Electrostatically deposited surface seeding and promotion of crystallization of sol-gel derived LaAl₁₁O₁₈ coating on oxide fibers

For the use as interface material in oxide/oxide-continuous fiber-reinforced composites, LaAl₁₁O₁₈-fiber coatings have been developed. The magnetoplumbite structure has an attractive property, due to the presence of mechanically weak cleavage planes between the stacked spinel blocks. Thus, easy cleavage or crack deflection resulting in reduction in energy release rate at the fiber/matrix interface can be provided during the fracture of an oxide/oxide-composite. The synthesis of LaAl₁₁O₁₈ via sol-gel route required high processing temperature which causes the instability of fibers. An optimization of the process, in terms of elimination of occurrence of an intermediate phase and promotion of complete crystallization at temperatures ≤1200 °C was necessary. This study describes a method to obtain continuous and well-crystallized LaAl₁₁O₁₈ fiber-coatings at temperatures as low as 1100 °C, benefiting from both the sol-gel-process and the seeding concept.