Solid Density of Pharmaceuticals: Assessing Flow Properties of Powders and Open Porosity of Tablets

Flow properties of pharmaceutical powders, as well as the open porosity of pharmaceutical tablets, are important material characteristics that can be assessed from solid density measurements. Two Anton Paar instruments – the Autotap and Ultrapyc 5000 – provide tapped density and skeletal density results, respectively. These extremely accurate volume measurements are required for the pharmaceutical industry and can be correlated to flow and porosity.


Solid density is an important property of pharmaceutical compounds from powder (drug or excipient) to tablet. Bulk and tapped density are related to flow properties of powder. Geometric and skeletal densities enable the calculation of open porosity of tablets. And skeletal density is related to the crystallinity, polymorphology, and purity of pharmaceutical compounds.

The flowability of a powder, in particular of an additive or excipient, is important to determine how that additive will affect the granulation or tableting process. In addition, this characteristic helps to predict the uniformity and dissolution of the final product. For example, good flowability ensures that there is appropriate, uniform filling of capsules such that consistent weight and dosage is achieved.

Knowing the open porosity of a tablet is critical to understanding many different tablet properties such as tablet strength, shelf life, bioavailability and dissolution within the body. For example, if we look at tablets of the same composition, more porous tablets will dissolve faster than tablets with less porosity. Some porosity is also important to prevent excipient fracturing during tablet compression.

For both powder flow information and tablet porosity, measurement of skeletal density using gas pycnometry enables you to assess these important pharmaceutical properties.

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