Milling KNO3

[JTO]

I decided to mill some KNO3 in my ball mill to get fine powder for later use, so that I would not have to powder it in a mortar every time I need it, and I got some really surprising results. I got no powder at all, instead, all of the KNO3 had turned into rock hard balls with sizes ranging from grape size to almost golf ball size. This was after 2-3 days of milling. They are so hard that I had to break them up with a hammer. I googled for some articles about milling KNO3 and they mentioned no problems. Any ideas?

[SharkWhisperer]

I decided to mill some KNO3 in my ball mill to get fine powder for later use, so that I would not have to powder it in a mortar every time I need it, and I got some really surprising results. I got no powder at all, instead, all of the KNO3 had turned into rock hard balls with sizes ranging from grape size to almost golf ball size. This was after 2-3 days of milling. They are so hard that I had to break them up with a hammer. I googled for some articles about milling KNO3 and they mentioned no problems. Any ideas?

Sounds like you had some moisture in there. KNO3 is mildly hygroscopic and wet chems and comps made with them are at risk of clumping (charcoal's another thirsty one). Dry it in the oven on a baking pan for an hour at 200-250F and mill it again. It shouldn't require days to mill KNO3 to dust...

[MadMat]

Was the humidity high when you attempted this? The humidity in my area has been sky high lately. I have completely suspended making anything until the humidity is lower. You don't want it too low either.

[JTO]

Sounds like you had some moisture in there. KNO3 is mildly hygroscopic and wet chems and comps made with them are at risk of clumping (charcoal's another thirsty one). Dry it in the oven on a baking pan for an hour at 200-250F and mill it again. It shouldn't require days to mill KNO3 to dust...

Thanks! I am going to try this. My mill is airtight so humidity should not be a problem after the oven treatment. Also, I am going to mill it for a shorter time, 24h maybe.

[JTO]

Why not too low? One would think the lower the better?

Was the humidity high when you attempted this? The humidity in my area has been sky high lately. I have completely suspended making anything until the humidity is lower. You don't want it too low either.

 

[SharkWhisperer]

Thanks! I am going to try this. My mill is airtight so humidity should not be a problem after the oven treatment. Also, I am going to mill it for a shorter time, 24h maybe.

You'd do well to store your dried/milled KNO3 in an airtight container with some desiccant such as silica gel packs or similar, if you're not using it all right away.

 

What kind of mill and media are you using that you need to mill anything for 24 hours??? That's an absurdly long time.

[MadMat]

When the humidity is very low, static electricity can become a problem. Static electricity can ignite things (like flash powder) and THAT is a problem

[rellim]

How pure is your KNO₃? Maybe it has some chloride in it.

[deepakpyro]

Thanks! I am going to try this. My mill is airtight so humidity should not be a problem after the oven treatment. Also, I am going to mill it for a shorter time, 24h maybe.

I am ball milling my granular nitrate. I used to ball mill for 30 mins max for BP and for other stars i mill it around hour or so max. But 24 hrs is waste of time and if you can't find diffence in particle size within 20 mins, then you have to fix your ball mill. What is the setup you are using?. What is media size and size of drum? RPM also matters

[Uarbor]

The one and only time I tried to Mill pure kno3 I got the rock hard balls. I put them in a mason jar in case I ever get desperate enough to break them up and use them LOL I had just made a batch of black powder with the same kno3 but I guess the charcoal absorb the extra moisture. It was shocking how hard they were. The best way to test for moisture is to put some of your chemical in a small ziplock bag and put it out in the sun with the bag semi inflated. Any moisture will condensate all over the inside of the bag and if there is that much you need to dry it. Edited September 3, 2021 by Uarbor

[dagabu]

Moisture and heat will do this and I think everybody has had a similar experience with clumping or like mine, one huge ball, including all my media as well!

 

I use silica gel cat litter in a cloth bag inside my 5 gallon pails of Kno3, it keeps it nicely dry. It's really the Charcoal that sucks up the water in my experience, so watch that as well.

[SharkWhisperer]

Moisture and heat will do this and I think everybody has had a similar experience with clumping or like mine, one huge ball, including all my media as well!

 

I use silica gel cat litter in a cloth bag inside my 5 gallon pails of Kno3, it keeps it nicely dry. It's really the Charcoal that sucks up the water in my experience, so watch that as well.

