Reference materials fall into three categories, namely:
In the thermal field these are an essential tool for the development, verification and use of apparatus and instruments that measure thermal properties such as thermal conductivity, diffusivity, expansivity, emissivity, enthalpy and melting point, among others.
- to calibrate measurement systems and instruments
Existing standards for the accreditation of testing and calibration laboratories (such as the international standard ISO 17025) stipulate the use of reference materials. Currently there is an insufficient number of such materials available for the needs of the thermal properties community. Finding additional materials that can be used as a reference for more than one property is one of the urgent goals of current research in the thermal properties arena.
As an example, a European research project was set up to investigate the characteristics of Pyroceram® 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 for use as a reference material for thermal conductivity, thermal diffusivity and specific heat capacity over the approximate temperature range 300K to 1300K 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 are supplied by international organisations (click here for the IRMM catalogue), research institutes (e.g. NIST, NPL, PTB, NMIJ) or by manufacturers and suppliers of instrumentation (e.g. Labsphere or Perkin Elmer). LGC Promochem claim to be Europe's most comprehensive supplier of reference materials and include reference materials for thermal conductivity (fibre board, iron, graphite, Pyrex glass) and thermal resistance (fumed silica, fibrous glass, expanded polystyrene) as well as RMs for thermal expansion and calorimetry.
In the table below is a selection of reference materials for thermal conductivity, thermal diffusivity and thermal resistance. A fuller list of reference materials for this and other properties, including enthalpy, specific heat, thermal expansion and emissivity, and their suppliers, is available through a search of Reference materials.
Reference materials for thermal conductivity & thermal diffusivity