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This manuscript expounds the crystallization behavior of CaO–SiO 2 –MgO–Al 2 O 3 (CSMA) slags towards the smooth operation of the blast furnace, where a structure-oriented elucidation for viscous flow was highlighted for deeper understanding of the crystallization behavior. The CCT curves collected from confocal laser scanning microscopy showed that the initial crystallization temperatures decreased with lower CaO/SiO 2 mass ratios, and the primary crystal phases transformed from a merwinite phase (Ca 3 MgSi 2 O 8 ) with a stronger crystallization ability to a melilite solid solution (Ca 2 Al 2 SiO 7 –Ca 2 MgSi 2 O 7 ) with a comparatively weaker crystallization ability, which correlates well with the variation of Mg/Al mole ratios in melilite and verifies the formation of Ca 2 MgSi 2 O 7 as one of the main reasons for the poor fluidity of the slag. Furthermore, a higher viscosity was observed for modified slags with CaO/SiO 2 mass ratios from 1.34 to 1.05, accompanied by the activation energy increased from 173.0 to 182.7 kJ/mol, which is consistent with the decreased NBO/Si value and the increased Q 3 /Q 2 ratio detected by Raman spectra. The crystal phase with melting point higher than the discharged temperature and the enhanced degree of polymerization of the slag structure will lead to the poor fluidity of the slag, which should be emphasized in the actual modification of the blast furnace slag.

Critical-sized calvarial bone defects remain a significant challenge in orthopedic surgery, especially for irregularly shaped bones. Herein, we devised a customizable scaffold using a combination of 3D-printing and salt leaching techniques. Polycaprolactone (PCL), sodium chloride, and a graphene oxide-merwinite (GOM) nanocomposite were 3D-printed and then immersed in water to remove residual salt. Subsequently, gelatin-based electrospun nanofibers incorporating insulin-like growth factor-1 (IGF1) were applied to the PCL-GOM scaffold. The addition of 15% of GOM nanoparticles to the PCL scaffold increased the compressive strength from 2.2 to 3.8 MPa and the elastic modulus from 17.2 to 29.8 MPa. Apatite precipitates were well formed on the fabricated scaffolds after 28 days of immersion in simulated body fluid. Moreover, the scaffold displayed a gradual release of IGF1 over 28 days. The MTT assay demonstrated non-toxicity of scaffolds towards the MG63 cell line. Interestingly, significantly higher expression of Collagen I, RUNX2, and Osteocalcin were observed in qRTPCR results. Following implantation in calvarial bone defect for 8 weeks, the optimal scaffold demonstrated excellent osteogenic behavior and new bone tissue formation. This work presents a promising biomaterial with potential clinical applications for the treatment of irregular critical-sized bone defects.

In term of hazardous waste vitrification, its slag utilization has become a pivotal part of achieving cost reduction. This research has demonstrated the potential of preparing foam glass ceramics through sintering vitrification slag (VS) and biochar (C). It was inferred in TG-DSC analysis that the appropriate sintering temperature for preparing the foam glass ceramics from VS and C was estimated to be roughly 1000-1050°C. The phase and structural transformation of the VS/C system during the sintering process showed that the C promoted the formations of aluminum oxide, grossular ferrian, and merwinite phase; however, the glassy phase still took a leading role. Synchronously, the crystalline phase forming may impact the pore construction. An excellent foam glass showing a dense glossy surface, an evenly distributed honeycomb structure inside, and outstanding integrated performance could be attained through sintering the VS with 2 wt.% C as well as 2 wt.% Na3P207 at 1050°C for 60 min. The discoveries could offer an emerging way of employing the VS.

Akermanite (Ak) has promising prospects as an innovative bio-ceramic for bone regeneration. The most common fabrication methods to produce pure Ak powders are long-lasting synthesis routes followed by calcination at high temperatures. This study focuses on the use of microwave irradiation of a solution to provide initial Ak-based powder product that after subsequent heat treatment changes to pure Ak powder. The novel process named microwave-assisted sol–gel method actually speeds up the initial and final stages of pure Ak powder production when compared to the traditional sol–gel with later heat treatment stage. The viscous solution containing magnesium nitrate hexahydrate, calcium nitrate tetrahydrate, and tetraethyl ortho-silicate was microwave irradiated for three minutes. X-ray diffraction showed that the microwaved products after calcination treatment at 1200 °C for 4 h were mostly made of Ak and a small amount of merwinite. However, by increasing the calcination treatment to 1300 °C, single-phase akermanite powder was achieved. By subjecting same precursor and subsequent heat treatments, the typical sol–gel method did not yield pure Ak powder. Thermal analyses and scanning electron microscopy examinations showed that the Ak crystallization temperature was lower in the case of the microwave irradiated product than in the conventional sol–gel route. The microwave irradiated product after calcination showed a porous structure formed by necking between the powder particles with a mean particle size of 2 µm. The results of the in vitro bioactivity evaluation indicated that synthesized Ak was bioactive through proving the formation of hydroxyapatite (HAp) on the surface of pure Ak disc after 7 days of immersion in simulated body fluid (SBF). The cell adhesion findings showed that MG-63 cells adhered and spread well on the Ak disc, suggesting that Ak discs possess good biocompatibility. The results of the MTT assay demonstrated that the cell proliferation of osteoblast-like MG-63 cells was enhanced with the increase in culture time. Our in vitro bioactivity, cell morphology, and adhesion evaluations and in vitro biocompatibility assessment suggested that Ak powders were bioactive and cytocompatible and have a great potential to be selected as an ideal candidate for bone tissue engineering applications. Graphical Abstract

