Effect of fluoride addition on electrochemical behaviors of V(Ⅲ) in molten LiCl-KCl

X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy were used to analyze the complexes in LiCl−KCl eutectic salt containing VCl_(3) and KF.The additional fluoride ions would replace chloride ions and combine with V(Ⅲ)to form VF_(6)^(3-).The electrochemical behavior of V(Ⅲ)was evaluated under condition of the molar concentration ratio of F−to Vn+(α)equal to 0:1,1:1,2:1,5:1,20:1 and 50:1,respectively.The results showed that a new reduction step appeared:VF_(6)^(3-)→V^(2+),and the reduction mechanism of vanadium ions became more complicated.The metallic vanadium was deposited on the tungsten electrode at−2.90 V in the LiCl−KCl melts for 6 h,and the products were characterized by SEM−EDS.It was indicated that the particle size of the product decreased with adding fluoride ions for the forming of the coordination compound VF_(6)^(3-).

Kinetic mechanism of magnesium production by silicothermic reduction of CaO·MgO in vacuum

The investigation of silicothermic reduction of CaO·MgO was carried out using a self-developed thermogravimetric analysis(TGA)instrument under vacuum and high temperature conditions.The TG data of pellets prepared with calcined dolomite,ferrosilicon and fluorite were determined at the heating rates of 1.5,2.0,2.5 and 3.0℃/min in 5 Pa vacuum at 300−1400℃,respectively.Model-free analysis and model-based analysis were applied for simulating the kinetic mechanism.By analyzing the characteristics of the initial and final reaction temperatures of TG curve,ratio of half-width of derivative TG curve and kinetic parameters,a conclusion was made that the most probable mechanism function is the first order formal chemical reaction with activation energy of 233.42 kJ/mol and pre-exponential factor of 5.14×1010 s−1.This study provides the basic data of dynamics of silicothermic magnesium production under vacuum conditions.

Selective laser melting high-performance ZrC-reinforced tungsten composites with tailored microstructure and suppressed cracking susceptibility

Selective laser melting(SLM)tungsten(W)constantly su ered from severe cracking phenomenon due to the high melting temperature and low intrinsic ductility of W material.To address this significant issue,active ZrC nanoparticles were introduced into the W matrix to form ZrC/W composites in situ by SLM to enhance the intrinsic toughness of W in this study.It mainly focused on the e ect of ZrC nanoparticle on the microstructure and cracking behavior of SLM W.Compared to SLM W,SLM ZrC/W composites showed finer equiaxed grains rather than columnar grains,because the ZrC nanoparticles provided many heterogeneous nucleation sites.Furthermore,ZrC nanoparticles could react with oxygen impurity at the grain boundaries(GBs),and then form stable ZrO2 and ZrW2O8 to purify and improve the cohesion strength of GBs.The columnar to equiaxed transition(CET)of grains and purified GBs played an important role in inhibiting the formation and propagation of the cracks in SLM W.Therefore,SLM ZrC/W composites exhibited lower crack density and higher mechanical properties compared to SLM W.This study provides a novel approach for suppressing the cracking susceptibility of SLM W.