SiO2 Melts Research Articles

Liquidus of SiO2 in the Li2O‐SiO2, Na2O‐SiO2, and K2O‐SiO2 systems

AbstractThe phase equilibria in the SiO2‐rich region of the Li2O‐, Na2O‐, and K2O‐SiO2 systems at 1550°C to 1650°C were experimentally studied to determine accurate liquidus of SiO2 in the systems. A classical equilibration/quenching method was used, and the equilibrated samples were analyzed by X‐ray diffraction (XRD) and electron probe microanalysis (EPMA). Samples were contained in sealed Pt crucibles and held at the target temperatures for 7–21 days to reach equilibrium condition. Sealed Pt crucibles were employed to avoid the volatile loss of alkali oxides during high temperature phase equilibration and hydration upon quenching. Accurate liquidus of SiO2 in alkali‐silicate systems was determined for the first time, and the results were analyzed using the limiting slope rule in order to understand the dissolution behavior of alkali oxides in SiO2 melt. It was confirmed that alkali oxide dissolves in SiO2 melt by producing Li+, Na+, and K+ cationic species rather than Li22+, Na22+ and K22+ species.

Ablation behavior and mechanisms of Cf/(CrZrHfNbTa)C‒SiC high‐entropy composite at temperatures up to 2450°C

AbstractThe oxide layer formed by ultra‐high melt point oxides (ZrO2, HfO2) and SiO2 glassy melt is the key to the application of traditional thermal structural materials in extremely high‐temperature environment. However, the negative effect of ZrO2 and HfO2 phase transitions on the stability of oxide layer and rapid volatilization of low viscosity SiO2 melt limit its application in aerospace. In this study, the ablation behavior of Cf/(CrZrHfNbTa)C‒SiC high‐entropy composite was explored systematically via an air plasma ablation test, under a heat flux of 5 MW/m2 at temperatures up to 2450°C. The composite presents an outstanding ablation resistance, with linear and mass ablation rates of 0.9 µm/s and 1.82 mg/s, respectively. This impressive ablation resistance is attributed to the highly stable oxide protective layer formed in situ on the ablation surface, which comprises a solid skeleton of (Zr, Hf)6(Nb, Ta)2O17 combined with spherical particles and SiO2 glassy melt. The irregular particles provide a solid skeleton in the oxides protective layer, which increased stability of the oxide layer. Moreover, the spherical particles have a crystal structure similar to that of Ta2O5 and are uniformly distributed in SiO2 glassy melt, which hinder the flow of SiO2 glassy melt and enhance its viscosity to a certain degree. And it reduces the volatilization of SiO2. In summary, the stable oxide layer was formed by irregular particles oxide and the SiO2 glassy melt with certain viscosity, thereby resulting in the impressive ablation resistance of the composite. This study fills a gap in ablation research on the (CrZrHfNbTa)C system.

Study on Micro Structural Properties of Alkali - Doped SiO2 Melt Using Molecular Dynamics Simulation

Molecular dynamics (MD) simulation could provide details about local microstructure at atomic level, so we use this method to investigate micro-structural properties of sodium in Na2O-doped SiO2 melt. Additionally, we calculated the Voronoi polyhedrons to determine the spatial distribution of atoms in the simulation models. The result shows that many bridging oxygen (BO) polyhedrons and all Si-polyhedrons do not contain Na atoms. Most non-bridging oxygen (NBO) polyhedrons contain 2, 1 or no Na atoms, where BO, NBF is the O bonded with 2 and 1 or no Si, respectively. Average volume per polyhedron decreases in order: NBFx-polyhedron ® BOx-polyhedron ® Six-polyhedron. Na atoms are found in NBFx-polyhedrons and frequently move through them leading to very fast diffusivity of Na in comparison with Si and O. The simulation shows that the number of neighbors around the NBFx-polyhedron is larger than that around the BOx-polyhedron.

