This is very cool indeed, but I laughed when I got to the conclusion:
> A limitation of this work is that the resulting de-oxygenated titanium contains yttrium, up to 1% by mass; yttrium can influence the mechanical and chemical properties of titanium alloy. After solving the yttrium contamination problem…
So the process removes the oxygen but then adds yttrium to the metal in significant amounts. That’s not quite the ultra pure titanium I was promised in the headline.
As always, I hope someone figures out the rest of the problem space. As-is, this looks like trading one problem for another.
Very small amounts of oxygen in titanium are enough to make it too hard and too fragile for most applications.
Adding less harmful impurities to bind the more harmful impurities that cannot be otherwise removed (a.k.a. gettering) has always been a major purification technique, both in metallurgy and in semiconductor technology.
Steel is purified in the same way from the more harmful impurities, by adding other impurities like calcium, silicon or manganese or rare-earth metals.
In some cases, the compounds that result from adding impurities may be removed later, e.g. like slag floating on molten steel, but in other cases they may remain in the metal or semiconductor that is the desired end product.
It remains to be seen whether the extra yttrium and yttrium oxide that remain in titanium are harmful enough to make it worth to attempt to remove them somehow. In some cases they may even have beneficial properties, though e.g. for dental implants I would want commercially pure titanium that does not have any other metallic impurities like yttrium (commercially pure titanium includes small amounts of oxygen and of iron, both of which have no harmful effects in living tissues).
> this looks like trading one problem for another.
Every choice trades one problem for another. At a minimum, the new problem is the cost in resources - time, money, personal energy (and in business, usually reputation risk and political capital) - but usually the cost is much more than that, especially when looking at alternative technical solutions. In advice to clients I always present the options as the minimum trade-off (it's my job to minimize it).
More generally, the question is, which scenario of outcomes do you want? It could be the scenario with 1% yttrium is far better than the one with oxygen, or that the ytrrium scenario has a very different set of costs and benefits which make it valuable for certain needs that the oxygen scenario doesn't fulfill. It could be that methods for removing yttrium are already mature and only need to be applied to this case.
But especially in this case, the report is about research & development. If there were no more problems to solve then it wouldn't be R&D. It's really self-defeating to criticize progress in R&D because some problems remain. 'We scored a goal, but that's just trading one problem for another - the other team has the ball!'
The problem in this case is that the headline claimed “ultra pure titanium” and the closing paragraph had a tiny oh-by-the-way mention that the process contaminates the titanium with yttrium.
Which is to say, makes it anything but ultra pure. :)
> It could be that methods for removing yttrium are already mature and only need to be applied to this case.
Sorry but no. That’s specially a problem they highlighted as needing a solution.
I was more terrified by the yttrium fluoride. That rings a pancreatic cancer bell very loudly. Additionally, you can be sure that people who understand much more chemistry than biology (or who might have accepted their own deaths) are going to make... different tradeoffs
That said, I welcome others to look into substituting, eg, aluminum for yttrium in these methods (since titalum is already a thing)
Aluminum would not be a substitute for yttrium. Aluminum can be used to deoxidize less reactive metals, like iron. For a metal like titanium, you need a metal that is much more reactive than it. Yttrium is more reactive than magnesium, though less reactive than calcium, which is why it has been chosen.
Moreover, aluminum is undesirable in titanium implants, even if many surgeons without scruples have used cheaper Ti-Al-V alloys taken from aviation suppliers, instead of more expensive alloys designed specifically for compatibility with living tissues, despite the fact that it was always pretty clear that such Ti-Al-V alloys are not suitable for long-term implants.
Yttrium is also not desirable for implants, so the titanium produced by this method is not good for implants, but it is good for most other applications of titanium, where yttrium is not harmful.
Delving into the paper: Al has defo been used for deoxidizing Ti but they claim it's "inadequate"
The stability of al oxyhalide with respect to al oxide and al halide is the key here? Not sure if that has been "adequately" explored either, especially in experiment
(For the sake of more collaborative conversations on HN, not just dissfests :)
It is likely that most of the titanium deoxidized with yttrium would not be used as such, but it would be used for producing titanium alloys.
For each kind of titanium alloy, depending on its chemical composition and on its intended crystal structure, yttrium may happen to be harmful or beneficial. Yttrium atoms are significantly bigger than titanium atoms. This can influence the crystal structure and the mechanical properties of the alloys, even with only a small percentage of residual yttrium.
Almost pure non-alloyed titanium (which normally contains residual quantities of oxygen and iron) is used in applications where chemical resistance is more important than mechanical resistance, e.g. for medical implants, vessels and pipes exposed to various chemicals, spoons, metal parts that will be in contact with a human body, e.g. rings or bracelets etc.
Yttrium may diminish somewhat the chemical resistance of titanium for such applications, but the resistance might still be adequate for many of these applications.
> Sorry but no. That’s specially a problem they highlighted as needing a solution.
Do you know anything about it? As far as the article goes, they just said it will be ready for production when the problem is solved, not how hard it is.
I'm not sure if it makes it easier, but there are some differences between the high oxygen titanium alloy and titanium with some yttrium in it that might make it easier to separate?
Presumably when you melt the titanium the yttrium doesn't react, whereas the oxygen dissolved in the titanium alloy at room temperature will form titanium dioxide when it's heated (if I'm reading correctly). So maybe you could "just" separate the molten metal by density afterwards? I'm not sure this would work though. For one, you'd need to avoid re-introducing oxygen contamination, but I guess you could do it under a vacuum (yes "just" spin the molten metal at high speed in a vacuum)?
This would seem to me to beg the question of why not just grind up the titanium in a vacuum to remove the oxygen and then melt it down, so I might be missing something here.
Agreed. The original paper states that they have a technique to remove oxygen from the surface of titanium. If that is the case, grinding could be viable. How hard is it to grind titanium?
Ah shit. I can't shift zeros. 1% of 28900 $/mt is $289. [Yeah: My initial assumption was that Yttrium is really expensive - and it fucking is - I ignored my own smell test - I should have caught my mistake].
That is say 5% of the current final price of Ti (ignoring purity) to end up with something with less oxygen but 1% fucked with Yttrium. You can't just increase price by percentage points for highly competitive commodities. You especially can't add dependencies on elements that are in limited supply and supply controlled/constrained by politics.
So this looks like another academic bullshit result that totally ignores economical realities.
> A limitation of this work is that the resulting de-oxygenated titanium contains yttrium, up to 1% by mass; yttrium can influence the mechanical and chemical properties of titanium alloy. After solving the yttrium contamination problem…
So the process removes the oxygen but then adds yttrium to the metal in significant amounts. That’s not quite the ultra pure titanium I was promised in the headline.
As always, I hope someone figures out the rest of the problem space. As-is, this looks like trading one problem for another.