Particle technology

Fluidized bed technology is a well-established process for coating and refining particles, which is most frequently used in the pharmaceutical industry. In the fluidized bed process, a nozzle system is used to apply thin layers of a liquid coating material to particles fluidized by a gas flow. The coating is solidified to core-shell particles during processing.

The fluidized bed systems available at the Fraunhofer ICT enable batch sizes of 200 g up to 5 kg, using either dried air or nitrogen as a process gas. Through modification of the equipment explosion-sensitive or hygroscopic core materials and also solvent-based coating materials can be safely processed.

The aim of particle coating is to improve the particle properties through:

• Increased compatibility with reactive substances in further processing
• Protection of hygroscopic materials from humidity and moisture
• Decrease in the sensitivity of energetic materials (desensibilization)
• Increase in mechanical strength

Functionalization of particle coatings or composite particles by incorporating (nanoscale) active substances such as stabilizers, burn rate modifiers or bonding agents.

Fraunhofer ICT's know-how in the field of cooling crystallization ranges from the measurement of fundamental crystallization data to new developments and the optimization of crystallization processes. Solids with a suitable melting behavior and sufficient stability in the melted phase can be reshaped into spherical morphologies using emulsion crystallization or prilling processes.

A toothed-ring dispersing device, an annular gap ball mill, a bead mill / dissolver combination, a pin mill and a jet mill are available for comminution. This enables energetic materials to be broken down to particle sizes between 1 and 30 µm. The combination of bead mills and dissolvers is suitable for the fine milling or the dispersion of highly-viscous suspensions. Water and a wide range of organic solvents can be used as suspension media. This allows particles to be broken down and simultaneously dispersed in the application fluid (e.g. in a liquid binder component (so-called “dirty binder”)). This means that time-consuming separation, drying and reintegration processes are no longer necessary. Nanoscale materials such as carbon nanotubes (CNTs) can be dispersed in almost any medium, or processed to form gels.

Adding foreign ions to the crystal lattice of ammonium nitrate can stop or modify its phase transition in order to create a volume-stable product. In our pilot plant, phase-stabilized ammonium nitrate is produced by spray crystallization for use in gas generators and rocket motors. Standard particle sizes are between 50 and 160 µm. With the atomization unit available at the institute, quantities of up to 50 kg can be processed.

Ammonium dinitramide (ADN) is a high-performance and environmentally friendly oxidizing agent for solid propellants. Emulsion crystallization is used to process the components to fabricate so-called ADN prills with medium sized particles of 50, 100 or 200 µm. Chemical stabilization of the raw material is also necessary to ensure non-porous prills with good processability. The material is used, for example, in the EU-funded projectGRAIL for the development of cutting-edge drive systems for space vehicles.

Co-crystals are an example of new structural models that are attracting significant attention, particularly in the pharmaceutical industry, as they widen the property spectra of substances. At Fraunhofer ICT, energetic co-crystals are fabricated and characterized with the aim of combining the high performance of explosive components with a reduced sensitivity.

• Measurement of medium particle size and particle-size distributions using laser diffraction spectroscopy
• Automated series measurement of the compression strength of individual particles in a granule strength testing system.
• Measurement of the specific surface of particle collectives using the BET method.
• Density measurement of particle collectives using gas pyknometry.
• Measurement of water content using Karl Fischer titration
• Optical particle analysis with a macroscope using image analysis and a focal depth module.

• Investigation of crystal and microstructure, polymorphism, crystallinity, crystal density, crystallite size and micro strain
• In-situ time and temperature-resolved investigations into dynamic processes
• Simulation of the molecule and crystal structure
• Workshop on time- and temperature-resolved X-ray diffraction, since 1992