Search

In the current study, the aggregation of CaO-Al2O3 inclusions with different CaO contents at the steel/Ar interface was in situ observed using the confocal laser scanning microscope. The critical acceleration distance and attractive force during the inclusion aggregation process were measured and calculated, and effects of inclusion composition and radius on the aggregation of inclusions were analyzed. When the CaO content in CaO-Al2O3 inclusions in 16Mn steels increased from 3 to 51 pct, inclusions gradually changed from solid to liquid. Solid and partial liquid inclusions aggregated to form large clusters with a maximum diameter of 446.2 μm. When the CaO content in inclusions increased from 3 to 26 pct, the critical acceleration distance between inclusion pairs decreased from 104.9 to 62.1 μm, and the attractive force between inclusion pairs decreased from 1.0 × 10−16 N~1.0 × 10−13 N to 1.0 × 10−18 N~1.0 × 10−15 N. As the host inclusion radius increased from 5~15 to 25~35 μm, the critical acceleration distance increased from 104.9 to 166.6 μm. For liquid inclusions, when the CaO content in inclusions increased from 38 to 51 pct, the critical deceleration distance increased from 59.7 to 93.6 μm, and the repulsive force increased from 1.0 × 10−17 N~5.0 × 10−15 N to 1.0 × 10−17 N~1.0 × 10−13 N. The liquid inclusion overcame the repulsive force and aggregated, when the host inclusion radius was larger than 10 μm, and the initial velocity of the guest inclusion was faster than 150 μm/s. The calculated attractive force between inclusions was larger than the theoretical value calculated by Kralchevsky-Paunov model. [ABSTRACT FROM AUTHOR]

The crystallization behaviors of CaF2–CaO–Al2O3–MgO–B2O3 slag for electroslag remelting of B-containing rack steel was investigated through a series of non-isothermal and isothermal crystallization experiments. The techniques employed for this determination included differential scanning calorimetry, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and FactSage 8.2. The results indicated that an increase in B2O3 content suppressed the crystallization of CaF2–CaO–Al2O3–MgO slag. The crystallization temperature decreased as the B2O3 content in the slag increased from 2 to 7 mass pct. In the slag containing 2 mass pct B2O3, spherical CaF2 precipitates first, followed by reticulate Ca12Al14F2O32 phase. Increasing B2O3 addition promoted the formation of Ca5(BO3)3F and calcium aluminate (Ca12Al14O33 or CaAl4O7), and decreased the crystallization of Ca12Al14F2O32 phase. The crystallization sequence transformed into CaF2 → CaAl4O7 → MgAl2O4 + Ca5(BO3)3F in the case of 7 mass pct B2O3. B2O3 addition inhibits the crystallization of the dominated phase CaF2, which would improving the lubrication and heat transfer performance of ESR-type CaF2–CaO–Al2O3–MgO slags. [ABSTRACT FROM AUTHOR]

This study explores a novel method for fabricating Ca-α-sialon ceramics using a calcium aluminate oxide eutectic additive. Conventional sintering techniques for Ca-α-sialon ceramics employ nitrogen-containing additives to facilitate the Si–N bond substitution mechanism with Al–O and Al–N bonds. In this work, calcium aluminate additives are utilized, leading to the formation of Ca-α-sialon ceramics via carbothermal reduction processes and partial nitridation of aluminum oxide. The influence of varying calcium aluminate content (5, 10, 15, 30, and 40 wt%) on the phase composition of Ca-α-sialon ceramics, produced by hot pressing at 1650 °C in a nitrogen atmosphere, was investigated. Results indicate that increasing the calcium aluminate content leads to the formation of a β-sialon phase, which subsequently transforms into Ca-α-sialon. At 40 wt% calcium aluminate, complete conversion of α-Si 3 N 4 to Ca-α-sialon is achieved, with significant glassy phase formation at the grain boundaries. The study elucidates the relationship between calcium aluminate content, phase composition, lattice parameters, mechanical properties, oxidation resistance, and thermal expansion of the ceramics. [ABSTRACT FROM AUTHOR]

Calcium oxide (CaO) which originated from calcium aluminate cement (CAC, binder) in alumina-magnesia refractory castables significantly deteriorates its high-temperature properties, particularly corrosion resistance. Hence, the development trend of castables is moving towards ultra-low cement and even cement-free castables. In the present work, the influence of different binders, including aluminate cement and alumina-silica gel bonding, on microstructural evolution, thermal-mechanical properties, and corrosion resistance of Al 2 O 3 -MgO castables has been investigated. The obtained results indicated the hot strength of the Al 2 O 3 -MgO cement castables was much higher than that of Al 2 O 3 -MgO castables with gel-bonding. While the latter possessed a better residual strength (9.1 MPa) and residual strength ratio (59.71 %) after thermal-shock testing when compared to the cement bonding sample (6.73 MPa, 50.12 %). Compared to the CACs-bonded samples, slag penetration resistance displayed a notable enhancement in the gel bonding sample. A typical corrosion mechanism based on FactSage® (Version 8.1) thermodynamic simulation was proposed to elucidate the corrosion behavior. [ABSTRACT FROM AUTHOR]

Monocarboaluminate is the major phase in calcium aluminate cements and is the main AFm phase in modern cement that incorporates limestone additions, including limestone calcined clay cement. This study reports thermal, elastic, and transport properties of monocarboaluminate obtained from molecular simulations. Properties and structural features are computed as a function of the relative humidity (RH) and water content. Full elastic, thermal expansion and thermal conductivity tensors are provided. Quantum‐corrected estimates are provided for the heat capacity and thermal conductivity. Self‐diffusion of interlayer species is also quantified, accounting for the subdiffusive regime. This work contributes to completing property data for critical phases in cement systems. [ABSTRACT FROM AUTHOR]

Alumina-spinel and alumina-magnesia castables are important for steel ladle applications primarily for the bottom and side wall areas respectively. Presence of spinel in alumina castables enhances the resistances against corrosion and thermal shock and improves the performance and service life of the steel ladles. Development of these type of castables is planned in the present study in presence of Cr 2 O 3 as an additive using high alumina cement as binder. Variation in spinel (10 and 20 wt%) and MgO (2.8 and 5.6 wt%) content was also explored, along with two different particle size distributions (q value 0.21 and 0.29) for different flow consistencies. The castable compositions were processed conventionally and evaluated for various refractory properties after heat treatments at 110, 1000 and 1550 °C. Both the castables showed well developed refractory properties with alumina-magnesia castable having better slag resistance due to greater extent of calcium hexa aluminate phase formation protecting the refractory. [ABSTRACT FROM AUTHOR]

