Sample preparation: how to disperse powder for amazing SEM images

By Willem van Zyl - November 16, 2018

The ability to analyze particles is becoming increasingly more important due to the rising prominence of additive manufacturing, leading to more stringent quality requirements for industrial manufacturers. Beyond maximizing yields, manufacturers need to ensure that their processes consistently deliver particles that have the appropriate size and morphology.

As we have outlined in a recent blog, sample preparation is a key step when performing electron microscopy analysis. When analyzing particles, in particular, this step is even more crucial.

In this blog, we discuss how to use the Nebula™ vacuum dispersion system as a tool to disperse powder samples in order to analyze individual particles using our in-house developed software.

Why the dispersion of powder samples prior to SEM imaging is necessary

To ensure that downstream analysis of particle properties is accurate, it is not only necessary to separate individual particles, but also to break apart agglomerates. Figure 1 shows the difference between adding a powder sample directly onto the carbon adhesive, and using the Nebula™ vacuum dispersion system.

Nebula vacuum dispersion

Figure 1: Comparison between applying a powder sample directly to carbon adhesive (left) and using the Nebula™ vacuum dispersion system (right). Images taken from our sample preparation E-guide are available here

How to use the Nebula for sample preparation

The steps to take when using the Nebula™ are shown in the schematic below. Before starting, the user removes the vacuum cylinder and takes a sample stub, typically made from aluminum. A holey carbon adhesive film (a) is applied before placing the stub on the Nebula™ pedestal (b) and replacing the vacuum cylinder. The vacuum valve is opened (c), which causes the pressure inside the vacuum cylinder to rapidly decrease.

By observing the pressure gauge, the user can adjust the vacuum level inside the cylinder(d). Once the vacuum is at the correct level, the vacuum valve is closed (e) and the sample of interest is placed on top of the vacuum cylinder (f). The vacuum is released by pressing down on the lever (g), which causes an influx of air into the cylinder. Once the air pressure inside the cylinder has reached ambient levels, the user can remove the cylinder, and proceed with imaging (h) and analysis (i).

Schermafbeelding 2018-11-15 om 14.01.15

I have perfectly dispersed powder, now what?

Once the particles in your sample have been evenly dispersed, you can start analyzing your sample using a SEM. The ParticleMetric software was developed in house and was specially designed with particle analysis in mind. This software package enables users to analyze particles in terms of parameters such as diameter, circularity or grayscale level. By revisiting outliers in the dataset, the user can perform elemental analysis via EDX for a powerful solution.

Recently, a group of researchers (Kotronia et al., available here) studied the encapsulation of oregano essential oils in β-Cyclodextrin. Using ParticleMetric, the average size of particles was determined, validating their experimental procedure.

In another use case, the Nebula™ was used for dispersing printer toner particles and particle size was determined using ParticleMetric, as part of a US patent application.

As can be seen from these examples, there are numerous solutions to problems you might encounter in your laboratory or industrial processes. If you would like to download the ParticleMetric & Nebula™ brochure, please click here.

Did you know? Coating your samples when performing particle analysis will remove elemental contrast, rendering particles less visible, so do not use coated samples. For other tips on sample preparation, please take a look at our sample preparation guide here:

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About the author

Willem van Zyl is an application specialist for the Thermo Scientific Phenom Desktop SEM product range at Thermo Fisher Scientific. He is excited by analytical instruments that are accessible and user-friendly, and truly believes that an SEM image is worth a kazillion words.

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