Spectroscopic and real-time imaging investigation of tantalum plasma electrolytic oxidation (PEO)

Stojadinović, Stevan; Jovović, Jovica; Petković, Marija; Vasilić, Rastko; Konjević, N.

doi:10.1016/j.surfcoat.2011.06.013

Cited by 87 publications

(38 citation statements)

References 26 publications

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“…Nowadays, light metals such as titanium [1][2][3][4], niobium [5][6][7][8][9], tantalum [10][11][12][13][14][15], and their alloys [16][17][18][19][20][21][22], after electrochemical treatment (electropolishing and/or plasma electrolytic oxidation), may be used as biomaterials (implant materials) because of their mechanical properties [23][24][25][26][27], good corrosion resistance [28][29][30][31] in body fluids, and osteointegration [32][33][34]. The electropolishing…”

Section: Introductionmentioning

confidence: 99%

Characterisation of Calcium- and Phosphorus-Enriched Porous Coatings on CP Titanium Grade 2 Fabricated by Plasma Electrolytic Oxidation

Rokosz

Hryniewicz

Gaiaschi

et al. 2017

Metals

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Abstract:In the paper, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) analyses of calcium-and phosphorus-enriched coatings obtained on commercial purity (CP) Titanium Grade 2 by plasma electrolytic oxidation (PEO), known also as micro arc oxidation (MAO), in electrolytes based on concentrated phosphoric acid with calcium nitrate tetrahydrate, are presented. The preliminary studies were performed in electrolytes containing 10, 300, and 600 g/L of calcium nitrate tetrahydrate, whereas for the main research the solution contained 500 g/L of the same hydrated salt. It was found that non-porous coatings, with very small amounts of calcium and phosphorus in them, were formed in the solution with 10 g/L Ca(NO 3 ) 2 ·4H 2 O, whereas the other coatings, fabricated in the consecutive electrolytes containing from 300 up to 650 g/L Ca(NO 3 ) 2 ·4H 2 O, were porous. Based on the GDOES data, it was also found that the obtained porous PEO coating may be divided into three sub-layers: the first, top, porous layer was the thinnest; the second, semi-porous layer was about 12 times thicker than the first; and the third, transition sub-layer was about 10 times thicker than the first. Based on the recorded XPS spectra, it was possible to state that the top 10-nm layer of porous PEO coatings included chemical compounds containing titanium (Ti 4+ ), calcium (Ca 2+ ), as well as phosphorus and oxygen (PO 4 3− and/or HPO 4 2− and/or H 2 PO 4 − , and/or P 2 O 7 4− ).

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Section: Introductionmentioning

confidence: 99%

Characterisation of Calcium- and Phosphorus-Enriched Porous Coatings on CP Titanium Grade 2 Fabricated by Plasma Electrolytic Oxidation

Rokosz

Hryniewicz

Gaiaschi

et al. 2017

Metals

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“…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).…”

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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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“…The average area ranged from 0.1 to 1.2 mm 2 at 10 mA cm −2 and from 0.2 to 2.6 mm 2 at 20 mA cm −2 . These values were slightly larger than the discharge size registered during galvanostatic anodization of Ta, Al and Ti [20,23,46]. During anodization of tantalum in acid solution [23], real-time imaging investigation revealed the presence of small microdischarges (< 0.1 mm 2 ), medium-size microdischarges (ranging from 0.1 mm 2 to 0.2 mm 2 ) and large microdischarges (> 0.2 mm 2 ), which noticeable only at the final part of the anodic oxidation.…”

Section: Resultsmentioning

confidence: 60%

“…In recent years, imaging techniques have been used to characterize the microdischarges parameters during the anodization of different metals such as Al, Ti, Mg and Ta under DC and AC regime [19][20][21][22][23][24][25]. Based on these studies, several mechanisms have been proposed to explain the electric breakdown phenomenon and the influence of the electrical microdischarges on morphology and microstructure of anodic films.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of electrical discharges during spark anodization of zirconium in different electrolytes

Santos

Lemos

Gonçalves

et al. 2014

Electrochimica Acta

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Spectroscopic and real-time imaging investigation of tantalum plasma electrolytic oxidation (PEO)

Cited by 87 publications

References 26 publications

Characterisation of Calcium- and Phosphorus-Enriched Porous Coatings on CP Titanium Grade 2 Fabricated by Plasma Electrolytic Oxidation

Characterisation of Calcium- and Phosphorus-Enriched Porous Coatings on CP Titanium Grade 2 Fabricated by Plasma Electrolytic Oxidation

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

Characterization of electrical discharges during spark anodization of zirconium in different electrolytes

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