Melt Infiltration Research Articles

High strength C/Si‒Ni‒C composites fabricated by reaction melt infiltration with Si‒Ni alloy at lower temperature

AbstractSilicon‒nickel alloy (Si‒Ni) was first used for fabricating continuous carbon fiber reinforced ceramic matrix composites by reaction melt infiltration process. Based on Si‒Ni phase diagram, 66.7 at.% Si‒Ni was chosen, which has a lower liquidus temperature of 1115°C. The C/Si‒Ni‒C composites were infiltrated at temperature of 1270°C‒1390°C, and the prepared composite consists of C, SiC, NiSi, and NiSi2 phases. The density of the composite is higher than 2.29 g/cm3 and their open porosity is below 3%, indicating the composite was infiltrated completely by the Si‒Ni alloy. The C/Si‒Ni‒C composite exhibits significantly higher flexural strength and fracture toughness compared to the C/C‒SiC composite infiltrated with pure silicon at 1500°C. Specifically, the flexural strength and fracture toughness of the C/Si‒Ni‒C composite infiltrated at 1390°C increase by 140% and 300%, respectively. The improvement of mechanical properties contributed to the low reactivity between silicon‒nickel with carbon fibers, and the lower infiltration temperature, which can reduce degradation of carbon fiber as reinforcement. Moreover, the NiSi2 and NiSi alloy phases in the C/Si‒Ni‒C composite replace the brittle silicon phase in the C/C‒SiC composite, which can obviously enhance the fracture toughness.

Microstructure and ablation behavior of C/C–HfC–SiC composites fabricated by reactive melt infiltration with Hf–Si alloy

AbstractC/C–HfC–SiC composites were prepared by reactive melt infiltration using Hf–Si alloy (Hf, more than 95 wt%) with a density of 3.86 g/cm3 and an open porosity of 8.34%. The microstructure, mechanical properties, and ablation behavior at high temperatures were studied in detail. SiC played a crucial role in alleviating the thermal mismatch between HfC and PyC, which formed at the interface between the carbon matrix and the HfC matrix. The flexural strength and modulus of C/C–HfC–SiC composites were 237 MPa and 37.6 GPa, respectively. The C/C–HfC–SiC composites exhibited excellent ablation resistance with a linear ablation rate of 8.9 × 10−3 mm/s and maintained a surface temperature above 2925°C during ablation. During this process, HfO₂ remained in a molten state with high viscosity and served as a thermal barrier, while the volatilization of SiO₂ effectively removed heat, protecting the composites from further ablation.

GENESIS OF EXTREMELY MAGNESIAN DAUGHTER OLIVINE OF SECONDARY MELT INCLUSIONS FROM OLIVINE MACROCRYSTS IN KIMBERLITE FROM THE UDACHNAYA-EAST PIPE (SIBERIAN CRATON)

The paper presents the results of studies of daughter olivine within secondary melt inclusions marking healed cracks in olivine macrocrysts from unserpentinized kimberlite from the Udachnaya-East pipe. Macrocrysts compose four olivine generations: core olivine (Ol1); olivine marking healed cracks (Ol2); daughter olivine of melt inclusions (Ol3); thin outer rims of olivine (Olr) around macrocryst cores. The relationship between different olivine generations and variations in its chemical composition indicate that macrocrystal cores (Ol1) are grains or grain fragments of disintegrated mantle rocks; melt inclusions and Ol2 were formed due to infiltration of kimberlite melts into the grain cracks. Crystallization of a hybrid melt of inclusions and formation of an extremely magnesian daughter olivine (Ol3) occurred later, at lower PT conditions. Among the daughter minerals in the melt inclusions, in addition to Ol3 there were identified alkaline carbonates, sulfates, chlorides, oxides, and sulfides. It has been shown that the daughter olivine of melt inclusions (Ol3) has high Mg# (97–98) content, high MnO (0.18–0.41 wt. %) and CaO (0.12–0.25 wt. %) concentrations, and low NiO (0.02–0.04 wt. %) contents. The ratios between the daughter minerals of the melt inclusions indicate that the hybrid melt from which extremely magnesian olivine was formed was alkaline carbonate or silicate-carbonate liquid with a low water content. Our study directly showed for the first time that almost pure forsterite is able to be crystallized from evolved kimberlite melts of carbonate or silicate-carbonate composition, which confirms the previously proposed model for the formation of extremely magnesian outer rims of olivine crystals from worldwide kimberlites during crystallization of evolved kimberlite melts of carbonate composition.

