Quartz Phase Research Articles

Dry Magnetic Separation and the Leaching Behaviour of Aluminium, Iron, Titanium, and Selected Rare Earth Elements (REEs) from Coal Fly Ash

Coal fly ash (CFA) is a commercially viable source of alumina comparable to traditional bauxite deposits. Due to its high silica content and alumina in the refractory mullite phase, the most suitable processing technique is the sinter-H2SO4 leach process. However, this process is energy-intensive, has low selectivity for Al, and generates a secondary solid waste residue. To develop a sustainable process that is economically attractive, Al can be extracted with REEs, Ti, and Fe as saleable products, while secondary solid waste is regenerated for further applications to achieve high-value and high-volume utilisation of CFA. This study focused on the potential extraction of selected REEs (Ce, La, Nd, Y, and Sc), Al, Ti, and Fe, using dry magnetic separation and the sinter-H2SO4 leach process. XRD analysis showed that CFA is predominantly amorphous with crystalline mullite, quartz, and magnetite/hematite. Further analysis using SEM-EDS and TIMA showed Al-Si-rich grains as the predominant phase, with discrete REE-bearing grains (phosphates and silicates) and Fe-oxide (magnetite/hematite) grains. Traces of REEs, Ti, Ca, Si, and Fe were also found in the Al-Si-rich grains. Discrete Fe-oxide was recovered using dry magnetic separation, and up to 65.9% Fe was recovered at 1.05 T as the magnetic fraction (MF). The non-magnetic fraction (non-MF) containing quartz, mullite, and amorphous phase was further processed for preliminary leaching studies. The leaching behaviour of Al, Ti, Fe, and the selected REEs was investigated using the direct H2SO4 and sinter-H2SO4 leaching processes. The maximum extraction efficiency was observed using the sinter-H2SO4 leach process at 6 M H2SO4, a 1:5 solid-to-liquid ratio, 70 °C, and a residence time of 10 h, yielding 77.9% Al, 62.1% Fe, 52.3% Ti, and 56.7% Sc extractions. The extraction efficiencies for Ce, La, Nd, and Y were relatively lower at 23.2%, 27.6%, 11.3%, and 11.2%, respectively. Overall, the results demonstrate that the extraction of REEs using the sinter-H2SO4 leach process is strongly influenced by the complex CFA phase composition and the possible formation of insoluble calcium sulphates. Appreciable extraction of Al, Fe, Ti, and Sc was also observed, suggesting a potential two-step leaching process for the extraction of REEs as a feasible option for the industrial recovery of multiple saleable products.

Evolution of the internal structure and physical properties of Tongxin sandstone under high temperature

The stability of the surrounding rock under high temperature is pivotal to the efficient and safe production of high-temperature fluidized mining engineering. To investigate the stability of rocks under high temperature, this paper takes the roof sandstone of Tongxin coal mine, examining changes in its physical parameters such as mass, dimensions, wave velocity, porosity, and permeability after treatment at various temperatures (20–700°C). The results showed that parameters like mass and wave velocity decreased with increasing temperature, while dimensions, porosity, fracture density, and permeability increased. The patterns of change in these physical properties with temperature exhibit a high degree of consistency. Additionally, composition analysis and thermal analysis were conducted to understand the physical and chemical changes occurred in sandstone. Scanning electron microscopy was used to observe microstructural changes in the sandstone. After analysis, the evolution of the internal structure of Tongxin sandstone with heat treatment is categorized into three stages. (1) stable change Stage (20–450°C, 650–700°C): Dominated by dehydration and thermal stress, where pore and fracture structures develop slowly; (2) rapid change stage (450–550°C, 600–650°C): Dominated by the kaolinite dehydroxylation, leading to increased porosity but decreased average pore size; (3) intense change stage (550–600°C): Dominated by the quartz phase transitions, where the thermal stress generated by quartz phase transitions causes dramatic alterations in the internal structure of the sandstone. Furthermore, a correlation model between wave velocity and permeability of sandstone at high temperatures was established based on the interrelationship of these physical properties, providing a new method for real-time monitoring of permeability under high-temperature conditions.

