Phase Relationship at Subsolidus Tem-perature of MgO-MgAl2O4-ZrO2 Subsystem

doi:10.19691/j.cnki.1004-4493.2020.01.001

China's Refractories ›› 2020, Vol. 29 ›› Issue (1): 1-6.DOI: 10.19691/j.cnki.1004-4493.2020.01.001

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Phase Relationship at Subsolidus Tem-perature of MgO-MgAl₂O₄-ZrO₂ Subsystem

GAO Zhenxin¹^,²^,^*()

1 Sinosteel Luoyang Institute of Refractories Research Co., Ltd., Luoyang 471039, China
2 Beijing Research and Development Center of Puyang Refractories Group Co., Ltd.,Beijing 100039, China

Online:2020-01-10 Published:2020-01-10
Contact: GAO Zhenxin
About author:Prof. Gao Zhenxin joined Tangshan Steel Plant in 1953. In 1972, he transferred to Luoyang Institute of Refractories Research of the Ministry of Metallurgy (now Sinosteel Luoyang Institute of Refractories Research Co., Ltd.). He has worked for more than 60 years and published more than 90 papers, 4 monographs and 1 translation book.

Abstract

Abstract:

Three groups of cylinder specimens (φ10 mm×10 mm) with 20%, 30% and 40% (by mass, the same hereinafter) of ZrO₂, were prepared using analytically pure MgO, Al₂O₃ and ZrO₂ powders as the starting materials. The specimens were fired at 1 600 ℃ for 5 h, 1 700 ℃ for 0 h and 1 800 ℃ for 7 h, respectively. The microstructure of the MgO-MgAl₂O₄-ZrO₂ subsystem was studied by FESEM. The results show that (1) in the temperature range of 1 600-1 700 ℃, solid phase reactions happen in the MgO-MgAl₂O₄-ZrO₂ subsystem, leaving three phases: periclase, spinel and ZrO₂ (solid dissolving with Mg²⁺ ) co-existing; spinellization affects the densification; (2) the specimen with 40% ZrO₂ fired at 1 800 ℃ has heterogeneous melting microstructure; some areas form typical ternary eutectic MgO-MgAl₂O₄-ZrO₂ with composition of MgO 35.2%-37.2%, Al₂O₃ 24.2%-26.6%, and ZrO₂ 37.2%-39.8%.

Key words: magnesia-magnesium aluminate spinel-zirconia subsystem, subsolidus, phase relationship, microstructure

GAO Zhenxin. Phase Relationship at Subsolidus Tem-perature of MgO-MgAl₂O₄-ZrO₂ Subsystem[J]. China's Refractories, 2020, 29(1): 1-6.

Figures/Tables 14

Fig. 1 MgO-Al2O3-ZrO2 system phase diagram

Table 1 Formulations of specimens and their locations in phase diagram

Specimens	Formulations /mass/%			Designed MA contents /mass/%	Locations
Specimens	MgO	Al₂O₃	ZrO₂	Designed MA contents /mass/%	Locations
1^#	32	48	20	66	In the M-MA-Z area close to the MA-Z join
2^#	20	50	30	70	On the MA-Z join
3^#	37	23	40	32	In the center of M-MA-Z area

Table 2 Linear shrinkage rate and bulk density of specimens fired at 1 600 ℃ for 5 h

Specimens	Linear shrinkage rate /%	Bulk density / (g · cm^-3)
1^#	10.7	3.00
2^#	4.7	2.74
3^#	19.6	3.75

Fig. 2 Microstructure of specimens fired at 1 600 ℃ for 5 h

Fig. 3 Agglomerates of ZrO2 submicron grains in specimen 1#

Fig. 4 Idiomorphism growth of MA in specimen 2#

Fig. 5 Agglomerates of ZrO2 submicron grains in specimen 3#

Fig. 6 Three phase coexistence of ZrO2+MA+MgO in specimen 2# fired at 1 700 ℃ for 0 h

Fig. 7 Microstructure of specimens fired at 1 800 ℃ for 7 h

Fig. 8 Exsolution phenomenon of ZrO2

Fig. 9 Step growth of MA

Fig. 10 Microstructure of heterogeneous melting

Fig. 11 Ternary eutectic in area A of Fig. 10

Fig. 12 Three phase coexistence in area B of Fig. 10

References 8

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Phase Relationship at Subsolidus Tem-perature of MgO-MgAl₂O₄-ZrO₂ Subsystem

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