Fluoride vaporization and crystallization of CaF2–CaO–Al2O3–(La2O3) slag for vacuum electroslag remelting. (February 2022)

• Record Type: Journal Article
• Authors: Li, Tengfei; Li, Guangqiang; Zhang, Zhan; Liu, Yu; Wang, Xijie
• Is Part Of: Vacuum. Volume 196(2022)
• Publication Date: 2022-02
• Subjects: Fluoride vaporization -- Crystallization -- Slag -- Electroslag remelting -- La2O3 addition; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2021.110807
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: The vaporization and crystallization of CaF2 –CaO–Al2 O3 slags with different La2 O3 contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag within 7.4 wt% La2 O3 content at 1723 K are CaF2 and AlF3 . The weight loss of CaF2 –CaO–Al2 O3 -(La2 O3 ) slags decrease with increase of La2 O3 content in both thermo gravimetric experiment and vacuum condition. The addition of La2 O3 within 7.4 wt% reduces the viscosity and breaking temperature of investigated slag, and the change of viscosity is not the main reason to inhibit the fluoride vaporization. The vapor pressure of CaF2 and AlF3 at 1723 K decreases with increase of La2 O3 content because of the changes in component activity. Thus, fluoride vaporization becomes weakened. The crystalline phases of CaF2 –CaO–Al2 O3 slag are 11CaO·7Al2 O3 ·CaF2 and CaF2, while the crystalline phases of slag within 7.4 wt% La2 O3 content are (CaLa)Al3 O7, La(AlO3 ) and CaF2 . The La2 O3 addition can decrease the crystallization temperature of CaF2 and prevent the precipitation of 11CaO·7Al2 O3 ·CaF2 . Highlights: The vaporization and crystallization of CaF2 –CaO–Al2 O3 -(La2 O3 ) were analyzed by TG-DSC. The viscosity of CaF2 –CaO–Al2 O3 -(La2 O3 ) slag was measured. The crystalline phases ((CaLa)Al3 O7, La(AlO3 )) were found in CaF2 –CaO–Al2 O3 -7.4wt% La2 O3 slag.