Topic: Aluminum Questions

[GrumpyOldFart]

I agree Al is usually not a good choice for weapons, although I have known SCAers with Al armor.

However, corrosion... Aluminum gets what's called a refractory oxide on the surface. It has much the same properties as normal aluminum, but its melting point is a lot higher, and it effectively seals off the metal underneath from corrosion. That's why things like window frames are made out of it, the scraping only damages the oxide surface, never the metal underneath.

So in that sense it's rather like a piece of iron that will get surface rust, but will never rust any deeper unless you take that surface rust off.

[Marc R]

It'd make weapons and armor lighter and unfortunately softer. . .in most instances of this context you actually want heavier or harder. . .heavier weapons hit harder, heavier armor soaks kinetic energy better, and harder is definitely an upside for both weapons and armor.

The closest modern context I can think of is tools. . . .and when's the last time you saw an Aluminum screw driver, hammer, saw, drill bit or shovel? With lots of aluminum in our economy, and with a wide range of tool costs from pure crap to very expensive high end pro tools, you're just not going to find any aluminum used anywhere as a working edge or surface.

Where you do find lots of aluminum is in places that are stressed, but not directly rubbed or subject to impacts, where weight reduction is a serious factor. Airplane framing and surfaces, backpack frames, the pole part of a 50' extension saw. . .

Considering where our modern economy chooses to use Al, I suspect it'd make a poor material for most weapon and armor applications where focusing impact energy or impact resistance are primary material qualities desired.

The military applications in a fantasy world would be more likely to be things like a Soldier's backpack frame, letting him carry 10 pounds more gear with a 10 pound lighter pack, or wagon or barge hardware, letting the logistics train carry 5-10% more per load, rather than in direct "Aluminum Sword and Mail" applications.

[GrumpyOldFart]

...heavier armor soaks kinetic energy better...

Yes but with something people have to wear, heavier armor also makes you more likely to get hit in the first place.

[Marc R]

I suspect the weight/strength ratio isn't good enough, you'd need to make the aluminum so thick that odds are you'd nullify any weight advantage in bulk.

Where you can get away with it, it might be perfect. . . .like aluminum plated ships might be able to plate thick enough to ward off missiles, yet take advantage of the light weight to not run low like an ironclad. . .until cannon are invented and any practical thickness of aluminum becomes prohibitively bulky. (A bullet will penetrate a block of aluminum, where it would ricochet or fragment when striking a block of iron or steel).

You can hammer a steel nail into a block of aluminum, or drill it out with a wood bit that would just shine the surface of a steel brick, which suggests to me that it lacks characteristics necessary to make for good armor at any practical thickness.

[GrumpyOldFart]

I'm not thinking it's a suitable replacement for steel, really anywhere, nor am I thinking "armor" on that kind of scale. In situations (or fighting styles) where mobility trumps protection, a lot of people would consider themselves "heavily armored" wearing hardened leather, and metal would be pretty much out of the question.... unless we were talking about something like aluminum. And even there you can only use it in spots where the leather it replaces doesn't have to be able to flex really at all.

The same cost/benefit might apply in plates for brigantine as well.

[Marc R]

Aluminum is 1/3 the density of steel.

High strength steel has 3x more strength to weight ratio than high strength aluminum. (Not 3x stronger per volume, 3x stronger per mass unit)

So to make something of aluminum as strong as steel, you'd need to make it 3x heavier, which means it would be 9x volume. . .so 1/8" thick steel plate = 1 1/8" aluminum plate.

Or if you made standard plate out of aluminum, it would be 1/3 as heavy, and 1/9 as strong.

Which isn't really much better than boiled leather. . .perhaps aluminum armor would be marginally better than rigid leather, but it would be hellishly more expensive, unless aluminum grows on trees. . .For the use, you'd need to be the royal heir warrior monk.

If you want to go for esoteric materials, why not uranium. . .hard, strong and heavy, your uranium sword would whack very hard indeed.

[kevinmccollum]

Depends on how one conceptualizes Mithril.

I use the standard Tolkein view of mithril.

[pastaav]

The closest modern context I can think of is tools. . . .and when's the last time you saw an Aluminum screw driver, hammer, saw, drill bit or shovel? With lots of aluminum in our economy, and with a wide range of tool costs from pure crap to very expensive high end pro tools, you're just not going to find any aluminum used anywhere as a working edge or surface.

I think that is a function of price mostly. Aluminum is a very common material, but painfully expensive to extract from ores. Our deluxe frying pan at home cost three times the price of normal frying pan. If you google on Aluminum screwdriver you get millions of hits and the ratio of price holds there also. The reason Aluminum tools will never be a mass market product has little to do with its qualities for tools and much to do with that we can make competitive steel alloys for a far lesser price.

