Monolithic Metal Oxide Thin-Wall Substrates with Closed and Open Cells: Optimal Designs by Theoretical Modeling and Experiment

Recently, ASMT has developed a process of making monolithic metal oxide thin-wall structures from mechanically assembled metal preforms, whose shape and internal configuration are retained in the (oxidation) process. Because metallic designs can be extremely diverse, the same varieties of designs are now possible in metal oxide ceramics. In particular, some unique metallic designs such as spiral winding structures (formed from flat and corrugated layers) with either closed or open cells have been realized for the first time in ceramics, such as hematite Fe₂O₃ and titania (rutile) TiO₂. In order to optimize these new ceramic designs, we have developed a theoretical model of layer distribution of mechanical stresses under external uniform radial pressure and of thermal stresses under typical heating/cooling regimes. The stress distribution is determined by various parameters, both structural (cell size and geometry, wall thickness, number of layers, etc.) and material (tensile wall strength, Young's modulus, thermal expansion coefficient, etc.). The analytical formalism and computational program are highlighted. Model results are presented for a variety of hematite and titania substrates, having closed or open cell structure, a cell density from 200 to 1000 cpsi, and wall thickness from 1 to 5 mils. Recommendations on optimal designs are given and supported by relevant experimental data. Automotive applications of new metal oxide thin-wall substrates are discussed.