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Micro-CT of a Firework Fountain

Micro-CT of a Firework Fountain

Using the Bruker SkyScan 1173

Micro-CT for Particle Size Analysis

Summer fireworks displays are actually made up of systems of burning particles flying through the nighttime sky. In most firework fountains — the devices that send showers of sparks high in the air — there is a tubular aerial shell filled with gunpowder, as well as small particles of explosive materials called stars.1 The aerial shell is shot into the sky where it explodes, and the stars embedded throughout the gunpowder become the points of light we see in a firework display. Firework stars are made of various metals that absorb energy during combustion and emit different colors.

For our study of micro-CT for particle analysis, we utilized our SkyScan 1173 scanner to look at a home-use firework fountain and explored the heterogeneity of the metal salt particle diameters within the charge. This is important because firework formulation requires careful balancing to ensure that the desired effect is achieved.2 We chose to use micro-CT to visualize the internal distribution of firework stars and their locations within the device. Coupled with our quantitative volumetric analysis software, CTAn, we were able to use the reconstructed images to determine the average star size along with a distribution of all of the star diameters calculated within the device.

Figure 1: Cross sectional views of a firework fountain

 

Micro-CT Scan of a Firework Fountain

After reconstructing the X-ray attenuation data into representations of the three-dimensional structure, we could see the relatively small size of the actual explosive charge within the much larger paper shell (Figure 1). Also evident was the asymmetrical orientation of the charge within the paper shell. (Whether this tilt was intentional or immaterial is not clear.) Shown in a binary colorization, the dense star particles were visible, but to really obtain detailed information on these components a full volumetric quantitative analysis was completed.

Table 1: Calculated Particle Values

Sample Firework Fountain
Total Star Volume (mm3) 1327
Total Star Surface Area (mm2) 7590
Average Star Diameter (mm) 1.12
Number of Stars 1746

 

Figure 2: Star diameter distribution plotted against particle contribution to total star volume

After running the quantitative analysis of the stars within the inner charge, the average diameter and other key measurements were recorded (Table 1). After calculating the volume properties of the scan data, we were able to generate a pore distribution graph (Figure 2) and a model of star diameters throughout the charge (Figure 3). Using this information, scans from the same product with changes made to either formulation or processing conditions could be quantitatively compared to identify key factors influenced by the changes.

 

Figure 3: Volumetric rendering of modeled firework stars colored by diameter

 

Figure 4: Reconstructed side cross-section view of firework fountain

Arising from differences in X-ray attenuation between the dense star particles and the remaining low density components, the phases readily separate from one another (Figure 4). In this rendered three-dimensional view, the higher density stars are colored in red, the lower density gunpowder and paper are in green, and the air is represented by black.

Conclusion

Micro-CT allows access to detailed quantitative information on internal features such as particles within samples, useful in fields ranging from structural biology and material science to geology, odontology, and many others. We hope you found this Image of the Month informative. If you have an Image of the Month sample that you would like us to scan, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com

Scan Specifications

Sample Firework Fountain
Voltage (kV) 130
Current (µA) 60
Pixel Size (µm) 60
Rotation Step 0.4
Scan Time (HH:MM:SS) 01:40:18

 

This scan was completed on our high energy SkyScan 1173 micro-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon and visualization of 2D and 3D results were completed using DataViewer and CTVox. Volumetric analysis was completed using CTAn.

Works Cited

  1. https://www.acs.org/content/dam/acsorg/education/resources/highschool/chemmatters/articlesbytopic/oxidationandreduction/chemmatters-oct2010-fireworks.pdf
  2. https://www.ch.ic.ac.uk/local/projects/gondhia/composition.html

 

 

 

 

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