In this article, we will address Particle size distribution and shape characterization. Milling or size reduction of solid materials is essential in many powder processing applications. The main goal of size reduction is to produce smaller particles. This process either increases surface area or meets specific shape, size, and quantity requirements. Typically, the final product consists of a mixture of particles with various sizes and shapes. By combining milling with a sieving screen, we can effectively narrow the particle size distribution. This approach creates a more uniform product.
Particle Size Distribution and Shape Characterization – Size Reduction Process
In our field testing area, we use various equipment with distinct mixing principles for solid material size reduction. Our ultra-centrifugal mill efficiently reduces soft to medium-hard and fibrous solids to a precise size distribution. This process occurs through impact and shearing forces from a high-speed rotor equipped with interchangeable ring sieve screens in the milling chamber. These screens enable adjustments in size distribution as needed.
The two-step grinding process ensures gentle yet rapid size reduction. The sample remains in the milling chamber for only a brief period, preserving its original characteristics. The centrifugal mill can achieve particle sizes as low as 40–50 micrometers. It is versatile for processing materials like bones, cereals, chemicals, coal, coffee beans, and more.
For even smaller particle sizes, we use ball milling as an effective alternative. This method relies on impact and attrition, where size reduction occurs as balls drop onto particles. Ball milling can achieve sizes of approximately 10 micrometers and is particularly suitable for smaller sample sizes, providing an efficient means to obtain finer particles.
Ball Mill
The ball mill is an essential tool for size reduction in materials such as coal, pigments, and clay. This milling process can be performed either wet or dry, with the wet process typically conducted at low speeds. In systems with multiple components, ball milling effectively enhances solid-state chemical reactivity. Additionally, ball milling is useful for producing amorphous materials.
For challenging materials, such as heat-sensitive or tough-to-mill substances, cryogenic milling is an effective solution. Cryogenic milling—also referred to as freezer milling, freezer grinding, cryogenic grinding, or cryo-milling—involves cooling a material before reducing it to a smaller particle size. For instance, cocoa nibs are difficult to grind into a powder at ambient temperatures because they tend to melt and form sticky clumps. However, when chilled with dry ice or liquid nitrogen, the cocoa nibs can be easily ground into powders suitable for various powder processing applications.
Particle Size Distribution and Shape Characterization – Laboratory Equipment Selection
When selecting suitable laboratory equipment for cryogenic grinding, several factors must be considered, including sample volume, dosing size, and desired particle size. Our system utilizes liquid nitrogen (–196 °C) to cool the feed material before and during milling, helping to prevent melting, decomposition, or embrittlement.
Cryogenic milling is widely employed in the food, beverage, and pharmaceutical industries. Throughout the various size-reduction procedures, particle size analysis can confirm the effectiveness of the process by measuring particle size distribution and verifying whether the desired size has been achieved.