Calcium aluminate phosphor nanomaterials co-doped with europium and dysprosium, (CaAl2O4: Eu2+, Dy3+) were prepared using a facile solution combustion technique. The structural and optical properties were investigated. The X-ray diffraction (XRD) results confirmed the presence of the monoclinic phase in all the samples. The Fourier-transform infrared analysis gave the expected chemical combustion results of the final product with few traces of Ca3Al2O6 impurities at low and very high Potential of Hydrogen (pH). The XRD patterns showed the presence of an impurity phase at low pH. This impurity phase was caused by preferential precipitation in the starting mixture due to a lack of homogeneity in the precursor mixture between the urea and metallic ions hence poor combustion. The diffraction angles of the major peaks shifted to lower 2θ for all the samples except for the sample synthesized at pH = 3.4 which shifted to higher 2θ. The crystallite sizes of the as-prepared samples were determined using the Debye-Scherrer equation. It was noted that there was variation in the crystallite sizes with a change in pH. The effect of pH was also observed in the Ultraviolet-Visible (UV-Vis) studies. It was also noted that the band gap increased with an increase in pH from 2.9 to 4.5. Scanning electron microscope (SEM) micrographs showed that all samples were agglomerated and had irregular shapes with pores and cracks. The study provides a simple route to synthesize CaAl2O4: Eu2+, Dy3+ phosphors with the optimum synthesis pH producing the most crystalline sample for application in lighting devices. [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]

The goal of the presented work was to find the most favorable conditions for the synthesis and stabilization of chemically pure ettringite and monosulfate. The reaction was carried out by mixing pure tricalcium aluminate (C3A) and gypsum (C S ¯ H2) in an excess amount of water. The impact of hydration time (2–7 days), C3A:C S ¯ molar ratio (1:1–1:3) and water vapor pressure of the selected drying agents (anhydrite-III and supersaturated CaCl2 solution) on the phase composition of the products was evaluated. After 7 days of hydration, either ettringite or monosulfate was obtained as the main product, depending on the C3A:C S ¯ molar ratio. The synthesis carried out at a C3A:C S ¯ molar ratio of 1:3 produced pure ettringite. In the case of the sample characterized by the ratio of 1:1 (typical of monosulfate), a considerable portion of ettringite (27.9%) was present in the final products along the AFm phase. Therefore, a different synthesis method has to be selected in order to obtain pure monosulfate. The results showed that thermal analysis, X-ray diffractometry and FTIR spectroscopy can be used to distinguish the characteristic features of ettringite and monosulfate. [ABSTRACT FROM AUTHOR]

A novel high-temperature resistant calcium aluminate cement-based electromagnetic wave absorption composites were prepared using carbon fibers, Al 2 O 3 hollow spheres, and expanded polystyrene spheres (EPS). EPS, as a pore forming agent, was oxidized as to form pores at high temperatures. The effects of carbon fibers doping levels and various high-temperature treatment on the permittivity of the composites from 0.3 to 18 GHz were investigated in detail. Additionally, a high-temperature resistant porous cone cement-based electromagnetic wave absorption structure was designed, and its microwave absorption mechanism was explored. The findings indicated that the permittivity of electromagnetic wave absorption composites exhibited stability even after undergoing high-temperature treatments below 350 °C, while experiencing a decrease at 500 °C. Following cyclic treatments at temperatures of 200 °C and 350 °C, the cone calcium aluminate porous cement-based composites still exhibited outstanding electromagnetic wave absorption performance, achieving reflection loss (RL) bandwidths below −30 dB of 17.4 GHz and 17.2 GHz, respectively, within the frequency range of 0.3–18 GHz. Furthermore, the RL of the composite from 4 to 18 GHz after 500 °C treatment remained less than −50 dB. Thus, present work associated with the materials and structural design of calcium aluminate porous cone cement-based composites provided a potential insight into the high-temperature electromagnetic wave absorption engineering applications. [Display omitted] • Cone cement-based wave-absorbing composites exhibit excellent broadband absorbing properties. • The cone composites maintain stable electromagnetic properties after cyclic treatment at a temperature of 350 °C. • The cone exhibits a RL below −50 dB in 4–18 GHz after treatment at 500 °C. [ABSTRACT FROM AUTHOR]

Sorption-enhanced steam gasification (SESG) has the potential to increase hydrogen (H 2) yield and facilitate the utilization of municipal solid waste (MSW) resource. However, the application of SESG technology in MSW still has broad research space. Therefore, this study innovatively used simulated MSW for gasification experiments. The bi-functional catalysts were prepared by co-precipitation method. In the CO 2 cyclic adsorption test, Ni0.1CA3 exhibited the highest total adsorption capacity, with 75% of the initial adsorption capacity still preserved. In the SESG test, Ni0.1CA3 showed excellent catalytic performance and the H 2 yield reached 31.69 mmol/g MSW. In addition, Ni0.1CA3 also demonstrated good stability and low carbon deposition in the SESG cycles. This could be attributed to the synergistic effect of the well-structured surface, appropriate basic sites, and calcium aluminate skeleton in Ni0.1CA3. This study served as a reference for the production of high-purity H 2 through the gasification of MSW, aligning with the development direction of green finance policy. [Display omitted] • MSW gasification realized the resource utilization of solid waste. • Ni0.1CA3 retained 75% of initial capacity after 10 CO 2 adsorption cycles. • Ni0.1CA3 showed superior hydrogen production potential in SESG of MSW. • The highest H 2 gas concentration reached 80.76 vol%. • The highest H 2 yield reached 31.69 mmol/g MSW. [ABSTRACT FROM AUTHOR]

A water-soluble ternary copolymer bearing carboxyl, sulfonic, and amide functional groups was synthesized using ammonium persulfate-catalyzed free radical polymerization in water, resulting in high monomer conversion. This copolymer was then complexed with aluminum sulfate, forming an admixture containing Al(SO4)(OH)·5H2O, which was subsequently combined with silica gel. Characterization revealed that the synthesized copolymer formed a large, thin membrane that covered both the aluminum compounds and the silica gel blocks. The introduction of this complex admixture, combining the copolymer and aluminum sulfate, not only reduced the setting times of the cement paste but also enhanced the mechanical strengths of the mortar compared to using aluminum sulfate alone. The complex admixture led to the formation of katoite, metajennite, and C3A (tricalcium aluminate) in the mortar, demonstrating significant linking effects, whereas pure aluminum sulfate could not completely transform C3S within 24 h. Further addition of silica gel to the complex admixture further shortened the setting times of the paste, slightly reduced compressive strength, but improved flexural strength compared to the initial complex admixture. The silicon components appeared to fill the micropores and mesopores of the mortar, accelerating cement setting and enhancing flexural strength, while slightly decreasing compressive strength. This study contributed to the development of new cementing accelerators with improved hardening properties. [ABSTRACT FROM AUTHOR]

To achieve homogeneous dispersion of CNTs in the SiC-based composites, calcium aluminate cement encased carbon nanotubes agglomerate (CNTs@CAC) was synthesized and used as a binder for castable CNTs/SiC composite. The EMW absorption, physical and mechanical properties of CNTs/SiC composite bonded with CNTs@CAC were investigated. SiC nanowires were in-situ generated in CNTs/SiC composite using CNTs from CNTs@CAC as the template. The uniform conductive network of SiC nanowires and CNTs and multiple heterogeneous interfaces promoted the dissipation of the incident EMW by conductance loss and polarization loss. As a result, the CNTs/SiC composite bonded with CNTs@CAC achieved a maximum EAB of 4.0 GHz in the X-band (8.2–12.4 GHz) at a thickness of 2.4 mm. Even after oxidation at 1000 °C for 8 h, the EAB covered the entire X-band. Moreover, RCS simulations were carried out via CST. The RCS values of CNTs@CAC bonded CNTs/SiC composites were all lower than those of mechanically mixed Secar71 and CNTs bonded CNTs/SiC composites under different incident angles of EMW, indicating that CNTs/CAC bonded CNTs/SiC composites can attenuate more electromagnetic energy. The bulk density of CNTs/SiC composite bonded with CNTs@CAC was 1.85 g/cm3, and flexure strength was 22.8 MPa. [ABSTRACT FROM AUTHOR]

