Some NPL reference materials (metals, ceramic, polymer) used for calibration of thermal property measurement apparatus.
A reference material is a material for which one or more of its property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus; assessment of a measurement method; or for assigning property values to other materials. (The International Vocabulary of Basic and General Terms in Metrology, or VIM, 1993).
Reference materials are carefully measured and usually certified materials (see Definitions at NIST for the different kinds of reference material). In the thermal field they are an essential tool for verification and use of instruments that measure thermal properties such as thermal conductivity, diffusivity, expansivity, emissivity, enthalpy and melting point, among others.
High purity indium (99.999%) for calibration of DSC apparatus.
Reference materials may be used to calibrate measurement instruments, to compare, develop and validate methods and to establish traceability of measurements, i.e. to ensure comparable measurement results between different laboratories. Present standards for the accreditation of testing and calibration laboratories (such as the international standard ISO 17025) stipulate the use of reference materials.
Reference materials must be homogeneous and stable, and the certified values must be accurate. Finding a material that can be used as a reference for more than one property is one of the goals of current research.
As an example, a European research project was set up to investigate the characteristics of PyroceramŪ 9606, a material developed by Corning Glass that is a hybrid of ceramic and glassy phases but is distinct in its composition, structure, and behaviour from either a pure ceramic or a pure glass. Its suitability to be used as a reference material for thermal conductivity, thermal diffusivity and specific heat capacity has been assessed and soon it will be available as a Certified Reference Material from the IRMM in Belgium, one of the seven institutes of the Joint Research Centre of the European Commission and one of the world's largest reference material producers.
Reference materials for thermal analysis and calorimetry are supplied by measurement standards institutes (e.g. NIST, PTB) or by companies (e.g. LGC).
In the table below is a selection of reference materials for thermal analysis and calorimetry, especially for temperature and enthalpy calibration and for heat capacity determination. A fuller list of reference materials for this and other properties, and their suppliers, is available through a search of Reference materials