Yup. Before: occasional clumping, especially with longer runs (>4h) in a tiny hobby mill. Rarely in larger mill. Now: Never a clumping issue, ever. Even in small mills left running overnight.

 

Only difference is that I religiously oven-dry my KNO3 and charcoals before use, and store working comps in airtight containers with desiccant like Dag mentions.

 

The color-changing silica gel packs work well, are cheap, and can be recycled in the oven when drying chems. Their outside wrapper is similar to a thick tea bag and will instantly turn black on contact with charcoal, so need to be protected by wrapping in a coffee filter or even a piece of regular writing paper/newspaper.

 

It really is a simple fix for a common issue. 200-250F for an hour or so, stored warm before it cools down (while reabsorbing atmospheric water). Charcoal especially, can hold a hell of a lot of water and appear perfectly dry to the touch. I've measured 20% water weight (which will throw off your comp ratios for sure) and others have reported up to 50% and I believe them. KNO3 only grabs up a few percent of water but that's sufficient to make those hard rocks and cause clumping issues. A simple fix. Remember if using a gas oven to vent the oven air periodically and at the end so your chems are not just sucking up the water of gas combustion. Not a concern with electric ovens. Either way, simples!

 

This has been mentioned so many times in multiple threads here that it amazes me that people still run into clumping issues...

[dagabu]

Yup. Before: occasional clumping, especially with longer runs (>4h) in a tiny hobby mill. Rarely in larger mill. Now: Never a clumping issue, ever. Even in small mills left running overnight.

 

Only difference is that I religiously oven-dry my KNO3 and charcoals before use, and store working comps in airtight containers with desiccant like Dag mentions.

 

The color-changing silica gel packs work well, are cheap, and can be recycled in the oven when drying chems. Their outside wrapper is similar to a thick tea bag and will instantly turn black on contact with charcoal, so need to be protected by wrapping in a coffee filter or even a piece of regular writing paper/newspaper.

 

It really is a simple fix for a common issue. 200-250F for an hour or so, stored warm before it cools down (while reabsorbing atmospheric water). Charcoal especially, can hold a hell of a lot of water and appear perfectly dry to the touch. I've measured 20% water weight (which will throw off your comp ratios for sure) and others have reported up to 50% and I believe them. KNO3 only grabs up a few percent of water but that's sufficient to make those hard rocks and cause clumping issues. A simple fix. Remember if using a gas oven to vent the oven air periodically and at the end so your chems are not just sucking up the water of gas combustion. Not a concern with electric ovens. Either way, simples!

 

This has been mentioned so many times in multiple threads here that it amazes me that people still run into clumping issues...

 

 

Keep in mind that perfectly dry BP is prone to static and perfectly stoichiometric BP contains 0.75% moisture approximately.

[JTO]

You'd do well to store your dried/milled KNO3 in an airtight container with some desiccant such as silica gel packs or similar, if you're not using it all right away.

 

What kind of mill and media are you using that you need to mill anything for 24 hours??? That's an absurdly long time.

I have been milling Al powders for 2-3 weeks :-)

[JTO]

I dried the KNO3 in an oven, but it only lost a few grams of weight for 1 kilogram of KNO3. Then I milled it for perhaps 10 hours and it turned out OK. It still cakes in the jar but that is the normal caking of KNO3 which is unavoidable. I am not sure whether the problem was the humidity (although it was really low) or the excessively long milling time or both. In any case it is OK now. I have never milled BP because my mill is steel with steel balls, this was KNO3 only.

 

Sounds like you had some moisture in there. KNO3 is mildly hygroscopic and wet chems and comps made with them are at risk of clumping (charcoal's another thirsty one). Dry it in the oven on a baking pan for an hour at 200-250F and mill it again. It shouldn't require days to mill KNO3 to dust...

 

[pyroSHVRK]

I have a rock tumbler/hobby mill and i milled some kno3 for 24hrs with chrome steel balls and i ran into the clumping issues along with the steel balls rusting turning the powder orange.

 

I cleaned everything out and switched over to ceramic cylinders. Milled for 2 hours and i got the finest kno3 ive seen so far. I also made sure to put everything into the barrel outside where it was warmer and the moisture in the air was about 30%.

[Arthur]

Ceramic is good, being lighter than lead it enables you to run a properly filled mill jar in a commercial (cheap!) rock tumbler.

 

Yes damp material clumps! A little time spent drying the ingredients is well worth it. Also remember that mixtures are defined by dry weight not with unknown added water.