Morpho-Structural Characterization and Electrophoretic Deposition of Xonotlite Obtained by a Hydrothermal Method

In this research, xonotlite was synthesized by a hydrothermal method in the Si-Ca-Na-H2O system. Detailed structural characterization by using the XRD technique revealed that the obtained material contains a small quantity of wollastonite (up to 3 %) as an impurity. Calcination of the obtained sample at 900 ˚C has resulted in a complete transformation of xonotlite to wollastonite which was detected as only a 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 the material was obtained using isopropanol containing 1 % water as dispersing medium and Ca-nitrate as a 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.