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Ti alloys are normally covered by one layer of 3nm thick native oxide , namely TiO2 , which provides excellent chemical inertness , corrosion resistance and biocompatibility .
 material: Ti alloys; process parameter: layer; material: oxide; material: TiO2; machanical property: chemical inertness; concept or principle: corrosion resistance; machanical property: biocompatibility
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 material: Ti alloys; process parameter: layer; material: oxide; material: TiO2; machanical property: chemical inertness; concept or principle: corrosion resistance; machanical property: biocompatibility