Simulation and Prediction of the Fluorides Migration in a Tailing Pond Using Modflow

The hydrogeological generalized model of a tailing pond in Qian’an was established. Based on this model, the migration rules of the fluorides in the study area were subjected to the fully implicit difference method of Visual Modflow software(MT3DMS). The study indicates that the direction of fluorides migration is consistent with the direction of the stream flow generally, and the concentration of the fluorides decreases with the increase of the migration distance. The simulation results can provide scientific bases for the assessment and management of the underground water in the contaminated zone.

Microstructure and magnetic properties of hot-deformed anisotropic Nd–Fe–B magnets prepared from amorphous precursors with different crystallization proportions

Anisotropic magnets were obtained by hot deformation with the partial crystallized precursor prepared via spark-plasma sintering （SPS）. Amorphous powders with the nominal composition of Nd_28.72Fe_balCo_5.66 Ga_0.59B_0.92 （wt%） were used as the starting material. The results show that the amorphous powders would suffer varying degrees of crystallization even below the crystal- lization point during the SPS process under high pressure. And the pre-crystallized grains in precursors have great impacts on the microstructure and magnetic properties of the hot-deformed magnets. The final obtained anisotropic magnets exhibit homogeneous microstructure consisting of well-aligned and platelet-shaped Nd_2Fe_14B grains without abnormal growth. It can be found that a reasonable pro- portion of pre-crystallized gains could promote the pref- erential orientation in the magnet, leading to the achievement of optimal magnetic properties among the magnets with identical composition and best magnetic performance is achieved in the magnet hot deformed from the 490 ℃ high-pressure hot-pressed precursor.

Microstructure and mechanical properties of WC-(Ti,M)(C,N)-Co cemented carbides with different nitrogen contents

Three kinds of(Ti,M)(C_(1-x),N_(x))(M=Ta,Nb,W) quaternary solid-solution powders with various nitrogen contents were synthesized by carbothermal reductionnitridation(CRN) process.Effect of nitrogen content on the microstructure and mechanical properties of WC-(Ti,M)(C_(1-x),N_(x))-Co cemented carbides fabricated by sinterhot isostatic pressing(HIP) were systematically investigated in this paper.The results show that the nitrogen content in the carbonitride raw powders strongly influences the morphology,the grain size and the compositions of the cemented carbides.All the cemented carbides with different nitrogen contents have a similar microstructural appearance:weak core-rim structure consisting of solidsolution phase embedded in WC-Co system.It is also observed that the carbonitride solid solution could somewhat reduce the WC grain growth,and the effectiveness of refining and the rim thickness are sensitively related to the nitrogen content of(Ti,M)(C_(1-x),N_(x)) solid solutions.In addition,with an increase in the nitrogen content,mechanical properties of these hard metals are enhanced,which were discussed in terms of the constituent,the microstructure and the solution behavior of the carbonitride solid solutions.