Controlled cracking of multilayer ceramic bodies

Cracking of granular ceramic films during drying is a well-known phenomenon. Previous work has shown that films cast above a critical thickness on nonporous substrates crack spontaneously. Films cast on previously cast layers crack at thicknesses that depend on the solids content of the slurry. Cracking occurs in this instance when films are cast above a critical saturation thickness (CST). The CST is defined as the thickness of granular material that would be 100% saturated by the liquid contained in the last cast layer. The CST is remarkably similar in magnitude to the critical cracking thickness obtained with similarly prepared slurries on dense substrates. For example, 0.5 μm Al₂O₃ slurries in water have a CST of 65 μm when cast on previously deposited layers of Al₂O₃. Similarly prepared slurries crack spontaneously when cast on single-crystal silicon at any thickness above approx. 60 μm.