Synthesis of(HfZrTiNbTa)N powders via nitride thermal reduction with soft mechano-chemical assistance

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(Si_(3)N_(4)))thermal reduction with soft mechanochemical assistance.The results show that metal oxides like hafnium dioxide(HfO_(2)),zirconium dioxide(ZrO_(2)),titanium dioxide(TiO_(2)),niobium pentoxide(Nb_(2)O_(5)),and tantalum pentoxide(Ta_(2)O_(5))can all be transformed into the corresponding metal nitrides in the presence of Si_(3)N_(4)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(Rw)of 94.31%±0.76%,Vickers hardness of 21.00±0.94 GPa,and fracture toughness(KIC)of 3.18±0.16 MPa·m1/2 are obtained with submicron-sized powders,which are superior to those obtained with micron-sized powders.

High-temperature phase relations of ZrN–ZrO_2–Y_2O_3 ternary system

Zirconium nitride(ZrN) ceramics were prepared via hot pressed sintering(HP) at 1750 ℃ in N_2 atmosphere with ZrO_2–Y_2O_3 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 –ZrO_2–Y_2O_3 ternary system and establish ZrN –ZrO_2–Y_2O_3 ternary phase diagrams. The results show that ZrN and tetragonal ZrO_2(t-ZrO_2) solid solution, face-centered cubic ZrO_2(c-ZrO_2) solid solution, body-centered cubic Y_2O_3(c-Y_2O_3) solid solution coexist in the system of ZrN –ZrO_2–Y_2O_3.

Low temperature hydrothermal synthesis of SrTiO3 nanoparticles without alkali and their effective photocatalytic activity

SrTiO3 nanoparticle (NP) photocatalyst was synthesized with a facile and environmentalfriendly hydrothermal method using tetrabutyltitanate,strontium oxide,and ethanolamine as precursors at low temperature without alkali as mineralizer for the first time.The SrTiO3 nanoparticles were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM),field emission scanning electron microscopy (FESEM),and N2 Brunauer-Emmett-Teller (BET) method.The SrTiO3 catalyst synthesized at 120 ℃ (STO-120) exhibited the highest photocurrent intensity among the samples synthesized at different hydrothermal temperatures.The high photocatalytic performance of STO-120 was mainly attributed to the more homogeneous and minimum nanoparticle size,the highest surface area,and the maximum light absorption property among the four different samples.This work presented an applicable and facile method to fabricate a highly active and stable SrTiO3 photocatalyst for organic pollutant degradation.