Extraction of silica from Bangka quartz sand using the alkaline digestion method

Abstract Bangka quartz sand is a strategic mineral that contains relatively high levels of silicon compared to other sources of silicon minerals. The silicon content in a mineral greatly determines the feasibility of processing its derivative products, one of which is very well known, namely silica. Silica is a functional material that is widely applied in various fields including energy, environment, food and medicine. In this research, the silica extraction process has been carried out from Bangka quartz sand using the alkaline digestion method. The main extraction process stages include preparation, digestion using NaOH, water leaching, and calcination. The effect of varying calcination temperatures: 600, 800, and 1000°C on the silica phase and content of Si element was studied comprehensively. Based on the research results, it shows that at a temperature of 600°C, amorphous silica is formed, while at temperatures of 800 and 1000°C, crystalline silica with a quartz phase is formed with the element content of Si at 800°C reaching 98.87%.

Investigation of ion irradiation effects on mineral analogues of concrete aggregates

Irradiation can cause prominent damage to reactor concrete aggregates leading to amorphization, strength and modulus decrease, radiation induced volume expansion (RIVE) and micro-cracking, which limits their long-term performance. To develop an improved understanding of irradiation effects in concrete, three mineral analogues of concrete aggregates (limestone, marble and quartzite) were irradiated by 5.5 MeV He ions and 13 MeV Ni ions to surface doses of 0.011 displacements per atom (dpa) and 0.23 dpa, respectively, at room temperature. The two different ion species allow irradiation spectrum effects (ionizing and displacive) to be examined. Irradiation induced cracks were observed in He irradiated limestone and marble, and Ni irradiated quartzite. Full amorphization was observed in Ni irradiated quartzite with 14.3 % RIVE, and ∼25 % hardness and modulus decrease, while almost no change was observed in He irradiated quartzite except 4.35 % RIVE, revealing a possible ionization enhanced diffusion effect for high energy light ions. Furthermore, partial amorphization was observed in Ni irradiated marble and limestone matrix with a 12 % hardness decrease in marble while no amorphization was observed for He irradiation with a 20 % hardness increase in limestone matrix. The role of knock-on damage and irradiation spectrum on amorphization, volumetric expansion and mechanical property changes are discussed. Moreover, the onset and critical doses for amorphization and RIVE in quartz are obtained for ion irradiations at room temperature. The dose dependence of RIVE exhibits a delay compared to the amorphization behavior. The superior irradiation resistance of calcite phase compared to quartz phase implies there could be advantages to using calcareous aggregates and lowering the usage of siliceous aggregates for concrete in nuclear power plants for extended operation beyond 60 years. However, other effects such as corrosion, aging and reactions during severe accidents should also be considered, and further investigations are needed.

SYNTHESIS AND CHARACTERIZATION OF ZEOLITES FROM COAL FLY ASH WASTE

South Sumatra had coal production through PT Bukit Asam Tbk, which had coal production since 1950. Tanjung Enim Steam Power Plant (PLTU) is the largest coal ash producer because coal is the primary fuel. Coal combustion by-products include coal fly ash (CFA) and coal bottom ash (CBA). The current utilization of the CFA Tanjung Enim Steam Power Plant is for a cement mixture of PT Semen Baturaja and planting media. This work attempts to optimize zeolite synthesis from CFA by examining the effects of hydrothermal duration on reducing coal waste. This research studies the effect of hydrothermal time with time variations of 5, 12, and 24 on the morphology and phase of zeolite obtained. CFA from the Tanjung Enim Steam Power Plant contains SiO₂ and Al₂O₃, which account for 47.7% and 28.7% of the total composition, respectively. The SEM characterization result shows that the synthesized zeolite forms aggregates with a particle size of about 8-15 μm. Based on XRD characterization of CFA hydrothermal time of 5 hours, the dominant phase is the gibbsite phase, but there is a sodalite phase. The 12-hour hydrothermal time showed the formation of quartz, gibbsite, and sodalite phases. The 24-hour hydrothermal time shows that the dominant phase is sodalite, but there are gibbsite and quartz phases. The peak of the quartz phase decreases the longer the hydrothermal time. In this study, the duration of the hydrothermal process affects the formation of the zeolite phase.

