How to simply and efficiently handle high-level radioactive waste is crucial for the sustainable development of nuclear energy. In this work, a solid solution of Fe3-xNdxO4 (0 <= x <= 0.9) was successfully synthesized by co-precipitation, with Nd(III) as a simulated radionuclide. The solid solution was characterized using inductively coupled plasma optical emission spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), etc. The results show that Nd(III) can be effectively incorporated into the Fe3O4 lattice via a substitutional doping mechanism. As x (0 <= x <= 0.9) increases, Fe3-xNdxO4 transitions from an inverse spinel to a more stable orthorhombic structure, enhancing the solid solution's capacity.XPS and FTIR analyses revealed that Nd(III) replaces Fe(III) in the lattice, forming new bonds with oxygen, while excess Nd(III) bonds with surface-adsorbed oxygen without changing its oxidation state. Vibrating sample magnetometer measurements indicated that the solid solutions maintain a high saturation magnetization and possess strong magnetic properties. By adjusting the Nd content, the magnetic properties of Fe3-xNdxO4 can be tuned for efficient recycling and separation. This work introduces a novel waste solidification matrix with high nuclide loading and easy recovery, offering a new strategy for nuclear waste reduction and recycling.

A new high-entropy MAX phase (V0.2Nb0.2Ta0.2Mo0.2W0.2)2AlC was successfully synthesized at 1500 ℃ by nonpressure sintering one-step solid phase reaction method. The microstructure, crystal structure and oxidation behavior of high-entropy (V0.2Nb0.2Ta0.2Mo0.2W0.2)2AlC MAX phase were investigated. Using thermogravimetry analysis to investigate the oxidative stability of (V0.2Nb0.2Ta0.2Mo0.2W0.2)2AlC in air environment at high temperature from 0 to 1000 °C, there is no volume change from 0 to 400 °C, and the morphology still exhibits a typical layered structure, demonstrating thermal stability. Oxidation rate gradually decreases with the increase in temperature, and the Kp3 value decreases to 0.86 × 10–4 kg2 m−4 s2 at 1000 ℃. The microscopic morphology analysis at different temperatures shows that the surface defects of the matrix gradually form under high-temperature conditions, in which the formation of carbide and Al2O3 layers hinds the further oxidation of the sample. The research provides a reference for the synthesis and thermal stability of new two-dimensional layered high-entropy MAX ceramics.

Absorbing materials face severe challenges in low-frequency electromagnetic wave absorption. This work successfully synthesized a new type of high entropy MAX phase (HE MAX) absorption material using a low-temperature one-step solid-state reaction method. By adding magnetic elements and controlling the grain microstructure, the sample achieves enhanced low-frequency electromagnetic wave (EMW) absorption. By further changing the solvent pool elements in the raw materials, the electromagnetic loss synergy and impedance matching (IM) enhancement of the materials were achieved, and the absorption frequency band further broke through to the low-frequency range. Among them, the sample of Al as a solvent pool (HE-MAX Al) successfully achieved a minimum reflection loss (RLmin) of -37.4 dB in the C-band. The prepared HE-MAX series ceramics are a new type of low-frequency band strong electromagnetic wave absorbing material, which is expected to be applied in extreme working environments such as strong irradiation, oxidation resistance, and corrosion resistance.

Electromagnetic wave (EMW) absorbing materials face severe challenges in achieving effective absorption in low frequency bands. This work successfully synthesized a new type of high entropy MAX phase (HE MAX) absorption material using a low-temperature one-step solid-state reaction method. By adding magnetic elements and controlling the grain microstructure, the sample has strong EMW absorption ability in low-frequency bands. By changing the elements used as solvent pool in the raw materials, the electromagnetic loss synergy and impedance matching enhancement of the materials were achieved, and the absorption frequency band broke through to the low-frequency bands. The minimum reflection loss (RLmin) of the sample using Al as the solvent pool (HE-MAX Al) reaches − 37.4 dB (3.0 mm) in the C-band. The HE-MAX series ceramics prepared are a new type of low-frequency band strong EMW absorbing material, which is expected to be applied in extreme working environments such as strong irradiation, oxidation resistance, and corrosion resistance.