Unravelling different mechanisms of metasomatism and geodynamic evolution of pyroxenite-veined subcontinental lithospheric mantle beneath the Central European Variscides

Abstract Pyroxenite-veined garnet peridotites from the Gföhl Unit of the Moldanubian Zone in the Bohemian Massif provide direct constraints on diverse mechanisms of mantle metasomatism and refertilization driven by a single pulse of melt beneath the Central European Variscides. Here, we provide a detailed study on an intriguing example of this rock association where the garnet peridotites show a fertile character (high Al2O3, CaO, TiO2), corresponding to the subcontinental lithospheric mantle (SCLM). By contrast, their conspicuous LREE depletion and Sr–Nd isotopic signatures (87Sr/86Sr338 ≤ 0.7028; εNd338 ~7.3) are typical of depleted mantle residue after melt extraction. Such signatures reflect transformation of an original refractory protolith (likely harzburgite) to fertile lherzolite through percolation of primitive tholeiitic melts, parental to garnet pyroxenite in veins. The SCLM refertilization is further documented by the whole-rock positive correlation between incompatible elements (Zr, Yb, Sc, V), and trace element composition of clinopyroxene (high Ti/Eu and Ti/Nb) and garnet (elevated ∑REE, Zr, Ti). Trace element and Sr–Nd isotopic systematics of pyroxenites (87Sr/86Sr338 ~0.7025–0.7029; εNd338 ≤ 7.9) correspond to a source of melt similar to the depleted MORB mantle (DMM). Three mechanisms of metasomatism related to the interaction of this melt with the host peridotites were distinguished: (i) stealth metasomatism, reflected by extensive clinopyroxene and garnet crystallization in lherzolite adjacent to pyroxenite veins, (ii) cryptic metasomatism, recorded by lower Mg# values of orthopyroxene and olivine in lherzolite, and (iii) modal metasomatism, resulting in crystallization of amphibole and phlogopite in lherzolite close to the veins. The percolating basaltic melt was hydrous, moderately enriched in fluid-mobile elements (Cs, Rb, Ba, Pb, U, Li). Immiscible liquids, dense Ti-Mg-Fe-rich oxide melt and C-O-H fluid, trapped and crystallized as mono/multiphase solid inclusions in garnet, likely separated from a basaltic melt upon cooling. The lherzolite-pyroxenite interface reveals strong micro-scale element fractionation due to differentiation of a basaltic melt within the percolation channel. Volatile-bearing liquids that segregated from the melts migrating through wall-rock peridotites most likely caused chromatographic enrichment in highly incompatible elements (e.g. LREE) in distal peridotites relative to the LREE-depleted lherzolites adjacent to the veins. The DMM-like affinity of pyroxenites and pressure-temperature estimates for lherzolite (3.9–5.4 GPa/1010–1200 °C) and pyroxenites (2.8–4.2 GPa/860–1020 °C) point towards exhumation-driven SCLM refertilization. This was linked to decompression-induced partial melting of upwelling asthenosphere producing basaltic melts penetrating through and metasomatizing the SCLM beneath the Variscan orogenic belt in Central Europe.

Sulfide and Fe-Ti-P liquid immiscibility in the Ni-Cu-Co ovoid deposit of the Voisey’s Bay complex, Labrador, Canada

AbstractIn the Voisey’s Bay complex, sulfide-matrix breccias developed through the percolation of dense sulfide melt, leading to the displacement of the silicate melt within partially molten silicate-matrix breccias. In these sulfide matrix-breccias, hydrous silicate rims are commonly present at the interface between the sulfide matrix and the silicate framework. Multiple lines of evidence support a magmatic origin of these hornblende-biotite rims, which was largely coeval with the emplacement of the sulfide melt in the magmatic breccias. The formation of the hornblende-biotite rims required the addition of alkalis and water that could not have entirely been sourced from either the sulfide melt or the silicate framework. Through the integration of compositional maps with major and trace element analyses of the main accessory minerals, we propose that the critical components required for the development of the hydrous silicate rims in sulfide-matrix breccias originated from an immiscible Fe-Ti-P melt. Distinct textural and compositional features of apatite, hercynite, ilmenite and magnetite support the presence of small amounts of Fe-Ti-P melt in the sulfide melt. This Fe-Ti-P melt likely formed through melt immiscibility in the early stages of the development of the Voisey’s Bay complex, and was transported in the magma conduits together with the sulfide melt.

