Properties of a ternary calcium sulfoaluminate–calcium sulfate–fly ash cement

In this paper, cement combinations based on calcium sulfoaluminate cement (CSAC) were developed and the effect of fly ash and the hemihydrate form of calcium sulfate on the properties of the systems was studied. Fly ash (FA), anhydrite (ANH), flue-gas desulfurization gypsum (FGDG) and plaster gypsum (PL) were used to develop appropriate CSAC/calcium sulfate and CSAC/calcium sulfate/addition systems, the hydration of which was studied. Tested properties of cements were the compressive strength and the setting times. The results suggest that the use of fly ash in the presence of anhydrite accelerates the formation of a strong ettringite-rich matrix that firmly accommodated unreacted fly ash particles, both synergistically contributing to a dense microstructure. At a given sulfate content, the use of anhydrite was shown to be favourable in terms of the setting times, heat patterns and strength development compared to the hemihydrate-based formulations.     

Preparation and phosphorus recovery performance of porous calcium–silicate–hydrate

Porous calcium–silicate–hydrate was synthesized and used to recover phosphorus from wastewater. The principal objective of this study was to explore the phosphorus recovery performance of porous calcium–silicate–hydrate prepared by different Ca/Si molar ratios. Phosphorus recovery mechanism was also investigated via Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectrum (EDS), Brunauer–Emmett–Teller (BET) and X-ray Diffraction (XRD). The law of Ca²⁺ release was the key of phosphorus recovery performance. Different Ca/Si molar ratios resulted in the changes of pore structures. The increase of specific surface area and the increase in concentration of Ca²⁺ release were well agreement together. The Ca/Si molar ratio of 1.6 for porous calcium–silicate–hydrate is more proper to recover phosphorus. The pore structure of porous calcium–silicate–hydrate provided a local condition to maintain a high concentration of Ca²⁺ release. Porous calcium–silicate–hydrate could release a proper concentration of Ca²⁺ and OH^? to maintain the pH values at 8.5–9.5. This condition was beneficial to the formation of hydroxyapatite. Phosphorus content of porous calcium–silicate–hydrate reached 18.64% after phosphorus recovery.     

The effect of natural dolomite admixtures on calcium zirconate–periclase materials microstructure evolution

The reaction sintering mechanism of dolomite–zirconia mixtures was investigated using fine grounded dolomite raw material and zirconium powder. The used dolomite raw materials differed by the content of impurities (SiO₂, Al₂O₃ and Fe₂O₃ oxides). The microstructure evolution of MgO–CaZrO₃ and CaZrO₃ sintered materials was presented as a temperature function. One- and two-step firing processes of calcium raw materials powder mixed with chemically pure zirconium oxide were applied. The kinetics of reaction of CaZrO₃ synthesis was estimated by determining the “free” calcium oxide by chemical and XRD analysis. The densification process was evaluated by firing shrinkage, apparent density, pore diameter and pore size distribution measurements. The microstructure of sintered materials was observed by SEM. It was observed that CaZrO₃ synthesis was definitely finished at temperature of 1500 °C in the both applied ways of the synthesis (one- or two-step process). The only phase present in the model material synthesized from chemically pure reagents (CaCO₃ and ZrO₂) after firing at temperature of 1500 °C was calcium zirconate.In the materials synthesized from natural dolomites and ZrO₂ two main phases were present—calcium zirconate and periclase. During firing of CaZrO₃–MgO materials at lower temperatures the presence of transient phases was detected (mainly ferrites and calcium aluminates, 4CaO·Al₂O₃·Fe₂O₃ or 2CaO·Fe₂O₃). These phases disappeared at higher temperatures. This is probably related to the dissolution of impurities in the main phases of CaZrO₃–MgO.The material obtained from the mixture of zirconium oxide and natural dolomite with the high impurities content has the highest densification level (～95% theoretical density of CaZrO₃–MgO) at 1500 and 1600 °C.     

Corrosion of spinel clinker by CaO–Al2O3–SiO2 ladle slag

Three different grades of sintered spinel clinker were used containing 47, 69 and 94 wt.% Al₂O₃, respectively, i.e. MgO-rich, stoichiometric and Al₂O₃-rich. Based on these clinkers, the corrosion mechanism of each spinel clinker by CaO–Al₂O₃–SiO₂ slag was investigated and the corrosion and penetration behavior of castables containing powdered spinel clinker examined. A layer of MgO·(Al, Fe)₂O₃ complex spinel formed at the slag-refractory interface was proportional to the MgO content of the spinel clinkers, and it depressed the slag corrosion. The free MgO and spinel minerals in each spinel clinker mainly trapped Fe₂O₃ from the slag. CaO–Al₂O₃ compounds were formed at the slag-clinker interface by the reaction between free Al₂O₃ in the Al₂O₃-spinel clinker and CaO from slag. Slag penetration into the spinel clinkers was retarded by these compounds. As a result of adding fine spinel powder to the matrix of Al₂O₃-based castables, it was observed that higher content of MgO in spinel clinker showed better resistance to slag corrosion but lower resistance to slag penetration.     

