Passivation coating on titanium powder surface via SnCl4-Ti gas-solid fluidization reaction

ABS T R A C T Titanium powder is easily oxidized in the forming and sintering process due to its active chemistry. In this study, a passivation coating is formed on Ti powder surface via SnCl4-Ti gas-solid fluidization reac-tion using fluidized bed. It is found that at 200-350 degrees C, Ti-Sn-Cl-O passivation layer is formed on Ti pow-der surface on account of the reaction among SnCl4, oxide film on powder surface, and Ti matrix. Upon further increasing the temperature to above 500 degrees C, deoxygenation reaction occurs accompanied by the formation of gaseous TiClm and TiOxCly escaping from Ti powder matrix, resulting in the decreasing of surface oxygen content. Besides, elemental Sn and Ti-Sn compounds are formed on Ti powder surface, and part of Sn is diffused into titanium matrix. The passivation behavior is mainly consisted of oxygen film destruction and oxygen removal with the fluidization temperature increasing. Overall, the suitable temperature is about 350 degrees C to form a passivation coating on Ti powder surface, which can achieve oxida-tion isolation and deoxygenation in subsequent forming and sintering process.(c) 2023 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.