Nickel Nanorods Research Articles

Oxidation kinetics of nickel solar absorber nanoparticles

The alumina matrix of an electrolytically deposited solar absorbercoating was etched away leaving nickel nanorods standing on an aluminiumsupport. The oxidation kinetics of the nickel nanorods, with an approximatediameter of 30 nm and a height of approximately 300 nm, was determined byinfrared (IR) spectroscopy. The IR absorption by longitudinal opticalphonons in NiO was measured before and after exposure to pure oxygen at 260,280, 300, 320 and 350 °C for different times. The absorptance peak height wasdetermined and used as a measure of the degree of oxidation. The fivedifferent isotherms showed power-law behaviour with an exponent varyingbetween 0.52 and 0.69. A fit to the homogeneous linear diffusion equation,derived for spherical geometry, gave parabolic rate constants, which are inagreement with data for larger nickel particles and bulk nickel. Thedeviations in the exponent from that of the parabolic law are discussed interms of particle geometry and particle agglomeration. The apparent activationenergy was determined, by the use of a master plot technique, to be 1.73 eV.

Oxidation Kinetics of Nickel Particles: Comparison Between Free Particles and Particles in an Oxide Matrix

The degradation of selective solar absorbers through oxidation has been studied. We compare the oxidation kinetics of nickel particles of various sizes. Both free particles and particles embedded in an oxide matrix were studied. The oxidation kinetics of polycrystalline nickel nanorods was determined by IR spectroscopy in the temperature range 300–500°C. The particles were oxidized when situated in the porous alumina matrix of an electrochemically deposited solar absorber coating. The oxidation kinetics was compared to that of free nanometer-particles at the same temperature and to micron-sized polycrystalline nickel particles, which were studied by thermogravimetry in a wider temperature range. It was found that the rate constant was markedly lower for the particles in the matrix. Implications for the durability of selectively solar absorbing coatings are discussed.