This study compared the reactivity of a plagioclase concentrate subjected to two processes: (1) direct acid leaching and (2) thermochemical treatment with ammonium sulfate followed by leaching. The sample was prepared from coarse-grained pyroxenite rock retrieved from the Bushveld Igneous Complex, South Africa. It contained 78% plagioclase (labradorite), 9% orthopyroxene (enstatite) and 13% quartz. The elements contained in the concentrate were categorized into three groups based on their susceptibility to direct acid extraction after 6 h of leaching. Group 1 consisted of the highly reactive main elements of plagioclase (Al, Ca and Na, with extraction efficiencies of 95%, 89% and 81%, respectively). Group 2 included elements predominantly present in enstatite (Mg and Fe with extraction efficiencies of 41% and 55%, respectively). Group 3 was composed of slowly extractable Si (25%) from mostly plagioclase. Increasing the duration of direct acid leaching to 24 h had no effect on the extraction of Group 1 elements, whereas the extraction of Mg and Fe (Group 2) increased to >60%, and that of Si (Group 3) increased from 25 to 80%. The latter correlated with the nearly complete disappearance of the plagioclase blueprint in the XRD pattern of the residues generated after 24 h of leaching. In contrast, plagioclase had limited reactivity with ammonium sulfate during thermochemical treatment. Direct acid leaching of plagioclase-rich tailings can therefore generate leachates to be used as precursors for the preparation of value-added products, such as silica nanoparticles via a sol–gel route and calcium aluminate nanoparticles via solution combustion. [ABSTRACT FROM AUTHOR]

Rare-earth-doped barium calcium aluminate (BCA) glasses, having extended infrared (IR) transmission (6 μ m), are attractive materials for near IR (NIR) photonic applications. Nd2O3-doped BCA glasses display broadband emission at 1.07 µ m, but they are limited, with poor glass-forming ability (GFA) and low emission cross sections. In the present study, four different barium zinc calcium aluminate (BZCA) glasses are synthesized with varied ZnO concentrations (from 9.5 to 24.5 mol%) and doped with 0.5 mol% Nd2O3 to decipher the effect on GFA and spectroscopic properties. The addition of ZnO enhances the GFA, and the NdBZCA20 glass shows the maximum GFA. Ultraviolet (UV)–visible (Vis)–NIR absorption spectra reveal a decreasing trend in the nephelauxetic effect, while J – O parameters, emission, and gain properties lead to no significant alteration with increasing ZnO, and the structure–properties correlation is established accordingly. However, the emission cross sections for all ZnO concentrations are found ∼4.5 × 10−20 cm2 accompanied by broadband emission (Δ λ eff ∼ 40 nm), which ensures the potentiality of these glasses for low-threshold high-gain laser applications as well as ultrashort pulse laser applications. Furthermore, a thorough analysis of 1.06 µ m emission as a function of Nd concentration in the BZCA20 glass is reported here. The emission spectra and decay time indicate that 0.5 mol% is the optimized doping concentration. Inokuti–Hirayama and Burshtein equations are adopted to study the decay kinetics and energy-transfer mechanisms, which confirm that the energy-transfer process due to cross-relaxation is dominant up to 0.5 mol% concentration, whereas, beyond that concentration, excitation energy migration via the hopping mechanism supersedes. [ABSTRACT FROM AUTHOR]

In this study, we report a base‐catalyzed transesterification reaction of glycerol, a waste product of the biodiesel industry, with various dialkyl carbonates, which act both as reactants and solvents, to convert glycerol carbonate into an industrially useful molecular building block. The catalyst, being used for the first time, is also a waste product from industry, present in bauxite residues and in the Portland cement, simply known as tricalcium aluminate. Despite being well‐known and readily available, this solid is only extremely poorly researched catalyst, nevertheless, using dimethyl and diethyl carbonate, glycerol conversion rates >80% and glycerol carbonate yields >60% could be achieved in just 1 h (under air atmosphere and reflux). In a comparison of the performance with other catalysts commonly researched today, as well as with other components of red mud and cements, the results showed that tricalcium aluminate is excellent, cheap, and largely environmentally friendly material for this purpose. Reusability studies of the catalysts have also shown that they provide high conversion and product yields even after repeated use, although different material characterization techniques showed intense glycerol‐catalyst surface interaction and intermediate product formation, the deactivating side effects of which could be avoided by catalyst regeneration steps. [ABSTRACT FROM AUTHOR]

This article provides information on ettringite, a hydrated calcium sulfoaluminate mineral that belongs to the ettringite group. It describes the physical characteristics of ettringite, such as its hexagonal, prismatic crystals and color variations. The article also mentions the origins of the name ettringite and its cotype localities in the Ettringen district of Germany. Additionally, it discusses the village of Ettringen and its association with outdoor activities like rock climbing in basalt quarries. The article further explores the Bellerberg volcanic lava flows and their use in manufacturing querns and millstones. It highlights the Kalahari manganese field in South Africa as the primary natural locality for ettringite specimens, with larger crystals than any others known. The article focuses on the identification and properties of yellow ettringite found in the Kalahari manganese field, emphasizing the challenges in visually distinguishing it from other minerals in the area. It also delves into the role of ettringite in the deterioration of concrete and its stability under different conditions. The research for this article was funded by the National Research Foundation and CIMERA. [Extracted from the article]

Sc2O3–CeO2–Y2O3– stabilized zirconia (ScCeYSZ) nanoparticles with different percentages of stabilizer agents [sample1: 1.8 wt.% (Sc2O3) 8.3 wt.% (CeO2) 1.9 wt.% (Y2O3), sample 2: 1.1 wt.% (Sc2O3) 9.0 wt.% (CeO2) 1.9 wt.% (Y2O3), sample 3:.5 wt.% (Sc2O3) 9.6 wt.% (CeO2) 1.9 wt.% (Y2O3) stabilized zirconia] were synthesized with Pechini method and consolidated by spark plasma sintered method. The results showed that despite the [(sample)1: 1.8 wt.% (Sc2O3) 8.3 wt.% (CeO2) 1.9 wt.% (Y2O3)] had lower density and higher porosity percentage compared to other samples, it had better calcium–magnesium–alumina–silicate (CMAS) corrosion resistance compared to other samples and the yttria‐stabilized zirconia nanopowders (nano‐YSZ) sample. It was due to the higher acidic nature and tetragonality of the (sample)1 sintered body compared to other samples and YSZ ceramic in the CMAS corrosive medium. Moreover, the results of phase and microstructural analysis following CMAS corrosion revealed the formation of the monoclinic phase and rod‐shaped CaAl2Si2O8 particles on the surface of the sampled sintered sample. However, the nano‐YSZ sample corroded homogenously and delamination occurred after the CMAS corrosion test. [ABSTRACT FROM AUTHOR]

