Corrosion boric acid with magnesium and magnalium

[Giammy7]

What does this corrosion cause?Possible dangers?

 

[Zumber]

Nitrates reacts with metals in presence of water.

Like uncoated aluminium reacts with nitrates in presence of water/moisture to produce ammonia and this is base driven reaction to prevent this a percentage of boric acid is added which is weak acid.

Boric acid only works in favour of aluminium nitrate reaction.

Magnesium and magnelium reaction in presence of water is also dangerous reactions in this case boric acid doesn't work rather it aids the reaction that's why it is totally avoided instead magnelium or magnesium is treated first with potassium dichromate or linseed oil then it is well dried and used.

Note-potassium dichromate is extremely poisonous and not touched with bare hand or inhaled it's fumes or not inhaled it's powder anyways.

Not try to attempt dichromate coating without any prior knowledge regarding health safety.

Edited July 31 by Zumber

[All10Fingers]

Is Indian blackhead considered "coated" aluminum? I believe I read before charcoal is added to prevent oxidation, which leads me to believe it's coated. But I don't actually know that as a fact or not

[Zumber]

I honestly have no idea whether it is coated or not.

At the time of manufacturing aluminium powder if stearin is added to prevent aluminium particles sticking together that aluminium is considered to be coated aluminium and it feels slippery between fingers.

Charcoal doesn't protect nitrate aluminium reaction.

As I have read it's data sheet it is manufactured by melting and ball milling not by stamping I assume it is uncoated. They haven't mentioned whether coated or not.

Here is data sheet of Indian black aluminium.

000.pdf

[Giammy7]

The dark aluminum powders are passivated, I don't know if this avoids the nitrate/aluminium reaction 

[All10Fingers]

If you read the "list of pyro terms and chemicals" pinned at the top of this section, it says Indian blackhead is coated. But doesn't say with what, why, or how.  Now I gotta go look up what passivated means

[Zumber]

2 hours ago, All10Fingers said:

If you read the "list of pyro terms and chemicals" pinned at the top of this section, it says Indian blackhead is coated. But doesn't say with what, why, or how.  Now I gotta go look up what passivated means

Visit MEPCO company website to know more about it or write email to them so that they will provide more details.

https://www.mepco.co.in/

[Giammy7]

Aluminum passivation is a chemical process by which a protective layer is created on the surface of the metal. This layer, usually composed of alum oxides or hydroxides.

This I found on passivation

[All10Fingers]

Thank you. I had thought the charcoal was added to prevent the formation of aluminum oxide. 

[Zumber]

1 hour ago, All10Fingers said:

Thank you. I had thought the charcoal was added to prevent the formation of aluminum oxide. 

Atomized aluminium,granulated aluminium or shredded aluminium foil is used to make aluminium power which is hammered or ball milled into thin flake in stamp mill and to prevent this flakes sticking together ,before milling again stearin is added this aluminium is stearin coated aluminium which feels slippery between your 🤞. And is is considered to be stable with aluminium nitrate reaction.

For dark aluminium, aluminium sheets are glued to very thin low ash paper and it is carbonised using heat and this carbon coated flakes are milled further into very fine powder without using lubricant so this aluminium is not under coated aluminium category.

Charcoal powder is not actually added while manufacturing dark aluminium and resulting dark colour may be a result of low ash carbonised paper.

[Mumbles]

Zumber, you might want to stop talking about things you have no idea about. I've seen an increasing amount of you trying to talk about things you're clearly not well versed in.

Blackhead aluminum, as are most flake aluminums, has some degree of stearin or stearic acid in it. It's quite obvious, especially when opening a fresh drum. It has sort of a sweet crayon odor to it to me at least. This is also exemplified in the "matter soluble in organic solvent" line of the specification.  It's not as coated some bright flakes can be.

You may also want to compare to German Blackhead, which is very clearly stated there is a coating.  https://www.eckart.net/en/standart-pyro-5413-h-super-aluminium-powder-047505e50

These types of materials are not at all safe from chemical reactions that can occur in stars.  In fact, they're one of the worst offenders.  The coating may keep them shiny or from impact welding together during manufacture, but it doesn't do a lot toward preventing chemical attack.  The process of mixing pyro compositions could distub the layer or allow chemicals it may react with to be intimately bonded to the surface due to the sticky nature of the waxy coating.  

The real driver of chemical reactions in stars is the disruption or dissolving of the passivating oxide layer on the surface of the metal.  Boric acid is not effective for Mg or MgAl because the oxide coating dissolves in both acid and base, where as aluminum oxide only really dissolves in base readily (with some exceptions not relevant to pyro).