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Optical transparency is of paramount importance for visual armor and certain optical devices when subjected to severe impact conditions. Shock wave loading not only generates high pressure during hypervelocity impacts but also diminishes optical transmittance. To investigate optical transparency of transparent polycrystalline ceramic under harsh shock wave compression, this study performed experimental measurements considering the grain size effect. The findings, which pertain to polycrystalline magnesium aluminate spinel (PMAS), indicate that PMAS with nano-sized grains within the 900–1500 nm wavelength range demonstrates superior optical transparency compared to conventional PMAS with micrometer-sized grains. This result highlights the excellent optical properties of nano-grain transparent ceramics and raises hopes for their widespread application at high shock pressures. [ABSTRACT FROM AUTHOR]

Micro-grained diamond-SiC composites have been prepared by sintering a mixture of micro-grained diamond and Si powder using high-temperature and high-pressure method at 1100–1500 ° C , and 5.5 GPa. Plate impact experiments in reverse—and forward—impact geometry were used to investigate the shock response of the micro-grained diamond-SiC composites within a shock pressure range from 22 to 195 GPa. The obtained plot of shock velocity (D) vs particle velocity (u) indicated that the double elastic wave responses are observed in the pressure range of 22–170 GPa, which is consistent with the previously reported diamond-SiC composites containing a small amount of tungsten carbide (WC) under shock compression up to ∼ 110 GPa [Li et al., J. Appl. Phys. 128, 245901 (2020)]. The results of shock experiments demonstrate that the Hugoniot elastic limit of micro grained diamond in SiC matrix is as high as 170 GPa, which is nearly twice as high as that of single crystal diamond. [ABSTRACT FROM AUTHOR]

We have synthesized the well-performance bulk diamond–SiC composite by the high-temperature and high-pressure method and employed the light gas gun launched flyer plates to investigate shock compression response of the diamond–SiC composite. The plots of shock velocity vs particle velocity demonstrate the presence of double elastic waves in the diamond–SiC composite under shock compression. The first elastic wave travels at 13.1 ∼ 13.6 km / s and leads to yielding at ∼ 12.75 GPa. The second elastic wave propagates at 12.8 ∼ 13.0 km / s and does not display the yielding up to ∼ 110 GPa. Such a Hugoniot elastic limit is apparently higher than that of the single crystal diamond. The strengthening mechanism underlying the diamond–SiC composite has been discussed. By simulations of the lattice-spring model, the results revealed that under shock compression, the silicon carbide matrix yields first in the composite, resulting in damage to the substructure surrounding the diamond particles. This damage releases the intense shear stress and protects the diamond from severe crushing. Due to diamonds being hydrostatically confined by the silicon carbide matrix, both dislocation migration and slip band sliding are suppressed significantly, which enhances the strength of diamonds. [ABSTRACT FROM AUTHOR]

Due to superior mechanical and optical properties, yttrium–aluminum–garnet (YAG) is emerging as a potential transparent armor material. Its dynamic behavior, however, remains largely unexplored. In this work, both impact experiments and mesoscopic simulations have been performed to better understand the dynamic response of YAG polycrystalline and single‐crystal transparent ceramics. Experimental results demonstrate that the two samples have remarkably different dynamic behaviors with the increasing shock pressure, in which the Hugoniot elastic limit basically keeps unchanged (∼14 GPa) in YAG polycrystalline ceramic, whereas it varies from 11 to 31 GPa in YAG single crystals. Moreover, elastic precursor decay is visible only in single‐crystal samples. Mesoscopic simulations with a lattice‐spring model reveal that the difference arises from the distinct fracture mode in the two samples. Less damage and coarser fragmentations in YAG single crystal also suggest a probability of better ballistic resistance as transparent armor materials. [ABSTRACT FROM AUTHOR]

The formation of the magnetic monoatomic layers in the MAX phases offers atomic-level control over magnetic layered material. The traditional high-temperature solid-phase synthesis method not only has a synthesis temperature as high as 1100 °C but also is easy to produce alloy mesophase impurities. In this work, pure-phase Ti3(Al, Fe)C2 solid solution was successfully synthesized by low-temperature replacement reaction using FeCl2 as the Fe source. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed that the pure-phase Ti3(Al, Fe)C2 solid solution was obtained at 650 °C for 3 h in an argon atmosphere, and the Fe atoms were introduced into the A sites of Ti3AlC2 to form the magnetic monoatomic layers. XRD analysis demonstrated that the formation of alloy mesophases during the synthesis process was avoided by the replacement reaction method. The vibrating sample magnetometer (VSM) test showed that the sample's saturation magnetization is up to 1.564 emu/g. In this research, a pure MAX phase with magnetic monoatomic layers was obtained at low-temperature for the first time, which has potential applications in the fields of spintronics and current sensors. [ABSTRACT FROM AUTHOR]

