## Introduction to Solid State Chemistry Lecture 24 Notes: Diffusion

Overview

Today’s lecture costs 52 minutes.

Details

Diffusion is random atomic motion.

Fick’s Law: Flux = -Di dCi/dx

Where the concentration is the greatest, the flux is the greatest.

R = Kb x Avogadro’s number = 8.314 J/Kmole

D = Do exp(-Q/RT)

Q represents an activation process or an activation energy.

THe idle speed is 10^13 cycles per second, the Debye frequency. The atoms are pulsating. The jump frequency is about 10^8 hertz, 1 try per 100,000 is successful. Q must involve the vacany formation + energy for atomic migration. Activation energy for diffusion scales with melting point.

Substituational atoms sit on a vacant site. Interstitial sites. THe pulsating lattice moves isotopes throughout a sample. C60 and C59 in a sample. The picture in the book has no vacancies. We need vacancies to jump.

Graphite is sp2, covalently bonded.

PV=nRT

Ci=ni/V=Pi/RT

Total charge = I x time

total mass loss = mass flow rate x area x time x J

dCi/dt = Di d2C/dx2

(C-Cs)/(Co-Cs) = erf (x/2sqrt(DT)) = x/2sqrt DT = x/sqrt DT

This will give you an order of magnitude calculation – minutes, hours, days. Like most teachers, he hooks as a consultant on the side.

Conversion efficiency has a nice compromise at 14.6:1. CO and HC are oxidation reductions, NO is a reduction reaction. We rely upon solid state diffusion which is slow so we add vacancies to increase speed.

V = (-RT/4F) ln (0.21/pO2)

Review

pH = pK + log base/acid

y=mx + b

Cuprite CU2O

Chalcocite CU2S

Chalcopyrite CuFeS2

Tenorite CuO

Hematite Fe2O3

Magnetite Fe3O4

Oxidising agents give oxygen to another substance.

Reducing agents remove oxygen from another substance.

Oxidation is loss of hydrogen.

Reduction is gain of hydrogen

MAC glass = mobility arrangement cooling rate

half life of C14 5720 years

IE13 electron acceptor, electrophile, nonmetal.