Characterizing Particle Size and Monitoring Agglomeration of Ceramic Powders during Ceramics Production

Powder properties in four phases (powder pretreatment, dispersion and mixing, molding, and sintering) typically impact the robustness of modern ceramic products. Particle size is the most important component to consider during the powder pretreatment step to get the best end product strength.

Image Credit: Bettersize Instruments Ltd.

This is because tiny particles with a high surface area and molecular gravity are more likely to agglomerate than coarse particles. Furthermore, agglomeration affects sintering efficiency and raises the likelihood of ceramic component failure. To increase the strength of ceramic products, it is critical to monitor and regulate aggregation in fine powder materials throughout the entire manufacturing process.

To assure the measurements of ceramic small particles, the Bettersizer S3 Plus employs the patented DLOI System (Dual Lenses and Oblique Incidence System) technology. During particle size measurements, the integrated high-resolution CCD camera enables manufacturers to see aggregation in real-time.

The particle size, size distribution and aggregates of aluminum oxide powder will be examined in this article to help manufacturers understand how to improve the strength of ceramic products.

Figure 1. The Bettersizer S3 Plus optical system. Image Credit: Bettersize Instruments Ltd.

Results

Fine Particles

In ceramic manufacture, precise monitoring of small particles is required. Aladdin Chemical Supplier provided the approved 0.4 µm sample.

The average D50 is 0.396 µm, according to the results in Table 1 and Figure 2, which is near to the SEM values of the sample in Figure 3. D50 has a repeatability of 0.39%, ensuring the accuracy of the analysis and conforming to the ISO 13320 standard.¹

Table 1. Typical size values of alumina sample. Source: Bettersize Instruments Ltd.

Figure 2. Particle size distribution and repeatability of 0.4 μm alumina sample. Image Credit: Bettersize Instruments Ltd.

Figure 3. SEM result of aluminum oxide sample. Image Credit: Bettersize Instruments Ltd.

Particle Size Distribution

Sintering is the process of compressing particles into a dense product (also known as the green body). The powders are heated to just below the melting point of the source material at this stage. The green body contracts and bonds develop between the particles.

As a result, the green body’s strength grows but its space reduces. The mechanism during the sintering process is depicted in Figure 4.

Figure 4. Mechanism of sintering. Image Credit: Bettersize Instruments Ltd.

Sintering rates are greatly influenced by particle size and size distribution. As the sintering driving force reduces as particle size increases, large powders cannot bind effectively.^{2, 3} In other words, the pore size cannot be reduced effectively. Mixing fine ceramic powders with large particles reduces the impact of large pores, allowing small particles to fill the pores during sintering.⁴

An alumina powder sample was obtained from a ceramic manufacturing company. Figure 5 and Table 2 demonstrate that the particles range in size from 3.633 µm to 23.41 µm, with the median being 11.49 µm.

Figure 5. Particle size distribution of aluminium oxide sample. Image Credit: Bettersize Instruments Ltd.

Table 2. Typical particle values of aluminum oxide sample. Source: Bettersize Instruments Ltd.

Figure 6 shows that the sample contains some very small particles. As a result, small particles in the sample may fill the pores, decreasing the possibility of large pores forming during sintering.

Figure 6. Particle image of aluminum oxide powder. Image Credit: Bettersize Instruments Ltd.

Agglomeration

In the ceramic industry, agglomerates or large particles have a significant influence on ultimate strength, in addition to particle size and size distribution. As demonstrated in Figure 7, the aggregated particles could be displayed in the real-time analysis window.

Since agglomeration greatly reduces the density of green bodies, the final products’ strength declines.⁴

Figure 7. Observed aggregates in the real-time display window. Image Credit: Bettersize Instruments Ltd.

Conclusion

Ceramic production requires precise measurement of ceramic particles. The Bettersizer S3 Plus has been shown to accurately;y measure particle size and size distribution in ceramic powder materials, as well as successfully monitor agglomeration.

As a result, the Bettersizer S3 Plus is an excellent instrument for displaying particle size and shape data. Manufacturers will be able to make high-performance ceramic products with the help of the Bettersizer S3 Plus.

Reference

1. ISO 13320 (2009) Particle size analysis – Laser diffraction methods.
2. Peelen, J. G. J. (1977). Alumina: sintering and optical properties. Technische Hogeschool Eindhoven.
3. W.D. Kingery et al (1976). Introduction to Ceramics, 2^nd Edition. John Wiley & Sons.
4. Kumar, A. (2013). Practical classes “Ceramics & Colloids”: TP 3 Sintering 1 TP 3-Ceramics: Sintering and Microstructure Responsable.

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.