Preparation of Ultra-fine NdB6 Powders by Combustion Synthesis and Its Reaction Mechanism

doi:10.3724/SP.J.1077.2014.13516

Abstract

Abstract:

Ultrafine powders NdB₆ were prepared by combustion synthesis with B₂O₃, Nd₂O₃ and Mg as raw materials. The effects of reaction atmosphere, sample pressure and raw materials ratio on the reaction product morphology and phases were studied. Characterizations by XRD and SEM show that the products consist of NdB₆, MgO and a little amount of Mg₃B₂O₆ and Nd₂B₂O₆. After reaction with sulphuric acid at low concentration to eliminate the latter three components, the pure NdB₆ is obtained (purity 99.1%). As the preparation pressure increases, the NdB₆ particle sizes become small. When the sample pressure is 20 MPa, the average particle size is less than 500 nm. The preparation reaction process is as follows: firstly, Mg reduces Nd₂O₃ to generate Nd and MgO; and then, the reaction between Mg and B₂O₃ are ignited to generate B and MgO; at the same time, the generated Nd and B are reacted to produce NdB₆. The apparent activation energy of the reaction is 691.59 kJ/mol and the reaction order is 3.2.

Key words: combustion synthesis, neodymium hexaboride, ultrafine powder, reaction mechanism

CLC Number:

TQ174

DOU Zhi-He, ZHANG Ting-An, WEN Ming, SHI Guan-Yong, HE Ji-Cheng. Preparation of Ultra-fine NdB₆ Powders by Combustion Synthesis and Its Reaction Mechanism[J]. Journal of Inorganic Materials, 2014, 29(7): 711-716.

Figures/Tables 6

Fig. 1 XRD patterns of combustion products (a) excessive 5% of Mg in contrast to the theoretical mass ratio of reaction (1) and preparing sample pressure at 20 MPa in air; (b) excessive 10% of Mg in contrast to the theoretical mass ratio of reaction (1) and preparing sample pressure at 20 MPa in vacuum

Fig. 2 XRD patterns of leaching products

Fig. 3 SEM images of burning products and EDS results (a) theoretical mass ratio of reaction (1); (b)~(d) excessive 5%, 10% and 20% amount of Mg, respectively, more than theoretical mass ratio of reaction (1); (e) and (f) excessive 10% amount of Mg more than theoretical mass ratio of reaction (1) and reaction pressure at 10 MPa and 20 MPa, respectively; (g) and (h) EDS results of region1 and region 2 in sample (c), respectively

Fig. 4 SEM images of NdB6 powders and EDS result The preparing pressures for samples (a)-(c) are 5, 10 and 20 MPa in atmosphere, respectively, and samples (d)-(f) are 5, 10 and 20 MPa in vacuum, respectively; (g) EDS result of region 1 in (f)

Fig. 5 DSC curves of different reaction systems (a) Mg~B2O3 system; (b) Mg~Nd2O3 system; (c) Mg~B2O3~Nd2O3 system

Fig. 6 Reaction mechanism of Mg-Nd2O3-B2O3 system

References 14

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Preparation of Ultra-fine NdB₆ Powders by Combustion Synthesis and Its Reaction Mechanism

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