The Rauer Group is located on the eastern margin of the early Paleozoic Prydz Belt in East Antarctica,and the typical ultrahigh-temperature(UHT,>900℃)granulites outcrop on Mather Peninsula.However,the timing of UH...The Rauer Group is located on the eastern margin of the early Paleozoic Prydz Belt in East Antarctica,and the typical ultrahigh-temperature(UHT,>900℃)granulites outcrop on Mather Peninsula.However,the timing of UHT metamorphism and P–T path of the UHT granulites have long been debated,which is critical to understanding the tectonic nature and evolution history of the Prydz Belt.Thus,both a sapphirine-bearing UHT metapelitic granulite and a garnet-bearing UHT mafic granulite are selected for zircon SHRIMP U-Pb age dating.The results show that metamorphic zircon mantles yield weighted mean^(206)Pb/^(238)U ages of 918±29 Ma and 901±29 Ma for the metapelitic and mafic granulites,respectively,while zircon rims and newly grown zircons yield weighted mean^(206)Pb/^(238)U ages of 523±9 Ma and 532±11 Ma,respectively.These new zircon age data suggest that the UHT granulites may have experienced polymetamorphism,in which pre-peak prograde stage occurred in the early Neoproterozoic Grenvillian orogenesis(1000–900 Ma),whereas the UHT metamorphism occurred in the late Neoproterozoic to early Paleozoic Pan-African orogenesis(580–460 Ma).This implies that P–T path of the UHT granulites should consist of two separate high-grade metamorphic events including the Grenvillian and Pan-African events,which are supposed to be related to assembly of Rodinia and Gondwana supercontinents respectively,and hence the overprinting UHT metamorphic event may actually reflect an important intracontinental reworking.展开更多
We developed a novel low-activation,ultrafine-grained W-Cr-V multicomponent alloy(MCA)with excel-lent thermal stability and desirable high-temperature strength.The as-sintered W70 Cr15 V15(at.%)alloy was mainly compos...We developed a novel low-activation,ultrafine-grained W-Cr-V multicomponent alloy(MCA)with excel-lent thermal stability and desirable high-temperature strength.The as-sintered W70 Cr15 V15(at.%)alloy was mainly composed of a body-centered cubic(BCC)solid solution matrix with an average grain size of-0.45μm,minor hexagonal close-packed(HCP)phase,and ultrafine oxides at grain boundary(GB)regions.The average grain size of the MCA was<2μm after heating at 1500℃for 1 h,showing a high thermal stability of the microstructure.Accordingly,the estimated grain growth exponent n(-7)and the corresponding activation energy(-433 kJ mol^(-1))of the MCA indicate that diffusion during the grain growth in the present W-Cr-V alloy is dominated by the GB diffusion.Such high thermal stability can be mainly attributed to the significant pinning effects from the in-situ formed oxides at GBs.Besides,the nonequilibrium segregation of Cr and V at GBs also contributes to the thermal stability of the alloy at temperatures of 1200℃and below.Furthermore,the average high-temperature compressive strength of the alloy was over 1376 MPa at 1100℃,mainly due to the prominent solid solution and GB strengthening which were still effective at the high temperature.The results indicate that the present low-activation W-Cr-V alloy system with exceptional thermal stability and high-temperature mechanical properties could be a promising candidate for structural materials in future fusion reactors.展开更多
Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance a...Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.展开更多
A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine ＋ quartz assemblage from two localities （Tonagh Island （TI） and Priestley Peak （PP）） in the Napier Comple...A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine ＋ quartz assemblage from two localities （Tonagh Island （TI） and Priestley Peak （PP）） in the Napier Complex,East Antarctica,provides unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during Neoarchean.The reaction microstructures associated with sapphirine ＋ quartz vary among the samples,probably suggesting different tectonic conditions during the metamorphic evolution.Sapphirine and quartz in TI sample were probably in equilibrium at the peak stage,but now separated by corona of Grt ＋ Sil ＋ Opx suggesting near isobaric cooling after the peak metamorphism,whereas the Spr ＋ Qtz ＋ Sil ＋ Crd ＋ Spl assemblage replaces garnet in PP sample suggesting post-peak decompression.The application of mineral equilibrium modeling in NCKFMASHTO system demonstrated that Spr ＋ Qtz stability is lowered down to 930 ℃ due to small Fe3＋ contents in the rocks （mole Fe2O3/（FeO ＋ Fe2O3） =0.02）.The TI sample yields a peak p-T range of 950-1100 ℃ and 7.5-11 kbar,followed by cooling toward a retrograde stage of 800-950 ℃ and 8-10 kbar,possibly along a counterclockwise p-T path.In contrast,the peak condition of the PP sample shows 1000-1050 ℃ and ＞12 kbar,which was followed by the formation ofSpr ＋ Qtz corona around garnet at 930-970 ℃ and 6.7-7.7 kbar,suggesting decompression possibly along a clockwise p-T trajectory.Such contrasting p-T paths are consistent with a recent model on the structural framework of the Napier Complex that correlates the two areas to different crustal blocks.The different p-T paths obtained from the two localities might reflect the difference in the tectonic framework of these rocks within a complex Neoarchean subduction/collision belt.展开更多
