Formation of plasma electrolytic oxidation coatings on pure niobium in different electrolytes

Ting Wu,Carsten Blawert,Maria Serdechnova,Polina Karlova,Gleb Dovzhenko,D.C Florian Wieland,Stevan Stojadinovic,Rastko Vasilic,Kristina Mojsilovic,Mikhail L Zheludkevich

doi:10.1016/j.apsusc.2021.151629

Ting Wu, Carsten Blawert + Show 8 more

Open Access

https://doi.org/10.1016/j.apsusc.2021.151629

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Abstract

The development of PEO surface treatments for Nb (niobium) provides a possibility to produce functionalized coatings with a combination of new compositions and phases. In the frame of this work, PEO coatings on pure Nb are produced in three electrolytes containing aluminate, phosphate and silicate. Furthermore, the influence of the electrolyte composition on the PEO process and the microstructure, composition and properties of the coatings were studied. It was observed that most of the coating forming species did not participate in the plasma reactions directly, while the chemical-, electrochemical- and thermal stimulated reactions are dominating the coating formation. The results show that all the coatings are mainly composed of the Nb2O5 phase. An additional mixture of oxides (Al2O3 and AlNbO4) is found in the coating formed in aluminate-containing electrolyte, and the coating formed in phosphate-containing electrolyte contains a small amount of Nb2(PO4)3 and amorphous phosphate. No additional crystalline phase other than the amorphous silica phase is detected in the coating formed in silicate-containing electrolyte. Additionally, different morphology of the coatings is revealed and the most uniform coating is produced in silicate-containing electrolyte, which further improves its corrosion resistance. This coating also shows the highest photocatalytic activity due to the combination of Nb2O5 and silica. Since all PEO coatings on pure Nb show superior corrosion resistance and photocatalytic activity, they might be interesting for a wide range of applications ranging from transportation, biomedical implants to environmental protection.

Highlights

Niobium (Nb) based materials are of great interest in various appli cations, strikingly for the fields of catalysis [1,2,3,4] and biomedicine [5,6,7,8,9] relying upon their catalytic activity and bio functionality
Since all Plasma electrolytic oxidation (PEO) coatings on pure Nb show superior corrosion resistance and photocatalytic activity, they might be interesting for a wide range of applications ranging from transportation, biomedical implants to environmental protection
The PEO coatings on pure Nb were composed of Nb2O5 oxide phase [30,31,57], which we find in the present work

Summary

Introduction

Niobium (Nb) based materials are of great interest in various appli cations, strikingly for the fields of catalysis [1,2,3,4] and biomedicine [5,6,7,8,9] relying upon their catalytic activity and bio functionality. Plasma electrolytic oxidation (PEO) is an advanced surface modifi cation process. It has been widely performed on light metals such as Al [17,18], Mg [19,20] and Ti [21,22] to form ceramic-like coatings. PEO technology is a promising candidate to produce functional coatings on pure Nb. The semiconducting Nb oxides in combination with the inherent porosity of PEO layer are potentially interesting for the catalytic effi ciency as well as for the osseointegration of bio-implants

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