Weak magnetic effect and free radical reaction mechanism on the dissolution of lightweight magnesia in CaO–Al2O3–SiO2 melts

Lightweight magnesia-based refractories play a crucial role in achieving energy savings and carbon reduction in steelmaking furnaces. The primary requirement is to make lightweight magnesia refractories with high corrosion resistance. The introduction of a weak static magnetic field is also a promising way to improve the slag resistance of lightweight refractories in addition to optimizing the composition and structure of the refractories. In this paper, the dissolution behavior of the lightweight magnesia in CaO–Al2O3–SiO2 molten slags at and above 1600 °C under weak static magnetic field is presented. The influence of the weak static magnetic field on the dissolution rate was analyzed, the behavior from the perspective of free radical and kinetics was discussed, and the influence of different calcia–silica weight ratios (C/S) on slag, magnetic flux density and the reaction mechanism are revealed. The results show that the dissolution rate of the lightweight magnesia in the molten slag presents a significantly weak magnetic effect, with a reaction inhibition interval of 2–4 mT in the range of 0–16 mT magnetic field intensity, and the key inhibition threshold surpasses that of alumina. The mechanism of the free radical formation and reaction during magnesia dissolution in high-temperature slag is explained and illustrated. The relationship between the magnetic flux density, superoxide radical content, and dissolution rate is presented, providing theoretical guidance for developing magnetic combined magnesia refractories.

Paleozoic Episodic Magmatism in Western Tianshan: Insight Into Assembling the Northeastern Pangea

AbstractThe late‐stage union of Pangea was associated with the convergence of Siberia with Laurussia, but the exact timing remains unclear. The orogenic duration of the Kazakhstan block can provide geochronological constraints as it connects Siberia, Baltica, and Tarim. Zircon petrochronology offers a reliable approach for ascertaining the lifespan of an ancient orogen. In this study, we explore three phases of magmatism recorded in detrital zircons from late Paleozoic and Mesozoic sandstone‐siltstones in Western Tianshan, that is, 400–470 Ma, 320–380 Ma, and 280–320 Ma. Based on their age‐propagated Hf isotopes, melt SiO2 contents, and crustal thicknesses, our findings suggest that the southern limb of Kazakhstan underwent the early Paleozoic amalgamation of microcontinents with arcs, the late Paleozoic maturation of an Andean‐like continental arc, and the late Carboniferous collision of Kazakhstan with the Junggar oceanic basin and the Tarim craton. Such characteristics manifest the long‐term orogenic progression of Kazakhstan. Combining published timelines and paleolatitudes of major orogens and blocks, we propose that the Kazakhstan block welded northeastern Pangea along with the cessation of these orogenic activities around it. Consequently, by docking Kazakhstan with surrounding cratons, the fundamental configuration of Pangea could have been established in the late Carboniferous.

Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200 °C

Over the past two decades, superhydrophobic surfaces that are easily created have aroused considerable attention for their superior performances in various applications at room temperature. Nowadays, there is a growing demand in special fields for the development of surfaces that can resist wetting by high-temperature molten droplets (>1200 °C) using facile design and fabrication strategies. Herein, bioinspired directional structures (BDSs) were prepared on Y2O3-stabilized ZrO2 (YSZ) surfaces using femtosecond laser ablation. Benefiting from the anisotropic energy barriers, the BDSs featured with no additional modifiers showed a remarkable increase from 9.2° to 60° in the contact angle of CaO–MgO–Al2O3–SiO2 (CMAS) melt and a 70.1% reduction in the spreading area of CMAS at 1250 °C, compared with polished super-CMAS-melt-philic YSZ surfaces. Moreover, the BDSs demonstrated exceptional wetting inhibition even at 1 400 °C, with an increase from 3.3° to 31.3° in contact angle and a 67.9% decrease in spreading area. This work provides valuable insight and a facile preparation strategy for effectively inhibiting the wetting of molten droplets on super-melt-philic surfaces at extremely high temperatures.