The efficiency of stabilization/solidification (S/S) treated heavy metal contaminated soils may be deteriorated by the changeable external environment. Thus, the toxicity characteristics leaching procedure (TCLP) and pH-dependent leaching test were carried out to evaluate the toxicity of zinc-contaminated soil treated by cement blended with soda residue with consideration of freezing–thawing (F-T) cycles. Results showed that F-T cycles had little impact on the toxicity of Zn-contaminated soils treated with cement-soda residue, and the leached Zn2+ concentration didn't exceed the regulatory limit defined by the standards. Dissolution/precipitation of zinc hydroxides was suggested to be the controlling mechanism for Zn2+ leachability. Besides, Zn2+ immobilized by chemical incorporation and encapsulation by calcium silicate hydrates (CSHs) and calcium aluminate hydrates (CAHs) still remained stable in an acidic condition. Results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) verified that F-T cycles impose little impact on the chemical properties of the specimens, but only alter the micro- and macrostructure characteristics. [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 residue generated during the production process of alumina, known as red mud, is a type of solid waste. The engineering properties of red mud can be significantly enhanced through the modification and solidification using inorganic materials. This study primarily utilized red mud as the raw material, supplemented with fly ash, lime, and clay, to conduct a solidification experiment of red mud. Orthogonal tests with three factors of two ash ratio (ratio of lime to fly ash), two ash content (total lime and fly ash), and red mud types were designed to study the changes of different ratios and maintenance conditions, etc., on the engineering properties of red mud. In addition, the micro-mechanisms of modified red mud were investigated by means of XRF, XRD, SEM and EDX. The results show that for optimum moisture content, red mud types are the most important influencing factor and for maximum dry density, two ash content is the most important influencing factor. For strength characteristics, the optimum two ash ratio was 1.5:1, the optimum two ash content was 50%, and the optimum red mud types were 70% CRM (red mud made of Chalco Shandong Co., Ltd) mixed with 30% clay. The addition of lime, fly ash, and clay improves the temperature shrinkage coefficient of the red mud. Through the analysis of microscopic composition and structure, it can be seen that goethite (α-FeO(OH)) and magnetite (γ-Fe2O3) in the red mud reacted with the modified materials to generate crystalline aluminosilicate and amorphous hydrated silicate gel, and these products together with the original calcium carbonate (CaCO3), tricalcium aluminate (Ca3Al2O6) and garnet (Ca3TiFeSi3O12) in the red mud which have certain strengths enhance the structural strength of the modified red mud. The optimum ratio obtained from the combined test results was lime: fly ash: CRM = 30:20:50. Therefore, using lime, fly ash and clay as modified materials can greatly enhance the engineering properties of red mud and realise the resourceful use of red mud. [ABSTRACT FROM AUTHOR]

In this study, a composite modifier (CMCDL) containing coal gasification residue, dicyandiamide waste slag, and lake sediments was used to modify steel slag at high-temperature. Five kind of raw materials was analyzed in physicochemical properties, mineral composition and microstructure, cementitious properties and soundness, and particle size analysis, the same to steel slag after high-temperature modification (SHTM). The new mineral phases were found that tricalcium aluminate (C 3 A), gehlenite (C 2 AS), magnetite (Fe 3 O 4), spinels (MgFe 2 O 4), quartz (SiO 2), celite (C 6 AF 2) and diopside (CMS 2) formed in the SHTM when the mass fraction increase from 10% to 30% in CMCDL. The HTM with CMCDL increases the glass phase and hydrated mineral (C 3 A, C 3 S, C 2 S) and in raw steel slag, promoting the disassembled of RO phase, turning the phase from FeO into MgFe 2 O 4 and Fe 3 O 4. MgFe 2 O 4 and Fe 3 O 4 have similar crystal structures, and they form mixed spinels. When the content of CMCCL (coal gasification residue: dicyandiamide waste slag: lake sediments =7:9:4) is 20%, the temperature is 1250 °C, result showed that the mass fraction of f-CaO in SHTM using CMCCL decreases from 4.81% to 1.86%, with a decrease of 61.3%, the 28-day activity index of SHTM increases up to 17.6% compared with raw steel slag, reaching 86.2%. Therefore, the CMCDL-blended SHTM can be applied harmlessly in cement and concrete, enabling low-energy fine grinding of steel slag. [ABSTRACT FROM AUTHOR]

Marl soil is highly prone to erosion when exposed to water flow, posing a potential threat to structural stability. The common practice of stabilizing soil involves the addition of cement and lime. However, persistent reports of severe ruptures in many stabilized soils, even after extended periods, have raised concerns. In stabilized marls, unexpected ruptures primarily result from the formation of ettringite, which gradually damages the soil structure. This article aims to assess the impact of nanosilica on the formation of ettringite and the nanostructure of calcium silicate hydrate (C-S-H) during the marl soil stabilization process with lime. To achieve this, marl soil was stabilized with varying percentages of lime and nanosilica. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were collected to observe changes in mineralogy and microstructural properties. Various geotechnical parameters, including granularity, Atterberg limits, compressive strength, and pH, were measured. The results indicate that the uniform distribution of nanosilica in marl-lime soils enhances pozzolanic activities, calcium aluminate hydrate growth (C-A-H), and the nanostructure of calcium silicate hydrate (C-S-H). According to XRD and SEM experiments, the presence of nanosilica reduces the formation of ettringite. Moreover, the compressive strength of modified samples exhibited an upward trend. In the experimental sample manipulated with 1% nanosilica combined with 6% lime, the compressive strength increased by 1.84 MPa during the initial 7 days, representing an approximately 18-fold improvement compared to the control sample. [ABSTRACT FROM AUTHOR]

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X‐ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self‐desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass‐balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed. [ABSTRACT FROM AUTHOR]

The surface tensions of molten oxides depend strongly on the structural relaxation of the surface region. The mechanism of surface structural relaxation for molten oxide slags is complex. The surface tension of calcium aluminate slag is minimal at an intermediate composition, although the critical reason has not been identified. Here, two novel approaches were used to evaluate the features of surface ionic structures in the molten state for the range of 25–50 mol% Al2O3: (1) X‐ray absorption analysis of oxygen and cationic elements in glass samples after surface relaxation treatment, and (2) molecular dynamics simulations, based on a polarizable‐ion model, of the ionic distribution in a molten slag with vacuum/melt interfaces. The results indicate that bridging oxygen (BO) ions are preferred to non‐BOs in the surface region. In calcium aluminate slag, BOs are formed by connecting two AlO4 tetrahedrons with charge compensation of two Al3+ ions with one Ca2+ ion. Additionally, the above approaches were used to qualify the effect on the surface ionic structure of adding 1–20 mol% SiO2 to the calcium aluminate slag. The results indicated that the SiO4 tetrahedrons incorporate the vertex connection with AlO4 tetrahedrons to form BOs in the surface region. [ABSTRACT FROM AUTHOR]

