Home > Uncategorized > Introduction to Solid State Chemistry Lecture 20

Introduction to Solid State Chemistry Lecture 20

Overview
Today’s lecture is 49 minutes. Looks like his tests are essay questions. Electronic structure dictates behavior. I just noticed that he lectures from notes. The notes are laid out on the table.

Details
The measured value of yield strength is about 1/10th of the theoretical value. To release a plane, bond strength x bond density. Dislocations allow one to shear a crystal cheaply. Make the kink and kick your foot. Misregistry

2D defects. One is the free surface defect and internal interfaces. Surfaces are high energy areas. Those on the surface won’t have the right number of neighbors or bonds. Bonds lower the energy of the system. Higher energy, higher reactivity. Good for catalysts, bad for corrosion.

Francois DuyGray.A grain is a zone of one orientation. Grain boundry engineering controls material properties. For high strength, fine grain structure, small gain size. For ductility, coarse grains.

Voids are vacancy clusters. Managed impurity clusters versus uncontrolled impurity clusters. Precipitation hardening (outside the lattice), solution hardening. Metallugry is dirt to metal (chemical) and change of shape (physical).

Elastic deformation is reversible. Strain only under stress. Displacement only under applied force. Force is the derivative of energy. It’s kind of like Hooke’s law. F=kdx=mg

Plastic deformation is permenant. Slippage is the mechanism. The applied force is ressolved at the atomic level. The slip plane is the one the strongest, the strongest is the one with the highest density plane. At the atomic level, they zigzag. Orthogonal to the slip plane is the weakest.

The slip system is the close packed plane and the close packed direction. Atoms slip, dislocations glide.

The Titanic sunk because of 3D defects.

Slag SiO2-CaO-Al2O3
Metal C-Fe-Si

During making, someone did not wait for the phase seperation. Silicate glass was in the metal. The hole was much larger than it should have been. Hardness means that enormous strength is needed to deform. Tough is the property of being able to take impacts.

These glass strings would have acted as perforations. They would have broke easily. What’s amazing is that there were no checks. It should have been easily detectable.

Making bonds releases energy, breaking bonds costs energy.

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