A blog dedicated to helping writers and worldbuilders create consistent, plausible Science Fiction.

Sunday, 11 June 2017

What's it made of? Part II: Supra-local Supermaterials

If more advanced technologies are available to reduce the cost of transport compared to the cost of extracting resources in the Solar System, it would be wise to consider a more general distribution of resources. 


In today's world, it costs very little to move large quantities of raw materials across the oceans. This has allowed iron from Australia, neodymium from China and lithium from Chile to end up in a Japanese factory. 
Human expansion into the Solar System might eventually create a similar sort of exchange. Resources readily available and easily obtained on one body, such as nitrogen on Triton, can be traded with buyers located on bodies that lack it, such as our Moon. 

With this in mind, it makes more sense to use the Solar System-wide distribution of resources when determining which materials will be used to build rockets and construct space habitats.


Solar distribution of elements


Please expand the image.
Above is a graph representing the relative abundance of the elements. It is logarithmic, so small differences (such as between Helium and Hydrogen) actually mean that Hydrogen is about ten times more abundant than Helium.
A more compact representation.
The most common elements.
Comparing the graphs, we can clearly see that the lighter elements are more abundant, with uncharacteristic dips in the abundance of Lithium, Beryllium and Boron. 

The reason for the dip is related to the fusion product chain in stars, which is another discussion.


Carbon, Nitrogen, Magnesium, Silicon, Iron. These are the six elements that will form the basis for most materials in a system-wide industry. 


Oxygen will be the primary oxidizing agent, Hydrogen the primary reducing agent. Neon is too inert to make anything out of and Sulphur does not form strong compounds.


From these elements, we can produce many of the materials already known for their high specific strength today. These include aramid fibres (carbon, nitrogen), carbon fibres (carbon) and high-strength steels (carbon, iron).


How will these elements be distributed inside the Solar System?



Condensation temperature vs Distance from Sun
The presence or absence of elements in the planetary bodies, asteroids and comets of our Solar System depends on how and where they were formed.

The first disk of gasses and dust that surrounded our young Sun contained a relatively homogeneous mix of elements. It created a temperature gradient across dozens of astronomical units, ranging from 6000K near its surface to near background 3K temperatures at the edges of the system.


Different elements condense (become solid) at different minimum temperatures during planetary formation. The lightest elements are boiled off the inner planets. Ices can only be found readily in the furthest gas giants and comets.

Layers of Titan (Organic: carbon-hydrogen molecules)
The condensation temperatures explain, for example, why there are large lakes of methane and other hydrocarbons on Titan, and suggests that Mercury has the highest percentage of heavy elements in its crust compared to other planets. 

We can conclude from this distribution that inner planets would prefer more metallic construction materials, while outer planets would have an easier time sourcing lighter elements such as carbon for their materials. 


Access to the deeper layers of the planets and moons, or to metal-rich asteroids, might however make this distinction irrelevant. 


Common materials 

What will be the 'bulk' materials used if we consider the factors mentioned so far?


The determinant characteristics for the most common materials will be resource availability, ease of production and features such as recyclability, endurance and multiple uses.

Bauxite mine in Guinea. 
On Earth, iron and concrete were for a long time was the most common materials. Iron was easy to find, and so were the ingredients for concrete. Both were strong, durable materials that could be recycled at the end of their useful lives. Smelting furnaces were a mature technology, while cement was easy to handle. 

In our solar system, it is likely that reinforced concrete, carbon fibre and basalt fibre pykretes will become prevalent.



Reinforced concrete foundations for a house.
Reinforced concrete is widely used today. It consists of regular concrete run through with metal wires that handle tensile forces. In space, it is an energy efficient, low-tech and easily sourced material. Since the metal content of the reinforced concrete is only a few percent, large quantities can be made using only small smelters. Forming concrete in vacuum can make it 25% stronger than the same concrete left to dry on Earth, since very little air remains inside.
Carbon fibre is very strong, lightweight and easy to produce. Many planets and moons will have useful amounts of carbon, such as Venus's atmosphere or the dry ice deposits in Callisto's craters. It has already been used in probes and the Space Shuttle. Its high specific strength greatly reduces the tank mass required to hold a certain quantity of propellant, allowing for greater deltaV than metal tanks. However, it is best to expose the entire production line to vacuum to prevent out-gassing damage, and to insulate the exposed fibres against extreme temperature variations to prolong their useful life. 


