Precise regulation of the phase transformation for pyrolusite during the reduction roasting process

The mechanism involved in the phase transformation process of pyrolusite (MnO_(2)) during roasting in a reducing atmosphere was systematically elucidated in this study,with the aim of effectively using low-grade complex manganese ore resources.According to single-factor experiment results,the roasted product with a divalent manganese (Mn^(2+)) distribution rate of 95.30% was obtained at a roasting time of 25 min,a roasting temperature of 700℃,a CO concentration of 20at%,and a total gas volume of 500 mL·min^(-1),in which the manganese was mainly in the form of manganosite (MnO).Scanning electron microscopy and Brunauer–Emmett–Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core Thermodynamic calculations,X-ray photoelectron spectroscopy,and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO_(2)→Mn_(2)O_(3)→Mn_(3)O_(4)→MnO phase by phase,and the reduction of manganese oxides in each valence state proceeded simultaneously.

Much enhanced electromagnetic wave absorbing properties from the synergistic effect of graphene/γ-graphyne heterostructure in both gigahertz and terahertz band ranges

Exploring advanced electromagnetic wave(EMW)absorbers is one of the most feasible ways to solve the increasing electromagnetic pollution in both military and civil fields.In this work,γ-graphyne(γ-GY)is synthesized by a mechanochemical route using CaC2 and hexabromobenzene(PhBr6).Then three-dimensional(3D)reduced graphene oxide/γ-GY(RGO/GY)heterostructures are prepared through facile solvothermal self-assembly and subsequent thermal reduction.The influences of calcination temperature and the content ofγ-GY of the composite on EMW absorption performance are fully investigated.The minimum reflection loss(RL)value of the RGO/GY composite foam is−71.73 dB at 10.48 GHz with the matching thickness of 3.54 mm,and the effective absorption bandwidth(EAB)less than−10 dB is 7.36 GHz.Moreover,excellent terahertz(THz)absorption property is also obtained at 0.2–1.6 THz.The RL of 84.08 dB is acquired,and the EAB covers 100%of the entire measured bandwidth.In addition,the composite is also a promising anticorrosive EMW absorber.This work provides encouraging findings,which are also instructive for the potential advantages of graphyne-based materials as highly efficient EMW absorbers in both gigahertz and terahertz band ranges.