Development and Manufacture of Porous Functional Materials

We develop capillary suspensions (CapS) with custom-designed porosities and strengths tailored to specific requirements. This enables us to create pore and materials gradients as well as complex geometries that optimize mass transport and increase the efficiency of energy conversion.

At Fraunhofer IWM, a comprehensive development chain is available, consisting of the production of capillary suspensions, the 3D printing of porous functional materials from the capillary suspensions, the functional validation of energy conversion generators realized from these materials, and the transfer to a wide variety of application areas.

Capillary suspensions are the ideal method for controlling ordered structures ranging from 100 nanometers to 100 micrometers. In combination with additive manufacturing techniques, multi-hierarchical meta-structures can be realized, enabling the control and design of new component geometries.

Capillary suspensions are ternary materials systems consisting of a particulate, solid phase of microscale, sinterable particles, a primary liquid, and a small part of an immiscible secondary liquid. The secondary liquid forms liquid bridges between the particles, leading to the formation of a self-organized particle network. This particle network makes it possible to adjust open porosities ranging from a few to hundreds of micrometers, thereby creating an additional hierarchical level of metastructuring. The capillary suspensions can also be easily processed using liquid-phase forming — a process that scales up well.

Furthermore, the characteristic shear-thinning effect of the suspensions allows for the adjustment of viscosities required for the direct ink writing process. Thus, porous structures can now also be processed using 3D printing, which enables metastructuring in the range from approximately 100 μm up to component size.

Controlled porous structures are crucial for a range of applications, such as porous transport layers in fuel cells and electrolysers, porous nickel foams for the conversion of nitrate to ammonia, porous electrodes in lithium-ion batteries, or additively manufactured thermoelectric generators.

Services

• Development and optimization of capillary suspensions
• Capillary suspensions can be developed for both ceramic and metallic functional materials. Particle size and morphology are critical factors here, and the specific application is decisive. The suspensions can be further processed using various production techniques. Accordingly, the rheological properties of the suspensions must be adjusted and optimized for the process.
  
• Establishment of process routes
• Suspension-based methods are ideally suited for industrially scalable process routes for the production of complex component geometries. On the one hand, complex prototypes or one-off parts can be produced with minimal effort using 3D printing. Wet forming or injection molding allows for the mass production of specified components and geometries, tape casting can be used to produce flat components or films, and the replica method enables the replication of complex structures.
• Adjustment of process parameters
• The process parameters are suitable for the targeted fabrication of multi-hierarchical porous structures. This allows for the adjustment of porosity gradients and controlled porosity and pore size distributions. The combination of different methods enables targeted structuring across multiple size scales.
  
• Development of novel manufacturing processes
• Special manufacturing processes can be developed for the production of dimensionally stable, precisely fitting, and mechanically robust porous sintered components. These enable the production of sintered components with particularly high dimensional accuracy and dimensional stability.
  
• Modification of materials
• By modifying the components of the capillary suspensions, the resulting components can also be chemically altered. This allows for doping and variation of the chemical composition in the region of the particle interfaces and particle surfaces. In this way, the functional properties — such as thermal or electrical conductivity, as well as dielectric and electromechanical properties — of the materials and components can be influenced.
  
• Characterization
• The porosity, mechanical strength, and microstructure of porous components and materials can be characterized and quantified across many length scales. With the help of AI-supported methods, statistical conclusions can also be drawn. A wide range of characterization methods is available.

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