DRYING OF GRANULAR CERAMIC FILMS .1. EFFECT OF PROCESSING VARIABLES ON CRACKING BEHAVIOR

Drying of binder-free granular ceramic films was studied to identify p rocessing variables which affect their cracking behavior. Films were p repared from electrostatically stabilized suspensions of alpha-alumina in water. A critical cracking thickness (CCT) was determined, above w hich films would spontaneously crack during drying. The effects of par ticle size, liquid surface tension, drying rate, dispersion stability, and sedimentation time were evaluated by a statistical design methodo logy. The CCT for films prepared on glass substrates was used as a mea sure of the effect of each variable on cracking. The statistically sig nificant variables were particle size, dispersion stability, and sedim entation time. The effect of substrate constraint was also studied by producing films on a Teflon substrate and a pool of liquid Hg. The obs ervations were consistent with a capillary formed tensile stress actin g on the entire film rather than differential stress generated by a mo isture gradient over the film thickness.