coating magnesium

[MadMat]

I know of a few methods of applying a "protective" coating on fine magnesium, such as; dichromate, linseed oil. An idea occurred to me today, what about using 'ol WD-40? I know that it is supposed to leave behind a protective coating after it dries and it would seem to me that it would dry a lot faster than linseed oil. Not to mention I think the coating would be much thinner and possibly produce less interference with flame color Anyone ever try this? Any ideas on how effective it would be?

Edited May 29, 2016 by MadMat

[lloyd]

The "protective coating" left behind when WD-40 "dries" is a motile oil. All it will do is make a sticky mass of the Mg after coating, and if dispersed in a mass of hard particulates (like oxidizers) will get rubbed off. It's liquid when 'dry' -- not a solid.

 

Dichromate leaves a conversion layer on the surface of each granule, and linseed oil coating leaves a hardened, dried 'varnish' (almost identical to old-fashioned 'spar varnish') on each particle.

 

Lloyd

[MadMat]

Do you know if the Magnesium chromate layer disassociates when subject to the heat of the flame? Otherwise, by creating the conversion coating, you are actually wasting a small percentage of the magnesium. I know this may sound a bit OCD or even anal retentive, but....

BTW, I worked in laboratories in the metal finishing industry, that's why I know about chromate conversion coatings.

If it does disassociate, I figure that will be my method of choice. This is because I am wondering if linseed oil will "dirty up" the flame color. Again I guess this may sound OCD, but one of the things I like about magnesium is that it seems to produce a better, more pure, color.

Edited May 29, 2016 by MadMat

[lloyd]

I assume that whether or not it dissociates depends upon the combustion temperature of the particular formula.

 

You're right... you sacrifice a tiny bit of the Mg if it does not dissociate during combustion. But rationally, the formula would have been adjusted to meet the need of more-or-less of the metal fuel as required after the coating process.

 

In any case, whether or not it dissociates, there will ordinarily be residual un-reacted dichromate dust in the mix, and that will serve as a catalyst. So, "pretty much everything changes" in a pyrotechnic mixture when you use conversion coatings to protect reactive metals.

 

Lloyd

Edited May 29, 2016 by lloyd

[MadMat]

I recently made some small samples of metal fueled red comp (made them small for safety). and test fired just the powders. I tried magnalium, a 50/50 mix of bright flake aluminum and -40+60 mesh magnesium and then just the magnesium. I must say I really preferred the look of the magnesium only comp. So now I figure I'm going to need to coat the Mg if I'm going to wet this comp and make it into stars.

[lloyd]

Well... the difference is plain, if you consider the combustion products.

 

Aluminum oxide is a high-temperature refractory substance, and opaque at ordinary combustion temps. MgO is also, although it can be mitigated, and often IS done so in carefully balanced formulae:

 

Its formation can ...."be inhibited by presence of carbon monoxide, either by negative oxygen balance of the composition in presence of organic fuels, or by addition of the colorant in the form of an oxalate, which decomposes to carbon dioxide and carbon monoxide; the carbon monoxide reacts with the magnesium oxide particles to gaseous magnesium and gaseous carbon dioxide."

 

Quote from a wiki. Also repeated in many pyro texts.

LLoyd

[MadMat]

Hmm... considering that, I wonder if linseed oil might be a better choice.

[lloyd]

I'm partial to dichromate. The linseed oil ultimately makes a dirty, carbonaceous flame that tends to discolor things. A conversion coating doesn't.

 

LLoyd

[MadMat]

That's what I originally thought of linseed oil. I guess I'll go with the dichromate. Thanks for the info! I really need to get some pyro literature. Most of what I have come across as of yet, is really basic beginning information and doesn't contain anything like what you have just told me.

[lloyd]

Like we discussed in PM... there is NO better 'supply' you can purchase for your pyro hobby than every SCRAP of good literature you can lay your hands on!

 

Not only will it improve your understanding of things, it will ultimately save you more money than it cost.

 

Lloyd

[MadMat]

If you could only have one pyro book, what would the title of that book be? (this will be the first book I look for ).

[lloyd]

Wow! What a decision that would be to make!

 

I guess, if I had to choose, it would be almost a toss-up between Shimizu's "Fireworks: the Art, Science, and Technique", and Lancaster's "Fireworks Principles and Practice"

 

I _think_ for practical day-to-day applications, I'd lean toward Lancaster. It's a little more "application oriented", while Shimizu's is more artful.