At present, electromagnetic wave (EMW) absorption materials face challenges in terms of high efficiency, strong absorption, and low-cost preparation. Based on the thermodynamic behavior analysis of the initial raw materials and the design of temperature curves, a novel (Mo0.2Zr0.2Ti0.2Nb0.2Ta0.2)B2 high-entropy ceramic with a small amount of oxide impurities was successfully synthesized under low-temperature conditions, using a simple thermal reaction method. Test analysis shows that the material has a two-dimensional nanostructured and excellent EMW absorption performance. Within the wide frequency range of 10.8–18.0 GHz, the reflection loss (RL) values of the samples are all less than − 10 dB. Especially, the minimum RL value (sample thickness 6 mm, at 11.4 GHz) can reach − 36.4 dB (99.9

In this study, (Ti1−xWx)3SiC2 (x = 0–0.3) MAX phase ceramics were prepared via a solid-phase reaction synthesis method. The phase and performance effects of W-doping Ti3SiC2 were investigated. The microstructure and homogeneity of samples were characterized by XRD and SEM–EDS. Structural analysis show that when the amount of W is less than 5 mol%, the multi-phase structure of (Ti1−xWx)3SiC2 phase, a small amount of impurity phase TiSi2 and SiC was observed. As the amount of W doping increases, obvious impurity phases appeared. The oxidation behaviors of (Ti1−xWx)3SiC2 solid solution have been investigated at 800 °C in air up to 200 h. The oxidation kinetics of (Ti1−xWx)3SiC2 samples follow parabolic law. Compared to pristine Ti3SiC2, the oxidation resistance of 5 mol% W-doped sample increases by 23.2% at 800 °C. This study shows that Ti3SiC2 can be used for a long time under high temperature environment, and W doping can effectively improve the oxidation resistance of the system. This work provides a reference for the application of (Ti1−xWx)3SiC2 materials in high-temperature environments.

This study demonstrated a simple and inexpensive route to synthesize molybdenum nitride (Mo2N) and molybdenum carbide (Mo2C) in a normal air atmosphere. Sodium molybdate (Na2MoO4) and dicyandiamide (C2N4H4) were selected as the reagent precursors. X-ray diffraction (XRD) results revealed that Na2MoO4 reacted with dicyandiamide to form Mo2N in the temperature range of 450-700 degrees C, whereas Mo2C formed at a higher temperature. Pure and highly crystalline Mo2N and Mo2C were obtained after washing the calcinated products with water. Transmission electron microscopy (TEM) results illustrated the size of Mo2N nanoparticles to be in the range of 3-10 nm. In comparison to conventional synthesis procedures, our method provides a better cost-effective alternative. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved.

MAX相材料因集合了陶瓷和金属的高硬度、高弹性模量、高温稳定性、可加工性、良好的导电/导热性等优异性能,在熔盐储热、熔盐电解、熔盐辅助合成和熔盐堆发电等变革性能源应用领域获得广泛关注,在高温、强腐蚀、高强辐照等极端恶劣环境具有很好的应用前景.全面综述了MAX相金属陶瓷材料的结构、物化性能和制备方法,跟踪了MAX相家族的新相合成以及MXene二维材料的最新研究进展,并提出MAX相金属陶瓷材料的应用前景和发展方向.

Ti3SiC2 is of interest due to its unique dual nature reminiscent of both brittle ceramics and ductile metals at ambient conditions. In this work, plate-impact experiments have been performed to study the dynamic behavior of Ti3SiC2 under shock compression up to 112 GPa by using laser velocity interferometer and electric pin techniques. Hugoniot elastic limits (HEL), spall strength, and Hugoniot equations of state have been obtained based on measured particle velocity profiles and shock wave velocities. The ratio of spall strength to HEL for Ti3SiC2 is larger than brittle ceramics but smaller than metals. This result indicates that the dual nature of Ti3SiC2 remains at least up to 10 GPa. On the other hand, the linearity of the Hugoniot equation of state, D = 6.901(22) + 1.153(53)up, suggests that the initial structure of Ti3SiC2 should be stable up to 112 GPa, in contrast to the result reported by Jordan et al. [J. Appl. Phys., 93 (2003) 9639].

