Are there any materials immune to the type of mass loss the IPK had

[TitaniumVCarbon]

The IPK gradually lost microscopic amounts of mass despite not being of a weak material and being far from the platinum alloy’s (it is made of a platinum-iridium alloy) failure point. Why does this happen and what materials are immune to this? Is it only materials that are made of pure elements (e.g. graphene, pure titanium, etc.) that are immune to this occurrence?

 

[berkeman]

IPK = International Prototype Kilogram?

https://www.theverge.com/2018/11/13/18087002/kilogram-new-definition-kg-metric-unit-ipk-measurement

 

[Bystander]

Vacuum casting techniques have evolved between then, 19th century, and today: from B's citation,

"The exact reason for this discrepancy isn’t known, but one theory is that handling protocol over the years might have been followed less than rigorously, leading the IPK to be contaminated in some way. BIPM director Milton suggests this is one possible cause, and points to the fact that the IPK’s mass changed between the 1940s and the 1990s, but not since then, as evidence. “What we do know is that the measurements in the recent era, the last 30 years, seem to be in good control,” says Milton."

 

[Baluncore]

The IPK gradually lost microscopic amounts of mass despite not being of a weak material and being far from the platinum alloy’s (it is made of a platinum-iridium alloy) failure point. Why does this happen and what materials are immune to this?

First, you need several models for the loss of mass, then you need to analyse the models, one by one.

My favoured model for the loss of mass is based on the fact that all metals that are melted and wetted, or welded, contain some dissolved hydrogen in their matrix. That hydrogen is under pressure and slowly diffuses through the matrix until it reaches the surface to escape. In some metals, trapped hydrogen can be destructive.
https://en.wikipedia.org/wiki/Hydrogen_embrittlement
Hydrogen is not normally a problem in platinum, as it has plenty of room to move through the open metal sieve. Unfortunately, if you store your platinum in a vacuum, like the IPK, it will suffer a loss of hydrogen mass, a diffusion loss, greatest in its early life.

Now, if you can select a (probably eutectic) alloy, with a small atom that plugs the holes in the sieve, and that crystallises in a well-ordered structure, you have a possible winner. Unfortunately, those alloys will be hydrogen-embrittled, so will be little used, and rejected from previous studies by the metallurgists. But if it was obtained and then processed as a single alloy crystal, like semiconductors are today, then it could be swept of hydrogen and impurities, to be used as a mass standard with longer term stability.

 

[TitaniumVCarbon]

Vacuum casting techniques have evolved between then, 19th century, and today: from B's citation,

"The exact reason for this discrepancy isn’t known, but one theory is that handling protocol over the years might have been followed less than rigorously, leading the IPK to be contaminated in some way. BIPM director Milton suggests this is one possible cause, and points to the fact that the IPK’s mass changed between the 1940s and the 1990s, but not since then, as evidence. “What we do know is that the measurements in the recent era, the last 30 years, seem to be in good control,” says Milton."

That doesn’t answer the question. The question is why materials that haven’t reached their failure or melting point still lose mass.

 

[TitaniumVCarbon]

IPK = International Prototype Kilogram?

https://www.theverge.com/2018/11/13/18087002/kilogram-new-definition-kg-metric-unit-ipk-measurement

Yes

 

[Rive]

The question is why materials that haven’t reached their failure or melting point still lose mass.

As a specific question the answer is just not known: as a general question there are just too many possible answers.
In extreme circumstances or for extreme requirements the behavior and interactions of materials can be very surprising, even 'lively'.

These kind of details just comes as somebody gathers experience in engineering. For me one such experience was to accidentally come across the 'tin whiskers' of the supposedly dead solders I use daily.

 

[f95toli]

That doesn’t answer the question. The question is why materials that haven’t reached their failure or melting point still lose mass.

As far as we know, they don't.
One of the (many) problems with standards based on artefacts is that you actually occasionally have to compare your secondaries to the primary. That is, you actually have to do a measurement. This in turn means that you have to handle the artefacts and no matter how careful you are it is always possible to you somehow "damage" them and they might gain or loose mass. There is no way to know if the IPK would have lost mass if it had just been left alone in a vault and never touched.

