Search

In this paper, the high-quality factor mullite microwave dielectric ceramic is employed to introduce in dielectric resonator antenna (DRA). The microwave dielectric properties of ɛr ∼ 5.8, Q × f ∼ 31 240 at 9.66 GHz, and loss tangent tanδ = 1/Q ∼ 2.7 × 10−4 can be obtained by the solid-state reaction method in mullite microwave dielectric ceramic sintered at 1700 °C. On this basis, the resonant modes of the proposed broadband high-gain rectangular DRA are analyzed by using a dielectric waveguide theoretical model and the antenna performance is evaluated by a commercial CST Microwave Studio 2021® software. It has been found that the proposed rectangular DRA can provide a broad bandwidth of 35.9%, a maximum gain of 10 dBi at 3.61 GHz, and a radiation efficiency of 90% in the range of 3.13–4.42 GHz. For demonstration, adequate consistency between the simulation results and the measurement results was achieved. The proposed DRA has great application potential and value in 5G communication scenarios requiring wideband and high-gain antenna. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The widespread use of alternative fuels in cement kilns requires improvement of the alkali attack resistance of mullite raw materials for the kiln linings. In this study, a novel mullite raw material with excellent alkali resistance was prepared by introducing kyanite tailings into low-grade raw bauxite. The effects of the microstructure, glass phase composition and phase distribution on the alkali attack resistance of such raw material were investigated. As the amount of kyanite tailings introduced increased, the glass-phase content of the specimens had little change, while the silica content in the glass phase increased obviously. Additionally, with increasing kyanite tailings content, the mullite phase gradually transformed from fine needle-like structures into columnar or tabular structures, allowing mullite to be better enclosed within the glass phase. The alkali attack test indicated that adding kyanite tailings significantly improved the alkali attack resistance of the specimens. This was explained as follows. (i) The silica-rich glass would be transformed into liquid phase during alkali attack, changing the corrosion process from the direct gas–solid reactions to dissolution–precipitation process. The formed liquid phase also densified the corrosion layer, effectively preventing further penetration of the alkali vapor. (ii) The mullite phase was wrapped in the silica-rich glass phase, preventing its direct reaction with alkali vapor and the resulting volume expansion. Besides, alkali attack resistance of the mullite phase was enhanced due to its particle coarsening. [ABSTRACT FROM AUTHOR]

The increase in size and efficiency of gas turbines leads to higher temperature in the combustion chamber, putting greater demands on the performance of the thermal insulation tiles. Corundum–mullite has been used because of its high‐temperature resistance, thermal shock resistance, and low thermal conductivity. However, how to inhibit heat transfer through composition regulation while ensuring the safe use of high‐temperature insulation tiles is the key to improving the heat conversion efficiency of gas turbines. In this study, thermal insulation tiles were prepared by casting molding. On the basis of determining the optimal corundum/mullite ratio (22:45 wt%) in the aggregate, the thermal conductivity of the sample was reduced by adding MgO (2 wt%). The results show that phonon intrinsic and defect scattering, caused by changes in phase composition, effectively reduce the thermal conductivity of the insulation tile sample to 2.05 W·m−1·K−1, which is 34.71 % lower than the maximum value before regulation. During 30 cycles of thermal shock (air‐cooling at 1000°C), the residual strength gradually decreased and tended to be stable, with a minimum of 8.6 MPa, indicating that the thermal insulation tile can provide better thermal insulation without affecting the safety of gas turbines, providing new ideas and methods for improving the thermal insulation performance of high‐temperature thermal insulation materials. [ABSTRACT FROM AUTHOR]

Oxide ceramic matrix composites (Ox‐CMCs) are composed of porous matrices reinforced by dense fibers to achieve high damage tolerance. It is generally assumed that their mechanical properties are fiber dominant. However, fiber strength can also be influenced by the surrounding matrix as it can affect fiber grain growth. Fiber–matrix interactions are studied in this work regarding fiber microstructural evolution and composite strength. Minicomposites containing Nextel 610 fibers and different matrix compositions (alumina, alumina–zirconia, and mullite–alumina) are evaluated after sintering and after additional heat treatment at 1200°C for 100 h. Fiber grain growth during sintering is faster in alumina matrix and slower in mullite–alumina matrix. Scanning transmission electron microscope–energy‐dispersive X‐ray spectroscopy (STEM–EDX) measurements show that Si diffuses between fiber and matrix grain boundaries. This outward or inward diffusion of SiO2 leads to the respectively different grain growth kinetics. Grain growth inhibition in alumina–zirconia matrix is only observed after the longer heat treatment, suggesting that ZrO2 diffusion is slower than SiO2. The resultant composite strength depends not only on fiber properties, but also on matrix densification. Minicomposite with alumina–zirconia matrix showed higher strength, while mullite–alumina composites showed higher thermal stability. In summary, the properties of Ox‐CMCs can be tailored by adjusting the matrix composition with the used fibers. [ABSTRACT FROM AUTHOR]

Colloidal silica-bonded castables offer several advantages compared to traditional calcium aluminate cement (CAC)-bonded castables, including lower torque values during mixing, superior drying properties, and a lower CaO content. Nevertheless, information on the combination of CAC and colloidal silica is limited, and the effect of CAC additions on the drying properties of colloidal silica-bonded castables remains unknown. In this study, these drying properties were measured by rapidly heating 400 kg samples to 500 °C and assessing the resulting damage to each sample. Additionally, the physical and chemical properties of small-scale samples were analyzed to evaluate the impact of CAC addition. The analyzed properties included cold crushing strength (CCS), density, permanent linear change (PLC) and weight loss. The microstructure of the samples was investigated by FESEM and EDS. The results indicate that adding 1.5 wt.% increased the cold crushing strength at 20 °C, while lower CAC amounts had no noticeable effect. A mullite phase was observed in the sample without CAC, and correspondingly, anorthite was found in those with CAC additions. The samples exhibited significant differences in the drying tests, with the degrees of damage increasing with the CAC addition. [ABSTRACT FROM AUTHOR]

