Why isn’t stainless steel attracted to a magnet? Stainless steel contains a high amount of iron. Isn’t that enough to make it attracted to a magnet?
In: Chemistry
>Fundamentally, the reasons why ferritic stainless steels are ferromagnetic while austenitic stainless steels are not are quantum-mechanical in nature. Suffice it to say a ferromagnetic metal consists of atoms that have an incomplete inner core of electrons and a crystal structure that results in a high density of electron states in the energy bands formed from the incomplete atomic inner core. It also has an atomic spacing that allows for exchange effects among electrons in the energy bands associated with the incomplete inner-core level. If the atoms in the metal crystal are too widely spaced, the exchange effects are too small to cause alignment of the magnetic moments of neighboring atoms and the crystal will not exhibit ferromagnetism. The requirement of a high density of states stems from the Pauli Exclusion Principle. This principle prohibits electrons with the same spin from occupying the same energy level. Consequently, if the density of electron states is relatively small, electrons will need to occupy higher energy states in order for all to have the same spin. If the increase in energy resulting from the occupancy of higher energy levels exceeds the decrease in energy resulting from electron exchange energy, the structure will not be ferromagnetic.
https://www.scientificamerican.com/article/why-dont-magnets-work-on/
Nickel and chromium are added to make it stainless; when the level is high enough it impedes the magnetic attraction.
Holy heck, I can’t wait to see one of the better explanations 🙂
Some stainless steel is magnetic. Austenitic stainless steels are not magnetic and are made with extra elements like nickel and the atoms are arranged in a very specific way. There is also ferritic stainless steel which is magnetic.
It’s not magnetic?
I never knew. TIL.
Now i wait for some smart guy to explain why.
Most stainless steels encountered by the average Joe have a grain structure that metallurgists call austenitic, while regular steel is ferritic. One of the differences between these is whether the material is magnetic or not. The grain structure of regular steel changes from ferrite to austenite at very high temperatures, but reverts back as it cools. If we add alloying elements like nickel, we can retain the austenitic structure through the cooling process.
Not all iron is magnetic iron is ferromagentic and there is a total of 6 types of magnitism
It isn’t the chemicals (types of atoms) the material is made of that makes it magnetic, it is a function of the types of microscopic structures those atoms form. Pure iron forms structures which can be magnetized at room temperature, but when you add extra elements, it can change the types of structures formed, and make the metal non-magnetic even if it is still mostly iron.
The opposite can also be true. Some chemicals which are generally not thought of as magnetic can become magnetic if they are mixed together in the right way.
Also interesting is that while iron is magnetic at room temperature, if you heat it hot enough, the shape of the internal structures changes, and iron looses its magnetism until it cools back down again. Blacksmiths use this as a way to estimate the temperature of a hot piece of metal.
This is why you need to be careful with stainless steel pans, particularly older ones, if you buy an induction hob. Cheap modern stainless pans (like aluminium pans) have a steel or iron disc in the base; better modern stainless pans use stainless steel which is not austenitic. But if you have good old pans, you might find they either don’t work or don’t work well.
When I bought an indiction hob I gave my (non-induction-using) daughters my lovely early 1990s Spring pans, because they don’t work. Spring pans are a sandwich of stainless and aluminium; the modern Spring pans do work, but they had to change the formulation of the stainless steel. I think it used to be 18/10 inside and out, now 18/10 inside and 18/0 outside? Something like that.
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