This work focuses on the relationship between structure and microwave dielectric properties of Ca3MgSi2O8 ceramic via Rietveld refinement, excluded porosity calculation model, complex chemical bond theory, and harmonic oscillator model. A merwinite phase with P21/c space group is confirmed based on analysis of XRD patterns. The permittivity calculated by refractive-ionicity Eq. (12.33) is within 2% of the measured value (12.56). The Ca–O and Si–O bonds play a crucial role in the dielectric constants and dielectric loss, respectively. The temperature coefficient is related to oxygen octahedron distortion [MgO6]. The infrared spectrum is carried out to analyze intrinsic dielectric properties, which indicates the contribution of the active modes in the far-infrared range to the intrinsic permittivity and loss is dominant.

Marly limestones from the Lower Silurian sedimentary units of the Tunguska basin (East Siberia, Russia) underwent metamorphism along the contact with the Early Triassic Kochumdek trap intrusion. At ≤ 2.5 m from the contact, the limestones were converted into ultrahigh-temperature marbles composed of pure calcite and sulfide-bearing calcsilicate layers. The sulfide assemblages in the gabbro and marbles were studied as potential tracers of spurrite-merwinite facies alteration. The gabbro-hosted sulfides show Fe-Ni-Cu-Co speciation (pyrrhotite and lesser amounts of chalcopyrite, pentlandite, and cobaltite) and positive δ34S values (+2.7 to +13.1‰). Both matrix and inclusion sulfide assemblages of prograde melilite, spurrite, and merwinite marbles consist dominantly of pyrrhotite and minor amounts of troilite, sphalerite, wurtzite, alabandite, acanthite, and galena. In contrast to its magmatic counterpart, metamorphic pyrrhotite is depleted in Cu (3–2000 times), Ni (7–800 times), Se (20–40 times), Co (12 times), and is isotopically light (about –25‰ δ34S). Broad solid solution series of (Zn,Fe,Mn)Scub, (Zn,Mn,Fe)Shex, and (Mn,Fe)Scub indicate that the temperature of contact metamorphism exceeded 850–900 °C. No metasomatism or S isotope resetting signatures were detected in the prograde mineral assemblages, but small-scale penetration of magma-derived K- and Cl-rich fluids through more permeable calcsilicate layers was documented based on the distribution of crack-filling Fe-K sulfides (rasvumite, djerfisherite, and bartonite).

Merwinite synthesized using different fuels were characterised using TGA-DTA, FTIR, SEM/EDX, and TEM/EDX. In vitro biomineralisation assay using simulated body fluid (SBF) as the mineralisation medium showed that both glycine and citric acid sets exhibited good HAp nucleation ability, with glycine sets showing higher degree of HAp nucleation. Mechanical studies demonstrated that glycine sets had the highest mechanical strength, with a compressive strength of 40 MPa compared to 30 MPa for citric acid sets and 20 MPa for urea sets. Antibacterial studies and antifungal assays were performed using the disk diffusion method and broth dilution technique against bacteria Escherichia coli , Staphylococcus aureus , and fungi Aspergillus niger and Fusarium oxysporum . Results showed that glycine sets had highest antibacterial activity against E. coli and S. aureus , with inhibition zone diameters of 25 mm and 20 mm, respectively, while urea sets exhibited lower antibacterial activity. Graphical abstract

Fluorine-based mold fluxes are critical for continuous casting of peritectic steels, controlling heat transfer and preventing cracks. However, environmental and health concerns associated with fluorine have spurred the search for alternative flux compositions. This study applied a factorial design to explore the effects of Na2O, TiO2, B2O3, and fluorine on key properties such as viscosity, crystallization temperature, and melting behavior. Analytical methods, including viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM-EDS), combined with thermodynamic modeling, were used to evaluate performance. Four formulations were selected based on factorial design results. Sample A, with high Na2O, exhibited intense crystallization of merwinite (Ca3MgSi2O8) and perovskite (CaTiO3). Sample B, incorporating B2O3, had reduced crystallization and suitable viscosity (2.97 Pa·s). Sample C, with a slightly higher fluorine content than Sample B and without B2O3, presented balanced low viscosity (1.75 Pa·s) with a moderate crystallization tendency. Sample D, free of fluorine and B2O3, showed high viscosity (4.58 Pa·s) and significant crystallization. These results demonstrate that fluorine-free fluxes with properties comparable to fluorine-based compositions can be developed, offering a sustainable alternative for steelmaking. Industrial trials are necessary to validate their performance under operational conditions.