Basically this is the same as for titanium...this is far superior material to both steel and aluminum. Problem is just that the process to extract titanium is even more expensive than aluminum so we the situation that steel is used for everyday applications. Aluminum is used for airplanes , rockets and other situations when high strength and low weight is desirable. In those situations when Aluminum does not cut it, it is replaced by titanium alloys. In a society where energy is not an issue production of materials is for free I think things would be done in Titanum, diamonds etc. Steel is dominant in our society mostly because of price.

As for the matter of corrosion...aluminum gets a protective layer of oxide over time that protect the material below it. Additionally if you compare pure aluminum then the proper comparable is iron. If we talking about steel then Aluminum alloys is the proper thing to look at and then aluminum has more interesting properties.

Finally speaking about good properties of armor...absorbing kinetic energy is preferably done by using cloth. Any attempt to use heavy mass of metal to absorb kinetic energy is doomed to end with an armor that will give a wearer that is too tired to move. The armor need to keep the sharp parts away from the protective layers that soften the blow of the attacker.   

[GrumpyOldFart]

Any good armor is in 2 parts, at least in terms of the physics. The hard shell doesn't soak up anything really, it just spreads the force over a larger area. Total force is the same, but the amount of force any given spot is taking is reduced.

The padding underneath is what soaks it up, and simply put the springier it is the better it soaks. The advantage of large surface plates is that a given area of padding doesn't have to soak up as much for an effective zero force to be transmitted through it.

[GrumpyOldFart]

On the one hand, I've been told that medieval European knights used their hair as helmet padding.

On the other hand, I had someone tell me they saw an old helmet... medieval German, maybe?... with an arrangement of leather and twine inside that looked remarkably like the "suspension" inside a modern hard hat.

That said, I don't have any direct information to confirm or deny either of those.

[jdale]

I agree Al is usually not a good choice for weapons, although I have known SCAers with Al armor.

Mine is 12 oz leather with plates of aircraft aluminum riveted underneath for reinforcement. Chosen because aluminum is lightweight, strong enough, but still malleable enough to be hammered into shape without a forge. A trait that would make it poorly suited for use as armor in real combat....

[Ynglaur]

In the ancient world, Aluminum was almost priceless, even though it had few useful functions per se.  It was considered far more valuable than gold, platinum, and many precious stones, simply because naturally-occurring aluminum is quite rare.  It wasn't until the 1800's (iirc) that we figured out how to pull aluminum from aluminum dioxide, which is, almost literally, as common as dirt.

This is very wrong. Aluminium does not occurs naturally on this planet. To extract it from its ores (mostly oxydes), you either need to reduce it with an alkaline metal (sodium or potassium) or to use electrolysis. Hence for about 40 years (1850-1890), aluminium was extremely valuable.

The last part is very true. Even today, no-one will  use aluminium for armor when steel is available (and alloys of Al with Cu and other common metals do not cut it either).

I could swear I read somewhere that some of the Pharaohic dynasties had a small bit of aluminum in their treasury...the source escapes memory at the moment, though.

[dutch206]

The problem with Aluminum is that in nature, it is almost always found in conjunction with bauxite.  It wasn't until relatively recently that people figured out how to separate the two minerals.  I suppose you could introduce Aluminum as a discovery of the Dwarves or something.

[smug]

The problem with Aluminum is that in nature, it is almost always found in conjunction with bauxite.  It wasn't until relatively recently that people figured out how to separate the two minerals.  I suppose you could introduce Aluminum as a discovery of the Dwarves or something.

Aluminium is in bauxite, not found in conjunction with it.

[dutch206]

  Too much information -- head will explode!

[Marc R]

Heh . . .back in RM2 days, there was an alchemy list in the Alchemy Companion I think was intended as a low level utility list for measuring and such. . . .but one spell on the list would separate out anything you cast it on into it's component compounds. . .I remember getting myself into a lot of trouble with that spell.

Aluminum refining needs a means to introduce heat without combustion. . .standard iron foundry techniques would just turn bauxite into aluminum oxide ash. Modern forges use electricity on ore submerged in a non reactive fluid to raise the heat enough to cause the ore to melt, but keep all oxygen out so you don't burn the aluminum as you smelt it.

With magic, the potential for heating without fire or air, or even just "Magic go rip me some aluminum out of that rock please" arises.

Heck, "I seal the smelter room, then have the fire elemental burn a pile of coal to exhaust all the oxygen in the chamber, then I have it melt the bauxite, the pure metal runs down this channel to pool over here. . .then I have the elemental damp down, and when the metal and room are cool enough, I break the seal to go in and collect the metal. I observe the process with a long eye spell to make sure I don't open the chamber prematurely."

