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Hydrogen storage materials

When using hydrogen as an energy carrier, effective and safe storage plays a central role. Storing hydrogen in its liquid state requires low temperatures and in turn, expends a great deal of energy. In a gaseous state, very high pressure is needed. This means that much more sophisticated designs are needed in order to keep the weight of the containers low enough to ensure acceptable storage densities. In addition, such pressure vessels pose a hazard and exhibit significant leakage losses.

Therefore, storing hydrogen in solids offers an interesting alternative. For example, light metal hydrides and alanates have a high theoretical storage density for hydrogen. However, with these materials, other complications arise. At present, the main problems are the slow hydrogen sorption kinetics and the lack of reversibility.

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High-performance ceramic structural materials

All-ceramic turbine blades

This project aims to identify the prospects for targeted development of an all-ceramic turbine blade for use at temperatures above 1400oC. This would allow a higher turbine inlet temperature to be achieved. Along with a significant reduction in the volume of cooling air needed, this would permit a further significant increase in the efficiency of a gas turbine.

Fibre structure made of Nextel fibresPhotograph: Fibre structure made of Nextel fibres

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Porous titanium-base implants

In ceramic moulding, placeholder materials have become established, for instance, in order to create defined pore channels for gas transport in fuel cell substrates. This approach has been successfully transferred to powder metallurgy.

biomedical applications - Hip cupDemonstration of the placeholder method on prototypes for biomedical applications - Hip cup

Biomedical applications - Dental implantDemonstration of the placeholder method on prototypes for biomedical applications - Dental implant

If suitable placeholder materials such as ammonium hydrogen carbonate are mixed and pressed with a metal powder, the compacted pellets then have adequate stability in an unsintered state (green state) to be worked into a near-net shape by means of conventional mechanical processing (drilling, turning, milling).

If metal powders that can be pressed well are used, this eliminates the need for organic binders or pressing aids. Removal of the placeholder occurs through degradation in air at temperatures < 150°C, leaving only minimal oxygen and carbon contamination behind.

After the degradation of the placeholder, the porous shaped body is sintered, which gives it the stability required for later use. Fractionation of the placeholder allows defined pore sizes in the range of 100–1000 µm and porosities of up to a maximum of 80 % to be created.

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Nickel-titanium-base shape memory alloys

Powder metallurgy of NiTi shape memory alloys

Within the framework of the special collaborative research project SFB459 "Shape Memory Technology" at Ruhr University Bochum funded by the German Research Foundation (DFG), the institute concerns itself with powder-metallurgic fabrication of shape memory alloys. Powder metallurgy offers the advantage of near-net-shape forming of this alloy, which can only be processed mechanically with a great deal of effort.

Figure: Metal injection moulding of nickel-titanium shape memory alloysFigure: Metal injection moulding of nickel-titanium shape memory alloys - clamping sleeve prototype and tensile test specimen

The studies focus on

  • Near-net-shape forming by means of metal injection moulding (MIM)
  • Forming by means of hot isostatic pressing (HIP)
  • Functional coating by means of plasma spraying
  • Porous NiTi shape memory alloys
  • Powder metallurgy of ternary NiTi-X alloys

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