Steps for producing basalt fibres.
Basalt fibres need only one ingredient: igneous rock. It is melted into a glass and woven in temperature-resistant, inert and immune to radiation damage fabrics. These can be exposed to direct sunlight and do not suffer from temperature variations. They can replace the steel in reinforced concrete while being four times lighter for the same strength. The fabrics can reach a tensile strength of over 4GPa.
Textile-reinforced concrete.
Basalt-fiber reinforced polymer composite
Mixed in with ice, they can provide a strong bulk material known as Pykrete. This is suitable for colder climates in the outer Solar System or for underground or otherwise insulated construction.

Advanced materials


There are many materials with fascinating properties that can be made using only the most common elements. High specific-strength, extreme temperature resistance or other useful characteristics are the norm. They will be necessary to replace many of the metals alloys with additives we rely on today.


Graphenes:

Graphene monoloayer composites
Graphene alone is extraordinarily strong, a surprise superconductor and is a heat conductor in one direction, and an insulator in the other. It is made purely of carbon, but its formation is quite difficult. Making large quantities is quite a technical challenge, although there are headways being made

If graphene remains hard to produce in the near future, it can be instead used alongside other materials to improve their properties. Graphene-reinforced aluminium or titanium, which is only 0.3% graphene by mass, contains a metal matrix embedded with graphene nanoflakes. They gain strength without losing ductility, an important quality for plates you don't want to shatter under stress. 


Graphene can also be used in monolayers grown through Chemical Vapor Deposition between sections of metal to vastly increase their strength. Nickel-Graphine is 180 times stronger than pure nickel, and copper-graphene is 500 times stronger, giving it a better specific strength than titanium. The best part is that these composites are only 0.00004% graphene by weight. 

Carbides:

Compounds of carbon and another element. They form some of the strongest materials currently used, such as tungsten or silicon carbide. If there is sufficient boron available, borides with similar structures can be created, forming exceptionally strong and temperature resistant ceramics. 

Carbides are made by burning a metal oxide in graphite at high temperatures. It is a relatively simple though energy-intensive process. The result is grains of carbide that must be bound together or used to coat another material through vapor deposition. 

Glass nanowires:


20 nanometer diameter silica nanowires.
High purity silicates, if produced with nearly no defects, can be used as wires of nanometer-scale diameters to produce materials with 10GPa of tensile strength. They are four times less dense than steel while achieving several times better strength values. The principal advantage, like their impure versions basalt fibres, is that the building materials (silicates) are widely available. Their main challenge is quality: the maximum length of a useful strand if limited by the number of production defects. 

Metallic Glass:


Also known as amorphous metal, these materials do not have regular atomic structures. This helps preventing cracks from forming and propagating. The technical term is absence of grain boundaries.

Metallic glasses need to be cooled extremely fast to prevent crystallization, but this can only currently be performed on very thin pieces of alloy. Millimeter-thick metallic glasses are 'bulk' or BMGs. Future cooling techniques, maybe taking advantage of the microgravity and vacuum environment in space, will allow for thicker pieces. 

Vitreloy or LiquidMetal is a commercial metallic glass that is is twice as strong as titanium. Magnetic metallic glass has high electrical resistance and magnetic susceptibility, which makes it perfect for electromagnetically-accelerated projectiles and magnetically-manipulated structures, such as self-replacing armor plating or extensible spaceship skeletons. A high elastic limit allows some alloys to absorb many impacts without permanent deformation, which reinforced its usefulness as armor material. BMGs made out of the most common elements might not be as strong as those containing zirconium, tungsten and other elements, but they will have better properties than regular crystalline alloys of those same materials.

24 comments:

  1. It's nice to know that many of these materials already are either in stock Children of a Death Earth, or are available as mods. You didn't seem to mention carbon nanotubes, vitreous carbon, diamond nanothreads, carbyne, borophene, ... Despite mentioning graphene.

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    1. Hi!

      I actually drew inspiration for this topic from discussions on COaDE forums. However, I did not go very deeply into carbon chemistry because one of the criteria for a material to become widespread is ease of production.

