Abstract: A seal located between ceramic electrolyte or mixed electrolyte cells, and ceramic components of similar or dissimilar compositions, ceramic components and metal components, or any other materials for use in electrochemical gas separation devices, fuel cells and other thermal electrochemical power generation devices, high temperature heat exchangers, thermal management devices or other applications requiring joining or gas-tight bonding where said seal is comprised of materials derived from pyrolysis of silicocarbon polymers and fillers of active and/or passive fillers.