Phase change materials

Phase change materials (PCM) are able to deliver thermal energy, which they absorb earlier in the process of melting, during the transition from the liquid to the solid state. Probably the most prominent example that uses this principle are heat packs or hand warmers which consist of a bag filled with a supersaturated salt solution. On squeezing the bag, the liquid inside starts to solidify, giving off heat in the process of crystallisation. By placing the bag in a pot with boiling water the solid liquifies and the heat pack can be used again.

Most current technical applications employ paraffins as phase change materials that can be tuned to certain melting ranges. However, the use of paraffins has two major disadvantages. Firstly, paraffins are petroleum products and hence the use of these materials is directly linked to the price development of crude oil. Secondly, paraffins are inflammable which represents a considerable safety concern for many applications. By formulation, paraffins can be made into powders or granules to improve their suitability but due to the presence of carrier materials these formulations contain only a relatively low percentage of energetically active material.

Another less important class of phase change materials are salt hydrates. The contents of the above-mentioned heat packs belong to this group. These materials offer the advantage that they are not petroleum products but they still have only a limited range of use with regard to operating temperatures compared to paraffins.

IoLiTec is currently working on the development of new phase change materials based on ionic liquids, including both their utilisation in neat form as well as in the form of formulations containing further performance-enhancing additives. Such materials can be used for the following purposes:

  1. cyclic storage and supply of thermal energy
  2. latent heat storage devices
  3. heat buffers
  4. cold buffers

In terms of product development IoLiTec has been investigating this topic since September 2005 as part of its contribution to a government-funded joint project with the Fraunhofer Institute for Environmental, Safety and Energy Technology (FhG UMSICHT) and the Fraunhofer Institute for Solar Energy Systems (FhG ISE). At the moment a number of promising systems exist at the prototype stage whose properties could result in their use as latent heat storage devices and as heat and cold buffers. The launch of these IoLiTherm® products is scheduled for 2007.

Further information on products from the phase change materials range can be accessed by clicking on the corresponding link in the menu on the right.

If you have any questions regarding our activities, applications or products in this field please feel free to contact us.