Alumina/epoxy interpenetrating phase composite coatings: I, Processing and microstructural development

Interpenetrating phase composite OPC) coatings consisting of continuously connected Al2O3 and epoxy phases were fabricated. The ceramic phase was prepared by depositing an aqueous dispersion of Al2O3 (0.3 mu m) containing orthophosphoric acid, H3PO4, (1-9.6 wt%, solid basis) and heating to create phosphate bonds between particles. The resulting ceramic coating was porous, which allowed the infiltration and curing of a second-phase epoxy resin. The effect of dispersion composition and thermal processing conditions on the phosphate bonding and ceramic microstructure was investigated. Reaction between Al2O3 and H3PO4 generated an aluminum phosphate layer on particle surfaces and between particles; this bonding phase was initially amorphous, but partially crystallized upon heating to 500 degrees C, Flexural modulus measurements verified the formation of bonds between particles. The coating porosity land hence epoxy content in the final IPC coating) decreased from similar to 50% to 30% with increased H3PO4 loading. The addition of aluminum chloride, AlCl3, enhanced bonding at low temperatures but did not change the porosity. Diffuse reflectance FTIR showed that a combination of UV and thermal curing steps was necessary for complete curing of the infiltrated epoxy phase. Al2O3/epoxy IPC coatings prepared by this method can range in thickness from 1 to 100 pm and have potential applications in wear resistance.