University:
York University
Course:
CHEM 1100 | Chemistry and Materials Science for Engineers
Academic year:

2021
Views:

128

Pages:

2
Author:

Nick T.

Title: 2 Major types of solid solutions Content: Substitutional Interstitial HOSTGUEST OR When guest replaces atoms of host: Substitutional solid soln. e.g., Cu in Ni RCu = 0.128 nm RNi = 0.125 nm FCC structure Close values of radius Interstitial solid soln. e.g., C in Fe RFe = 0.124 nm RC = 0.071 nm Small voids in metals due to ???. Interstitial atom should be very small. Less than 10%. Carbon is way less in radius. If I have 2 metals: Chromium (HCP) Copper (FCC) Why if I put them together they cannot form substitutional solution easily? Why same structure is important? Bonding in FCC and HCP is different. Number of neighbors and coordination number is different. S also what would be the final structure: FCC or HCP? We have energies to break more bonds and then outperform lattice together in order to mix them. Solid Solution = preservation of Structure Ag (92.51) Host Cu (7.5%) Guest If more Cu is added, it will form more unit cells because at this percentage, it's totally dissolved. Every crystal has a unique unit cell, a certain arrangement of atoms in space. Cu will be randomly distributed, so no new crystal will be formed. How do we know there is no new crystal? (Only way) X-ray Diffraction will help us monitor solid solutions. Exactly same peaks mean new crystals were introduced. But they will be slightly shifted. That depends on the impurity size. In host Ce-Sm shift to left? In host Ce-Zr shift to right? Bigger guest added to host, unit cell will shrink instead. Smaller guest was added to host, shift to left? Ce3+ (102.5 pm) vs. Zr4+ (72 pm) (radius difference 30%) 50% of guest, 20% only of host, which applies stress on lattice. SM3+ = 127 pm Unit cells will be expanded because bigger atom replaced host. Second phase particle: Different composition Often different structure