditioned cements results in the formation of polymorphic hydrated calcium silicates (C-S-H), whose differences in carbon sequestration capacity have not been systematically investigated. However, the micro-nano structures and carbon sequestration capacities of C-S-H are controlled by the dynamic effects of pore solution alkalinity and Ca/Si. Accordingly, different alkalinity and Ca/Si were set to simulate the cement hydration environment for the synthesis of C-S-H, and tests such as thermogravimetric and ²⁹Si nuclear magnetic resonance (NMR) were used to investigate the effects and mechanisms of initial alkalinity and Ca/Si on the morphology of the synthesized C-S-H, the CO₂ uptake. The results showed that the C-S-H synthesized at pH 7.2–12.0 and Ca/Si ratio of 1.0–2.3 was in flocculated and acicular forms, which were well crystallized and dominated by Q², while its CO₂ uptake was positively correlated with Ca/Si. On the contrary, the synthesized C-S-H was poorly crystallized under the conditions of pH increasing to 13.5 and Ca/Si ratios of 1.0–2.3. With the increase in Ca/Si, the synthesized C-S-H evolved from Q²-dominated foil to Q¹-dominated porous structure, and its CO₂ uptake was non-positively correlated with Ca/Si. This was mainly related to the average pore diameter of C-S-H and its silica-oxygen tetrahedral structure. This was mainly related to the average pore diameter of C-S-H and its silica-oxygen tetrahedral structure. Full article

The increasing demand for sustainable mining practices has driven the development of environmentally friendly reagents for mineral processing. This study investigates vitamin E sodium succinate (VE_SS), a novel bio-based collector, for its potential in hematite flotation. The performance of VE_SS was benchmarked against sodium oleate (NaOL), a widely used conventional collector in mineral processing. To assess the flotation performance of VE_SS, micro-flotation experiments were conducted using hematite, sourced from a mine, and silica, a common associated gangue mineral. These tests were complemented by comprehensive surface characterizations, including contact angle measurements, zeta potential analysis, Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), to investigate the adsorption mechanisms of VE_SS in comparison to NaOL. The results demonstrate that VE_SS effectively enhances hematite recovery, achieving levels comparable to NaOL. Furthermore, VE_SS exhibited reduced sensitivity to pH, addressing a key limitation of NaOL, which performs well in neutral to alkaline conditions but shows significantly lower recovery under acidic pH. These findings highlight the potential of VE_SS as a bio-based alternative to conventional collectors, contributing to the advancement of more sustainable mineral processing practices. Full article