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Grinding aids for fine grinding

Solve individual requirements

Many comminution tasks in the field of mechanical process engineering can be successfully solved with different mill types and their specific loading mechanisms. However, there are certain applications where conventional laboratory mills reach their limits, even with extensive accessories.

Particularly challenging is the comminution of materials that contain residual moisture but cannot be dried. Raw materials containing oil and fat, as well as soft or elastic samples, also frequently pose problems. Wet grinding is often necessary, especially for ultrafine grinding—for example, for the production of ultrafine powders through high energy input.

In such cases, the use of grinding aids should be considered. These are additives that can activate, accelerate, or improve chemical or physical processes during the grinding process.
It is important that these additives do not negatively impact subsequent analysis or further processing. Therefore, careful testing is always required before use in sample preparation.

Types of grinding aids

Grinding aids are differentiated according to their state of aggregation:

  • Solid additives (e.g. powder, granules, pellets) – to bind fat and/or moisture
  • Liquid additives (e.g. water, alcohols, petrol) – to avoid agglomerates
  • Gaseous additives (e.g. inert gases, cooled air) – for temperature control and reaction prevention
  • Additionally: Temperature control – e.g. cooling with liquid nitrogen or heating to specifically change the sample properties

Solid additives

When preparing samples for X-ray fluorescence analysis, it is common practice to add analytically neutral pellets—such as cellulose-based Spectromelt—during the comminution process in planetary ball mills or vibrating disc mills. When used in the correct ratio, these pellets improve the comminution effect and prevent the material from sticking together in the grinding vessel. They can also serve as a binding agent in a subsequent pelletizing process.

Another example is sodium sulfate, which is used in the processing of insects, small marine animals, or moist soils. It specifically binds fat and moisture, whose content is then determined. Trituration is usually carried out in mortar mills and allows for complete recovery of the ground material.

Liquid additives

Petroleum ether is often used in the processing of oil-containing seeds such as rapeseed, soybeans, or mustard seeds in ball or mortar mills. It ensures better homogenization and serves as an extraction fluid for subsequent oil content determination.

In areas such as the ceramics industry, powder metallurgy, or mineralogy, where ultrafine ground products are required, wet grinding is often essential. Water or isopropanol are used as dispersants – usually in ball or mortar mills.

Gaseous additives

Through targeted ventilation of a shredding system – for example, using a cyclone separator or filter system – frictional heat can be effectively dissipated. This prevents excessive heating of the material being ground and simultaneously increases throughput.

Additionally, gassing with inert gases such as nitrogen or argon during the grinding process can be beneficial. This prevents reactive particles from reacting with the oxygen in the air, thus protecting against unwanted oxidation processes.