CMAS probes are made from user-specified sensing materials, including carbon steels, stainless steels, and nickel-, aluminum-, and copper-based alloys. They can also be made from customer supplied materials that have the same microstructure/heat treatment as the system component materials to be monitored. The size of the sensing electrode varies from 0.1 to 3 mm (0.004" to 0.12") in diameter, depending on the application. Typical numbers of electrodes in a CMAS probe are 9, 16 or 25 for online corrosion monitoring and vary from 8 to 100 for laboratory corrosion and electrochemical studies. Other sizes and numbers of electrodes are available.