The interfacial reactions of Mo-Si-B with Al-Si metallic coatings during processing to achieve high-temperature corrosion protective mullite coating for advanced turbine materials are discussed. Al-Si is being deposited on the Mo-Si-B substrate material by immersion in liquid Al-Si alloy, molten salt cathodic deposition, and organic electrolysis, to achieve adhesion and compositional gradients across the interfacial region. The interfacial region during Al-Si deposition is the precursor to the formation of compositionally graded mullite by annealing and subsequent oxidation. The optimum Al-Si content of this metallic layer, which will be attained by deposition combined with silicon diffusion from Mo-Si-B, is described. Characterization of the constitution and gradients across the interfacial region is reported. Transport modeling in this precursor layer and the substrate is discussed. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.