Spectroscopic characterization of plasma during electrolytic oxidation (PEO) of aluminium

Jovović, Jovica; Stojadinović, Stevan; Šišović, N. M.; Konjević, N.

doi:10.1016/j.surfcoat.2011.06.031

Cited by 71 publications

(40 citation statements)

References 27 publications

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“…The majority of investigations have dealt with the study of micro-discharges by means of high-speed video imaging [13] and optical emission spectroscopy [27][28][29] treat actually a large number of events 10 5 per dm 2 per second). To overcome this difficulty, the Gordon Laboratory has developed a setup that makes it possible to study one individual discharge at a time [10,19,30] and to simultaneously record its current and image its shape [26,31].…”

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confidence: 99%

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

et al. 2017

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The present communication shows the possibility of observing micro-discharges under cathodic polarization during Plasma Electrolytic Oxidation (PEO) at high frequency. Cathodic micro-discharges can ignite beyond a threshold frequency found close to 2 kHz. The presence (resp. absence) of an Electrical Double Layer (EDL) was put forward to explain how the applied voltage can be screened, which therefore prevents (resp. promotes) the ignition of a discharge. Interestingly, in the conditions of the present study, the EDL requires between 175 and 260 µs to form. This situates the expected threshold frequency between 1.92 and 2.86 kHz, which is in good agreement with the value obtained experimentally.Plasma Electrolytic Oxidation (PEO) is at a pivotal moment of its development. If this process has undeniable assets for surface treatments of light alloys (high growth rate, high ultimate coating thickness, ecofriendliness, wear and corrosion resistance, etc.), the high energy consumption and the lack of understanding of the fundamental processes underlying the breakdown and the oxidation mechanisms still limit a larger scale development.Improving the energetic efficiency of PEO is a major stake and several strategies can then be followed: dual treatments[1], addition of nanoparticles [2,3], electrolyte composition [4,5] and electric regimes [5][6][7][8]. Here, we focus on the influence of the electric regime as it has a direct and strong influence on both the space and time properties of micro-discharges (MD), which affect the coating growth. Interestingly, the best properties and the highest growth rates of coatings are obtained while using bipolar current waveform [5,9] even though MDs are only observed during the anodic (i.e. positive) half-period [10][11][12] in these conditions.To explain this observation, one should keep in mind that the growth of PEO coatings relies on a balance between the constructive effect of MDs (oxidation and coating growth) and their destructive effect (large craters and porosities). Several studies conducted either by high speed video imaging [5,6,[11][12][13][14][15][16][17][18] or by direct electrical measurements [10,19] have investigated this balance. They made it possible to correlate space and time parameters of MDs (number, life-time, size) and the properties of as-grown coatings (thickness, porosity). In short, large and long-lived discharges promote the growth of high temperature phases but create large porosities (several tens of µm), high roughness at limited growth rates (strong destructive effect of MDs). On the other hand, too small and short-lived MDs will create more homogeneous coating but with lower amount of high-temperature phases and also at limited growth rates (weak constructive effect).Nevertheless, all these studies support the same conclusion: adjusting the cathodic half period probably opens up the possibility to tune the behaviour of anodic MDs. Then, combining high-growth rates, low levels of large-scale porosity (bigger than 10 µm) and a significant proportio...

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High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

et al. 2017

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“…[120][121][122][123][124][125][126][127][128][129][130] Relative line intensity measurements of species originating in the substrate or in the electrolyte were used for the determination of the electron temperature. The main difficulty in the application of OES for PEO characterization comes from space and time inhomogeneity of the microdischarges appearing randomly across the anode surface.…”

Section: Determination Of Plasma Compositionmentioning

confidence: 99%

“…The main difficulty in the application of OES for PEO characterization comes from space and time inhomogeneity of the microdischarges appearing randomly across the anode surface. 122,123,[126][127][128] The molecular vibrational temperature was determined from the luminescence of AlO 129 and MgO. [120][121][122][123][124][125][126][127][128][129][130] Relative line intensity measurements of species originating in the substrate or in the electrolyte were used for the determination of the electron temperature.…”

