Why has magnesium fallen out of favor?

[AzoMittle]

It seems almost all older texts use magnesium for colored/electric stars, while almost all newer formulas use magnalium. When did this switch occur and why? What benefit/drawback is there to each? Both have to be treated and they cost roughly the same.

[pyrokid]

I never heard that MgAl has to be treated. Isn't this property the reason it has come into favor? MgAl gives much of the color purity of Mg with the stability of Al.

 

I believe the cost equality argument comes more from suppliers playing games with the prices than reality. The only image many of us have of the supplies market is that provided by the suppliers.

[Seymour]

MgAl is avaliable, but in the days of old it simply was not.

 

Like Pyrokid said "MgAl gives much of the color purity of Mg with the stability of Al." to be accurate I'd change it to say "much of the stability of Al" since Al is definitely more stable.

 

MgAl definitely does not have to be treated in all situations. With NH4ClO4 I coat with dichromate but otherwise just use it as is. It is attacked by KNO3 and water but in KClO4 it has a long shelf life. I'd say that most people don't treat MgAl and expect coloured comps with it to last years, even if wetted with water. I don't have that much experience with Mg, but I feel that Mg alone exposed to only air would not be very good after a year or two.

 

Ultimately MgAl is a lot more stable. Although many of the issues with Mg can also occur with MgAl, it is much, much worse with pure Mg.

 

While the stability difference is by far the biggest benefit to MgAl, it also has a lower boiling point and so it is easier to turn it in to a gas, avoiding sparks and making a cleaner coloured flame.

Edited March 15, 2016 by Seymour

[lloyd]

Seymour,

Your use of the term "stability" is wrong, and misleads the reader. Mg is every bit as "stable" as aluminum. It happens to be more reactive to oxidizers than Al, but that has nothing to do with 'stability'. Both Al and Mg (and their alloys) are solid metals that are stable at normal temperatures and pressures.

 

Also, the boiling point of an alloy has virtually zero effect on its use as a pyrotechnic fuel. Surface area and reactivity play much larger roles in determining burn rate and "cleanness" in pyrotechnic duty. To the point, Mg/Al 50/50 alloy does NOT produce a cleaner-coloured flame than does Mg.

 

In fact, when it can be used, magnesium is the preferred metal for 'clean' fires.

 

The fact that it is so much more reactive than Al prevents its use in some formulae, but that has nothing to do with the cleanliness of its burning.

 

LLoyd

[AzoMittle]

Also, the boiling point of an alloy has virtually zero effect on its use as a pyrotechnic fuel. Surface area and reactivity play much larger roles in determining burn rate and "cleanness" in pyrotechnic duty. To the point, Mg/Al 50/50 alloy does NOT produce a cleaner-coloured flame than does Mg.

 

In fact, when it can be used, magnesium is the preferred metal for 'clean' fires.

 

The fact that it is so much more reactive than Al prevents its use in some formulae, but that has nothing to do with the cleanliness of its burning.

 

LLoyd

 

 

Lloyd, would you mind giving a more in depth explanation of this? Or perhaps point me to some reading material? Much appreciated.

[Seymour]

Ok, Lloyd, you are completely right about the lower boiling and melting points having not having much to do with cleanliness compared to particle size.

 

I am aware that hot Al2O3 produces more visible light than MgO and this means that MgAl will also "wash out" colours more than Mg, especially when there is enough chlorine hanging out to make much of the Mg form a chloride, which gives off much less light than Aluminium chloride or either oxide.

 

And certainly Mg is the optimum metal fuel for "clean" flames. I'm assuming that this is a large part of why coloured flash is all Mg and not MgAl. I love using Mg simply because it is the best but also avoid it because it is difficult.

 

Perhaps I made it seem like I was saying that MgAl is cleaner than Mg, which I did not mean and is not true. I guess the lower mp and bp are largely irrelevant, but I was too keen to think of differences.

 

As for Stability, I'm not sure that I was wrong. Perhaps I just don't know the true meaning of the word in this context, but I suspect I was just lazy and did not clarify the details of what I was trying to say.

 

You seem to be talking about volatility? Yes they are both stable in the fact that they are solids at standard pressure and temperature. However unless treated both Mg and MgAl will react with air at room temperature. I consider this to be a form of chemical instability. Mg does it A LOT faster than MgAl.

 

If I put the word "chemical" before "stability" does this correct things, or not? Personally I think that if substance undergoes a chemical reaction in air at room temperature it is not very stable (in a chemical reaction way). It can mean reactive too, but I feel the two are not the same.

 

I'd say Iron is much less (chemically) stable than Aluminium, in the context of both metals in air, and some pyro chemicals, though of course Aluminium is much more reactive. What do you have to say about this?

 

And yes, of course you can come up with conditions in which the reactivity of Aluminium causes it to corrode much faster than Iron, but I'm talking about this in specific situations, specifically in air when the Al2O3 layer holds up. I suspect Iron corrodes faster than Al in most pyro comps too.

Edited March 15, 2016 by Seymour

[Puls0r1]

Shouldn't melting point of a chemical and boiling point be more important then you are saying it is LLoyd? if I were to say make a fire work with MgAl and it burns hot enough to boil the metal then the display would not be as "colorful". am I right about that or am I being stupid?

[lloyd]

Seymour,

"Reactivity" is the word you're looking for.

 

Pulsor,

Why would you use a metal fuel, the end result of which is to boil it off as a vapor? The purpose of metals in pyrotechnic compositions is either to serve as fuels or spark generators.

 

If a metal is boiling in the fire, it's not serving its intended purpose. Besides - as I said - powdered metals that do NOT survive the fire (like titanium for sparks) are consumed by the oxidizer IN the flame. Why would you make a composition hot enough to lose all its color, and become white, unless your purpose was a white flame. (and um.... where did the high-temperature fuel come from to make it that hot? Oh... burning metal... I see!)

 

<G>

Lloyd