Reactive Quenching at Liquid-Solid Interface Induced by Pulsed Ruby Laser Treatment: Aqueous Oxidation of Iron.
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REACTIVE QUENCHING AT LIQUID-SOLID INTERFACE INDUCED BY PULSED RUBY LASER TREATMENT: AQUEOUS OXIDATION OF IRON.
S.B.Ogale, P.P.Patil, D.M.Phase, S.A.Kulkarni, S.V.Ghaisas and V.G.Bhide Department of Physics, University of Poona, Pune - 411 007, India.
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 M5ssbauer 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 A° 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.
INTRODUCTION In recent years considerable interest has grown in the use of high power lasers for the processing of material surfaces by employing both the thermal and photochemical aspects [1-3]. Pulsed lasers are of particular interest in this regard in view of their highly nonequilibrium processing character, which allows synthesis of novel phases of materials. In most of the experiments on laser-material interactions the main emphasis has been laid on use of material systems in the solid state and hardly any attempts have been made to explore the possibilities of synthesizing new materials by pulsed laser induced reactions in liquid media and at liquid-solid interfaces. Work has been reported in the literature on laser induced changes in chemical etching rates of solids in liquid media [4-61, however, such studies employ laser power primarialy to activate the surface mediated physico-chemical processes and do not involve massive energy transfer to the interface leading to interesting synthesis possibilities. In this paper we report the results of our experiments performed specifically to explore the latter concept. To our knowledge this is the first study of its kind to be reported in the literature. In the work presented here we have studied the influence of high power Q-switched Ruby laser pulses (30 ns pulsewidth) on the interface between Iron and water. This
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