10 - platinum platinum-rhodium thermocouple brittle fracture failure analysis

Abstract: for use in reducing atmosphere under 10 - platinum platinum-rhodium thermocouple ( Hereinafter referred to as the platinum rhodium thermocouple) Happened accidentally silk phenomenon of brittle fracture are analyzed. Using metallographic microscope and electron probe of platinum-rhodium thermocouple wire I wire solder joints and I think after fracture tests: the root cause of brittle fracture failure is formed by the Si and Pt Pt5Si2 low-melting-point eutectic material, make accidentally silk due to lower partial melting point and melting, the subsequent brittle fracture.

10 - platinum platinum-rhodium thermocouple have the use of more than 100 years history, it is still the highest in the thermocouple temperature measuring precision, stability is best, the largest output a precious metal thermocouple. Platinum rhodium thermocouple in the oxidizing and neutral atmosphere without pollution medium environments, such as the long-term use of maximum temperature can reach 1400 ℃, its various performance indicators is stable. But when 10 - platinum platinum rhodium thermocouple used in H2 and CO in reducing atmosphere, often accidentally breaks due to brittle fracture and cause of the thermocouple wire.

1 experimental method of chongqing instrument materials research institute for some smelting enterprise platinum-rhodium thermocouple during the use of thermocouple failure due to accidentally wire fracture, after communicate with technical personnel of the enterprise, the enterprise USES platinum rhodium thermocouple is mainly used for measuring the operating temperature in the process of lead and zinc reduction. The lining of the thermocouple protection tube for corundum protection tube, outer layer using silicon carbide protection tube. Experiment with the brittle fracture of accidentally silk sample platinum-rhodium thermocouple made from have failed, the failure of the platinum rhodium thermocouple use environment is in the lead and zinc reduction process, such as: sampling parts of accidentally wire solder joints, accidentally wire fracture and accidentally wire surface. Instrumentation: push around - GX51 metallographic microscope, electron probe JCXA - 733. 1 fracture macroscopic representation of thermocouple wire

as shown in figure 1 and figure 1 in the thermocouple wire breaking into a 5 mm to 30 mm section, I also lost the original wire surface smooth, level off. There is an obvious of wire can be seen at the same time, I accidentally wire melting bond together. Pure platinum melting point is 1769 ℃, platinum, rhodium 10 melting point is 1847 ℃. And in the process of lead and zinc reduction reaction temperature is 900 ~ 1000 ℃, far below the melting point of accidentally silk. In relative to accidentally wire melting point of low temperature, happen accidentally wire melting wire should be because I use dual wire pollution factors exist in the environment. 2 broken accidentally wire solder joint surface morphology

take good platinum rhodium 10 - platinum thermocouple wire solder joints, comparative observation: well I wire solder joint surface is smooth, look no grain boundary and particle phase, morphology as shown in figure 2 a shows. Wire broken accidentally after cleaning in the JCXA - 733 electron probe sample room, detection of surface, clear boundary, can be observed on the solder joint surface around the particle phase, was able to see the damage and solder joint surface cracking, its surface morphology is shown in figure 2 b. In figure 2 c, grain boundary on the surface of the solder joints has been melted, deep wide. Solder joint distribution of the surface of the particle phase material is clearly visible, because grain boundary melting and the formation of the deep groove, particle material enrichment. Through qualitative analysis of the particle material, its main composition is silicon. As shown in figure 2 d. 3 I wire fracture and I silk surface morphology of the

in figure 3 a, accidentally wire on the surface of the fracture surface appeared throughout the deep grooves, had a clear in the circle is melted to form holes. From Pt - Si alloy phase diagram shows [1] : low melting eutectic silicon platinum compounds Pt5Si2 melting point is 830 ℃, and refractory materials such as corundum tube, silicon carbide protection tube containing SiO2. These facts can be thought of: in such a high temperature and reducing atmosphere, reduction of refractory material of SiO2 of elemental Si, Si and Pt, generate low melting eutectic Pt5Si2, melt Pt5Si2 left in the fracture cavity. In figure 3 b I silk surface raised grain boundary, accidentally wire is distributed over the surface of particle phase. 4 metallographic examination

get accidentally wire metallographic specimen observation found accidentally wire damage mainly along the grain boundary to expand internal, shape as shown in figure 4.

3 knot theory ( 1) The fracture S from accidentally silk surface morphology observation, the wire has been seriously polluted, the fracture surface have been formed in the second phase.

( 2) For the second phase by electron probe analysis, this phase contained more for Si element.

( 3) According to the alloy phase diagram, Si element and can form than pure Pt and Pt platinum rhodium much lower melting point alloy phase.

( 4) If accidentally silk surface covered by the high quality of Al 2 O 3 & middot; Y 2 O 3 coating ( Sol - Gel - Dip - Coating process can be done) , can isolate effectively Si under the reducing atmosphere and the effect of Pt, avoid platinum rhodium 10 - platinum thermocouple in the brittle fracture failure problem in reducing atmosphere [2].

the author: platinum rhodium thermocouple

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