The Madurai Block in the Southern Granulite Terrane(SGT)of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly.This block is composed of three sub-blocks:the Neoarchean No...The Madurai Block in the Southern Granulite Terrane(SGT)of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly.This block is composed of three sub-blocks:the Neoarchean Northern Madurai block,Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block.The margins of these blocks are well-known for the occurrence of ultrahigh-temperature(UHT)granulite facies rocks mostly represented by Mg-Al metasediments.Here we report a dismembered layered mafic–ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block.The major rock types of the layered intrusion include spinel orthopyroxenite,garnet-bearing gabbro,gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture.The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel,cordierite and orthopyroxene.The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions.Conventional thermobarometry yields near-peak metamorphic conditions of 9.5–10 kbar pressure and a minimum temperature of 980℃.We computed P–T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases,which yield temperature above 1000℃.FMAS petrogenetic grid,Al-in-orthopyroxene isopleth,conventional thermobarometry and calculated pseudosection reveal a clockwise pressure–temperature(P–T)path and near isothermal decompression.The U–Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca.2.0 Ga and the metamorphic overgrowths yield weighted ^(206)Pb/^(238)U mean ages ca.520 Ma.Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded ^(206)Pb/^(238)U weighted mean ages of ca.532 Ma and 523 Ma marking the timing of metamorphism.We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting,defining the Ganguvarpatti area as part of a collisional suture assembling the Northern and Central Madurai Blocks.The Paleoproterozoic magmatism and late Neoproterozoic-Cambrian UHT metamorphism can be linked to the tectonics of the Columbia and Gondwana supercontinents.展开更多
Dense monolithic(Ti,Zr,Hf,Ta)CN/SiCN ceramic nanocomposites are prepared via the pyrolysis of novel(Ti-,Zr-,Hf-,Ta)-containing single-source precursors(SSPs)and spark plasma sintering(SPS)with a high heating rate.The ...Dense monolithic(Ti,Zr,Hf,Ta)CN/SiCN ceramic nanocomposites are prepared via the pyrolysis of novel(Ti-,Zr-,Hf-,Ta)-containing single-source precursors(SSPs)and spark plasma sintering(SPS)with a high heating rate.The synthesis,polymer-to-ceramic transformation,and structural evolution of the nanocomposites are thoroughly investigated.The mechanical properties and air‒plasma ablation resistance of the nanocomposites are also investigated.The results show that the nanocomposites are characterized by multicomponent(Ti,Zr,Hf,Ta)CN nanoparticles uniformly distributed within the SiCN matrix(composed of SiC and/or Si_(3)N_(4)).The phase composition and molar ratios of metal elements within the(Ti,Zr,Hf,Ta)CN nanoparticles can be precisely controlled via the molecular design of the SSPs and control of the reaction sequence.The nanocomposites exhibit excellent mechanical properties,with hardness,Young’s modulus,and flexural strength of 35-37,357-417,and 532-603 MPa,respectively,owing to multicomponent solid solution strengthening and interface strengthening.The linear ablation rate of(Ti_(0.1)Zr_(0.3)Hf_(0.5)Ta_(0.1))CN/SiCN with approximately 80 wt%(Ti_(0.1)Zr_(0.3)Hf_(0.5)Ta_(0.1))CN at 2200℃is 0.033μm/s,which is 2 orders of magnitude lower than those of other multicomponent ultrahigh-temperature ceramics(UHTCs)under similar conditions.The excellent ablation resistance can be attributed to the nanoscale grain size of the multicomponent(Ti,Zr,Hf,Ta)CN phase and its excellent homogeneity within the SiCN matrix,which enables the formation of a continuous and dense oxide layer with a Hf(Zr,Ti)O_(2)skeleton filled with SiO_(2)/Ta_(2)O_(5)展开更多
Ultrahigh-temperature(UHT)metamorphism is critical for understanding the most extreme thermal evolution of continental crust.However,UHT metamorphism predominantly occurred in the Precambrian and is rarely observed in...Ultrahigh-temperature(UHT)metamorphism is critical for understanding the most extreme thermal evolution of continental crust.However,UHT metamorphism predominantly occurred in the Precambrian and is rarely observed in the modern Earth.Here,we report the discovery of~25 Ma UHT granulites from the Mogok metamorphic belt(MMB)in Myanmar via a combined study of petrology and geochronology.The studied pelitic granulites well preserve a peak mineral assemblage of garnet+sillimanite+plagioclase(antiperthite)+K-feldspar+quartz+Ti-rich biotite+rutile+ilmenite.Pressure(P)-temperature(T)pseudosections and conventional geothermobarometry data only constrain the P-T conditions of the peak stage to<12 kbar and 780–890°C.However,high Zr contents in the matrix rutile(3005–4308 ppm)and high Ti contents(up to 9.2 wt% TiO_(2))in the biotite demonstrate that the Mogok granulites may have experienced UHT metamorphism.The Zr-in-rutile thermometer and X_(Grs) isopleth in the pseudosections yield peak P-T conditions of~12 kbar and>900°C.In situ SIMS and LAICP-MS U-Pb dating and trace element analyses show that both metamorphic zircon cores and rims have flat heavy rare earth element(HREE)patterns with negative Eu anomalies.The metamorphic zircon rims show the lowest HREE contents and yield ^(206)Pb/^(238)U ages of 24.9±0.5 and 25.4±0.6 Ma,respectively,representing the timing of UHT metamorphism.Our results indicate that the central MMB underwent~25 Ma UHT metamorphism,which is possibly induced by continental rifting along the thinned orogenic lithosphere.Our data,as well as reported Cenozoic UHT events,further suggest that UHT metamorphism can be produced in the modern plate tectonic regime by lithospheric extension.展开更多
Ultrahigh-temperature ceramics(UHTCs)have a unique combination of high melting points,high strengths,and high chemical stabilities,which makes them unique materials for a wide range of ultrahigh-temperature(>2000&#...Ultrahigh-temperature ceramics(UHTCs)have a unique combination of high melting points,high strengths,and high chemical stabilities,which makes them unique materials for a wide range of ultrahigh-temperature(>2000°C)applications.Herein,we first report a novel highly porous dual-phase high-entropy UHTCs material composed of a high-entropy boride(HEB)phase and a high-entropy carbide(HEC)phase,which was fabricated via foam-gelcasting-freeze drying technology and high-temperature sintering with mixed borides and carbides as raw materials.The as-fabricated samples have a uniform pore structure and a firm skeleton that consists of random alternating distributions of HEB and HEC particles.The porous dual-phase high-entropy UHTCs samples have ultrahigh porosities of 96.4%–90.1%,low densities of 0.31–0.87 g/cm3,high strengths of 0.45–4.17 MPa and low thermal conductivities of 0.202–0.281 W/(m·K),as well as better oxidation resistance than single-phase HEC.The present results highlight the potential of as-prepared porous dual-phase high-entropy UHTCs as promising materials for ultrahigh-temperature thermal insulation applications.展开更多
