Oxidation Characteristics of Magnesium Diboride

doi:10.15541/jim20180428

Abstract

Abstract:

The oxidation characteristics and energy releasing characteristics of MgB₂ were studied using oxygen bomb calorimeter, thermal analyzer and tube furnace. Results show that the combustion heat and combustion efficiencies of MgB₂ are all higher than those of amorphous boron. In the temperature range explored (298-1673 K), four successive phases are observed in the oxidation process of MgB₂ under slow heating rate. The primary oxidation stage of MgB₂ occurrs between 1200 K and 1665 K. However, the primary oxidation stage of amorphous boron occurrs nearly 1919 K. At 1665 K, the oxidation percentage of MgB₂ is 94.3%, compared to 43.6% of amorphous boron. Compared with amorphous boron, the fact that complete oxidation of MgB₂ can be achieved at lower temperature indicates its superiority.

Key words: boron, magnesium diboride, oxidation characteristics, combustion efficiency

CLC Number:

TJ55

GUO Yang, ZHANG Wei, ZHOU Xing, DENG Lei. Oxidation Characteristics of Magnesium Diboride[J]. Journal of Inorganic Materials, 2019, 34(8): 873-878.

Figures/Tables 12

Table 1 Combustion heats and combustion efficiencies of amorphous boron and MgB2

Sample	Theoretical combustion heat /(J·g^-1)	Experimental combustion heat /(J·g^-1)	Combustion efficiency /%
B	-58826	-22465±114	38
MgB₂	-38781	-23943±788	62

Fig. 1 TG and DTA curves of MgB2 oxidation in air flow

Fig. 2 SEM images of MgB2 oxidation residues (a) Without oxidation; (b) 1165 K; (c) 1300 K; (d) 1405 K; (e) 1520 K

Fig. 3 XRD patterns of MgB2 oxidation residues

Temperature /K	${{n}_{\text{MgO}}}/{{n}_{{{\text{B}}_{\text{2}}}\text{O}}}_{_{\text{3}}}$	Fraction of unoxidized Mg/mol%	Fraction of unoxidized boron/mol%	${{n}_{\text{B}}}/{{n}_{\text{Mg}}}$
1165	1.14 : 1	81.11	83.38	2.06 : 1
1300	3.04 : 1	22.73	74.62	6.56 : 1
1405	1.52 : 1	6.35	38.35	12.08 : 1
1520	1.26 : 1	2.14	22.30	20.89 : 1

Fig. 4 B2O3-MgO binary phase diagram[23] M: MgO; MB2: MgB4O7; M2B: Mg2B2O5; M3B: Mg3B2O6

Fig. 5 Cross-sectional SEM image of oxide layer structure of MgB2 pellet after being heated up to 1665 K

Fig. 6 Linear EDS mapping of MgB2 pellet across the oxide layer

Table 3 EDS results of the internal and external oxide layer of MgB2 pellet

Position	B/mol%	O/mol%	Mg/mol%
Internal	11.78	51.22	37.00
External	—	56.43	43.57

Fig. 7 XRD pattern of the internal porous oxide layer

Fig. 8 Schematic diagram of evolution of MgB2 oxidation reaction

Fig. 9 TG and DTA curves of amorphous boron oxidation under ultra-high temperature[24]

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