How do the physical properties of the isotope Iron-54 differ from the more common Iron-56?

Submitted by Colonel__Kernel t3_11paxmb in askscience

Iron-54 is a naturally occurring stable isotope of iron, consisting of 5.845% of natural iron found on earth, according to the isotope table found here https://applets.kcvs.ca/IPTEI/IPTEI.html

If one were to separate a mostly pure amount of Fe-54, how would its physical properties differ from the more common Iron-56, which composes 91.754% of natural iron? There is certainly some Iron-54 among normal pieces of iron, but only about 5.8%. For example, if you were to make a sword out of nearly 100% Iron-54, how would it differ from one made out of normal iron? Would it heat treat and temper differently? Would it be ever so slightly more lightweight than normal iron, due to it not having as many neutrons in its nucleus? Would it be more or less resistant to rusting?

16

Comments

You must log in or register to comment.

robot_egg t1_jbyrpjr wrote

You would be very hard pressed to tell the two isotopes apart.

The density of Fe-54 would be slightly lower; a mole of Fe-54 would have the same volume, but would weigh 4% less than a mole of Fe-56. The difference in density could have some secondary effects like relative diffusion rates, etc.

The chemistry of the two isotopes would be identical, except that some reactions of Fe-54 would be slightly faster (specifically where a covalent bond to the iron is being broken in the reaction's transition state).

16

loci_existentiae t1_jbyw309 wrote

Thank you for this cogent easy to understand answer for folks like myself.

Does Fe-54 conduct electricity in the same way as 56? Is it as magnetic? And do we find it commonly enough to build with it like we do with 56? (Last one I'm guessing is a big no and we may never know if we were using it in our materials.)

5

robot_egg t1_jbyywyg wrote

I'm an organic chemist, not a metallurgist. I believe that conductivity and magnetism would be the same, but it's a little outside my wheelhouse.

You're not going to find pure Fe-54 or -56 in nature. They'll be mixed in more or less the natural abundance ratio anywhere you find iron. It's certainly possible to separate them; much easier than enriching uranium.

9

mfb- t1_jbznvga wrote

As long as you don't go to nuclear physics, they behave essentially the same apart from the small weight difference. Conductivity, magnetism and so on is all determined by the behavior of the electrons which don't change here.

The isotope ratio of iron is essentially the same everywhere for the same reason: There is no natural process that would separate them or even accumulate one isotope much more than the other. No matter where you get your iron from you'll have 5.85% of Fe-54 and 91.75% of Fe-56 with only really tiny variations. Artificially you can separate them, if you absolutely want a sword that's 4% lighter.

For iron no one cares, but for uranium these isotope ratios are closely monitored to make sure no one steals it or tries to extract enriched uranium or similar. That's why it was a big deal when uranium from a mine in Oklo had just 0.6% uranium-235 (the main isotope used in reactors and nuclear weapons) instead of the normal 0.72%. Did someone steal something? Turns out this site had a natural fission chain reaction two billion years ago, reducing the amount of U-235.

8

luckyluke193 t1_jbzknt1 wrote

It's extremely rare to have qualitative changes in physical properties due to a change in isotopes. Normally, phase transformations occur at slightly different temperatures, and that's about it.

The only example I can think of is SrTiO3, which becomes ferroelectric at cryogenic temperatures when common oxygen 16 is replaced by the rarer oxygen 18.

6

Lazz45 t1_jc6lxor wrote

Chemical engineer by education, Process engineer in a steel mill by trade (we manufacture electrical steel).

There are no metallurgical differences nor chemical differences to my knowledge. I work in decarburization (carbon removal) and finishing(we anneal then coat the steel in a non conductive coating), but talk to the metallurgists who control the heat chemistry and what they DO care about are

-Carbon

-Manganese

-Phosphorous

-Silicon

-Chromium

-Nickel

-molybdenum

-Titanium

-Copper

-Tin

-Aluminum

-Nitrogen

-Oxygen

-Lead

-Boron

Some of these are only present up to ~3% while others are on the orders of PPM (parts per million) or PPB (parts per billion).

To the original question, any one of these elements being out of wack can ruin the heat and make it a different grade of steel or completely ruin its properties. I have never heard of Iron 54 or 56 ever even mentioned regarding melt chemistries. So I would say this supports a lack of difference both chemically and metalurgically between the isotopes

2