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Is the powder mix homogenous ?

input time:2018-08-17 10:10:41    hits:

Definition of homogeneity for a particular process

It must clear that the 1st step is to define for the application considered what means "homogeneous" and what means "non homogeneous". Almost all powder mixtures will have a degree of inhomogeneity. The 1st thing to do is to determine the tolerances which are exclusively dependent on the application for which the mixture is intended. Tolerances can be defined internally, or externally by a regulation or a customer.
Example 1 : The mixture is used internally for an other unit operation within the same factory : specifications are defined within the company, and maybe are quit large in order to ensure a smooth operation.
Example 2 : The mixture is sold directly, an infant formula for example, specifications are regulated by law, and can be very narrow

Defining the scale of scrutiny

Declaring a powder mix "homogeneous" means nothing if the sampling size from which the components will be analysed has not been defined. The larger the sample size, the higher will be the chances of concluding that the powder mixture is homogeneous. Contrary, when reducing the sampling size, the variability of composition will go up and higher will be the chances of concluding that the mix is not homogeneous.
The sampling size, or scale of scrutiny, must always be defined according to the use that will be made of the mixture. For example, for a food product, the sampling size is the serving size. It would make no sense to sample a quantity that the customer will never use for preparing his food : either too small or too big. For this particular example, not chosing the right sampling value could have catastrophic consequences for a company whose products would be sampled by a government agency and found not compliant (company QA found the mix homogeneous but using a sampling size much larger than the serving size used by the consumer and as a consequence the government). For pharmaceuticals products, the sampling size will have to be in line with the dose to be contained in a capsule for example.