 

I still communicate once or twice a month with Ron Lancaster... he's still working in pyro, despite his age! And he's still sharp!

 

Now... if I wanted a "builder's guide", I'd invest in the entire Pyrotechnica Series... but that's a bit of money. Worth every penny, but not cheap! (available from Prometheus Publications) (as an aside, it contains the articles now so famous about cylinder shell construction, in issues IX and XI)

 

LLoyd

[MadMat]

Thanks. Yeah I've been looking for Shimizu's book. There are a number of book resale stores around here that carry some rather unique stuff for GOOD prices, but so far nada. I guess I'm just going to have to open the wallet....

[schroedinger]

I would be with FAST and pyrotechnica 9 + 11 to cover the basics.

 

There also is the possibility to coat the mg with parlon.

[MadMat]

I tried coating my magnesium with dichromate, but failed to get a discernible color change on the Mg. I tried the 5% potassium dichromate adding boiling water... after which I filtered the water off and added a boiling saturated solution of potassium dichromate. I now have the Mg spread out on a plastic mat to dry. the only difference I see in the color is probably from the remaining dichromate on the metal. ??? For a short time I noticed a little bit of gas (hydrogen?) bubbling up, but it was not close to the reaction I was expecting.

As a side note, when working in laboratories in the metal finishing industry, there were a number of chromate conversion coatings. Some were applied to zinc plating, while there was one used on aluminum and aluminum/magnesium alloys. It was a proprietary coating called iridite, which gave the metal a base of yellow with a rainbow of colors throughout. The point I'm getting at is; this coating was done at room temperature, but, there was dichromate, some proprietary chemicals, a small amount of ammonium bifluoride (to dissolve any silicon from the surface), and about 2% (? this was a long time ago!) nitric acid. The parts were cleaned, dunked in the chromate solution for a few seconds and rinsed off.

[taiwanluthiers]

I tried dipping aluminum parts in a solution of dichromate and it doesn't do anything... might as well dip it in water.

[MadMat]

I am just wondering if my Mg is safe to use in stars now. I would feel better it I saw a color change on the MG.

[OldMarine]

I treat all of my magnesium and magnalium with dichromate. I've not noticed anything other than a slight reddish trace on the dehydrated metal. I actually have to spread the metal on white paper to see it.

[MadMat]

Well... that makes me feel better

[OldMarine]

Well... that makes me feel better

I actually doused some mg that was dichromate treated with peroxide and noticed no adverse effects.

I don't know what long-term effects might occur but there are none that I can find in the short-term.

[schroedinger]

I am just wondering if my Mg is safe to use in stars now. I would feel better it I saw a color change on the MG.

Make a solution of AP and put some of the mg into it. If you see some strong bubbling, it didn't work.

[MadMat]

I don't have any AP, but I do have KClO4 and since that's what is going to be in the stars I make, I suppose if it doesn't react to that I should be safe.

[pyrojig]

If Im not mistaking , it can react with perchlorate still ( The major issue is water based binders ) If your using a alcohol or acetone binding sys it should be fine . mag perch is very deliquescent, in fact a discantant in lab use. I would not take a chance in long storage of mag comps unless proper treating and precautions are taken .

[Rushfire]

I can vouch for the Mg not changing color with the dichromate treatment. Mixed up a measured aqueous solution of the dichromate, added a mix of milled 60-120 mesh MgAl + 325 mesh Mg 50:50 which bubbled profusely at first but then halted after about 10 minutes. Saw no color change so let it sit with occasional mixing for about 4 hours and still no color change. I guess the dichromate solution turned a little more yellow/green instead of orange...

 

Anyway, filtered the Mg out in some paper towel and dropped some in an AP solution with a little mixing and there was no reaction. To make doubly sure I added a pinch of untreated Mg powder to the AP solution and it began mildly fizzing and got cloudy. Strange since I have read the treated Mg should turn "brown" but eh... at least it worked.

Edited June 26, 2016 by Rushfire

[Crazy Swede]

If the magnesium powder is only treated with a saturated solution of a dichromate the conversion is actually not taking place to any larger extent and the particles are mostly just superficially covered with the dichromate after drying.

 

This method is still often effective enough and has the advantage of not reducing the reactivity of the magnesium as much as the true conversion method.

 

In the original method not only a dichromate salt is used but also an activator, something that can act as an electron donor during the reaction. I have always preferred magnesium sulfate, using the same weight as the dichromate (i.e. about 15 g dichromate and 15 g sulfate per 100 ml of water).