Influence of novel shrinkage-reducing polycarboxylate superplasticizer on the nature of calcium–silicate–hydrates

Currently, a novel shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the influence of SR-PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR-PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR-PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR-PCA has a milder impact on C–S–H crystallinity. SR-PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR-PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR-PCA is attributed to the lower adhesion energy of the C–S–H/SR-PCA interface due to the weaker Ca–O bond strength.     

Search of high-capacity cathode materials based on lithium–iron silicate compounds

The crystal structures of 197 lithium–silicate compounds have been analyzed using the method of crystal chemistry analysis (TOPOS software package). The compounds whose structures are characterized with a combination of high values of such parameters as the channel radius, stability, gravimetric capacity, and capacity per volume unit have been revealed: LiFeSiO₄ (R3?), Li₄Fe₂Si₃O₁₀ (C2/c), Li₂FeSiO₄ (Pc2₁ n), and Li₂FeSiO₄ (C222₁). It has been demonstrated that lithium–iron silicates of the monoclinic syngony have high values of the capacity per volume unit, as compared to those of the rhombic syngony. The structural stability of the Li₂FeSiO₄ (Pc2₁ n) framework has been corroborated using the method of computer simulation within the scopes of the electron density functional theory. The obtained information could facilitate creation of novel cathode materials of high capacity and specific accumulated energy.     

Quality design of belite–melilite clinker

We have developed a new cement clinker, consisting mainly of belite and melilite, which is capable of increasing the amount of recycled waste as a part of its raw materials. We analyzed clinkers with a wide range of compositions, and clarified the quantitative relationship between the chemical and mineral compositions. Clinkers consisting mostly of belite and melilite were successfully obtained at the CaO/SiO₂ mass ratio of 1.7 to 1.9. Test cements were prepared using these clinkers and mixed with OPC for the evaluation of fluidity and strength. The belite–melilite cement was found to have good fluidity, and the belite–melilite cement mixed with OPC at up to 30% exhibited a satisfactory long term strength equivalent to the OPC, demonstrating the potential as an alternative to OPC. Electron probe microanalysis revealed the relatively high concentration of diphosphorus pentaoxide in belite, suggesting this component might contribute to the strength enhancement of the cement.     

The impact of mechanical grinding on calcium aluminate cement hydration at 30 °C

Calcium aluminate cement (CAC) was ground for 1 and 2 h to investigate the impact of mechanical grinding on CAC hydration at 30 °C and CAC-bonded castable strength. Phase composition and microstructure of unground and ground cements after hydration for predetermined times and terminated by the freeze-vacuum drying were compared. The results indicate that the particle size and particle size distribution of CAC were reduced and narrowed, respectively by grinding, thereby favoring the hydration rate and the conversation of C₂AH₈ to C₃AH₆. Then enhanced cement hydration also increases the strengths of castables bonded with milled CAC after drying and firing.     

The Mechanism-Based Inactivation of CYP3A4 by Ritonavir: What Mechanism?

Ritonavir is the most potent cytochrome P450 (CYP) 3A4 inhibitor in clinical use and is often applied as a booster for drugs with low oral bioavailability due to CYP3A4-mediated biotransformation, as in the treatment of HIV (e.g., lopinavir/ritonavir) and more recently COVID-19 (Paxlovid or nirmatrelvir/ritonavir). Despite its clinical importance, the exact mechanism of ritonavir-mediated CYP3A4 inactivation is still not fully understood. Nonetheless, ritonavir is clearly a potent mechanism-based inactivator, which irreversibly blocks CYP3A4. Here, we discuss four fundamentally different mechanisms proposed for this irreversible inactivation/inhibition, namely the (I) formation of a metabolic-intermediate complex (MIC), tightly coordinating to the heme group; (II) strong ligation of unmodified ritonavir to the heme iron; (III) heme destruction; and (IV) covalent attachment of a reactive ritonavir intermediate to the CYP3A4 apoprotein. Ritonavir further appears to inactivate CYP3A4 and CYP3A5 with similar potency, which is important since ritonavir is applied in patients of all ethnicities. Although it is currently not possible to conclude what the primary mechanism of action in vivo is, it is unlikely that any of the proposed mechanisms are fundamentally wrong. We, therefore, propose that ritonavir markedly inactivates CYP3A through a mixed set of mechanisms. This functional redundancy may well contribute to its overall inhibitory efficacy.     

