Preparation of Coating Material of Welding Electrode from Marine Placer via Carbothermic Reduction

Abstract

The preparation of coating material of welding electrode from marine placer via carbothermic reduction was systematically investigated. Four stages were observed in the carbothermic reduction of marine placer–coal mixture. The release of the volatiles in coal occurred at the first stage (≤600°C), and the solid–solid reduction and gas–solid reduction occurred at the second (600–960°C) and third stages (960–1350°C), respectively. The reduction rate of iron oxide at the third stage was higher than that at the second stage because of the high carbon gasification rate. A slowdown in the total mass loss at approximately 1350°C occurred at the fourth stage. X-ray diffraction patterns show that the reduction process of the marine placer exceeded 1100°C and can be written as: FeTiO₃→FeTi₂O₅→Fe+TiO₂. The quality index of the reduced ilmenite was evaluated in terms of the TiO₂ and FeO content. The TiO₂ content gradually increased as the reduction temperature increased from 1000°C to 1300°C, and the reduction time exerted lesser influence than temperature. The FeO content initially decreased rapidly and then exhibited a downward trend that became slower after 120 min with increasing reduction time. The TiO₂ index could be achieved easily because of the high TiO₂ content of the raw material. The FeO content could reach 8.45% after reduction at 1300°C for 180 min, which exceeded the technical requirement of 9%.