Like Fe(OH)3 or CuCrO4. The latter is even harder. I use a buchner funnel and vacuum. After the first water removal the mass becomes very dense. It is
impossible to mix it with water in the funnel itself - it sticks to a glass rod and doesn't want to become less dense, forming clots. So, I put it
into the flask to mix with water but transferring is a very messy process, it sticks to everything. It's not possible to remove it from a flask neck
or spatula without a paper towel.
Is there any technique, any way that can help to wash such fine powders?Ubya - 2-7-2019 at 05:47
by boiling the solution for prolonged amounts of time the particles coalesce in bigger particles, making it easier to filter.
for the washings, use a beaker, wash the powder with lots of water inside the beaker, let it settle, filter the water without letting much of the
powder in the funnel, repeat the washings as needed. teodor - 2-7-2019 at 06:30
Thank you, Ubya, I like your method.
[Edited on 2-7-2019 by teodor]Tsjerk - 2-7-2019 at 11:27
You could try washing it with acetone after the first water is pulled of by the vacuum, that dries your material, possibly not making it sticky
anymore.
[Edited on 2-7-2019 by Tsjerk]DavidJR - 2-7-2019 at 17:11
For materials that are a pain in the ass to filter - avoid filtering!
Instead, you can often just allow to settle and then decant the supernatant. Repeat as needed for washings.
Or, if you have less patience, get a centrifuge. I got a cheap one on eBay which has been very useful for work on phthalocyanines which are an
absolute nightmare to filter.teodor - 2-7-2019 at 21:52
You could try washing it with acetone after the first water is pulled of by the vacuum, that dries your material, possibly not making it sticky
anymore.
[Edited on 2-7-2019 by Tsjerk]
I also thought about another solvent, but in the case of washing CuCrO4 acetone possible will not work. The main impurity is K2CrO4. According to
wikipedia K2Cr2O7 is insoluble in acetone, I think the same should be true for K2CrO4. Also some solvents will be oxidized. But of course I can try
several and select which works.
Or do you mean to make one wash with water and one with another solvent to remove the water and to make the mass more sparse and remove cracks, and
than again with water and so on? I will try that, it could be interesting.
[Edited on 3-7-2019 by teodor]
[Edited on 3-7-2019 by teodor]
[Edited on 3-7-2019 by teodor]teodor - 2-7-2019 at 21:57
For materials that are a pain in the ass to filter - avoid filtering!
Instead, you can often just allow to settle and then decant the supernatant. Repeat as needed for washings.
Another problem that fine powders are also good absorbents. Washing with the method of settling in water could be endless especially if I need the
material for analytical purposes.
Or, if you have less patience, get a centrifuge. I got a cheap one on eBay which has been very useful for work on phthalocyanines which are an
absolute nightmare to filter.
Yes, the time matters. I am thinking about a centrifuge. May be I will buy or make one if will not find another solvent which will work.
