Particle Size Analysis
Overall, about 50 percent of the products in chemistry occur in a dispersed state, and many of the others go through a dispersed state during production. There is therefore a huge number of potential products and application areas. In process engineering, for example, the bulk density or flow behavior of particle collectives is highly dependent on the particle size distribution. When it comes to coating systems, the size of the pigments is important to ensuring the coating surface is even at a later stage. In pharmaceutical products, the particle size distribution is important for producing tablets. Other areas of application include the food industry, the construction materials industry, environmental protection and many others.
As a customer, you want to know what the final properties of your product will be. For disperse systems, these are determined by the chemical properties of the substances involved, the state of dispersity and the interfacial forces. Here at CURRENTA Analytics, we can characterize the state of dispersity for you. This includes the particle size distribution, in particular.
Depending on the size range and matrix, different measuring methods can be used. The laser diffraction technique can be used for suspensions, emulsions and mixtures in a size range of about 0.01 μm to 3,500 μm.
Monochromatic radiation is passed through the measuring cell, where the sample is distributed as evenly as possible. Behind the cell, a characteristic diffraction pattern is generated on the detectors. Small particles are able to diffract the light at a large angle and with low intensity, whereas large particles diffract the light at a small angle and with high intensity. The size distributions of particle mixtures can be calculated using either the Fraunhofer or the Mie theory. The particle sizes are given as the diameter of spheres equivalent in volume. In addition to dry dispersion, it is also possible to use aqueous suspensions (polar) or organic solvents (non-polar), meaning your sample can be measured in the state it will be used in later – which is a key factor for practical application. The particle size analysis is carried out by experienced analysts in accordance with ISO 13320. What’s more, emulsifiers or ultrasonic baths can be used to measure an optimal dispersed system.
Let’s say, for example, a metal powder had to be tested with other metal powders for product inspection. In its dry state, the powder could be measured using laser diffraction. The volume histogram and the key figures D10, D50, D90 were output as results. There is also the option to specify other distribution diagrams or key figures. The result showed that all metal powders had the same particle size distribution (see Figure 1).
Another tried-and-tested measuring method is analytical ultracentrifugation. This high-resolution method can be used in the range of approx. 0.001 μm to 10 μm. In an artificial centrifugal field, the particles form a sediment in the dispersion over a longer period of time. The sample concentration is detected with a suitable optical system equipped with a laser. During this process, the rotor rotates at a speed of up to 40,000 revolutions per minute. This enables measurements in the nanometer range, resulting in a differential or integral particle size distribution, much like that achieved by laser diffraction (see Figure 2).