The microstructure evolution and mechanical properties of WC-cu-10Ni-5Mn-3Sn cemented carbides containing NbC prepared by pressureless melt infiltration

WC-based cemented carbides with different contents of NbC (0, 0.6, 0.8, 1.0, 1.2, and 1.4 wt%) are prepared via pressureless melt infiltration at 1200 °C for 1.5 h. Microstructure evolution regularity of WC-based cemented carbide is investigated to establish the effect of NbC addition and microstructure peculiarities on mechanical properties (flexural strength, hardness, and impact toughness) of final product. Experimental results reveal that NbC firstly dissolves in binder alloy during melt infiltration, which slows down dissolution-precipitation reaction of WC, thus refining WC grains. With the increase in NbC content, average WC grain size shows varying trend, achieving the minimum (3.779 μm) at NbC addition of 1 wt%. When NbC is added in smaller amounts, Nb is mainly distributed throughout binder alloy. With the increase in NbC content, Nb elements tend to form aggregates and attach to WC particle boundaries. Some WC and NbC also decompose under experimental conditions. At NbC addition greater than 1 wt%, decomposition products (Nb, W, and C) combine with other elements in binder phase to form new phases such as (Nb,W)C, Ni2W4C, Nb2C, and Nb4Ni2C. These phases further act as bridges for WC grain coarsening. Meanwhile, excessive NbC is detrimental to mechanical properties of the alloy. With the increase in NbC content, hardness and flexural strength of the alloy increase and then decrease, reaching the maximum values of 93.4 HRA and 1808.786 MPa, respectively, at 1 wt% NbC addition. In turn, impact toughness of the alloy shows consistently downward trend. Therefore, changes in mechanical properties of WC-based cemented carbides are mainly related to WC grain size, the appearance of new phases in binder phase, and their morphology.

Multi-physics coupling numerical simulation of variable porosity in reactive melt infiltration process

Abstract The hypersonic craft necessitates significant advancements in thermal shielding to safeguard against the extreme aero-thermal environments encountered during flight at hypersonic speeds in near space or upon reentry from space. Carbon fiber-reinforced ceramic matrix composites (FRCMCs) have attracted increasingly interesting attention as advanced structural materials for application in thermal protection. The reactive melt infiltration (RMI) process is preferred for the preparation of FRCMCs because of its low cost and short processing time. However, the RMI process includes the complex interplay of melt flow, reaction dynamics, and thermal fields, with existing models failing to accurately predict these processes due to their uncoupled nature and neglect of pore structure changes. This study introduces a coupled model that integrates mass transfer flow, chemical reaction, and heat transfer, incorporating variable pore structures to more accurately evaluate the RMI process. This approach allows for a comprehensive assessment of internal pressure, temperature, and porosity changes during silicon infiltration into porous media, marking an improvement over the previous model. The model has been validated for use in predicting the exotherm of RMI processes. In conclusion, this coupled model presents a promising avenue for enhancing the fabrication of FRCMCs, either considering the melt infiltration from multiple locations in the RMI process or adjusting the pore structure at the infiltration location to larger pores.

Ablation behavior of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-SiC-Si ceramics via reactive melt infiltration

(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-SiC ceramics with an open porosity of only 0.49 % were successfully fabricated in this work by the reactive melt infiltration (RMI) method. Air plasma flame ablation behavior of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-SiC ceramics under 2300 °C temperature exhibited excellent resistance with mass and linear ablation rates of 3.66 mg/s and 0.88 μm/s, respectively. During ablation, the transition from continuous melting sublimation of Si and oxidation of SiC to oxidation of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 occurred. The uphill diffusion of Ti atoms transited (Ti,Zr,Hf,Nb,Ta)Ox to Ti(NbxTa1-x)2O7 while Zr0.5Hf0.5O2 continuously precipitated. A multicomponent oxide layer of (Ti,Zr,Hf,Nb,Ta)Ox along with (Zr,Hf)6Ta2O17, (Hf,Zr)(TiO4)2, and (Zr,Hf)x(Ti,Ta)1-xO embedded in SiO2 melt was eventually formed on the ceramic surface. This oxide layer was spread above the high melting point Zr0.5Hf0.5O2, Ti(NbxTa1-x)2O, and low oxygen content (Ti,Zr,Hf,Nb,Ta)Ox to form a stable, dense, and high viscosity protective layer.

