Thermal barrier coating on the polyimide matrix composites was successfully fabricated at 400 degrees C via the combined sol-gel/sealing treatment process. In this approach, zirconia coating was firstly deposited onto substrate by sol-gel process, followed by penetration of aluminum phosphate into the final coating. Sealing mechanisms of phosphate sealant were based on the adhesive binding of phosphates and the chemical bonding. After thermal cycling at 400 degrees C for 135 cycles, no apparent delaminations and spallations appeared in the ZrO2/phosphates dual coating, and the average bonding strength was 5.83 MPa. Thermal oxidation of substrate coated with the ZrO2/phosphates dual coating could be retarded at about 900 degrees C. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.