Original Article

Effect of Fe_tO on viscosity and structure of Na₂O₃-B₂O₃-CaO-SiO₂-Al₂O₃ slag

¹ Jiangxi Key Laboratory of Advanced Copper-based Materials, Institute of Applied Physics, Jiangxi Academy of Sciences, Nanchangc 330096, PR China
² Ganjiang Innovation Academy, Chinese Academy of Sciences, Ganzhou 341003, PR China
³ School of Mechanical Engineering, Henan University of Science and Technology, Luoyang 471000, PR China

^* e-mails: lyguojunli@163.com (Guo Junli); huqiang1225@163.com (Hu Qiang)

Received: 18 March 2024
Accepted: 31 October 2024

Abstract

The effects of Fe_tO on the characteristic melting temperature, viscosity, and structure of Na₂O₃-B₂O₃-CaO-SiO₂-Al₂O₃ slag were investigated. Understanding the viscous behavior and structure of borate slag containing Fe_tO can guide the design of mold powders for copper alloy casting. The melting temperature (T_h) suddenly increased and exceeded 800 °C when the Fe_tO content increased from 15 to 23 wt%. The viscosity changed significantly with increasing Fe_tO content when the temperature was below 1050 °C. The slag structure exhibited a boron–iron anomaly. The viscosity of the Na₂O₃-B₂O₃-CaO-SiO₂-Al₂O₃ slag gradually increased with increasing Fe_tO content. When the content of Fe_tO was low, sufficient oxygen in the slag promoted iron and boron to enter the network structure in the form of [FeO₄] and [BO₄], thereby reducing free oxygen and free [BO₃]. As the Fe_tO content exceeded a certain value, free oxygen decreased proportionally, and some iron ions existed in the form of [FeO₆] with the network modifiers. Simultaneously, the amount of free [BO₃] that is not bound to oxygen increased. Based on the optical basicity viscosity prediction model, the viscosity of borate slag with high iron content was predicted, and the M–O bond strength reflected by optical basicity was closer than the strength predicted for the network structure based on slag viscosity.