FAILURE STRENGTH OF SILICONE CARBIDE CERAMICDISKS UNDER BIAXIAL FLEXURE WHEN EXPOSED TOELEVATED TEMPERATURES AND CONCENTRATED SULFURIC ACID

摘要

A new generation of heat exchangers is being designed to extract hydrogen using the Sulfur-Iodine (SI) cycle. These heat exchanger materials are subjected to temperatures in the range of930 °C and sulfuric acid. Under these conditions, alloys are unable to sustain structural integrity.Ceramics, however, are known to withstand high temperatures and are corrosion resistant. Thebehavior under these combined effects is not well-understood, especially in the case whenceramic components have extremely narrow channels (less than 1 mm). Two types of circularsilicon carbide (Si-C) ceramic disk specimens are evaluated: one with flat surfaces and the otherwith small micro-channels on one surface. They are loaded to failure in biaxial flexure using aball-on-three-ball configuration. Disks are tested at room temperature and 930 °C. The disks aretested in their as manufactured condition, or after ninety-six hours exposure to sulfuric acidvapor, or after ninety-six hours immersion in 100% concentrated sulfuric acid. The failure loadswere used to create a Weibull graphs that can predict the ceramic disks survival probability at agiven load. The Weibull charts also explore the survivability of the two types of ceramic disks,with different sulfuric acid exposure, at a given load.