The ceramic honeycomb substrate in a catalytic converter must have thin walls, contain many cells, and also resist the frequent and drastic temperature changes that occur inside an automobile engine.
The thin walls and numerous cells are necessary to provide a large surface area, to assure that a high percentage of the pollutants are decomposed.
Modern ceramic substrates have about 350 to 400 cells per square inch (54 to 62 cells per square centimeter) and a wall thickness of about 0.0055 inch (0.14 millimeter).
They are a marvel of manufacturing technology.
A complete substrate is shown in figure 9-3, and a close-up showing the small size of the openings and the thinness of the walls is shown in figure 9-4.
Normal ceramics can't withstand the thermal shock imposed by the rapid thermal cycles of the catalytic converter, especially she you start your car on a cold winter morning.
To solve this problem, Corning, Inc. developed a material, called cordierite, with near-zero thermal expansion.
Since 1974 , over 350 million cordierite ceramic-honeycomb catalytic converter have been installed in cars, trucks, and buses and have reduced pollution by 1.5 billion tons.