Study on SiO2 Melting Rule Based on Image Analysis

Study on SiO2 Melting Rule Based on Image Analysis

Rare-earth elements improving the corrosion resistance of YSZ/CMAS heterojunction with stacking faults: First-principles calculation

Stacking faults cannot be fully eliminated from yttrium partially stabilized zirconia (YSZ) ceramic coatings. However, their influence on the corrosion resistance of YSZ ceramics has remained unclear up till now. In this study, the impact of stacking faults on the corrosion resistance of YSZ with or without Nd dopant in CaO, MgO, Al2O3 and SiO2 (CMAS) melts was characterized via first-principles calculations. As expected, the stacking faults decrease the corrosion resistance of YSZ, especially at the saddle point along the slip way within the YSZ(111)V surface. Moreover, the Nd dopant can increase the corrosion resistance of YSZ due to its enhanced structural stability and enlarged wetting angle. Thoroughly analyzing the growth of stacking faults, it is found that the most pronounced effect of Nd dopant on the corrosion resistance of YSZ occurs only at the initial and final stages, whereas being less noticed at the saddle point of the slip way of faults. In addition, compared to the earlier studies, it is established that the largest penetration depth within the ceramic is achieved by Si ions, which broadens the knowledge about the main corrosion factors, as well as reveals the weakest O-Ca bond and the largest diffusion constants of Ca and Mg ions. Thus, the findings of this work open up new prospects for understanding the corrosion mechanism of YSZ TBCs in CMAS melt.

Microstructure evolution and ablation mechanisms of Csf/ZrB2-SiC composites at different heat fluxes under air plasma flame

In this study, short carbon fibre (Csf) reinforced ZrB2-SiC composites were fabricated via direct ink writing followed by precursor infiltration and pyrolysis. The ablation behaviour of the composites was investigated at heat fluxes of 4–6 MW/m2 under an air plasma flame, which revealed excellent ablation resistance with negative linear ablation rates of − 0.1 to − 0.5 µm/s. The results showed that ZrO2-SiO2 oxide layer was formed on the ablation surface after ablation, which provided effective protection to the internal materials. With an increase in heat flux, ZrO2 precipitated from the SiO2 melt first in the form of nano-tetragonal ZrO2 (t-ZrO2), owing to the vaporisation of SiO2. During cooling, the nano t-ZrO2 particles were retained, and some of them reacted with SiO2 to form ZrSiO4, thus improving the thermal stability of the SiO2-ZrO2 oxide layer. In contrast, t-ZrO2 agglomerated and grew owing to capillary force and finally transformed into monoclinic ZrO2 (m-ZrO2). Moreover, a higher heat flux led to the size of precipitation ZrO2 increases, meanwhile increasing the content of t-ZrO2 and ZrSiO4 in the oxide layer.

Investigation on surface tension of CaF2–CaO–SiO2 (–MgO–Al2O3) melts

In this work, the surface tension of CaF2–CaO–SiO2 melt with high CaF2 contents was measured by pulling cylinder method at 1773 K. The effects of CaF2 content, basicity, and the addition of MgO and Al2O3 on the surface tension were also investigated by considering the change in the melt structure. It was observed that as the CaF2 content increased from 30 to 80 mass%, there was no further depolymerizing effect on the silicate structure of the melt, maintaining a constant basicity of 1. However, the surface tension of the melts decreased from 397 to 325 mN/m due to the surface-active effect of CaF2. With the increase of basicity from 0.5 to 3, the surface tension of the melt initially increased from 342 mN/m to a maximum value of 390 mN/m, then decreased to 368 mN/m. The maximum value occurred at a basicity of 2. Furthermore, at constant basicity, the addition of MgO from 0 to 10 mass% led to a decrease in the surface tension of the melt decreased from 358 to 326 mN/m. Similarly, with the basicity ranging from 1 to 3, the addition of 10 mass% Al2O3 resulted in a decrease in the surface tension of the melt.

Multi‐ion diffusion model and application to solid dissolution in CaO–Al2O3–SiO2 melts

AbstractA general multi‐ion diffusion model for liquid slag is developed for silicate melts by combining the tracer diffusivities of ions and chemical potentials from the CALculation of PHAse Diagrams thermodynamic database. For the demonstration of the model, the tracer diffusivities of Ca, Al, Si, and O ions in CaO–Al2O3–SiO2 melts were optimized as functions of temperature and composition using available isotope experimental data. The present model successfully simulates liquid‐junction diffusion in the CaO–Al2O3–SiO2 system and the dissolution of solid SiO2 and Al2O3 particles in CaO–Al2O3–SiO2 melts. Furthermore, the model can be readily expanded to multicomponent systems, making it potentially applicable to refractory dissolution in liquid slag and various other diffusion‐controlled high temperature processes involving liquid oxide melts.