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.

Pyrochlore is regarded as a potential host matrix for actinides of high-level radioactive wastes. Thorium-doped neodymium zirconate pyrochlore samples were prepared by spray-pyrolysis method and characterized by XRD, SEM-EDS and Raman spectroscopy. The solubility limit of Th in Nd2-xThxZr2O7+8 (x = 0.0-2.0) pyrochlore was estimated up to be 20 at%. The multi-phase ceramic structure composed of pyrochlore, fluorite thoria and tetragonal zirconia was observed at x > 0.4. Rietveld refinement and Raman analysis of Nd2-xThxZr2O7+8(x = 0.0-0.3)samples showed the single pyrochlore structures, the lattice parameter decreases with Th content increasing. The lattice parameter and O48f positional parameter of the Nd1.6Th0.4Zr2O7 sample have increased significantly,indicating that the crystal structure undergoes a phase transition from ordered pyrochlore to disordered pyrochlore due to the distorted BO6 octahedron. The Nd2-xThxZr2O7+8 (x = 0.0-0.4) pyrochlore samples exhibit low leaching rate. From these results, the high solubility of actinides, structure stability and chemical durability are reflected in the Th-doped Nd2Zr2O7 pyrochlore samples. The present work provides a potential synthetic method and nuclear waste forms for the immobilization of high-level radioactive waste in the nuclear industry.

SnO2 compact layer (c-SnO2) frequently suffers from degradation in high temperature processes (HTP) such as crack, worse interfacial contact, and electrical properties, that is, annealing effect. To solve this problem, a kind of bifunctional SnO2 colloid is developed by using small molecular oxalate whose organic components can be removed clearly at a low temperature process (LTP). The c-SnO2 and SnO2 mesoporous layer (m-SnO2) derived from the fresh and aged sols with the same colloid show no annealing effect, decreasing oxygen vacancy, and adsorbing water on increasing annealing temperature. The champion devices of LTP and HTP SnO2 planar perovskite solar cells (PSCs) achieve, respectively, stabilized photoelectric conversion efficiencies (PCEs) of 20.74% and 20.70%. In contrast, the performance of champion devices of their mesoporous counterparts is significantly improved, showing nearly hysteresis free character with stabilized PCEs of 22.40% and 22.37%, respectively. The inclusion of m-SnO2 plays a role of an energy bridge, improving electrons collection efficiency, which is supported by photoluminescence and transient photoluminescence characterizations. HTP SnO2 mesoporous PSCs can preserve 97.6% and 80% of their initial PCEs after aging for 25 weeks and 8-h irradiated/16-h dark cycle within 104 h. The high stability of HTP SnO2 PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO2.

In shock wave precision physical measurements, the shock impedance of sapphire (Al2O3) transparent windows and Fe samples cannot be completely matched, which seriously affects the measurement accuracy. Adjusting the components of the anion and cation in the gamma-Al2O3 structure is a possible solution. N-3(-) and Mg2+ were introduced into the gamma-Al2O3 matrix to form Al(8+x)/3 square(1/3-x/3)O4-xNx (square denotes the vacancy, AlON) or Mg1-yAl2+yO4-yNy (MgAlON). Using the first-principles method coupled with the shock wave theory, the shock response behaviors and optical properties of AlON and MgAlON were studied in this work. Due to a more obvious effect was induced by Mg2+ than N3-, MgAlON had a wider shock impedance adjustment range compared with AlON. The simulation results of the shock pressure-particle velocity curves (sigma(xx)-U) demonstrated that the shock impedance of MgAlON can be completely matched with that of the Fe samples in a wide pressure range (0-20 GPa) by tuning its composition. In addition, AlON and MgAlON show good transparency between 0 and 20 GPa. This discovery provides theoretical guidance for selecting transparent ceramic windows with optimized structures and compositions that match the shock impedance of the Fe samples. (c) 2021 Elsevier B.V. All rights reserved.