The synthesis of Ti3Al(Sn)C2 usually uses elemental powder as the raw material, and the synthesis temperature is up to 1500 °C. Low-temperature ceramic sintering is the key to inhibit the formation of competitive phases and reduce the ceramic sintering cost. In this paper, a new method of low-temperature synthesis of Ti3Al(Sn)C2 was proposed, and high-purity Ti3Al(Sn)C2 sample was successfully prepared at low temperature by using the replacement reaction method. Research shows that the temperature of 600 °C for 5 h is the optimal process conditions for Ti3Al(Sn)C2 synthesis. Furthermore, the introduction of Sn changed the high-temperature oxidation resistance of Ti3AlC2. Compared to pristine Ti3AlC2, the oxidation resistance of Ti3Al(Sn)C2 at 900 °C increases by 33%. The comparative analysis of the formation energy of replacement Ti sites and Al sites shows that the formation energy of Sn-replaced Al sites is lower. These results have broad reference implications for low-temperature synthesis of other MAX phases. [ABSTRACT FROM AUTHOR]

Almost completely dense (>99%) TiC composites toughened by TiSi2-SiC agglomerates were fabricated by high pressure in-situ reaction sintering of TiC and Si at a lower temperature of 1150°C. In the agglomerates of TiSi2 and SiC interlocking structures, the size of TiSi2 particles is controlled on the nanometer and submicron scales. The precursors used in the preparation were TiC and Si. The addition of Si in the precursor can effectively improve the sintering activity of TiC ceramic. Doping a certain amount of Al and increasing the sintering pressure can significantly improve the toughness of the composite. For the first time, TiSi2-SiC composites were introduced into TiC ceramics, which greatly inproved the toughness of TiC ceramics. [ABSTRACT FROM AUTHOR]

A detailed investigation of planetary ball‐milling for coarsened AlON powder was carried out. Our results showed that the weight ratios of milling ball‐to‐powder, the revolution rate and the planetary ball‐milling time have significant impacts on the microscopic morphology, particle size distribution and average particle size of powder. The process and mechanism were analyzed, and the outcome of our study can be used to optimize the complicated planetary ball‐milling method by controlling the planetary ball‐milling time or adjusting the revolution rate at the final stage of planetary ball‐milling. Sequentially, using fine and uniform AlON powder by optimized planetary ball‐milling with an average particle size below 300 nm and excellent sintering properties, highly transparent AlON ceramic with an in‐line transmittance of 84% at 2000 nm was successfully prepared through pressureless sintering at 1880°C for 6 hours using the elaborative treated powder synthesized from carbothermal nitridation method. [ABSTRACT FROM AUTHOR]

We report growth of high-purity single crystals of the sodium molybdenum bronzes NaxMoO3 through high pressure solid-state reaction routes. Our results demonstrate that the crystallite sizes of NaxMoO3 can rapidly grow to ∼25 μm under a moderate pressure of 4.0 GPa in just 10 min. This discovery provides a starting point for the growth of large single crystals of alkali metal molybdenum bronzes under high pressure. [ABSTRACT FROM AUTHOR]

In this paper, synthesis of titanium silicon carbide (Ti3SiC2) under high pressure and high-temperature condition has been investigated by using the reactant systems Ti/Si/C, Ti/SiC/TiC, Ti/SiC/C and Ti/TiC/Si. Results reveal that Ti/TiC/Si is unsuited to the synthesis of Ti3SiC2 under a high pressure of 2.0 GPa, while an elemental mixture of Ti/Si/C is applicable. By the addition of Al, Ti3SiC2 with 95.8 wt% purity was obtained from elemental mixture with a large excess of silicon. The optimum experimental parameters were determined as Ti/Si/Al/C having the molar ratio of 3:1.5:0.5:1.9, holding at 2.0 GPa and 1300 °C for 60 min. [ABSTRACT FROM AUTHOR]

