The Brazil Nut Effect is a type of equilibration process that granular systems with a distribution of particle sizes will undergo. It occurs with agitation and proceeds in such a manner as to result in a final state with the center of mass as low as possible. The equilibrated state results in the larger particles migrating towards the top and the smaller particles filling the void spaces down low. According to the above Wikipedia site, certain container shapes can suppress or enhance this effect.

In the merchant chemical business, suppliers strive to provide customers with the maximum quality that is feasible.  Some applications require high chemical purity and others require less purity. The trick is to pay for the purity that you need.  Excess purity is an unnecessary expense.

In many applications a chemical substance must be both chemically pure and of a certain specific physical form.  For applications where the solid must be blended to form a suspension, a slurry, or it must dissolve rapidly, a small particle size is often desirable. Particle size control and analysis is an art that many synthetic chemists can go through their entire careers and never encounter.

In the process of filtration, solids often compact along surfaces to afford flakes and angular chunks that may retain their shape until they reach the package. Lumps can arise from incomplete washing and drying and may be indicative of chemical inhomogeneity in the bulk material. 

Chemical products that are used in compounding for very exacting applications- catalysts, coatings, polymer compounding- may have specifications that require the absence of lumps in the bulk solid. Free flowing homogeneous powders can be prepared by milling or sieving or even spray drying. Compounds that are air, moisture, or light sensitive may not respond well to excessive handling. Before you accept business involving powdered products with bulk solid specs, you need to demonstrate that it is art that you can actually perform.

This is where a smart buyer is worth their weight in gold. Instead of having their own company take the burden of particle sizing, they make the vendor do it. And if the vendor fails, find another.

Where the Brazil Nut Effect seems to enter my life is when the product finally arrives at the customers facility.  If your nice powder had even a single hidden clump in it, you can bet that on arrival it has migrated to the surface to greet the frowning customer. I have received digital photographs of this from customers who wished to drive home the point. So, you just buck up and apologize as sweetly as you can manage and give them your FedEx number so they can send it back.

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