Perhaps said Dwarves could come up with a way to harness Lava heat, and some airtight container to hold the ore, and smelt that way. . .like "Put all the bauxite in that Mithril crucible, seal it shut, then drop it into that pool of lava on the mithril chain. . .when the mithril crucible is evenly red, pull it back out, and wait for it to cool, and open it in half. . .the silvery layer in the resulting slug of rock slag is pure aluminum."

Or something like that. . . .it's not impossible, just not so easy.

Of course, if the dwarves have a megawatt generator in their lair, then aluminum smelting per the modern method is possible, but then, so are a lot of things.

In the end, if the GM wants aluminum, I'm sure they can come up with some sort of justification.

I just suspect the resulting product would be used for something other than weapons and armor.

[thirqual]

Aluminum refining needs a means to introduce heat without combustion. . .standard iron foundry techniques would just turn bauxite into aluminum oxide ash. Modern forges use electricity on ore submerged in a non reactive fluid to raise the heat enough to cause the ore to melt, but keep all oxygen out so you don't burn the aluminum as you smelt it.

With magic, the potential for heating without fire or air, or even just "Magic go rip me some aluminum out of that rock please" arises.

Heck, "I seal the smelter room, then have the fire elemental burn a pile of coal to exhaust all the oxygen in the chamber, then I have it melt the bauxite, the pure metal runs down this channel to pool over here. . .then I have the elemental damp down, and when the metal and room are cool enough, I break the seal to go in and collect the metal. I observe the process with a long eye spell to make sure I don't open the chamber prematurely."

Perhaps said Dwarves could come up with a way to harness Lava heat, and some airtight container to hold the ore, and smelt that way. . .like "Put all the bauxite in that Mithril crucible, seal it shut, then drop it into that pool of lava on the mithril chain. . .when the mithril crucible is evenly red, pull it back out, and wait for it to cool, and open it in half. . .the silvery layer in the resulting slug of rock slag is pure aluminum."

It is alas not so simple. Aluminium is present as an oxide in bauxite. You need to reduce this oxide to obtain the metal, and you cannot do that with charcoal (or pure coal) as it is done for iron. The electricity is not only used to melt the stuff, but to reduce (give electrons) to the aluminium atoms.

If you heat aluminium oxide and carbon together (with no gas or an inert gas present), the oxygen will stay bonded to aluminium. Moreover, you cannot hope to melt aluminium oxide, even with lava. It melts at more than 2000C (lava from a basaltic volcano is at ~1300C at most, lava from other volcanoes are cooler).

So you either need to put aluminium ore in contact with something which has a greater affinity to oxygen (like sodium or potassium) or you need to use electrolysis.  The catch with sodium or potassium ? they are produced with electrolysis too.

Finding native, non-meteoritic, iron on Earth is almost unheard of (only in a few very special places where lava intrusions went through layers rich in kerogens if I remember correctly). Aluminium is worse than that.

[markc]

thirqual;
 Thanks for the science lesson it is much appreciated. I am thinking about making a ritual/spell that will do the electrolysis part as well as producing pure Al. I was thinking about making it a 20th rank spell/ritual as it would greatly increase the quantity and availability of Al in the general population.
 I love to use magic to get around hard Chem/Physics in Real Life.
MDC

[GrumpyOldFart]

I love to use magic to get around hard Chem/Physics in Real Life.

To me, that's what Alchemists spells are supposed to do. The spell would be a very simple variation on a lightning bolt, and you'd require some sort of gas control as well to maintain a reducing atmosphere.

An Alchemist in combat should be like a surgeon in combat. He's not trained to use a scalpel as a weapon, and it's not something someone would normally choose as one... but that doesn't mean he can't kill you with it if you get too close. Same for an Alchemist's smelting and refining spells.

Make a RR against a spell that's attempting to separate you into your component elements. 

Iron enough to make a nail,
Lime enough to paint a wall,
Water enough to drown a dog,
Sulfur enough to stop the fleas,
Poison enough to kill a cow,
Potash enough to wash a shirt,
Gold enough to buy a bean,
Silver enough to coat a pin,
Lead enough to ballast a bird,
Phosphor enough to light the town.

 

[arakish]

Just for reference, here are some web pages I found on the process for aluminium extraction.

http://sam.davyson.com/as/physics/aluminium/siteus/extraction.html

http://www.chemguide.co.uk/inorganic/extraction/aluminium.html

http://en.wikipedia.org/wiki/Aluminium#Production_and_refinement

http://www.britannica.com/EBchecked/topic/18071/aluminum-processing/81511/Extraction-and-refining

Virtually all are the same.  Enjoy.

rmfr