The corrosion resistance of microsilica-containing Al2O3–MgO and Al2O3–spinel castables

Microsilica addition in Al₂O₃–MgO and Al₂O₃–spinel castables helps to improve their flowability and partially accommodate their residual expansion after firing. Nevertheless, there is a lack of conclusive statements in the literature regarding the effects of microsilica on one of the main requisites for steel ladle refractories: corrosion resistance. In the present work, the performance of alumina–magnesia and alumina–spinel with or without microsilica when in contact with a steel ladle slag was evaluated based on three aspects: the material's physical properties, its chemical composition and the microstructural features before the slag attack. According to the attained results, microsilica induced liquid formation and pore growth during sintering, favoring the physical slag infiltration. Moreover, due to this liquid, CA₆ was formed in the matrix, mainly for the Al₂O₃–spinel composition, which also favored the castable dissolution into the molten slag.     

Additive manufacturing of Ca–Mg silicate scaffolds supported by flame-synthesized glass microspheres

Novel manufacturing techniques such as additive manufacturing also referred to as 3D printing hold a critical role in the preparation of novel bioactive three-dimensional glass-ceramic scaffolds. The present paper focuses on the use of Ca–Mg silicates microspheres (Ca₂MgSi₂O₇, i.e. 40 mol% CaO, 20% MgO and 40% SiO₂) for the fabrication of 3D structures by additive manufacturing. In the first step, the crystallization of the åkermanite system was avoided, by feeding nearly fully crystallized precursor powders prepared by conventional melt quenching into oxygen-methane (O₂/CH₄) torch, and solid glass microspheres (SGMs) with diameters bellow 63 μm were prepared. In the second step, the crystallization was utilized to control the viscous flow of SGMs during firing of reticulated scaffolds, obtained by digital light processing (DLP) of the SGMs suspended in a photocurable acrylate binder. The spheroidal shape facilitated a high solid content, up to 77 wt% of the SGMs in the suspension. After burn-out of the organic binder, a fast sintering treatment at 950 °C, for 30 min, led to scaffolds preserving the macro-porosity from 3D printing model (diamond cell lattice) but with well densified struts. The crystallization of 3D scaffolds during the sintering process led to 3D structures with adequate strength-to-density ratio.     

Hot corrosion of RE2SiO5 with different cation substitution under calcium–magnesium–aluminosilicate attack

Rare earth (RE) silicates have been applied as advanced environmental barrier coatings (EBCs) to protect silicon carbide fibers reinforced silicon carbide ceramic matrix from water vapor and molten salt corrosion in engines. This process, however, is limited by volcanic ash corrosion as assessment of ash-induced corrosion is anecdotal and quantitative data are insufficient. In this account, the corrosion behavior of RE monosilicates (RE₂SiO₅, RE = Y, Lu, Yb, Eu, Gd, and La) by calcium–magnesium–aluminosilicate (CMAS), with similar composition as volcanic ash, was comprehensively investigated. Results indicated that RE₂SiO₅ could react with CMAS at 1200 °C at the interface, where the products crystallized in CMAS glass. RE₂Si₂O₇ was formed by the reaction between RE₂SiO₅ and silica (SiO₂) in CMAS, which was followed by corrosion of RE₂Si₂O₇ by CMAS. RE₂SiO₅ with Type B structure showed better resistance toward CMAS than RE₂SiO₅ with Type A structure. Moreover, RE₂SiO₅ with larger radii of RE³⁺ cations led to easy formation of oxyapatite phase; however, RE₂SiO₅ with smaller radii of RE³⁺ cations easily formed garnet phase. Besides, smaller radii RE³⁺ cations induced slower reactions. These findings can contribute to identifying, preventing, and minimizing the damage to matrix components with EBCs caused by volcanic ash.     

The development of a thermodynamic model for Al2O3–MgO refractory castable corrosion by secondary metallurgy steel ladle slags

Alumina magnesia in situ spinel castables are used as ladle refractory lining in the steel industry. In contact with slag, they suffer degradations which limits their performance. The purpose of this article is to predict the thermochemical attack of a slag on alumina magnesia refractory using Factsage^® thermodynamic modeling. To evaluate the reliability of the thermodynamic results, a validation step was carried out, which supported that the database was well adapted to the alumina magnesia spinel system. The corrosion phenomenon was then computed for a simple to a complete system to understand the mechanism and the influence of specific oxides. The model was also compared to corroded microstructures from a steel ladle to evaluate the contribution of each constituent in the castable. The aggregates of alumina react with slag to produce monomineral layers of lime aluminates (CA6 and CA2), while complex spinels (Mg, Fe, Mn)O (Fe₂, Al₂)O₃ are formed from the reaction of the slag with the matrix of the castable. Several oxides (MnO, FeO, Fe₂O₃) from the slag contribute to the formation of the spinel structures. The microstructures of refractories used in steel ladles confirm the main conclusions and the thermodynamic approach.     

