This article investigates the relationship between particle size, true density, and the compressive strength of hollow glass microspheres (HGMs). Using the Bettersizer 2600 laser diffraction particle size analyzer and BetterPyc 380 gas pycnometer, this article confirms that particle size and true density have an effect on compressive strength. These insights offered by Bettersize provide significant contributions to the field of HGMs material engineering.
Introduction
Hollow Glass Microspheres are inorganic, nonmetallic spherical materials created by specific processes, commonly with diameters in the range of 10 to 250 μm and wall thicknesses of 1 to 2 μm (Figure 1).
These microspheres are well known for their exceptional properties, including abrasion and corrosion resistance, low water absorption, radiation shielding, and chemical stability. They have a wide range of uses as composite material fillers in construction, coatings, rubber, marine, aerospace, and other fields.
The compressive strength of HGMs is a critical physical parameter, as it can directly influence their applicability and end product quality in various fields.
Figure 1. HGM structure. Image Credit: Bettersize Instruments Ltd.
According to the theoretical fracture strength formula for an individual hollow glass microsphere: 1,2
P is the compressive strength
α is the shape factor (the ratio of diameter D to wall thickness t)
E is the theoretical Young's modulus for the HGM
ν is the Poisson's ratio of the wall materials
The compressive strength of HGMs is related to the diameter ‘D’ and wall thickness ‘t’, as these elements combined influence the shape factor. Since HGMs powder is composed of numerous particles with varying sizes, it is essential to account for the entire impact of particle size and distribution when assessing their properties.
Measuring the wall thickness of HGMs directly is a time-consuming process. However, evaluating this thickness through the measurement of true density offers a more practical approach.
Accurate measurement and analysis of both the particle size distribution and the true density of HGMs powders are crucial for enhancing our understanding of their performance across different applications. This understanding not only helps in optimizing the filling quantity and methods but also contributes to improving the stability and performance of composite materials that incorporate HGMs.
Measurement Method
The study outlined in this article used the Bettersizer 2600 laser diffraction particle size analyzer and BetterPyc 380 gas pycnometer to explore the particle size distribution and true density of four sets of identical formulations of HGMs. The results were then analyzed to investigate the relationship between compressive strength, particle size distribution and true density.
Leveraging Mie theory, which aligns with ISO 13320 standards, the Bettersizer 2600 is designed to swiftly gather information on particle size and distribution. This is achieved by measuring the diffraction angle and intensity of particles when they interact with a laser (as illustrated in Figure 2).
Thanks to its rapid testing capabilities, data results from the Bettersizer 2600 are available in just one minute. When employing the wet method for analysis, the refractive index values for the HGMs and the solvent medium (distilled water) were 1.46 and 1.33, respectively.
Figure 2. System diagram of Bettersizer 2600. Image Credit: Bettersize Instruments Ltd.
The BetterPyc 380 gas pycnometer is built using the ideal gas state equation and uses the gas displacement method (compliant with ISO 12154:2014) with the temperature control system.
The method facilitates the measurement of the volume of HGMs and, subsequently, their true density.
In this study, helium was used as the analytical gas, with measurements conducted at a pressure of 19.5 psig and a controlled equilibrium rate of 0.005 psig/minute, all at a temperature of 20 ℃. This instrument boasts fast testing speeds and operates non-destructively, making it an efficient and reliable approach for density testing.
Figure 3. System diagram of BetterPyc 380. Image Credit: Bettersize Instruments Ltd.
Result
Table 1 shows the common particle size and true density data of four sample groups. The samples HGM-1 and HGM-2 are similar in particle size and distribution, with true densities of 0.6033 g/cm3 and 0.3842 g/cm3 respectively. Their compressive strengths are 83 MPa and 38 MPa, respectively.
According to the theoretical fracture strength formula, maintaining a constant diameter while achieving a higher true density suggests an increase in wall thickness. This increase in wall thickness leads to a reduction in the shape factor, which in turn enhances the compressive strength. The findings of this experiment are well aligned with the theoretical expectations.
Table 1. The particle size distribution, true density and compression strength of HGMs samples. Source: Bettersize Instruments Ltd.
| Sample |
Particle Size Distribution (μm) |
True Density
(g/cm3) |
Compression
Strength (MPa) |
| D10 |
D50 |
D90 |
| HGM-1 |
16.62 |
40.57 |
79.76 |
0.6033 |
83 |
| HGM-2 |
16.34 |
40.48 |
79.82 |
0.3842 |
38 |
| HGM-3 |
12.09 |
20.43 |
33.12 |
0.5033 |
110 |
| HGM-4 |
4.510 |
10.11 |
21.06 |
0.7824 |
207 |
In Figure 4, a comparative analysis of HGM-2, HGM-3, and HGM-4 is presented, illustrating that a decrease in the particle size D50 corresponds to a gradual increase in true density (as indicated by wall thickness), resulting in a smaller shape factor.
This phenomenon explains the increase in compressive strength associated with the reduction in particle size and increase in true density. The findings underscore the critical role of particle size and density in influencing the mechanical properties of HGMs.
Figure 4. D50, True density and compression strength of HGM-2, HGM-3 and HGM-4. Image Credit: Bettersize Instruments Ltd.
Conclusion
In summary, for HGMs with identical formulations, manipulating the particle size range through sieving facilitates the production of samples with diverse strength characteristics. Optimizing the manufacturing process to increase the true density of HGMs is a viable strategy to meet specific particle size criteria and potentially boost their compressive strength.
Bettersizer 2600. Image Credit: Bettersize Instruments Ltd.
BetterPyc 380. Image Credit: Bettersize Instruments Ltd.
The Bettersizer 2600 laser particle size analyzer and BetterPyc 380 gas pycnometer designed by Bettersize can offer crucial references and monitor for material design and engineering applications.
References and Further Reading
- P.W. Bratt, J. Cunnion, B.D. Spivack, Advances in Materials Characterization 441 (1983).
- S.P. Timoshenko, J.M. Gere, Theory of Elastic Stability, McGraw-Hill, New York, 19
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.