Measurement of high temperatures, greater than 1000 C, using ceramic based thermocouples is actually a well established process. To carry out this successfully the resistance wires throughout the thermocouple must be insulated and protected.
The usage of Ceramic materials to shield the platinum based wire is a technique which has been used for many years, due to the exceptional heat resistant properties of such materials. The temperature sensor thermocouple is considered the most commonly used heat measurement implement and is also useful for measuring the temperature within a furnace, typically getting used for the melting or heat management of metal or indeed for manufacturing ceramic products.
The ceramic components within a typical thermocouple device are definitely the outer protection tube that may be subjected to the furnace. Sometimes multiple tubes are used inside one another to supply the degree of insulation and protection required.
Ceramic insulators (Tubes with 2 or maybe more core holes through them) can also be utilized to isolate the 2 or more wires that go to the bi-metallic joint at the head which is the point that sens0rs temperature is measured.
The typical material used for your tube is a 99.7% alumina material, impervious tube, that is attached typically into a metal thermacouple head, containing a terminal block which is used for connecting to some standard wire on the instrumentation. In the less demanding heat atmosphere a mullite tube may be used as a cheaper alternative, that will work sufficiently around 1600 ‘oc. The mullite tube is additionally an impervious tube and has 60% alumina content.