The youngest lunar zircon reveals an extremely fractionated nature of Chang’e-5 basalt

The U(Pb)-Pb age of zircon is commonly used to represent the crystallization age for igneous rocks due to its high closure temperature and robust resistance to impact disturbance. However, no zircon crystallization age has yet been reported for Chang'e-5 (CE-5) basalt due to their limited occurrence in mare basalt. In this study, rare zircon grains from CE-5 lunar samples were investigated by the in-situ Pb isotopic analysis, and a precise zircon crystallization age of 2036 ± 19 Ma was determined from Pb-Pb isochron. This is hitherto the youngest reported crystallization age of lunar zircon, similar to the ages of CE-5 lunar basalts obtained by zirconium (Zr)-bearing minerals such as baddeleyite, tranquillityite, and zirconolite. Petrographic evidence and rare-earth element geochemistry indicate that zircon in the CE-5 lunar basalts were formed by the reaction of early-formed baddeleyite with SiO2 melt within the latest residue of extreme fractionation of a non-KREEP (an acronym for potassium, REE, and phosphorus) basaltic magma. In contrast to the prevailing view that lunar zircon have formed in late-stage enriched melts resulting from extensive fractional crystallization of the Lunar Magma Ocean, this study shows that zircon could be derived from extreme fractionation of non-KREEP basaltic magma unrelated to Lunar Magma Ocean.

Large-scale Molecular-dynamics Simulations of SiO2 Melt under High Pressure with Robust Machine-learning Interatomic Potentials

We have carried out molecular-dynamics simulations of SiO2 melt at 60 GPa in a system of about 30,000 atoms, with robust machine-learning interatomic potentials based on ab initio calculations. The large-scale simulations not only reproduced the ab initio calculations, but were also found to significantly improve the precision of the intermediate-range structure. Interatomic potentials determined using machine learning easily destabilize simulations of highly covalent melts under high pressure in an extended system with over one order of magnitude more atoms than those in the initial calculations used for data generation. The combination of potential averaging and active learning can efficiently suppress computational instability.

Effects of H2O–CO2 Fluids, Temperature, and Peridotite Fertility on Partial Melting in Mantle Wedges and Generation of Primary Arc Basalts

Abstract Many lines of evidence from high P–T experiments, thermodynamic models, and natural observations suggest that slab-derived aqueous fluids, which flux mantle wedges contain variable amounts of dissolved carbon. However, constraints on the effects of H2O–CO2 fluids on mantle melting, particularly at mantle wedge P–T conditions, are limited. Here, we present new piston cylinder experiments on fertile and depleted peridotite compositions with 3.5 wt.% H2O and XCO2 [= molar CO2 / (CO2 + H2O)] of 0.04–0.17. Experiments were performed at 2–3 GPa and 1350°C to assess how temperature, peridotite fertility, and XCO2 of slab-derived fluid affects partial melting in mantle wedges. All experiments produce olivine + orthopyroxene +7 to 41 wt.% partial melt. Our new data, along with previous lower temperature data, show that as mantle wedge temperature increases, primary melts become richer in SiO2, FeO*, and MgO and poorer CaO, Al2O3, and alkalis when influenced by H2O–CO2 fluids. At constant P–T and bulk H2O content, the extent of melting in the mantle wedge is largely controlled by peridotite fertility and XCO2 of slab-fluid. High XCO2 depleted compositions generate ~7 wt.% melt, whereas, at identical P–T, low XCO2 fertile compositions generate ~30 to 40 wt.% melt. Additionally, peridotite fertility and XCO2 have significant effects on peridotite partial melt compositions. At a constant P–T–XCO2, fertile peridotites generate melts richer in CaO and Al2O3 and poorer in SiO2, MgO + FeO, and alkalis. Similar to previous experimental studies, at a constant P–T fertility condition, as XCO2 increases, SiO2 and CaO of melts systematically decrease and increase, respectively. Such distinctive effects of oxidized form of dissolved carbon on peridotite partial melt compositions are not observed if the carbon-bearing fluid is reduced, such as CH4-bearing. Considering the large effect of XCO2 on melt SiO2 and CaO concentrations and the relatively oxidized nature of arc magmas, we compare the SiO2/CaO of our experimental melts and melts from previous peridotite + H2O ± CO2 studies to the SiO2/CaO systematics of primitive arc basalts and ultra-calcic, silica-undersaturated arc melt inclusions. From this comparison, we demonstrate that across most P–T–fertility conditions predicted for mantle wedges, partial melts from bulk compositions with XCO2 ≥ 0.11 have lower SiO2/CaO than all primitive arc melts found globally, even when correcting for olivine fractionation, whereas partial melts from bulk compositions with XCO2 = 0.04 overlap the lower end of the SiO2/CaO field defined by natural data. These results suggest that the upper XCO2 limit of slab-fluids influencing primary arc magma formation is 0.04 < XCO2 < 0.11, and this upper limit is likely to apply globally. Lastly, we show that the anomalous SiO2/CaO and CaO/Al2O3 signatures observed in ultra-calcic arc melt inclusions can be reproduced by partial melting of either CO2-bearing hydrous fertile and depleted peridotites with 0 < XCO2 < 0.11 at 2–3 GPa, or from nominally CO2-free hydrous fertile peridotites at P > 3 GPa.

