Bicarb Stars, Drying Issues?

[psyco_1322]

So I had some stars laying around that have a bicarb in them, and with high humidity, they just crumble. I know I have had some batches of Win20 that were stubborn to get dry, but never thought about the bicarb causing it before. Is there any way to get around this issue other than using a non-aqueous binder, and hoping they don't soak up moisture after they dry?

[TheArchitect23]

Harbor freight has a nice dehydrator for $20 that drys stars well. Edited June 5, 2013 by TheArchitect23

[Mumbles]

Why would you ever dissolve bicarbonate into your spraying water?

 

You might be having an adverse reaction if your stars are staying wet. I've never personally had any problems with most bicarbonate containing stars. If the typical nitrate/Aluminum reaction starts, which is promoted by basic things like bicarb, you generate potassium and/or hydroxide in the process. Those two things are extremely hygroscopic, and might be the cause of your soggy stars.

[TheArchitect23]

doh!

Meant boric acid!

and because is prohibits the effects from the aluminum and nitrate

Edited June 5, 2013 by TheArchitect23

[psyco_1322]

Why would you ever dissolve bicarbonate into your spraying water?

 

You might be having an adverse reaction if your stars are staying wet. I've never personally had any problems with most bicarbonate containing stars. If the typical nitrate/Aluminum reaction starts, which is promoted by basic things like bicarb, you generate potassium and/or hydroxide in the process. Those two things are extremely hygroscopic, and might be the cause of your soggy stars.

 

Who said anything about it in the "spraying water"? It's in the comp...the wetting mix is just alky water. There really is no fine Al to cause that kind of reaction, and I doubt that is the issue. Sodium Bicarbonate is quite moisture hungry.

 

I have made stars with bicarb and got them bone dry, and they are good. These stars, I tested some and they shattered, so I was curious if they became a bit wet or if there was just not enough binder. These I put into the drier, made sure they were good and dry. A few days later in a room of nearly 75-80% humidity, I can crumble them back to powder in my fingers. When they were dry, they were a bit weak, I plan to add more binder, but they were nowhere as weak as they are now.

 

Do you think more binder could inhibit the ability for them to draw in moisture? I new batch with more oxidiser and binder set with a fan blowing on them for about 4+ days...they still don't even have the slightest clink when tapped together, if I was to squeeze them gently, they would crumble.

[marks265]

How much and which binder did you use? I've swapped between bicarb and sodium oxalate a lot last year and never had an issue. Are you putting them in a storage container of some kind?

[marks265]

and were they pumped or rolled?

[Carbon796]

Not to sound rude, but why don't you post the actual formula your having problems with. And what you used to wet the comp with. The phrase, I had some stars laying around with bi-carb in them. Doesn't give us enough information to give you an educated answer.

 

- Rich

Edited June 6, 2013 by Carbon796

[AirCowPeacock]

I figure when they dryed out a little sodium nitrate was formed (from you KNO3) maybe that's you hydroscopy problem. Maybe try using less water to bind.

[psyco_1322]

There is no formula, it's a batch of scratch stars. The first test stars were hand pumped, then second was cut. The wetting solution was water, with some isopropanol in it.

 

I had guessed at having enough dextrin, but I think I was on the low side, so this last test batch got an extra 3% to harden up the stars...once they dry.

 

KNO3

Sulfur

Charcoal

Dextrin <----------that's the binder!!!

Coarse Atomised Al

Atomised TI

200mesh Magnalium

Mixed FeTi

Fe2O3

NaHCO3 (~5%)

A Pinch of Bright Al from some leftover star comp I added in.

[Carbon796]

Was the charcoal air float or coarse, did you use any boric acid in the formula ?

I always write the formula I'm going to mix on a post-it note for mixing in the shop. That way you don't have to guess what you have in there, and you can adjust it as your mixing if you change something. Then later record it in a note book if its worth keeping.

[psyco_1322]

It was airlfoat, not that it really makes a difference, but it was commercial airfloat. This was a large batch, to make use of some bad star comp (effect I was after didn't happen, but the stars burning fine). There was no intent to later duplicate the stars. I made a small sample to test, so I would know if I need to adjust something. I had a bit of fallout, which I didn't know if it was from being damp or not, or if I needed to add some extra oxidizer. No boric acid was used, there is no reason too, I had never noticed any kind of amid?(think thats the right word..) reaction with them.

[FlaMtnBkr]

Did you happen to use the cheap atomised aluminum that Cracker was selling?

[psyco_1322]

Did you happen to use the cheap atomised aluminum that Cracker was selling?

 

Negative, this stuff is some crap skylighter was handing out a few years ago, it's got to be 30-40mesh.

 

Also I have had D1 glitter do the same thing. If I leave the stars out in the open air, and it's humid, they get damp and soft. I'm certain it's the bicarb. Although I can not recall a time when any Win20 set out and got damp, just some batches that seemed to be "driven in".