Study On Oxidation And Dislocation Characteristics Of Platinum And Its Effect In Thermometers

The Platinum Resistance Thermometer（SPRT）is one of the most important interpolation instruments for international temperature scales.From the first real practical temperature scale in 1927 to the current 90 international temperature scale,the standard platinum resistance thermometer as an important interpolation instrument for the 90 international temperature scale has always penetrated the development process of the temperature scale and played an increasingly important role.The main factors affecting the performance of platinum resistance thermometer are:oxidation performance,purity,dislocation and crystal structure of platinum wire.Among them,the oxidation performance of platinum wire and the dislocation of platinum wire are the two most important factors.Therefore,the oxidation and dislocation characteristics of platinum wire are studied.For the improvement of the standard platinum resistance thermometer manufacturing process,the stability and accuracy of the platinum resistance thermometer in the mass transfer are improved and improved,and the specification and 90 temperature scale of the metrological verification procedure are guaranteed.The development is very important.In this paper,PtO₂ powder,high purity platinum wire sample,three platinum resistance thermometers（SPRT）with internal pressure change,and 10 new SPRTs produced by China Institute of Metrology are used to study differential scanning calorimetry（DSC）.X-ray photoelectron spectroscopy（XPS）analysis of PtO₂ powder produced and decomposed under different temperature heating,combined with the use of high-precision temperature measuring bridge to measure the triple point resistance of water produced by SPRT due to internal platinum wire oxidation.Change,from the microscopic point of view,the oxidation characteristics of platinum wire inside SPRT at different temperatures;In addition,the X-ray diffraction method（XRD）is used to observe the dislocation changes of platinum wire at different temperatures,and combined with the experimental results of SPRT water triple point resistance change after annealing,the platinum wire dislocation density and SPRT stability are obtained.Relationship between.The results show that PtO₂ can be decomposed into elemental Pt and PtO by heating above 550°C.The temperature at which PtO₂ is rapidly decomposed into platinum is higher than 650°C,and the temperature at which PtO is rapidly decomposed into platinum is higher than 800°C.Under normal pressure,the platinum element will become a two-dimensional PtO₂ with the increase of temperature,then generate three-dimensional PtO₂,and finally decompose into PtO.After heating at 156°C,232°C,420°C for three hours,the maximum change of the three-point point value of water reaches 1mK,and high-precision measurement and traceability of the value need special attention.The average dislocation density of the new platinum wire with a diameter of 0.07mm（purity of 99.999%）is exponentially decreased with the annealing time.After 100h annealing,the dislocation density decreases from 10¹²cm²to 10¹¹cm².After 300h,the dislocation density is basically It is stable;the new SPRT has a significant decrease in the water triple point resistance value 300h before annealing.After 300h annealing,the water triple point value change is less than 3mK and tends to be stable.The result is basically consistent from the heat treatment time and the platinum wire dislocation test result.