Carbon materials(graphite or C/C composites)are widely used in aerospace applications due to their unique performance advantages,including low density,high specific strength and low coefficients of thermal expansion.H...Carbon materials(graphite or C/C composites)are widely used in aerospace applications due to their unique performance advantages,including low density,high specific strength and low coefficients of thermal expansion.However,carbon materials are highly susceptible to destructive oxidation in high-temperature oxygen-containing environments,limiting their application scope and service life.Coating technology is an effective approach for solving the above problem,and ceramic coatings are the most widely used protective system.In this review,the latest research progress regarding different types of silicon carbide-based antioxidation and anti-ablation ceramic coatings on the surfaces of carbon materials is described,and the protective properties and mechanism analysis of the SiC and modified SiC coatings by ultrahigh-temperature ceramic borides,carbides,silicides and other reinforcements are elucidated.In addition,the current main challenges of ceramic coatings are carefully analysed,and the perspectives for the future development of ceramic protection coatings are also discussed.展开更多
Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts,...Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts, which is usually identified in the granulite-facies rocks. UHT rocks are recognized in all major continents related to both extensional and compressive tectonic environments. UHT metamorphism spans different geological ages from Archean to Phanerozoic, providing information of the nature, petrofabric and thermal evolution of crusts. UHT metamorphism is traditionally identified by the presence of a diagnostic mineral assemblage with an appropriate bulk composition and oxidation state in Mg-Al-rich metapelite rocks. Unconventional geothermobarometers including Ti-in-zircon （TIZ） and Zr-in-rutile （ZIR） thermometers and phase equilibria modeling are increasingly being used to estimate UHT metamorphism. Concentrated on the issues about UHT metamorphism, this review presents the research history about UHT metamorphism, the global distribution of UHT rocks, the current methods for constraints on the UHT metamorphism, and the heat sources and tectonic settings of UHT meta- morphism. Some key issues and prospects about the study of UHT metamorphism are discussed, e.g., identification of UHT metamorphism for non-supracrustal rocks, robustness of the unconventional geothermometers, tectonic affinity of UHT metamorphic rocks, and methods for the constraints of age and duration of UHT metamorphism. It is concluded that UHT metamorphism is of great importance to the understanding of thermal evolution of the lithosphere.展开更多
The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of ...The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of the Xiwangshan area.The rocks contain the representative granulite-facies minerals such as garnet,clinopyroxene,orthopyroxene,plagioclase,amphibolite,rutile and quartz,and also well-developed melt pseudomorph and antiperthite.Although the prograde metamorphic stage(M1)cannot be retrieved due to rare preservation of pre-peak-stage mineral associations,three distinct mineral assemblages that formed in different metamorphic stages can be identified,based on petrography and mineralogy characteristics.The peak stage(M2)is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs,and a post-peak decompression stage(M3)contains a mineral assemblage of Grt3+Opx3+Cpx3+Amp3+Pl3,while a later-retrogression stage(M4)is featured by coronas of Amp4+Pl4 surrounding garnet.By calculating metamorphic P-T conditions using THERMOCALC,stage M2 was constrained to be 13.2–14.8 kbar and 1050–1080℃,and M3 recorded P-T conditions of 5.7–7.3 kbar and 825–875℃,while M4 yielded P of^5 kbar and T of^660℃,consistent with amphibolite facies metamorphism.Taking into account of all these petrological data,we propose that the mafic granulite experienced a high-pressure(HP)and ultra-high temperature(UHT)granulite-facies metamorphism during the peak metamorphism,which was accompanied with a clockwise P-T path.U-Pb dating of metamorphic zircons in the granulites yields two groups of ages at 1853±14 and 1744±44 Ma,respectively.We suggest that the older age corresponded to the HP-UHT metamorphism,while the younger age represented an retrograde metamorphic event during cooling.展开更多
Zircon is a key accessary mineral for metamorphic geochronology and geochemical tracing,but it has been a challenge to interpret its complex chemical zoning and age record acquired during multiple episodes of anatecti...Zircon is a key accessary mineral for metamorphic geochronology and geochemical tracing,but it has been a challenge to interpret its complex chemical zoning and age record acquired during multiple episodes of anatectic metamorphism in collisional orogens.This is illustrated by a combined study of petrography,phase equilibrium modeling and metamorphic P-T-t determination for granulites from the Bohemian Massif in the Variscan Orogen.These rocks record multiple episodes of zircon growth during anatectic metamorphism.They started from the compressional heating for prograde metamorphism to high-pressure(HP)to ultrahigh-pressure(UHP)eclogite facies with low degrees of partial melting.Afterwards,they underwent a decompressional stage from UHP eclogite facies to HP granulite facies for dehydration melting.These were followed by a further decompressional stage either to kyanite granulite facies or to sillimanite granulite facies at ultrahigh-temperature(UHT)conditions.Episodes of zircon growth are linked to specific metamorphic conditions for peritectic reactions on the basis of zoning patterns,trace element signatures,index mineral inclusions in dated domains and textural relationships to coexisting minerals.The results indicate that relict zircon domains are preserved even at UHT granulite facies conditions.A few zircon domains in the kyanite granulite grew during the prograde to peak UHP metamorphism,possibly corresponding to consumption of biotite and plagioclase but growth of garnet.During the decompressional exhumation to the HP granulite-facies,relict or prograde zircon domains were mostly dissolved into anatectic melts produced by muscovite breakdown.Most zircon grains grew during this transition to the HP granulite-facies in the kyanite granulite and are chemically related to continuous growth of garnet,whereas abundant zircon grains grew subsequently at the UHT granulite facies in the sillimanite granulite and are chemically related to garnet breakdown reactions.Another peak of zircon growth occurred at the final crystallization of anatectic melts in the sillimanite granulite rather than in the kyanite granulite,and these zircon grains mostly show oscillatory zoning,low HREE+Y contents and significantly negative Eu anomalies.In terms of the inference for protolith nature,it appears that zircon in metasedimentary rocks can grow at a short timescale in different stages of anatectic metamorphism,and its dissolution and growth are mainly dictated by anatectic conditions and extent,the property of peritectic reactions,and the stability of Ti-rich minerals.展开更多
