Comparison of different silica sources in the development of plasma sprayed 45S5 bioactive glass coatings

Abstract 45S5 bioactive glass coatings were deposited by plasma spraying from liquid feedstocks. In these feedstocks, the SiO2 needed to achieve the 45S5 bioactive glass composition has been provided either as tetraethyl orthosilicate (typical precursor of glasses by sol–gel), or as colloidal silica suspension or mixtures of both sources. The synthesised materials were analysed in terms of rheology and sedimentation tests, and subsequently deposited onto metallic substrates under two different spraying distances. The resulting coatings were characterised on the basis of microstructure and phase nature. All feedstocks developed preserved the composition of the 45S5 bioactive glass and showed adequate viscosity and stability to be transported and injected into the plasma plume. However, different coating microstructures were achieved when using tetraethyl orthosilicate or colloidal silica suspensions. Besides, regardless the source of silica an improvement of the coatings microstructure and phase nature have also been observed when the spraying distance was significantly reduced.