Nanocrystalline mullite was synthetized by annealing a highly porous 3D structure consisting of nanofibrous aluminum oxyhydroxides treated with ethoxysilanes. The chemical, structural, and phase transformations in the aluminosilicate nanosystem were studied in the temperature range between 100 and 1600 °C. The features of the solid-phase synthesis of mullite at the interface of crystalline alumina with a liquid silica layer are discussed. It was established that chemical modification of the alumina surface with ethoxysilanes significantly limits the interphase mass transport and delays the phase transformation of the amorphous oxide into γ-Al2O3, which begins at temperatures above 1000 °C, while the basic structural nanofibrils are already crystallized at ~850 °C. The formation of mullite was completed at temperatures ≥ 1200 °C, where the fraction of γ-Al2O3 sharply decreased. [ABSTRACT FROM AUTHOR]

Porous mullite ceramics have good properties for high‐temperature applications, but porosity gives place to ceramics with low mechanical strength, which restricts the service life in their potential applications. Therefore, performing modifications at the microscale to increase the mechanical strength has become a current challenge to expand its application fields. This work describes the properties of a porous mullite–zirconia composite produced by ceramic processing, using industrial kaolin and stabilized zirconia as raw materials. The growth of mullite needle‐like grains to reinforce the ceramic was promoted by the addition of a molybdenum oxide precursor. The effect of zirconia on the composite was analyzed through an experimental multi‐technique approach and considering a pure mullite sample, identically processed, as a reference. The novel composite has a porosity of about 50%, and presents a homogeneous microstructure, with interlocked mullite needle‐like grains and dispersed rounded zirconia grains. This morphology restricts the mullite tendency to shrink during sintering, giving the material a higher stiffness. In particular, the presence of zirconia in the composite improves both the flexural strength and the apparent Young modulus of the material (about 20% and up to 600%, respectively). These results encourage further investigations to establish this composite for different technological applications. [ABSTRACT FROM AUTHOR]

This study evaluates Algerian kaolin (Djebel Debbagh (DD1) and Tamazart (KT2)) as potential substitutes for commercial kaolin (Lab) in the production of mullite‐based ceramics. Three compositions were prepared by incorporating the appropriate percentage of alumina to each calcined kaolin to achieve stoichiometric mullite precursors. The phase evolution of individual kaolin powders, as well as their mixtures with alumina, depends strongly on the calcination temperature and kaolin impurities. The differential scanning calorimetry combined with thermogravimetric analysis (TGA) showed lower secondary mullite formation temperature for the KT2‐based mixture. However, X‐ray diffraction revealed a complete mullitization in DD1 mixture. The K2O hindered cristobalite formation and reduced secondary mullite formation rate. Microstructure analysis showed lath‐shaped primary mullite and equi‐axed secondary mullite particles. After sintering at 1600°C, The KT2‐based sample (M3) exhibited higher density (3.013 g/cm3) and hardness (9.9 GPa), whereas the DD2‐based sample (M2) showed moderate densification (2.91 g/cm3) and higher flexural strength (159.42 MPa). Impurities (mainly Fe2O3, and K2O) promoted liquid phase sintering, resulting in greater densification in M3, whereas M2 showed more homogeneous microstructure, refined grains, and lower glassy phase content, contributing to enhanced strength. [ABSTRACT FROM AUTHOR]

The physical mechanism of self-organization of a multilayer nanolaminated coating based upon non-equilibrium (TiAlCrSiY)N/(TiAlCr)N nitride on a cutting tool during high-speed (600 m/min.) dry cutting of N13 steel is established. Using a set of modern surface analysis methods coating degradation and tribo-oxidation are studied within the running-in and steady stages of wear. It is shown that during cutting, amorphous-nanocrystalline films of oxides similar to Cr2O3, TiO2, Al2O3 (sapphire) and Al2O3 · 2 (SiO2) (mullite) are formed within a wear crater. Using computer calculations by a finite element method, heat transfer is considered in the cutting zone during formation of protective tribo-oxides. It is found that among all tribo-oxides, mullite has the best thermal barrier properties. Oxidation is the main adaptation mechanism of a cutting tool under extreme mechanical and thermal shock during high-speed cutting. The topography of chip contact surface is studied at various cutting stages, which makes it possible to establish a change in plastic deformation mechanisms of treated metal and friction cutting modes. Quantum chemical calculations of the electron structure of mullite show the highest degree of its electron polarization and explain the radical drop in friction coefficient during film formation upon a wear surface. In this case, mullite acts as a solid lubricant. [ABSTRACT FROM AUTHOR]

The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε', especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε', frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases. [ABSTRACT FROM AUTHOR]