Ultrahigh-temperature ceramics(UHTCs)are prominent candidates for use in thermal protection systems in the aerospace and nuclear industries.This study introduces a nitrogen-doped zirconium carbide that demonstrates re...Ultrahigh-temperature ceramics(UHTCs)are prominent candidates for use in thermal protection systems in the aerospace and nuclear industries.This study introduces a nitrogen-doped zirconium carbide that demonstrates remarkable ablation resistance,outperforming conventional carbide ceramics.The oxidation mechanisms of this material are elucidated through experimental and ab initio molecular dynamics simulations,representing the first analysis of such ultrahigh melting point ceramics from the perspective of structural development during the oxidation process.Transmission electron microscopy(TEM)analysis revealed the precipitation of nanocarbon and Zr–C–N–O phases at the interface between the oxidized and unoxidized regions following nitrogen doping.Nitrogen atoms preferentially combine with zirconium atoms at temperatures below the melting point of the oxide,forming robust Zr-C-N-O oxide network structures.These structures minimize oxide loss and maintain integrity during ablation,enhancing the material's performance in extreme environments.This study underscores nitrogen doping as a promising strategy to improve the ablation resistance of UHTCs,offering valuable insights for their application under demanding conditions.展开更多
Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Z...Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Zr,Hf)-containing single-source precursors(SSPs),followed by spark plasma sintering(SPS).A thorough characterization was conducted to elucidate the synthesis of the SSPs,polymer-to-ceramic transformation,chemical/phase compositions,and microstructure of the SiTiZrHfC-based ceramics.The results revealed the feasibility of synthesizing nanocomposites with high(Ti,Zr,Hf)C contents using the SSP method.These nanocomposites were characterized by a unique microstructure with in situ generated(Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed withβ-SiC.The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s.Impressively,the nanocomposites exhibited excellent ablation resistance,and the lowest linear ablation rate reached−0.58μm/s at 2200°C.Notably,the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the(Ti,Zr,Hf)C phase via the molecular design of the SSPs.The formation of a multiple-oxide layer with both a high-meltingpoint phase((Ti,Zr,Hf)O_(2))and low-melting-point phases((Zr,Hf)TiO_(4))and glassy SiO_(2),as well as their structure,played a critical role in the enhanced ablation resistance.The uniform distribution of the high-melting-point(Ti,Zr,Hf)O_(2)nano/microparticles throughout the glassy SiO_(2)matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect,offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.展开更多
A series of AIN nanostructures were synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport（PVT） process. Energy dispersive X-ray spectroscopy（EDX）, X-ray diffraction（XRD）, X-Ray photoel...A series of AIN nanostructures were synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport（PVT） process. Energy dispersive X-ray spectroscopy（EDX）, X-ray diffraction（XRD）, X-Ray photoelectron spectroscopy（XPS）,high resolution transmission electron microscopy（HRTEM） detection show that high quality AIN nanowires were prepared. Nanostructures including nanorings, nanosprings, nanohelices, chainlike nanowires, six-fold symmetric nanostructure and rod-like structure were successfully obtained by controlling the growth duration and temperature. The morphology evolution was attributed to electrostatic polar charge model and the crystalline lattice structure of AIN.展开更多
Zircon as a multi-objective typomorphic mineral commonly contains diverse trace elements with specific petrogenetic significances.The Hf abundance in zircon is sensitively indicative of melt fractionation during zirco...Zircon as a multi-objective typomorphic mineral commonly contains diverse trace elements with specific petrogenetic significances.The Hf abundance in zircon is sensitively indicative of melt fractionation during zircon growth on one hand,and on another,the Ti content is a robust temperature sensor of zircon crystallization and has been effectively u tilized in thermometric estimation.A Hf-Ti negative correlation was previously reported in igneous zircons,and thus a potential Hf thermometry was then speculated.In this work,we performed reliable electron microprobe(EMP)measurements of Hf and Ti in ultrahigh temperature(UHT)zircons from the North China Craton,in optimizing point,line and grid analysis.The EMP contents of Hf and Ti both show a wide range of fluctuation owing to the smaller probe spot,and some of them are higher than the LAICPMS data.The Hf-Ti correlation in UHT zircons displays dual and thus complicated patterns in contrast with the previous consideration,which implicates some other factors controlling the geochemical behaviors of Hf and Ti in zircons.Generally,the estimated Ti temperatures based on the EMP analyses are obviously higher than the LA-ICPMS outcomes,but are well consistent with the actual peak condition of the parent rock.It explains the common underestimation of Ti temperatures in hightemperature metamorphic rocks,by using LA-ICPMS analyses.展开更多
基金supported by the National Nature Science Foundation of China(Grant no.41972050).