Growth of In2O3 Nanowires Catalyzed by Cu via a Solid–Liquid–Solid Mechanism

In₂O₃ nanowires that are 10–50 nm in diameter and several hundred nanometers to micrometers in length have been synthesized by simply annealing Cu–In compound at a relatively low temperature of 550°C. The catalysis of Cu on the growth of In₂O₃ nanowires is investigated. It is believed that the growth of In₂O₃ nanowires is via a solid–liquid–solid (SLS) mechanism. Moreover, photoluminescence (PL) peaks of In₂O₃ nanowires at 412 and 523 nm were observed at room temperature, and their mechanism is also discussed.     

Crystallization of calcium silicate at elevated temperatures in highly alkaline system of Na2O–CaO–SiO2–H2O

In Na₂O–CaO–SiO₂–H₂O system, systematic investigations of phase and morphology of calcium silicate in hydrothermal conditions were concisely conducted for high-value utilization of silicon resource in high-alumina fly ash (HAFA). The results show that crystal composition and phase may be affected by relatively low concentration of NaOH, and sodium ions are rearranged into the structure to form NaCaHSiO₄ and Na₂Ca₃H₈Si₂O₁₂ with different C/S ratio at high concentration of NaOH. In addition, phases in wollastonite group possess the morphology of nanofiber. Formation of nanofiber is attributed to the difference of surface energies between axial and radial direction, and higher temperatures lead to easier growth along radial direction. The preparation of C–S–H with different phases and morphologies can guide for the application of silicate solution with high alkalinity with different purposes.     

Effects of temperature on the atomic structure of synthetic calcium–silicate–deuterate gels: A neutron pair distribution function investigation

Due to the nanocrystallinity of the calcium–silicate–hydrate (C–S–H) gel in ordinary Portland cement-based paste combined with the presence of nanoscale heterogeneities such as varying calcium-to-silicon ratios and incorporation of aluminum in the structure, standard characterization techniques fail to fully capture the complex atomic structure and nanoscale morphology of this important binder phase. Here, neutron pair distribution function (PDF) analysis is applied to a range of deuterated C–S–H gels with varying Ca/Si ratios (denoted C–S–D). In situ temperature measurements reveal that the local atomic bonding environments in C–S–D gel undergo large structural rearrangements due to exposure to elevated temperature (above ~ 200 °C), including the collapse of the C–S–D gel interlayer spacing to 9.6 Å and the emergence of a disordered dicalcium silicate phase (similar to larnite). At lower elevated temperatures, the atom–atom correlations are dominated by scattering from deuterium atoms and therefore can be used to quantify the dehydration kinetics.     

Peculiarities of the composition of solid phases formed in aqueous calcium–silicate systems with a medium of variable acidity

The effect of a medium’s acidity on the composition of the solid phase formed in aqueous calcium-silicate systems is investigated. Solutions of Са(NO₃)₂ and Na₂SiO₃ are used for the synthesis; the pH values were varied in the range 7.00–12.00. Freshly precipitated solid phases and products of their annealing at 1000°C were studied by the methods of Fourier IR spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM).     

Re-crystallization of silica-based calcium phosphate glass prepared by sol–gel technique

Bioactive glass (BG) is a potential material for treating dentin hypersensitivity owing to its high solubility. In this study, we synthesized 80S-BG bioactive glass samples using a sol–gel technique and mixed with various hardening agents. The obtained material could be used in human dentinal dentinal tubule occlusions. X-ray diffraction (XRD), scanning electronic microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) measurements were employed to investigate the physiochemical properties and dentinal dentinal tubule occlusion efficiency by mixing the 80S bioactive glass (80S-BG) with various hardening agents.The major crystallite phase obtained on mixing 80S-BG with phosphoric acid (PA) was Ca(H₂PO₄)₂·H₂O. The mixture of 80S-BG powders and 20, 30, or 40 wt% PA acted as a hardening agent and achieved a dentinal tubule penetration depth of 30.7–62.6 µm.80S-BG on mixing with suitable PA agents exhibited a short reaction time and good operability, making it feasible for use in occluding dentinal tubules. 80S-BG mixed with hardening agents exhibited a greater potential for treating dentin hypersensitivity as compared to the 80S-BG not mixed with any hardening agents.     

The effect of glass composition and structure on photochromic properties of LiF–Al2O3–B2O3 glassy materials

Theoretical Foundations of Chemical Engineering - The glass-forming region of the LiF–Al2O3–B2O3 system and the phase diagram of this region have been studied. Properties of glasses and...