Due to the large increase in human population, the need for more buildings and other amenities is widening. Concrete is considered one of the most abundant and popular materials used in the structure and construction fields. It is known as a composite mix composed of cement and aggregates including fine and coarse and water. Despite its good properties, its capability to be formed in different shapes and its ability to resist severe conditions, concrete will struggle with the presence of extremely high temperatures. So, different types of concrete must be found to resist those challenging conditions. Refractory concrete can be considered a good choice to be used in places exposed to elevated temperatures and severe conditions. Mainly, refractory concrete is made up of ordinary Portland cement replacement well known as refractory cement, specific types of fine and coarse aggregates and are known as refractory or temperature-bearing aggregates and water. To the best authors' knowledge, review papers about refractory concrete are rare. For this reason, more than 65 papers were consulted including many recently published. This review describes the different types of materials used in refractory concrete. Furthermore, the different fresh, hardened, structural, durability and thermal properties of refractory concrete are also included such as slump, density, compressive strength, flexural strength, tensile strength, modulus of elasticity, ultrasonic pulse velocity, shrinkage, mass loss, porosity, water absorption, damage level and thermal conductivity. [ABSTRACT FROM AUTHOR]

Aerosols deposited on the surfaces of alloys and coatings used in high-temperature applications react with the protective thermally grown oxide (TGO) and accelerate component degradation. Understanding how the TGO composition effects these reactions is essential to develop corrosion-resistant materials. This work studies the corrosion of Haynes-214 alloy, which forms a bilayer Ni(Cr,Al)2O4 (spinel) + Al2O3 TGO, exposed to complex oxide and sulfate deposits to understand how the Cr and Ni oxides affect the corrosion mechanisms. The deposit compositions were systematically varied to understand the effect of anion makeup (mixed oxides, oxide-sulfate, and sulfates). The results are compared to a FeCrAlY alloy that forms a simple Al2O3 TGO. On the Haynes-214 alloy, deposits containing mixed oxides (with or without sulfates) have limited corrosive effect. In contrast, a pure CaSO4 deposit reacts aggressively with the TGO to form calcium chromate and aluminate reaction products (RP) that substantially increase the TGO + RP thickness compared to that on the FeCrAlY alloy. Surprisingly, a deposit composed of a mixture of sulfates caused less severe corrosion than the CaSO4 alone since magnesium chromate formation appears to limit aggressive reactions involving Ca. The results are discussed in the context of opportunities for corrosion-resistant alloy design. [ABSTRACT FROM AUTHOR]

Cement production is responsible for 5%–7% of global CO2 emissions, highlighting the need for sustainable alternatives like geopolymer composite (GCOMP) to meet the growing demand for concrete. This study investigates the mechanical, microstructural, and thermal properties of GCOMP by incorporating nano‐alumina (n‐alumina) and MSF (MSF). The n‐alumina content was varied at 1%, 2%, and 3% by weight of the mix, while the MSF content remained fixed at 0.5% by weight. Thermal characterization was conducted up to 800°C. The performance of GCOMP blends with n‐alumina was compared to a control blend consisting of only 0.5% MSF. Various mechanical properties were evaluated for all GCOMP blends. Microstructural and mineralogical characteristics were analyzed using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier‐transform infrared spectroscopy (FTIR). Thermogravimetric and differential thermal analysis were performed up to 800°C for the thermal analysis of the GCOMP mix. The results indicate that the optimal mechanical properties were achieved with 2% n‐alumina (compressive and flexural strength increased by 35.65% and 77.7%, respectively). Additionally, the incorporation of n‐alumina improves the interfacial zones and results in a denser structure. GCOMP mortars portrayed a mass loss between 25°C and 250°C, with a marginal mass loss occurring between 250°C and 715°C. No mass loss was observed between 715°C and 800°C. The MSF‐reinforced GCOMP mortars experienced an ultimate mass loss of approximately 12%, with the MSF showing negligible influence. The addition of n‐alumina particles to MSF‐reinforced GCOMP resulted in the development of stronger samples characterized by the presence of C–S–H, calcium aluminate oxide hydroxide, and quartz. [ABSTRACT FROM AUTHOR]

An alkali-free liquid accelerator was prepared with aluminium sulfate and aluminium formate as the main components. The effects of the accelerator on the setting of paste and the mechanical strength of mortar were studied, and the impact of the accelerator on the early hydration behaviour and hydration products of the paste were investigated by isothermal calorimeter analysis, X-ray diffraction analysis, scanning electron microscopy and thermogravimetric analysis. The results show that the accelerator is excellent for the rapid setting and hardening of the cement. When the content of the accelerator was 8 wt%, the initial setting time and final setting time of the paste were 85 s and 180 s, respectively, and the strengths of the mortar at 1 day and 28 days were 9.52 MPa and 44.42 MPa, respectively. The proposed accelerator can accelerate the dissolution and hydration of tricalcium aluminate and tricalcium silicate and promote the formation of ettringite, formate and portlandite. [ABSTRACT FROM AUTHOR]

The problem of loss of strength caused by the conversion reaction with calcium aluminate cements (CAC) is well known. It has been shown that the addition of ground granulated blast furnace slag (GGBS) to CAC inhibits the conversion process. Different slags can have a different chemical and mineralogical composition depending on their origin and production process, which can significantly influence their reactivity. This work investigated the extent to which the R3 test, developed for Portland cement and based on isothermal calorimetry and/or bound water, was used to predict the reactivity of ground granulated blast furnace slag in a CAC. Mortars and cement pastes with a 30% replacement of slag were tested to evaluate their compressive strength and microstructure. The results show that slags with higher reactivity due to their hydraulic properties lead to a lower compressive strength loss within the first 6 h, a higher strength loss after 24 h due to stratlingite formation and a lower strength loss after 28 days due to pozzolanic reaction and stratlingite formation. The results also confirm that the R3 test was used as a rapid method to predict the effects of slag on the compressive strength of CAC. [ABSTRACT FROM AUTHOR]

We investigated the impact of CaCO3 addition on the density and compressive strength of calcium aluminate cement (CAC)-based cementitious materials in binder jetting additive manufacturing (BJAM). To confirm the formation of a uniform powder bed, we examined the powder flowability and powder bed density for CaCO3 contents ranging from 0 to 20 wt.%. Specifically, powders with avalanche angles between 40.1–45.6° formed a uniform powder bed density with a standard deviation within 1%. Thus, a 3D printing specimen (green body) fabricated via BJAM exhibited dimensional accuracy of less than 1% across the entire plane. Additionally, we measured the hydration characteristics of CAC and the changes in compressive strength over 30 days with the addition of CaCO3. The results indicate that the addition of CaCO3 to CAC-based cementitious materials forms multimodal powders that enhance the density of both the powder bed and the green body. Furthermore, CaCO3 promotes the formation of highly crystalline monocarbonate (C4AcH11) and stable hydrate (C3AH6), effectively inhibiting the conversion of CAC and showing compressive strengths of up to 5.2 MPa. These findings suggest a strong potential for expanding the use of BJAM across various applications, including complex casting molds, cores, catalyst supports, and functional architectural interiors. [ABSTRACT FROM AUTHOR]

Tricalcium aluminate (C3A) and tricalcium silicate (C3S) with gypsums play an important role in the hydration of oil well cement. This study aims to assess the influence of C3S and C3A with various gypsums on the hydration of oil well cement at 30, 50, and 80 °C through the analyses of hydration heat evolution by isothermal calorimetry analysis, setting and thickening times, strength, and hydration products by X-ray diffraction. The result reveals that C3A hydrates, in the presence of gypsums, rapidly at 80 °C to produce the C3AH6 phase leading to higher heat evolution. The conversion of AFt to AFm is observed in oil well cement paste at 50 °C. An increase in C3A leads to an increase in compressive strength and a decrease in permeability at 80 °C. An increase of C3S leads to the reduction of cumulative heat evolution and early compressive strength before 28 d. Gypsums shorten cement setting and thickening times opposite to the commonly known retardation effect due to the lower content of C3A and its acceleration on C3S hydration. Dihydrate and hemihydrate gypsums show a greater promotion effect on strength at 30 and 50 °C, while anhydrous gypsum presents a greater enhancing effect at 80 °C. Gypsum increases the permeability while the others show an unobvious effect at 80 °C. [ABSTRACT FROM AUTHOR]