文摘The Rauer Group is located on the eastern margin of the early Paleozoic Prydz Belt in East Antarctica,and the typical ultrahigh-temperature(UHT,>900℃)granulites outcrop on Mather Peninsula.However,the timing of UHT metamorphism and P–T path of the UHT granulites have long been debated,which is critical to understanding the tectonic nature and evolution history of the Prydz Belt.Thus,both a sapphirine-bearing UHT metapelitic granulite and a garnet-bearing UHT mafic granulite are selected for zircon SHRIMP U-Pb age dating.The results show that metamorphic zircon mantles yield weighted mean^(206)Pb/^(238)U ages of 918±29 Ma and 901±29 Ma for the metapelitic and mafic granulites,respectively,while zircon rims and newly grown zircons yield weighted mean^(206)Pb/^(238)U ages of 523±9 Ma and 532±11 Ma,respectively.These new zircon age data suggest that the UHT granulites may have experienced polymetamorphism,in which pre-peak prograde stage occurred in the early Neoproterozoic Grenvillian orogenesis(1000–900 Ma),whereas the UHT metamorphism occurred in the late Neoproterozoic to early Paleozoic Pan-African orogenesis(580–460 Ma).This implies that P–T path of the UHT granulites should consist of two separate high-grade metamorphic events including the Grenvillian and Pan-African events,which are supposed to be related to assembly of Rodinia and Gondwana supercontinents respectively,and hence the overprinting UHT metamorphic event may actually reflect an important intracontinental reworking.
基金funded by the National Natural Science Foundation of China(Grant Nos.51971248,52201154,52101166,52020105013)the Natural Science Foundation of Hunan province in China(Grant Nos.2023RC1013,2021JJ10056,2021JJ40736)support provided by the Fundamental Research Funds for the Central Universities of Central South University(Grant No.2020zzts072)is also acknowledged.
文摘We developed a novel low-activation,ultrafine-grained W-Cr-V multicomponent alloy(MCA)with excel-lent thermal stability and desirable high-temperature strength.The as-sintered W70 Cr15 V15(at.%)alloy was mainly composed of a body-centered cubic(BCC)solid solution matrix with an average grain size of-0.45μm,minor hexagonal close-packed(HCP)phase,and ultrafine oxides at grain boundary(GB)regions.The average grain size of the MCA was<2μm after heating at 1500℃for 1 h,showing a high thermal stability of the microstructure.Accordingly,the estimated grain growth exponent n(-7)and the corresponding activation energy(-433 kJ mol^(-1))of the MCA indicate that diffusion during the grain growth in the present W-Cr-V alloy is dominated by the GB diffusion.Such high thermal stability can be mainly attributed to the significant pinning effects from the in-situ formed oxides at GBs.Besides,the nonequilibrium segregation of Cr and V at GBs also contributes to the thermal stability of the alloy at temperatures of 1200℃and below.Furthermore,the average high-temperature compressive strength of the alloy was over 1376 MPa at 1100℃,mainly due to the prominent solid solution and GB strengthening which were still effective at the high temperature.The results indicate that the present low-activation W-Cr-V alloy system with exceptional thermal stability and high-temperature mechanical properties could be a promising candidate for structural materials in future fusion reactors.
基金Foundation item： National Natural Science Foundation of China （50671081）
文摘Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.
基金Partial funding for this project was produced a Grant-in-Aid for Scientifc Research (B) from Japan Society for the Promotion of Science (JSPS) to Tsunogae(Nos.20340148,22403017)a Grant-in-Aid for JSPS Fellows to Shimizu (No.23-311)
文摘A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine ＋ quartz assemblage from two localities （Tonagh Island （TI） and Priestley Peak （PP）） in the Napier Complex,East Antarctica,provides unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during Neoarchean.The reaction microstructures associated with sapphirine ＋ quartz vary among the samples,probably suggesting different tectonic conditions during the metamorphic evolution.Sapphirine and quartz in TI sample were probably in equilibrium at the peak stage,but now separated by corona of Grt ＋ Sil ＋ Opx suggesting near isobaric cooling after the peak metamorphism,whereas the Spr ＋ Qtz ＋ Sil ＋ Crd ＋ Spl assemblage replaces garnet in PP sample suggesting post-peak decompression.The application of mineral equilibrium modeling in NCKFMASHTO system demonstrated that Spr ＋ Qtz stability is lowered down to 930 ℃ due to small Fe3＋ contents in the rocks （mole Fe2O3/（FeO ＋ Fe2O3） =0.02）.The TI sample yields a peak p-T range of 950-1100 ℃ and 7.5-11 kbar,followed by cooling toward a retrograde stage of 800-950 ℃ and 8-10 kbar,possibly along a counterclockwise p-T path.In contrast,the peak condition of the PP sample shows 1000-1050 ℃ and ＞12 kbar,which was followed by the formation ofSpr ＋ Qtz corona around garnet at 930-970 ℃ and 6.7-7.7 kbar,suggesting decompression possibly along a clockwise p-T trajectory.Such contrasting p-T paths are consistent with a recent model on the structural framework of the Napier Complex that correlates the two areas to different crustal blocks.The different p-T paths obtained from the two localities might reflect the difference in the tectonic framework of these rocks within a complex Neoarchean subduction/collision belt.
基金funded by Foreign Expert grants to M.Santosh from the China University of Geosciences(Beijing)。
文摘The Madurai Block in the Southern Granulite Terrane(SGT)of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly.This block is composed of three sub-blocks:the Neoarchean Northern Madurai block,Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block.The margins of these blocks are well-known for the occurrence of ultrahigh-temperature(UHT)granulite facies rocks mostly represented by Mg-Al metasediments.Here we report a dismembered layered mafic–ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block.The major rock types of the layered intrusion include spinel orthopyroxenite,garnet-bearing gabbro,gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture.The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel,cordierite and orthopyroxene.The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions.Conventional thermobarometry yields near-peak metamorphic conditions of 9.5–10 kbar pressure and a minimum temperature of 980℃.We computed P–T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases,which yield temperature above 1000℃.FMAS petrogenetic grid,Al-in-orthopyroxene isopleth,conventional thermobarometry and calculated pseudosection reveal a clockwise pressure–temperature(P–T)path and near isothermal decompression.The U–Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca.2.0 Ga and the metamorphic overgrowths yield weighted ^(206)Pb/^(238)U mean ages ca.520 Ma.Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded ^(206)Pb/^(238)U weighted mean ages of ca.532 Ma and 523 Ma marking the timing of metamorphism.We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting,defining the Ganguvarpatti area as part of a collisional suture assembling the Northern and Central Madurai Blocks.The Paleoproterozoic magmatism and late Neoproterozoic-Cambrian UHT metamorphism can be linked to the tectonics of the Columbia and Gondwana supercontinents.
