Abstract
This paper shows that the subject of porous coatings fabrication by Plasma Electrolytic Oxidation (PEO), known also as Micro Arc Oxidation (MAO), is still current, inter alia because metals and alloys, which can be treated by the PEO method, for example, titanium, niobium, tantalum and their alloys, are increasingly available for sale. On the international market, apart from scientific works/activity developed at universities, scientific research on the PEO coatings is also underway in companies such as Keronite (Great Britain), Magoxid-Coat (Germany), Mofratech (France), Machaon (Russia), as well as CeraFuse, Tagnite, Microplasmic (USA). In addition, it should be noted that the development of the space industry and implantology will force the production of trouble-free micro- and macro-machines with very high durability. Another aspect in favor of this technique is the rate of part treatment, which does not exceed several dozen minutes, and usually only lasts a few minutes. Another advantage is functionalization of fabricated surface through thermal or hydrothermal modification of fabricated coatings, or other methods (Physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel), including also reoxidation by PEO treatment in another electrolyte. In the following chapters, coatings obtained both in aqueous solutions and electrolytes based on orthophosphoric acid will be presented; therein, dependent on the PEO treatment and the electrolyte used, they are characterized by different properties associated with their subsequent use. The possibilities for using coatings produced by means of plasma electrolytic oxidation are very wide, beginning from various types of catalysts, gas sensors, to biocompatible and antibacterial coatings, as well as hard wear coatings used in machine parts, among others, used in the aviation and aerospace industries.
Highlights
IntroductionSurface modification of metals and alloys may be carried out by electrochemical polishing [1,2,3,4,5,6,7,8,9], magnetoelectropolishing [10,11,12,13,14] and electropolishing with high-current densities [15,16,17], as well as by chemical and electrochemical machining treatment [18,19,20,21,22,23,24,25]
The usage of electrolyte containing Ca(CH3 COO)2 ·H2 O, NaH2 phases of SrTi4 (PO4) ·H2 O, NaOH and complexing compounds, such as Sodium Gluconate (GA) or Triethanolamine (TEA), or (Ethylenedinitrilo)tetraacetic acid disodium salt (EDTA-2Na), or Ethylenediamine tetramethylene alendronate (EDTMPS) in different concentrations in the Plasma Electrolytic Oxidation (PEO) process (300–350 V, 50 Hz, 30 min) resulted in the creation of porous coatings containing TiO2 for the coatings obtained in the electrolytes containing GA, TEA, EDTMPS, and CaTiO3 for the layers formulated in solutions with the addition of EDTA-2Na
To fabricate porous coatings enriched with phosphorus and copper, an aqueous electrolyte containing NaOH, NaH2 PO4, and copper nanoparticles may be used in a five-minute PEO process with a current stabilization on the level of 20 A/dm2
Summary
Surface modification of metals and alloys may be carried out by electrochemical polishing [1,2,3,4,5,6,7,8,9], magnetoelectropolishing [10,11,12,13,14] and electropolishing with high-current densities [15,16,17], as well as by chemical and electrochemical machining treatment [18,19,20,21,22,23,24,25]. This activity allows to fabricate expected and requested porous coatings which may be used for modification both, machine parts and biomaterials. Further modification of the received surfaces is possible by thermal, hydrothermal treatments, or re-oxidation by PEO in other solution
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