Hexagonal Phase Transformation in the Engineered Scavenger Compound Lithium Titanate

摘要

Engineered scavenger compounds (ESC's) developed by the U.S. Bureau of Mines are a novel class of compounds that selectively can recover a desired element from a solid or molten alloy. Lithium titanate (Li2Ti3O7 or Li2O center dot 3TiO2) is used as an ESC to recover lithium (Li) from aluminum-lithium (Al-Li) alloys. X-ray diffraction measurements have shown that Li2Ti3O7 undergoes a phase change during scavenging from an orthorhombic structure to a hexagonal structure. This change is due to the incorporation of lithium in the matrix of the material and the effect of temperature. Although both phases are metastable, the hexagonal phase that forms during the scavenging of lithium from Al-Li alloys appears to be the more stable phase. Recovering lithium from the ESC by electrodeposition does not cause the structure to revert to the orthorhombic phase. The orthorhombic and the hexagonal structures of Li2Ti3O7 have similar scavenging capacities for lithium. The report proposes a new mechanism for the phase transformation.