Quantum mechanics

Titanium nitride

Engineering

Oxide

Metallurgy

Materials science

Layer (electronics)

Thermogravimetry

Telecommunications

Computer science

Radiochemistry

Inorganic chemistry

Chemical engineering

Nitrogen

Zirconium nitride

Thermodynamics

Physics

Organic chemistry

Oxygen

Degradation (telecommunications)

Zirconium

Partial pressure

Isothermal process

Kinetics

Chemistry

Nitride

Nucleation

Zirconium alloy

Journal of Nuclear Materials

Zirconium-based alloys used in PWR cladding show an acceleration of their oxidation kinetics in air at high temperature compared to their behaviour under oxygen or steam alone. This paper presents an analysis of the oxidation kinetics in order to explain the role of nitrogen during the accelerated corrosion. Isothermal thermogravimetry on alloy thin plates was used to collect kinetic data during the reaction of Zircaloy-4 at 850 °C in oxygen and nitrogen mixtures. The influence of oxygen and nitrogen partial pressure on the degradation kinetics was studied by a jump method. The presence of nitrogen in the reacting gas enables the formation of zirconium nitride near the oxide–metal interface which acts as a catalytic phase. A three steps reaction path composed of nitride oxidation, α-Zr(O) nitridation and oxidation is proposed. A detailed mechanism and the rate-determining step of the overall process are proposed that account for the experimentally observed dependence of the kinetic rate with the oxygen and nitrogen partial pressures; a kinetic model based on surface nucleation and growth of regions attacked by nitrogen was successful in describing the mass variations with time of exposure at 850 °C.

Modelling of Zircaloy-4 accelerated degradation kinetics in nitrogen–oxygen mixtures at 850 °C