Water vapor corrosion behavior of SiC-Al40Y ceramics fabricated by reactive melt infiltration and thermal diffusion

The corrosion resistance of Y-Al diffused SiC ceramics (SiC-Al40Y) at 1100-1300 °C was investigated. The results show that the weight gain curves comply with the parabolic fitting formula, then the oxidation rate constant and the activation energy were calculated to be 1.653×10-5 (1100 °C), 3.704×10-5 (1200 °C), 9.306×10-5 (1300 °C) mg2/cm4s and 154.7 kJ/mol. Compared with reported SiC (41-147 kJ/mol), the higher activation energy indicates the better corrosion-resistant performance. And it is found that the Y-Al diffusion layers can be transformed to corrosion-resistant YAlSixOy layers under corrosive atmosphere. Eventually, based on experimental results, the corrosion-resistant mechanism is analyzed: chemical potential gradient caused by preferential oxidation of Y-Al prompts the immigration of Y-Al from matrix to surface, gradually forming a continuous Y/Al-silicate layer on the surface and thus can hinder the further corrosion of H2O, O2.

Li enrichment in peridotites and chromitites tracks mantle-crust interaction

The ultramafic massifs of the Serranía de Ronda in southern Spain are the Earth's largest exposures of subcontinental lithospheric mantle (SCLM) peridotites (∼450 km2). These ultramafic massifs experienced asthenosphere melt percolation during their crustal emplacement. Mixing of these mafic melts with anatectic melts and fluids led to the formation of a world's unique Ni-arsenide-rich chromitite ores (hereafter CrNi ores) associated with orthopyroxenite and/or cordieritite (i.e., > 90 % volume of cordierite) hosted within the peridotites. This study uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate the Li in rock-forming minerals of peridotite and CrNi ores to evaluate the role of Li as crustal tracer. Clinopyroxene crystallized from asthenospheric melts exhibits high Li contents (up to 8.5 ppm), exceeding the average values of the upper mantle (∼ 0.7 ppm), whereas orthopyroxene, olivine, and Cr-spinel from peridotite are mostly Li-depleted. In contrast, all rock-forming minerals of CrNi ores have abnormally high Li contents, displaying an overall Li enrichment trend toward the external parts of ultramafic massifs, on the way to the crustal rocks. This trend is evident in Cr-spinel from the CrNi ores, which display 6.9–7.9 ppm Li in the deepest portions of the massif (Arroyo de la Cala CrNi ore) up to 1.4–8.5 ppm in the shallowest part (La Gallega CrNi ore), as well as in orthopyroxenes that have 31.3–44.7 ppm Li in Arroyo de la Cala, and 45.1–51.4 ppm Li in La Gallega. Cordierite is present only in the CrNi ores situated in the external part of the ultramafic massifs, exhibiting 113.15–160.82 ppm Li in the Barranco de las Acedías CrNi ore and 36.5–60.5 ppm Li in La Gallega CrNi ore. Similarly to Li, LREE, fluid-mobile elements (K, Rb, Ba), and Sr in orthopyroxenes from the CrNi ores display enrichment from the inner to the outer parts of the ultramafic massif. These geochemical variations suggest that Li enrichment in CrNi ores and host peridotites was a twofold process: (1) asthenospheric melt percolation slightly increased Li abundances in the SCLM peridotites by modal and cryptic metasomatism involving clinopyroxene; (2) additional infiltration of Li-bearing crustally-derived fluids during the intracrustal emplacement of the mantle section boosted the Li contents of minerals in the CrNi ores. Our results highlight that Li may effectively track the interaction of the SCLM with crustal components.

Synthesis of complex concentrated silicide coatings via reactive melt-infiltration: Exploring interfacial phenomena between Si-B melt and MoNbTaW high-entropy alloy

High-entropy silicide (HES) coatings are a promising solution to the problem of poor oxidation resistance of metallic refractory alloys. However, their practical development is still in the early stages. For the first time, this study evaluates the feasibility of synthesizing complex concentrated silicide coatings using a reactive melt infiltration approach. For this purpose, a sessile drop experiment was carried out in which a binary eutectic silicon‑boron alloy (Si8B at.%) was subjected to contact heating with the MoNbTaW refractory high entropy alloy (RHEA) substrate at temperatures up to 1450 °C. After the high-temperature test, the solidified couple was characterized by X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, electron backscatter diffraction systems, and microhardness techniques. The coating had an average thickness of 75 μm and was composed of different layers, including a primary MSi2 layer, a transition MSi2 + M5Si3 silicide layer, and M5Si3 silicides (M = metal). Additionally, borosilicides and boride particles were dispersed throughout the layers. However, future research should prioritize refining process parameters to eliminate porosity and improve the integrity of the coating layer.

