8
Working with coolants:
Please follow the safety instructions.
Crushing causes the mill feed to heat up. This may not always be desirable as the
mill feed can change when heated (e.g. increased oxidation, loss of moisture,
evaporation of volatile components, etc.).
It may only be possible to crush mill feed which is viscous or has a high fat content
by embrittling using coolants.
The
A 11 basic
offers two cooling processes:
Dry ice cooling (CO
2
): approx. –78 °C:
First put the feed product into the grinding beaker and then add crushed dry ice.
Thoroughly mix the dry ice with the mill feed. Only attach the drive once the dry
ice is completely vaporized, otherwise high pressure can build up in the grinding
chamber.
Please note that the mill feed heats up again extremely quickly during crushing
(it may reach room temperature again after approx. 10 seconds of grinding). You
may have to repeat the process several times if the product is not adequately
crushed after one cooling process.
Liquid nitrogen cooling (N
2
): approx. –196 °C:
Please follow the safety instructions for liquid nitrogen cooling in particular and
always wear your personal protective equipment (safety goggles, protective
gloves, etc.).
Use a beater (A 11.1 or A 11.3) to crush mill feed embrittled with liquid nitrogen.
The cutter (A 11.2) is not recommended for this purpose (becomes blunt quickly).
Grinding beaker A 11.5 (included in delivery) is made of fluoroplastic (ETFE) with a
stainless steel insert.
First pour the feed product into the grinding beaker Pour liquid nitrogen into the
grinding beaker using a suitable Dewar vessel, ensuring that the sample is completely
covered or swimming in liquid nitrogen. Only attach the drive once the nitrogen is
completely vaporized, otherwise high pressure can build up in the grinding chamber.
Please note that the mill feed heats up again extremely quickly during crushing (it
may reach room temperature again after approx. 20 seconds of grinding).
If the feed product has a fine fraction or if the same sample is cooled several
times, use filling funnel A 11.7 (
IKA
accessories). The funnel is attached to the
grinding beaker before filling and prevents fines from the mill feed from swilling
out of the grinding beaker when you are pouring in the liquid nitrogen and during
vaporization. The funnel’s close - meshed stainless steel wire cloth (mesh size
0.063 mm) retains the fine fraction of the sample and allows you to pour in the
nitrogen more easily.
The outer edge of the grinding beaker and filling funnel
can also get very cold and must only be handled using
personal protective equipment.
Fill liquid nitrogen only into the grinding beaker! Avoid
strictly any contact of liquid nitrogen with all other parts!
Please note that the grinding beaker can ”ice up”, especially in the case of repeated
cooling. As a result, it may be difficult or even impossible to screw it on. If so, you will
need to ”clean” the grinding beaker, i.e. let it thaw out or wash it in a dishwasher.
Always dry the grinding beaker before using it again.
Liquid nitrogen cooling is not permitted in grinding beaker
A 11.4 (250 ml beaker made of polycarbonate). The
beaker would break during cooling.
CAUTION
NOTICE
NOTICE
