THIN-FILMS BY CONSOLIDATION AND SINTERING OF NANOCRYSTALLINE POWDERS

Nanocrystalline CeO2 and Y2O3-doped CeO2 powders (particle size of 10- 15 nm) were prepared Under hydrothermal conditions at temperatures bet ween 100 and 300 degrees C. X-ray diffraction and transmission electro n microscopy revealed that the particles were crystalline. The particl e size distribution followed approximately the Lifshitz-Slyozov-Wagner theory for Ostwald ripening controlled by the diffusion step. Powder compacts were sintered to nearly full density below 1350 degrees C. Th in adherent films (0.5 to 1 mu m thick) on rigid substrates were prepa red by spin-coating or dip-coating of stabilized suspensions, followed by drying and sintering. Dilute suspensions in aqueous solvents were stabilized electrostatically at pH values of 3.5 to 4. However, increa sing particle concentration produced flocculation. Higher particle con centrations can be achieved without flocculation through the use of st erically stabilized suspensions with polyvinylpyrrolidone (PVP) as a d ispersant. With these suspensions, homogeneous films were deposited on porous or dense substrates. The shrinkage kinetics of the adherent fi lms were approximately the same as those for the powder compacts. The use of nanocrystalline powders offers a unique advantage for the produ ction of adherent films with controlled microstructures on dense or po rous substrates at relatively low temperatures. (C) 1997 Elsevier Scie nce Limited. All rights reserved.