Fraunhofer ISC, Center for High Temperature Materials and Design HTL, Bayreuth
Fraunhofer ISC, Center for High Temperature Materials and Design HTL, Bayreuth

Research Areas:

Ceramics

Foams

Fraunhofer Center HTL develops inorganic and carbon-based foams for various applications. Compared to dense materials, foams are characterized by a high porosity, which typically exceeds 50 vol.-% and can be either open or closed. The high porosity and low density result in a unique property profile, which is characterized by:

  • high specific surface area
  • high permeability for fluids
  • low thermal mass
  • thermal and acoustic insulation properties
  • high thermal cycling resistance
  • high weight-specific strength and stiffness

At the same time, ceramic foams usually have high thermal and chemical resistance, as well as high hardness and abrasion resistance compared to fiber-based insulation materials. This qualifies inorganic foams for applications such as thermal and acoustic insulation components, filters, kiln furniture, lightweight construction or bone substitute materials.

Design of Foam Material

The design of the foam material is based on customer requirements. The systematic methods of the HTL for material selection and component development are used for this purpose. Alternatively, custom materials can be transformed into foams. The performance of the foam materials and components is simulated under various mechanical, thermal, and mechanical-thermal loads, and the most material- and resource-efficient solution is developed based on this. Economic and ecological conditions are particularly taken into account during this process.

Foam Production and Shaping
Mechanical direct foaming process
© Fraunhofer Center HTL
Mechanical direct foaming process: Slurry production (I), mechanical foaming (II), molding and curing (III), and final sintered foam board (IV).
SEM image of the pore structure of a mullite foam
© Fraunhofer Center HTL
SEM image of the pore structure of a mullite foam from direct mechanical foaming (25x, WD 15 mm, EHT 10 kV, SE detector)

The HTL has developed and patented a cost-effective direct foaming process for the production of foam material based on renewable raw materials1. In this process, a so-called slurry material, which consists of water, at least one powder raw material of the base material, and environmentally friendly additives, is mechanically foamed. By adjusting the composition, flow behavior, and process control, the pore size distribution can be set. The achievable open porosity is in the range of 50 to >90 vol.-%, and the pore sizes can be adjusted in a range of 20-600 µm.

After the mechanical direct foaming process, the foamed slurry material is shaped into a mold and cured and dried at temperatures < 100 °C. This results in a stable and mechanically workable green foam. Subsequently, it is usually debinded and sintered. Casting or molding enables the near-net-shape production of semi-finished products or components with limited complexity.

If required, the inorganic foams can be infiltrated with molten metals to produce composites, for example, for abrasion-resistant cooling components, in a cost-effective way. Additionally, the foams can be coated, for example, for abrasion protection or hermetic sealing purposes.

1 DE10 2018 200 969B3 or EP3514122B1

Service Offering:

  • Consultation and selection of suitable base materials for foams
  • FE-based design of foam materials and components, taking into account mechanical, thermal, and thermomechanical loads, among others
  • Feasibility studies for transforming customer materials into foams
  • Developments of novel foams
  • Environmentally friendly and cost-efficient direct foaming process
  • Infiltration of foams for composite production
  • Coating of foams
  • Testing of foams for mechanical, thermal, thermomechanical, and chemical stability