Sciencemadness Discussion Board - Magnesium and water

Magnesium and water

hkparker - 19-1-2011 at 21:27

As we all know, burning magnesium reacts quite vigorously with water (just look at <a target="tab" href="http://www.youtube.com/watch?v=rogZBXNqaMo">this... interesting video</a>

. I have done this reaction on a smaller (but still large) scale.

I have heard (from many sources) two explanations for this.

1) The heat of magnesium's reaction with air thermally decomposes the water to it's elements, then ignites it.

2) Water reacts with magnesium to afford magnesium oxide and hydrogen. The hydrogen quickly burns off.

So my question is what is actually happening? A little bit of both?

Sedit - 19-1-2011 at 21:53

I just assume its due to Magnesiums reaction with water being Mg + H2O = MgOH + H2. This is analog to Na or K in water except you must provide the initial heat in order to sustain the reaction.

I did a simular demonstration of the kids on new years since I didn't have fireworks albeit much smaller then these people by setting Mg on fire and knocking it into the snow. Caught me a little off guard since I only used a small amount and was still seeing green and pink for sometime after even though I quickly looked away.

MrHomeScientist - 20-1-2011 at 08:01

I agree with Sedit - #2 sounds more plausible to me. We already know Mg reacts with water in this way, and giving it more energy by igniting it would serve to accelerate that reaction. The hydrogen produced would then ignite from the heat, which is exactly the same thing that happens when sodium "explodes" in water (again, just like Sedit said).

I imagine you could test this by enclosing your setup so that air is in limited supply, and then immerse the burning Mg in water. If #1 is correct, it would produce its own supply of both hydrogen and oxygen and would continue to burn to completion. If #2 is right, it would only be making H2 and would run out of atmospheric oxygen with which to react and so would burn out early.

At least, that's what I think.

ScienceSquirrel - 20-1-2011 at 08:09

Magnesium will react with boiling water and a lot faster with steam.
I suspect that the water hits the burning magnesium, part of it is turned into steam and part of it to hydrogen and magensium oxide. The steam and hydrogen expands in a gas cloud mixing with air and then it ignites.
You can see burning pieces of white hot metal being thrown out of the fire pit by the explosions.
On the scale they are doing it, it looks like a good attempt at a Darwin award.
A bit bigger and standing closer and they might have scored.

[Edited on 20-1-2011 by ScienceSquirrel]

DJF90 - 20-1-2011 at 08:56

We should be happy that they're so willing to remove themselves from the gene pool...

Anyway, a nice way to show the reaction of magnesium with water is the following. Glass wool soaked with water is packed into the bottom of a boiling tube. The tube is mounted horizontally, and a small pile of magnesium is placed about halfway along the tubes length. A stopper with a glass tube leading to an inverted cylinder for gas collection (in a water trough) is attached. The magnesium is then strongly heated, and after a short while the glass wool is also heated, but much more gently. (The reaction setup is very similar to the cracking of hydrocarbons with alumina). Perform the reaction behind a safety screen and its preferable to use a bunsen valve. An old teacher of mine had this demo explode previously so do be careful.

MrHomeScientist - 20-1-2011 at 14:05

I just now watched the video, thats insane. The guy giggling like a schoolgirl and the other guy flailing around in the background were particularly hilarious.

I'd like to try this some day (on a MUCH smaller scale!), as well as its reaction with CO2 as in <a href="http://www.youtube.com/watch?v=EFdiMp_HzeY&feature=related">this video</a>. Basically I want to make a video about how dangerous burning magnesium is

edit: found a better video.

[Edited on 1-20-2011 by MrHomeScientist]

hkparker - 20-1-2011 at 14:20

Ill check out that video when I get home. Yea that guy giggling like an idiot made the video fun to listen to haha. Though I have heard from many sources say its thermal decomp, I think this is what's going on:

Mg + H<sub>2</sub>O --> MgO + H<sub>2</sub>

As well as some thermal decomp. My reason is the thich white smoke is evidence of MgO

franklyn - 20-1-2011 at 15:16

Magnesium flares were used in the world war II firebombings of Japan.
One time a flare ignited inside a bomber , a crew member picked it up
with both hands to discard it outside , loosing both forearms from the
burns. He was awarded a congressional medal of honor.

