Influences of La2O3 Addition on Connectivity of Phase Compositions and Microstructural Evolution of Weld Slag

In this work, the influences of La2O3 addition on the connectivity of the glass network, phase compositions and microstructural evolution of weld slag were investigated through Raman spectrum, X-ray powder diffraction (XRPD), SEM and EBSD technologies. All experimental results indicated that La2O3 addition could modify the whole glass network’s connectivity and short-ordered units. According to the Raman spectrum, only 1 wt.% La2O3 addition resulted in the occurrence of a unique linking mode of Si-O and Al-O tetrahedrons that was assigned to feldspar phases (albite or anorthite). Further XRPD examination showed that the primary phases were albite and anorthite, which agreed with the Raman results. Moreover, enhanced linkage between Si-O and Al-O tetrahedrons needs a large amount Na+ to achieve electric neutrality. This repaired the connectivity of the slag network due to the lack of Na+. Additionally, the solubility of La2O3 in the slag matrix was limited to about 3 wt.%. Adding further La2O3 to this weld slag, the existence form of La2O3 retained its original status. Thus, La2O3 addition that exceeded 3 wt.% had little effect on the slag connectivity besides providing a phase interface. In conclusion, La2O3 addition in weld slag could promote the hardness and the formation of feldspar phases. Feldspar is an extremely fragile silicon aluminate crystal. The factors mentioned above caused the detachability to be enhanced when adding La2O3.