Tin deoxidation by atmospheric pressure plasma treatment.

Treatment of materials by atmospheric-pressure plasma technology is used in all sectors of industrial production and is a lower cost technology. Among the possible applications, the reduction of metallic oxides by plasma is often needed to prepare the surface of the substrates before treatment or to deoxidise materials which contain metals. In this work the deoxidation of metallic Sn by atmospheric pressure plasma treatment whit N2-H2 gas mixture was investigated. The particles of Sn metallic are very thermal sensitive and the use of atmospheric pressure plasma whit gas containing H2 for the removal of surface oxide is a promising technique to increase the soldering process efficiency. For pure tin, SnO grew faster under humid conditions than in dry air and a very thin layer of SnO2 was formed on the top surface under humid conditions; the mixture of both SnO and SnO2 grew for oxidation at 150°C. Electrochemical reduction analysis is a relatively precise technique to measure quantitatively both the type and the thickness of oxides on metal surface. The surface of tin was degreased and polished according to the standard metallographic techniques and the test samples was fully reduced electrochemically at a high current density before being placed in an furnace. The oxidized specimens are treated whit a rotating jet atmospheric plasma which works whit a frequency of 16-20 kHz and generate a plasma whit a maximum power of 1 kW. This plasma is created in a jet through the action of a stepped, high-frequency, pulsed current that turns the gas (N2 99% - H2 1%) into a beam of plasma. The plasma generated at atmospheric pressure (1 bar) with low power consumption (E = 290 V) is directed onto the tin surface trough a torch which can be moved on the material’s surface at different rates. The electrochemical reduction analysis was carried out in a borate buffer solution: a constant cathodic current (-20 microA) is applied between the surface and an inert counter electrode (Pt). The change of cathode potential of the oxidized surface during reduction is recorded as a function of time relative to a reference electrode. The potential-time curve was performed by AMEL 551 potentiostat - galvanostat equipped with an AMEL 567 function generator using a saturated calomel electrode (SCE) as reference and consists of a series of potential durations, which is characteristic of each type of oxides and indicate the results achieved in the deoxidation.