HENRY E. ERWIN
Rank and organization: Staff Sergeant, U.S. Army Air Corps, 52d
Bombardment Squadron, 29th Bombardment Group, 20th Air Force.
Place and date: Koriyama, Japan, 12 April 1945.
Entered service at: Bessemer, Alabama.
Born: 8 May 1921, Adamsville, Alabama.
G.O. No.: 44, 6 June 1945.

S/Sgt Erwin was the radio operator of a B-29 airplane leading a group
formation to attack Koriyama, Japan. He was charged with the additional
duty of dropping phosphoresce smoke bombs to aid in assembling the
group when the launching point was reached. Upon entering the assembly
area, aircraft fire and enemy fighter opposition was encountered. Among
the phosphoresce bombs launched by S/Sgt. Erwin, one proved faulty,
exploding in the launching chute, and shot back into the interior of the
aircraft, striking him in the face. The burning phosphoresce obliterated his
nose and completely blinded him. Smoke filled the plane, obscuring the
vision of the pilot. S/Sgt. Erwin realized that the aircraft and crew would
be lost if the burning bomb remained in the plane. Without regard for his
own safety, he picked it up and feeling his way, instinctively, crawled
around the gun turret and headed for the copilot's window. He found the
navigator's table obstructing his passage. Grasping the burning bomb
between his forearm and body, he unleashed the spring lock and raised
the table. Struggling through the narrow passage he stumbled forward
into the smoke-filled pilot's compartment. Groping with his burning hands,
he located the window and threw the bomb out. Completely aflame, he
fell back upon the floor. The smoke cleared, the pilot, at 300 feet, pulled
the plane out of its dive. S/Sgt. Erwin's gallantry and heroism above and
beyond the call of duty saved the lives of his comrades.

.

franklyn - 30-3-2011 at 17:52

http://books.google.com/books?id=ACEDAAAAMBAJ&pg=PA102

.

I G N O R E . T H E . L I N K . A B O V E

franklyn - 6-4-2011 at 15:47

USE THIS ONE INSTEAD

http://www.popsci.com/archive-viewer?id=ACEDAAAAMBAJ&pg=...

.

Magnesium Fires

The WiZard is In - 6-4-2011 at 16:24

James H. Meidl
Flammable Hazardous Materials
Second Edition
Glencoe Publishing Company
Encino, California 1978

Hazards of Magnesium

Take good notes there will be a test.

To the fire fighter, the future of the magnesium industry is less important than the
problems the metal brings us now. Although inhalation of magnesium fumes or
magnesium dust may cause some irritation of the throat and lungs, and the brilliant
white light of burning magnesium has been known to hurt the eyes. it is not its toxicity
but the flammable potential of magnesium that concerns us most. Uses of the metal
and its powders reflect this property: pyrotechnics, photographic flash powders,
military flares, and incendiary bombs. Magnesium, combined with white phosphorus in
a bomb, makes a fearful device: the same water that controls the phosphorus causes
flareups of the burning magnesium.

Magnesium melts at 1204°F. (651°C.) and boils at 2048°F. (1120°C.). The ignition
temperature of a solid chunk is close to this melting point. Fine shavings and loose
scrap will ignite at less than 1000°F. (538°C.); powder, another hundred degrees F.
lower. Some magnesium alloys catch fire at less than 800°F. (427°C.). What is
significant about these temperatures is that all of the common ignition sources reach
these temperatures. This is especially true with respect to magnesium powder, whether
deliberately produced for some purpose or unavoidably created by the grinding
operations of a machine shop. As can be expected, heavier pieces of magnesium are
far more difficult to ignite and are often stored in the open like other metals. As a
wooden log will transmit heat away from a point source of ignition, so will a metal with a
higher rate of heat conductivity. Although an entire piece of solid magnesium must be
raised to its ignition temperature before it ignites, this is easily done in a fire. In addition,
magnesium is one of those metals that melts as it burns. Larger pieces will contribute
far more molten metal to the situation than an equivalent weight in smaller pieces
because the smaller pieces are more likely to be completely consumed. When heated,
the magnesium molecule not only wants to combine with oxygen, it is positively fanatical
about it. it will burn in pure carbon dioxide, combining with the 02 in CO2. While tests
have shown that carbon dioxide does not accelerate burning a great deal, we expect
something more from an effective extinguisher. Dry sand is also ineffective. Oxygen is
jerked out of the silicon dioxide. If the sand is wet, the burning metal may produce
steam and blow the sand pile apart. Burning magnesium will use asbestos as an
oxidizing agent and continue burning even if the asbestos cuts off the air. The hunger
for oxygen in burning magnesium is so great that it will burn more violently on a
concrete floor than on a wooden one because the metal reacts with witt oxygen in the
concrete's aggregate. In spite of this, magnesium should not be stored on wooden
floors.

