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1、Pressless process for isotropic magnets and its application,Manlong Xia27 November 2015 DTU Energy s annual PhD symposium,Outline,IntroductionThe application of magnet The Press-less Process (PLP)Experimental workThe Pressless and compact magnets from strip cast materialDiscussion about PLP method u
2、sing for recycling magnetsConclusion,Critical elements for clean energy technology-U.S. strategy,U.S. Department Of Energy, Critical Materials Strategy, December 2011,Alternative supplies of RE to Danish industry,RFeBmagnets,Applications,R metal,Rare earth oxides,Mineral,Rock,RFeB Powder,Waste ! Rec
3、ycling?,R2Fe14B magnetic alloy,Nedko Drebov et al, Ab initio screening methodology applied to the search for new permanent magnetic materials. New Journal of Physics 15 (2013) 125023,N48M commercial magnet,Vacuumschmelze,Patent: EP 0 680 054 B2 (2004),T1: Nd2Fe14B,T2: Nd1+Fe4B4,Sagawa et. al., “NdFe
4、B Permanent Magnet Materials,” Jpn. J. Appl. Phys., vol. 26, pp. 785-800, 1987.P. Bjse, PhD thesis 1990.,Phase diagram,Press Less method Sagawa (2012),Patent: EP 2 472 535 A1 (2012),Jet Mill,Graphite mould,Compacting,Alignment magnet,Heating coils (250 oC),Vacuum furnace,Mould stacking,M.Sagawa prep
5、ared 0.3m powder by HDDR+HD+He jet mill,The principle for Pressless process,compact,PLP,PLP process can produce low oxygen content of sample by enclose the whole system in argon.,K. Hono and H. Sepehri-Amin. Scripta Materialia 67 (2012) 530535,Pressless process and traditional compact method in expe
6、riment,Two kinds of strip-cast NdFeB alloys were used in our experiment: Dy = 0 wt% (BL8214)Dy = 4 wt% (48508)The strip cast alloys were subjected to hydrogen in 2 hours for rough grinding. Dry high energy ball milling in DTU and jet milling in Tallinn Technology University were used to produce fine
7、 powder. For Pressless method, tap the fine powder into graphite crucibles to a density of 3 g/cm3.To make a comparison with samples prepared by Pressless method, we also compact the sample with axial press (445MPa pressure). The samples were transport into furnace tube to do pump and prepare for si
8、ntering. The sintering program is shown below. The sintering time will be 2 h and we sintered samples at 1090, 1110 and 1130, and then cool down.,Sintering profile,25/4-2012,time,Temp oC,2 oC/min,250 oC*1h,2 oC/min,Tsinter*2h,5 oC/min,570 oC*1h,cooling,Successful magnets microstructure: thin grain b
9、oundary,The microstructure of 48508 (4 wt % Dy) 1130 PLP sample.,Backscattered electrons(BSE),Secondary electrons(SE),2 m,2 m,Grain boundary,Grain boundary,0 wt% Dy (BL8214) PLP samples,1090*2h,1110*2h,1130*2h,4 wt% Dy (48508) PLP samples,1110*2h,1090*2h,1130*2h,PLP vs compact magnets,25/4-2012,The
10、interesting fact about Pressless Process,Oxygen content 4 wt% Dy PLP sample was sintered at 1110 for 2h, the samples oxygen content is 6101 ppm, however, the coercivity of the sample is still 368 kA/m.Initial powder sizeUsing high energy ball milling to dry mill 4 wt% Dy sample, we got powder whose
11、mean size is 46.18 m (laser). Using these to do pressless process and sintered at 1110 for 2h, we got sintered samples whose magnetic properties are: Hci = 1022 kA/m, Br = 0.69 T.,Conclusion,We successfully prepared high density samples by Press-Less process by jet milling powder and high energy dry ball milling powder. The key issue for this process are acquired.We found the Pressless process can acquire similar properties as traditional compaction method, which especially can apply to recycle magnets, with a cheaper price.,Thanks !,