Aluminum recycling is an important step to achieve high value-added utilization of fly ash to improve the leaching efficiency of Al. In this paper, Na2CO3 was used as the flux and HCl as the leaching solution to extract Al from CFA by using the roasting activation-acid leaching process to investigate the influencing factors of the leaching rate of Al to analyze the mineral composition of the roasting products explore the activation process of CFA roasting. The experimental results showed that compared with NaF, CaO, and NaOH, the highest Al leaching rate was achieved when Na2CO3 was used as a flux, at which time the leaching rate could reach up to 81.62%, and it was about 63% higher than that of extracting Al from the fly ash using direct roasting-acid leaching method. When the roasting time is 90 min, the roasting temperature is 850°C, the CFA/Na2CO3 is 1.5, the hydrochloric acid concentration is 4 mol/L, the acid leaching temperature is 90°C, the S/L is 1:4, and the maximum leaching rate of Al is 81.62%. According to the thermodynamic theory, Na2CO3 and mullite gradually reacted with each other above 800 K to form chalcopyrite, and Na2CO3 reacted with mullite and quartz in CFA to form chalcopyrite more easily. According to the reaction kinetic model, the acid leaching process of CFA is mainly controlled by diffusion, and a semi-empirical equation is proposed to describe the whole leaching process. [ABSTRACT FROM AUTHOR]

It was previously demonstrated that geopolymers can be synthesized using organic bases rather than alkali hydroxides, thereby removing the alkali cations from the composition and allowing other ceramics to be made. This work compared the microstructures of Al2O3·2SiO2 and Al2O3·4SiO2 bodies made using guanidine and tetramethylammonium hydroxide (TMAOH) with equivalent sodium geopolymers. The guanidine and sodium samples were similar, whereas TMAOH caused a clear difference in structure. Sodium and guanidine geopolymers with overall compositions of 3Al2O3·2SiO2 were also synthesized with the aim of developing a castable route to bulk mullite. The development of crystalline phases was followed by powder x‐ray diffractometry for all of these compositions after thermal treatment at temperatures up to 1600°C. The microstructures after firing at 1600°C were examined by scanning electron microscopy. When heated, the Al2O3·2SiO2 and Al2O3·4SiO2 compositions transformed from amorphous phases into a mixture of fine, needle‐shaped, mullite crystals and amorphous silica, while 3Al2O3·2SiO2 compositions became entirely mullite, with the shape of the mullite crystals being dependent on the type of precursors used. All samples exhibited substantial amounts of porosity, which could be reduced with improved processing techniques. This work demonstrated that alumina‐rich guanidine geopolymers are a potential route to casting bulk mullite bodies. [ABSTRACT FROM AUTHOR]

Compared to traditional gas separation methods， membrane separation technology has advantages in low cost， easy operation， and high separation efficiency. In this study， the whisker mullite hollow fiber membrane （M0） with excellent high-temperature resistance， high strength， and large flux was used as the supporting layer. The PDMS with controllable viscosity was used as the intermediate transition layer. The PDMS coated on the surface of M0 and covered the defects on the substrate. Subsequently， the UiO-66-NH2 nanoparticles were modified with amino groups via the hydrothermal method. Trimesoyl chloride was used as the oil-phase monomer， and cysteamine was used as the water-phase monomer for interfacial polymerization. Through this interfacial polymerization process， UiO-66-NH2 was loaded on the top layer of the composite membrane to form the M0-PUi composite membrane. The properties of the membrane before and after modification were characterized by FT-IR， XRD， SEM， and water contact angle of the membrane surface. The CO2/N2 separation performance of the membrane was tested using a self-made gas separation device. The results show that the CO2 permeance of the composite membrane reaches 2765.3 GPU at room-temperature and under 0.2 MPa operating pressure， and its separation selectivity for CO2/N2 is 3.2. The stable separation selectivity of the composite membrane for CO2/N2 is 3.2-3.4 after continuous use at 80 ℃ or 120 ℃ for 6 h.

Abstract The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε’, especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε’, frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases.

Ceramic saggars of mullite‐cordierite are currently used to produce cathode powders for lithium‐ion batteries. Strong interactions occur between the LiNi0.8Mn0.1Co0.1O2 (NMC) precursor in the temperature range of calcination (750–1000°C) leading to corrosion and formation of cracks in the saggar. The frequent failure of saggar causes a lot of waste, which could be reduced by choosing corrosion‐resistant materials. To understand the corrosion mechanism in the system MgO–Al2O3–SiO2, the materials MgO, Al2O3, MgAl2O4, and SiC (instead of SiO2) were embedded in premixed NMC precursor and calcined at T = 780°C for 50, 100, 150 and 200 h. The formed phases were determined by phase and microstructure analysis. Finally, the formation of LiAlO2 and Li5AlO4 is associated with a lower growth rate of the corrosion layer compared with Li4SiO4, while MgO is inert. The reactivity with NMC can be ordered as follows: SiO2 > Al2O3 > MgO. [ABSTRACT FROM AUTHOR]

A more generalized approach for predicting the steady‐state creep rate of ceramic fibers under extensive stress ranges is proposed. Creep rate equations derived from dimensional analysis, such as Almeida's creep equation and Arrhenius' creep equation, were evaluated using Buckingham's method, and the corresponding π groups were determined. Subsequently, a new equation is proposed using the usual semi‐empirical constants for the diffusional and power law creep phenomena, along with an additional power law exponent to account for changes in creep mechanisms at higher stresses. The proposed equation was used to fit the creep rate data of the fiber Nextel 720 at various temperatures and constant stress, which demonstrated a good fit with an adjusted R‐squared of.96. Subsequently, the equation was used to predict the creep rate at constant temperature and various stresses, exhibiting an adjusted R‐squared of.77 and.85, depending on the scatter of the used data. The predictive results of the proposed equation were then compared to those obtained using the Arrhenius creep equation, which tends to higher rates at high stresses. In summary, the novel equation can be more efficiently applied in predicting the creep rate of ceramic fibers across a broader spectrum of stress. [ABSTRACT FROM AUTHOR]