Binder jetting and melt infiltration for ceramic-metal fuel fabrication

This study explored the feasibility of fabricating a ZrO2-Zr2Cu ceramic-metal (CERMET) fuel through additive manufacturing (AM) followed by melt infiltration. ZrO2 was selected as a surrogate for UO2 owing to its similar properties, and Zr2Cu was selected owing to its low melting point and neutron absorption cross-section to explore the feasibility of forming a uniform distribution of ceramic particles within a metal matrix. The binder jetting (BJ) AM technique was employed to fabricate preforms with precise control over the particle distribution, addressing the challenges associated with particle agglomeration and ensuring preform shape integrity. Subsequently, spontaneous melt infiltration was employed to achieve a dense and homogeneous CERMET structure. This study emphasized the significance of controlling wettability and surface energies for successful melt infiltration, focusing on the interfacial reactions between Zr2Cu and ZrO2. These results indicate that this novel approach can significantly enhance the thermal and irradiation performance of CERMET fuels.

Catalytic Pyrolysis of Polyethylene with Microporous and Mesoporous Materials: Assessing Performance and Mechanistic Understanding.

Testing the performance for the catalytic pyrolysis of plastic waste is hampered by mass transfer limitations induced by a size mismatch between the catalyst's pores and the bulky polymer molecules. To investigate this aspect, the behavior of a series of microporous and mesoporous materials was assessed in the catalytic pyrolysis of polyethylene (PE). More specifically, a mesoporous material, namely sulfated zirconia (Zr(SO4)2) on SBA-15, was synthesized to increase the pore accessibility, which reduces mass transfer limitations and thereby enables to better assess the effect of active site density. To demonstrate this approach, mesoporous SBA-15 wascompared to microporous zeolite Y. Using the degradation temperature during thermogravimetric analysis as a measure of activity, no correlation between acidity and activity was observed for microporous zeolite Y. However, depending on the Mw of PE, the reactivity of the mesoporous catalysts increased with increasing Zr(SO4)2 weight loading, showing that utilizing a mesoporous catalyst can overcome the accessibility limitations at least partially, which was further confirmed by polymer melt infiltration and in situ X-ray diffraction. Product analysis revealed that more aromatics and coke were produced with zeolite Y. The mesoporous material remained active and structurally intact and catalyses PE degradation via acid- and radical-based pathways.

Ablation behaviour and mechanical performance of ZrB2-ZrC-SiC modified carbon/carbon composites prepared by vacuum infiltration combined with reactive melt infiltration

Ablation behaviour and mechanical performance of ZrB2-ZrC-SiC modified carbon/carbon composites prepared by vacuum infiltration combined with reactive melt infiltration

Microstructure and ablation behavior of Zr-based ultra-high-temperature gradient composites

To obtain high-performance Zr-based ultra-high-temperature composites, Zr-based ultra-high-temperature gradient composites were prepared by changing the laying method of the infiltrant via reactive melt infiltration. The effects of different infiltrant laying methods on the microstructure and ablative properties of Zr-based ultrahigh-temperature gradient composites were investigated. The results showed that the gradient structure of the Zr-based ultrahigh-temperature gradient composites differed when the composition ratio of the infiltrant was changed. When the thicknesses of the Zr/Mo/Si layers were 6/4/12 mm and 8/2/12 mm, the SiMoZrC solid solution content in the samples increased and decreased along the infiltration direction, respectively. The gradient samples were ablated in an oxyacetylene flame at 3000 °C for 40 s. The ablation resistance of the sample was the highest when the infiltrant was a powder and the thickness of the Zr/Mo/Si layer was 6/4/12 mm.

