Nd-Fe-B系スプレー造粒粉中のPVAの熱分解挙動 Thermal Decomposition Behavior of PVA as Organic Binder of Spray Dried Nd-Fe-B System Powder
Debinding process under hydrogen atmosphere is effective to eliminate the residual carbon contents in Nd-Fe-B system green body which is compacted by using spray dried powder. But it is not effective for elimination of residual oxygen contents comparatively. The emitted gas from compacted body of Nd-Fe-B system spray dried powder including poly(vinyl alcohol)(PVA) as a binder was analyzed by mass spectroscopy. Much emission of a fragment with m/z=16 was observed only when spray dried powder was heated under hydrogen atmosphere. The fragment was proved to be methane by gas chromatography. DTA curve measured simultaneously for spray dried powder showed absorption of hydrogen by Nd-Fe-B in the vicinity of 220°C, and the desorption of hydrogen started above 230°C. The latter was accompanied by enhancement of the emission of hydrocarbon such as methane. Hydrogen atom sent out from Nd-Fe-B powder would make the fragments from main chain of PVA stable, and accelerates the debinding by vaporization of methane and other hydrocarbon with low mass number. In contrast, degraded side-chain of PVA would immediately combine with neodymium of Nd-Fe-B powder and form Nd<SUB>2</SUB>O<SUB>3</SUB> which remains in the sintered body.
粉体および粉末冶金 45(7), 646-651, 1998-07-15
Japan Society of Powder and Powder Metallurgy