In this study, the reaction interfaces of four kinds of oxide refractories (corundum, spinel, mullite, and zirconia) with lanthanum oxide (La2O3) and lanthanum aluminate (LaAlO3) under different atmospheres at high temperatures (1550°C) were analyzed. The results show that the four oxides have a strong reaction with La2O3, and the corresponding rare earth aluminate, rare earth silicate, and rare earth zirconate are formed respectively. The reaction with LaAlO3 is weak, and almost no reaction occurs. Mullite has poor structural stability in a high‐temperature reduction atmosphere, easy decomposition, and strong reaction with La2O3. This study provides an important reference for the study of the reaction mechanism between rare earth steel and lining materials and the research and development of special lining materials for rare earth steel. [ABSTRACT FROM AUTHOR]

In the field of ceramics, mullite has drawn plenty of attention due to its low thermal expansion and thermal conductivity as well as its high chemical stability and creep resistance. This work reported the mineral phase, liquid phase, and microstructure evolution of the sintered mullite, using coal‐series kaolin as the raw material and potash feldspar as well as phosphorus pentoxide as additives. The effects of K2O and P2O5 on the content and viscosity of the liquid phase in mullite were calculated using FactSage 8.1. The results showed that the introduction of K2O could inhibit the formation of cristobalite effectively. Adding K2O and P2O5 improved the content of the liquid phase formed during the calcination process. After introducing K2O and P2O5, mullite developed acicular and columnar structures, with average lengths of 9.76 and 7.97 µm, respectively. Furthermore, introducing K2O and P2O5 improved the physical properties of mullite significantly. [ABSTRACT FROM AUTHOR]

Bu çalışmada; seramik ve porselen sektörünün önemli hammaddelerinden biri olan kilin daha temiz ve kaliteli bir şekilde yumuşak porselen üretimi sektörüne kazandırılması amaçlanmaktadır. Bu çalışmanın en büyük amaçlarından biri geleneksel seramik endüstrisinde kullanılan killerde yüksek oranlarda bulunan demirin renklenmesini engellemektir. Çalışmada; SAN-90 kiline ağırlıkça %0, %2, %4, %6, %8, %10 oranlarında iki tip demir (Fe2O3 ve FeCl3) ilave edilmiştir. Demirin mullit ile etkileşimi incelenmiştir. Fe kristal yapıya girdiğinde FeO parçalanacak ve renklenme etkisi önlenecektir. Belirtilen formülasyonlar ile hazırlanan numuneler 1200 oC'de pişirilmiştir. SAN-90 kilinin kimyasal özelliklerini belirlemek için XRF (X-ray Floresans), XRD (X-ray Kırınımı) analizi ve termal özelliklerini belirlemek için TG/DTA (Thermal Gravimetry / Differential Thermal Analysis) analizleri yapılmıştır. Daha sonra sinterlenen numunelerin yoğunluk, su emme ve porozite testleri yapılarak L*a*b* değerleri ölçülmüştür. Bunlara ek olarak sinterlenmiş numuneler üzerinde XRD analizi yapılarak demir ilavesinin sıcaklık ile davranışı incelenmiştir. Ayrıca mullitin kristal parametreleri hesaplanarak mullitteki demir çözünürlük limiti belirlenmiştir. Yüzey görüntüleri ve mullit kristallerinin büyümesi SEM (Taramalı Elektron Mikroskobu) analizi ile incelenmiştir. Çalışma kapsamında SAN-90 killerinin porselen/seramik endüstrisinde kullanılabilirliği, yüksek demir çözünürlüğünü barındıran yüksek mullitleşme oranı ile avantajlar sağlamaktadır.

The article presents the results of a study of phase transformations in sintered compositions "kaolin-dolomite-alumina". It has been established that the nature of the location of melting isotherms on the triple diagram indicates the spread of neoformation processes into the region of the internal compositions of the triangle and the formation of crystalline phases of the mineral's spinel, corundum, mullite. It is shown that based on alumina-containing waste and kaolin, as well as partially introduced dolomite, it is possible to develop compositions of low-temperature sintering ceramic masses for technical materials. [ABSTRACT FROM AUTHOR]

High-sulfur coal gangue is used as the primary raw material, and in conjunction with municipal solid waste incineration(MSWI)fly ash, porous glass has been produced. The process not only immobilizes heavy metals such as Pb, Cd, Zn, Cr, Cu, and Mn found in the MSWI fly ash but also achieves the harmless disposal and resource utilization of multiple solid and hazardous wastes. This study employs two strategies address the challenge of balancing lightweight and high strength in porous glass. Firstly, by adjusting the atmosphere to create a weakly reducing environment, the premature reaction of residual carbon is hindered, allowing the residual carbon in the high-sulfur coal gangue to react with Fe2O3 at temperatures above 1 000 °C to generate CO2 gas. Thereby the foaming of the melt can be promoted, reducing the bulk density of the porous glass from 900 kg/m³ to 300 kg/m³. Secondly, by adding kaolin to the raw material mixture, the primary crystalline phase of the porous glass walls shifts from feldspar to mullite. The unique interlocking structure of mullite crystals imparts higher strength, enhancing the strength of the porous glass by 80% when the bulk density is at 500 kg/m³. Toxicity leaching tests on the porous glass indicate that the leaching concentrations of various heavy metals are far below the specified standards (5.0 mg/L). The leaching concentration of Pb in the porous glass is reduced to 1.1X10-2 mg/L, and the concentrations of other heavy metals also show a significant downward trend. The results show that porous glass has a good fixation effect on multi-element heavy metals. [ABSTRACT FROM AUTHOR]

