Part 38: Closed Tournament - Round 4 - The Chem

The Chem in SpaceChem, Closed Tournament Round 4

Winner’s finals: Fantastic Metals
Inputs: Pt/Au, Fe/Ti, Cu/Al
Outputs: Fe/Al, Au/Cu, Pt/Ti

I wasn’t quite sure where to start with this one. You see, as a chemist I don’t really know all that much about alloys. The different sizes of metal atoms can give an alloy a different crystal structure compared to the pure metals. That can give alloys quite unexpected properties. But that’s the kind of stuff materials scientists think about, not me.

So, I’ll talk a bit about the pure metals first, then I’ll look at the alloys.

I discussed iron (Fe) in Round 8 of the Open Tournament, and Aluminium (Al) and Copper (Co) in the first round of the Closed Tournament.

Gold, Au
Melting point: 1064 °C, 1948 °F
Boiling point: 2856 °C, 5173 °F
Atomic mass: 197 u
Density: 19.3 kg/L

And that’s why they call gold a heavy metal.

The main use of gold is in monetary investments and jewelry. It’s also used in some specific electronics, as it’s a good conductor and as a noble metal it won’t corrode easily. With the right chemicals, it’s still possible to make many gold salts.

Aqua regia (king’s water), a mixture of nitric acid and hydrochloric acid will react with gold. In this reaction, the nitric acid will oxidize a tiny amount of gold atoms into Au³⁺. Then the hydrochloric acid will convert those ions into AuCl₄^- ions. As the Au³⁺ is constantly removed from solution, the nitric acid reaction can keep going.

In jewelry, they usually don’t use pure gold, as it’s very malleable, and you could easily bend it with your hands. The gold content in alloys is given in ‘carats’. 24 carats means 99.9% gold, so a carat equals 4.17 mass-%. Confusingly, ‘carat’ is also the name of a mass unit for gemstones, equaling 0.2 grams. Speaking of unusual units, precious metals such as gold are often weighed in troy ounces instead of grams. I guess economists hold on to traditions more tightly than chemists.

The color (and the shine) of a metal is caused by loose electrons in the crystal. A certain electron effect causes an ultraviolet (ie. invisible) color in most metals. However, relativistic effects slow down these electrons in gold, causing a visible yellow color. An unusual case where the laws of relativity matter in chemistry.

By the way, remember the alchemists who wanted to make gold from less precious metals? Last century, nuclear scientists did manage to make gold from mercury by neutron bombardment. However, this only resulted in radioactive gold atoms, showing once and for all that hubris leads to radiation sickness.

Platinum, Pt
Melting point: 1768 °C, 3215 °F
Boiling point: 3825 °C, 6917 °F
Atomic mass: 195 u
Density: 21.5 kg/L

Another rare and precious metal. The price of platinum is much more volatile than that of gold, because it’s used mainly in the industry. Its single main use is in catalytic converters in cars. Platinum is actually a really good catalyst for a lot of reactions.

In catalytic converters, it converts toxic exhaust gases into less dangerous ones. A catalytic converter contains no more than a gram or two of platinum, but that’s still worth about $100. You’d think that’d be worth recycling, but the problem is that a solid catalyst works best if it’s spread out as thinly as possible. It’s quite hard to separate the platinum layer from the rest of the device. It’s expected that as platinum prices continue to rise, recycling becomes more common.

Titanium, Ti
Melting point: 1668 °C, 3034 °F
Boiling point: 3287 °C, 5949 °F
Atomic mass: 47.9 u
Density: 4.51 kg/L

Titanium is a rather light metal that is known for its strength. It’s about as strong as low-grade steel, but 45% lighter. Like aluminium, it oxidizes quite fast but becomes passive by forming an impenetrable titanium oxide coating. However, in regular air it burns before it melts, which probably makes it more difficult to cast. It also reacts with the usually inert nitrogen gas to form titanium nitride.

The metal has a lot of different applications in alloys, and it’s used for certain products where its strength, corrosion resistance and light weight are important, such as bike frames and tennis rackets. It is rather expensive, so it’s mostly used in higher-end products.

