Too often when we ask a customer why they want to use one of our techniques, be it light scattering, image or chemical analysis, rheology, Nanoparticle Tracking Analysis (NTA), then the response often comes back “For QA/QC”, “Because the boss says so” and the worst of all, IMHO, “Characterization” ……
Many of you will be familiar with the Douglas Adams books such as “Restaurant at the End of the Universe” and “The Hitchhiker’s Guide to the Galaxy” and so on. In these tomes, the answer to life the universe and everything was given as ‘42’ because we’d forgotten the question that was formulated in the beginning (when the big computer was programmed to find the answer to the meaning of life…).
The same is true in every technique we utilize in our studies. We need to relate the (stable) numbers we obtain to some aspect of product performance or requirement. These performance attributes need to be pre-defined. These attributes could be dissolution rate of a powder, reactivity of a catalyst, hydration rate of cement, combustion of a fuel, effective insecticide droplet size etc. All the preceding attributes are a function of the primary particle size free from agglomerates. Other performance attributes could relate to the transport and materials handling properties of the system – filter blockage, lumpiness, bridging, conveyability, rheology of a slurry….. These relate to the bulk size of the material. In order to get from the bulk size to the primary size then energy is required…. Without knowledge of how we want to apply the answers then we cannot define the analysis route or technique. Customers may ultrasonically mill their material down to some tiny size in order to get a small number unrelated to the problem in hand. They’ll then complain that 15 minutes at 100% ultrasound power doesn’t produce the same result on every ultrasound unit. For clues why, view one of my past webinars, ‘Ultrasound, cavitation, and the singing kettle.’
The inherent heterogeneity of the material isn’t explored never mind understood. Help can be provided in this area too, at my Pittcon 2014 Short Course on Sampling.
Harold Heywood couldn’t have said it better than when he did in the year that the English soccer team won the World Cup (Jules Rimet Trophy then) for the only time:
“However, it must be realised that particle size analysis is not an objective in itself but is a means to an end, the end being the correlation of powder properties with some process of manufacture, usage or preparation” H Heywood Proc. 1st Particle Size Anal. Conf. September 1966 p 355 – 359 (Heffer)
Brian Scarlett too:
“A particle size measurement does not have a meaning unless the objective of the measurement is also specified” B. Scarlett “25 Years of Particle Size Conferences” Particle Size Analysis, Eds. N.G. Stanley-Wood, R.W. Lines,. Royal Society of Chemistry (1992)
You have been told! Happy characterization!