This study aimed to assess the feasibility of manufacturing fracturing proppants by microwave sintering and using low‐grade bauxite as raw material. The effects of microwave hotspot SiC and sintering additive MnO2 content on the performance of the mullite‐based structural materials were studied, respectively. The optimum sintering condition was determined by single‐factor experiments. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) mullite ceramic composites could be successfully prepared only with SiC added and with poor interparticle bonding microstructure. (2) With the addition of MnO2 and CaO, the granular‐shaped mullite crystals transformed into rod‐like mullite crystals, forming a net structure. (3) As the input power increased, the overfast sintering rate would reduce proppants' mechanical properties, and it was also necessary to select a reasonable sintering time to avoid overburning. (4) When the mass ratio of MnO2:CaO:SiC:bauxite was 2:1.5:12:84.5 and under the sintering condition of 1000 W, 2 h, the performance (breakage ratio of 8.5% under 28 MPa closed pressure, apparent density of 2.58 g/cm3, turbidity of 52 FTU, and acid solubility of 6.77%) could meet the requirements of the Chinese Petroleum and Gas Industry Standard (SY/T 5108–2014). This study provides a powerful way for reducing the fracturing cost, which not only improves the low‐grade bauxite utilization scale within the ceramic industry, but also expands the application of microwave sintering technology in mullite structural materials for the petroleum and gas industry. [ABSTRACT FROM AUTHOR]

Amorphous refractory castable were prepared by using different types of aluminate cement and fused mullite, and the changes in linear change rate,apparent porosity, bulk density, mechanical properties and load softening temperature after calcination at different temperatures were studied. The phase composition and microstructure were analyzed by XRD.SEM and EDS. The results show that the rate of linear change shows a trend of shrinkage after different calcination temperatures, apparent porosity increases with increasing temperature, and the bulk density increases first and then decreases with increasing temperature. After being calcined at different high temperatures, the bending strength of mullite castable increases continuously with increasing temperature, while the compressive strength decreases continuously with increasing temperature. The softening temperatures of CA80 and CA70 samples under load were the highest, which were 1462 °C and 1442°C respectively. [ABSTRACT FROM AUTHOR]

Nanomaterials exhibit distinct characteristics from conventional materials as a result of their extensive surface area and condensed dimensions. Additionally, it possesses unique and outstanding functionalities that render it a valuable addition to asphalt pavement. The optimal production process parameters were determined by the characteristics of the binder and nanomaterial. In this work, styrene–butadiene rubber (SBR) was loaded with a synthesized nanoceramic powder, namely, mullite (3Al2O3–2SiO2) in different concentrations (1, 2.5, 5 and 10 wt%) concerning the weight of rubber. Mullite is a scarce silicate mineral having a high abrasion resistance and acceptable thermal stability. In the current work, it was synthesized through the sol–gel method providing a ceramic powder. It was sintered up to 1000 °C producing nano-sized ceramic particles. We attempt to introduce synthesized mullite into the elastomeric matrix of SBR to boost its abrasion resistance. Novel nanocomposites of SBR and mullite were prepared mechanically. Subsequently, they were molded in a hot press forming thin films as sheets for investigations. Scanning electron microscopy showed a good dispersion for the ceramic particles inside the elastomeric matrix. The produced hybrid rubber/ceramic (organic/inorganic) nanocomposites can be applied as favorable linear sheets in industrial and construction applications. [ABSTRACT FROM AUTHOR]

This research investigates the fabrication of porous mullite filter material from reaction sintered mullite grains for high-temperature applications. Current filter types are not suitable for application in high-temperature and corrosive environments despite their high porosity. Acicular Mullite Ceramics are known for their highly porous microstructures with excellent mechanical integrity. Fabrication of a rod-like porous mullite filter from mullite grains produced from pyrophyllite clay and Al2O3 via reaction sintering was investigated. Pure mullite phase was produced at 1600 °C, and the use of a binder and foaming agent helped to obtain a porous structure. Above 1700 °C, acicular mullite grain growth via two-dimensional heterogeneous nucleation was promoted. A friable and structurally poor material was produced at temperatures just below 1800 °C. Above 1800 °C, the structural integrity of the ceramic material was improved. The measured total porosity and average pore diameter at 1800 °C were 36.20% and 29.32 µm, respectively. The measured density was 1.99 g/cm3, and the average compressive strength was 12.60 MPa. The characteristic strength was 14.49 MPa, with a Weibull modulus of 2.67. [ABSTRACT FROM AUTHOR]

Mullite fiber felt is a promising material that may fulfill the demands of advanced flexible external thermal insulation blankets. However, research on the fabrication and performance of mullite fiber felt with high-temperature resistance and thermal stability is still lacking. In this work, mullite fibers were selected as raw materials for the fabrication of mullite fibrous porous materials with a three-dimensional net structure. Said materials' high-temperature resistance and thermal stability were investigated by assessing the effects of various heat treatment temperatures (1100 °C, 1300 °C, and 1500 °C) on the phase composition, microstructure, and performance of their products. When the heat treatment temperature was below 1300 °C, both the phase compositions and microstructures of products exhibited stability. The compressive rebound rate of the product before and after 1100 °C reached 92.9% and 84.5%, respectively. The backside temperature of the as-prepared products was 361.6 °C when tested at 1500 °C for 4000 s. The as-prepared mullite fibrous porous materials demonstrated excellent high-temperature resistance, thermal stability, thermal insulation performance, and compressive rebound capacity, thereby indicating the great potential of the as-prepared mullite fibrous porous materials in the form of mullite fiber felt within advanced flexible external thermal insulation blankets. [ABSTRACT FROM AUTHOR]

