Reactive quenching at liquid-solid interface induced by pulsed ruby laser treatment: aqueous oxidation of iron

Abstract

This paper demonstrates that metastable compounds can be synthesized on solid surface, via pulsed laser induced processes at the liquid solid interface. Specifically, it is shown that the metastable oxides of iron can be obtained when an iron foil immersed in water is treated with ruby laser pulses [ A =693.4 nm, pulse width 30 ns, energy density 10 J/cm ²]. The oxide has been characterized by using the techniques of conversion electron Mossbauer spectroscopy, x-ray diffraction and Rutherford backscattering spectrometry. The oxygen concentration near the surface as well as the depth scale over which it falls to zero can be varied by changing the laser treatment parameters such as pulse to pulse overlap, energy per pulse etc. A near-surface composition of iev 50 at.%and a depth scale of oxygen incorporation of a few thousand Å can be easily achieved. The phase transformation of a metastable oxide under thermal treatment is also explored. The mechanisms which could be responsible for the observed effects are commented upon. Some iron foils have been treated in air using comparable laser pulse parameters to obtain a comparision between treatment in air and liquid. Interestingly these foils show presence of 'f-Fe, which is a high temperature phase of iron known to be unstable at room temperature when pure. Other possible applications of laser processing of solids in liquid media are also discussed.