Potassium Nitrate.. Hygroscopic?

[ghost808]

Hey i recently started to realize that when i would grind up just potassium nitrate by itself and let it sit, it would become really clumped up and seem like its really damp. I stuck my finger inside of it and it felt dry but in about 45 seconds the KNO3 on my finger became really wet. Like sweat....

And i was just wondering if potassium nitrate is hygroscopic, and how much it is.

Also is there a solution? Can i add in some Cab-O-Sil to make it not like this?

 

Or am i all wrong and just imagining things?

Thanks

[ChrisNZ]

Good question. I was wondering this myself too.

 

This is from Wikipedia:

It is not very hygroscopic, absorbing about 0.03% water in 80% relative humidity over 50 days.

Source

 

I guess it is hygroscopic.

 

Until I get better sorted and find some air-tight containers I keep mine in dual zip-lock bags. The first has the KNO3 in it, I lay it down and fill the whol area of the bag before sealing, and try to puch out as much air as possible. Then place that bag upside down in another of the same size using the same method.

[ghost808]

Hmmm I wonder whats up with mine then... Maybe has some different types of agents in there.

Also i live in hawaii so... Yeah it always has a high humidity.

I'll try purify it and let you guys know the results.

[NightHawkInLight]

Hmmm I wonder whats up with mine then... Maybe has some different types of agents in there.

Also i live in hawaii so... Yeah it always has a high humidity.

I'll try purify it and let you guys know the results.

At 90-100% humidity it gets damp pretty darn quick, within a matter of hours.

[WSM]

Hmmm I wonder whats up with mine then... Maybe has some different types of agents in there.

Also i live in hawaii so... Yeah it always has a high humidity.

I'll try purify it and let you guys know the results.

 

Hawai'i?! Oh yeah, you ought to dry the nitrate with a food dehydrator or on a shallow tray in an oven with the temperature turned down low (try 150 to 200 degrees, max) before and after milling. Storing it in a zip-lock freezer bag with a desicant bag wouldn't hurt either. I live within a few miles of the Pacific Ocean and it's constantly 50% to 80% humidity here.

 

The thought of using Cab-O-Sil isn't new. The problem is, when you make anything that needs to be consolidated without binders, the Cab doesn't help it ram tight (it wants to stay fluffy and doesn't want to stay consolidated, if you understand what I'm saying). Plus, I'm told silica screws up glitter effect to some degree.

 

Which island? I have family living near Oahu's north shore.

 

WSM

[dagabu]

Hawai'i?! Oh yeah, you ought to dry the nitrate with a food dehydrator or on a shallow tray in an oven with the temperature turned down low (try 150 to 200 degrees, max) before and after milling.

 

WSM

 

Keep in mind that with a gas stove (you are probably electric) that water is part of the exhaust and it can lead to very long drying times. The food dehydrator works well for me.

[ghost808]

Hawai'i?! Oh yeah, you ought to dry the nitrate with a food dehydrator or on a shallow tray in an oven with the temperature turned down low (try 150 to 200 degrees, max) before and after milling. Storing it in a zip-lock freezer bag with a desicant bag wouldn't hurt either. I live within a few miles of the Pacific Ocean and it's constantly 50% to 80% humidity here.

 

The thought of using Cab-O-Sil isn't new. The problem is, when you make anything that needs to be consolidated without binders, the Cab doesn't help it ram tight (it wants to stay fluffy and doesn't want to stay consolidated, if you understand what I'm saying). Plus, I'm told silica screws up glitter effect to some degree.

 

Which island? I have family living near Oahu's north shore.

 

WSM

 

 

 

I live on oahu.. more on the east side though.

 

 

Well if i was to just make the composition as soon as i grind up the nitrate would that help the process? Or would it still become a damp. For example should i just make black powder as soon as i finish?

[Mumbles]

It still gets damp, though the charcoal in BP helps to keep it from clumping. I never noticed it to be a problem, but my nitrate was probably saturated to begin with. When I dried my nitrate I gave it 4hr in a 250F electric oven stirring every 30 min. It clumps up pretty good for the first hour, so maybe stir every 15-20 min. I ground it to -30 mesh for this process. The first time I did this I weighed it every 30 min until I got 3 consecutive consistent measurements. I found my nitrate had 0.8% moisture in it. Even if I put freshly ground material into a sealed container it still clumped.

 

I often hear of calcium nitrate being a contaminant in some KNO3, and it's fairly hygroscopic. You may want to try to do a flame test on your nitrate. Mine always tested with a clear lilac flame and pretty much neutral pH, so I have no idea what was in there.

[50AE]

Mine does absorb some moisture, when humidity is between 80 and 90%.

[billofca]

Hey i recently started to realize that when i would grind up just potassium nitrate by itself and let it sit, it would become really clumped up and seem like its really damp. I stuck my finger inside of it and it felt dry but in about 45 seconds the KNO3 on my finger became really wet. Like sweat....

And i was just wondering if potassium nitrate is hygroscopic, and how much it is.

Also is there a solution? Can i add in some Cab-O-Sil to make it not like this?

 

Or am i all wrong and just imagining things?

Thanks

 

Are you sure you are talking about potassium nitrate and not sodium nitrate (Chile Salt Peter)? Sodium Nitrate is very hygroscopic and will actually become wet like you said. Potassium nitrate is only a teeny weeny bit hygroscopic and it won't wet your fingers. The little bit of moisture Potassium Nitrate can pick up from the atmosphere tends to cause the crystals to grow back together and form hard lumps and cakes. I lived in Hawaii for 3 years and the humidity there is no where as bad as it gets in New York in the Summer. The reason is hot air absorbs more water for a given relative humidity, and the summer temperature in New York gets hotter than in Hawaii. Hawaii's mean summer temperature during the day is in the low to mid 80sF with it rarely going over 90. Yet I've never had Potassium Nitrate ever wet my fingers in NY on the worst hot humid days.