      Glassy carbon does not have a particularly high tensile strength, nanotubes and carbyne are extremely difficult to make in bulk and boron composites are hampered by the rarity of boron.

      Graphene is also hard to make, but it can be used in composites 0.00004% by weight in graphene. So with 1kg of graphene, you can make 2500 tons of graphene composites...

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    2. What applies to graphene also seems to apply to carbon nanotubes and diamond nanothreads. Glassy carbon makes for a decent radiator panel material (light, high melting point).

      The ease of finding the resources for basalt fiber really threw me of though. I wonder why it's so expensive in CDE.

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    3. That is true, but again, there is a significant difference between having to create bulk carbon nano-materials and tiny quantities of graphene for composites.

      You are correct about glassy carbon for radiators. This reminds me, I should move my 'radiators' topic up the list.

      I think CDE considers basalt fibres to be as difficult to make as aramid fibres, despite the fact that they only need to be melted and extruded like pasta.

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  2. As always, the dismal science of economics will have a say. Exotic materials will only be used where the advantage of using them outweighs the costs of using normal materials (or if using normal materials will be impossible to do the job).

    Most structures, habitats, shelters etc will be made of basalt reinforced concrete, since that is the cheapest and most readily available bulk material for the job. Rocket powered vehicles will make maximum use of lightweight materials due to the tyranny of the rocket equation, and I suspect engineered materials will be worth investigation, especially as they promise to have the strength of high cost alloys yet have the density of aerogels: http://newatlas.com/llnl-ultralight-metamaterial/32589/. You can probably see an economic divide between the use of high strength, lightweight materials for flight articles vs concrete and basalt materials for shelters, storage units, habitats and so on.

    The super rich will flaunt their wealth by building habitats out of high cost engineered materials, and you can probably gauge the wealth of a person in space by looking at the percentage of aerospace materials in their habitat vs the percentage of basalt reinforced concrete.

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    1. The economics is the reason why I restricted the examples to only the most common elements.

      Overall, I think the use of materials will follow the current aerospace and construction industry trends. We start out with whatever is easiest to make in bulk, so ice pykrete for buildings and steel for spaceships. As the infrastructure settles in for more complex production chains, buildings will see themselves made of multi-function materials such as basalt fibres that double as insulation and structural support while being more durable than ice, while spaceships integrate more and more complex materials to take advantage of deltaV savings.

      If a propellant tank can be made 50% lighter, the mass saved in propellant for the same deltaV multiplied by the number of trips eventually surpasses the cost of using more complex materials.

      Aerogels are a great material category I didn't think to mention!

      Wealthy people in extraterrestrial habitats will probably not focus their attentions to the foundation materials the habitats are made out of - modern millionaires do not flaunt their wealth using more expensive types of brick or stronger concretes, but use the much more visible and appreciable decorations.

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    2. From a structural aspect, aerogels might not be entirely appropriate here. The block-form aerogels tend to be quite resistent to compression forces (although it is important to remember that these blocks have extremely low mass, so the actual mass that a block will support is not as high as it seems by the numbers typically cited); however, they also tend to be extremely brittle. The aerogel fabrics, on the other hand, can endure much greater stresses, but do not actually offer any real structural support.
      Aerogels are excellent as "filler" layers, for isolation and related thermal protection, but are not useful structurally. It should also be noted that aerogels are incredibly porous.

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    3. Tangeantial question about aerogels: they are known to be extremely heat-resistant, for example with the space shuttle tiles.
      Why aren't they used to line reactor nozzles? In addition to be lighter (though it would still need structural support), one imagine this could avoid the need for regenerative cooling and subsequent complexity.

      I am also thinking about that for continuous wave detonation engines, who are (sold by prototypers as) cheaper, lighter, more efficient, but heating their nozzles more.

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    4. First, I will have to check my sources, but I am not certain that aerogels are sufficiently heat resistent to survive high temperature exhaust. While they share similar properties with the shuttle tiles (the ability to hold in bare hands while heating with a blowtorch), I am not at all confident that the actual toleration of heat exposure extremes is one of them.

