When I tell people at cocktail parties that we specialize in Particle-Size Analysis. I usually get a polite response of ------ “OH !!,” which translates to “So who cares?”
I have finally decided to answer that question.
Well, it seems that most companies that perform milling or grinding have a vital interest in the size and distribution of the resulting particles. These include companies in the fields of Pharmaceuticals, Chemicals, Mining, Building Materials, Food Processing to name a few.
Soooo.... there really is a significant need for particle-size analysis.
How is this accomplished? The most economical and easiest method is to utilize a series of sieves, with each one having different sized holes from the others. The product is sifted through these sieves and the amount that passed through each size hole is then measured. Such methods have been used since ancient Egyptian farmers sorted their grain this way. Today however, there is a growing number of materials; many with unique characteristics -- that inhibit particle separation. Furthermore, there is an accelerating trend toward smaller and even nano particles.
Standard test sieves, which are made of woven wire mesh, can work to sizes down to the 25 micron range -- smaller than a human hair. As wire mesh sieves reach their limits, sieve mesh made with the Electroforming Process may be needed. (Electroforming is a process for fabricating high-precision mesh by electro-deposition in a plating bath.
Some powder materials and small particles are difficult to separate. In these cases, particle-size distribution analysis calls for sophisticated shaking or separation methods such as ultrasonic vibrating or vacuum sieving.
After the capabilities of mechanical sieving have been exhausted, one of the new measuring methods available is Particle Sizing by Laser Diffraction. In a recent article, Bryn McDonagh of ATA Scientific did a magnificent job of describing this highly complex technique.
“Laser diffraction has become one of the most commonly used particle sizing methods, especially for particles in the range of 0.5 to 1000 microns. It works on the principle that when a beam of light (a laser) is scattered by a group of particles, the angle of light scattering is inversely proportional to particle size (i.e. the smaller the particle size, the larger the angle of light scattering). Laser diffraction has become very popular because it can be applied to many different sample types, including dry powders, suspensions, emulsions and even aerosols. It is also a very fast, reliable and reproducible technique and can measure over a very wide size range.”
Laser diffraction is often the method-of-choice when particles are very small or hard to separate mechanically.
If the test material can be separated mechanically and the particles are within the size ranges of wire or electroformed mesh, sieving provides the most economical approach by a wide margin. Sieve testing is easy to administer and requires little training.
Bottom line: If sieving will work, use it. Otherwise, you need to consider more elaborate processes such as Laser Diffraction.
Now that I have prepared this discourse, perhaps I can get more people at cocktail parties excited about Particle Size Analysis.
Thanks for listening,
P.S. How do you do your particle size analysis?