Investigation of chloride impurities in hydrogenated–dehydrogenated Kroll processed titanium powders

Abstract

An investigation to identify the chlorides in hydrogenated–dehydrogenated Kroll processed titanium powder was carried out in this study. Jigsaw-like agglomerates containing submicroscopic particles were observed on titanium particles, and the microcompositional analysis suggests the presence of magnesium and chlorine. Further detailed surface chemical analysis carried out by X-ray photoelectron spectroscopy and corresponding curve fitting work revealed that the magnesium and chlorine mainly exist as Mg(OH)Cl and titanium chloride respectively. A mechanism is provided to explain the presence of these chlorides in the Ti powder. The chlorides are considered to arise from the decomposition of hydrated magnesium chloride during the hydrogenation–dehydrogenation process and are supported by thermal analysis of a pure hydrated magnesium chloride. This analysis suggests that the Mg(OH)Cl can further decompose into hydrogen chloride gas and magnesium oxide at high temperature. The implications of the formation of these gaseous species on the sintering of Ti powders are discussed.

Keywords:

• Titanium
• Kroll process
• Chloride impurities
• Microstructural characterisation
• X-ray photoelectron spectroscopy

Acknowledgements

This work is financially supported by University of Waikato, under subcontract to Foundation for Research, Science and Technology (contract no. UOWX0802). The authors also acknowledge Dr P. Cao (University of Auckland, New Zealand) and Dr Y. Liu (Central South University, China) for useful discussion.