二硼化镁的热氧化特性研究

doi:10.15541/jim20180428

摘要/Abstract

摘要：

利用氧弹式量热计、热分析仪器、高温管式炉等实验装置及手段, 研究了MgB₂颗粒的热氧化特性和能量释放特性。结果表明, MgB₂的实测燃烧热值和燃烧效率均高于无定型硼。在298~1673 K的温度区间内, MgB₂在缓慢升温条件下的热氧化反应包含四个阶段, 其主要的氧化放热和增重都发生在1200~1665 K之间。而无定型硼主要的氧化放热和增重都发生在1919 K附近。在1665 K时, MgB₂的氧化率高达94.3%, 而无定型硼的氧化率仅为43.6%。与无定形硼相比, MgB₂可以在更低温度下充分氧化, 热氧化特性优于无定形硼。

关键词: 硼, 二硼化镁, 氧化特性, 燃烧效率

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

中图分类号:

TJ55

郭洋, 张炜, 周星, 邓蕾. 二硼化镁的热氧化特性研究[J]. 无机材料学报, 2019, 34(8): 873-878.

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

图/表 12

表1 无定型硼和MgB2的燃烧热及燃烧效率

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

图1 空气气氛中MgB2的热氧化TG和DTA曲线

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

图2 MgB2氧化产物的SEM照片

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

图3 MgB2氧化产物的XRD图谱

Fig. 3 XRD patterns of MgB2 oxidation residues

Table 2 Chemical analytical results 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

图4 B2O3-MgO二元相图[23]

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

图5 MgB2块体在1665 K氧化后的表层剖面SEM照片

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

图6 MgB2块体表层剖面的线扫描EDS能谱

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

表3 MgB2块体氧化表层的EDS能谱结果

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

图7 内层氧化物XRD图谱

Fig. 7 XRD pattern of the internal porous oxide layer

图8 MgB2的氧化反应历程

Fig. 8 Schematic diagram of evolution of MgB2 oxidation reaction

图9 超高温条件下无定形硼的热氧化TG和DTG曲线[24]

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

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