ELECTROPHORETIC DEPOSITION AS AN EFFECTIVE AND SIMPLE PROCESSING TECHNIQUE FOR FABRICATION OF MAGNESIUM SILICATE HYDRATE (M-S-H) COATINGS ONTO STAINLESS STEEL SUBSTRATES

Abstract

Magnesium silicate hydrate (M-S-H) was prepared via one-pot hydrothermal synthesis and electrophoretically deposited (EPD) onto stainless steel substrate (Type 304), varying different process parameters. The optimal conditions for the EPD process were found to be as follows. A stable suspension of material was achieved using isopropanol containing 1% water as dispersing medium and Mg-nitrate as charging additive. The best coating was obtained after three successively repeated EPD processes at a voltage of 30 V, accompanied by drying at room temperature between each EPD cycle. The coating showed a thickness of 31 µm and very smooth surface. After calcination at 900 °C coating retains its adherence to the substrate but undergoes a structural transformation from poorly crystallized M-S-H to well-crystallized clinoenstatite phase which is known for its biocompatibility. As a result, it densifies and shrinks giving grainy and slightly rough surface. Structural properties and parameters of the magnesium silicate hydrate (M-S-H) and clinoenstatite were acquired by XRD technique, while morphology was examined by the analysis of SEM micrographs. This study demonstrates that: i) M-S-H can be synthesized through simple hydrothermal route starting from simple, low-cost precursors, ii) EPD process is an effective technique for deposition of M-S-H materials onto stainless steel and iii) inosilicate mineral (clinoenstatite) can be successfully obtained from M-S-H by calcination at 900 °C. HIGHLIGHTS Magnesium silicate hydrate (M-S-H) was prepared via a one-pot hydrothermal synthesis. The optimal conditions for the electrolytic deposition process were determined. Kinetics of the process were investigated using the Hamaker`s equation. Clinoenstatite can be successfully obtained from M-S-H by calcination.