From April 19 to 21, 2016, Anton Paar will be at the POWTECH exhibition in Nuremburg, Germany. POWTECH is one of the leading events for experts with a focus on powder and bulk material technologies. As a strong partner of this industry Anton Paar produces measuring instruments for powder analysis which are used in quality control and research.
Powders are not only the end products of industrial production lines, they can also be the intermediate stage of a production process. Besides the actual end product, the industrial use of powders includes the processing, transport and storage of these materials. Important properties for powders such as size, stability and flow properties are essential parameters for the characterization of these interesting systems.
Industrial use of powder
For the transport and processing of powder it is important to know about the powder’s flow properties. It is essential to understand the flow properties such as cohesion strength or air retention capacity in order to optimize industrial processes such as the transport through processing plants. If powder is used in surface treatment or surface functionalization, the homogeneous application of the powder on the surface plays a decisive role. In this case a suitable liquid matrix can serve as the transport medium. When powders come into contact with a liquid matrix this can lead to the formation of suspensions.
The solubility of a powder in a liquid matrix is dependent on – among other things – the interaction between the particles and the matrix. If the particle-matrix interaction dominates over the interaction between the particles (particle-particle interaction) then the suspension will be stable over time. Conversely, if the interaction between the particles is stronger than the interaction between the matrix and the particles then this can lead to agglomeration or separation. Both effects are unwanted in many processes and need to be avoided. A measure of which of these interactions gains the upper hand is the second virial coefficient. This can be measured using light-scattering methods.
Another parameter is the zeta potential. The zeta potential is measured in volt and gives insight into the surface charge of a powder particle in the solution. The zeta potential values of particles in solution can be measured using electrophoresis: Particles in solution in a state of equilibrium are subject to Brownian motion. An additional electrical field applied from outside exerts a force on the particles. The result is a superimposed additional movement along the electrical field. This movement – electrophoretic mobility – is a measurement parameter which has a direct correlation with the zeta potential. Technological advances in this measuring method, such as cmPALS (continuously monitored Phase Analysis by Light Scattering), shorten the measurement time and deliver better information.
The flow behavior of suspensions and other liquid media is characterized by rheological measuring methods. These allow, for example, characterization of the shear-rate-dependent viscosity and the thixotropic properties of liquid. This allows conclusions to be drawn about the storage stability of the suspensions.
Powder coating makes surfaces more resistant to mechanical influences and also allows the functionality of the surface to be optimized. To create a successful coating a number of questions need to be answered: Will the powder stick to the surface? Does the surface need to be pretreated? – for example: surface modification such as plasma treatment. Will the powder coating cause the surface to harden? The first questions can be answered by looking at the zeta potential. In this case, zeta potential measurements are based on streaming potential or streaming current measurements. The last question about surface hardness can be answered via instrumented indentation testing. In this case, a diamond with a defined geometry (Berkovich/Vickers) and set load penetrates the coating. The test load and penetration depth are measured dynamically during a load and displacement test. Hardness and elastic modulus can be calculated directly from the resulting load-displacement curve.
On the way from powder to solid, Anton Paar supports the user with individual solutions. These yield important information during the production steps and in further processing. For more information, visit us at PowTech, Booth 456 in Hall 1 . We look forward to meeting you.