This article outlines the technique to analyze the particle size of calcium carbonates using laser diffraction.
Calcium carbonates fulfill a wide variety of functions in different industries:
- Elastomers and rubber: as an extender and filler
- Plastics: as a rheology controller and filler
- Paper: as an acidity controller, coating pigment, and filler
- Surface coatings and paints: as an extender and finishing aid, filler, and pigment
- Pharmaceuticals: as a bulking agent or filler
- Hygiene and household products: as a mild abrasive
- Foods: as an extra source of calcium
- Mining: as a bridging component in drilling mud
- Fertilizers: as a source of calcium and a filler
- Construction: as a filler for concrete, asphalt, grout, and roofing materials
- Pet and animal feeds: as a digestion aid and a source of calcium
- Sealants and adhesives: as a viscosity controller and fillers
Measuring the Particle Size of Calcium Carbonates
Calcium carbonates are available with varied surface coatings and particle sizes in order to provide this range of functionality. The Mastersizer 3000 laser diffraction system is capable of measuring particle size from nanometers to millimeters, and also allows measurements over the range to be achieved within a few minutes.
This range and measurement speed allows the particle size of calcium carbonates to be tracked during the production processes as well as in quality control of end products.
How to Disperse Calcium Carbonates
The Mastersizer 3000 laser diffraction system has a variety of accessories that enable the use of dry dispersion or liquid for measurements. The calcium carbonate’s particle size and processing method will establish whether dry dispersion or liquid is preferable.
Huge sample volumes can be measured using dry dispersion, providing reproducible results for coarser particle sizes. Liquid dispersion provides more control over the dispersion state for the finest grades, producing reproducible results.
The Mastersizer 3000 installation can be used to examine a range of samples because of the ability to rapidly change between dry and liquid dispersion units.
Compressed air is used by the Aero S dry powder disperser to disperse the sample, and the dispersion is ensured by selecting the suitable air pressure. In liquid dispersion, calcium carbonates are generally measured in water using the Hydro dispersion units.
A short duration of ultrasound is needed to disperse agglomerates, and additives such as sodium hexametaphosphate or sodium pyrophosphate are used to stabilize the dispersion.
Figure 1 displays the particle size distributions for a calcium carbonate sample that is measured using both dry (at 1bar) and liquid dispersion (after 1 minute of ultrasound). These findings highlight the positive agreement between dry and liquid dispersion which confirms that that the sample is completely dispersed in both states.
Figure 1. Overlay of a calcium carbonate sample measured in liquid (wet) and dry dispersion
Specifying the Particle Size of Calcium Carbonates
Laser diffraction creates volume-based particle size distributions, which allow a wide range of parameters to be specified. For example, the 10th percentile (Dv10) can be employed to detect the fine particles in the distribution, whereas the 90th percentile (Dv90) helps to detect the coarse particles in the distribution.
In addition to this, calcium carbonates are often specified on the percentage material in specific size ranges, for example the percentage above 10 µm or 45 µm at the coarser end of the range and the percentage below 1 µm and 2 µm for the finer grades.
Figure 2 displays the particle size distributions for four grades of calcium carbonate covering a size range from 0.1 µm up to 1000 µm, and Table 1 highlights the parameters for these samples.
Figure 2. Particle size distributions for four grades of calcium carbonate.
Table 1. Particle size parameters for four grades of calcium carbonate.
||%V < 1µm
||%V < 2µm
||%V > 45µm
Laser diffraction is a technique that is commonly used to analyze calcium carbonates due to its flexible dispersion options, wide dynamic range, reproducibility of results, and measurement speed.
This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.
For more information on this source, please visit Malvern Panalytical.