Furthermore, if oxygen is not available, magnesium will "make do" with whatever
is on hand. It will decompose carbon tetrachloride violently, getting at the chlorine
atoms to support combustion. Even "inert" nitrogen gas supports combustion.
Magnesium combines with it, forming magnesium nitride, and will burn in a pure
nitrogen atmosphere. Argon. helium, and neon still remain aloof and will extinguish the
burning metal.

Water on Magnesium Fires

In spite of what we have already mentioned, there is some disagreement over use
of water on burning magnesium. The Magnesium Association in its bulletins to metal
finishing shops states flatly: "Never use water, fog spray, foam, common gas, or liquid
fire extinguishers on magnesium."

But other authorities, such as the A1A and the NFPA, partially disagree with this
absolute ban on water.

Magnesium, if hot enough, reacts violently with water with liberation of
hydrogen, but the idea has been overdone that water should never be
used on any kind of a magnesium fire.

When experts disagree, we must look for ourselves. We have two basic methods
of applying water to a fire of any type: straight streams or fog patterns. Which method
we will use on magnesium, if either, depends upon our sizeup. What amounts of metal
are involved? What form is it in—powder, pieces, or large chunks? What is the extent
of the tire? How long has it been burning? What is the type of building construction?

How and where is the metal stored? What are the exposures?

If magnesium powder is present, it can be blown into the air by a straight stream.

A dust explosion of tremendous intensity is possible. Straight streams must be used
with extreme caution if magnesium dust is present. When there is a fire in a large
quantity of small pieces, a straight stream can penetrate into the pile and cause an
explosive scattering of molten and burning particles. The danger to personnel is evident.

Although this scattering is often mistaken for a hydrogen explosion—the residue of the
H2O molecule after the oxygen is pirated away for combustion—most often it is simply a
more intense version of an old-fashioned steam explosion, caused by the trapping of
water.

If molten metal is involved, however, fog is much safer, for it will flash into steam
immediately. But fog will not do the job properly. A small magnesium tire in chips and
pieces simmers rather quietly if there is no moisture present. If water is applied,
particularly water fog, the burning metal flares up amazingly into a hot, blinding white
flame. Those who have seen experiments in which oxygen is deliberately applied to a
burning combustible have seen a reasonable approximation of this intensive accelera-
tion. Literally, the same thing is happening. Water is being decomposed by the
ravenous desire of magnesium to combine with oxygen. Only large amounts of water
can overcome this increase in burning rate and lower the temperature of the metal
below its ignition temperature. This is particularly true when massive pieces are
involved, the pieces most likely to produce molten metal.

To summarize, fog patterns are much more likely to accelerate the burning rate of
magnesium, but there is less chance of a steam explosion. A straight stream can stir up
an explosive dust cloud. There is more likelihood of a steam explosion if molten metal
flows over pools of water we create or if water is trapped beneath the surface of a pile of
chips. Yet, a stream produces more water in less time and we must have this volume of
water to cool the metal below its ignition temperature and the temperature at which it
combines so avidly with oxygen.

Modern methods call for a compromise between fog and straight streams,
extinguishing and cooling the burning metal with a stream at lower pressures that will
break up into drops over the fire. These coarse drops will not violently accelerate a
magnesium fire the way fog will, but they will flow over the metal and cool it. After this,
coordinated hose streams can be worked into the fire. Small but well-advanced
magnesium fires have been extinguished by this method in a short time. If large
quantities of metal are involved, it may be necessary to use large streams from a
distance.

