The Effect of Sodium Silicate Concentration on The Properties of the Coating Formed on Pure Zirconium by Microarc Oxidation Coating Technique

摘要

In this study, zirconium oxide coatings were formed on pure zirconium by microarc oxidation technique with the electrolytes containing KOH and different amounts of sodium silicate (0-40 gr/lt) for the same coating duration of 2 hours. The microstructure, surface roughness, phase content and chemical composition of the coatings were characterized by using scanning electron microscopy, profilometery and X-ray diffractometry. It was found that the coatings on surface of zirconium consist of monoclinic ZrO_2 (m-ZrO_2) and tetragonal ZrO_2 (t-ZrO_2) phases and the addition and increasing sodium silicate concentration in the electrolyte increases amount of t-ZrO_2 phase. The coatings were well adhered to Zr substrate with some cracks and porosities in the coating for all concentrations of sodium silicate. The coating thickness and surface roughness increased with sodium silicate concentration in the electrolyte. A glaze like Si rich structure and its increase with Si rate was evident in the outermost region of the coating.