Given the increasing concern regarding the global decline in rare earth reserves and the environmental burden from current wet-process recycling techniques,it is urgent to develop an efficient recycling technique for ...Given the increasing concern regarding the global decline in rare earth reserves and the environmental burden from current wet-process recycling techniques,it is urgent to develop an efficient recycling technique for leftover sludge from the manufacturing process of neodymium-iron-boron(Nd-Fe-B)sintered magnets.In the present study,centerless grinding sludge from the Nd-Fe-B sintered magnet machining process was selected as the starting material.The sludge was subjected to a reduction-diffusion(RD)process in order to synthesize recycled neodymium magnet(Nd2Fe14B)powder;during this process,most of the valuable elements,including neodymium(Nd),praseodymium(Pr),gadolinium(Gd),dysprosium(Dy),holmium(Ho),and cobalt(Co),were recovered simultaneously.Calcium chloride(CaCl2)powder with a lower melting point was introduced into the RD process to reduce recycling cost and improve recycling efficiency.The mechanism of the reactions was investigated systematically by adjusting the reaction temperature and calcium/sludge weight ratio.It was found that single-phase Nd2Fe14B particles with good crystallinity were obtained when the calcium weight ratio(calcium/sludge)and reaction temperature were 40 wt% and 1050℃,respectively.The recovered Nd2Fe14B particles were blended with 37.7 wt% Nd4Fe14B powder to fabricate Nd-Fe-B sintered magnets with a remanence of 12.1 kG(1 G=1×10^-4T),and a coercivity of 14.6 kOe(1 Oe=79.6A·m^-1),resulting in an energy product of 34.5 MGOe.This recycling route promises a great advantage in recycling efficiency as well as in cost.展开更多
As the cathode with the highest electron emission capability in the thermionic cathode,the scandate cathode has attracted more and more attention in recent years,especially the scandia doped tungsten matrix scandate c...As the cathode with the highest electron emission capability in the thermionic cathode,the scandate cathode has attracted more and more attention in recent years,especially the scandia doped tungsten matrix scandate cathode.Experimental studies show that scandia doped tungsten matrix scandate cathodes with submicron microstructures exhibit excellent emission capacity,and the pulse emission current density in the space-charge region can be over 35 A cm^(−2) at 850°Cb.In the direct current(DC)condition with temperature compensation,the emission current density could reach 25 A cm^(−2) at 850°Cb.The device lifetime is over 3700 h after operating at 950°C_(b) with the DC loading of 40 A cm^(−2).The emission mechanism of the scandate cathode including the effect of the surface structure and composition on the work function of the cathode are systematically reviewed.展开更多
基金financially supported by the National High Technology Research and Development Program of China(2012AA063201)the Beijing Municipal Natural Science Foundation(2172012)the State Key Laboratory of Rare Earth Permanent Magnetic Materials Opening Foundation(SKLREPM17OF02).
文摘Given the increasing concern regarding the global decline in rare earth reserves and the environmental burden from current wet-process recycling techniques,it is urgent to develop an efficient recycling technique for leftover sludge from the manufacturing process of neodymium-iron-boron(Nd-Fe-B)sintered magnets.In the present study,centerless grinding sludge from the Nd-Fe-B sintered magnet machining process was selected as the starting material.The sludge was subjected to a reduction-diffusion(RD)process in order to synthesize recycled neodymium magnet(Nd2Fe14B)powder;during this process,most of the valuable elements,including neodymium(Nd),praseodymium(Pr),gadolinium(Gd),dysprosium(Dy),holmium(Ho),and cobalt(Co),were recovered simultaneously.Calcium chloride(CaCl2)powder with a lower melting point was introduced into the RD process to reduce recycling cost and improve recycling efficiency.The mechanism of the reactions was investigated systematically by adjusting the reaction temperature and calcium/sludge weight ratio.It was found that single-phase Nd2Fe14B particles with good crystallinity were obtained when the calcium weight ratio(calcium/sludge)and reaction temperature were 40 wt% and 1050℃,respectively.The recovered Nd2Fe14B particles were blended with 37.7 wt% Nd4Fe14B powder to fabricate Nd-Fe-B sintered magnets with a remanence of 12.1 kG(1 G=1×10^-4T),and a coercivity of 14.6 kOe(1 Oe=79.6A·m^-1),resulting in an energy product of 34.5 MGOe.This recycling route promises a great advantage in recycling efficiency as well as in cost.
基金the National Key Research and Development Program of China(Grant 2017YFB0305600)National Science Foundation of China(Grant 51534009,51621003)Beijing Municipal High Level Innovative Team Building Program(Grant IDHT 20170502).
文摘As the cathode with the highest electron emission capability in the thermionic cathode,the scandate cathode has attracted more and more attention in recent years,especially the scandia doped tungsten matrix scandate cathode.Experimental studies show that scandia doped tungsten matrix scandate cathodes with submicron microstructures exhibit excellent emission capacity,and the pulse emission current density in the space-charge region can be over 35 A cm^(−2) at 850°Cb.In the direct current(DC)condition with temperature compensation,the emission current density could reach 25 A cm^(−2) at 850°Cb.The device lifetime is over 3700 h after operating at 950°C_(b) with the DC loading of 40 A cm^(−2).The emission mechanism of the scandate cathode including the effect of the surface structure and composition on the work function of the cathode are systematically reviewed.