The problems of a big magnesium fire, in a finishing plant for magnesium castings,
are described in AIA Bulletin 171, condensed below:

The fire is of special interest as showing the value of hose streams on
fires involving magnesium. A spark, from plugging in an electric drill,
started the fire.

Accumulated magnesium dust aided the fire's rapid spread to the
wooden roof, filings and sawdust on the floor and shipping cartons.
Employees turned in the alarm promptly, tried to fight the fire with
sand but were forced to flee. All 50 escaped unhurt.

The first companies of the Los Angeles Fire Department on the scene
knew what was in the building from recent inspections; fire coming out the
front windows and through roof skylights also had the brilliant white light of
burning magnesium. To meet the need for many heavy streams, a second
alarm was sent in at once.

Mounting a skillful attack, the firemen took hose lines into the
adjoining sections of the building and onto the roof to stop the fire's
spread: other streams, directly from the street, worked on the burning roof
and on stocks of finished casting set afire by an early collapse of a portion
of the roof. Twelve 2½-inch hose lines, with 1/8- or 1¼-inch nozzles,
brought the fire in the structure under control and then moved in from all
sides to attack and extinguish the burning castings.

Water running off the roof and falling on burning magnesium produced
minor puffs with some particle spattering but when heavy streams were
applied directly to the burning magnesium, heavier explosions occurred.
The early collapse of the roof, while offering a vent, allowed pieces of
burning magnesium and metal containers to soar about 100 feet into the
air. Windows were broken up to a block away, but no one was hurt. Pieces
of burning magnesium, falling on the roofs of other buildings were quickly
extinguished; many seemed to burn out before landing. Magnesium on the
floor of the building, submerged in several inches of water bubbled but did
not burn as long as it remained covered. The fire was under control in less
than two hours and was confined to the section of the building where it
started. About 8,500 pounds of castings, worth at least $2.300, were
undamaged.

Failure to use heavy amounts of water would have resulted in a total
loss of all the magnesium in the fire area and a probable spread of the fire
to buildings across the street and the rest of the plant, with subsequent
serious damage. Reports by the fire captains and chiefs who fought this
fire are unanimous in saying only water applied in large quantity could
have done the job. They also commented, however, that buildings for
working magnesium should be of one story, with large window and
skylight area, located outside of congested city districts. Magnesium
explosions, in a more confined space, would have been much more
severe.

Sprinklers

But why not prevent the formation of molten magnesium in the first place? Large
pieces of the metal must burn for a time before molten pools will form. If extinguishment
or control is immediate, these pools may not be created. An automatic sprinkler
system above magnesium storage would be invaluable. The A1A and the Factory
Insurance Association conducted a series of tests on magnesium dust, turnings, and
small and large pieces with these thoughts in mind, and, as reported in AIA Bulletin
202, drew these conclusions:

Automatic sprinkler protection is of definite value in the control of
fires involving magnesium. Sprinklers, properly spaced and supplied with
adequate water, should protect a structure from serious tire damage with
burning of considerable quantities of magnesium therein. All tests and
experience today show that water applied from sprinklers will not
produce any reaction of sufficient violence to cause structural damage
and therefore sprinklers should be allowed to operate until the fire
reaches the quiescent stage. In certain other tests and in some fires,
rapid evolution of steam and hot gases, capable of doing structural
damage, have occurred when molten magnesium in quantity flowed into
water which had accumulated to a depth of several inches from hose
streams. Similar results might occur where conditions permit a quantity
of water to flow into a mass of molten magnesium, but under automatic
sprinkler protection the formation of molten magnesium would be
lessened and with proper floor drainage the likelihood of such explosive
effect would be greatly reduced.

When the magnesium in a stack or pile becomes well ignited, it may
be expected that a major part or all of the magnesium in that stack or pile
will be consumed: automatic sprinkler protection can be expected to
prevent the ignition of nearby stacks or piles of magnesium, as well as to
reduce fire damage to other nearby equipment and materials.

