Splat formation and microstructure of solution precursor thermal sprayed Nb-doped titanium oxide coatings

Daniel Tejero-Martin,Zdenek Pala,Simon Rushworth,Tanvir Hussain

doi:10.1016/j.ceramint.2019.10.253

Daniel Tejero-Martin, Zdenek Pala + Show 2 more

Open Access

https://doi.org/10.1016/j.ceramint.2019.10.253

Copy DOI

Journal: Ceramurgia International	Publication Date: Oct 31, 2019
Citations: 13	License type: cc-by

Affiliation: University of Nottingham, Wilton Park

Abstract

Solution precursor thermal spray can become a breakthrough technology for the deposition of coatings with novel chemistries; however, the understanding of the process that the feedstock material undergoes is still lacking when compared to more traditional presentations (i.e. powder and suspension). In this paper, niobium-doped TiO2 coatings were deposited by solution precursor high velocity oxy-fuel thermal spraying, studying its microstructure and phase. It was reported that a lower flame temperature produced a highly porous coating, while the porosity was reduced at higher flame temperature. Investigation of the phase content showed that, contrary to our current understanding, a higher flame power implied an increase of the anatase phase content for solution precursor spray. Three methods were used: Rietveld refinement, peak height and peak area of the x-ray diffraction patterns. Additionally, single splats were analysed, showing that as the precursor travels through the flame, pyrolysis and sintering takes place to form the solid material. These results were used to derive a model of the physico-chemical transformation of the solution precursor. This work proves that solution precursor thermal spray is a promising technique for the deposition of doped ceramic coatings, being the microstructure and phase content controllable through the spraying parameters.

Highlights

Titanium oxide coatings are widely used in a number of fields owing to its unique properties, such as a prominent photocatalytic effect (Ref [1]), its electrochemical activity (Ref [2]), its coherent change in electrical conductivity under gas exposure (Ref [3]) or its ability to produce transparent coatings (Ref [4,5])
All of the three methods applied in the quantification of the anatase phase have shortcomings, the results shown in Fig. 5 clearly indicate that an increase in the flame power results in an increase in the anatase content
The results show that the flame power, chosen in this study to be 25 kW and 75 kW, has critical implications on the microstructural features and phase content of the produced coatings

Summary

Introduction

Titanium oxide coatings are widely used in a number of fields owing to its unique properties, such as a prominent photocatalytic effect (Ref [1]), its electrochemical activity (Ref [2]), its coherent change in electrical conductivity under gas exposure (Ref [3]) or its ability to produce transparent coatings (Ref [4,5]). The properties of titanium oxide ( known as titania) can be tailored to be more beneficial through doping (Ref [6,7,8,9,10,11]) Among those elements, niobium presents some desirable properties that makes it a suitable candidate for the formation of doped titanium oxide coatings. Niobium presents some desirable properties that makes it a suitable candidate for the formation of doped titanium oxide coatings It effectively increases the electrical conductivity which, in addition to the favourable electrochemical properties of TiO2 (such as high capacity and low volume expansion during ion charge/discharge (Ref [12,13,14])), makes it a viable option as an anode material for high-power Li-ion batteries. In addition to the improvement in electrical conductivity, Nbdoped TiO2 coatings have found application as sensors, as the niobium limits the grain growth and inhibits the anatase to rutile phase transformation to temperatures up to 650 °C (Ref [19]), being the rutile phase traditionally considered detrimental for sensing applications (Ref [11,20,21,22,23])

Methods

Results

Conclusion