Research On Oxidation Characteristics Of Platinum Wire And Its Application In Platinum Resistance Thermometer

Temperature measurement is widely used in energy,metallurgy,electronics,new materials,health care,national defense,aerospace and other fields.In order to ensure temperature measurement has the same value scale in different circumstances,the concept of temperature scale was proposed.At present,the ITS-90 is international temperature scale.The standard platinum resistance thermometer as the interpolation instrument of ITS-90 plays an irreplaceable role in high-precision temperature measurement of industry life and the temperature value transfer chain.The platinum resistance thermometer platinum is affected by varies factors,such as crystal structure,platinum impurities,platinum wire oxidation and platinum wire strain and so on.The oxidation and crystal structure of platinum wire is the main two factors of affecting the platinum resistance thermometer platinum.Therefore,research on oxidation characteristics of platinum wire and grain size changes caused by high temperature oxidation has a very important significance to improve the measurement accuracy and stability of platinum resistance thermometer platinum.In this paper,PtO₂ powder,high purity platinum foil and two standard platinum resistance thermometers that can change the internal pressure were used for researching by using differential scanning calorimetry Technology?DSC?and X ray photoelectron spectroscopy?XPS?,aiming to obtain the decomposition temperature of PtO₂ and high pure platinum film oxidation products information.The effect of platinum wire oxidation to SPRT was researched by analysising the oxidation characterics of platinum wire from the micro level;In addition,the change of platinum wire internal structure caused by heating at a high temperature lead to the change of resistivity,then affect the measurement accuracy of SPRT.Therefore,the relationship between resistivity changes measured by high precision bridge and grain size observed by scanning electron microscope was achieved.The results show that:?1?PtO₂ can be decomposed into Pt and PtO at temperatures above 550?.The rapid decomposition temperature of PtO₂ is above 620?,The rapid decomposition temperature of PtO is above 820?.?2?Platinum wire can generate two-dimensional PtO₂ with O₂ by heating at 175? under atmospheric pressure and the resistance value of SPRT increases firstly and then tends to be stable as the time of heating goes by;Platinum wire can generate there-dimensional PtO₂ with O₂ by heating at 375? and the speed of oxidation did not slow down after heating 666h;Platinum wire can generate PtO₂ and a small amount of PtO by heating at 500? and the resistance value of SPRT increases firstly and then tends to be stable as the time of heating goes by.?3?Two-dimensional and three-dimensional oxide PtO₂ and oxide PtO was generated in turn on the surface of platinum wire with the rises of temperature under atmospheric pressure.The biggest change of SPRT resistance value up to 4.9mk after heating 666 h in 175??375??500?.Therefore,the SPRT used in high precision measurement and the transmission of temperature required to give special consideration.?4?The grain size of the platinum wire is gradually increased and the resistivity decreases with the rises of heating temperature.The grain size of the platinum wire is inverse proportional to the resistivity and has a relationship of Exponential function.There the effects caused by the change of grain size of the platinum wire must be taken into consideration.