Identifying and quantifying nanoparticles in powder materials is a time-consuming and expensive task, but it is also important. Currently, electron microscopy imaging techniques are primarily used to count and measure the dimensions of thousands of individual particles. This allows us to determine what percentage (by number) of the particles are nanoparticles. However, this is only a relative nanoparticle content and is therefore limited in the answers it can provide.

We present the new PowMaster particle analyzer, which allows the measurement of the absolute number of nanoparticles in one gram of powder. The underlying measurement concepts rely on aerosolized particles that are separated based on their mass-to-charge ratio, not dissimilar to a mass spectrometer, followed by a rapid measurement of the diameter via electrophoresis. Within 10 minutes, the instrument scans over the whole size distribution, while the particles are constantly counted. Especially for complex-structured materials, such a rapid and affordable multiparameter particle characterization is required.

We screened commercially available color and white pigments, fillers, pearlescent pigments and battery materials and compared the relative and absolute nanoparticle content. Some of those materials can be described as core-shell structures, which tend to release nanoparticles during dispersion. Especially for silica-coated titanium dioxide pigments, examples have been found where gentle mixing or an ultrasound treatment led to the delamination of the pigment particles.

In some cases, more than 10¹³ nanoparticles per gram of pigment have been observed. A number that provides information different than “50% nanoparticle content”.

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