Alternative binders offer an avenue for advancing ultra-low-cement and cement-free castables while reducing carbon emissions and energy consumption. In this study, geopolymer binders partially or fully replaced calcium aluminate cement (CAC) in high-alumina castables. The formulations underwent diverse testing, including flowability, physico-thermo-mechanical measurements, and XRD, ATR-FTIR, and SEM analyses. The findings highlighted the feasibility of utilizing geopolymers to craft innovative refractories. The formulation comprising 2.7 wt% CAC and 1.3 wt% geopolymer (AT-3 C-1 G*) exhibited the most successful performance. At 1400 °C, these samples displayed shrinkage of 1.18%, elastic modulus of 135 GPa, flexural strength of 39.1 MPa, and high thermal shock resistance (∆T∼1000 °C). The interaction between CAC and geopolymer inhibited cement hydration while enhancing the geopolymerization process. Moreover, firing the samples at 800–1400 °C led to liquid phase and nepheline formation from the geopolymeric gel, resulting in viscous sintering and improved ceramic densification. These developments produced refractories with remarkable overall performance, surpassing the reference material. [ABSTRACT FROM AUTHOR]

The AFm phase found in hydrated Portland cements refers to a family of calcium aluminate phases. Their layer structure is derived from that of portlandite (calcium hydroxide (Ca(OH)2)), but with one third of the Ca2+ ions replaced by a trivalent ion, nominally Al3+ or Fe3+. The resulting charge imbalance gives the layers a positive charge, which is compensated by intercalated anions; the remaining interlayer space is filled with water (H2O). Hydrated cements will contain mixtures of AFm phases and their solid solutions. Portland cement is often modified by addition of soluble nitrate or nitrite salts to protect embedded steel or to shorten the setting time. These nitrate and nitrite ions are capable of entering and occupying AFm anion sites, hence impacting overall phase balances between cement hydrates. In this study AFm phases and solid solution formations were investigated between AFm phases containing SO42−, CO32−, OH−, Cl− and NO2− NO3− ions. Samples were synthesised and subsequently characterised using X-ray diffraction and through the measurement of aqueous solution compositions after 180 days of equilibration in water. [ABSTRACT FROM AUTHOR]

The synthesis and the structural and luminescence studies of samarium-doped calcium aluminate phosphors are reported. These phosphors are synthesized by the solid-state reaction method with a variable concentration of doping ions (0.5–3.0 mol%). The synthesized phosphors are characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The XRD studies show that the doped phosphors have a cubic structure. The SEM images reveal that the Sm3+- doped Ca3Al2O6 phosphor represents a combination of some rod-like and flower-like structures. The FTIR studies confirm the formation of a Ca3Al2O6:Sm3+ phosphor. The photoluminescence (PL) emission measurements upon excitation by 273 nm (ultraviolet light) show the characteristic emission peaks of Sm3+ at 579, 589, 600 and 619 nm. The characteristic orange-red emission is observed for samarium ion. The excitation spectra of the Ca3Al2O6:Sm3+ phosphor mainly consist of a more intense charge transfer band (CTB) of Sm3+ located at 273 and 395 nm with some peaks centred at 319 and 362 nm. The CIE coordinates are calculated by the spectrophotometric method using the spectral energy distribution of the Ca3Al2O6:Sm3+ sample. The prepared phosphors can act as a single host for orange-red light emission in display devices. [ABSTRACT FROM AUTHOR]

The experimental research focused on the influence of solutions containing chicken manure, pig slurry, and silage on the hydration processes of cements and clinker minerals such as C3S, β-C2S, C3A, and C4AF. The results showed that the hydration of C3S and β-C2S led to the formation of various phases, including Ca(OH)2, CaCO3, and various types of poorly crystalline C-S-H phases contaminated with Mg, S, P, Ti, K, and Cl elements. The C3A phase was the most susceptible to biological corrosion, while the C4AF phase was the most resistant. Studies on model cement demonstrated a significant influence of solution pH on bacterial presence, where pH ≥ 9 prevented their occurrence, while pH ≤ 4 and pH 6-7 favored their presence. The addition of γ-C2S and C12A7 phases to the model cement caused a modification of the sample's microstructure and revealed exceptional density, where all spaces were fully occupied by hydration products. Such a model of cement matrix construction prevents and limits the penetration of the corrosive agent into the sample interior. The obtained research results suggest the possibility of using such cement for bioreactor construction and employing additions of calcium aluminates and calcium ferrites to further enhance cement resistance to biological corrosion. [ABSTRACT FROM AUTHOR]

Nano-calcium carbonate (NC) is a novel ultrafine solid powder material that possesses quantum size effects, small size effects, surface effects, and macroscopic quantum effects that ordinary calcium carbonate lacks. As a nanomaterial with superior properties, graphene oxide (GO) has been studied extensively in the field of construction. In microscopic characterization, the reaction between NC and tricalcium aluminate (C3A) formed a new hydration product, hydrated calcium aluminum carbonate (C3A·CaCO3·11H2O), which enhanced the arrangement of hydration products and optimized the distribution of pore size in the mortar. Regarding the mechanical properties, the addition of GO and NC significantly enhanced the early-age mechanical performance of the mortar. In terms of durability, the incorporation of GO and NC significantly improved the water permeability, chloride ion permeability, and resistance to sulfate attack of the cement mortar. In this study, it was found that adding 1 wt% NC and 0.02 wt% GO not only improves the mechanical and durability properties but also promotes the hydration reaction according to the microstructure analysis. With the help of NC, compared with other studies, the amount of GO is reduced, while the cost is reduced, and the application of GO in the field of cement-based materials is promoted. [ABSTRACT FROM AUTHOR]

Critical-sized bone defects are those that would not heal spontaneously despite surgical stabilisation. These defects are treated using autografts, allografts, xenografts and synthetic bone grafts. The present study was undertaken to evaluate the efficacy of biphasic hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) bioceramic scaffolds in treating critical-sized segmental bone loss in rats. The study was conducted in sixty male Wistar rats aged between 8-12 weeks, weighing 200-250 g body weight with critical-sized defects in the right femur. A six-mm segmental mid-diaphyseal femoral defect was created under general anaesthesia. The bone defect was bridged with biphasic hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) bioceramic scaffolds and retained in position with microplate and screws. Fifteen rats were sacrificed as per the guidelines of CCSEA during the 4th, 8th, 12th and 16th week post-surgery. The treated bone and contralateral femur were harvested and subjected to a three-point bending test, torsion test and compression test to compare the regained strength of the repaired right femur with that of the intact contralateral left femur. From the present study, it was observed that the use of biphasic hydroxyapatite and β-tricalcium phosphate bioceramic scaffolds in the treatment of critical-sized long bone defects in rats resulted in biomechanical properties of the healed right femur greatly superior to the femur with untreated critical-sized diaphyseal defect by sixteenth week post-surgery and was only slightly inferior to the normal intact left femur. The results were suggestive of using biphasic hydroxyapatite and β-tricalcium phosphate bioceramics scaffolds as a safe and promising alternative for the treatment of critical-sized bone defects. [ABSTRACT FROM AUTHOR]