Composite Melt–Rock Interactions in the Lowermost Continental Crust: Insights from a Dunite–Pyroxenite–Gabbronorite Association of the Mafic Complex from the Ivrea–Verbano Zone (Italian Alps)

Abstract The processes leading to the building of the continental crust through magmatic underplating are fundamentally unknown, mainly because of the rare accessibility to deep level sections of the continental crust. The Italian Alps expose the Permian Mafic Complex, an 8-km-thick gabbronorite–diorite batholith that intruded the lower continental crust during the post-Variscan transtensional tectonics. We present here a petrological and geochemical study of a concentric dunite–pyroxenite–gabbronorite association, called Monte Mazzucco sequence, enclosed at deep levels of the Mafic Complex, thereby allowing us to provide new insights into the magmatic processes driven by emplacement of mantle melts in deep crustal continental areas. The studied sequence includes a ~ 60-m-thick dunite lens, in which olivine (82 mol % forsterite) is associated with accessory Cr-spinel including blebs and lamellae made up of magnetite. The dunite lens is permeated by mm- to cm-scale thick magmatic veins, which range in composition from hornblende lherzolite to olivine hornblendite and hornblende websterite. The lens is mantled by a m-scale ring consisting of amphibole-bearing (≤1 vol %) websterite, and the websterite ring is in turn enclosed by amphibole-free gabbronorites. Both magmatic veins within the dunites and mantling websterites typically include an oxide association of Al-spinel and magnetite. Remarkably, the hornblende websterite veins and the mantling websterites are typically plagioclase-free and include clinopyroxene and amphibole with chondrite-normalized rare earth element patterns characterized by negative Eu anomaly. The mantling websterites display a subtle, gradual outward decrease of Mg# for orthopyroxene, clinopyroxene and accessory olivine, coupled with an increase of the negative Eu anomaly in clinopyroxene and amphibole. The enclosing gabbronorites are amphibole-free and have a chemically evolved signature. We propose a petrogenetic scenario including two major events of melt–dunite interaction. The first resulted from focused reactive melt infiltration and formed the magmatic veins within dunites. The hornblende lherzolite and the olivine hornblendite veins were produced by focused reactive melt migration through dunite grain boundaries, involving dissolution of olivine and recrystallization of Cr-spinel into Al-spinel and magnetite, whereas the hornblende websterite veins crystallized from melts penetrating through narrow fractures and recording earlier plagioclase fractionation. Most likely, the infiltrating melts were overall derived from an evolving H2O-rich magma emplaced below the dunite body. The second event of melt–dunite reactive interaction developed the websterite ring around dunites. We envision that the outermost domain of the dunite body was replaced by websterites in response to reaction with an invading H2O-poor melt, which had previously undergone plagioclase fractionation. The dunite replacement occurred under dynamic conditions, which promoted the reaction progress, thereby leading to total or almost total dissolution of precursor olivine, and started to form the lens shape of the Monte Mazzucco ultramafic association. The gabbronorites closely adjacent to the websterite ring represent the crystallization products of the invading melt.

A 187Re-187Os and highly siderophile element study of diamondiferous kimberlite melt-mantle interactions and the inferred age of continental lithosphere

The ∼ 1.15-billion-year-old (Ga) Premier kimberlite pipe (Cullinan diamond mine), South Africa, is composed of several distinct kimberlite facies (Grey, Brown, Pale Piebald, Dark Piebald, Black Coherent [Type 3C], Blue/Brown Transitional, and Fawn). We report bulk rock Re-Os isotope data for Premier kimberlite facies, as well as for a suite of entrained peridotite and mafic xenoliths. These data are complemented by bulk rock highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os), major- and trace-element abundances. Measured 187Os/188Os for the kimberlite facies range from 0.1223 to 0.1672 (ΥOsi of −2.5 to + 17.4), peridotite xenoliths range from 0.1096 to 0.1244 (ΥOsi of −13.3 to −1.1), and pyroxenite xenoliths range from 0.1796 to 0.938 (ΥOsi of + 27 to + 419). A single measured amphibolite xenolith has the most radiogenic measured 187Os/188Os of 2.86 (ΥOsi of + 43). Harzburgite xenoliths yield time of rhenium depletion model ages (TRD) of ∼ 1.5 to 2.8 Ga, consistent with average TRD ages for Premier peridotites (2.4 ± 0.4 Ga). With these and published data, we considered the relationships between kimberlite and mantle xenoliths, compare estimates of relative peridotite incorporation to sampled diamond grade, and explore recratonization versus refertilization arguments with regards to TRD model ages. Kimberlite melt infiltration into Premier peridotite xenoliths is evident from melt veins accounting for ∼ 2 and ∼ 14 modal % of samples, and has led to incompatible element enrichment, including elevated Re. In turn, kimberlites show geochemical evidence for addition of peridotite xenolith fragments, with Type 3C having > 30 % more peridotite contribution than the Brown volcaniclastic facies. Kimberlites and peridotites plot on a 187Re/188Os versus 187Os/188Os mixing line (R2 = 0.92), with kimberlites having older apparent ages than the true age of crystallization. This mixing line provides estimates of lithospheric incorporation into the kimberlites, where the units with higher peridotite incorporation do not correlate with diamond grade. This is likely due to lithological and post-emplacement alteration heterogeneity within the kimberlite units, perhaps also reflecting the eclogitic paragenesis of many Premier diamonds. The peridotites provide evidence for the nature of the lithosphere beneath Premier prior to ∼ 1.15 Ga. Metasomatism of the peridotites is possibly linked to the Bushveld Igneous Event at ∼ 2 Ga, as well as to other magmatic events that affected the Kaapvaal craton from the Archean to the Mesoproterozoic. Premier peridotites do not suggest that the cratonic lithosphere beneath the region was completely replaced. Samples with Proterozoic TRD eruption model ages may represent Archean lithosphere that experienced alteration by metasomatism and modification, such as during the Bushveld Igneous Event.

