Crystall structures of Cu, Al, and Fe at different temperatures.

[SrEstroncio]

I was wondering if someone could tell me (in pedestrian terms) what are the crystal structures of aluminum, copper and iron as a function of the temperature.
I just read the chapter on crystalline arrays of Callister's Materials Ecience & Eng. but the book just says that Cu and Al have a FCC structure at room temperature, while Fe has a BCC structure, but it doesn't go much farther than that, and as I have basically no previous knowledge of the subject, I can't easily read more advanced texts.

Thanks in advance.

Note. Since this isn't a standard problem-solution type of question I posted it here instead of the homework help sections; please tell me if I should change this.

 

[johng23]

The phenomenon of a single element having multiple crystal structures is called allotropy. Here's the wikipedia article on the allotropes of iron for example: http://en.wikipedia.org/wiki/Allotropes_of_iron

If you only want to know what the crystal structures are at various temperature, that's probably information that you can search for. As for the exact reason why an element takes the crystal structure that it does at a given temperature, I'm afraid that that's a complicated condensed matter physics problem, which probably doesn't have any intuitive explanation in most cases. I expect it has to do with the energy distribution of the electrons in the solid at a given temperature, among other things. It probably requires some complicated theoretical modelling.

It can also depend on the exact conditions in which the material forms, but that's kind of a less fundamental issue.

Maybe there is a simple physical picture in some of these cases, but I wouldn't hold your breath! Let me know if you find out. :)

 

[luoye]

well, there is a concept called polymorphism.including displacive and reconstructive.You can get well understanding if you have a look of the book "Fundamentals of Materials Science"

 

[luoye]

normally, Fe will translate from γ-Fe to α-Fe at 912℃. and the former is FCC, while the latter is BCC. The polymorphism will cause the change of coordination number, which will further cause the change of the radii of the atom. Just take Fe for example, the coordination number changes from 12, FCC, to 8, BCC, and the change of the unit volume is about -0.00641

 

[alphy]

Sure, I'd be happy to explain the crystal structures of copper, aluminum, and iron at different temperatures in simpler terms.

First, let's define what a crystal structure is. A crystal structure is the arrangement of atoms or molecules in a solid material. It is like a 3D puzzle where the atoms fit together in a specific pattern. This pattern determines the properties of the material, such as its strength, electrical conductivity, and melting point.

Now, let's look at the three elements you mentioned: copper, aluminum, and iron. At room temperature, which is about 25 degrees Celsius, copper and aluminum have a crystal structure called FCC, or face-centered cubic. This means that the atoms are arranged in a cube shape with an atom at each corner and one in the center of each face. This structure is very stable and allows for the atoms to be tightly packed together, making copper and aluminum strong and malleable.

On the other hand, iron has a crystal structure called BCC, or body-centered cubic, at room temperature. In this structure, the atoms are arranged in a cube shape with an atom at each corner and one in the center of the cube. This structure is also stable, but not as tightly packed as the FCC structure. This makes iron less malleable than copper and aluminum, but it is still a strong material.

Now, as the temperature changes, so does the crystal structure of these elements. For example, if we heat up copper to 1084 degrees Celsius, it will change from FCC to a different structure called BCC, just like iron. This is because at higher temperatures, the atoms have more energy and can move around more, causing the structure to change.

In summary, copper and aluminum have a FCC crystal structure at room temperature, while iron has a BCC crystal structure. At higher temperatures, all three elements can change to the same BCC structure. I hope this helps to explain the crystal structures of these elements in simpler terms. If you have any further questions, please let me know.