Calcium aluminate phosphor nanomaterials co-doped with europium and dysprosium (CaAl2O4: Eu2+, Dy3+) were prepared using a facile solution combustion technique. The structural and optical properties were investigated. The X-ray diffraction (XRD) results confirmed the presence of the monoclinic phase in all the samples, with few impurity phases in the samples synthesized at 300 °C and 400 °C. The Fourier-transform infrared analysis gave the expected chemical combustion results of the final product with few traces of Ca3Al2O6 impurities at low and very high synthesis temperatures. The XRD patterns displayed diffraction angles of the major peaks shifting to higher 2 theta as the synthesis temperature increased. This is attributed to an increase in particle sizes, which led to an increase in lattice parameters. The intensity of the prominent peak increased up to 500 °C due to improved crystal quality. The crystallite sizes of the as-prepared samples were determined using the Debye-Scherrer equation. It was noted that there is variation in the crystallite sizes with synthesis temperature. The UV–Vis graph shows that absorption edges also shifted to lower wavelengths with an increase in synthesis temperature. It was noted that the band gap increased with an increase in synthesis temperature up to 500 °C, but at temperature of 1000 °C, the band gap was observed todecrease. Scanning electron microscope micrographs showed that the samples had irregular shapes with pores and cracks. The study provides a simple route to synthesize CaAl2O4: Eu2+, Dy3+phosphors with optimum synthesis temperature, producing the most crystalline sample for use in lighting devices.

Calcium aluminate (CaAl 4 O 7 or CA2) prepared by a surfactant assisted (PEG-PPG-PEG, MW:5800) co-precipitation method were employed as catalyst support for potassium modified (1–3% wt.%) 7 wt% nickel catalysts in reforming of methane with carbon dioxide. The X-ray diffraction (XRD), nitrogen adsorption analysis, H 2 chemisorption, temperature programmed reduction (TPR) and oxidation (TPO) and scanning electron microscopy (SEM) techniques were used to charactrize the fresh and spent catalysts. The catalytic activity results revealed relatively high conversions (CH 4 and CO 2) and stability for all the K 2 O modified catalysts. About 2–6% decrease of CH 4 conversion was observed after promotion of 7%Ni/CA2 with K 2 O. The decrease was attributed to increase in Ni particle size or decrease in Ni dispersity, which caused reduction of available active site for the DRM reaction. Among the promoted catalysts 7%Ni–1%K 2 O catalyst with 62% CH 4 conversion at 700 °C showed highest catalytic activity. K 2 O promoter increased CO 2 affinity, coke resistance and CO 2 coke gasification rates of catalysts. After 5 h on stream the TPO analysis of spent catalysts revealed lower carbon deposition with increase of K 2 O loading from 1 to 3%. 7%Ni–3% K 2 O showed 45 % decrease in carbon deposition compared to unmodified catalyst. TPO analysis detected atomic, fibrous and graphitic carbon deposition over spent catalysts, with filamentous type as the major type. SEM results only detected fibrous carbon for modified and unmodified spent catalysts. • Ni–K 2 O/CaAl 4 O 7 catalysts with different K 2 O amount were introduced for DRM. • The coke deposition decreased with addition of K 2 O promoter to Ni/CaAl 4 O 7. • 7%Ni–1%K 2 O revealed highest catalytic activity among the promoted catalysts. • 7%Ni–3%K 2 O showed lowest carbon deposition. • Promoted catalysts performed great stability after 5 h on stream. [ABSTRACT FROM AUTHOR]

Alite(C3S)-Ye'elimite(C4A3$) cement is a high cementitious material that incorporates a precise proportion of ye'elimite into the ordinary Portland cement. The synthesis and hydration behavior of Alite-Ye'elimite clinker with different lime saturation factors were investigated. The clinkers were synthesized using a secondary thermal treatment process, and their compositions were characterized. The hydrated pastes were analyzed for their hydration products, pore structure, mechanical strength, and microstructure. The clinkers and hydration products were characterized using XRD, TG-DSC, SEM, and MIP analysis. The results showed that the Alite-Ye'elimite cement clinker with a lime saturation factor (KH) of 0.93, prepared through secondary heat treatment, contained 64.88% C3S and 2.06% C4A3$. At this composition, the Alite-Ye'elimite cement clinker demonstrated the highest 28-day strength. The addition of SO3 to the clinkers decreased the content of tricalcium aluminate (C3A) and the ratio of Alite/Belite (C3S/C2S), resulting in a preference for belite formation. The pore structure of the hydrated pastes was also investigated, revealing a distribution of pore sizes ranging from 0.01 to 10 μm, with two peaks on each differential distribution curve corresponding to micron and sub-micron pores. The pore volume decreased from 0.22 ± 0.03 to 0.15 ± 0.18 cm3 g−1, and the main peak of pore distribution shifted towards smaller sizes with increasing hydration time. [ABSTRACT FROM AUTHOR]

Refractory materials containing calcium aluminate cement (CAC) are commonly used in the metallurgical and petrochemical industries due to their exceptional mechanical resistance, even at temperatures exceeding 1000 °C, and do not require additional reinforcement. This study seeks to advance this practice by developing ultra-high-performance structures that offer building protection against fire and explosions. Such structures require bar reinforcement to withstand accidental tension stresses, and the bond performance becomes crucial. However, the compressive strength of these materials may not correlate with their bond resistance under high-temperature conditions. This study investigates the bond behavior of ribbed stainless austenitic steel bars in refractory materials typical for structural projects. The analysis considers three chamotte-based compositions, i.e., a conventional castable (CC) with 25 wt% CAC, a medium-cement castable (MCC) with 12 wt% CAC, a low-cement castable (LCC), and a low-cement bauxite-based castable (LCB); the LCC and LCB castables contain 7 wt% CAC. The first three refractory compositions were designed to achieve a cold compressive strength (CCS) of 100 MPa, while the LCB mix proportions were set to reach a CCS of 150 MPa. Mechanical and pull-out tests were conducted after treatment at 400 °C, 600 °C, 800 °C, and 1000 °C; reference specimens were not subjected to additional temperature treatment. This study used X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) methods to capture the material alterations. The test results indicated that the bonding resistance, expressed in terms of the pull-out deformation energy, did not directly correlate with the compressive strength, supporting the research hypothesis. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) is advantageous in marine engineering, and using materials directly from the sea when mixing CAC can reduce both construction costs and ecological pollution to the sea. However, using seawater as the mixing water in CAC is difficult due to the strength reduction. In this work, CACs were prepared with siliceous minerals (SMs) (diatomite and silica fume (SF)) and sodium chloride solution (SCS) as the mixing water. For comparison, other samples were immersed in SCS rather than mixed with SCS. The strength, mass and length changes of CAC mortars cured at 20°C and 40°C were determined. The phase assemblages and morphology were assessed using X-ray diffraction, thermogravimetric-differential scanning calorimetry and scanning electron microscopy. Using SCS as the mixing water was beneficial to the later strength development of CAC. It promoted the formation of C2ASH8 in CAC pastes and showed no strength loss even when cured at 40°C. The strengths of the SM-modified CAC mortars mixed with SCS were higher than those immersed in SCS. The combination of diatomite and SCS significantly increased the CAC strength, especially at 20°C, while SF contributed to better stability in mass and length. [ABSTRACT FROM AUTHOR]