      Second, as for the block aerogels, even if they are sufficiently heat resistent (as opposed to simply extremely low thermal conductivity), they would be much too fragile to use in nozzles, which actually have to sustain a lot of stress.
      The fabric aerogels would likely be able to handle the stresses involved. However, these would likely be much less tolerant of the actual thermal exposure.

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    5. Could putting the block aerogel in sturdier material work for the stress problem?

      Also if the aerogel is ablated, this could still be used in non-reusable engines, as long as the ablation time is longer than the designed lifetime of the engine. And otherwise, changing only the nozzle may still be cheap enough.

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    6. If the aerogel is very structurally weak, it could be vulnerable to mechanical ablation (chunks being pulled off by the friction and pressure of the gas flow) that would create unsustainable ablation rates.

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    7. My understanding is Aerogels and similar materials are extremely light and strong, but also quite pourous and fragile in many environments. The most common use to date is insulation and as the "sandwich filler" material in some forms of composite material. Using aerogels to make lightweight composite sandwich will be useful for making lightweight materials.

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    8. Eth:

      First, the process of making aerogel is rather complex and (as I understand it) still rather expensive. I don't think you would want to waste the effort on an ablative material.
      Second, it is important to consider HOW a material ablates. Although rocket nozzles might LOOK like big, solid, assemblies, they are actually built pretty close to structural tolerance as it is. The thermal and shock ablation (especially the latter, in this case) can shear off large chunks that could do significant damage to the nozzle. It could also produce vibrations throughout the thruster that could damage other important assemblies.

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  3. OT: Have you considered doing a thread on space elevators? (Apologies if you already did; I looked and didn't see one, but might have missed it.)

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    1. I haven't yet.
      I have a big list of drafts for different topics and series, I try to work through them and post 2-3 times a month. I'll add space elevators :)

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    2. Cool, thanks.

      While we're at it, another topic I'll bet you'd be amazing on is 3D printing. Specifically: all the future and theoretical capabilities of it, printing in zero G, "4D" printing, etc.

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    3. You're welcome!
      I'll definitely include 3D printing in a 'Future manufacturing' post.

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  4. One cautionary note re vacuum cement:
    Perhaps more than anything else, the tensile strength of concrete relies on a very precise water content (even though excess water content decreases the strength of the concrete), through the strong bonds formed between the water molecules and those of the cement and aggregrate.
    In the fabrication description, the steam that forms the (low grade) vacuum simultaneously helps to saturate the concrete with water.
    In the vacuum of space, however, there IS no such excess steam water. Instead, the (extremely high grade) natural vacuum of space tends to extract water through evapouration. This would likely render the cement rather brittle, as there would be insufficient water to form the network of bonds.

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    1. This sounds like an engineering problem. The concrete could be made in two steps: steam saturation followed by vacuum drying.

      I doubt it would not be possible to have excess steam water if we just pump enough of it into the mixture with not enough room to escape.

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    2. I agree that it is probably an engineering problem. It could probably be resolved by having an enclosed "press". I was just cautioning that you probably would not want to make it in exposed vacuum.
      One thought DID cross my mind, that might actually work in exposed vacuum. From what I've een reading, it would seem to me that the cement process might lend itself well to 3D printing (and vise versa). The components could be sprayed out with the exact amount of water necessary to form the bond, layer by layer, into the desired matrix. The two down sides that I can see is that the material will need to be rather fine grain in order to be "sprayed"; and, this requirement (as well as the conditions of 3D printing alone) would likely offset the benefits that make the material relatively cheap. OTOH the 3D print process might be reserved for the highest quality concretes... such as those that would be directly exposed to space throughout their service lives.

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    3. That seems like a reasonable requirement. High quality cement on the outside, bulk quantities of low quality cement for the interior.

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  5. Given the recent demonstration of 'negative matter', have you considered a post looking at the niche uses of such a material? It would be obviously extremely expensive, but I suspect there might be a small scale use for it.

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    1. Could you link this demonstration?

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    2. Turns out I fell for some newspaper hype, the negative mass is only'effective' mass...

      HOWEVER: that might not rule out some interesting uses for the effect elaborated on the comments of this link.

      http://backreaction.blogspot.co.uk/2017/04/no-physicists-have-not-created-negative.html

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