6 replies to this topic

[knackers]

could someone please shed some light on the use of hygroscopic sulphates for strobe stars please, namely calcium sulphate and magnesium sulphate,
would it be acceptable to use the afore mentioned if it was bound with NC laquer and then primed, or would i be wasting time and chemicals ?

[Arthur Brown]

Calcium sulphate is plaster of paris! The powder is the hemi hydrate form and the lump is the 4H2O form. Both work. Weingart suggests an alcohol based binder others suggest just wetting them to set hard. In fact I have a formulation for a underwater illuminating flare using plaster and Mg

[knackers]

Excellent ! i was hoping they would be useable, thanks Arthur

[MDH]

could someone please shed some light on the use of hygroscopic sulphates for strobe stars please, namely calcium sulphate and magnesium sulphate,
would it be acceptable to use the afore mentioned if it was bound with NC laquer and then primed, or would i be wasting time and chemicals ?

Hygroscopic compositions can be protected with waxes and various rubbers dissolved in solvents such as acetone. KNO3 and Sugar for instance is protected by paraffin oil or wax.

There is room for development. I imagine chlorowax could be used to protect copper sulfate. Though, I can't do such tests myself, so it only remains a suggested thought.

[seymour]

Rubbers, Waxes, or Nitrocellulose.

NC is superior in this regard, which is why it is used in Ammonium perchlorate/Mg strobe compositions.

[Arthur Brown]

It's more the amount of water contained! CaSO4 is a hemi hydrate as a flowing powder and sets to plaster as a tetrahydrate, so the wetted comp contains four waters per molecule of sulphate. Lithium salts simply continue to take water from the atmosphere and delequesce to a liquid.

The properties of the dry mix govern the properties of the product, if there is enough energy content then the water will be boiled off, or enter the reaction.

The properties of the stable comp govern the shelf life, once plaster has it's water or crystalisation then it absorbs no more from the air and the comp can stabilise, Lithium salts tend to go to a solution in their water accumulated by deliquescence and the comp can use this liquor to enable other reactions during standing, hence reducing the shelf life, including to the point of unusability.

[Mumbles]

I've heard from respected manufacturers that MgSO4 strobes are beautiful, but have a shelf life of about 2 weeks. Potassium sulfate or Barium Sulfate both make very nice white strobes.

Why would you mess with copper sulfate when blue and purple strobes are so easy with Potassium or barium sulfate?