Correlation analysis of composition, microstructure, and final properties of porcelain tiles: an experimental study

Abstract This study deals with the intricate relationship between composition, microstructure and the final properties of porcelain tiles namely bulk density, water absorption, thermal expansion coefficient, strength, and Young's modulus. In order to achieve this, a comprehensive set of 16 experimental trials were carried out, involving the preparation of eight distinct formulations characterized by varying Seger values and ratios which were subsequently subjected to sintering at two distinct firing temperatures. The analysis was conducted through a comprehensive correlation matrix, revealing significant relationships between composition, phase content and the final properties. The glassy phase emerges as a key contributor, positively influencing bulk density, reducing water absorption and linear shrinkage, and enhancing Young's modulus. The coefficient of thermal expansion correlates positively with residual quartz and inversely with mullite content, highlighting their impact on this property. Strength is positively correlated with mullite content, while quartz, albite, and anorthite phases exhibit negative correlations due to their intricate influence on the overall microstructure. These findings provide essential insights into the complex interplay between composition, microstructure and properties, contributing to the advancement of materials engineering for tailored porcelain tiles.

Preparation and characterization of quartz ceramic proppant replacing natural quartz sand by solid waste silica fume

AbstractThe improper disposal of industrial wastes will cause environmental pollution and economic losses due to the loss of active ingredients. Solid waste silica fume and pyrolusite powder were used to synthesize quartz ceramic proppant by pelleting and sintering to replace natural quartz sand for unconventional oil and gas exploitation. The effects of pyrolusite powder content and sintering temperature on the apparent density, breakage ratio, and acid solubility of the proppant were thoroughly studied. The phase composition and microstructure of the proppant were characterized by X‐ray diffraction and scanning electron microscopy, respectively. The results revealed that the main crystal phase of the proppant prepared without pyrolusite was cristobalite, while that with pyrolusite was cristobalite and quartz, and the content of quartz phase increased gradually with increasing the pyrolusite content. The addition of pyrolusite remarkably increased the density and improved the performance of the proppant due to the resulting glass phase at high temperatures and the presence of andradite. As adding 20% pyrolusite, the apparent density of the proppant sintered at 900°C was 2.26 g/cm3, while the breakage ratio under 28 MPa closed pressure and acid solubility reached the minimum, 9.89% and 5.3%, respectively, meeting the industrial standard requirements.

Prospect for recycling critical elements in combustion residues of coal, lignite, and biomass feedstocks

The combustion residues derived from coal, lignite, biomass, and spent wash could be recycled to extract critical elements required for energy transition. To recycle these elements from the combustion residues, it is necessary to understand their chemical mode of occurrence in the ash. This study presents the content of critical elements and their chemical mode of occurrence in coal, lignite, biomass, and incinerator ash. Lignite ash, rich in Ca and Si, offers Sc (31 mg/kg) and Nd (212 mg/kg), while coal ash, dominated by Si and Al, contains Ga (44.8 mg/kg). Biomass and spent wash ash, characterized by K, Ca, and S, present substantial potential for potash and Sc. Lignite ash primarily contains rare earth elements (REEs) in metal oxide-bound fractions, whereas in coal ash, the REEs are associated with the hard mullite or quartz phase. Biomass and incinerator ashes have significant water-soluble potash, and the Sc is associated with metal oxides. Green acids can extract critical elements from lignite, biomass, and incinerator ashes, but extracting from coal ash requires harsh conditions. Future research should concentrate on green extraction processes considering the chemical patterns of occurrence of critical elements.

Thermomechanical response and crack evolution of sandstone at elevated temperatures

Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O2 due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.

Experimental vs. natural fulgurite: A comparison and implications for the formation process

Abstract Fulgurites are glassy structures formed when lightning strikes the ground, causing ground material (e.g., rocks, sediments, or soil) to melt and fuse. While fulgurites are relatively rare, they provide valuable insights into paleoecology and may play a key role in prebiotic chemistry. Despite their significance in nature, understanding the conditions underlying the formation of fulgurites poses severe challenges, as the physical parameters and timing of the fulgurite-generating lightning event still need to be discovered. Here, we use a unique opportunity from the recent in situ discovery of a natural fulgurite still embedded in its protolith. (The natural fulgurite-generating event is visible in the World Wide Lightning Network data.) Using a high-voltage setup, we further compare this natural fulgurite with the experimentally generated fulgurite obtained from the original protolith. The natural and experimental fulgurites exhibit evidence of similar melting sequences and post-melting recrystallization structures. Using Raman spectroscopy applied to the quartz phase transition, we estimate the thermal gradient present in the fulgurite during formation to be a minimum of 1600 °C at the inner wall of the fulgurite and ca. 600 °C at the outer wall of the fulgurite. Those findings suggest that the current responsible for the cloud-to-ground lightning discharges that generated the natural fulgurite lay in the range of 11 960 to 14 473 kA. The state of the experimental fulgurites matched that of the natural fulgurite, validating the experimental option for studying fulgurite generation.