基金the National Natural Science Foundation of China(Nos.52472082 and 52102085)the National Natural Science Fund for Excellent Young Scholars(Overseas)the State Key Laboratory of Powder Metallurgy,Central South University,China(No.621022335)for financial support.
文摘Dense monolithic(Ti,Zr,Hf,Ta)CN/SiCN ceramic nanocomposites are prepared via the pyrolysis of novel(Ti-,Zr-,Hf-,Ta)-containing single-source precursors(SSPs)and spark plasma sintering(SPS)with a high heating rate.The synthesis,polymer-to-ceramic transformation,and structural evolution of the nanocomposites are thoroughly investigated.The mechanical properties and air‒plasma ablation resistance of the nanocomposites are also investigated.The results show that the nanocomposites are characterized by multicomponent(Ti,Zr,Hf,Ta)CN nanoparticles uniformly distributed within the SiCN matrix(composed of SiC and/or Si_(3)N_(4)).The phase composition and molar ratios of metal elements within the(Ti,Zr,Hf,Ta)CN nanoparticles can be precisely controlled via the molecular design of the SSPs and control of the reaction sequence.The nanocomposites exhibit excellent mechanical properties,with hardness,Young’s modulus,and flexural strength of 35-37,357-417,and 532-603 MPa,respectively,owing to multicomponent solid solution strengthening and interface strengthening.The linear ablation rate of(Ti_(0.1)Zr_(0.3)Hf_(0.5)Ta_(0.1))CN/SiCN with approximately 80 wt%(Ti_(0.1)Zr_(0.3)Hf_(0.5)Ta_(0.1))CN at 2200℃is 0.033μm/s,which is 2 orders of magnitude lower than those of other multicomponent ultrahigh-temperature ceramics(UHTCs)under similar conditions.The excellent ablation resistance can be attributed to the nanoscale grain size of the multicomponent(Ti,Zr,Hf,Ta)CN phase and its excellent homogeneity within the SiCN matrix,which enables the formation of a continuous and dense oxide layer with a Hf(Zr,Ti)O_(2)skeleton filled with SiO_(2)/Ta_(2)O_(5)
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41822202,41490614).
文摘Ultrahigh-temperature(UHT)metamorphism is critical for understanding the most extreme thermal evolution of continental crust.However,UHT metamorphism predominantly occurred in the Precambrian and is rarely observed in the modern Earth.Here,we report the discovery of~25 Ma UHT granulites from the Mogok metamorphic belt(MMB)in Myanmar via a combined study of petrology and geochronology.The studied pelitic granulites well preserve a peak mineral assemblage of garnet+sillimanite+plagioclase(antiperthite)+K-feldspar+quartz+Ti-rich biotite+rutile+ilmenite.Pressure(P)-temperature(T)pseudosections and conventional geothermobarometry data only constrain the P-T conditions of the peak stage to<12 kbar and 780–890°C.However,high Zr contents in the matrix rutile(3005–4308 ppm)and high Ti contents(up to 9.2 wt% TiO_(2))in the biotite demonstrate that the Mogok granulites may have experienced UHT metamorphism.The Zr-in-rutile thermometer and X_(Grs) isopleth in the pseudosections yield peak P-T conditions of~12 kbar and>900°C.In situ SIMS and LAICP-MS U-Pb dating and trace element analyses show that both metamorphic zircon cores and rims have flat heavy rare earth element(HREE)patterns with negative Eu anomalies.The metamorphic zircon rims show the lowest HREE contents and yield ^(206)Pb/^(238)U ages of 24.9±0.5 and 25.4±0.6 Ma,respectively,representing the timing of UHT metamorphism.Our results indicate that the central MMB underwent~25 Ma UHT metamorphism,which is possibly induced by continental rifting along the thinned orogenic lithosphere.Our data,as well as reported Cenozoic UHT events,further suggest that UHT metamorphism can be produced in the modern plate tectonic regime by lithospheric extension.
基金supported by the National Natural Science Foundation of China(Grant Nos.U21A2063,U2441266,52372071,and 52302076)the International Partnership Program of the Chinese Academy of Sciences(Grant No.172GJHZ2022094FN)the LiaoNing Revitalization Talents Program(Grant No.XLYC2203090).
文摘Ultrahigh-temperature ceramics(UHTCs)have a unique combination of high melting points,high strengths,and high chemical stabilities,which makes them unique materials for a wide range of ultrahigh-temperature(>2000°C)applications.Herein,we first report a novel highly porous dual-phase high-entropy UHTCs material composed of a high-entropy boride(HEB)phase and a high-entropy carbide(HEC)phase,which was fabricated via foam-gelcasting-freeze drying technology and high-temperature sintering with mixed borides and carbides as raw materials.The as-fabricated samples have a uniform pore structure and a firm skeleton that consists of random alternating distributions of HEB and HEC particles.The porous dual-phase high-entropy UHTCs samples have ultrahigh porosities of 96.4%–90.1%,low densities of 0.31–0.87 g/cm3,high strengths of 0.45–4.17 MPa and low thermal conductivities of 0.202–0.281 W/(m·K),as well as better oxidation resistance than single-phase HEC.The present results highlight the potential of as-prepared porous dual-phase high-entropy UHTCs as promising materials for ultrahigh-temperature thermal insulation applications.
