Progress with Solids Takes Shape

Improvements in particle characterization bolster processing.

By Seán Ottewell, Editor at Large

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Particles pose unique challenges — their size, size distribution, shape, cohesiveness and other attributes can dramatically affect how they act. So, a good grasp of particle properties often is key to successful processing. Fortunately, new research initiatives and technologies will help engineers get a much firmer grip.

One such initiative is the Engineering Research Center (ERC) for Structured Organic Particulate Systems based at Rutgers University, Piscataway, N.J. Freeman Technology, Malvern, U.K., a particle analysis and characterization expert and developer of the FT4 powder rheometer (www.ChemicalProcessing.com/articles/2009/095.html), is the latest company to join the ERC.

As part of this initiative, Freeman has installed FT4s at Rutgers, New Jersey Institute of Technology, Newark, N.J., and Purdue University, West Lafayette, Ind., to do studies on particle formation and functionalization.

There are two major goals here: to develop new methods for controlled-size particle formation that can be effectively scaled to the manufacturing level; and to control and optimize physicochemical properties of materials such as size, shape and stability through systematic functionalization. Both goals require development of requisite characterization techniques for effective measurement of critical particle properties and process monitoring.

Overall, the plan is to replace empirical methods currently used in the processing industries with a predictive framework for science-based product and process development.

Real-World Relevance
The aim of this and the company's own research, according to Reg Freeman, managing director, is to be able to describe and predict the various behavior modes of powders that occur in everyday processing.

Underpinning this is the company's conditioning process, which ensures that the packing condition of a powder sample is reproducible for testing. Repeatability (on a specific instrument and with a particular operator) and reproducibility (for any instrument/operator around the world) is very important and impossible to achieve without a conditioning process, he says.

"For example, a single light tap when placing a sample onto a work surface would cause flow energy to increase by typically 30%. Conditioning removes such an effect and also ensures that the operator's methodology for loading the sample, etc., does not affect the measured result," he notes.

The Freeman approach is to provide high reproducibility and sensitivity of measurement for all types of powder behavior. The FT4 powder rheometer (Figure 1) gives dynamic flowability measurement and determines bulk properties including compressibility, permeability and bulk density.

"The subject is challenging due to the inherent complexity of powder flow and the difficulty of predicting flow behavior in real processing environments. Much research is being done by companies and universities worldwide and we have collaborative projects with some of these as well as with other instrumentation companies like Malvern Instruments," Freeman adds.

Understanding powder behavior can be daunting but a pragmatic approach can be very effective, says Freeman. It involves making good use of process experience most companies already have.

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