Morpho-structural characterization and electrophoretic deposition of xonotlite obtained by a hydrothermal method

Abstract

In this research, xonotlite was synthesized by a hydrothermal method in the Si-Ca-Na-H2O system. Detailed structural characterization by using XRD technique revealed that obtained material contains a small quantity of wollastonite (up to 3 %) as impurity. Calcination of the obtained sample at 900 ˚C has resulted in complete transformation of xonotlite to wollastonite which was detected as only crystal phase. Crystallite size and lattice strain of all crystal phases were calculated using Scherrer and Williamson-Hall method. SEM observation of xonotlite morphology revealed tiny needle-like crystals joined together forming dendritic or globular aggregates. Optimal conditions for electrophoretic deposition of xonotlite on 304 type stainless steel have been achieved by appropriate selection of electric field strengths, dispersing medium and dispersants. Stable suspension of material was obtained using isopropanol containing 1 % water as dispersing medium and Ca-nitrate as charging additive. Native layers of xonotlite have a very smooth morphology, while after calcination, the appearance of small cracks in the coating can be observed but the adhesion strength of the coatings to the substrate is improved.