Oxidation kinetics of refractory carbides at low oxygen partial pressures

摘要

The interaction kinetics of sinteredrefractory carbides such as NbC,TiC,VC and ZrC withatmospheres at low oxygen partial pressure is reportedfrom ambient to 1000℃ and from 0.8 to 20 Pa at thetotal pressure of 1.6bar(rel) in Ar. Depending on theexperimental conditions, the isothermal reaction ratewas found decreasing or increasing on time. Thisbehaviour has been linked to the parameterΓ,definedas the ratio between the weight change of the sampleand the number of moles of oxygen consumed. Adecreasing trend of the reaction rate corresponds toa null value ofΓ.In this case, no growth of oxideoccurs but an increase of atomic disorder on thesurface of the carbide is expected. A positive trendof the reaction rate impliesΓ?0 as well as the growthof an oxide layer driven by a solid state mechanism.The oxidation kinetics was never found parabolic. Itis linear at the highest temperatures regardless ofthe oxygen partial pressure value and it approachesto be parabolic by decreasing the temperature andincreasing the oxygen partial pressure.