Nano Powder

Pyrogenic silicic acid Aerosil

Aerosil is an extremely fine particled silicic acid first made in 1942 and now produced in a large number of variants.Originally it was developed as a reinforcing filler for car tires. Now it improves the material properties of technical rubber articles, improves the flow of a wide variety of powders like laser toner, hardens lacquers against scratches, optimizes the flow properties of toothpaste and is used as a polish for microchips.

The particles of the powder are in the nm range and when stirred up in a closed bottle they settle quite slowly due to their small weight. Settling times of tens of seconds can be observed. With a short movie of the settling process a time constant of 9 sec was measured with 30 cm³ of powder in a 100cm³ bottle.

fig 1 Settling of the Aerosil powder over time (in seconds)
When the particles are falling down they build up a higher flow resistance for the enclosed air, releasing it more and more slowly. During this time still with much air inside, the powder behaves like a very thin liquid. Under vertical vibration of for instance 20Hz the resonating waves appear on the surface and the process of settling is further delayed depending on the intensity of the vibration.
fig 2 Vibration at 20Hz