Metal post

(snip)

Please explain this, it sounds like an oxymoron.

David

Sure are. :-)

Yes, when magnesium burns in steam, or when you have a largish chunk of burning Mg and throw water on it, the Mg combines with the oxygen from water and releases hydrogen gas. And the H2 burns in air. Lots of fun.

Mg + H2O --> MgO + H2

Similar reactions with CO2 and with sand:

Nope. Say you have a reaction that "goes" but is much too slow, such as nitrogen reacting with hydrogen to give ammonia. A *catalyst* is something that makes that sort of reaction go faster. The catalyst is recovered after the reaction, it is not consumed.

When magnesium burns, it's *consumed*. Gone.

And in case the inevitable question arises....no, you can't economically fuel a car on magnesium or hydrogen or as long as the fuel chosen is obtained by electricity. UNLESS that electricity is generated from an inexhaustible source (sun, wind) or cheap renewable source (plant matter). To make Mg or H2 requires electrical energy that is exactly equal to (well, MORE than) the energy obtained by burning that material.

It's the whatever law of thermogoddamics, I forget which one. :-)

-- Best -- Terry

The Second, TANSTAAFL.

jsw

Sigh. Don't they teach anybody elementary physics any more? Extracting hydrogen from water requires more energy input than can ever possibly be recovered by burning the hydrogen.

It's called "conservation of energy," one of the fundamental "Laws of Physics."

Hope This Helps! Rich

There are only a couple types of extinguishing agents that will actually put magnesium. Class D agents like Sodium Carbonate, Graphite/Copper powder and similar.

Sand, Dirt and the like will work because they stop all oxygen from reaching the mg.

You can use water BUT you need a LOT of it VERY fast to do any good. You need to drop the entire amount of magnesium below ignition temperature and keep it there long enough for the reaction to stop. Not easy to do even with a fire hose!

OH and FYI, for folks who think they don't need to worry about it. Don't look over your vehicles! MANY parts are made of magnesium alloys.

You beat me to it (except for point 3, which I hadn't thought about).

What I'd like to know is what these bars were. ISTR that tracer rounds are made of (or contain) magnesium. I suppose these could have been part of some sort of incendiary device which hadn't gone off properly?

We surmised that they were flares that did not ignite. Some flares are for illumination, others are to fool enemy radar and missiles.

Steve

OK, so ill be patient and hope you follow. Theres this elderly guy walks into my hardware store looks at the pick and shovel and wheel barrow section. So I goes over and ask if I can help. He says he needs to dig a trench what size I ask? he replies its 100 yds wide,2 yds deep and 500 yds long so I ask how long does he think it will take? he replies not very long. So,

1. as an sales person, do I agree with him? saying the tools are ideal for his job and ability and sell him the tools he asks for? Or2. do I take him outside and show him the Euclid excavator that will do the job without taking the rest of his lifetime and kill him in the process? the Co I worked for would have fired me on the spot if I had advised option 1. Ted.

Just as I did when I used to sell stuff, you sell the customer what he needs to get the job done and he'll be back when he's ready for the next job.

Sales and Marketing is where someone decides how to sell the product before it's out of R&D and before the specs are known. See "Dilbert".

David

It's surprisingly hard to get solid magnesium to light up. The cases of NeXT computers were cast from magnesium, and Simson Garfinkel set out to light it up. He had to heat it up significantly (like, with a torch) to ignite the solid metal:

No problem there whatsoever. I have a torch.

Steve

Not real hard in a vehicle fire....

Yes, clearly so. If you do this, the odor of ammonia in the air is unmistakable. The free hydrogen combines with the nitrogen from the air. If there's hydrogen floating around, that must have come from the water.

First, you would have to supply a lot of magnesium and get it hot enough to ignite. This is likely even more energy-intensive than electrolyzing water, not to mention the fire hazards and cost of the magnesium.

Well, as any chemist of physicist would know, the heat of formation of water is really high, and there's no way to get at the hydrogen without investing that much energy. There are tricks to lowering that energy by moving into a different set of initial conditions, like heating the water to 1000 C in a high pressure cell, and then recovering the heat and pressure when you bring the H2 and O2 out of the cell. But, that all involves more complicated machinery.

Finally, if you have to crack the water apart and then just want to burn in in an IC engine, or use it in a fuel cell, you just get the same energy back out, so it almost HAS to be a losing proposition. If there was an easy way to circumvent the laws of thermodynamics, somebody would have already figured this out by now.

Jon

Actually, the guy you want is George Goble at Purdue. Just Google George Goble and you should find info and links. Dave Barry just reported on George's exploits. I sold George a compressor that he used in some tests of his R-12 refrigerant replacement formula.

Jon

Yeah, the old VW microbuses had a magnesium crankcase - or was it transaxle? I saw one go up, the firemen were just standing around watching it burn. It started dripping big globs of white-hot metal on the pavement. Then, another fire department combo truck pulled up and delivered what seemed to be a tiny liquid-type fire extinguisher. They sprayed this yellow stuff on the fire, and then two guys with booster hoses ran up and let it have a blast of water. It was like a 4th of July ground display, with streamers of white hot metal flying in all directions. Totally AWESOME, and if these guys didn't have the special high-temp shielding suits on, they would have been severely burned.

I was amazed at how little damage it did to the pavement, if you didn't know about the fire, you wouldn't have even noticed the spot.

Jon

I burned magnesium on concrete, and the concrete spalled, it was fun to watch.

Be nice, Ted is a real metalworker, please don't drive him away.

Wes

The article says it was difficult to ignite because it was a magnesium alloy designed to be fire resistant.