Traditionally, densification and grain growth are two competing processes in sintering of ceramics. To improve the density, while limiting grain growth at the same time, an ultrahigh pressure (>1 GPa) is employed here and results in plastic deformation as the dominant densification mechanism during the sintering process. In this way, fully dense boron carbide (B4C) structural ceramics without grain growth is prepared under the pressure of 4.5 GPa at low temperature of 1300°C in 5 minutes, while showing excellent mechanical properties such as Vickers hardness of 38.04 GPa, Young's modulus of 487.7 GPa, and fracture toughness of 3.87 MPa·m1/2. This study should also facilitate the development of other structural ceramics for practical applications. [ABSTRACT FROM AUTHOR]

Ceramics typically have very high hardness, but suffer from poor toughness. Here, we use graphene to enhance the toughness of bulk boron carbide ceramics. The reduced graphene oxide (rGO) platelets are homogenously dispersed with boron carbide particles after sintering at 1350°C, under high pressure of 4.5 GPa with a multi-anvil apparatus. Fracture toughness of the composites is increased ~131% (from ~3.79 to ~8.76 MPa·m1/2) at 1.5 vol% rGO platelets as a result of a toughing effect of graphene along with a little sacrificing of the hardness and elastic modulus, compared with those of pure boron carbide. The remarkably enhanced fracture toughness in the boron carbide ceramics is associated with graphene sheets crack bridging and graphene interface sliding effect. This study holds much significance for the understanding and development of high-performance graphene reinforcing ceramics. [ABSTRACT FROM AUTHOR]

Shock wave is associated with dynamic loading that can result in phase transition (PT), optical and mechanical property changing, and chemical reaction on materials. Here, we report recent progress about shock-induced PT of polycrystalline iron, the underlying mechanism of the optical emission from sapphire, and the synthesis from single-phase RuSi in the National Key Laboratory of Shock Wave and Detonation Physics. Results indicated that grain boundary (GB) could affect the PT pressure threshold and rate of iron, the pressure threshold decreases with decreasing GB defects, and the PT rate shows a variation with increasing GB size; wavelength-dependent optical emissivity (non-gray-body emission) would be generated that was not revealed previously for shocked sapphire, and the observed luminescence was from the shock-induced shear bands, but without superheating phenomenon; shock compression could be an effective way to synthesis Ru-Si nanocrystals, when the shock pressure was appropriate; and Ru-Si powder could completely transform to fine-grain structure CsCl-type Ru-Si at 40.4 GPa. [ABSTRACT FROM AUTHOR]

ZnO ceramics with giant dielectric constants have been synthesized via a high pressure treating method. SEM results reveal that the ceramics using high pressure treated powders are porous, and the dielectric constant of the specimens first increases and then decreases with increasing density. Ceramics sintered at 1050 °C possess the optimal giant room temperature dielectric constants (~1.8 × 104 at 100 Hz) with low relative density and dielectric loss. The improved dielectric constant can be attributed to enhanced Maxwell-Wagner poly-dispersive relaxation due to the high pressure treating process, which makes ZnO porous ceramics a potential material for high dielectric constant applications. This approach is generic and provides a new avenue to obtain porous ceramics with excellent dielectric properties. [ABSTRACT FROM AUTHOR]

Antigorite is one kind of hydrous serpentine that is present in meteorites and in the Earth mantle. In order to understand its dynamic behaviors, metastability and decomposition, shock experiments on antigorite have been conducted using a two-stage gas gun, and wave profiles of particle velocities have been measured to obtain the Hugoniot up to ~130 GPa and sound velocity at high pressures. The results show three regions of low-pressure phase below ~43 GPa and its metastable extension above a pressure of ~43 GPa for short durations of shock and high-pressure phase(s) above a pressure of ~43 GPa for long durations of shock. The dynamic behaviors of antigorite depend on not only the pressure but also the compression duration. Metastable extension state indicates that antigorite may survive beyond the stability depending on the shock conditions. Shock temperatures for antigorite are calculated along the Hugoniot. The pressure-density, sound velocity-pressure and shock temperature-pressure plots demonstrate that the decomposition reaction of antigorite into high-pressure phase(s) is accompanied by a volume expansion, sound velocity increase and temperature decrease, relative to the metastable extension phase above ~43 GPa. The decomposition should be sluggish and needs enough reaction time to complete and to overcome the activation energy. As a result of the high metastability of antigorite and possible decomposition assemblages, the hydrous serpentine (antigorite) may play a crucial role for the origin of water during the Earth accretion. [ABSTRACT FROM AUTHOR]

