A lot of plastic parts are cheap to make because they can be mass-produced. This also holds true for metals which can be injection-molded in powder form. Examples are provided by mini-reactors made of stainless steel which can detect microorganisms or sterilize liquids.
A clear trend in biotechnology, chemical analysis and reaction technology is the use of small, inexpensive and efficient mobile devices. The costs of such complex metallic components can be reduced by producing them in large volumes. The series production is highly successful when using fusible plastics, however, it is often problematic when using metals. While material properties such as high thermal and electrical conductivity, chemical and thermal resistance as well as component recycability are ideal for mini-reactors, their hardness and high melting points limit the extent to which they can be processed for this purpose. Stamping only comes into consideration for simple geometries; complex structured components can often only be produced by turning, milling or drilling. Every part has to be manually machined – material losses are unavoidable.
Metal powder injection molding is a technique which uses the advantages of the corresponding plastic process. At the Fraunhofer Institute for Manufacturing and Advanced Materials IFAM in Bremen, scientists modified this process in order to produce micromechanical and microfluidic components up to pilot stage production. “Depending on the geometry and the type of the subsequent treatment we can produce cost effective already at volumes of 500 components compared to conventional techniques,” emphasizes Natalie Salk from the micro engineering department. “Additionally, more freedom in design is provided by this process.” This is how it works: Metal powder is mixed with a binding agent and the paste-like mass is injection-molded like a highly filled plastic. In the second stage, the component is gradually heated in an inert gas atmosphere. The binding agent decomposes and escapes. At temperatures well below the melting point, the powder particles of the metal sinter together; the component becomes compact and attains up to 99 percent of its maximum density.
This way a stainless steel mini-reactor was produced and coated with a titanium dioxide layer. In cooperation with the Institute of Environmental Process Engineering (IUV) of the University Bremen and the company Q-Bioanalytic in Bremerhaven, IFAM scientists have proved that such a mini-reactor shows the effect of deactivating germs when radiated with ultraviolet light. It can therefore be applied in the area of water purification. A second type of reactor will determine the type and number of germs present in liquids. The aim is to achieve a measurement time of less than five minutes – conventional laboratory devices currently need up to one and a half hours.