Spectroscopic Investigation of Direct Current (DC) Plasma Electrolytic Oxidation of Zirconium in Citric Acid

Abstract

Plasma electrolytic oxidation of zirconium in citric acid was investigated using optical spectroscopy. A rich emission spectrum consisting of about 360 zirconium and 170 oxygen atomic and ionic lines was identified in the spectral regions 313-320, 340-516, and 626-640 nm. It was shown that the remaining features observed in the spectrum could be ascribed to various molecular species, which involve zirconium, oxygen, hydrogen, and carbon. The temperature of the plasma core (T = 7500 ± 1000 K) was determined using measured Zr line intensities, and the temperature of peripheral plasma zone (T = 2800 ± 500 K) was estimated from the intensity distribution within a part of an OH spectrum. The composition of the plasma containing zirconium, oxygen, and hydrogen, under assumption of local thermal equilibrium, was calculated in the temperature range up to 12,000 K and for pressure of 10(5) and 10(7) Pa, in order to explain the appearance of the observed spectral features.

Characterization of plasma electrolytic oxidation of magnesium alloy AZ31 in alkaline solution containing fluoride

“…[21] (11000 ± 2000) K, and very similar to the temperatures estimated in our studies on Al [37] (8000 ± 2000) K, derived from the intensity distribution within two band sequences of the B 2 Σ + -X 2 Σ + spectral system of AlO, and those obtained based on the intensities of Zr spectral lines (7500 ± 1000) K [33]. Based on our experience, as well as on the results of other authors [22,[38][39][40][41] and keeping in mind large stochastic fluctuations from one experiment/record to another, we still do not find it justified to speak about different temperatures at PEO of Al, Mg, Zr and other metals considered.…”

“…Refs. [21] and [33], has been found to be considerably lower does not automatically mean that there is no equilibrium between rotational, on one side, and vibrational and electronic motions, on the other side. As discussed in detail in Refs.…”

“…This was the procedure we used in our recent studies on Zr [33] and Al [34]. It consists of plotting the function ln(I nm λ nm /g n A nm ) vs. E n , where I nm is the intensity of the spectral line appearing at the emission transition from the level n to m, λ nm is the wavelength of this line, g n the statistical weight of the level n, A nm is Einstein transition probability, and E n is the excitation energy of the level n. The temperature is determined from this plot from the slope of the corresponding nearly straight line.…”

“…Indeed, for the construction of Fig. 5 we utilized these overlapping spectral ranges to adjust the line intensities, as described in detail in our study on Zr [33]. Unlike in the present situation, in this former study we had at disposal as many as 85 spectral lines in a rather narrow wavelength range (420-516 nm) which made it possible to determine the temperature reliably.…”

Zirconia films formed by plasma electrolytic oxidation: Photoluminescent and photocatalytic properties

“…This process is accompanied by visible light emission and gas evolution [18]. Various processes including chemical, electrochemical, thermodynamical, and plasma-chemical reactions occur at the discharge sites, due to increased local temperature (10 3 -10 4 K) and pressure ($10 2 MPa) [19]. These processes are responsible for modifying the structure, composition, and morphology of obtained oxide coatings.…”