Characterization of potential nanoporous sodium titanate film formation on Ti6Al4V and TiO2 microspherical substrates via wet-chemical alkaline conversion

Matthew D Wadge,Reda M Felfel,David M Grant,Zakhar R Kudrynskyi,Matthew J Carrington,Hannah Constantin,Kazi M Zakir Hossain,Timothy P Cooper,Ifty Ahmed,Md Towhidul Islam,Kieran Orange,Jason Greaves

doi:10.1016/j.matchar.2022.111760

Abstract

The authors present novel insights into the formation of nanoporous, wet-chemically produced sodium titanate films onto microspherical substrates of varying composition. Microspheres of Ti6Al4V (atomised; ca. 20–50 μm), which were utilised due to their ubiquitous industrial usage relative to metallic titanium, were compared with TiO2 microspheres (flame spheroidised anatase and rutile powders; average ca. 30–40 μm). These were then suspended in 5 M NaOH solutions (60 °C, 24 h), and then characterized (SEM, EDS, XRD, XPS) to determine the extent of sodium titanate generation, and the potential inhibition of formation due to oxygen content. It was found that excessive oxygen content (flame-spheroidised rutile and anatase powders) resulted in inhibition of nanoporous titanate formation, apart from the top few nanometres of the surface, since a diffusion barrier of TiO2 prevents further conversion. The characteristic nanoporous titanate structures were formed on the Ti6Al4V microspheres, ca. 1 μm (999 ± 25 nm) in thickness, whereas no visible alteration to the TiO2 microspheres were seen. High surface concentration (ca. 9.5–17.6 at.%) of Na was seen in all samples via XPS, including the TiO2 microspheres (despite no morphological change), however, only the Ti6Al4V microspheres exhibited moderate Na content (ca. 4.7 at.%) via EDS, illustrating a diffusion gradient during formation. The confirmation of these structures onto microspherical substrates opens the possibility for application in biomaterials, water treatment, and energy fields.

Highlights

Alkaline titanate structures have garnered significant attention, in a wide variety of fields, due to their multifunctional properties [1,2]
From work into antibacterial gallium-doping of the sodium hydrogen titanate structure [20], to the potential translation of nanoporous sodium titanate coatings onto the surface of alternative, non-Ti containing materials (316 L SS [21], Mg [22]) through conver sion of sputtered Ti films, information has been gleaned regarding the formation mechanism of these structures
It was interesting to compared the potential formation of nanoporous titanate films onto Ti6Al4V and TiO2 microspherical substrates, at lower tem peratures seen for titanate-converted TiO2 literature far

Summary

Introduction

Alkaline titanate structures have garnered significant attention, in a wide variety of fields, due to their multifunctional properties [1,2] Fields such as photocatalysis [3], biomaterials [4], radioactive waste water treatment [5], and batteries [6], just to name a few, have benefited from the research into these structures. The present authors have conducted several published studies looking into the formation of nanoporous alkaline titanate films, as opposed to nano-tubular and nano-sheet formations, mainly for biomedical applications This is due to the improved cellular viability on Materials Characterization 185 (2022) 111760 such nanoporous structures, with enhanced functionality via cationic exchange. The production of nanoporous titanate films onto microspherical substrates is somewhat limited in the literature, as well as comparing this with TiO2 microspheres

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Discussion

Conclusion