Grand Slam v MOAB....

[pbehn]

I know what corundum is, I just didn't know it was Aluminum oxide.

Then you did not know what carborundum is. Corundum is one of the oxides of aluminium with a chemical composition of Al2O3 and a hexagonal crystal structure.https://www.google.co.uk/search?q=c...firefox-b&gfe_rd=cr&ei=DLsDWYfgFOnv8AeB7riACg

As for rockets, I'm not sure why aluminum oxide would be used then unless it had to do with the fact that everything is mixed in.

You have already been told it was aluminium not its oxide by Mikewint.

I didn't know aluminum burned, but pretty much anything burns under the right set of circumstances.

Mike used the term burned, it is a laymans term, correct when speaking in laymans terms, on a forum which has some experts posting but is open to the public and "laymen". Mike should have posted "reacts".

Aluminium is extremely reactive, while it is the third most abundant element after Oxygen and Silicon it is almost never found in its natural state. No one has ever seen Aluminium in a natural environment because it self passivates to stable non corrosive state at its surface, it is always covered in a thin layer of oxide, which is stable and prevents further reaction. There are oxides of gold and platinum, that doest mean that they literally burn but they can react with oxygen. It is beyond my knowledge to be certain but as far as I know all elements can combine with oxygen, burning is just a violent representation of oxidisation.


Zipper, you are a special character, you obviously have some good knowledge in some areas yet seem unaware of what I learned at the age of ten in others. I well remember as a ten year old being told that if air contained enough oxygen then we wouldnt have coal or coke fires you could just ignite the iron fire grate.

 

[Shortround6]

Aluminum burns rather well, it the main combustible (fuel) material in Thermite after all.

However it needs a high surface to volume ratio (powder works really well.) large blocks not so well. The heat is dispersed through the large object before you reach ignition temperature in a local area. You also need enough oxygen in the local area to sustain combustion. Thin aluminium sheet in an aircraft with a several hundred mph wind is going to burn a of different than an aluminum I beam with zero wind speed. Please note that aluminium looses strength very quickly. While it melts at around 1220- degrees F it actually looses a lot of strength between 300-500 degrees F (will slump or loose shape if under load)

In Thermite you have the heat of the reaction liberating oxygen from the iron oxide.

 

[pbehn]

Aluminum burns rather well,


In Thermite you have the heat of the reaction liberating oxygen from the iron oxide.

All the engineers want is a reaction, Hydrogen peroxide was popular as a fuel because it releases oxygen as a fuel and forms water which expands massively in volume when hot. Oh it explodes when not correctly handled too.

 

[Shortround6]

Hydrogen peroxide can be used as sort of a mono-propellant. When broken down by a catalyst it gives you the water and free oxygen you mentioned. I believe (but could well be wrong, going by memory) that the output is around 750 degrees F. The Free oxygen in this case is a by product but since even 212 degree steam needs about 1100 times the volume of the liquid it came from we obviously have plenty of pressure to run a turbine or even just use as rocket thrust. If you want to inject some kerosene into the product from the catalyst chamber you have the free oxygen to support combustion and you have an ignition source in the superheated steam.

Hydrogen peroxide doesn't actually explode like regular high explosives (the difference between detonation and deflagration is that in a detonation the flame front moves through the material faster than the speed of sound in that material) any quantity of a liquid flashing to steam at that 1100:1 ratio will rupture any normal container with enough force to throw pieces/liquid considerable distances.
Practical difference to anyone standing nearby is minimal, despite dictionary difference.

 

[pbehn]

I agree SR, there is a difference between a laymans term and a scientific definition. People talk about tyres exploding when actually they rupture under pressure, no consolation at all the the family and friends of the poor sod who inflated a large tyre outside of a safety cage.

 

[mikewint]

I didn't know aluminum burned, but pretty much anything burns under the right set of circumstances.

