Industrial Automation Magazine India

Rare Metal Thermocouples

Published on : Tuesday 30-11--0001

Toshniwal Sensors supplies high-temperature thermocouples for measurement & control of temperatures in furnace and chambers. Because of high temperature and corrosive environment conditions, platinum clad ceramic protective tubes are used in some applications. According to the melting composition, strong oxidation may occur.

Toshniwal Sensors design, supply, maintain and service a broad range of glass customer specified high temperature thermocouples around the globe. In fact almost all is possible; thermocouples with single/double and triple type S, R or B element, thermo element wire diameters from 0.15mm to 0.5mm; Protective thimbles made from pure Pt, PtRh10% and PtRh13%; Precious metal thimbles from diameter of 6mm up to 12mm or even more; Wall thickness starting from 0.2mm; thermocouple length & dimension according to needs & demands.

Platinum/Rhodium Protective tubes known as thermocouple thimbles are inert to molten glass and provide unequaled resistance to erosion. They withstand thermal cycling, ceramic cracking and several removals/ insertions. In glass melts, presents reducing conditions may cause low melting phases of oxides (aluminium, silicon, arsenic, lead) with platinum, which quickly penetrate into the grain boundaries. Furthermore, conventional alloys show strong coarse-grain formation at higher operating temperatures. Structure damage by contamination leads to loss of stability and breakage of components. Also the sulphur in glass can react with rhodium in Pt-Rh alloys leading to the formation of a eutectic that melts at 925°C, thus destroying the thimble. The introduction of dispersion hardening (DPH) for platinum and its alloy has solved these problems to large extend. DPH Platinum/rhodium alloys give increased mechanical strength and durability.

Pt DPH is an oxide dispersion hardened grade of pure platinum which is used in high temperature applications when the use of solid solution hardening by alloying elements such as rhodium, iridium or gold cannot be tolerated. The finely dispersed oxides impede grain growth and dislocations just below the melting point. This results in a clear reduction of the creep rate and an increase in stress rupture strength especially at high temperatures. Because grain growth is impeded, a fine grained structure is formed, which remains stable even at the highest application temperatures. The current platinum DPH materials (Pt DPH, PtRh 10 –DPH) distinguish themselves through following advantages:

• High creep and stress rupture up to the highest application temperatures.
• Excellent corrosion resistance, even in aggressive glass melts.
• Ideal Micro-structural stability in long-term service.
• Less Crystallization.
• Good formability.

Toshniwal Sensing Devices Pvt Ltd,Tel:+91-8003779056,[email protected]