The main use of the element titanium is in TiO₂. Titanium dioxide is used as a pigment in paints, foods, toothpastes and so on. It’s high refractive index also makes it very useful as an UV blocker in sunscreen.

The alloys
As I said, I don’t know too much about this stuff, so please let me know if I miss something obvious.

Raw Platinum, Pt/Au
The alloy of gold with a white metal (such as platinum) is called ‘white gold’. Platinum/gold is sometimes used in jewelry. I can’t find much more info on it. Wikipedia says that in nature, platinum is found by itself or alloyed with iridium, not with gold. Sometimes, ‘pebbles’ of platinum were found in or near gold deposits, though.

Ferrotitanium, Fe/Ti
Ferrotitanium is used in steel making as a cleansing agent. Pure titanium would work, but its higher melting point and lower density makes it bothersome. Most alloys are not actually 50/50, and one source says ferrotitanium usually is either 40% Ti or 70% Ti.

Aluminium Bronze, Cu/Al
Once again, there are different grades of this alloy. The most common ones are 5 – 11% Al. Aluminium Bronze has a golden color and as a higher strength and corrosion resistance than many other bronze alloys. It is used in undersea applications, as marine organisms such as barnacles will not colonize the material. It’s also used for tools in non-sparking environments, for some anti-corrosive applications, and sometimes in jewelry.

There are other Cu/Al alloys. One of them is Nordic gold, made of mostly copper and aluminium, with small amounts of tin and zinc. 10, 20 and 50 eurocent coins are made from this alloy. Another one is duralumin, which has aluminium as its main component. There’s 4% copper and small amounts of magnesium and manganese in this alloy. Duralumin is age-hardenable, which means that if it’s left at room temperature for a few days after quenching, it will slowly harden. It’s not as corrosion resistant as pure aluminium, though.

It was notably used to build airship frames in the 1920’s and 1930’s. The frame of the Hindenburg was made of duralumin. Nowadays, duralumin is used in aircraft and spacecraft.

Adamantine, Fe/Al
The words adamantine and diamond have a similar etymology. They come from a Greek word meaning ‘untameable’. ‘Adamantine’ is often used poetically to describe any very hard material. There is a real mineral called adamantine, but that’s just a form of corundum (Al₂O₃, that stuff that also forms rubies and sapphires).

The actual alloy is just called ferroaluminium. One site describes its main benefit is that it increases the heat sensitivity of alloys it’s added to. It lowers the melting point of alloys and increases their combustibility. Iron oxide and aluminium together form ‘ferroaluminium thermite’, which reacts to release a huge amount of heat. It’s used for welding and in fireworks.

Orichalcum, Au/Cu
This is a rather interesting one. Apparently, a lot of ancient cultures made a valuable alloy that may or may not have been Cu/Al. Each culture had a different name for the stuff. It’s been called Corinthian Bronze (Greek/Latin), Hepatizon (which was a less valuable kind of Corinthian Bronze), Orichalcum (Greek/Latin; both the name of a legendary metal from Atlantis and this alloy, Tumbaga (name given by Spaniards to the metal they found in South American artifacts) and Shakudō (Japanese). It seems the stuff was mostly used for religious artifacts and other kinds of trinkets.

In modern times, the alloy is called rose gold (75% gold/25% copper), red gold (50/50) or pink gold, due to its color. It’s used in jewelry. There is also ‘crown gold’ which is 22 karat (91.7% gold) and which is used in gold bullion coins, for instance in England and for the American Gold Eagle coin.

A Cu/Au alloy also exists naturally, in that case it’s called auricupride.

Mithril, Pt/Ti
The name Mithril originally came from Tolkien’s Lord of the Rings. If you don’t know what it is, I suggest you go read the books.

Searching for the actual alloy yields a few papers. It doesn’t seem to have a specific name. One article notes that adding a few percent of titanium to platinum hardens it so that it can be used for jewelry that doesn’t get scratched as easily. It seems it might also have certain catalytic properties. The alloy might also have a use as a catalyst in some kind of fuel cell.

Feasibility of the reaction
Feasibility: medium.

