Deposition of strontium phosphate coatings on magnesium by hydrothermal treatment: Characteristics, corrosion resistance and bioactivity

Deposition of strontium phosphate (Sr-P) coatings on magnesium using 0.1M Sr(NO3)(2) and 0.06M NH4H2PO4 (pH: 3.00) by hydrothermal treatment at 80, 120, 150 and 200 degrees C for 30 min and, evaluation of its characteristic properties, corrosion resistance and bioactivity are addressed. The surface morphology of the Sr-P coatings revealed that they are uniform and compact. The coating weight, density and average surface roughness of the coating are increased with an increase in treatment temperature from 80 to 200 degrees C. X-ray diffraction patterns confirmed that the Sr-P coatings are highly crystalline and consisted of Mg phosphates and Sr phosphates as the major constituents along with minor quantities of Mg(OH)(2) and Sr(OH)(2). SrHPO4 is the predominant phase along with moderate amounts of Sr-3(PO4)(2) and Mg phosphate phases, when the deposition temperature is increased from 80 to 200 degrees C. The formation of these phases are further supported by the presence of stretching and bending vibrations pertaining to HPO42- and PO43- groups in the FT-IR and Raman spectra. The Sr-P coated Mg offered a higher corrosion resistance when compared to the uncoated Mg in HBSS. Among the Sr-P coated ones, those prepared at 200 degrees C for 30 min exhibited a better stability. The higher coating weight, better surface coverage, increase in crystallinity and increase in volume fraction of strontium phosphate phases are considered responsible for this behaviour. The formation of apatite phase after immersion in SBF for 240 h confirmed the bioactivity of Sr-P coated Mg. The study concludes that Sr-P coatings deposited on Mg by HT exhibit good structural integrity, higher corrosion resistance and bioactivity. It is believed that deposition of Sr-P coatings on Mg by HT is a useful surface modification approach for the development of Mg based cardiovascular stents, small pins, screws and needles. (c) 2018 Elsevier B.V. All rights reserved.