Experimental Equilibrium and Fractional Crystallization of a H2O, CO2, Cl and S-Bearing Potassic Mafic Magma at 1.0 GPa, With Implications for the Origin of Porphyry Cu (Au, Mo)-Forming Potassic Magmas

ABSTRACT The origin of intermediate to felsic potassic magmas is debated, and not much is known about the volatile content of potassic magmas associated with porphyry Cu (Au, Mo) deposits. To better understand the liquid line of decent of mafic potassic magmas and the behavior of volatiles during magma differentiation, we performed 19 experiments at 1.0 GPa and 1150 °C to 850 °C using piston cylinder presses. We developed a new experimental technique that involves a capsule liner made of single-crystal zircon to prevent the loss of Fe and S in the starting material to the noble metal capsule. The starting material is a high-Mg, basaltic trachyandesite (52 wt% SiO2, 12 wt% MgO, 1.9 wt% Na2O and 5.3 wt% K2O) from the Sanjiang region in southwestern China, doped with geologically realistic amounts of volatiles (i.e. 4.0 wt% H2O, 0.34 wt% CO2, 0.27 wt% Cl and 0.25 wt% S). The addition of 0.25 wt% S in the form of anhydrite internally buffered the experiments at an oxygen fugacity of 2.0 ± 0.5 log units above the fayalite–magnetite–quartz buffer, which is similar to the redox state of the Sanjiang variously evolved potassic magmas. The experimentally produced silicate melts match well with the Sanjiang intermediate to felsic magmas in terms of major, minor and trace element compositions, and also with regard to the S and Cl contents. The sequence of crystallizing minerals (olivine + clinopyroxene –> biotite ± orthopyroxene –> apatite –> K-feldspar) also fits with the one observed in the Sanjiang mafic to intermediate magmas. These results suggest that the Sanjiang intermediate to felsic magmas, including the porphyry Cu (Au, Mo)-forming magmas, can form solely by differentiation of potassic mafic magmas without any involvement of old crustal material. During experimental differentiation at 1.0 GPa, the S content of the evolving silicate melt first increased until ~57 wt% melt SiO2, and then decreased in response to precipitation of sulfides, sulfate melt and/or anhydrite, whereas the H2O and Cl contents of the evolving silicate melt increased exponentially until saturation in a CO2-rich fluid was reached at 60 to 65 wt% melt SiO2 and ~ 8 wt% melt H2O. During further magma differentiation the H2O and Cl contents of the evolving silicate melt remained constant until ~70 wt% melt SiO2, after which point the Cl content of the silicate melt decreased due to increased partitioning of Cl into the fluid phase ± increased fluid/melt ratio. Based on these experimental results and petrographic and geochemical evidence from natural samples, the Sanjiang porphyry Cu (Au, Mo)-forming magmas (65–70 wt% SiO2) are interpreted to have formed through differentiation of primitive, mantle-derived, potassic magmas in the lower crust (≥1.0 GPa), and to have ascended ±directly from the lower crust to shallow crustal levels. They likely contained 8 to 13 wt% H2O, 0.37 to 0.90 wt% Cl and 0.07–0.29 wt% S. This case study on the magma evolution in the Sanjiang region may have implications for the origin and nature of intermediate to felsic potassic magmas in various tectonic settings.

