Modification of niobium surfaces using plasma electrolytic oxidation in silicate solutions

Progress in Niobium Oxide-Containing Coatings for Biomedical Applications: A Critical Review

Typically, pure niobium oxide coatings are deposited on metallic substrates, such as commercially pure Ti, Ti6Al4 V alloys, stainless steels, niobium, TiNb alloy, and Mg alloys using techniques such as sputter deposition, sol-gel deposition, anodizing, and wet plasma electrolytic oxidation. The relative advantages and limitations of these coating techniques are considered, with particular emphasis on biomedical applications. The properties of a wide range of pure and modified niobium oxide coatings are illustrated, including their thickness, morphology, microstructure, elemental composition, phase composition, surface roughness and hardness. The corrosion resistance, tribological characteristics and cell viability/proliferation of the coatings are illustrated using data from electrochemical, wear resistance and biological cell culture measurements. Critical R&D needs for the development of improved future niobium oxide coatings, in the laboratory and in practice, are highlighted.

Plasma Electrolytic Oxidation (PEO) Process-Processing, Properties, and Applications

Plasma electrolytic oxidation (PEO) is a novel surface treatment process to produce thick, dense metal oxide coatings, especially on light metals, primarily to improve their wear and corrosion resistance. The coating manufactured from the PEO process is relatively superior to normal anodic oxidation. It is widely employed in the fields of mechanical, petrochemical, and biomedical industries, to name a few. Several investigations have been carried out to study the coating performance developed through the PEO process in the past. This review attempts to summarize and explain some of the fundamental aspects of the PEO process, mechanism of coating formation, the processing conditions that impact the process, the main characteristics of the process, the microstructures evolved in the coating, the mechanical and tribological properties of the coating, and the influence of environmental conditions on the coating process. Recently, the PEO process has also been employed to produce nanocomposite coatings by incorporating nanoparticles in the electrolyte. This review also narrates some of the recent developments in the field of nanocomposite coatings with examples and their applications. Additionally, some of the applications of the PEO coatings have been demonstrated. Moreover, the significance of the PEO process, its current trends, and its scope of future work are highlighted.

Niobia Nanofiber-Reinforced Protective Niobium Oxide/Acrylate Nanocomposite Coatings

In the present study, the corrosion resistance of a new niobium oxide/acrylate hybrid nanocomposite coating doped with niobia nanofibers is investigated. Nanofibers were initially synthesized from niobium(V) chloride precursor in a novel autoclave approach before fabricating the base coating from a two-step process involving the syntheses of acrylate resin via free radical polymerization and niobium oxide gel from niobium ethoxide via a sol-gel technique. Variants of the synthesized nanocomposite coating were incorporated with varying concentrations of niobia nanofibers before spin-coating on Q235 steel substrates to inhibit corrosive electrolytic ion percolation and further enhance corrosion resistance when treated with chloride-enriched corrosive media. The corrosion resistance of these nanocomposite coatings increased with nanofiber content up to an optimum concentration due to the corrosion-inhibiting and protective effects of niobium barrier layers within these coatings. The presence of the niobia nanofibers also promoted improved surface contact angle and toughened mechanical strengths.

Microstructural and Corrosion Properties of PEO Coated Zinc-Aluminized (ZA) Steel

Plasma Electrolytic Oxidation (PEO) is a surface treatment, similar to anodizing, that produces thick oxide films on the surface of metals. In the present work, PEO coatings were obtained on zinc-aluminized (ZA) carbon steel using a solution containing sodium silicate and potassium hydroxide as electrolyte, and working with high current densities and short treatment times in Direct Current (DC) mode. The thickness of the coating, as well as the surface morphology, were strongly influenced by the process parameters, with different dissolution grades of the ZA layer depending on the current density and treatment time. A compromise between thickness and porosity of the coating was found with low current density/long treatment time or high current density/short treatment time. The PEO layer was mainly composed of aluminum oxides and silicon compounds. The corrosion resistance increased remarkably in the samples with the PEO coating. These PEO coated samples are suitable for sealing treatments that further increase their corrosion properties or will be also an ideal substrate for commercial painting, assuring improved mechanical adhesion and protection even in the presence of damages.

Osteogenic differentiation of bone marrow-derived mesenchymal stem cells on anodized niobium surface

Currently, titanium and its alloys are the most used materials for biomedical applications. However, because of the high costs of these metals, new materials, such as niobium, have been researched. Niobium appears as a promising material due to its biocompatibility, and excellent corrosion resistance. In this work, anodized niobium samples were produced and characterized. Their capacity to support the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs) was also tested. The anodized niobium samples were characterized by SEM, profilometry, XPS, and wettability. BM-MSCs were cultured on the samples during 14 days, and tested for cell adhesion, metabolic activity, alkaline phosphatase activity, and mineralization. Results demonstrated that anodization promotes the formation of a hydrophilic nanoporous oxide layer on the Nb surface, which can contribute to the increase in the metabolic activity, and in osteogenic differentiation of BM-MSCs, as well as to the extracellular matrix mineralization.

Surface modification of valve metals using plasma electrolytic oxidation for antibacterial applications: A review

Plasma electrolytic oxidation (PEO) is an advance technique to develop porous oxidation layer on light metals, primarily to enhance corrosion and wear resistance. The oxidation layer can also offer a wide variety of mechanical, biomedical, tribological, and antibacterial properties through the incorporation of several ions and particles. Due to the increasing need of antimicrobial surfaces for biomedical implants, antibacterial PEO coatings have been developed through the incorporation of antibacterial agents. Metallic nanoparticles that have been employed most widely as antibacterial agents are reported to demonstrate serious health and environmental threats. To overcome the current limitations of these coatings, there is a significant need to develop antibacterial surfaces that are not harmful for patient's health and environment. Attention of the readers has been directed to utilize bioactive glasses as antibacterial agents for PEO coatings. Bioactive glasses are well known for their excellent bioactivity, biocompatibility, and antibacterial character. PEO coatings incorporated with bioactive glasses can provide environment-friendly antimicrobial surfaces with exceptional bioactivity, biocompatibility, and osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 590-605, 2018.