Measurement of high temperatures, more than 1000 C, using ceramic based thermocouples is a well known process. To do this successfully the resistance wires throughout the thermocouple have to be insulated and protected.
The usage of Ceramic materials to protect the platinum based wire is a technique which has been used for quite some time, due to exceptional heat resistant properties of such materials. The thermocouplers is easily the most commonly used heat measurement implement and it is used for measuring the temperature on the inside of a furnace, typically getting used for your melting or heat therapy for metal or indeed for manufacturing ceramic products.
The ceramic components inside a typical thermocouple device would be the outer protection tube which is open to the furnace. In some cases multiple tubes are being used inside each other to deliver the level of insulation and protection required.
Ceramic insulators (Tubes with 2 or even more core holes through them) are also used to isolate the several wires that go to the bi-metallic joint on the head the point from where sens0rs temperature is measured.
The normal materials used for the tube is really a 99.7% alumina material, impervious tube, that is attached typically into a metal thermacouple head, containing a terminal block which is often used for connecting to your standard wire on the instrumentation. In a less demanding heat atmosphere a mullite tube may be used being a cheaper alternative, that can work sufficiently approximately 1600 ‘oc. The mullite tube is additionally an impervious tube and has 60% alumina content.