Ultrasonic Dispersion in the Particle Size Analysis of Titanium Dioxide

As a high grade white pigment, titanium dioxide is utilized extensively across a variety of chemical applications. Due to its exceptional gloss, stability whiteness and hiding power, titanium dioxide is suitable for coatings, plastics, papers, printing inks, chemical fibers, rubbers, cosmetics, etc.

The high surface energy of oxygen atoms means that there is a powerful interaction in the surface of inorganic oxide particles resulting in the titanium dioxide forming agglomerated particles.

Generally, analysis accuracy of single-particle size will be affected in laser diffraction and SEM (Scanning Electron Microscope) measurements because of the agglomeration of the titanium dioxide particles.

However, ultrasonic technology can help undo the agglomeration of titanium dioxide; here, this short article chronicles this beautiful change.

Figure 1 exhibits an SEM image of the titanium dioxide powder, signifying that the titanium dioxide crystals are comparatively uniform and miniscule, the particle size ranges between about 20 and 30 nm.

In Figure 2, the SEM camera is zoomed-out and demonstrates that the titanium dioxide agglomerates are effectively made up of a significant number of ‘primary’ particles.

Thus, with a wide-angle view it is observed that titanium dioxide is made up of a great number of ‘aggregate’ structures. For this reason, laser diffraction and SEM occasionally play a considerable role in particle analyzer results.

SEM is extremely good at acquiring the morphology of individual primary crystals, while a laser particle size analyzer is better suited for measuring the size of ‘aggregated’ particles and statistical size distribution. So, what happens when ultrasound is applied to these agglomerates?

SEM image of titanium dioxide powder.

Figure 1. SEM image of titanium dioxide powder. Image Credit: Bettersize Instruments Ltd.

SEM zoom out image of titanium dioxide powder.

Figure 2. SEM zoom out image of titanium dioxide powder. Image Credit: Bettersize Instruments Ltd.

Ultrasound Dispersion in Titanium Dioxide

Although the titanium dioxide generated amasses easily, an excellent dispersion effect was achieved when ultrasonication was lightly applied using the Bettersizer 2600.

Sample A is a titanium dioxide powder, and its size experienced an exceptional change after the ultrasonic treatment was applied. Figure 3 displays sample A without any ultrasonic treatment and Figure 4 shows sample A treated with ultrasonic treatment.

The contrast between of Figure 3 and Figure 4 demonstrates that the average particle size of sample A has altered from about 600 nm to around 300 nm after ultrasound. While there was a significant increase of small particle content, the mean particle size obviously decreased.

Results of Sample A with no ultrasound in Bettersizer 2600 measurement.

Sample D10 D50 D90
Sample A-1 0.191 0.612 1.073
Sample A-2 0.195 0.613 1.079
Sample A-3 0.192 0.612 1.072
Repeatability 1.08% 0.09% 0.35%

 

Figure 3. Results of Sample A with no ultrasound in Bettersizer 2600 measurement. Image Credit: Bettersize Instruments Ltd.

Results of Sample A with ultrasound in Bettersizer 2600 measurement.

Sample D10 D50 D90
Sample A-Ultrasonic-1 0.041 0.339 1.038
Sample A-Ultrasonic-2 0.041 0.339 1.026
Sample A-Ultrasonic-3 0.040 0.332 1.025
Repeatability 1.42% 1.20% 0.59%

 

Figure 4. Results of Sample A with ultrasound in Bettersizer 2600 measurement. Image Credit: Bettersize Instruments Ltd.

Ultrasound effect on the particle size distribution of titanium dioxide sample.

Sample D10 D50 D90
Sample A-3 0.192 0.612 1.072
Sample A-Ultrasonic-3 0.040 0.332 1.025
Repeatability 92.66% 41.95% 3.17%

 

Figure 5. Ultrasound effect on the particle size distribution of titanium dioxide sample. Image Credit: Bettersize Instruments Ltd.

In conclusion, the ultrasonic dispersion system has the ability to disperse the agglomerated particles and produce particles that are dispersed uniformly across medium.

If dispersal of the agglomerated particles is not conducted, results will become inconsistent affecting the accuracy of particle size analysis by both SEM and laser particle size analyzer. Thus, ultrasonic dispersion is of significant value and a key component for the determination of titanium dioxide samples.

This information has been sourced, reviewed and adapted from materials provided by Bettersize Instruments Ltd.

For more information on this source, please visit Bettersize Instruments Ltd.

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