Depends on your definition of BURN. Oxygen is truly nasty stuff and combines chemically with many substances but there are many exceptions, like the Inert Gasses, gold, silver, platinum, and anything that has already reacted with it like water, carbon dioxide, ceramics, or ALUMINIUM OXIDE. Aluminium oxide like carbon dioxide and water have already reacted and will not react further.
Aluminum is a HIGHLY reactive metal. It is never found in its pure state in nature and ores of aluminum are very nonreactive making it very difficult to extract the pure aluminum. Napoleon III, the first President of the French Republic, served his state dinners on aluminum plates. Rank-and-file guests were served on dishes made with gold or silver. Aluminum reacts very readily with oxygen (albeit slowly) to form the oxide. That's why aluminum doors are a dull grayish color. That dull gray is aluminum oxide or corundum which is stronger and tougher than the aluminum itself. That tough oxide layer seals the rest of the aluminum preventing further oxidation.
Now in light of that consider Aluminum. It is invariably coated with the oxide. Burning the aluminum FIRST requires that you breach the oxide shell which occurs at 3680F. Once the oxide shell is breached the Aluminum reacts with oxygen (burns) and the temperature quickly soars to 6920F

As for rockets, I'm not sure why aluminum oxide would be used then unless it had to do with the fact that everything is mixed in.

You keep postulating that and I can only suggest that you revisit your source material. Aluminum oxide is not and cannot be a fuel.
Solid rocket fuel is the original rocket fuel, dating back to the early fireworks developed by the Chinese centuries ago. For the SLS (Space Launch System) boosters, aluminum powder serves as the fuel and a mineral salt, ammonium perchlorate, is the oxidizer.
The powerful aluminum-ammonium perchlorate reaction fuels the twin SLS solid rocket boosters.
Aluminum is the most abundant metal on Earth. It's also highly reactive. Aluminum is so reactive, in fact, that it's not found naturally in its pure form but only in combination with other minerals. It's this ability to readily combine with other elements (Oxygen) that makes aluminum so useful.
Ammonium perchlorate, the salt of perchloric acid and ammonia, is a powerful oxidizer (explosive). In the boosters, the aluminum powder and ammonium perchlorate are held together by a binder, polybutadiene acrylonitrile, or PBAN. The mixture, with the consistency of a rubber eraser, is then packed into a steel case.
When it burns, oxygen from the ammonium perchlorate combines with aluminum to produce aluminum oxide, aluminum chloride, water vapor and nitrogen gas – and lots of energy.
This reaction heats the inside of the solid rocket boosters to more than 5,000 degrees Fahrenheit, causing the water vapor and nitrogen to rapidly expand. Just like in the liquid engines, the nozzle funnels the expanding gases outward, creating thrust (Newtons Third Law – Action/Reaction Pairs) and lifting the rocket from the launch pad.


Compared to liquid engines, solid motors have a lower specific impulse – the measure rocket fuel efficiency that describes thrust per amount of fuel burned. However, the propellant is dense and burns quite quickly, generating a whole lot of thrust in a short time. And once they've burned their propellant and helped propel SLS into space, the boosters are discarded, lightening the load for the rest of the spaceflight.

 

[mikewint]

Hydrogen peroxide can be used as sort of a mono-propellant.

Yup. The most important part of these rockets is the catalyst pack. Nitrogen used to pressurize the peroxide tank which causes the peroxide to pass through a flow valve and injects it into the injection plate of the rocket. The catalyst is made of many silver screens. During the reaction these screens convert the liquid hydrogen peroxide into very hot steam and oxygen at high pressure. This jet of gas is used to power the vehicle.
This kind of rocket, whether using steam or hot water, is the safest of all the rocket engines. Sometimes considered a "cool rocket," it does not produce flame, and therefore can be made of stainless steel.
The Hydrogen Peroxide is the same product commonly used as a household antiseptic at 3% concentration, but here used at 80% to 98% strength.
The Hydrogen Peroxide is the only product used in the reaction, this places it in the monopropellant liquid rocket fuel classification.
For each volume of liquid injected at the catalyst, after the reaction you get 5000 times that volume in gas expelled at the nozzle.

 

[Zipper730]

Depends on your definition of BURN.

Combust, burst into flames, etc.

Aluminum is a HIGHLY reactive metal. It is never found in its pure state in nature and ores of aluminum are very nonreactive making it very difficult to extract the pure aluminum.

Pbehn already covered this...

That dull gray is aluminum oxide or corundum which is stronger and tougher than the aluminum itself.

