Handling of highly dispersed powders

About seven years ago, in spring of 1997 the Senate of the German Research Foundation (“Deutsche Forschungsgemeinschaft” DFG) decided to establish a new “Priority Research Program” (“Schwerpunktprogramm” SPP) numbered 1062 and entitled “Handling of highly dispersed powders”. By this program, an attempt should be made to smooth the way between the demands of modern material sciences for powders of nanoscaled particles (with particle sizes < 100 nm) and the classical possibilities of the mechanical process engineering. At this time, the state of the art of mechanical process engineering was characterized by lower limits of particle sizes of about 10 µm, where the influence of gravitational effects become negligible at the expense of particle interaction forces due to the high surface area of the powders. Because of these circumstances the Research Program had to compromise by include projects dealing with the handling of powders characterized by particle sizes <10µm. This result in the somewhat fuzzy term “highly dispersed powders” which includes nanopowders as well as micropowders. Thus, the Priority Research Program addresses to a broad community of disciplines interested in the handling of very fine powders starting from material sciences and mechanical process engineering over pharmacy and food process engineering up to physical chemistry and theoretical physics. In the beginning of the program four topics of powder handling were envisaged: conditioning, mixing, conveying and storage of powders. The actual list of topics in the contents of this book is clearly more extensive due to “the life of its own” of the programme. It was an absolutely outstanding aspect of this programme – induced by the group of referees and the responsible officers of the DFG - that an unusual close and direct cooperation arose between research groups supported by the German Research Foundation and the Degussa AG as an important exponent of the German industry engaged in the field of ultrafine powders. Results of this copious cooperation within the so-called “Project House Nanomaterials” can be found in chapter I. The following chapters reflect different steps of the production of highly dispersed powders and their subsequent handling, beginning with new insights in particle formation processes and their controlling, over various techniques of conditioning, suspending and mixing of ultrafine powders, over experimental studies and theoretical models concerning the granulation and sintering of nanoscaled particles and finally ending with results of investigations regarding adhesion, conveying, compaction, flow and storage of ultrafine powders.