Application Note | Microparticle Compression
Microparticles: Compression Strength and Micro Indentation by Testing Salts
Flat-Punch Crushing Strength of Single Salt Crystals
Research & Experimental Testing
Jorge Ramirez
Visual Design & Editorial
Andrew Shore
Introduction
Compression strength has become vital to quality control in developing and improving new and existing microparticles and micro features (pillars and spheres). Microparticles have various shapes and sizes and can be made from ceramics, glass, polymers and metals. Uses include drug delivery, food flavor enhancement, concrete formulations and many others. Controlling the mechanical properties of microparticles or micro features is critical to their success and requires the ability to quantitatively characterize their mechanical integrity.
Importance of Depth versus Load Compression Strength
Standard compression instruments are not capable of low loads and fail to provide adequate depth data for microparticles. Using nano or microindentation, the compression strength of nano or microparticles, soft or hard, can be measured accurately and precisely.
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Measurement Objective
In this application note, we measure the compression strength of salt with the NANOVEA Mechanical Tester in microindentation mode.
NANOVEA CB500 Advanced Compact
Mechanical Tester
Test Conditions
| Parameter | Value |
|---|---|
| Maximum force | 30 N |
| Loading rate | 60 N/min |
| Unloading rate | 60 N/min |
| Indenter type | Flat punch, steel, 1 mm diameter |
Table 1: Test conditions.
Results and Discussion
Particle failure was determined to be the point where the initial slope of the force vs. depth curve began to noticeably decrease. This behavior shows that the material has reached a yield point and is no longer able to resist the compressive forces being applied. Once the yield point is surpassed, the indentation depth increases rapidly for the rest of the loading period. These behaviors can be seen in the load vs. depth curves of both samples.
| Particle | Particle height (µm) | Failure load (N) | Strength at failure (MPa) |
|---|---|---|---|
| Particle 1 | 377 | 12.5 | 88 |
| Particle 2 | 250 | 3.4 | 54 |
Table 2: Height, failure force and strength for Particle 1 and Particle 2.
Conclusion
In conclusion, we have shown how the NANOVEA Mechanical Tester in microindentation mode is a great tool for compression strength testing of microparticles. Although the particles tested are made of the same material, the different failure points measured in this study were likely due to pre-existing micro cracks in the particles and varying particle sizes. For brittle materials, acoustic emission sensors are available to detect the beginning of crack propagation during a test.
The NANOVEA Mechanical Tester offers depth displacement resolution down to the sub-nanometer level, making it a great tool for the study of very fragile microparticles or features as well. For soft and fragile materials, loads down to 0.1 mN are possible with the nanoindentation module.
Frequently Asked Questions About Microparticle Compression
Why measure microparticle compression strength?
Microparticles of ceramics, glass, polymers and metals are used in drug delivery, food flavor enhancement, concrete and more; their mechanical integrity must be quantified to control quality.
Why not use a standard compression tester?
Standard compression instruments cannot apply low enough loads and do not give adequate depth data for microparticles; nano or microindentation measures their compression strength precisely.
How were the salt particles tested?
With a 1 mm diameter steel flat punch loaded to 30 N at 60 N/min, then unloaded at 60 N/min.
How is failure identified?
At the point where the initial slope of the force vs. depth curve noticeably decreases: the particle has yielded and can no longer resist, and the depth then increases rapidly.
What strengths were measured?
Particle 1 (377 µm high) failed at 12.5 N, 88 MPa; Particle 2 (250 µm high) failed at 3.4 N, 54 MPa.
Why did the two particles differ?
Though made of the same material, the difference is likely due to pre-existing micro cracks and varying particle size; for brittle materials, acoustic emission sensors can detect the start of cracking.