As a crystal, it has a hardness of 9.0, with diamond being 10

Now in light of that consider Aluminum. It is invariably coated with the oxide. Burning the aluminum FIRST requires that you breach the oxide shell which occurs at 3680F. Once the oxide shell is breached the Aluminum reacts with oxygen (burns) and the temperature quickly soars to 6920F

That's hotter than an oxyacetylene torch...

For the SLS (Space Launch System) boosters, aluminum powder serves as the fuel and a mineral salt, ammonium perchlorate, is the oxidizer.

Okay, so the presence of aluminum in the boosters, and aluminum oxide in bombs simply has to do with the reactivity of the aluminum itself, but in different ways?

Ammonium perchlorate, the salt of perchloric acid and ammonia, is a powerful oxidizer (explosive). In the boosters, the aluminum powder and ammonium perchlorate are held together by a binder, polybutadiene acrylonitrile, or PBAN. The mixture, with the consistency of a rubber eraser, is then packed into a steel case.

The rubberized characteristic I already knew about. I think it was in a documentary about the Challenger explosion.

When it burns, oxygen from the ammonium perchlorate combines with aluminum to produce aluminum oxide, aluminum chloride, water vapor and nitrogen gas – and lots of energy.

Compared to liquid engines, solid motors have a lower specific impulse – the measure rocket fuel efficiency that describes thrust per amount of fuel burned. However, the propellant is dense and burns quite quickly, generating a whole lot of thrust in a short time. And once they've burned their propellant and helped propel SLS into space, the boosters are discarded, lightening the load for the rest of the spaceflight.

Honestly, the fast burning thing didn't occur to me with solid-boosters, though I'm already aware of the effect of boosters and staging. I figured they burned at the same rate, but the fuel was smaller and allowed a smaller vehicle to be built around it.

 

[mikewint]

aluminum oxide in bombs simply has to do with the reactivity of the aluminum itself, but in different ways?

OK, Once more into the Breech. I don't know how much more clearly I can say it or in what language:
THERE IS NO - ZERO - NADA - NICHT - NINGUNA - CERO - ACUN - ZADEN ALUMINUM OXIDE IN ANY BOMB! IT IS VERY FINELY POWDERED ALUMINUM METAL. IT BECOMES THE OXIDE AFTER
IT REACTS WITH OXYGEN

Combust, burst into flames, etc.

A solid bar of steel will burst into flames if it is placed in an atmosphere of fluorine gas as will water, human flesh, even ceramics.
COMBUSTION is a rapid oxidation process. Steel oxidizes to rust but the process is slow HOWEVER, very fine 0000 steel wool will burn quite rapidly becoming a combustion in effect. A bar of pure Aluminum will also oxidize slowly to form Aluminum "rust" or Aluminum oxide BUT very finely powdered Aluminum will combust very rapidly as oxidation occurs on the surface only and powders have massive surface areas. Flour mills, grain elevators, coal mines produce fine dust that will combust so rapidly it appears to be an explosion. Black Powder e.g. is NOT an explosive but it does combust very rapidly.

Slippery things are words!

 

[dogsbody]

The difference between a propellant and an explosive is just a slower rate of combustion in the propellant.


Chris

 

[pbehn]

Slippery things are words!

In ancient times the wise ones could select a Yule log which was a huge part of a tree that would burn for the 7 days of the winter solstice celebrations, that is very slow combustion. Let the wood dry and chop it into small pieces than it burns quickly and hot enough to set off a fire in a coke fire/furnace. However if you get enough wood dust in a wood mill it can be destroyed in such a fashion that it takes a month to make the place safe and find the bodies. No consolation at all to tell the relatives that it wasnt actually an "explosion" merely rapid combustion.
Bosley - Wikipedia

 

[pbehn]

The difference between a propellant and an explosive is just a slower rate of combustion in the propellant.


Chris

That is not always the property of the chemicals concerned but also the environment. If you lose control of a propellant it is an explosive.
This applies to a car fuel tank at one end and the space shuttle at the other.

 

[dogsbody]

That is not always the property of the chemicals concerned but also the environment. If you lose control of a propellant it is an explosive.
This applies to a car fuel tank at one end and the space shuttle at the other.

I probably should have added " under normal circumstances ".


Chris