Development of mullite and mullite/Al2O3 precursor sols for electrophoretic deposition of oxidation protection coatings

Whereas a low H2O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H2O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H2O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C.