Capillary water absorption is an important parameter to evaluate the durability of cement mortars. For testing the capillary water absorption of cement mortars, drying is a necessary and crucial procedure. However, different standards have different requests on drying temperatures for doing the tests. Since the calcium aluminate cement-hemihydrate gypsum (CAC-C S ¯ H0.5) mortars are temperature-sensitive, three temperatures of 20 °C, 40 °C and 70 °C were selected to study the effect of hydroxypropyl methyl cellulose (HPMC) on the capillary water absorption of these mortars. The influence of temperature on the capillary water absorption of the mortars was analyzed from the perspectives of pore structure and hydration. The results show that when the viscosity of HPMC is the same, the higher the dosage of HPMC used, the higher the capillary water absorption of mortars. When the dosage of HPMC is the same, the higher the viscosity of HPMC, the greater the capillary water absorption of mortars. The addition of HPMC can significantly increase the total porosity of mortars, especially the volume of the large pores. However, pore structure is not the main factor influencing the capillary water absorption of HPMC-modified CAC-C S ¯ H0.5 mortar. When the drying temperature rises to 40 °C, a small amount of AFt is decomposed. When the drying temperature reaches 70 °C, most of AFt is carbonized to form hemicarboaluminate and AH3, and the latter is the key to refining the pore structure of mortars. The temperature change causes a phase transition of the hydration products, thereby altering the pore structure. 40 °C is suggested as an appropriate drying temperature for the capillary water absorption test of the investigated mortars. [ABSTRACT FROM AUTHOR]

We investigated the reaction kinetics and initial chemical conditions in the production of silicon alloys, employing aluminum as the reductant for calcium silicate slag, to enhance process economics and scalability to industrial levels. The apparent kinetics and transient chemical conditions were studied by immersing solid aluminum into molten slag, allowing the reaction to proceed for varying durations without external agitation, before quenching the reaction for chemical and microscopic analyses of the resulting silicon alloy and slag. The majority of the conversion was observed within the first 15 s at 1650 °C, driven by significant chemical interactions and interfacial turbulence introduced upon aluminum immersion. For Al-SiO2 stoichiometries ranging from 0.5 to 1.2, the slag phase reaction conformed to first-order kinetics during the initial two minutes, when it approached equilibrium. The mass transfer coefficients for Al2O3 were estimated at 1–2 × 10−4 m/s, comparable to those for SiO2 and CaO. A constant mass transfer coefficient could not be established for stoichiometries of 1.6 and 2, as these deviated from the standard slag mass transfer relationship and did not adhere to established relationships. Despite near-complete reactions, alloy–slag mixing was extensive, decreasing with lower stoichiometry values. [ABSTRACT FROM AUTHOR]

To improve the performance of shotcrete in high-altitude and low-temperature environments, emulsified asphalt shotcrete (EASC), which can be used in negative-temperature environments, was prepared by using low-freezing-point emulsified asphalt, calcium aluminate cement, and sodium pyrophosphate as modified materials. The effect of emulsified asphalt on the performance of shotcrete was investigated through concrete spraying and indoor tests. Then, the modification mechanism of emulsified asphalt with respect to EASC was analyzed by combining scanning electron microscopy images and the pore structure characteristics of EASC. The results showed that in a negative-temperature environment, the incorporation of emulsified asphalt delayed the formation of the peak of the cement hydration exotherm, slowed the rate of the cement hydration exotherm, reduced the thermal perturbation of permafrost by EASC, increased the cohesion of the concrete, improved the bond strength between EASC and permafrost, and reduced the rate of rebound. The mechanical strength of the studied EASC decreased upon increasing the amount of emulsified asphalt in the admixture, and its resistance to cracking gradually improved. A content of less than 5% emulsified asphalt could improve the internal pore structure of EASC, thus improving its durability. Increasing the content of emulsified asphalt affected the hydration process of the cement, and the volume content of the capillary pores and macropores increased, which reduced the durability of the EASC. [ABSTRACT FROM AUTHOR]

In order to increase the utilization rate of stainless steel slag, reduce storage needs, and mitigate environmental impacts, this study replaces a portion of limestone with varying amounts of stainless steel slag in the calcination of Portland cement clinker. The study primarily examines the influence of stainless steel slag on the phase composition, microstructure, compressive strength, and free calcium oxide (ƒ-CaO) content of Portland cement clinker. The results show the following: (1) Using stainless steel slag to calcine Portland cement clinker can lower the calcination temperature, reducing industrial production costs and energy consumption. (2) With an increase in the amount of stainless steel slag, the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases in Portland cement clinker initially increase and then decrease; the C3S crystals gradually transform into continuous hexagonal plate-shaped distributions, while the tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) crystal structures become denser. When the stainless steel slag content is 15%, the dicalcium silicate and tricalcium silicate phases are at their peak; the C3S crystals are continuously distributed with a relatively dense structure, and C3A and C4AF crystals melt and sinter together, becoming distributed around C3S. (3) As stainless steel slag content increases, the compressive strength of Portland cement clinker at 3 days, 7 days, and 28 days increases and then decreases, while ƒ-CaO content decreases and then increases. When the stainless steel slag content is 15%, the compressive strength at 28 days is at its highest, 64.4 MPa, with the lowest ƒ-CaO content, 0.78%. The test results provide a basis for the utilization of stainless steel slag in the calcination of Portland cement clinker. [ABSTRACT FROM AUTHOR]

SiC-based materials have been hot research topic in the field of high-temperature electromagnetic wave (EMW) absorption materials. SiC–Al 2 O 3 composite EMW absorption materials were prepared via casting process using carbon nanofibers/calcium aluminate cement (CNFs@CAC) as the binder. Effects of CNFs@CAC content on EMW absorption properties of SiC–Al 2 O 3 composites were investigated. Results show that the effective absorption bandwidth (EAB) of SiC–Al 2 O 3 composites first increases and then decreases with the increase in CNFs@CAC content. SiC–Al 2 O 3 composites with 10 wt% CNFs@CAC (denoted as F10) have excellent EMW absorption properties in X-band (8.2–12.4 GHz), with minimum reflection loss (RL) of −66.12 dB at a thickness of 2.1 mm and a wide EAB of 3.27 GHz. This is attributed to synergistic effects of the network of SiC nanowires generated with CNFs as templates during sintering process and irregular porosity of the structure, which results in SiC–Al 2 O 3 composites having good impedance matching and multiple EMW attenuation mechanisms. In addition, sample F10 exhibits exceptional mechanical properties and oxidation resistance, as indicated by its flexural strength of 25.6 MPa. After oxidation at temperatures in the range of 800 °C-1000 °C for 8 h, EAB of sample F10 is in the range of 3.15–3.30 GHz. Above results indicate that SiC–Al 2 O 3 composites are promising EMW absorption materials for use in harsh environments. [ABSTRACT FROM AUTHOR]