The paper analyzes the effect of nanoadditives of zirconium dioxide, partially stabilized by Y2O3, on the Al2O3–SiO2 matrix during hot pressing by the electroconsolidation method. The microstructure obtained at different compositions and sintering modes is studied. It was established that the introduction of nanopowder ZrO2–3 mol % Y2O3 increases the crack resistance of sintered samples not only due to the transformation of the tetragonal phase to the monoclinic phase, but also due to the formation of a solid solution with aluminum oxide at the interphase boundaries. Starting from a temperature of 1400 °C, complete densification occurs with the formation of nonporous composites while preserving the nanostructure. At this temperature, the formation of mullite with cristobalite phases also begins. The high value of thermocycles makes it possible to use this composite material as a cryogenic one. The fabrication of mullite-corundum composites with additions of ZrO2–3 mol % Y2O3 nanopowders via the method of electrosolidification has enabled the attainment of high fracture toughness, K1C = 14.5 MPa⋅m1/2, and hardness HV10 = 14 GPa. These results evidence excellent mechanical properties, thereby expanding the potential applications of this material. [ABSTRACT FROM AUTHOR]

Indian coal fly ash generally comprises 50–60% $Si{O_2}$ Si O 2 , and 25–35% $A{l_2}{O_3}$ A l 2 O 3 can potentially replace bauxite as an aluminum resource. Aluminum recovery from coal fly ash is highly dependent on removing amorphous silica, activating the inactive mullite phase, and increasing the $Al/Si$ Al / Si ratio. This work thoroughly investigated and compared the alkali-desilication operation by two widely used alkalis, $KOH$ KOH and $NaOH$ NaOH , based on four operational parameters: liquid-to-solid ratio, $KOH$ KOH or $NaOH$ NaOH concentration, leaching time and temperature. Using SEM, EDX, and XRD, the morphology and phase of fly ash and solid byproducts were analyzed. $NaOH$ NaOH was more effective than $KOH$ KOH in $Si{O_2}$ Si O 2 dissolution at all operational parameters. A 20 wt% concentration, 5:1 liquid-to-solid ratio, 2hrs leaching time, and 100°C temperature were the optimum removal conditions for silica from fly ash using $NaOH$ NaOH. With $KOH$ KOH , the ideal desilication conditions were obtained at 28 wt% concentration, 3hrs leaching time, and 150°C temperature. The highest $Al/Si$ Al / Si ratios were obtained under the same optimal desilication conditions. Using $KOH$ KOH and $NaOH$ NaOH , the $Al/Si$ Al / Si ratio was enhanced from 0.58 to 1.26 and 1.45, respectively. The main zeolitic products obtained were Hydroxysodalite in $NaOH$ NaOH -treated fly ash and Linde F zeolite and Kalsilite in $KOH$ KOH -treated fly ash. [ABSTRACT FROM AUTHOR]

This work aims at finding an effective and low-cost new process for the preparation of porous aggregates,while alleviating the pressure of industrial solid wastes.Porous mullite ceramic-based aggregates were developed through low-temperature sintering using low-voltage electroceramic wastes and secondary aluminum dross as the main raw materials,and activated carbon powder as the pore-forming agent.The influence of the secondary aluminum dross addition (5 mass% to 40 mass%) on the properties of the samples was studied.The results show that:(1)with the increasing addition of secondary aluminum dross,the bulk density of the samples gradually decreases,while the apparent porosity gradually increases,and finally both tend to be stable;the linear shrinkage ratio first slightly increases and then decreases,and the cold compressive strength gradually decreases;(2)the addition of secondary aluminum dross promotes the formation of mullite crystalline nuclei,reduces the viscosity of the alumina-silica liquid phase,making it easier for internal gases to diffuse through the liquid phase to the material surface,forming large pores;moreover,the increase in the linear growth rate of mullite crystals accompanied by volume expansion further inhibits the sintering shrinkage of the liquid phase;the decrease in the cold compressive strength of the samples is related to the decrease in the liquid phase viscosity;after cooling to room temperature,a coating of alumina-silica glass phases forms on the surface of the aggregates,reducing the number of micropores and increasing the number of macropores,leading to increased stress concentration around the pores;(3)when the secondary aluminum dross addition is 25 mass%,the comprehensive performance of the sample is optimal. [ABSTRACT FROM AUTHOR]

