Refractory Ceramics

Refractory materials include dense shaped refractory products, lightweight and insulating bricks, fibre-based refractory products and unshaped products. They primarily have a load-bearing and insulating function. Refractory products must withstand high temperatures and corrosive media - e.g. as furnace linings in high-temperature furnaces. Depending on where they are used, they are exposed to mechanical, thermal and chemical stresses. Refractory materials used in furnace linings require a certain minimum strength and creep resistance in order not to break or creep under dead load. A high thermal or pressure fire resistance is also a prerequisite for the required dimensional stability, i.e. creep and post-sintering of the refractory materials are not permissible. The temperature cycles planned for use also require a high thermal shock resistance and resistance to thermal shock. High slagging resistance is also an important requirement for applications in which the refractory materials have direct or indirect contact with corrosive gases or melts. For insulating components, e.g. in backwalls, on the other hand, low thermal conductivities and heat capacities are crucial in order to be able to design compact and energy-efficient refractory linings.

The above-mentioned properties cannot all be realised in one refractory material and are sometimes even contradictory. High strength usually requires high relative density, but this leads to increased thermal conductivity and volume-related heat capacity. Reducing the relative density by creating additional porosity results in lower thermal conductivity, but this usually worsens the mechanical properties and abrasion resistance. Dense materials with low thermal conductivities are in turn often susceptible to thermal shock. Systematic evaluation criteria are needed to optimise properties in this conflict of objectives.

At Fraunhofer-Center HTL, refractory materials with optimised property profiles are being developed in order to find resource- and energy-efficient solutions for a wide range of refractory applications and to open up technological and economic advantages for manufacturers and end users. The refractory materials developed include acidic, basic and contact-indifferent materials made of oxide and non-oxide components as well as combinations thereof. With its test facilities and computer programmes, the HTL covers the entire manufacturing chain for the development of refractory components: from material selection and component design to backfill preparation and shaping as well as heat treatment and testing. For example, in addition to common processes such as pressing, ramming and casting, special in-house developments of the HTL are also available for shaping.

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Further Information

Highly Porous Ceramic Foams

One example of refractory materials developed at the HTL is highly porous ceramic foams, which are produced using a specially developed direct foaming process. This manufacturing process begins with the production of a slurry consisting of water, ceramic powder and foaming agents, binders and stabilisers.

Ceramic Fibres

Another area of the HTL's work is the development of ceramic fibres for insulating elements, among other things. The HTL is able to map the entire process chain for the production of ceramic fibres. This includes the synthesis and preparation of spinning masses, spinning, thermal preparation of the fibres and the application of various fibre coatings.

Fibre Mesh Reinforcement

To increase the damage tolerance of refractory materials, the HTL has developed a patented fibre mesh reinforcement. The mode of action of the fabric grid is based on the defined connection between the fibre and the matrix material. This stops or diverts cracks at the interface between matrix and fibre material. Fracture energy is dissipated and a quasi-ductile damage-tolerant behaviour is created.

3D Printing Process

The HTL develops and manufactures components made of ceramics, metal and metal-ceramic composites using additive manufacturing, commonly referred to as 3D-printing.

Ceramic Coatings

The HTL develops ceramic coatings for use at high temperatures. Based on the customer request, a concept for the development is drawn up and agreed on with the customer. At this occasion, questions about the requirements of the coating, coating technology, substrate material, operating conditions etc. are clarified.

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