Time can be of the essence in magnesium fires. Sprinkler systems can perform a
vital function by holding down the extent of the fire until our arrival. If we can catch a
magnesium fire while it is still small, several alternative courses of action may be
available to us.

Dry Powders

Two types of dry powders have been approved for use on dry or oily magnesium
chips, turnings, and castings. (The phrase "dry powder" refers to metal extinguishing
agents. If a dry extinguisher is designed for such purposes as flammable liquids, it is
officially called a "dry chemical.") One of them, PYRENE. G-1, is a graphite powder
which conducts heat away from the burning metal, with a possible additive which turns
into a gas when heated and helps exclude oxygen. The other, ANSUL MET-L-X, is a
salt (sodium chloride), with additives to prevent caking, combined with a plastic which
melts and fuses the powder into a solid cake over the fire. Met-L-X will cling to vertical
surfaces, a helpful property when larger pieces are involved. Both of these powders
are noncombustible and nontoxic. They will not increase the combustion rate of
magnesium if we run out prematurely. However, we must get close to fire before we
can use them. The graphite must he applied by a hand scoop or shovel. The range of
the sodium chloride extinguisher is less than 10 feet (3 meters), and care must be
exercised not to blow burning metal around with the force of the ejected powder. If
possible, good training should include practice with both of these powders.

Cooling water cannot be used on the magnesium fire in conjunction with these
extinguishers. Not only would the flareup prevent close approach, but the water would
destroy the cake we are trying to form over the burning metal. This cake should be an
inch or so in thickness. Once it is in place, leave it alone. It will take some time for the
metal to cool down.

Other possibilities exist for fighting a small magnesium fire. If the metal is on a
combustible floor, we can put down a two-inch layer of powder, shovel the metal on
top, and cover it with more powder. More sensibly, if a clean dry drum is available, we
can make our magnesium sandwich inside it and carefully haul the drum to a safe
place. A few burning chips can be quickly handled by dropping them in a bucket of
water. (These dry powder extinguishers have not been approved for magnesium
powder by the Under-writers' Laboratories.) If the metal powder is exposed to a fire,
try to separate the two before the powder becomes heated. Be careful about the use
of water. Remember that damp magnesium powder can heat, generate hydrogen,
and possibly explode.

Storage and Use of Magnesium

The Magnesium Association makes several recommendations for safe machining
and grinding. Keep their advice in mind when making inspections.
When machining magnesium, take heavy cuts with sharp tools, never permit a tool
to rub on the work, and always back off the tool when the cut is finished. When taking
fine cuts, use a mineral oil sealant, nor a water-soluble oil. Sweep up chips frequently
and store in covered metal containers.

When grinding magnesium, it is "magnesium only" for a grinder unless the wheels
are thoroughly cleaned before changing metals. All dust must be carefully cleaned up
and not allowed to accumulate on clothing, surrounding floor areas, beams or sills.
Use a wet dust collector (the dust is caught by a water spray as soon as it is formed
and settles as sludge) for extensive grinding. Use the collector for magnesium only.

Remove sludge regularly, preferably at least once a day. Place in covered, vented
containers and remove to a safe location for immediate disposal. Partially dry sludge
is highly flammable. Dispose of the wet sludge by burning outdoors in an isolated area
on a well-drained layer of fire brick, free from previous residue. Place dry combustible
refuse, paper and wood, on top of a 3" to 4" layer (7 to 10 cm.) of sludge and ignite the
paper in a safe manner to avoid burns from a possible hydrogen flash. Observe
burning from a safe distance upwind.

Different forms of magnesium should be separated in storage. Finely divided
pieces should be stored in noncombustible buildings with the finest in containers
protected from sources of ignition, moisture, and contamination by halogens and
acids. Large pieces may be stored out of doors.

Magnesium is shipped in all forms, from large ingots down to the powder in closed
metal or cardboard containers. The scrap and powder must carry a DOT red label:

_flammable solid, and the dangerous-when-wet label (see Figure 9-2).