High pressure and high temperature synthesized MoB2and WB2compacts were investigated using X-ray diffraction, energy dispersive spectroscope, scanning electron microscope, Vickers indentation test and ultrasonic measurements. Experiments showed that both MoB2and WB2compacts are phase pure and with a grain size of 100–200 nm. Vickers indentation test under a large loading force of 49 N showed that the Vickers hardness of MoB2and WB2are about 21 and 22 GPa, respectively. The bulk modulus and shear modulus are about 296 GPa, and 190 GPa for MoB2and 349 and 200 GPa for WB2through ultrasonic measurements. Our results indicate that MoB2and WB2are both hard materials with a hardness similar to that of tungsten carbide, which is widely used in industry. [ABSTRACT FROM PUBLISHER]

Shock recovery experiments were performed on ruthenium–silicon powder mixtures by a flyer plate impact technique. The flyer velocities were in the range of 0.46–2.73 km/s, and the incident shock pressures were calculated to be ∼2.9–∼40.4 GPa by the impedance matching method. The recovered samples were characterized by X-ray diffraction and scanning electron microscopy. Results indicate that shock could induce a reaction between ruthenium and silicon. The shock pressure was found to affect reaction kinetics and microstructure of the recovered sample significantly. The dynamic reaction has a threshold pressure, and the samples loaded above threshold pressure almost completely reacted to a single-phase intermetallic compound of CsCl-type RuSi. These results indicate that shock compression could be an effective way to synthesize RuSi. [ABSTRACT FROM AUTHOR]

A theoretical study of structural and electronic properties of β-HMX crystal is performed using density-functional theory (DFT). The total density of states (TDOS) is presented. The atomic orbit projected density of state (PDOS) from the p-type orbit of C, N, O and the s-type orbit of H is discussed. The study by analyzing the PDOS shows that the structure of β-HMX crystal possesses C-H...O intra- and inter-molecular hydrogen-bonding. There exists a hydrogen bonding between H-1s and O-2p orbits, between H-1s and O-2p orbits of intra molecules, and between H-1s and O-2p orbits of inter molecules. The Mulliken population analysis is also made. [ABSTRACT FROM AUTHOR]

Photocatalysis of TiO2 has recently drawn considerable attention, while the photoefficiency of TiO2 is limited by its large band-gap energy and usually fast electron-hole recombination. Here, we present an unconventional heterostructure of Ag nanoparticles modified TiO2 nanofibers synthesized by one-step electrospinning process, to improve the photoefficiency of TiO2 host. The efficient promotion of the visible light photocatalysis of Ag/TiO2 nanofiber heterostructures can be ascribed to the electronic excitation of Ag nanoparticles under visible light and the transfer of the electrons to TiO2 conduction band, which deeply depends on the number of Ag/TiO2 junctions and the height of Schottky barrier. The Ag/Ti molar ratio can be easily controlled by the electrospinning process and the Ag/TiO2 nanofibers with Ag/Ti molar ratio of 0.05 exhibit the highest photocatalytic activity. Simultaneously, the Ag/TiO2 nanofiber heterostructures show excellent photocatalytic stability. [ABSTRACT FROM AUTHOR]

A series of shock compression experiments on hexagonal α-Ce3Al have been carried out using a two-stage light gas gun. No phase transition was observed in the recovered sample shock compressed at 23.5 GPa. However, as the shock pressure was increased to 27.3 GPa, a face-centered cubic Ce3Al phase was detected in the samples recovered at ambient conditions. Furthermore, a Ce2Al phase was found in the 37.1 GPa shocked sample with a space group Fd-3m and lattice parameter a = 8.26(1) Å. These Ce-based alloys may have potential industrial applications due to the heavy-fermion related properties. [ABSTRACT FROM AUTHOR]

We report the preparation of nanostructured diamond-TiC composites with high fracture toughness and high hardness starting from a ball-milled mixture of nano-sized Ti3SiC2 and submicron-sized diamond by simultaneously tuning the pressure-temperature conditions. The phase segregation of Ti3SiC2 at pressure of 5.5 GPa were investigated by X-ray diffraction and high resolution transmission electron microscopy, we found that the Ti3SiC2 could decompose into nanosized TiC and amorphous Ti-Si at 600-700 °C. The subsequent reaction between diamond and Ti-Si led to an amorphous Ti-Si-C matrix in which diamond and TiC crystals are embedded. With a loading force of 98 N, the measured fracture toughness KIC and Vicker's hardness HV of the synthesized composites reach up to 14 MPa m1/2 and 45.5 GPa, respectively. Our results demonstrate that the nanocrystalline/amorphous bonding matrix could largely enhance the toughness of the brittle composites. [ABSTRACT FROM AUTHOR]