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by A_D_E_P_T 941 days ago
Almost everything about the article is wrong, oversimplified, or misleading.

Take this paragraph, for instance:

> But despite its abundance, it's only recently that civilization has been able to use titanium as a metal (titanium dioxide has been in use somewhat longer as a paint pigment). Because titanium so readily bonds with oxygen and other elements, it doesn’t occur at all in metallic form in nature. One engineer described titanium as a “streetwalker," because it will pick up anything and everything. While copper has been used by civilization since 7000 BC, and iron since around 3000 BC, titanium wasn’t discovered until the late 1700s, and wasn’t produced in metallic form until the late 19th century.

As this is basically a bunch of bullet points in paragraph form, it'll be easier to handle if we break it down:

> But despite its abundance, it's only recently that civilization has been able to use titanium as a metal (titanium dioxide has been in use somewhat longer as a paint pigment).

The same also applies to aluminum, magnesium, nickel, etc.

> Because titanium so readily bonds with oxygen and other elements, it doesn’t occur at all in metallic form in nature.

The same also applies to aluminum, magnesium, and even iron. (I mean, there's some meteoric iron, but it's very rare.) Pure metals are very rare in nature. What distinguishes iron and copper from aluminum and titanium is the energy required to split the oxide into metal.

> One engineer described titanium as a “streetwalker," because it will pick up anything and everything.

Titanium is not more reactive than aluminum and it's far less reactive than magnesium. In fact, it's slightly less reactive than iron overall. (i.e., more chemically stable under normal conditions and in contact with common acids.)

> While copper has been used by civilization since 7000 BC, and iron since around 3000 BC, titanium wasn’t discovered until the late 1700s, and wasn’t produced in metallic form until the late 19th century.

This has everything to do with the temperature required to separate the metal from the oxygen atoms binding it, and nothing to do with anything else. What's more, it applies even more strongly to aluminum, which was discovered in 1825 -- three decades after the discovery of titanium. (1791.) So there's absolutely nothing unique about titanium in this regard.

I could go on. But basically this is an "I hecking love science" article that barely scratches the surface of the subject -- and still manages to be subtly misleading.

2 comments

> The same also applies to aluminum, magnesium, nickel, etc.

the oxides of aluminum, magnesium, and nickel were not in use as paint pigments

> What distinguishes iron and copper from aluminum and titanium is the energy required to split the oxide into metal. (...) Titanium is not more reactive than aluminum

the particularly relevant issue here, as i understand it, is that titanium has a stable carbide, which prevents you from reducing it carbothermically; you end up with titanium carbide instead of titanium metal. aluminum's carbide is unstable even in water, while iron's carbide is mechanically strong but still easy to reduce to iron with air. copper's carbide is poorly characterized and even more unstable, and it even occurs native

there are other things that titanium reacts more strongly with than aluminum does. titanium tetrachloride, for example, which is mentioned in the article, isn't a mere salt like normal chlorides; it's a volatile fuming liquid, because titanium forms covalent bonds with the chlorine like a motherfucking nonmetal. you can argue about whether this makes it more or less reactive than aluminum in this context; the reaction produces more energy per metal atom but less energy per chlorine atom

this kind of dirty trick is why titanium wasn't isolated until decades after the creation of metallic calcium, sodium, potassium, aluminum, and even the isolation of some of the rare earths

so i think the characterization in the article is fair

> the oxides of aluminum, magnesium, and nickel were not in use as paint pigments

Aluminum oxides were used as a pigment, predominantly in blue (cobalt aluminum oxide) but also in white.

In any case, the dominant white dyes of the Early Modern period -- and prior periods -- were lead based. The presence of TiO2-based pigments is actually one good way to identify a modern forgery.

> the particularly relevant issue here, as i understand it, is that titanium has a stable carbide

This turned out to be solvable via calciothermic or magnesiothermic reduction -- which is now effectively the go-to method for just about everything that can't be reduced with carbon. All titanium dioxide reduction processes demand quite a lot of energy, though; more than aluminum and far more than iron.

people don't make titanium via calciothermic or magnesiothermic reduction of the ore, i don't know why

the magnesiothermic reduction is the actual reduction step of the kroll process, though

The article may be an oversimplification, but your comment is an equal oversimplification. There are many environmental conditions that need to be assumed when comparing reactivity.

For instance, if you have pure Titanium, pure Magnesium, pure aluminum in a vacuum at room temperature and proceed to introduce oxygen, you get the following reactions (simplified elemental chemical reactions, the Enthalpy of formation is what is important here):

Ti + O2 -> TiO2 (Std. Enthalpy of formation is -945kJ/mol)

Mg + O -> MgO (Std. Enthalpy of formation is -601kJ/mol)

4Al + 3O2 -> 2 Al2O3 (Std. Enthalpy of formation is -1675kJ/mol)

As a result, aluminum is most reactive, followed by titanium, then magnesium.

This is the reason why aluminum is used in solid rocket motors and various other explosive devices.

Under different conditions, these numbers may change: for instance a reaction with water instead of air may yield different enthalpies. At quick glance in water, titanium is actually least reactive when compared to aluminum and magnesium.

You can make a general benchmark assumption, e.g. in the Reactivity Series:

https://en.wikipedia.org/wiki/Reactivity_series

So from a high enough vantage point, Ti is very slightly less reactive than Al, less reactive than Mg, and not too far from Fe. A far cry from being "a streetwalker" of a metal.

to make a fair comparison here, you need to normalize per mole of metal. these enthalpies of formation are reported per mole of oxide, but there's twice as much Al per mole of Al2O3 than Ti in TiO2.