Beryllium

The WiZard is In - 6-4-2011 at 17:14

Quote: Originally posted by franklyn

Magnesium flares were used in the world war II firebombings of Japan.
One time a flare ignited inside a bomber , a crew member picked it up
with both hands to discard it outside , loosing both forearms from the
burns. He was awarded a congressional medal of honor.

HENRY E. ERWIN
Rank and organization: Staff Sergeant, U.S. Army Air Corps, 52d
Bombardment Squadron, 29th Bombardment Group, 20th Air Force.
Place and date: Koriyama, Japan, 12 April 1945.
Entered service at: Bessemer, Alabama.
Born: 8 May 1921, Adamsville, Alabama.
G.O. No.: 44, 6 June 1945.

S/Sgt Erwin was the radio operator of a B-29 airplane leading a group
formation to attack Koriyama, Japan. He was charged with the additional
duty of dropping phosphoresce smoke bombs to aid in assembling the
group when the launching point was reached..

The Sargent was in a Pathfinder aircraft and was dropping
a white phosphorus smoke bomb to mark targets for the following
planes.

The magnesium used in WW II incendiary bombs was Electon metal developed
by the Bosh in 1909 although not used by them until 1939 is consisted of (Fisher) —

Magnesium 86%
Aluminium 13
Copper "some"

It was stronger and less expensive then pure magnesium.

You will never guess who owns an original copy of —

96th Congress 1st Session
Senate Committee Print No. 3
Medal of Honor Recipients 1863-1978

----------
I don’t have the time to expend this into a treatise on incendiary
warfare so I will just not in passing I shelve:—

George J.B. Fisher
Incendiary Warfare
McGraw-Hill, 1946

Incendiary Warfare
A SIPRI Monograph
The MIT Press/Almqvist & Wiksell, Sweden.,
1975

E. Bartlett Kerr
Flames Over Tokyo : The U.S. Army Air Forces’ Incendiary
Campaign Against Japan 1944-1945
Donald I. Fine, Inc. 1991

Sir Donald Banks, K.C.B., D.S.O., M.C., T.D.
Flame Over Britain : A Personal Narrative of Petroleum Warfare
Sampson Low, Marston, & Co. London, ND

More than you ever wanted to know 'bout British plans to use
Fougasse &c. in WW II.

Major J.W. Mountcastle
The Holocaust : American Incendiary Bombs of World War II
Master of Military Art and Science (MMAS) Thesis.
US Army Command and General Staff College
10 Jun 1977
AD A042872

Noted in passing—

The US Army built typical Japanese and German buildings at
Dugway Proving Ground [UT] and dropped incendiary bombs on
them "to learn what happened when bombs of certain types struck
enemy structures." "They also dropped phosgene, cyanogen
chloride, and hydrogen cyanide bombs ranging in size from 100 to
4,000 pounds....."

LP Brophy, & et al
United States Army in World War II
The Technical Services
The Chemical Warfare Service : From Laboratory to Field
Department of the Army, 1959.

The US army set a hanger and a generals car a fire with incendiary
(phosphorus) carried by bats!

Jack Couffer
Bat Bomb : World War II's Other Secret Weapon
U of Texas Press, 1992

There is a phrase in Latin by Virgil that best describes this book –
Apparent rari nantes in gurgite vasco. I translate it as — This book
is Long on Chit-chat and BS.

IndependentBoffin - 16-4-2011 at 07:39

Quote: Originally posted by hkparker

As we all know, burning magnesium reacts quite vigorously with water (just look at <a target="tab" href="http://www.youtube.com/watch?v=rogZBXNqaMo">this... interesting video</a>

There is another thing which hasn't been mentioned yet. Magnesium and aluminium burn in the vapour phase. A lump of magnesium burns steadily in air because a dynamic equilibrium exists between vapourisation of the metal and diffusion/convection of oxygen into the metal vapour cloud.

If the supply of oxygen to the metal is increased by turbulence (in this case steam + hydrogen gas generation) or an oxygen donor (in this case water) then the reaction rate proceeds much quicker and potentially explosively. If you pump steam into a burning magnesium cloud fast enough you effectively have a thermobaric explosion.

It would be interesting to compare the effect of water on the burning of iron or titanium (liquid phase metal + oxide) and zirconium (solid phase metal + oxide).