Research Centre Germany
In our research group we are working on the laser evaporation technique for the production of nanoscaled powders. In this special process we evaporate coarse (micrometer…millimeter) starting powders in the focus of a CO2 laser beam (laser power up to 2 kW).
Due to the very steep temperature gradient between the hot evaporation zone around the beam focus and the surrounding atmosphere nucleation, condensation and coagulation are very fast resulting in ultrafine nanoscaled particles. Our method and the generated powders are characterized by
- a continuous powder production of up to 100 g/h (depending on the powder itself and the process parameters) under well defined and stable conditions,
- the control of powder properties by the process parameters (beam intensity, continuous or pulsed beam, process gas and process gas flow),
- a broad spectrum of various product powders: oxides, nonoxides, composites including functional materials (magnetic, conducting, ferroelectric… powders are or should be possible),
- high flexibility, because no special precursors are needed (generally the chemical compositions of the product powder and the starting powder are identical), and
- generally spherical primary particles, a low degree of agglomeration, chemical pureness and narrow size distributions of the primary particles.
Furthermore the product powders can be coated or homogeneously mixed “in situ” with (organic) additives or can be separated directly in suspensions.
On this background it is our main goal to expand the product spectrum of this highly versatile and capable technique from ceramic powders towards functional nanoscaled powders including composites. In order to accomplish this goal, we are currently working with and are looking for research partners.
Ideally these partners have tasks or want to develop new applications requiring nanoscaled powders not yet commercially available and with special properties which can be achieved with our method(s). Given this case it would be our part to customize and optimize the laser evaporation process including the in-situ coating or in-situ mixing with technologically necessary additives and/or the separation in suspension in close cooperation with our partners until the properties of the generated nanopowder fulfill the needs of their tasks or applications. Ideally our partners are technically well equipped in order to screen our powders in their conceived applications.
In this manner synergy effects arise which optimize existing applications, make new applications possible and at the same time very efficiently widen the field of application of the laser evaporation technique.
Even so our research interest hence is not limited to only one or two special nanopowders or new applications in the following some points of our interests are given:
Micro structured functional ceramic devices
Micro structured ceramic devices made by sintering of powders require nanoscaled powders. Beside the microscaled structure, i.e. the form, also functions should be integrated into the devices. Concrete devices could include
o magnetic micro actuators controlled or driven by external (alternating) magnetic fields,
o micro heaters operated electrically or magnetically,
o piezoelectric micro actuators changing their extends controlled by the impressed (alternating) voltage, or
o composite micro devices bearing their functions in the core, which is enclosed in a shaping ceramic sheath.
These micro devices could be used
o in chemical micro reactors as pumps, valves, bubblers or blenders for example,
o as heaters in sensors or chemical micro reactors,
o in micro mechanical drives or gears, or
o as micro electrodes.
In order to achieve the aforementioned functionalities starting materials for the laser evaporation could be
o magnetic materials, especially the iron oxides maghemite (-Fe2O3) or magnetite (Fe3O4),
o electrically conducting materials like the transparent indium tin oxide (In2O3/SnO2, ITO), or
o ferroelectric materials (as base material for piezoelectric devices) like strontium titanate (SrTiO3, STO) or barium titanate (BaTiO3, BTO), or
o mixtures of these (or other) materials with ceramic materials in order to generate functionalized ceramic nanopowders. For example, starting from maghemite (-Fe2O3) and silica (SiO2) super paramagnetic or from titanium nitride (TiN) and silicon nitride (Si3N4) electrically conducting composite powders can be generated.
• Nanoscaled magnetic or super paramagnetic iron oxide powders (FexOy or FexOy@SiO2) for medicine technological applications
o One medical application area of magnetic iron oxide nanopowders is the hyperthermia or thermoablation for the therapy of tumors. Precondition for the use of magnetic particles as absorbing material are high specific hysteresis losses in an alternating magnetic field. Magnetic nanoparticles with nearly ideal losses have been found in magnetotactic bacteria. Their magnetosome particles show hysteresis losses which are by one magnitude higher than those of commercial iron oxide powders. Hence only marginal amounts of these special magnetosome particles are available. It could be a rewardable task to develop a technique based on our methods which allows for the generation of magnetic iron oxide nanopowders in utilizable amounts with significantly higher losses compared to the commercial powders.
o Magnetic particle imaging (MPI) is a new diagnostic imaging technique which makes use of the nonlinear magnetization (B-H) curve of the nanoparticles in special external magnetic fields. The nanoparticles injected into the target area allow for an imaging of morphologic structures with high contrast. But in order to fully exploit the potential of this imaging technique the particle properties have to be optimized.
• TiO2 and ZnO powders suitable for UV filtering coatings
o One characteristic property of nanoscaled particles is the high transparency of their suspensions. Due to the light scattering suspensions of less fine particles are opaque. Below particle sizes of about 250 nm the intensity of the scattered light strongly decreases and finally becomes negligible for sizes smaller 50 nm. Because of this sensitive dependency of the scattered light intensity on the particle size preferably small particles in narrow size distribution and with low degree of agglomeration have to be used in order to achieve high transparency.