Even things like routine cleaning of mass artefacts (secondary standards are still used for calibration) is far from trivial; if you are too harsh you might remove mass; if you don't do it well enough it might gain mass because it picked up stuff (dust, pollution etc) from the environment.
There are -literarily- scientists who has spent a large portion of their careers developing techniques for this. If you do a search you should be able to find plenty of papers on the subject.

 

[TitaniumVCarbon]

As far as we know, they don't.
One of the (many) problems with standards based on artefacts is that you actually occasionally have to compare your secondaries to the primary. That is, you actually have to do a measurement. This in turn means that you have to handle the artefacts and no matter how careful you are it is always possible to you somehow "damage" them and they might gain or loose mass. There is no way to know if the IPK would have lost mass if it had just been left alone in a vault and never touched.

Even things like routine cleaning of mass artefacts (secondary standards are still used for calibration) is far from trivial; if you are too harsh you might remove mass; if you don't do it well enough it might gain mass because it picked up stuff (dust, pollution etc) from the environment.
There are -literarily- scientists who has spent a large portion of their careers developing techniques for this. If you do a search you should be able to find plenty of papers on the subject.

It still doesn’t make sense how the material is losing mass even far from its failure point. Maybe the lost mass is electrons?

 

[Baluncore]

It still doesn’t make sense how the material is losing mass even far from its failure point. Maybe the lost mass is electrons?

That hydrogen is under pressure and slowly diffuses through the matrix until it reaches the surface to escape.

 

[TitaniumVCarbon]

Yes, but someone mentioned even just cleaning it removed atoms.

 

[Tom.G]

It still doesn’t make sense how the material is losing mass even far from its failure point. Maybe the lost mass is electrons?

Then it would have a positive charge and collect dust and pollen and....

 

[f95toli]

Yes, but someone mentioned even just cleaning it removed atoms.

Which is entirely possible. Remember that we are talking about surfaces here; not the bulk material. Real life surfaces are very, very messy and unless the material is kept in ultra-high vacuum (which the IPK was not) the surface will be covered in all sorts of stuff: hydrocarbons, water etc. This means that even if the bulk is very stable you can easily add/remove atoms/molecules from a surface simply by simply wiping it down.

Secondly, if you look around online you should be able to find images of what the surface of the secondary standards actually look like (we can assume that the surface of the IPK looks similar). As expected, it is not an atomically flat surface but one can see scratches, grain boundaries etc. This is just what a real surface looks like. This also means that there are plenty of places where the surface might be a bit weaker (meaning you might remove atoms) and/or where impurities can accumulate.

 

[TitaniumVCarbon]

Which is entirely possible. Remember that we are talking about surfaces here; not the bulk material. Real life surfaces are very, very messy and unless the material is kept in ultra-high vacuum (which the IPK was not) the surface will be covered in all sorts of stuff: hydrocarbons, water etc. This means that even if the bulk is very stable you can easily add/remove atoms/molecules from a surface simply by simply wiping it down.

Secondly, if you look around online you should be able to find images of what the surface of the secondary standards actually look like (we can assume that the surface of the IPK looks similar). As expected, it is not an atomically flat surface but one can see scratches, grain boundaries etc. This is just what a real surface looks like. This also means that there are plenty of places where the surface might be a bit weaker (meaning you might remove atoms) and/or where impurities can accumulate.

So three possibilities

- the bulk strength is different from the atom atom bond strength

- making atom atom bond strengths that mean single atoms don’t get wiped off is hard or impossible (even carbon, with its atom bond strength loses atoms in this case)

- these hydrocarbons weaken atom bonds enough to allow for mass loss

Why would the messiness of the surface affect mass loss? It doesn’t change the atom bonds or bulk properties

 

[Vanadium 50]

The inside is chemically inert. The outside is sitting in a bath of chemically active materials - water, oxygen, carbonic acid, hydrogen, dust (which is filled with icky stuff) and so on.