Pre-Crushing Hard Samples for Grinding to the Nanoscale

The FRITSCH Jaw Crusher PULVERISETTE 1 can be used to pre-crush medium-to-hard materials with edge lengths measuring up to 95 mm. A number of FRITSCH mills can be used to obtain an additional fine comminution.

These include:

  • Planetary Ball Mills like PULVERISETTE 4, PULVERISETTE 5, PULVERISETTE 6, and PULVERISETTE 7
  • Mortar Grinder PULVERISETTE 2
  • Vibrating Cup Mill PULVERISETTE 9
  • Vibratory Micro Mill PULVERISETTE 0
  • Disk Mill PULVERISETTE 13 classic line
  • Mini-Mill PULVERISETTE 23

These instruments can grind material quickly to “analytical fineness” - a size smaller than 63 µm. However, the Mortar Grinder PULVERISETTE 2 and the Disk Mill PULVERISETTE 13 classic line cannot produce the significantly finer materials which act as the starting point for the creation of nano-powders.

Planetary Mono Mill

The planetary ball mills from FRITSCH’s product range were previously the only thing that could be used to produce particles under 1 µm.

Because of this, the company developed the Planetary Mono Mill PULVERISETTE 6 classic line, and when this machine was used to grind quartz sand as the preferred “model” material, and without any use of liquid, an appropriate test situation was created.

The completion of the “dry grinding” process was indicated when the material adhered to the grinding balls and the bowl wall. For this test series, 20 mm grinding balls of zirconium oxide (ZrO2) and a 250 ml grinding bowl of the same material were used.

  • 1 4 — quartz sand starting product for the tests for production of nano particles
  • 2 2 — quartz sand 5 minutes PULVERISETTE 6, dry grinding, 250 ml ZrO2 bowl, 20 mm balls, average
  • 3 3 — quartz sand 10 minutes PULVERISETTE 6, dry grinding, 250 ml ZrO2 bowl, 20 mm balls, average
  • 4 31 — quartz sand 15 minutes PULVERISETTE 6, dry grinding, 250 ml ZrO2 bowl, 20 mm balls, average
  • 5 43 — quartz sand 30 minutes PULVERISETTE 6, dry grinding, 250 ml ZrO2 bowl, 20 mm balls, average

After 10 minutes (curve 3), the level of “analytical fineness” required is achieved and the material is fine enough for normal analysis tasks. With x10 < 0.8 µm - x50 < 2.8 µm - x90 < 11.9 µm, a material is produced after 30 minutes (curve 5) that has the appropriate particle size required for further attempts to produce nanopowders.

New Insights

When tests were conducted using the Planetary Micro Mill PULVERISETTE 7 classic line, it was found that there was no further increase in the fineness of the ground material when the grinding time was extended from 60 to 240 minutes.

A substantial increase in the fineness was achieved in a short time by replacing the 10 mm grinding balls used in this test with balls approximately 1 mm in size.

Results and Discussion

These experiences led to a continuation of the test, where a 250 ml bowl of ZrO2 and the Planetary Mono Mill PULVERISETTE 6 classic line were used again. Grinding beads made of ZrO2 and with a diameter significantly smaller than 1 mm were used in place of the 20 mm diameter grinding balls utilized earlier.

To calculate the quantity required, grinding beads of 1 mm with an equivalent weight of the 20 mm grinding balls were used with 100 ml of water and 50 g of model substance from the first test.

After two hours of processing, the particle size distribution was determined using the Laser-Particle-Sizer ANALYSETTE 22 NanoTec (curve 2).

  • 1-4 3 — quartz sand 30 minutes PULVERISETTE 6, 250 ml ZrO2 bowl, dry grinding, 20 mm balls, average
  • 2 221 — quartz sand 120 minutes PULVERISETTE 6, 2nd step, 250 ml ZrO2 bowl, wet grinding, 320 g of 0.4 mm ZrO2 balls
  • 3rd — test series, average

With x10 < 140 nm - x50 < 180 nm - x90 < 240 nm, a convincing result was achieved that showed that FRITSCH’s Planetary Ball Mills can easily produce nanoparticles.

After half an hour, an intermediate sample with the results x10 < 180 nm - x50 < 250 nm and x90 < 580 nm demonstrated that FRITSCH technology can crush a boulder into nanoparticles in just 60 minutes.

Critical Factors in Production of Nano-Particles

  • physical properties of the grinding media
  • physical properties of the grinding sample
  • size of the grinding ball
  • ratio of quantity of grinding materials to grinding balls and liquid
  • maximum possible energy application available with the mill

Finally, the Planetary Ball mill PULVERISETTE 6 classic line, patented by FRITSCH, has optimal speed ratio between the grinding set and the sun disk.

This guarantees the maximum possible impact energy through the resulting trajectories of the grinding balls that collide radially with the walls of the grinding bowl, providing the best performance ratio/cost of any mill available.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH - Milling and Sizing.

For more information on this source, please visit FRITSCH GMBH - Milling and Sizing.

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