In May this year Anton Paar’s powder rheometer celebrates its first birthday. For this reason we say “Happy Birthday” and take a closer look at this application. Powder rheology is a relatively new discipline and Anton Paar is forging new paths here.
With the new Powder Cell from Anton Paar, the modular compact rheometers of the MCR series become fully functional powder rheometers. This setup can be used to characterize the flow behavior of all kinds of granular materials – from the finest powders to larger particles like rice grains.
What are granular materials and why do we need to investigate their flow properties? Examples of granular materials and “powder” can be found in the kitchen: salt, crystal sugar, rice, starch or coffee powder. Before these products land in our kitchen cupboards, they are produced, processed, stored and transported. Within – and between – many of these process steps, the powder is in motion – it flows! However, sometimes it doesn’t flow as well as it should, so it may clog up a funnel, for example, because the powder is too humid after production. How well a powder flows can be determined using the powder rheometer. This helps prevent the funnel getting clogged up and the customer saves time and money.
Complex flow behavior
One thing is common to all powders: Their flow behavior is complex and determined by numerous factors such as particle size, particle shape, chemical structure, humidity or surface morphology. Whichever of these factors influence the powder’s flow behavior, the new powder rheometer from Anton Paar can provide a measuring value as a sum of all causes, to determine changes to the powder’s flow behavior. This allows simple and reproducible quality control without the need for users to understand the exact physical effects in the powder flow.
However, the powder rheometers are much more than just tools for quality control. Using this cell, for the first time all methods from “liquid rheology” can be applied to the field of granular media. In this way, for example, the system also provides measuring values for the technical process architecture in the field of freely flowing powders (e.g. for pneumatic transport through a pipe, for fluidized bed reactors or powder coatings).
Powder rheology at specialist conferences
The new powder rheometer was presented for the first time in May last year at CHoPS in Tel Aviv (Israel). This is one of the most important specialist conferences on the subject of transporting and handling bulk materials (for more, see here: http://blog.anton-paar.com/how-to-characterize-powder-flow/). Besides this, a complete system was given away as a prize in a competition at the Society of Rheology Meeting 2015 in Baltimore (USA). Members of the Society and others were asked to send in their ideas related to the question “How would you use a powder rheometer?”. John F. Brady from the Division of Chemistry and Chemical Engineering at California Institute of Technology was awarded a brand new powder rheometer for his idea (read more here: http://blog.anton-paar.com/how-would-you-use-a-powder-rheometer-the-most-innovative-answer-to-this-question-has-been-rewarded/).
His idea was to measure the powder flow of colloid particles before, during and after a chemical reaction which takes place in the measuring cell itself. “This powder rheometer provides us with an important in-house experimental verification of our understanding of active substances. Before we had to rely on theory and calculations or on the experiments of other research groups,” Brady explains the the importance of the powder rheometer for his work.
The Powder Cell from Anton Paar
The Powder Cell from Anton Paar turns almost every rheometer of the renowned MCR series into a versatile powder rheometer. This versatility makes it so special. As the Powder Cell can be used and removed as required, the same instrument can also be used for rheological measurements of all kinds on substances ranging from low-viscosity materials to highly viscous substances.
The intuitive operation and speed of the measurements are further distinguishing features of this new powder characterization. Results can be obtained within two minutes. The safety of users also plays an important role. The Powder Cell has a unique dust protection device which protects users from fine particles. It is therefore possible to detect the smallest changes in the powder flow – not only quickly but also completely safely.