Polymeric Sulfur sample

Presented sample is way too small to use a jaw crusher for pre crushing. Basically it can be fed directly into the requested Disk Mill PULVERISETTE 13. Results of a Disk Mill usually are about d50 < 150 µm with max. particles still > 300 µm because particles only need to comply the gap setting in one dimension to pass the grinding chamber. Therefore, also this tool is not coming into question to comminute the sulfur to d50 < 35 µm.

A Planetary Micro Mill PULVERISETTE 7 premium line which was requested is beneficial to grind samples down into sub micrometer range. For the required level of fineness, every classic line tool is suitable when a sample can be ground; also classic line mills are available with up to 500 ml grinding bowls and up to 4 bowl positions (for the Planetary Mill PULVERISETTE 5 classic line). Therefore, a classic line Planetary Mono Mill PULVERISETTE 6 or Planetary Mill PULVERISETTE 5 classic line should be chosen for comminution of your particular kind of request.

Elemental sulfur has dry lubricant properties; because of this, a fine grinding of sulfur is very tricky.

We used the Planetary Mono Mill PULVERISETTE 6 classic line for comminution and picked zirconium oxide as a ceramic material for the grinding equipment to avoid discolorations (by abrasion). We fed 100 grams of the sample into the bowl which was equipped with 25x 20 mm Ø grinding balls for pre crushing of sample.

We started with 600 rpm speed setting and dry ground the sample for the first minute. The sample already stuck slightly to the used grinding balls. The bowl wasn’t covered with sulfur. After one minute, the sample appears to be very fine, but by sieving, we still found 80 % of sample > 63 µm.

We proceeded dry grinding for two further minutes (3 minutes of total grinding time) and found, that the sulfur already got compressed much harder to grinding balls and the bowl as well. A longer dry grinding is not possible anymore.

We added 70 grams of isopropyl alcohol and proceeded grinding for a total grinding time of 10 minutes. To avoid too much of heating, we programmed 30 seconds of comminution with two minutes of pausing times for chilling. Surely even longer pausing times can be programmed to keep minimize temperature stress. A max. heating of 30 °C is very hard to achieve because larger capacities of bowls have a bad surface-volume ratio in order to lead away the heat which was generated.

After 10 minutes of total grinding time, typical surface marks are visible when a grinding ball is hitting the bowls wall directly. This is indicating that the used grinding balls are pushing the sulfur away and there will be no further reduction of size anymore.

We exchanged the 20 mm Ø grinding balls against 2000x 5 mm Ø grinding balls to have a much better chance hitting a particle with every rotation of the bowl.

After a total grinding time of 15 minutes (5 minutes with the exchanged 5 mm Ø grinding balls), we checked the size of particles by optical microscopy. Within the sample we took, majority of sample was already comminuted < 35 µm width as desired.

We packed the sample best possible into a plastic bottle. To dilute the very pasty sample, we had to add further 35 grams of isopropyl alcohol. If a dry sample is required, we recommend a speedy evaporation of the used solvent to minimize hardness of agglomerates. This can be performed by rotary speed evaporation or by spray drying.