S. B. Ogale

Ion beam mixing at Fe:Al2O3 interface: A conversion electron Mössbauer spectroscopy study

The effect of ion beam induced atomic mixing and subsequent thermal transformations at the Fe:Al2O3 interface have been investigated by means of conversion electron Mössbauer spectroscopy [CEMS]. It is shown that the asdeposited and ion beam mixed samples exhibit distinctly different features. In particular, the ion beam mixed sample in as-mixed state shows the presence of FeAl2O4 along with non-stoichiometric FeO. Upon annealing at 600°C it shows precipitation of α-Fe with reduced contribution of FeAl2O4. The study of dose dependence of ion beam mixing has also revealed interesting features regarding the ion beam induced interface reactions.

Deposition of stainless steel film using pulsed laser evaporation

Abstract Stainless steel has been deposited in thin film form on glass, iron and carbon substrates using pulsed laser evaporation from bulk 304 steel specimens. Phase identification in the deposited film has been carried out using conversion electron Mossbauer spectroscopy and low angle X-ray diffraction techniques. Rutherford backscattering spectrometry and energy-dispersive analysis of X-rays of these films indicate the preservation of the target stoichiometry in the transfer of matter from the bulk to the film. It is shown that the laser-deposited steel film can serve as protective coating for iron against thermal oxidation.

Electrochemical corrosion behaviour of ion-beam-mixed Fe-Al alloy: A conversion electron Mössbauer spectroscopic study

Abstract The electrochemical corrosion behaviour of ion-beam-mixed Fe-Al composites has been studied by using the technique of interface-sensitive conversion electron Mossbauer spectroscopy (CEMS). Polycrystalline aluminium foils deposited with a film 50 A thick of the 57 Fe Mossbauer isotope and an overlayer 250 A thick of natural iron have been bombarded with 100 keV Ar + ions at a dose in the range of about (1–3)×10 16 ions cm -2 to induce atomic mixing at the interface. A number of as-deposited and ion-beam-mixed composites have been subjected to electrochemical corrosion treatment in a buffer solution by employing the three- sweep potentiokinetic polarization technique. It has been shown that the atomically mixed interface region exhibits corrosion behaviour considerably different from that exhibited by either iron or aluminium foils. The as-deposited as well as the ion-beam-mixed composites have been characterized by 57 Fe CEMS prior to the corrosive attack and after passivation so as to identify the structural state of the interface and the transformations occuring in the interface as a result of the corrosive reactions. The standard Mossbauer fitting procedure was used in conjunction with a method of obtaining hyperfine field distributions to establish that the corrosive action of the aqueous medium on the ion-beam-mixed Fe-Al composite leads to the elimination of the magnetic spectral components and to the growth of passive non-magnetic phases such as β-γ-FeOOH and FeO.

Pulsed laser treatment at Fe/C6H6 interface: A Mössbauer effect study

The pulsed ruby laser induced reactive-quenching process at Fe/C6H6 Ibenzenel has been investigated using conversion electron Mössbauer spectroscopy [CEMS]. It is shown that iron carbide phases can be synthesized when an iron foil immersed in benzene is treated with ruby Laser pulses [λ=694 nm, pulse width ∼30 ns, energy density =15 J/cm2]. The results indicate the formation of ε-carbide and Fe5C2 phases in the as-treated sample and its transformation to Fe3C upon thermal treatment. The result of the CEMS measurements are supported by small angle X-ray diffractometry.

Effect of laser nitridation on the electrochemical corrosion behaviour of 316 stainless steel

Nitridation of 316 stainless steel is achieved by using pulsed-laser-induced reactive quenching at the interface between the steel sample and a thin liquid nitrogen overlayer. The electrochemical corrosion behaviour of the virgin sample, the as-nitrided sample, and the nitrided and annealed sample is studied by the potentiokinetic polarization technique. It is shown that the nitrided and annealed sample has a considerably higher corrosion resistance than does the virgin sample. The state of the sample surface after the different treatments is characterized by small-angle X-ray diffraction, scanning electron microscopy and conversion electron Mossbauer spectroscopy.

Surface oxides produced during discharge in water ambient iron surface: A conversion electron Mössbauer spectroscopic study

Oxide layers are produced on iron surface, under discharge in water ambient, applying both anodic and cathodic potentials to iron foil. Non-stoichiometric Fe1−xO containing different ratios of Fe3+ and Fe2+ has been detected by using CEMS. Corrosion of these samples in 0.5 M H2SO4 shows that, cathodically discharge treated iron foil has higher corrosion resistance as compared to the anodically treated sample. This is attributed to the microstructural differences in the Fe1−xOx films formed during the discharge.

A conversion electron mössbauer spectroscopic study of structural relaxations and diffusive transport near the surface of Fe67Co18B14Si1 metglass

Structural relaxations and diffusive transport near the surface of Fe67Co18B14Si1 metglass have been studied by means of conversion electron Mössbauer spectroscopy [CEMS]. It is shown that the relaxations occurring near the surface of the metglass consequent on thermal treatment exhibit distinctly different features as compared to those in the bulk. The difference in the thermally induced atomic transport near the surface region of the metglass and, that at the interface between the metglass and a deposited overlayer of iron has also been investigated.

Ion implantation effects in laser-deposited amorphous carbon films

Abstract Ion implantation effects have been studied in the pulsed-laser-deposited amorphous carbon (a-C) films having a diamond-like character. 80 keV Ar + ions were implanted at various doses, and the optical and electrical properties of the films were studied as a function of ion dose. It was observed that the electrical resistivity and optical band gap decrease as the ion dose increases. The transparency increases from 80% (for the as-deposited a-C) to over 97% in the wavelength range 2.5–4 microm for the sample implanted at 1 × 10 13 ions cm −2 and at higher doses it decreases. Raman measurements at higher doses show the loss of sp 3 hybridized carbon atoms with no sign of microcrystallinity. The absence of the Raman contribution at 600 and 1275 cm −1 in samples implanted at doses greater than 1 × 10 15 ions cm −2 corresponds to an implantation-induced sp 3 -to-sp 2 transformation without graphitization.

Compound synthesis by an electric-field-generated plasma at the liquid-solid interface

Abstract Interface reactions induced at the liquid-solid interface by a field-generated plasma are used to synthesize metastable forms of iron oxide, carbide and nitride. The resulting chemical and microstructural changes on the surface of iron are studied using conversion electron Mossbauer spectroscopy, while the information regarding the surface morphology is obtained through scanning electron microscopy.

Effect of N 2 + ion implantation on the electrochemical corrosion behaviour of Fe−Ni alloy in. 1N H2SO4 solution

A three sweep potentiokinetic technique was employed to study the electrochemical corrosion behaviour of Fe-50 at % Ni in .1N H2SO4 solution. The as received foil did not show any passivation but it was observed in case of Fe−Ni samples implanted with N2+ ions at an energy of 100keV. Also it was seen that the primary passivation potential Epp and the critical current density in the corrosion experiment decrease as the implanted nitrogen ion dose increases from 5*1015 to 1*1017 ions/cm2. The identification of products formed during corrosion experiment has been attempted with the help of conversion electron Mössbauer spectroscopy (CEMS), X-ray diffraction (XRD) and X-ray photoemission spectroscopic (XPS) techniques, and the possible mechanism of reactions is discussed with reference to their results.