Development and Characterization of Phosphate-Based Glass Coatings via Suspension High-Velocity Oxy-Fuel (SHVOF) Thermal Spray Process

Phosphate-based glasses (PBGs) are promising materials for biomedical applications due to their biocompatible and fully resorbable characteristics in aqueous environments. These glasses can be coated onto metal substrate via the technique of suspension high-velocity oxy-fuel (SHVOF) thermal spraying to produce nanostructured coatings with improved physical and mechanical properties. PBGs coatings were produced using SHVOF thermal spray process at 50 and 75 kW flame power. The 75 kW coating was rougher (R_a = 3.6 ± 0.1 µm) than the 50 kW coating (R_a = 2.7 ± 0.1 µm), whereas the 50 kW coating was much thicker (24.6 ± 2.3 µm) than the 75 kW coating (16.0 ± 3.4 µm). Due to the rougher surface, the 75 kW coating showed high degradation and ion release rates. Moreover, structural changes were observed by Raman analysis, and the initial glass formulation contained Q¹ (phosphate tetrahedra with one-bridging oxygen) and Q² (phosphate tetrahedra with two-bridging oxygen) species. However, the coatings showed a reduction of Q² species and higher concentrations of Q¹ and Q⁰ (phosphate tetrahedra with no-bridging oxygen) species, which led to lower degradation rates and reduced ion release profiles in the glass coating compared to the initial glass.