基金supported by the“Jie Bang Gua Shuai”of Science and technology Projects of Liaoning Province in 2021,grant number 2021JH1/10400091Liao Ning Revitalization Talents Program,grant number XLYC2005002+3 种基金Liaoning BaiQianWan Talents Program,grant number[2020]78Scientific Research Funding Project of the Educational Department of Liaoning Province in 2020,grant number LZ2020002Shenyang Science and Technology Program-Major Key Core Technology Project,grant number 20-202-1-15Provincial Doctoral Research Initiation Fund Program,grant number 2021-BS-187.
文摘Carbon materials(graphite or C/C composites)are widely used in aerospace applications due to their unique performance advantages,including low density,high specific strength and low coefficients of thermal expansion.However,carbon materials are highly susceptible to destructive oxidation in high-temperature oxygen-containing environments,limiting their application scope and service life.Coating technology is an effective approach for solving the above problem,and ceramic coatings are the most widely used protective system.In this review,the latest research progress regarding different types of silicon carbide-based antioxidation and anti-ablation ceramic coatings on the surfaces of carbon materials is described,and the protective properties and mechanism analysis of the SiC and modified SiC coatings by ultrahigh-temperature ceramic borides,carbides,silicides and other reinforcements are elucidated.In addition,the current main challenges of ceramic coatings are carefully analysed,and the perspectives for the future development of ceramic protection coatings are also discussed.
基金supported by the National Natural Science Foundation of China (Nos. 41772054, 41572039 and 41372076)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (No. CUGQYZX1704)
文摘Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts, which is usually identified in the granulite-facies rocks. UHT rocks are recognized in all major continents related to both extensional and compressive tectonic environments. UHT metamorphism spans different geological ages from Archean to Phanerozoic, providing information of the nature, petrofabric and thermal evolution of crusts. UHT metamorphism is traditionally identified by the presence of a diagnostic mineral assemblage with an appropriate bulk composition and oxidation state in Mg-Al-rich metapelite rocks. Unconventional geothermobarometers including Ti-in-zircon （TIZ） and Zr-in-rutile （ZIR） thermometers and phase equilibria modeling are increasingly being used to estimate UHT metamorphism. Concentrated on the issues about UHT metamorphism, this review presents the research history about UHT metamorphism, the global distribution of UHT rocks, the current methods for constraints on the UHT metamorphism, and the heat sources and tectonic settings of UHT meta- morphism. Some key issues and prospects about the study of UHT metamorphism are discussed, e.g., identification of UHT metamorphism for non-supracrustal rocks, robustness of the unconventional geothermometers, tectonic affinity of UHT metamorphic rocks, and methods for the constraints of age and duration of UHT metamorphism. It is concluded that UHT metamorphism is of great importance to the understanding of thermal evolution of the lithosphere.
基金supported by the National Natural Science Foundation of China (No. 41761144061)the Shandong Provincial Natural Science Foundation (No. ZR2016DM04)the University Students Innovation Program of SDUST (No. 2015TDJH101)
文摘The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of the Xiwangshan area.The rocks contain the representative granulite-facies minerals such as garnet,clinopyroxene,orthopyroxene,plagioclase,amphibolite,rutile and quartz,and also well-developed melt pseudomorph and antiperthite.Although the prograde metamorphic stage(M1)cannot be retrieved due to rare preservation of pre-peak-stage mineral associations,three distinct mineral assemblages that formed in different metamorphic stages can be identified,based on petrography and mineralogy characteristics.The peak stage(M2)is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs,and a post-peak decompression stage(M3)contains a mineral assemblage of Grt3+Opx3+Cpx3+Amp3+Pl3,while a later-retrogression stage(M4)is featured by coronas of Amp4+Pl4 surrounding garnet.By calculating metamorphic P-T conditions using THERMOCALC,stage M2 was constrained to be 13.2–14.8 kbar and 1050–1080℃,and M3 recorded P-T conditions of 5.7–7.3 kbar and 825–875℃,while M4 yielded P of^5 kbar and T of^660℃,consistent with amphibolite facies metamorphism.Taking into account of all these petrological data,we propose that the mafic granulite experienced a high-pressure(HP)and ultra-high temperature(UHT)granulite-facies metamorphism during the peak metamorphism,which was accompanied with a clockwise P-T path.U-Pb dating of metamorphic zircons in the granulites yields two groups of ages at 1853±14 and 1744±44 Ma,respectively.We suggest that the older age corresponded to the HP-UHT metamorphism,while the younger age represented an retrograde metamorphic event during cooling.
基金supported by the Natural Science Foundation of China(Nos.41673030,41590624)the Strategy Guide Project B of the Chinese Academy of Sciences(No.XDB18020303)+1 种基金the Youth Innovation Promotion Association of CAS(No.2013283)the Fundamental Research Programs for the Central Universities。
文摘Zircon is a key accessary mineral for metamorphic geochronology and geochemical tracing,but it has been a challenge to interpret its complex chemical zoning and age record acquired during multiple episodes of anatectic metamorphism in collisional orogens.This is illustrated by a combined study of petrography,phase equilibrium modeling and metamorphic P-T-t determination for granulites from the Bohemian Massif in the Variscan Orogen.These rocks record multiple episodes of zircon growth during anatectic metamorphism.They started from the compressional heating for prograde metamorphism to high-pressure(HP)to ultrahigh-pressure(UHP)eclogite facies with low degrees of partial melting.Afterwards,they underwent a decompressional stage from UHP eclogite facies to HP granulite facies for dehydration melting.These were followed by a further decompressional stage either to kyanite granulite facies or to sillimanite granulite facies at ultrahigh-temperature(UHT)conditions.Episodes of zircon growth are linked to specific metamorphic conditions for peritectic reactions on the basis of zoning patterns,trace element signatures,index mineral inclusions in dated domains and textural relationships to coexisting minerals.The results indicate that relict zircon domains are preserved even at UHT granulite facies conditions.A few zircon domains in the kyanite granulite grew during the prograde to peak UHP metamorphism,possibly corresponding to consumption of biotite and plagioclase but growth of garnet.During the decompressional exhumation to the HP granulite-facies,relict or prograde zircon domains were mostly dissolved into anatectic melts produced by muscovite breakdown.Most zircon grains grew during this transition to the HP granulite-facies in the kyanite granulite and are chemically related to continuous growth of garnet,whereas abundant zircon grains grew subsequently at the UHT granulite facies in the sillimanite granulite and are chemically related to garnet breakdown reactions.Another peak of zircon growth occurred at the final crystallization of anatectic melts in the sillimanite granulite rather than in the kyanite granulite,and these zircon grains mostly show oscillatory zoning,low HREE+Y contents and significantly negative Eu anomalies.In terms of the inference for protolith nature,it appears that zircon in metasedimentary rocks can grow at a short timescale in different stages of anatectic metamorphism,and its dissolution and growth are mainly dictated by anatectic conditions and extent,the property of peritectic reactions,and the stability of Ti-rich minerals.