XRD and SEM analysis of fly ash obtained from TPPs of Raipur district of Chhattisgarh

This paper deals with the study of fly ash samples with respect to its physical, chemical and structural properties collected from distinct sites of Raipur district of Chhattisgarh state in India. XRD diffractogram for the original fly ash confirms the fly ash is mainly an amorphous material with the presents of crystalline phase of quartz. Fly ashes samples consist of mostly glassy, hollow, spherical particles, which are cenospheres (thin-walled hollow spheres); the micro structure appearance of the original fly ash is well agreed. Equal amounts of Al2O3, Fe2O3, MnO, TiO2 were found in both the samples which are good fit for construction application. SEM images revealed the amorphous nature of the fly ash.

Study on the radon exhalation rate of phyllite under thermal effects

As a result of human underground mining activities, phyllite has been extensively reused to make raw ceramic materials and concrete aggregates. Building materials are a significant source of indoor radon, and radon gas emitted from phyllite poses radiation risks to humans. High temperatures can alter the structural properties of rocks, impacting radon exhalation. Thus, this study examined phyllite's radon exhalation rate after heat treatment ranging from 25 °C to 1000 °C. The effects of changes in pore structure and mineral composition on phyllite's radon exhalation were analyzed in detail using nuclear magnetic resonance (NMR), polarizing optical microscopy (POM), three-dimensional microscopy (3DM), and scanning electron microscopy (SEM). Results indicate that the radon exhalation rate initially increases and then decreases with rising temperature. This rate correlates positively with both total porosity and micropore porosity. Processes such as free water evaporation, pyrite oxidation, quartz phase transformation, and chlorite dehydroxylation within phyllite contribute to pore development and the movement of free radon within pore spaces. The highest total porosity and radon exhalation rate occur at 700 °C, measuring 8.6 % and 6.14 Bq/m2·h, respectively—4.30 times and 1.18 times higher than at 25 °C. Additionally, mineral decomposition and melting reduce pore connectivity and effective porosity, hindering radon migration. These findings offer guidance for assessing radon radiation risks and indoor radon potential in phyllite-based building materials.

Valorization of oil‐based drilling cuttings as a substitute for bauxite in fracturing proppants application

AbstractThis study aimed to increase the scale of oil‐based drilling cuttings (OBDCs) resource utilization in the ceramic industry. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) The main ceramic‐technological characteristics of the OBDC were determined, which belonged to high‐silica solid waste with a high Si–Al ratio and a low acid–base ratio of oxides. (2) The low meltability temperature of the OBDC could largely influence the determination of the sintering temperature range for ceramic products. (3) The chemical components OBDC provided were involved in the formation of molten phases, which could affect dimensional accuracy and mechanical properties. Meanwhile, the dolomite promoted the formation of closed pores and enhanced lightweight performance. (4) Before 800°C, dolomite decomposed and reacted with SiO2 to form silicate, and then a new feldspar crystal appeared. After 1000°C, orthoclase completely melted into the molten phase, only two phases of quartz and diopside existed in the material until 1150°C. When the temperature was higher than 1350°C, the glass transition of the phase was basically intensified. (5) In the analyzed scenarios, the results indicated OBDC can only be doped in low contents and degrades the ceramic material properties.

The Role of α−β Quartz Transition in Fluid Storage in Crust From the Evidence of Electrical Conductivity

AbstractAqueous fluids are extensively present in the middle to lower crust, as revealed by seismic and magnetotelluric soundings. The α−β quartz phase transition significantly affects many physical properties and leads to substantial microcracks that can provide pathways for the migration of crustal fluids. A systematic investigation of macroscopic physical properties and microstructure of quartz is crucial to elucidate their correlation. In the present study, the effects of water content, trace elements, orientations, and phase transition on the electrical conductivity of quartz were thoroughly evaluated at 400−900°C and 1 GPa. Individual annealing experiments were simultaneously conducted on quartz single crystals at different peak temperatures and 1 GPa to investigate the evolution and spatial distribution of microcracks using X‐ray microtomography (CT) and backscattered electron imaging. We found that trace element content and orientations, rather than H2O, are the dominant factors controlling the conductivity of quartz. The distinct changes in conductivity of single crystals at around α−β phase transition temperature are attributed to the transformation of microcracks from isolated to interconnected networks, as confirmed by two‐dimensional (2‐D) and three‐dimensional (3‐D) microstructure images. Based on the variation in electrical conductivity and microstructure across the transition, it thus is proposed that the intragranular microcracks caused by quartz phase transition can serve as fluid or melt pathways within highly conductive zones present in the middle to lower crust, while α‐quartz acts as an impermeable cap.