为研究锕系元素铀、钍在烧绿石中的固化行为,通过喷雾热解-高温烧结成功合成了含铀、钍的系列Nd2Zr2O7烧绿石固化体,并采用XRD、SEM、EDS、Raman光谱和XPS等方法对所得固化体样品进行了表征.结果 表明:铀、钍均能进入Nd2Zr2O7晶格的A位形成稳定的烧绿石结构.Th在固化体中的固溶量(摩尔分数,下同)达到40％,固化体保持较好的烧绿石单相结构;随着Th含量的增加,固化体转变为烧绿石、立方ZrO2和ThO2共存的多相陶瓷结构.U在Nd2-xUxZr2O7烧绿石中的固溶量仅为10％,固化体结构无序化明显增加;随着U含量的增加,固化体快速转变为萤石结构,铀固溶量约为20％.铀、钍在Nd2 Zr2O7烧绿石固化体中固溶量存在较大差异.XPS分析发现,Th在烧绿石固化体中以+4价存在;U在固化体中以+4价和+6价存在,导致固化体A位离子的配位结构发生变化,更多氧离子进入烧绿石体系,导致体系转变为无序化萤石结构,固溶量明显下降.

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.

Herein, we report a novel method for producing nanoscale tungsten nitride (WN) nanoparticles, the main feature of which is the use of dicyandiamide (C2H4N4) as a non-toxic nitrogen source without an inert atmosphere. The WN nanoparticles were successfully synthesised by a temperature-programmed reaction of Na2WO4 and C2H4N4 powders at an intermediate temperature of 500-800 degrees C in air. Transmission electron microscopy (TEM) results revealed that WN nanoparticles with good crystallinity and an average size of 5.58 nm were obtained at a sintering temperature of 600 degrees C. This method can be extended to synthesise other transition metal nitride materials in air atmosphere.

Theoretical prediction is the most important method for discovering new structure. The stability of the nitride MAX phase (N-MAX) M(n+1)AN(n), (A = Al, Si, M = Ti, Zr, Hf) was studied using first principles. The formation energy analysis of the competitive phases shows that N-MAX tends to form the larger n-index M(4)AN(3) structure. The formation energy of the Mn+1SiNn system is higher than that of the Mn+1AlNn system, indicating that the Mn+1AlNn system has greater phase stability and experimental synthesis possibility than the Mn+1SiNn system. In all computing systems, the formation energy of Hfn+1AlNn is the lowest, indicating the largest synthesis possibility. Among all the considered structures, Hf2AlN is the material with the best comprehensive performance, such as the bulk modulus reaches 800 GPa. Due to its high elastic anisotropy, Hf4SiN3 is the excellent candidate for the precursor of MXene 2D nanosheets. The study provides a theoretical prediction for the synthesis of potentially undiscovered phases in the N-MAX systems.

MgAlON and AlON powders have been synthesized by carbothermal reduction and nitridation (CRN) from C-Al2O3-7.8 wt% MgO and C-Al2O3 systems, respectively. The phase and morphology of the systems were investigated under 1100-1750 degrees C via XRD, DTA, SEM and NMR. The results showed that, MgO could significantly effected the stabilization region and morphology of the (Mg)AlON products. The formation of spinel MgAl2O4s intermediate phase was key to obtain MgAlON at lower temperature with smaller particles than that of AlON. Under the optimized compositions, single-phase MgAlON and AlON were obtained at 1600 degrees C and 1720 degrees C, respectively. When sintered at 1850 degrees C for 24 h, the MgAlON sample was clear with highly transparency (82.5% at 3.7 um), while AlON was opaque with lower transmittance (similar to 8.0% at 4.7 mu m) due to lower sintering activity of the powder. (C) 2019 Elsevier B.V. All rights reserved.