9 replies to this topic

[marble]

Purchased a 50kg bag of potassium nitrate in prilled form and when i crush it up it clumps together, ball milling it was extremely ineffective btw. I then made a batch of BP and compared to my previous batch (kno3 was powdered & expensive) it seems to clump together in small chunks. When i opened the ball mill there were large chunks of it stuck together which were easy to break apart. Does anyone have any ideas why? and is there a way around this problem?

Seeing as the kno3 was prilled could there have been some sort of clumping agent added?



Cheers

Edited by marble, 29 April 2007 - 06:48 AM.

[Andrew]

Purchased a 50kg bag of potassium nitrate in prilled form and when i crush it up it clumps together, ball milling it was extremely ineffective btw. I then made a batch of BP and compared to my previous batch (kno3 was powdered & expensive) it seems to clump together in small chunks. When i opened the ball mill there were large chunks of it stuck together which were easy to break apart. Does anyone have any ideas why? and is there a way around this problem?

Seeing as the kno3 was prilled could there have been some sort of clumping agent added?
Cheers

Welcome to the forum, nice first post.

Your describing very typical Potassium Nitrate behaviour. KNO3 can absorb water from the air and become quite damp, not quite to the degree that Ammonium Nitrate or Sodium Chlorate does though.

Tip for storage, don't leave out in the open, keep in cool dry sealed container.

Try getting a small batch of raw KNO3 and heating it up under a strong lamp, it will dry out and go really fluffy when crushed. When I've milled raw KNO3, and left it over night it has formed one massive clump, which as you have already observed breaks up really easily.

Tip for milling, mill a smaller batch, then before opening give the jar a really good shake. Then follow rule one.

Finely powdered KNO3 has a shelf life if you will. After time, in the presence of enough water (which is very little) it recrystallises to form larger clumping crystals. This effect is particularly well know and observed in Potassium Perchlorate. One day it is nice and soft, and with in two to three days it is like a brick, no joke, I reckon you put easily put it through a car windscreen it is that hard. KNO3 behaves in a similar way but again not to the same extent.

Tip for Storage, keep powdered KNO3 in a half full zip lock bag and massage it every week or so to break up any start at clumping.

When you make BP the charcoal usually has the capacity to absorb the vast majority of the water, BP will stay powdered for half a year or so before it starts to turn hard because of the same mechanism as described before.

Tip for Storing Meal, give the jar/bag a shake very couple of months or so to keep it in fine powder form.

It sounds like you have too much water in the equation, I don't know of any clumping agents used in KNO3, it completely defeats to object of the applications of the material. Farmers like free flowing material as it is far easier to spread. It some time has free flow agents in!

For your description it definitely sounds like too much water. Prilled i.e. in granular (3-6mm) form, is made in one of two ways, the KNO3 is melted under very controlled conditions and frozen in pellets. Or the cheap way, it is dissolved in water and the water is driven off to form larger crystals, however, not all the water is driven off as it would make the pellets turn into a fluffy mess. You would probably do well to put the KNO3 in a desiccator or cook it on a low heat (140℃) in the oven for an hour or so. And then you should be sorted, just keep it as dry as you can after that.

Do report back on how it goes.

BTW, don't up BP in the oven to dry .

[marble]

Cheers mate,

Ill give that a go. If that fails i can dissolve it in water and filter out the pure crystals and dry those. I'm fairly sure its fairly pure (burns well with standard sugar).





The clumps in the photo fall apart when touched

I have dissolved about 120g (kno3) in hot near boiling water, its has cooled down and there are large crystals so ill refrigerate it and filter them out and then try drying them.

Edited by marble, 29 April 2007 - 11:53 AM.

[marble]

Filtered out the crystals and dried in the oven on 150c for maybe 30 mins (not long enough it seems), had to break them up and tried some more bp. results were better but not great. Im not to keen on having this stuff drying in the oven for hours on end in something we use daily (kno3 isnt that toxic.....)

[Creepin_pyro]

How long are you milling for? I'm fairly sure that over-milling can lead to BP clumping like that...

[aquarius]

Well, does it burn ok?
One way could be to wet and granulate the powder, using hot water and a touch of alcohol. If the powder burns ok straight from the mill, this might save your batch.

[Andrew]

That BP looks absolutely fine. The more you mill it the finer it becomes. As it roles around in the container, if it is fine enough, it will form soft clumps like that, just like making a snowball. I would not worry about that as it is perfectly within limits of what is considered normal. It's good in colour as well, how fast does it burn? I suspect you've good a good batch there...

Looks like job well done! And a little undue alarm! Do report on how it burns.

You still have to be careful to avoid long standing BP from clumping, as it goes as hard as concrete over the period of six months or so. Hard enough to require you to hit it hard enough to consider not doing it, and just bin the batch. Keep shaking it every month or two to avoid real clumping, or develop the hobby that much that a batch never lasts that long!!!

[pudi.dk]

If you don't want the clumps just run it through a mesh screen. Although I don't think it's just unnecessary work.

[marble]

Burns well but i cant pour it at all which make filling small tubes very hard. Been looking around and have been told i should add some cabosil to it as it absorbs water and is a anti clumping agent. Does that sound alright?


Only problem is its not cheap


Cheers

[Andrew]

Cab-o-Sil is a fairly expensive free flow agent (you don't need much), but you really do not need it, your BP looks and sounds fine when doing small tubes, use a small spoon or the handle of a spoon. Or use a funnel and ram it past the throat. It's standard practice because BP is like that. Making it run like granulated sugar is not that easy, because BP is more like icing sugar.

Edited by Andrew, 01 May 2007 - 04:37 PM.