Abrasive particles can cause significant problems in technical systems, especially in areas where friction occurs. Therefore, it is often crucial to prevent the ingress of such particles and to check them regularly. Below you will find important information about the properties and risks of abrasive particles.
properties of abrasive particles
During the operation of technical systems, mechanical abrasion of various components occurs over time. The entry of hard particles is particularly problematic, as these can significantly accelerate wear. Abrasive wear occurs when friction partners are damaged by scratches, micro-machining and scoring. Particles with high hardness and sharp edges are particularly damaging.
A typical example of abrasive particles in ambient dust are silicon oxide particles (SiO₂, also known as quartz). The Mohs mineralogical hardness scale is used to assess the abrasiveness of such particles. Minerals with a hardness of over 7 on the Mohs scale are harder than most materials and therefore have an abrasive effect. These materials include many carbides and certain naturally occurring minerals.
The following table lists some materials and their hardness:
| material | Chemical Compound/Elements | Hardness according to Mohs |
| minerals and carbides | ||
| Diamond | C | 10 |
| silicon carbide/nitride | SiC/Si3N4 | 9,5 |
| boron carbide | B4C | 9,5 |
| tungsten carbide | WC | 9,5 |
| vanadium carbide | VC | 9-9,5 |
| aluminum oxide, e.g. corundum |
Al2O3 | 9-9,5 |
| Boron nitride | BN | 9 |
| titanium carbide | TiC | 8-9 |
| silicon oxide e.g. quartz |
SixOy | 7 |
| Metals | ||
| Steel case-hardened |
after alloy | 8 |
| Chromium (hard, electrolytic) |
Cr | 8 |
| tungsten | W | 7-7,5 |
| Manganese | Mn | 7 |
| Cobalt | Co | 5 |
| Nickel | Ni | 3,5-7 |
| Iron | Fe | 3,5-4,5 |
| Copper | Cu | 3 |
| Aluminium | Al | 2-3 |
| tin | Sn | 2 |
| lead | Pb | 1,5 |
Investigation of abrasive particles and their influence on wear
Strongly accelerated wear in technical systems is often due to the presence of abrasive particles. An examination of the affected components and lubricants can provide valuable information. The GWP uses scanning electron microscopy with X-ray micro-area analysis (SEM-EDX) in particular to precisely analyze particles.
Analysis methods:
- Particle analysis from lubricants: Particles are filtered out of lubricants and examined using SEM-EDX. Element distribution images support the search for abrasive components. Relevant elements include silicon, carbon, tungsten, vanadium, titanium and zirconium. Conspicuous particles are analyzed for elemental composition and morphology.
- Surface analysis of the components: Abrasive particles can cause abrasion and erosion on component surfaces, often leaving typical impressions or embeddings. This damage allows conclusions to be drawn about the type of wear.
Example: Wear of plain bearings due to silicon oxide
A bronze plain bearing showed sudden wear, combined with a significant clouding of the lubricating oil. Particles in the oil were recovered by filtration with a gold core pore filter and then analyzed using SEM-EDX. The examination showed a heavy filter coverage with chips, which indicates wear. The elemental analysis showed copper and tin as the main components, which indicates bronze as the source material and thus confirmed that the bearing was worn.
To determine the cause of the high wear, element distribution images were created to identify abrasive materials such as carbon (e.g. diamond and carbides), silicon (silicon oxides), aluminum (aluminum oxides) and titanium (titanium carbides). These materials are often introduced into the system through external inputs and can accelerate wear. This analysis particularly identified silicon accumulations, which were highlighted by blue markings in the image.
The detailed analysis of the particles revealed silicon oxide (SiO₂) with high hardness and sharp-edged morphology, as occurs in mineral silicon (e.g. quartz). Due to the small particle size (usually < 5 µm) and high hardness, these particles have highly abrasive properties. In lubricated systems, such particles can act between friction partners and lead to micro-chips.
Result and cause analysis:
It turned out that the bearing surfaces had previously been treated with a polishing paste containing silicon oxide. It was suspected that residues of this paste had entered the lubricant after inadequate cleaning. An additional SEM-EDX analysis of the polishing paste showed that the particles in it had the same elemental composition, morphology and particle size as the particles found in the bearing. This similarity suggests that the inadequate cleaning process led to contamination of the lubricant and thus caused the increased wear.
