발간논문

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A new process to extract Nd from domestic Nd-Fe-B magnet scraps was developed. The scraps were roasted in air and leached with H2SO4. The selective extraction of Nd was investigated in terma of roasting temperature, H2SO4 concentration, and leaching temperature and time. The increase in roasting temperature resulted in a significant reduction in the extraction rate due to the formation of FeNdO3. Nevertheless, Nd could be extracted more selectively since the extraction of Fe was retarded by the concurrent formation of Fe2O3 at higher temperatures. The selective extraction of Nd was observed to increase with shorter leaching time, lower H2SO4 concentration and leaching temperature. The solubility difference between FeSO4 and Nd2(SO4)3 was utilized to precipitate Nd as Nd2(SO4)3, which was separated as residue during the solid/liquid separation process after leaching. When scraps roasted at 700℃ was leached at the pre-determined optimum conditions(H2SO4 concentration: 4M, leaching temperature: 70℃, leaching time: 180 minutes, pulp density 100g/1) about 70% of Nd could be selectively separated as Nd2(SO4)3 precipitates. The Nd/Fe ratio in the precipitate was found to be about 18.33.

keyword : Neodymium, Nd-Fe-B magnet, Scraps, Selective Extraction

Effect of the initial melt temperature on the microstructure of the sprayformed 2014 Al billet was studied with particular emphasis on the effect of superheating on the liquid fraction(FL) in the sprayed droplets. In order to determine the average liquid fraction within the sprayed droplets, the cooling rate and the flight time of droplets were calculated. The measured cooling rate of droplets was in the vicinity of ~104℃/sec and the flight time before impinging the preform ranges from 6 to 9 msec depending on the size of droplets. The obtained results from the experiments were in good agrement with those of theoretical models by P. Grant et al. and/or Lee et al. The liquid fraction of droplets did not vary significantly with the initial melt temperature such that FL was calculated to be 24% when Ti = 800℃ while FL = 19.5% when Ti = 720℃, resulting in considerable amount of porosity within the preform. Such a result indicates that the initial melt temperature control may not be effective for fabricating preforms with a minimal amount of porosity.

keyword : Spayforming, Aluminum alloy, Cooling rate, Solid fraction