Some powders are sensitive to air (oxygen) or water (humid air). Also for these types of samples, it is interesting to know the particle size of the powder produced. With many particle-size instruments, it is difficult to measure these types of samples, as there is no option to measure inert. Therefore at Delft Solids Solutions, we have developed a method to measure the particle size distribution in an inert way so that air-sensitive materials can still be measured.

In order to investigate if the material cakes and problems occur during storage uni-axial testing was performed on the absorbent. For the experiments, it was investigated the optimal moisture content in order to minimize storage problems. Three moisture contents were selected: dry, approx.—30% moisture content, and immersed in water. The absorbent was placed in the uni-axial sample cell with a closed hole on the bottom and a pressure of 18 kPa was placed onto the powder bed and stored for 7 days at 20°C, 65%RH inside a climate chamber.

After storage, the pressure was removed and the hole in the bottom of the sample cell was opened. The absorbent consists of spherical particles of

approx. 1 mm and as expected when opening the sample cell containing the dry absorbed no caking occurred and it immediately started flowing.

The absorbent containing 30% moisture did not flow after opening the bottom of the sample cell and approx. 6 kPa was needed to initiate flow. The higher pressure required for flow is due to the liquid bridges between the particles resulting in a more cohesive behavior.

Lastly, the absorbent immersed in water also did not show caking and immediately started flowing after opening the bottom of the sample cell. In this case, the moisture content was high enough that the absorbent started to behave as water and flowed like a liquid out of the sample cell.

For storing the absorbent, both dry and immersed in water are a good option. However, in order to obtain dry absorbent after the process it needs to be dried after the process requiring a lot of energy, immersing the absorbent in water may therefore seem to be the better option but the bulk density is much higher, requiring stronger support for the silo and creates more wastewater.

Our message of the week:
water can both help and prevent the discharging of your material

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