High-entropy nitride powders are one of prerequisite materials for the preparation of high-performance high-entropy nitride ceramics. In this paper, high-entropy (HfZrTiNbTa)N powders were synthesized via nitride (i.e., silicon nitride (Si₃N₄)) thermal reduction with soft mechano-chemical assistance. The results show that metal oxides like hafnium dioxide (HfO₂), zirconium dioxide (ZrO₂), titanium dioxide (TiO₂), niobium pentoxide (Nb₂O₅), and tantalum pentoxide (Ta₂O₅) can all be transformed into the corresponding metal nitrides in the presence of Si₃N₄ at 1700 ℃, and solid solution of the metal nitrides can be formed as the temperature increases to 2100 ℃. The high-entropy (HfZrTiNbTa)N powders with submicron-sized particles, a narrower size distribution, and a single face-centered cubic (fcc) structure are obtained from raw material mixtures ground for 10 h and subsequently sintered at 1800 ℃. In addition, the high-entropy bulk nitride ceramics with relative density (R_w) of 94.31%±0.76%, Vickers hardness of 21.00±0.94 GPa, and fracture toughness (K_IC) of 3.18±0.16 MPa·m^1/2 are obtained with submicron-sized powders, which are superior to those obtained with micron-sized powders.

In this paper, a high-entropy composite bulk ceramic of (Hf_0.2Zr_0.2Ti_0.2Nb_0.2Ta_0.2)N/silicon carbide (i.e., HEN-SiC) was fabricated via spark plasma sintering (SPS) at 2100°C with submicron-sized single-phase (Hf_0.2Zr_0.2Ti_0.2Nb_0.2Ta_0.2)N (HEN) powder as a raw material and SiC particles as a sintering aid. The crystal structure, phase composition, and grain size/morphology of the composite were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The relative density and the mechanical property (i.e., bending strength, Vickers’ hardness and fracture toughness) of the composite bulk ceramic were analyzed. The results show that the relative density of the composite bulk ceramics incorporated with SiC particles content increasing from 0 to 10.0 wt.% increases from 93.08±0.13% to 99.12±0.12%. The high-entropy composite bulk ceramic with SiC particles content of 10.0 wt.% exhibits the optimum mechanical property (i.e., Vickers’ hardness of 23.34±0.67 GPa, fracture toughness of 4.35±0.13 MPa·m^1/2, and bending strength of 409±11 MPa), compared to the ceramic without SiC particles (i.e., Vickers’ hardness of 19.16±0.56 GPa, fracture toughness of 3.78±0.09 MPa·m^1/2, and bending strength of 335±11 MPa). It is indicated that SiC particles can be distributed and filled at the HEN grain boundaries in the ceramic matrix, promoting the composite densification via pinning grain boundaries and inhibiting the grain growth. The enhanced fracture toughness can be mainly due to fine-grain toughening besides lamellar/chain structures toughening. The use of SiC as a sintering aid can promote the densification and fracture toughness of high-entropy nitride bulk ceramics, providing a promising approach for the preparation of high-density, high-performance high-entropy nitride bulk ceramics.

The change law of alkaline steel slag cementitious activity was investigated by mechanical excitation, alkaline excitation, and salt excitation methods. The effect of grinding time, chemical activators, and content of steel slag on the properties of cement replaced by steel slag was studied. The hydration products of cement replaced by steel slag were analyzed by XRD and SEM. The results show mechanical excitation can effectively improve the particle size distribution and cementitious activity of steel slag. The best mechanical properties are obtained when grinding for 20 min and adding 10% steel slag. Chemical excitation can further improve the cementitious activity of steel slag based on mechanical stimulation. The optimal mechanical properties are obtained when the dosage of sodium hydroxide is 1.0%, the dosage of early strength agent is 2.0%, and the dosage of steel slag is 25%. The main hydration products of cement replaced by steel slag are calcite (CaCO₃), calcium hydroxide (Ca(OH)₂), dicalcium silicate (Ca₂SiO₄), and C-S-H gel. The microstructure presents a fibrous network structure, laying the foundation for improving mechanical properties.

The novel hollowed Ni-Co layered double hydroxide polyhedron (H-(Ni, Co)-LDHP) is synthesized via a template-sacrificing approach using ZIF-67 as template. The morphology, crystallinity, porous texture, and chemical state of H-(Ni, Co)-LDHP are examined. It demonstrates that the H-(Ni, Co)-LDHP not only provides rich redox sites but also promotes the kinetics due to presence of numerous rational channels. As a result, the H-(Ni, Co)-LDHP manifests the desirable lithium ions storage performance when employed as anode. This study paves a new way for preparing hollowed nanostructure toward advanced electrochemical applications.

Zirconium nitride (ZrN) ceramics were prepared via hot pressed sintering (HP) at 1750 °C in N₂ atmosphere with ZrO₂–Y₂O₃ as sintering additive. X-ray diffraction was applied to analyze the phase composition of the as-prepared ceramics to study the high temperature phase relation in ZrN–ZrO₂–Y₂O₃ ternary system and establish ZrN–ZrO₂–Y₂O₃ ternary phase diagrams. The results show that ZrN and tetragonal ZrO₂ (t-ZrO₂) solid solution, face-centered cubic ZrO₂ (c-ZrO₂) solid solution, body-centered cubic Y₂O₃ (c-Y₂O₃) solid solution coexist in the system of ZrN–ZrO₂–Y₂O₃.