The hardest possible substance known to man?

[UncleAl]

If you want a forever capsule then Hastelloy C-2000 or Inconel 686, the most corrosion-resistant alloys commercially available. Green Death, Yellow Death, boiling concentrated sulfuric acid, molten alkali... corrosion rates of a few mils/year. Single phase, austenitic, low-carbon, nickel-chromium-molybdenum-tungsten alloys. Hastelloy C-2000 contains copper rather than tungsten.

Organics and carbon composits (kevlar, spectra, zylon, carbon fiber) are destroyed by sunshine. Brittle ceramics and inorganics break. Look up the ceramics used to make turbines in automobile turbochargers.

[Mercedes Benzene]

Hmmm. Interesting. Do you know what alloy is generally used in nuclear reactor cores Al?

[CraigD]

Originally Posted by UncleAl

If you want a forever capsule then Hastelloy C-2000 or Inconel 686, the most corrosion-resistant alloys commercially available. Green Death, Yellow Death, boiling concentrated sulfuric acid, molten alkali... corrosion rates of a few mils/year. Single phase, austenitic, low-carbon, nickel-chromium-molybdenum-tungsten alloys. Hastelloy C-2000 contains copper rather than tungsten.

Thanks for the introduction to steel alloys, UncleA1, and welcome back to hypography after a long absence – you’ve been much missed.

I skimmed a couple of specification pages and wikipedia articles to get a feel for of the subject of alloys, and found myself comparing the compositions of a few of the Special Metals Corp’s Inconel alloys to each other and a couple common, familiar stainless steels. Here’re the tabular fruits of my labors:

             Inconel    Inconel    Inconel    Inconel    SAE        SAE
             600        625        686        718        316        304
Aluminium    -          0.4        -          0.65-1.15  -          -
Boron        -          -          -          0.006      -          -
Carbon       0.15       0.1        -          0.08       0.08       0.08
Chromium     14.0-17.0  20.0-23.0  20.5       17.0-21.0  16–18       18–20
Cobalt       -          1.0        -          1.0        -          -
Copper       0.5        -          -          0.2-0.8    -          -
Iron         6.0-10.0   5.0        1          11.1-22.5  63-69      66.5-71
Manganese    1.0        0.5        -          0.35       2          2
Molybdenum   -          8.0-10.0   16.3       2.8-3.3    2.0–3.0     -
Nickel       72.0       58.0       57         50.0-55.0  10–14       8–10.50
Niobium      -          3.15-4.15  -          4.75-5.5   -          -
Nitrogen     -          -          -          -          0.1        0.1
Phosphorus   -          0.015      -          0.015      0.045      0.045
Silicon      0.5        0.5        -          0.35       0.75       0.75
Sulfur       0.015      0.015      -          0.015      0.03       0.03
Titanium     -          0.4        -          0.3        -          -
Tungsten     -          -          3.9        -          -          -

Notice that the big differences are in the iron and nickel fractions. Though perhaps an oversimplification, I’m led to think of Inconel 600 and 700 series alloys as stainless steels with the proportions of iron and nickel swapped.

Originally Posted by UncleAl

Organics and carbon composits (kevlar, spectra, zylon, carbon fiber) are destroyed by sunshine.

Even more ordinary synthetic high-strength products, like nylon and polypropylene rope, suffer from potentially disastrous UV degradation. Years ago, I spent a few months commuting over a wood, steel, and roughly 15-year old hillbilly engineered nylon rope suspension bridge that was a regular source of anxiety for everybody who used it. Fortunately, I had a compact car massing about 900 kg empty – folk with full-sized pickups were really scared of the bridge, and most with larger trucks didn’t dare use it at all.

[UncleAl]

Nuclear reactors use hafnium-free Zircaloys. Can't have a neutron sponge in there. Stainless steels require oxygen to form their protective mixed oxide coatings. Anaerobic stainless can pit corrode into Swiss cheese. The fabulous screw-up with 316SS is to use it as a drip tray when diddling with hydrazine. Molybdenum is a specific hydrazine decomposition catalyst.

Inconel 686 is a terrible thing to slip analytical. Nothing in a wet lab touches it - and it doesn't make a difference what kind of lab it is. Emission spectroscopy to have a chance: - arc, spark, laser blast, x-ray fluorescence.