Effects of temperature on pure mode-I and mode-Ⅱ fracture behaviors and acoustic emission characteristics of granite using a grain-based model

To investigate the effects of thermally induced microcracks on the pure mode-I and mode-Ⅱ fracture behaviors of the granite, a Grain-based model (GBM) was used to build cracked straight-through Brazilian disc (CSTBD) granite specimens. Splitting tests were conducted on the CSTBD specimens treated at various temperatures under pure mode-I and mode-Ⅱ loadings, and the moment tensor algorithm was utilized to record the acoustic emission (AE) events generated by fracture during loading. The results indicate that thermally induced microcracks predominantly consist of intergranular and intragranular tensile cracks, with quartz phase transition significantly increasing the number of intragranular tensile cracks. With the increase in heat-treatment temperature, thermally induced microcracks gradually guide the initiation direction of load-induced cracks, making the crack propagation path more tortuous. The AE characteristics reveal that the fracture behavior of the CSTBD specimen heat-treated at 600 ℃ transitions from brittle to ductile. Furthermore, thermally induced microcracks can constrain the propagation distance of load-induced cracks, increasing the small-scale AE events and the b-value, thereby reducing the AE magnitude during failure.

Evaluating pumice as a sustainable raw material in porcelain tile production: impact on technical properties

Pumice, a porous rock resulting from the rapid cooling of tuff fragments during volcanic activity, exhibits a spongy texture and light color due to its low density. Found predominantly in Central Anatolia and Eastern Anatolia, it has drawn interest for industrial applications. This study delved into utilizing micronized pumice within the porcelain tile manufacturing process. Comparative analyses were conducted between formulations incorporating micronized pumice and the standard ceramic tile recipe. In place of feldspar, micronized pumice was introduced at concentrations of 3%, 5%, and 7%, while clay was substituted with micronized pumice at concentrations of 3%, 5%, 7%, and 10% by weight. The prepared bodies were fired in an industrial kiln at 1210 °C for 54 min, and various physical and mechanical properties were evaluated. These included viscosity, sieve residue, green strength pre-firing, firing shrinkage, water absorption, firing strength, and firing color after-firing. The results indicated that the samples incorporating micronized pumice closely matched the physical and mechanical properties of the standard porcelain tile. Phase and microstructural analyses revealed the presence of mullite and quartz phases. Notably, micronized pumice demonstrated promise as a substitute for clay or feldspar, with the optimal usage rate determined to be 7% in the porcelain tile recipe. This indicates that pumice has the potential to be an alternative raw material in the production of porcelain tiles.

Impact of Different Mineral Reinforcements on HDPE Composites: Effects of Melt Flow Index and Particle Size on Physical and Mechanical Properties.

The use of mineral reinforcements in polymer matrix composites has emerged as an alternative for sustainable production, reducing waste and enhancing the physical and mechanical properties of these materials. This study investigated the impact of the melt flow index (MFI) of HDPE and the particle size of two mineral reinforcements, Bahia Beige (BB) and Rio Grande do Norte Limestone (CRN), on the composites. All composites were processed via extrusion, followed by injection, with the addition of 30 wt.% reinforcement. Chemical analyses revealed similar compositions with high CaO content for both minerals, while X-ray diffraction (XRD) identified predominantly calcite, dolomite, and quartz phases. Variations in the MFI, reinforcement type, and particle size showed a minimal influence on composite properties, supported by robust statistical analyses that found no significant differences between groups. Morphological analysis indicated that composites with lower MFI exhibited less porous structures, whereas larger particles of BB and CRN formed clusters, affecting impact resistance, which was attributed to poor interfacial adhesion.