Trace element partitioning coefficients between terrestrial silicate melts and plagioclase feldspar: Improved and simplified parameters

Nernst partition coefficient data are compiled and parameterized against commonly measured and petrologically significant Input Variables, allowing plagioclase/meltD values for 37 trace elements to be calculated. With few exceptions plagioclase/meltDs increase with decreasing temperature, anorthite-content of plagioclase (An), wt% melt MgO and FeO* (all iron as FeO), molar melt Mg/(Mg + Fetotal); and with increasing wt% melt SiO2 and Na2O + K2O. High field strength cations and rare earth elements (REE) with similar ionic radii have nearly fixed ratios of LnD (e.g. LnDLa/LnDCe). These can be linked as a chain to construct a nearest-neighbour plagioclase/meltDREE (NN-DREE) profile from a point of origin at DCe. Correlations between LnDCe and An content in the partitioning data were regressed to connect these variables algebraically. Analysis of these NN-DREE profiles with the Lattice Strain Model (LSM) requires a temperature value, which was pre-defined by fitting simplified temperature-An paths to experimental data binned for melt H2O content. In the LSM, r3+0 is the size of the site into which REE substitute. Three published r3+0 parameterizations were tested. The Dohmen and Blundy (2014) parameterization of r3+0 [Å] (r3+0 = 1.331 − 0.067An) yielded the best fits to the NN-DREE profiles when values of D3+0 and E3+M were optimized. D3+0 is the strain compensated partition coefficient and E3+M is Young’s Modulus of the M-site hosting REE. Starting from the preferred r3+0 parameterization, NN-DREE profiles at many An contents were fit with a LSM by varying D3+0 and E3+M. These multiple fits yielded a tight linear trend of increasing LnD3+0 with decreasing An content [LnD3+0 = (−2.8323An) – 0.0538] applicable to all three temperature-An functions. Previously proposed parameterizations of Young’s Modulus E3+M can reproduce DREE profiles of very calcic plagioclase (>An0.9), but yield profiles that are too steep to fit DREE profiles of more sodic compositions. The LSM fits for dry melts (H2O < 1%) yield a trend of linearly-decreasing LnE3+M with decreasing An content [LnE3+M = (1.2808An) + 3.4897]. The temperature-An functions for wet (1–5% H2O) and very wet (>5% H2O) melts yield similar LnE3+Mvs An trends, but at lower LnE3+M to compensate for lower temperatures. With these parameterizations of temperature, r3+0, D3+0 and E3+M, the NN-DREE Lattice Strain Model reproduces the increasingly flatter and higher DREE profiles of plagioclase crystallizing from basaltic to rhyolitic melts, with An-content as the sole Input Variable needed.

Contraints on Petrogenesis and Fe Fertility of Intrusive Complexes in the Han–Xing Region, North China Craton from Apatite Geochemistry

The Han–Xing (Handan–Xingtai) region is famous for its endowment of skarn iron deposits in China. These deposits are mainly spatially and genetically associated with diorite rocks, but these rocks show different Fe ore potential. Major and trace elements composition of apatite from the Kuangshan and Fushan diorite complexes were investigated to explore the potential of apatite as a proxy of petrogenesis and Fe fertility of these rocks. All the investigated apatite grains are identified as fluorapatite, which is typical for magmatic apatite. The Sr, Y, Mn, and Heavy Rare Earth Elements (HREE) contents of apatite in the Kuangshan diorite complex are positively correlated with the increase of melt SiO2 content compared to that in the Fushan diorite complex. Apatite geochemistry indicates that magmas of the Fushan complex mainly experienced the fractional crystallization of hornblende in the deep crustal reservoirs, whereas the Kuangshan complex has experienced the fractional crystallization of hornblende in the deep and the shallow plagioclase fractional crystallization. The F, Cl and S content of the Kuangshan complex estimated by apatite volatile (F = 2632 ppm, Cl = 4100 ppm, SO3 = 140 ppm) is significantly higher than that of the Fushan complex (F = 2488 ppm, Cl = 3400 ppm, SO3 = 90 ppm). The Eu, Ce anomalies, Mn, and SO3 contents of apatite show that both of the two complexes have higher oxygen fugacity (Δ FMQ), but the oxygen fugacity of the Kuangshan complex calculated by Mn and SO3 content (Δ FMQ + 2.41) is higher than that of the Fushan complex (Δ FMQ + 1.77), which may also be one of the reasons for the great difference in ore-forming scale between the two complexes. Our results suggest that the high volatile contents and oxidation states of magma estimated by apatite, as well as the lower Sr/Y in apatite reflect favorable conditions for skarn iron mineralization. Therefore, our study shows that magmatic apatite geochemistry may be a useful tool to distinguish the Fe fertility of plutonic rocks related to skarn deposits.