Evidence for low-pressure incongruent melting of limestone containing up to 40 wt% of silicate minerals (marly limestone) is reported from the Khamaryn–Khural–Khiid Combustion Metamorphic (CM) complex in East Mongolia. Marly limestone exposed to high-temperature metamorphism during wild coal fires has acquired a mineral assemblage consisting of gehlenitic melilite and Al-diopside-to-kushiroite-dominant clinopyroxene as main phases and rare phases of celsian, spinel, perovskite, geikielite, etc. Melting of silicate minerals and calcite produced silicate melts of different compositions and stoichiometric calcitic (CaCO3) or non-stoichiometric carbonatite-like (CaCO3 + CaO) melts. Coalescence of silicate melt drops was followed by the formation of silica-undersaturated Ca-rich and Na-bearing paralava melts. Melilite-nepheline paralavas discovered in the Khamaryn–Khural–Khiid and Nyalga CM complexes in Mongolia have exceptional features of mineralogy and chemistry due to a rare combination of P–T conditions associated with wild coal fires and combustion metamorphism: a high temperature (> 1250 °C) and fluid pressure above 4 MPa that prevented decomposition of calcite. Such paralavas from the two CM complexes are composed of similar mineral assemblages made up of melilite, clinopyroxene, plagioclase, nepheline, Fe–Ca olivines (Ca-fayalite and kirschsteinite), K-Ba feldspars (celsian and hyalophane), spinel-group minerals, and rhönite-kuratite, with broad composition variations. Paralavas of this kind have never been reported before from anywhere. Their local mineralogical and geochemical specificity may be due to variations in the composition of carbonate protolith and in physicochemical conditions above the coal fire foci (T, P, gas composition, oxygen fugacity, and melt cooling rate). Low-pressure melting of calcite and the formation of carbonate (calcitic or carbonatite-like) melts have implications for phase relations in carbonate rocks altered by high-temperature metamorphism and metasomatism, as well to the origin of carbonatites. Calcite in carbonate sediments exposed to low pressures and high temperatures (above the invariant point Q1 in the CaCO3 phase diagram) does not decompose and can melt. Correspondingly, metamorphic decarbonation reactions do not produce CaO required for the crystallization of many Ca-rich index minerals of spurrite–merwinite facies. The melting point of calcite decreases markedly with increasing H2O content in the H2O–CO2 fluid, which may lead to melting of calcite in carbonate sediments and to formation of calcite-rich carbonatites at P–T crustal conditions.

Homogeneous single crystals of synthetic monticellite with the composition Ca0.88Mg1.12SiO4 (Mtc I) were annealed in a piston-cylinder apparatus at temperatures between 1000 and 1200∘C, pressures of 1.0–1.4 GPa, for run durations from 10 min to 24 h and applying bulk water contents ranging from 0.0 to 0.5 wt% of the total charge. At these conditions, Mtc I breaks down to a fine-grained, symplectic intergrowth. Thereby, two types of symplectites are produced: a first symplectite type (Sy I) is represented by an aggregate of rod-shaped forsterite immersed in a matrix of monticellite with end-member composition (Mtc II), and a second symplectite type (Sy II) takes the form of a lamellar merwinite–forsterite intergrowth. Both symplectites may form simultaneously, where the formation of Sy I is favoured by the presence of water. Sy I is metastable with respect to Sy II and is successively replaced by the latter. For both symplectite types, the characteristic spacing of the symplectite phases is independent of run duration and is only weeakly influenced by the water content, but it is strongly temperature dependent. It varies from about 400 nm at 1000∘C to 1200 nm at 1100∘C in Sy I, and from 300 nm at 1000∘C to 700 nm at 1200∘C in Sy II. A thermodynamic analysis reveals that the temperature dependence of the characteristic spacing of the symplectite phases is due to a relatively high activation energy for chemical segregation by diffusion within the reaction front as compared to the activation energy for interface reactions at the reaction front. The temperature dependence of the characteristic lamellar spacing and the temperature-time dependence of overall reaction progress have potential for applications in geo-thermometry and geo-speedometry.