Tribooxidation is the main mechanism to adapt the cutting tool to extreme mechanical and thermal loads during high-speed cutting. Wear and tribooxidation processes in the single layer TiAlCrSiYN and multilayer TiAlCrSiYN/TiAlCrN non-stoichiometric coatings on cutting tools after dry cutting with speed of 500 m/min on the running-in and steady wear stages were studied by the set of modern surface analysis methods. The reasonable preference of the multilayer coating comparing to the single layer one was demonstrated. It was established that oxide films with an amorphous-nanocrystalline structure are formed on the surface of the wear hole. Their composition is close to k Cr2O3, TiO2, Al2O3 (sapphire) and Al2O3 · 2(SiO2) (Mullite 1:2). Prospects of yttrium addition in the complex nitride were estimated by quantum chemical calculations, which has shown that such polyvalent metals as Ti+4, Cr+5,6, Y+4, Al+3 in a multicomponent nitride form a very complex spatially organized electronic structure of double and triple bonds with unoccupied π*-orbitals of nitrogen atoms. Quantum-chemical calculations of the oxidation susceptibility of these coatings with Y microadditions confirmed that this element is more inert than chromium and it is predominantly involved in the formation of interatomic bonds with Al, Ti, Cr affecting the mechanical properties of nitride coatings. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ceramics / Taoci Xuebao is the property of Journal of Ceramics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, porous ceramics have been widely studied because of their excellent technological properties. The intrinsic technological characteristics depend on the forming process and the application for which the materials are intended. A clay raw material (75 mass%) which is rich in melting oxides and waste peanut shells (25 mass%) were used to manufacture porous ceramics for the removal of arsenic from borehole water in Burkina Faso. A borehole water analysis shows a concentration of arsernic of 39 μg L−1 above the WHO standard. The porous ceramics were obtained from samples shaped by unidirectionnal pressing and after sintering at 900 °C (MKOR9) or 1100 °C (MKOR11). Unlike MKOR9 materials, MKOR11 materials consist of 27 % mullite phases. MKOR9 and MKOR11 porous materials presented a diametrical compression stress to rupture greater than 0.15 MPa, as recommended in the literature for ceramic filters. The obtained permeability value of MKOR11 ceramic materials (53,802 L/h.m2.bar) is much higher than that of MKOR9 (18596 L/h m2 bar), although its open porosity (61 %) is lower than that of MKOR9 materials (65 %). The removal rate obtained with MKOR9 is 24 % compared to 95 % for MKOR11. MKOR11 filters almost completely reduce arsenic concentration below the WHO limit values, which is not the case for MKOR9 materials. The adsorption kinetics and thermodynamic parameters showed that the adsorption process is the chemisorption. This work has shown that MKOR11 ceramic filters have a very impressive effectiveness, and they could be manufactured for the benefit of the remote population.

Industrial wastewater treatment increasingly relies on membrane separation, with ceramic membranes offering many advantages such as thermal stability and pH resistance. The resistance of ceramic membranes to extreme pH conditions indicates their ability to maintain structure and performance when exposed to highly acidic or alkaline environments. A high-permeability ceramic nanofiltration membrane was developed, boasting excellent rejection rates through a multilayer asymmetric design. Initially, two tubular porous supports, mullite and mullite-alumina, with a weight percent of 50, were fabricated using the extrusion method. Subsequently, a colloidal sol of titania (TiO2) and titania-zirconia (TiO2- ZrO2) was prepared via the sol–gel method and coated on the ceramic supports using the dip-coating method. After analyzing the membrane microstructure using SEM, XRD, and BET, the efficiency of the membranes in treating synthetic oily wastewater was evaluated. The results underscore the significant impact of the Donnan exclusion mechanism on the rejection of nanofiltration (NF) membranes. An increase in pressure led to a rise in rejection rates up to 7 bars. The Chemical Oxygen Demand (COD) rejection for mullite-titania zirconia (MTZ) and mullite-alumina-titania zirconia (MATZ) membranes was 98.65 % and 98 %, respectively. The pure water permeability test results for mullite and mullite-alumina supports, as well as MTZ and MATZ membranes, were recorded as 254, 382, 70, and 89 L bar-1m-2h−1, respectively.

Mullite substrates with two different porosities were 3D printed, and tested as humidity sensors. To evaluate the effects of porosity on humidity sensitivity, the samples were sintered at 1400 °C (Sensor 1) and 1450 °C (Sensor 2). The sensors were tested in a range from 0% to 85% relative humidity (RH) at room temperature. When exposed to water vapor at room temperature, the impedance value dropped down from 155 MΩ under dry air to 480 kΩ under 85 RH% for Sensor 1 and from 115 MΩ under dry air to 410 kΩ for Sensor 2. In addition, response time and recovery time were below 2 min, whatever the firing temperature, when RH changed from 0% to 74%. Finally, tests carried out involving ammonia, methane, carbon dioxide and nitrogenous oxide, as well as ethanol and acetone, showed no interference.

The solid‐state synthesis of perovskite BiFeO3 has been a topic of interest for decades. Many studies have reported challenges in the synthesis of BiFeO3 from starting oxides of Bi2O3 and Fe2O3, mainly associated with the development of persistent secondary phases such as Bi25FeO39 (sillenite) and Bi2Fe4O9 (mullite). These secondary phases are thought to be a consequence of unreacted Fe‐rich and Bi‐rich regions, that is, incomplete interdiffusion. In the present work, in situ high‐temperature X‐ray diffraction is used to demonstrate that Bi2O3 first reacts with Fe2O3 to form sillenite Bi25FeO39, which then reacts with the remaining Fe2O3 to form BiFeO3. Therefore, the synthesis of perovskite BiFeO3 is shown to occur via a two‐step reaction sequence with Bi25FeO39 as an intermediate compound. Because Bi25FeO39 and the γ‐Bi2O3 phase are isostructural, it is difficult to discriminate them solely from X‐ray diffraction. Evidence is presented for the existence of the intermediate sillenite Bi25FeO39 using quenching experiments, comparisons between Bi2O3 behavior by itself and in the presence of Fe2O3, and crystal structure examination. With this new information, a proposed reaction pathway from the starting oxides to the product is presented. [ABSTRACT FROM AUTHOR]