Enhanced mechanical properties and tribological performance of anodic oxide coating by using thermal power plant waste material

Numerous researchers have dedicated their efforts to exploring the utilization of industrial waste, specifically fly ash (FA), as a reinforcement for developing economical composites and minimizing ecological pollution problems. FA consists of multiple phases, including quartz (SiO2) and mullite (3Al2O3·2SiO2), which can significantly enhance the mechanical properties of materials. In tribological applications, incorporating FA into surface coatings can offer a cost-effective alternative to enhance surface properties. Meanwhile, the usage of FA and its difference from other commercial ceramics (e.g., SiO2) is still unknown. Thus, the present study aims to clarify the role of FA and factors that contribute to improving mechanical properties and tribological performance with commercial SiO2 as a comparison using electrochemical anodization. The growth mechanism was investigated by varying the anodizing times while maintaining a constant (100 g/L FA) in the electrolyte for the first phase. Meanwhile, the mechanical and tribological properties of different reinforcement content (0, 10, 50, and 100 g/L) were determined for the second phase. Then, evaluations were conducted on the surface morphology, chemical composition, surface hardness, and tribological properties. The results revealed that growth of oxide coating was initiated within the first 5–10 min by forming the barrier layer. Pores began to appear visibly after 30 min of anodizing time, while the complete formation of porous anodic oxide coating was achieved at 60-min with pores dimension (width: 30.75 ± 14.45 μm and depth: 13.4 ± 6.43 μm). Interestingly, 100 g/L of FA-reinforced anodic oxide coating demonstrated lower surface roughness (4.08 ± 0.41 μm), higher surface hardness (444.4 ± 8.63 HV), lowest coefficient of friction (COF) (0.46), and low wear rate (reduction almost 31.8 %) compared to 100 g/L of commercial SiO2 reinforced anodic oxide coating. The electrophoretic deposition effect, combined with the quartz (SiO2) and mullite (3Al2O3·2SiO2) phase structure, enhances mechanical properties and tribological performance.

An effective utilization of raw fly ash obtained from thermal power plants using thermal spray technique to improve corrosion resistance for marine applications

Marine-grade steel structures in offshore environments often corrode due to the aggressive environmental conditions. Many ceramic materials can cater to this demand. However, as per economic and ecological concerns, fly ash (FA), an industrial waste, can be another strong contender to control corrosion. Therefore, the present study developed composite coatings of fly ash with additives ((50-48) wt.% Al2O3; 0–2 wt% carbon nanotube (CNT)) onto marine-grade steel using a plasma spray technique to improve its corrosion resistance. The microstructure of 1 wt% CNT-reinforced alumina-FA (1CAF) coating was denser than 2 wt% CNT-reinforced alumina-FA (2CAF) coating due to the uniform dispersion of CNT and, thereby, uniform remelting of coating at localized sites. Consequently, the microhardness and adhesion strength of the 1CAF coating were improved by ∼14.66 % and ∼15.96 %, respectively. Further, Rietveld's analysis of coatings showed that quartz, being the primary phase for corrosion control, was 19.23 ± 0.87 %, 16.33 ± 1.04 % and 14.60 ± 1.87 % for alumina-FA (AF), 1CAF, and 2CAF, respectively. The electrochemical impedance spectroscopy and the salt spray corrosion tests showed that 1CAF coating corrosion resistance was improved by ∼11.2 % compared to AF coating, even with a lower quartz phase (∼15.08 %) due to the densification of coating. This densification was due to the remelting by CNT to seal pores in the coating. Furthermore, for the same reason, an increase in coating resistance and charge transfer resistance of 1CAF coating by ∼80.9 % and ∼19.93 %, respectively, were seen in the equivalent circuit analysis, showing great promise in controlling interfacial corrosion. Further post-treatments like plasma or laser treatments can seal the coatings further to improve corrosion resistance. Therefore, such coatings are expected to withstand harsh, corrosive environments and are well-suited for marine applications.

Growth behavior of cristobalite SiO2 coating on 4H–SiC surface via high-temperature oxidation

When SiO2 films undergo oxidation on 4H–SiC, a distinctive crystalline phase, cristobalite, emerges at elevated temperatures. We deeply explored the growth mechanism of the crystallite, focusing on its dependence on the silicon sublimation process (SSO). Activation energy calculations confirmed that the oxidation after SSO above 1350 °C exhibits a lower activation energy. The reduced activation energy suggests the elimination of the solid-phase diffusion process during oxidation. We devised a controllable growth process for the quartz phase to achieve a seamless transition from 0 to 100 % in the area proportion of cristobalite in SiO2. This strategic approach facilitates the precise preparation of oxide layers and holds potential applications in semiconductor device manufacturing.