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The requirements for thermal analysis instruments are increasing in terms of increasing the measurement ranges and improving their accuracy due to the development of scientific and technological progress in the field of metrological supervision, chemical and pharmaceutical industries. The study of determining the melting point of organic substances is of particular relevance for the metrological support of the applied thermal analysis instruments and traceability to the base units of physical quantities.The purpose of the research was to test the possibility of using organic substances on the basis of sodium acetate and sodium methanesulfonate as phase transition temperatures standards for candidate material to certified reference materials for phase transition temperatures (CRMs) traceable to the SI unit of the «temperature» value.The procedure for measuring the phase transition temperatures (melting point) was performed by differential scanning calorimetry using an STA 449 F5 JUPITER thermal analyzer from the GET 173–2017 State Primary Standard. The determination of the CRM certified value was performed in accordance with GOST ISO Guide 35–2015, the contributions to the uncertainty from the heterogeneity of the starting materials were evaluated, and the short-term and long-term stability of the materials were studied.The obtained metrological characteristics of the investigated batch of CRMs are as follows: the range of permissible certified characteristics of the melting point of the phase transition for anhydrous sodium acetate (328.35–330.35) °C, for sodium methanesulfonate (352.05–354.05) °C. Comparison of the certified melting point values of the developed CRMs with the reference melting point values presented in IUPAC showed that the certified characteristics of the CRMs are consistent within ±1.4 °C.The theoretical significance of the obtained results lies in the proof of the possibility of applying the method of differential scanning calorimetry for the development of certified reference materials for phase transition temperatures (a set of TPKR CRMs) GSO 11928–2022/GSO 11929–2022.The practical significance of the results obtained makes it possible to expand the possibility of establishing and controlling the calibration dependence of thermal analysis measuring instruments; certification of measurement procedures (methods) and accuracy control of the measurement results of the phase transition temperatures of metals, metal salts, metal oxides, polymeric materials, organic and inorganic substances.

The requirements for thermal analysis instruments are increasing in terms of their metrological support with the development of scientific and technological progress in the field of metrological supervision and electronics industry. The study of determining the phase transition temperature, namely the Curie temperature, is of particular relevance for the metrological support of the applied thermal analysis instruments and traceability to the basic physical units.The purpose of the research was to test the possibility of using materials based on alumel, nickel and iron silicide (trafoperm) as phase transition temperature standards for candidate reference materials of phase transition temperatures (RMs) traceable to the SI unit of the «temperature» value.The procedure for measuring the phase transition temperatures (Curie temperature – TC) was carried out by the thermomagnetometric method using an STA 449 F5 JUPITER thermal analyzer from the State Primary Standard GET 173-2017. The determination of the RM certified value was carried out in accordance with GOST ISO Guide 35–2015, the contributions to the uncertainty from the heterogeneity of the initial materials were evaluated, and the short-term and long-term stability of the materials were studied.A comparison of the certified values of the developed RMs with the reference values of the Curie temperature showed that they are consistent.The theoretical significance of the results obtained is proof of the possibility of using the thermomagnetometric method for the development of certified reference materials of phase transition temperatures GSO 12005–2022/GSO 12007–2022. The possibility of applying the method of differential scanning calorimetry in determining the Curie temperature was also confirmed.The practical significance of the results obtained allows expanding the possibilities for constructing the calibration dependence of measuring instruments for thermogravimetric analysis and monitoring its stability, as well as increasing the measurement precision of the Curie temperature of various substances and materials.

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