Micronization and Laws of Comminution

In June, the most recent Particle Engineering article, we discussed various techniques to create particles. In this article we will look at Micronization.

Particle engineering is about creating the optimum particle size and size distribution as well as other aspects of the particle’s morphology as well as specific surface characteristics and homogeneity. Micronization is the most widely used size-reduction technique. In this article we will address the various types of micronization and more importantly the Laws of comminution/ size reduction.


A mill is generally comprised of a cylindrical drum that usually contains spheres, and is able to grind, crush, or cut the solids material. As the drum rotates the spheres inside collide with the solid material, crushing them into the desired diameter range.


During the grinding process the solids are shaped by trapping the solids between grinding units which rub against each other, thus reducing the particle size.

Laws of comminution (size reduction)

It is almost impossible to find out the accurate amount of energy required to affect the size reduction of a given material. This is because there is wide variation in size and shape of particles as well as flexibility and hardness both in the process feed as well as with the base product, and second point is some energy is wasted as heat which cannot be determined exactly, therefore it’s impossible to accurately calculate the energy requirement for size reduction on a precise level.

Through various formulas, we are able to calculate the needed level of energy in size reduction. The various laws do not take the mechanical losses of the grinder into account. There are three laws of comminution to be taken into account. The laws date back to the 19th and mid-20th century, yet are still widely used.

Let’s start with the Kicks law, it can be applied to the crushing of solids and states that the amount of energy required to crush a given quantity of material to a specified fraction of its original size is the same, regardless of the original size. The second law we will address is Rittinger’s Law, which states that the energy required for size reduction is directly proportional, not to the change in length/ width dimensions, but to the change in surface area It has been found, experimentally, that for the grinding of abrasive particles in which the increase in surface area is relatively small, Kick’s Law is a reasonable estimate. However in the case of size reduction of fine powders, with large surface areas, Rittinger’s Law fits the experimental data better and is therefore more accurate in regards to larger (newly created) surface areas.

Both Kick’s as well as Rittinger’s law are determined experimentally, by running mill tests with the material to be crushed, they thus have limited application.

A more representative method for predicting power consumption in crushing as well as grinding was proposed by Bond in 1952. Bond’s law says that effort (energy) required to form particles from very large particle size is proportional to the square root of surface to volume ratio of the product. So here we have both surface as well as volume ratio and effort required for crushing the feed of large size to the required product size.

In Conclusion

To calculate the energy requirements/ consumption needed to grind coarse-sized solids materials such as gravel, Kicks law can apply and does suffice. If we deal with cement or raw meal for example we can use Bond’s law because it is applicable at intermediate size and if we are dealing with pigments or very fine particle we can use Rittingers law, so these are the ranges of applicability of three laws of comminution/size reduction.