SPS densification and ablative performance of ZrB2–SiC–ZrC composites derived from the ternary powders by sol-gel

ZrB2–SiC–ZrC (ZSZ) composite ceramics were successfully prepared by sol-gel method combined with spark plasma sintering (SPS) technology. ZrB2–SiC–ZrC multiphase powders with a scale of about 100 nm were firstly synthesized by sol-gel method at 1500 °C. The sintering performance of the sol-gel powders was compared with compositionally similar commercial powders mixture by SPS. The relative densities of the corresponding target composite (ZSZ1) and reference composite (ZSZ2) were reached to 96.2% and 92% under 2000 °C/40 MPa, respectively. The densification curves indicated that the residual SiO2 and B2O3 oxides derived from the precursor triggered the liquid phase sintering mechanism of sol-gel powders above 750 °C. The removal of oxide impurities through carbothermal reduction, and the diffusion and attachment of the liquid phase at the grain boundary jointly promote the densification of ZSZ1. ZSZ1 presented better oxidation/ablation resistance than ZSZ2 during the oxyacetylene ablation tests for 200 s. The mass and line ablation rate of ZSZ1 were only −4.268 × 10−4 g/s and −8.32 × 10−3 mm/s, respectively, which is attributed to be the structure of ZrO2 fine particles uniform distributed in SiO2 melt.

Ultrasonic assisted reactive synthesis and characterization of Al–MgAl2O4 in-situ composite

The current study investigates the impact of Ultrasonic Treatment (UT) upon the microstructure and mechanical characteristics of Al–MgAl2O4 in-situ composite prepared using SiO2 oxide source and Al-2wt.% Mg alloy. According to the findings, because of UT in composite melt SiO2 reaction has been enhanced (86%) resulting MgAl2O4 particles of size ranging from 0.2 to 5 μm. The released Si after the silica reaction with Al–Mg has made in-situ alloying with matrix resulting Mg2Si phase formation along with α-Al. In UT composite 67% decrease in overall grain size was observed in the matrix material in comparison with Al–MgAl2O4 non-UT composite. The reinforcement of MgAl2O4 particles, combined with grain size refinement, has substantially enhanced the mechanical properties of the UT composite specifically hardness and tensile yield strength by 40 and 47%, respectively.

Structural Features of K2O-SiO2 Melts: Modeling and High-Temperature Experiments

Despite numerous investigations, the thermodynamic properties of potassium silicates remain apparently contradictory. In situ experiments are complicated by the unstable behavior of a K2O–SiO2 melt in the region of compositions with a high potassium oxide content. In this paper, we study the structure of melts by the method of physicochemical modeling, taking into account the results of high-temperature Raman spectroscopy. To do this, the Raman spectra were curve-fitted, taking into account the second coordination sphere of silicon atoms. From the interpretation of the spectra of K2O–SiO2 glasses and melts having a K2O content of up to 55 mol.%, quantitative characteristics of the system were obtained. Since available information on the thermodynamic properties of potassium silicates is known to be contradictory, coordinated thermodynamic characteristics of potassium silicates, some of which were evaluated, were used as input data for modeling. Structural modeling of glasses and melts of the K2O–SiO2 system was carried out across a range of compositions up to 60 mol.% potassium oxide. The database of structural units of melts of the potassium silicate system, updated according to experimental data, will find practical application in chemistry, geochemistry and engineering fields.