Measurement of high temperatures, in excess of 1000 C, using ceramic based thermocouples is a well known process. To do this successfully the resistance wires within the thermocouple have to be insulated and guarded.
The use of Ceramic materials to protect the platinum based wire is a technique which has been used for several years, because of the exceptional heat resistant properties of the materials. The thermocouple sensors is considered the most widely used heat measurement implement and is used for measuring the temperature on the inside of a furnace, typically used for that melting or heat treatments for metal or indeed for manufacturing ceramic products.
The ceramic components in a typical thermocouple device are the outer protection tube that is exposed to the furnace. Occasionally multiple tubes are used inside each other to provide the amount of insulation and protection required.
Ceramic insulators (Tubes with 2 or maybe more core holes through them) can also be employed to isolate the two or more wires that proceed to the bi-metallic joint at the head the point that sens0rs temperature is measured.
The typical materials for your tube is actually a 99.7% alumina material, impervious tube, which happens to be attached typically to some metal thermacouple head, containing a terminal block that is utilized for connecting to some standard wire for the instrumentation. Inside a less demanding heat atmosphere a mullite tube can be utilized being a cheaper alternative, that will work sufficiently around 1600 ‘oc. The mullite tube can also be an impervious tube and it has 60% alumina content.