NMR study of the short range order in Fe–B amorphous powders prepared by borohydride reduction

Abstract

The Fe–B amorphous alloys powders with high boron concentration can be prepared by borohydride reduction (BHR). By adjusting technological factors, the Fe100−xBx amorphous powders with compositions ranging from x=17 to 40 can be easily obtained, but it is difficult to make the amorphous ribbons with such a high B concentration by using rapidly quenched technique, which can usually obtain the amorphous ribbons with the compositions ranging from x=12 to 25. Up to now, there are different points of view about if the short range order (SRO) in the Fe–B amorphous powders prepared by the BHR around room temperature is the same with that in the amorphous ribbons made by rapidly quenched and vapor depositing techniques. In this paper, the SRO in Fe100−xBx amorphous powders with various boron concentration prepared by the BHR have been studied by the zero field spin echo nuclear magnetic resonance (NMR) technique. It was shown that the types of SRO in these samples vary with the B concentration. There exist Fe3B- and Fe2B-like SRO and a small amount of α-Fe in the samples with lower B concentration, while there are Fe3B- and FeB-like SRO in the alloys with higher B concentration. Fe3B-like SRO, however, only exists in the amorphous ribbons obtained by rapidly quenched method. It can be concluded that there are different types of SRO in the amorphous alloys prepared by different methods. This conclusion can explain the reason why the average hyperfine field at Fe sites deceases with the B concentration increasing.

Cobalt precipitation by reduction with sodium borohydride

“…Amorphous materials can used as ferrofluids, catalysts, and magnetic recording materials [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

“…The rate of the formation of zinc borohydride is probably much faster than that of the cobalt reduction. According to the literature [135], the following reactions may occur: (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) According to this scheme, the zinc borohydride decomposes into zinc hydride and borane both of which hydrolyze rapidly. The hydrolysis of zinc hydride produces zinc ions which further react with borohydride ions and thus catalyze the hydrolysis of borohydride.…”

“…The commercial importance of sodium borohydride reached its first peak in the fifties in U.S. military research programs [4,5]. Recently borohydride reduction of metal ions is the basis of several commercial processes including: (1) the preparation of selective catalysts, magnetic materials [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], (2) the recovery of precious metals (silver, gold, platinum and palladium group metals) [6,[25][26][27][28][29][30][31][32][33][34][35], (3) the removal and recovery of heavy metals (mercury, lead, copper, nickel, cobalt and silver) from aqueous discharge streams [36][37][38][39][40][41][42][43][44][45][46][47], and (4) the electroless plating of nickel, cobalt, copper, silver and gold o...…”