Based on coal gangue and clay with median particle diameters of 0.22 and 0.21 nm as the main raw materials, starch is used as the pore-forming agent, the mullite porous ceramics are prepared by the hydraulic forming method and the solid sintering method, and the sintering temperature and the amount of clay added are studied. The mechanism influence on the performance of mullite porous ceramics. Through thermogravimetric analysis (TG-DSC), flexural properties, X-ray diffractometer (XRD), scanning electron microscopy (SEM), mercury intrusion method and other technical methods, the thermal stability, mechanical strength, crystal phase composition, Performance indicators such as microscopic morphology and pore size are characterized. The results show that the mullite porous ceramics prepared under the conditions of sintering temperature of 1300 °C and clay content of 40 wt.% have the best performance, with a porosity of 34%, a bulk density of 1.79 g/cm3, and a volume shrinkage rate. 11.88%, flexural strength of 33.28 MPa, uniform pore distribution and more mature mullite crystals. The research results open a new way to explore the high-value utilization of coal-based wastes. [ABSTRACT FROM AUTHOR]

Mullite substrates with two different porosities were 3D printed, and tested as humidity sensors. To evaluate the effects of porosity on humidity sensitivity, the samples were sintered at 1400 °C (Sensor 1) and 1450 °C (Sensor 2). The sensors were tested in a range from 0% to 85% relative humidity (RH) at room temperature. When exposed to water vapor at room temperature, the impedance value dropped down from 155 MΩ under dry air to 480 kΩ under 85 RH% for Sensor 1 and from 115 MΩ under dry air to 410 kΩ for Sensor 2. In addition, response time and recovery time were below 2 min, whatever the firing temperature, when RH changed from 0% to 74%. Finally, tests carried out involving ammonia, methane, carbon dioxide and nitrogenous oxide, as well as ethanol and acetone, showed no interference. [ABSTRACT FROM AUTHOR]

This study aimed to investigate and develop a cost-effective and superhydrophobic ceramic membrane for direct contact membrane distillation (DCMD) applications. Two types of mullite-based composite membranes were prepared via extrusion and sintering techniques. To create a small and narrow pore diameter distribution on the membrane surface, the dip-coating technique with 1 µm alumina was employed. The hexadecyltrimethoxysilane eco-friendly grafting agent was adopted to modify low-cost multilayer mullite-based composite membranes, transforming them from hydrophilic to superhydrophobic. The prepared membranes were characterized via field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), liquid entire pressure (LEP), contact angle, atomic force microscopy (AFM), porosity, and membrane permeability. The results of the prepared membranes validate the appropriateness of the material for membrane distillation applications. The optimized membrane, with a contact angle of 160° and LEP = 1.5 bar, was tested under DCMD using a 3.5 wt.% sodium chloride (NaCl) synthetic solution and Persian Gulf seawater as a feed. Based on the acquired results, an average permeate flux of 3.15 kg/(m2·h) and salt rejection (R%) of 99.62% were found for the 3.5 wt.% NaCl solution. Moreover, seawater desalination showed an average permeate flux of 2.37 kg/(m2·h) and salt rejection of 99.81% for a 20-h test without any pore wetting. Membrane distillation with a hydrophobic membrane decreased the turbidity of seawater by 93.13%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering & Architectural Faculty of Eskisehir Osmangazi University / Eskişehir Osmangazi Üniversitesi Mühendislik ve Mimarlık Fakültesi Dergisi is the property of Eskisehir Osmangazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Industrial Minerals & Processing / Huagong Kuangwu yu Jiagong is the property of Industrial Minerals & Processing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For the energy‐saving and safe utilization of industrial furnaces, it is essential to develop refractories with low thermal conductivity and high strength. In this study, low‐grade bauxite and coal gangue were used as the main raw materials to prepare microporous mullite refractories with low thermal conductivity and high strength by the in situ decomposition method. The effect of coal gangue content and sintering temperature on the structure and properties of mullite refractories was also investigated. The results show that the average pore size of mullite refractories containing coal gangue is between 1.3 and 4.4 μm; with the addition of coal gangue, the apparent porosity of mullite refractories increases and their thermal conductivity decreases. Coal gangue reduces the number of pores larger than 14 μm, improves the microstructure uniformity of mullite refractories, and increases their cold compressive strength. The strength of microporous refractory treated at 1500°C containing 36.2% coal gangue as raw material is up to (105.6 ± 1.7 MPa); and its thermal conductivity tested at 1000°C is only.442 W/(m K)). [ABSTRACT FROM AUTHOR]

Copyright of Refractories / Naihuo Cailiao is the property of Naihuo Cailia (Refractories) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article investigates the high-temperature interaction and sintering processes of samples of low-temperature firing high-alumina for technical ceramics based on the kaolin – alumina-containing component – dolomite ternary system and establishes the areas of formation of high-alumina body for technical ceramics on the ternary diagram. It is shown that as a result of high-temperature interaction, the formation of new crystalline phases of minerals occurs, including mullite, corundum, β-cristobalite, as well as in a small amount of anorthite and an amorphous glassy phase, which impart the necessary physical and mechanical properties to the fired sample. The area of optimal compositions for obtaining low-temperature sintering high-alumina ceramic bodies based on the kaolin – alumina-containing waste – dolomite ternary system was determined. [ABSTRACT FROM AUTHOR]

Refractory and heat-resistant materials with a coarse-grained and large-porous structure were obtained using silica glass suspensions with mullite, spinel, alumina, and quartz fillers. The influence of sintering temperature on the phase composition, structure, porosity, and density of the materials were studied. Although the strength of the ceramics was found to increase in the temperature range 1300 – 1400°C, it decreases at 1500 – 1600°C due to the crystallization of the silica glass. Composites in the silica glass-alumina system were found to have the most stable strength characteristics. [ABSTRACT FROM AUTHOR]