Table of Contents
- 1 Does BCC have octahedral voids?
- 2 Why are tetrahedral voids smaller than octahedral voids?
- 3 Where are octahedral voids in BCC?
- 4 How many octahedral interstices are there in BCC?
- 5 What is the solubility limit of carbon in BCC iron?
- 6 Where are octahedral voids located in BCC?
- 7 What is the ratio of octahedral voids to effective atoms?
- 8 What is the ratio of tetrahedral voids to atoms in FCC?
Does BCC have octahedral voids?
So, bcc has 2 atoms, then the number of octahedral voids will be 2 and the total number of tetrahedral voids will be = 2 x 2 = 4. Note: The total number of octahedral voids in fcc (face-centered cubic) will be 4 and the total number of tetrahedral voids will be 8 because the number of atoms in fcc is 4.
Why are tetrahedral voids smaller than octahedral voids?
The size of the tetrahedral void is smaller than that of the octahedral void. The size of tetrahedral void is equal to that of the octahedral void. The size of tetrahedral void may be larger or smaller or equal to that of the octahedral void depending Upon the size of atoms.
Why a higher concentration of carbon will dissolve in FCC iron than in iron that has a BCC crystal structure?
FCC interstitial radius(0.41R) is larger than BCC (0.291R). R is the radius of atom.so more carbon atoms are soluble in FCC then BCC. Reason is a carbon atom occupies octahedral interstitial sites in these crystals. Octahedral interstitial site of BCC ferrite is much smaller for carbon than that of FCC austenite.
How many octahedral voids per unit cell of BCC are present?
Total number of octahedral voids present in unit cell of cubic close packing, including the one that is present at the body centre, is four.
Where are octahedral voids in BCC?
A body-centered cubic unit cell has six octahedral voids located at the center of each face of the unit cell, and twelve further ones located at the midpoint of each edge of the same cell, for a total of six net octahedral voids.
How many octahedral interstices are there in BCC?
We have 12/4 +1 = 4 positions per unit cell. Here we have octahedral sites in the bcc lattice. We have 12/4 + 6/2 = 6 positions per unit cell.
Is octahedral void larger than tetrahedral void?
Tetrahedral voids are bigger. Octahedral voids are smaller as compared to tetrahedral voids.
Why diffusion coefficients of carbon in BCC and FCC iron at temperature 912 C are difference?
The diffusivity of C is higher in bcc iron due to lower atomic packing and more interstitial void space compared to the fcc structure. More space leads to easier interstitial impurity motion.
What is the solubility limit of carbon in BCC iron?
The carbon interstitials can occupy edge centered or face centered sites in the bcc unit cell. The iron – Fe3C phase diagram indicates that the maximum solubility of carbon in ferrite occurs at the eutectoid temperature of 727 C and is 0.022 wt \% C in the iron matrix.
Where are octahedral voids located in BCC?
3 Answers. BCC doesn’t have any tetrahedral voids, however we have octahedral holes at face centres. Four adjacent corners and two closest body centres. In a homogeneous lattice the octahedral is compressed along the body-centre-atom axis.
How many irregular octahedral voids are in a BCC unit cell?
So the number of irregular octahedral voids per cell is 3 (at faces)+3 (at edges) = 6 per cell. Since a BCC unit cell has 2 atoms per cell, the number of octahedral voids per atom is 6/2=3 per atom.
What is the difference between tetrahedral and octahedral void in gamma-iron?
In gamma-iron (FCC), the octahedral void can accommodate-fit a spherical atom of 0.52 A radius, whereas the tetrahedral void in the FCC gamma-iron can accommodate-fit an atom of 0.28 A radius. Thus, the carbon atom (0.77 A radius) or the nitrogen atom (0.71 A radius) sits in the larger octahedral void with an expansion of the lattice.
What is the ratio of octahedral voids to effective atoms?
As there are 4 atoms per unit cell in FCC crystal, the ratio of octahedral voids to effective atoms per unit cell is 1: 1. The largest sphere (solute atom) which touches its six solvent large spheres, and which can fit tight in an octahedral void is 0.414 r x where r x is the radius of solvent atom.
What is the ratio of tetrahedral voids to atoms in FCC?
Thus, the ratio of tetrahedral voids to atoms per unit cell of FCC comes out to be 2:1. The size of the atom which can fit tight in the tetrahedral void is 0.225 r; where r is the radius of the solvent atom in the close packed arrangement.