CMAS is formed from siliceous material ingested with the air intake (sand, dust, cement, volcanic ash and runway debris) of aircraft and industrial turbine engines. However, more recently it WP-1066 has become the ‘catch-word’ for all airborne particles, including volcanic ash. TBCs are susceptible to degradation by CMAS, especially in aircraft engines that operate in dust-laden environments . Degradation of TBCs by low melting point slags/fluxes has been problematic since the 1980s. Early attention was drawn to this subject when low cost fuels, with appreciable amounts of impurities such as V, S and P were found to potentially degrade the zirconia-based TBCs and possibly attack the thermally grown oxide (TGO) . The temperature within the TBC ceramic, even taking into account the thermal gradient across the TBC system, is higher than the melting points of vanadate and sulphate salts hence the molten salts will infiltrate the entire TBC. A similar mechanism based on melt infiltration is known to operate for CMAS . One of the consequences of CMAS attack is a substantial reduction in thermal conductivity and the strain tolerance of the TBC .