Making alloys is the easy part, just melt the pure metals and mix them. But to do so, we first need to get the pure metals. Fractional melting (like distillation, but you separate liquid from solid instead of gas from liquid) won’t work, because alloys often form an eutectic mixture, that has a lower melting point than the constituent metals. In certain cases it might be possible to melt an alloy and wait for the heavier metal to sink to the bottom. Differential dissolution (in acids) or differential electrolysis may be better options. It’s possible to separate alloys, but it’s a lot of trouble and it might not be worth the cost.

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Precious Tears
Input: Silver
Output: 1-Sulfinylpropene

Silver, Ag
Melting point: 962 °C, 1763 °F
Boiling point: 2162 °C, 3924 °F
Atomic mass: 108 u
Density: 10.5 kg/L

Ah, I think this is the last of the ‘medal’ metals. As a noble metal, it’s used in jewelry, coins, expensive mirrors and of course ‘silverware’. Most jewelry silver is actually Stirling Silver, an alloy of 92.5% silver and 7.5% copper. That stuff is sturdier than pure silver.

Silver has the highest electrical and thermal conductivity of all metals, but because of the big cost difference, it’s not used nearly as much as copper in electrical applications. Silver also forms many compounds. For some decades, the main use of silver was in silver nitrate and silver halides on photographic film.

Historically, silver was used to ward off evil and diseases. It was believed that silver stops the supernatural, such as werewolves. It does actually inhibit the growth of bacteria and fungi, and was used to preserve foodstuffs. About a century ago, silver was approved for use in wound healing creams. People took colloidal silver (tiny grains of silver suspended in water) as an antibiotic. It didn’t work very well and in the 1940’s it was replaced by better and safer antibiotics. Research has shown that the skin creams aren’t very effective either, and can even slow the healing process.

For some reason, colloidal silver popped up as an ‘alternative medicine’ in the 1990’s. This time, quacks claim it cures everything, from cancer to diabetes to AIDS. This has led to a few recent cases of argyria. The silver can’t leave the body anymore and gets stored in body tissue such as skin instead. This causes argyria, a condition in which the skin irreversibly turns bluish-gray. Doesn’t look pretty.

1-Sulfinylpropene, syn-Propanethial-S-oxide, C₃H₆SO
Melting point: Unknown
Boiling point: 101 °C, 214 °F (predicted)
Molecular mass: 90.14 u
Density: ~1kg/L (predicted)

This one is confusing me. Let’s start with the facts. This substance is released as a gas from onions when you cut them. It irritates the eyes, causing you to cry. The S-O group is called sulfinyl or sulfoxide. The S-O bond is actually somewhere between a double bond and a polar single bond, with a negative charge on the O and a positive on the S.

The first confusing bit is the name. Wikipedia uses the 1-sulfinylpropene name, while many other resources call it 1-sulfinylpropane. Usually, the S in S-O is bonded to two carbons, and there’s no naming confusion. In this case, it has that S=O double bond. But propene implies there’s a C=C double bond. Call it sulfinylpropane, and it might be confused for the compound propyl-SO-propyl (as chemists sometimes leave the 'di' out in such cases). The IUPAC may or may not have a rule for this, their ways are mysterious.
To avoid confusion we can use its alternative name propanethial-S-oxide. Propanethial is CH3-CH2-CH=S. Add S-oxide to say there’s an oxygen bonded to the S and we’re done. The syn has to do with stereochemistry.

The second confusing thing is the lack of information. No measured melting point, boiling point or density, and nothing much else either. That’s really weird for a molecule that’s that common. There’s some articles about how it’s formed in onions, but that’s about it. I did find a post by someone who ran into the same problem researching this molecule. By the way, the predicted boiling point might be way off. Substances (such as water) form vapor below the boiling point, but the amount of vapor is pretty low at room temperature. Either this stuff is strong even at low concentrations, or the real boiling point is way lower.

I still can’t wrap my head around the fact that they did identify this compound but there’s no physical information available at all. It doesn’t strike me as something too unstable to work with.

Feasibility of the reaction
Nuclear reaction. 'nough said.