Reference materials

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Resin bonded glass fibre board (CRM440) reference material from IRMM used to calibrate heat flow meter apparatus.

 

Some specimens (polymer, glass, wood) for measurement of thermal conductivity in a 50 mm heat flow meter apparatus.

 

A reference material is a material or artefact that is both durable and highly stable and has well established uniform properties which are unaffected by external variables over the temperature range of operation such that it can be used for the calibration of an apparatus; assessment of a measurement method; or for assigning property values to other materials. See also (The International Vocabulary of Basic and General Terms in Metrology, or VIM, 1993).

Reference materials fall into three categories, namely:

  • Standard (or Certified) (SRM or CRM) that are from a well characterised stock and have reproducible property values based on the results of a significant testing and evaluation programme by a national measurements laboratory
  • Reference (RM) usually available commercially and having consensus property values based on measurements by a number of organisations;
  • Transfer Standard (TS) a specimen or artefact of a given shape having a unique property(s) based on measurement by an absolute method. (See also Definitions at NIST).

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.

 

Pyroceram 9606, a polycrystalline glass ceramic for use up to at least 1000 C. The material should soon be available from IRMM as a certified reference material for thermal conductivity and thermal diffusivity.

 

    
Reference materials are also needed:

- to calibrate measurement systems and instruments
- to establish traceability of measurements (i.e. to ensure comparable measurement results between different laboratories
- for use by materials and users of materials to question or verify competitive claims.

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

Reference material Property Notes Link

Pure iron CRM

Thermal conductivity (including electrical resistivity)

25 mm and 50 mm diameter stock available in desired length

Inconel 600 CRM

Thermal conductivity (including electrical resistivity) and thermal diffusivity

25 mm and 50 mm diameter stock available in desired length or thickness

310 stainless steel CRM

Thermal conductivity (including electrical resistivity) and thermal diffusivity

25 mm and 50 mm diameter stock available in desired length or thickness

321 stainless steel CRM

Thermal conductivity (including electrical resistivity) and thermal diffusivity

25 mm and 50 mm diameter stock available in desired length or thickness

Nimonic 75 CRM

Thermal conductivity (including electrical resistivity) and thermal diffusivity

25 mm and 50 mm diameter stock available in desired length or thickness

Alumina CRM

Thermal diffusivity

12 mm diameter 2 mm thick disc

Aluminium CRM

Thermal diffusivity

12 mm diameter 3 mm thick disc

Expanded Polystyrene TS

Thermal conductivity/thermal resistance

For guarded hot-plate and heat-flow meter. 305 mm square (-10 C to 70 C); and 610 mm square (-5 to 40 C) in various thicknesses, (singly and in pairs)

Nylon TS

Thermal conductivity

For guarded hot-plate and heat-flow meter (-20C to 80C); 305mm square (sold in pairs)

Polymethyl-methacrylate (Perspex) SRM and TS

Thermal conductivity

For guarded hot-plate and heat-flow meter (-10 C to 60 C); 305 mm square (sold in pairs) and other smaller sizes

Glass fibre board TS

Thermal conductivity

For guarded hot-plate and heat-flow meter (-10 C to 80 C); 610 mm square

Foam glass TS

Thermal conductivity

For guarded hot-plate and heat-flow meter (100 C and above); small pieces and off cuts

Microtherm TS

Thermal conductivity

For guarded hot-plate and heat-flow meter (100C and above); Small pieces and offcuts

Resin bonded glass fibre board (CRM440)

Thermal conductivity/thermal resistance

For guarded hot-plate and heat-flow meter (-10 C to 50 C); 610 mm square 300, 500 and 600 mm square boards 35 mm thick

IRMM

Pyroceram 9606

Thermal conductivity, thermal diffusivity

Certified in the frame of the EU project BCR 724. Specimens in a variety of dimensions are in preparation and will be available soon.

IRMM

Glassy carbon

Thermal diffusivity

10 and 12 mm diameter discs

 AIST

High purity alumina

Thermal diffusivity

10 and 12 mm diameter discs, 2 to 4 mm thick. Other sizes available.

 Japanese Fine Ceramics Centre (JFCC)

Expanded polystyrene

Thermal conductivity/thermal resistance

305 mm and 600 mm square in various thickness

Fibrous glass board

Thermal conductivity/thermal resistance

305 mm and 600 mm square in various thicknesses

 

Dense mineral oxide fibre board (candidate SRM)

Thermal conductivity/thermal resistance

305 mm square, 25 mm thick

Pyrex glass (CRM 039)

Thermal conductivity

For guarded hot plate, guarded heat flow meter, comparative and transient methods (-75 C to 195 C ), 20, 30 and 50 mm thick, maximum 300 mm square but can be smaller

 IRMM

Expanded polystyrene board (NIST SRM 1453)

Thermal resistance

930 mm x 660 mm x 13.4 mm (for manufacture of calibration panels for testing fenestration systems)

Fumed silica board (NIST SRM 1449 and 1459)

Thermal conductivity/thermal resistance

300 mm and 600 mm square 25.4 mm thick. (Certified values as a function of density and gas pressure.)

Fibrous glass board (NIST SRM 1450c)

Thermal conductivity/thermal resistance

610mm square 25.4 mm thick (can be cut to smaller sizes)

Graphite (NIST RM 8424 and RM 8426)

Thermal diffusivity

6.4 and 25.4 mm diameter, 50 mm long
(Temperature range 5 to 2500K)

Electrolytic iron (NIST RM 8420 and RM 8421)

Thermal conductivity and electrical resistivity

6.4 and 31.8 mm diameter, 50 mm long
(Temperature range 2 to 1000K)



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