=manufacturing =materials =composites
The strongest available materials
today are fiber composites. If you want something with higher specific
strength than steel, the cheapest and most common choice is glass fiber
("GF") composite.
The best carbon fiber ("CF") is stronger than GF,
but it's much more expensive. There are also various polymer fibers, but
they all have much lower compressive strength than GF and CF, because the
molecules have weaker transverse strength so the fibers buckle.
M5 fiber is a polymer
fiber with ~50% the compressive strength of CF, but it's very expensive.
That's several times the compressive strength of Kevlar, which is still
expensive, much more expensive than GF. Usually, the only reason to use
polymer fibers instead of glass fiber is if you want fabric that bends
easily rather than something with high compressive strength. (M5 fiber is
made by an interesting route, with dihydroxyterephthalic acid coming from
Claisen
condensation of dimethyl succinate, but that certainly doesn't make it
cheap.)
So, GF is the main fiber for composites, with >30x the annual
production of carbon fiber, and there's no good alternative. The raw
materials for GF are abundant, so that might seem fine, but there's a
problem.
Glass fiber is made by extruding
molten glass through small holes with bushings made of platinum alloy.
Platinum is the only material that works for this; every refractory metal
and simple ceramic was tried. It has a single surface layer of oxygen, which
is able to match the oxygen patterns of molten glass, so glass wets it well,
but it doesn't dissolve (much) in the molten glass to be surrounded by
oxygen.
A small amount of platinum does dissolve in the glass, and
platinum is now $29/g. Stronger glass compositions tend to require higher
temperatures and dissolve more platinum; this is the main tradeoff between
cost and performance. This application uses perhaps 10% of platinum today;
the main use is currently catalytic converters for cars.
That amount
of use isn't a problem, especially if some piston-engine cars are replaced
by electric cars, but what if you want to start replacing steel and concrete
with fiberglass? If GF production increased 10x, then platinum availability
would be a major problem.
So, mine more platinum? That's not easy.
Platinum is currently a byproduct of copper and nickel production. Mining
platinum by itself would be very expensive, and if platinum prices go up
10x, then GF would also become more expensive.
This is a major reason
why I bother spending any time thinking about high-strength polymer fibers
despite them being generally much worse than GF and CF. But obviously,
that's only a potential longer-term issue, and what we'll see in the short
term is more GF production. Yes, theoretically some cheaper CF production
process could be developed instead, but CF remains expensive despite
large-scale production and fairly low profit margins, and polymer fibers
have more potential routes to better cost-performance.