State Primary Special Standard of the Unit of Thermal Conductivity of Solids in the Temperature Range from 2 K to 300 K Get 141-2020

This article presents the relevance of precise thermal conductivity measurements of solid materials used in heat exchange and heat insulating devices at low temperatures. The dependence of thermal conductivity of solids on the chemical composition and methods of mechanical and thermal processing of the material are considered at low temperatures. The device, principle of operation, and results of metrological studies of the State primary special standard of the unit of thermal conductivity of solids in the temperature range from 2 K to 300 K GET 141-2020 are presented. Compared to GET 141-84, in effect until 2020, GET 141-2020 includes the fabricated cryostat and a cell for measuring thermal conductivity. The range of reproduction of the unit of thermal conductivity of solids in GET 141-2020 is expanded compared to that of GET 141-84 from 0.1-10 W/(m center dot K) to 0.05-15 W/(m center dot K), and the range of temperature change is increased from 4.2-90 K to 2-300 K. A method of thermal conductivity measurements using the developed cryostat is described. Methods for ensuring a reliable thermal contact between the test sample and the heat-measuring plates of the heater and of the cell body are elaborated. The metrological characteristics of GET 141-2020 are analyzed; the measurement uncertainty budget is calculated when reproducing the unit of thermal conductivity of solids. GET 141-2020 is used to calibrate thermal conductivity measurements during the verification and calibration of equipment for measuring thermal conductivity.