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Ceramic Thermocouple Tubes
Ceramic thermocouple protection tubes are available in a variety of sizes and materials with Alumina, Mullite, and Zirconia being the most commonly used. Ceramic thermocouple protection tubes are typically used to protect Platinum thermocouple elements at high process temperatures above 2200°F.
When choosing a ceramic protection tube material, careful consideration should be taken into account in regards to its unique thermal shock characteristics and physical strength.
Alumina has a maximum service temperature of 3450oF or 1900oC in both oxidizing and reducing atmospheres. Alumina thermocouple protection tubes are considered to have better mechanical strength (twice the tensile strength of Mullite) and better chemical resistance than Mullite thermocouple protection tubes. Alumina thermocouple protection tubes also have excellent abrasion resistance. Secondary metal tubes can be added for additional protection from mechanical damage. Alumina protection tubes are considered to be gas tight so they make excellent primary protection tubes. All tubes, which are used in horizontal installations and at elevated temperatures, should be supported to prevent mechanical breakage. Alumina tubes can be for primary and secondary protection tubes on Noble Metal (Platinum based) thermocouples. Alumina has a very low silica content so they will not contaminate Platinum thermocouple elements above (2200oF or 1200oC) as a Mullite protection tube.