基金funding by the National Natural Science Foundation of China(No.52302128)the Foundation of State Key Laboratory of Science and Technology on Advanced Ceramic Fibers and Composites(No.6142907230303).
文摘Ultrahigh-temperature ceramics(UHTCs)are prominent candidates for use in thermal protection systems in the aerospace and nuclear industries.This study introduces a nitrogen-doped zirconium carbide that demonstrates remarkable ablation resistance,outperforming conventional carbide ceramics.The oxidation mechanisms of this material are elucidated through experimental and ab initio molecular dynamics simulations,representing the first analysis of such ultrahigh melting point ceramics from the perspective of structural development during the oxidation process.Transmission electron microscopy(TEM)analysis revealed the precipitation of nanocarbon and Zr–C–N–O phases at the interface between the oxidized and unoxidized regions following nitrogen doping.Nitrogen atoms preferentially combine with zirconium atoms at temperatures below the melting point of the oxide,forming robust Zr-C-N-O oxide network structures.These structures minimize oxide loss and maintain integrity during ablation,enhancing the material's performance in extreme environments.This study underscores nitrogen doping as a promising strategy to improve the ablation resistance of UHTCs,offering valuable insights for their application under demanding conditions.
基金the National Natural Science Foundation of China(Nos.52102085 and 52072410)the National Natural Science Fund for Excellent Young Scholars(Overseas)the State Key Laboratory of Powder Metallurgy,Central South University,China(No.621022335)for financial support.
文摘Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Zr,Hf)-containing single-source precursors(SSPs),followed by spark plasma sintering(SPS).A thorough characterization was conducted to elucidate the synthesis of the SSPs,polymer-to-ceramic transformation,chemical/phase compositions,and microstructure of the SiTiZrHfC-based ceramics.The results revealed the feasibility of synthesizing nanocomposites with high(Ti,Zr,Hf)C contents using the SSP method.These nanocomposites were characterized by a unique microstructure with in situ generated(Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed withβ-SiC.The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s.Impressively,the nanocomposites exhibited excellent ablation resistance,and the lowest linear ablation rate reached−0.58μm/s at 2200°C.Notably,the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the(Ti,Zr,Hf)C phase via the molecular design of the SSPs.The formation of a multiple-oxide layer with both a high-meltingpoint phase((Ti,Zr,Hf)O_(2))and low-melting-point phases((Zr,Hf)TiO_(4))and glassy SiO_(2),as well as their structure,played a critical role in the enhanced ablation resistance.The uniform distribution of the high-melting-point(Ti,Zr,Hf)O_(2)nano/microparticles throughout the glassy SiO_(2)matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect,offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.
基金Project supported by the Natural Science Foundation of Tianjin,China(No.15JCQNJC03700)the National Natural Science Foundation of China(Nos.51702297)
文摘A series of AIN nanostructures were synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport（PVT） process. Energy dispersive X-ray spectroscopy（EDX）, X-ray diffraction（XRD）, X-Ray photoelectron spectroscopy（XPS）,high resolution transmission electron microscopy（HRTEM） detection show that high quality AIN nanowires were prepared. Nanostructures including nanorings, nanosprings, nanohelices, chainlike nanowires, six-fold symmetric nanostructure and rod-like structure were successfully obtained by controlling the growth duration and temperature. The morphology evolution was attributed to electrostatic polar charge model and the crystalline lattice structure of AIN.
基金supported by the National Natural Science Foundation of China(Grant No.41872190)。
文摘Zircon as a multi-objective typomorphic mineral commonly contains diverse trace elements with specific petrogenetic significances.The Hf abundance in zircon is sensitively indicative of melt fractionation during zircon growth on one hand,and on another,the Ti content is a robust temperature sensor of zircon crystallization and has been effectively u tilized in thermometric estimation.A Hf-Ti negative correlation was previously reported in igneous zircons,and thus a potential Hf thermometry was then speculated.In this work,we performed reliable electron microprobe(EMP)measurements of Hf and Ti in ultrahigh temperature(UHT)zircons from the North China Craton,in optimizing point,line and grid analysis.The EMP contents of Hf and Ti both show a wide range of fluctuation owing to the smaller probe spot,and some of them are higher than the LAICPMS data.The Hf-Ti correlation in UHT zircons displays dual and thus complicated patterns in contrast with the previous consideration,which implicates some other factors controlling the geochemical behaviors of Hf and Ti in zircons.Generally,the estimated Ti temperatures based on the EMP analyses are obviously higher than the LA-ICPMS outcomes,but are well consistent with the actual peak condition of the parent rock.It explains the common underestimation of Ti temperatures in hightemperature metamorphic rocks,by using LA-ICPMS analyses.
