Research On Metal Carbon Eutectic And Peritectic High Temperature Fixed Point

With the evolution of science and technology, accurate measurement ofhigh temperature is vital and imminently required. However, the uncertaintyin high temperature measurement increases rapidly with increasingtemperature, since the currently implemented international temperature scale(ITS-90), relying upon radiation thermometry above the silver point (962C)is in lack of reference fixed points above the copper point (1084C). Thediscovery of high-temperature fixed points (HTFPs) based upon metal-carboneutectics and peritectics will drastically change the situation. In this paper wewill f℃us on research of improving the temperature scale above the copperpoint by using these HTFPs.The construction of HTFPs, the ITS-90temperature assignment to them, key factors influencing the implementationof HTFPs, international comparisons of the ITS-90, as locally realized, bymeans of HTFPs will be studied in turn in this thesis, in Chapters2to6,respectively.Experimental systems-crucibles, ingots and furnaces-were developed tofill and subsequently realize HTFPs, i.e. providing the conditions toreproducibly realize melting and freezing curves. A high temperature furnacewas modified for use up to2800℃to satisfy the demand of filling andrealizing the WC-C peritectic fixed point. Several sets of Co-C (nominaltemperature1324℃), Pt-C (1738℃), Re-C (2474℃), WC-C(2747℃) fixedpoints of different structure were filled by different filling methods, and theyall showeds robust, stable and accurate metrological characteristics.The T90assignments to HTFPs were studied. Non-linearity of radiationthermometers, one of the main components in the uncertainty budgetass℃iated with the realization of ITS-90by radiation thermometry-above thesilver point-was studied, using the superposition method and involving LEDswith high radiance output.In any temperature scale, to get a unique point for reference, the phase transition temperature to be referred to, is that of the system inthermodynamic equilibrium, in its pure state. How to extrapolate to thisunique point, in the case of the selected HTFPs, and the key influence factorsto be taken into account, are important subjects discussed in this thesis. Pt-Cwas chosen and experimentally studied through freezing rate experiments tovalidate the procedures and models involved. The model will be adopted byCCT-WG5to assign thermodynamic temperature to HTFPs. The effect ofimpurities on the eutectic phase transition temperature was studiedtheoretically, and the method to correct for the impurity effect is reported here.Finally, the furnace-gradient effect on the realization of the Co-C point wasexperimentally studied as reported in this thesis.The reproducibility of the Co-C, Pt-C, and Re-C HTFPs–in terms ofmelting characteristics filled by NIM, China,NPL, UK and CEM, Spain,were studied at NPL with NPL’s ITS-90as a reference, with as result that forall the three kinds of HTFPs the reproducibility was better than0.1℃. Aprototype comparison of the ITS-90, as realised by NIM, NPLand CEM, usingCo-C, Pt-C, and Re-C as transfer standards is reported. From thesemeasurements a comparison reference value (CRV) was derived. At the Co-Cand Pt-C points the deviation from the CRV was <0.1℃for all threeinstitutes, at the Re-C point the deviation was <0.4℃. Given the consistentperformance of the HTFPs they should be seriously considered as scalecomparison artefacts of choice when comparing l℃al realisations of theITS-90and of l℃al measurements of thermodynamic temperature.