Section: Determination Of Plasma Compositionmentioning

confidence: 99%

A multidisciplinary study on magnesium

Ranković

Stojadinović

Sarvan

et al. 2012

JSCS

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During plasma electrolytic oxidation of a magnesium alloy (96% Mg, 3% Al, 1% Zn) we obtained a luminescence spectrum in the wave number range between 19 950 and 20 400 cm-1. The broad peak with clearly pronounced structure was assigned to the v’-v” = 0 sequence of the B 1Σ+ → X 1Σ+ electronic transition of MgO. Quantum-mechanical perturbative approach was applied to extract the form of the potential energy curves for the electronic states involved in the observed spectrum, from the positions of spectral bands. These potential curves, combined with the results of quantum-chemical calculations of the electric transition moment, were employed in subsequent variational calculations to obtain the Franck-Condon factors and transition moments for the vibrational transitions observed. Comparing the results of these calculations with the measured intensity distribution within the spectrum we derived relative population of the upper electronic state vibration levels. This enabled us to estimate the plasma temperature. Additionally, the temperature was determined by analysis of the recorded A 2Σ+ (v’ = 0) - X 2П (v” = 0) emission spectrum of OH. The composition of plasma containing magnesium, oxygen, and hydrogen under assumption of local thermal equilibrium was calculated in the temperature range up to 12 000 K and for pressures of 105, 106, 107, and 108 Pa, in order to explain the appearance of the observed spectral features and to contribute to elucidation of processes taking place during the electrolytic oxidation of Mg. [Projekat Ministarstva nauke Republike Srbije, br. 172040

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“…Hussein et al 10 calculated the T e of PEO reactions on pure Al and observed that the T e (by Al I lines) increases with increasing current density. Jovović et al 13,18 studied the PEO spectra on Mg, Al and Ta alloys, and the spectra were divided into discharging luminescence and discharging strong ionic/atomic emission. Therefore, the OES technique presents a unique advantage over PEO process and mechanism investigations, and much more work is urgently needed to disclose the coating formation mechanisms by this technique, especially the proper combination of OES technique with the traditional analytical methods.…”

Section: Introductionmentioning

confidence: 99%

Study on coating growth characteristics during the electrolytic oxidation of a magnesium–lithium alloy by optical emission spectroscopy analysis

et al. 2015

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The aim of this study is to analyze the composition, structure and growth characteristics of plasma electrolytic oxidation (PEO) coatings through optical emission spectroscopy (OES). The PEO coatings were prepared on a magnesium-lithium alloy in a phosphate system at various frequencies. The composition and structure of the coatings were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), as well as energy-dispersive X-ray (EDX). The discharge sparks of the PEO process were measured by optical emission spectroscopy. The results show that the PEO coating prepared at 50 Hz is composed of crystalline MgO and crystalline Mg 3 (PO 4 ) 2 , and that the coating at 500 Hz is composed of crystalline MgO and amorphous Mg 3 (PO 4 ) 2 .The coating prepared at 50 Hz has a greater degree of roughness than that prepared at 500 Hz, and the sizes of the micropores on the coating prepared at 50 Hz are considerably larger than that at 500 Hz, whereas the numbers of the micropores at various frequencies change in opposition to the pore sizes.The plasma temperature (T e ) calculated with OES at 50 Hz is about 3100 K higher than that at 500 Hz. This means that more energy generated per cycle was applied to the electrode surface at 50 Hz than 500 Hz, which consequently influenced the structure and composition of the coatings. Based on the OES analysis, the growth characteristic of the PEO coatings was proposed to explain the changes of the coating roughness and the formation mechanism of crystalline or amorphous Mg 3 (PO 4 ) 2 at various working frequencies by the T e and the liquid-cooling effect, which was further proven by the experiments designed by changing the electrical parameters of the PEO process. This study also illustrates that the adjustment of the phase composition and structure by the electrical parameters can be well explained by OES. Besides, the corrosion resistance of the MAO coatings was evaluated by the polarization curves in 3.5 wt% NaCl solution. The corrosion resistance of the coatings is mainly determined by thickness and roughness, and the coatings prepared under 500 Hz generally present better corrosion resistance than those prepared under 50 Hz. Fig. 8 Typical time variation of T e by Na I lines (a) and Na 589.0 nm/Li 670.8 nm ratios (b) at 50 Hz and 500 Hz.This journal is

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Spectroscopic characterization of plasma during electrolytic oxidation (PEO) of aluminium

Cited by 71 publications

References 27 publications

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

A multidisciplinary study on magnesium

Study on coating growth characteristics during the electrolytic oxidation of a magnesium–lithium alloy by optical emission spectroscopy analysis

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