Interaction of iron melt with tungsten and WFe composite structure evolution

Development of new plasma facing components (PFC) draw attention of numerous scientific groups in fusion energy field. Tungsten as a main PFC material main have poor machinability, thus various designs were proposed to overcome this problem. However, such technologies as functional graded layers, sintering and additive technologies are limited in production size and have low cost-efficiency. This research considers the alternative approach of steel melt injection or melt infiltration of tungsten mesh. The results obtained establish the mechanism of phase evolution during interaction of solid W with liquid steel and iron. Energy dispersive spectroscopy, X-ray diffraction and Thermocalc calculations used to analyze the phase composition of tungsten wetted with various steels and pure iron. Results show that interaction rate significantly depends on melt temperature and overheating above its liquidus. Then the overheating exceeds 150 °C erosion of tungsten occur.

Oxidation behavior of SiC‐AlN ceramics exposed to dry oxygen and water oxygen environments at 1100–1300°C

AbstractThe corrosion of SiCf/SiC composites in gas environment threatens their long‐term service in aeroengines as hot‐end structure components. Addition of corrosion‐resistant phases into SiC matrix is a potential strategy to improve the service performance of SiCf/SiC materials. Here, AlN added SiC ceramics were prepared by reactive melt infiltration, and the effect of AlN phase on the oxidation resistance of the ceramics was emphasized. The oxidation tests were performed in dry oxygen and water oxygen atmospheres at 1100°C–1300°C, respectively. The oxidation mechanism was discussed based on the microstructure evolution of the oxide layer. The results show that the oxide layer is composed of aluminum silicate glass and Al2O3 flakes dispersedly distributed in the glass phase. As the temperature rises, the oxide layer gradually grows and thickens. Finally, a smooth and dense protective layer could be formed on the surface of ceramics to resist oxidation. This study can provide a profound insight to construct SiCf/SiC composites with excellent oxidation resistance.

Nanoconfinement of an ammine magnesium borohydride composite electrolyte in a mesoporous silica scaffold

Improvements of magnesium ionic conducting materials are important for the development of novel magnesium solid-state batteries. Here we investigate the effect of nanoconfinement of one of the most conductive magnesium electrolytes − the (Mg(BH4)2·NH3)x(Mg(BH4)2·2NH3)1−x composite. The synthesis of nanoconfined Mg(BH4)2·1.47NH3 in a mesoporous silica scaffold (SBA-15, pore size 5.8 nm) is achieved through melt infiltration. Various degrees of pore filling are investigated, ranging from 100 to 300 %. Solid-state 11B nuclear magnetic resonance analysis confirms the successful stabilization of the highly dynamic eutectic molten state of Mg(BH4)2·1.47NH3 through nanoconfinement. The confined sample exhibits notable thermal stability, maintaining integrity up to approximately 100 °C, and the eutectic molten composite does not recrystallize within five months after synthesis, upon storing at room temperature. Notably, among the confined samples, 200 % pore filling displays promising Mg2+ ionic conductivity within the range of 9.1 × 10−6 to 2.7 × 10−4 S cm−1 and a low activation energy of 0.69 eV at temperatures from 32 to 80 °C. Furthermore, the compound was found to have a low electronic conductivity of 7.93 × 10−11 S cm−1 at 70 °C resulting in an ionic transport number close to unity.