1. Engineering Materials
Corrosion
Types of corrosion
Corrosion can be classified according to the appearance of the corroded metal;
Uniform or general corrosion
Pitting corrosion
Galvanic corrosion
Crevice corrosion
1. Uniform or General Corrosion
The metal loss is uniform from the surface.
Often combined with high-velocity fluid erosion, with or without abrasives.

2. Engineering Materials
Corrosion
Types of corrosion
Pitting Corrosion
The metal loss is randomly located on the metal surface. Often combined with stagnant fluid or in areas with low fluid velocity.

3. Engineering Materials
Corrosion
Types of corrosion
Galvanic Corrosion
Occurs when two metals with different electrode potential is connected in a corrosive electrolytic environment.
The anodic metal develops deep pits and groves in the surface.

4. Engineering Materials
Corrosion
Types of corrosion
Crevice Corrosion
Occurs at places with gaskets, bolts and lap joints where crevice exists.
Crevice corrosion creates pits similar to pitting corrosion.

5. Engineering Materials
Corrosion
Methods of corrosion control or prevention:
Metallic
Nonmetallic
Materials selection
Metallic
Inorganic
Organic
Coating
Avoid excessive stresses
Avoid dissimilar metal contact
Avoid crevices
Exclude air
Design
Corrosion control
or prevention
Cathodic & anodic protection
Temperature
Velocity
Oxygen
Concentration
Inhibitors
Cleaning
Environmental control

6. Engineering Materials
Corrosion
Cathodic protection

7. Engineering Materials Ceramic and Glasses materials
Ceramic material:-
Inorganic, nonmetallic materials that consist of metallic and nonmetallic elements bonded together primarily by ionic and/or covalent bonds.
Distinguishing Features
Most have a regular arrangement of atoms (except glasses)
Compounds of Metallic and Non-Metallic elements
Density lower than Metals
Hard and stronger than Metals
Low resistance to Fracture
Brittle (low ductility)
High Melting Points (Refractory (ceramic) material)
Poor Conductors of Electricity and Heat (except Graphite, Diamond)
Can be opaque, semi-transparent or transparent

8. Engineering Materials
Ceramic and Glasses materials
APPLICATIONS OF CERAMICS
Electrical Insulators
Thermal insulations and coatings
Abrasives
porcelain
Glasses (Windows, TV screens, Optical fibers)
Cement, Concrete
Ceramic tiles for space shuttles
Furnace Lining brick
Hi-tech ceramics => electronic, communication, computer hardware, aerospace industries
Ceramic tiles
porcelain
Furnace Lining brick

9. Engineering Materials
Ceramic and Glasses materials
CERAMIC MATERIAL EXAMPLES
Diamond, Graphite
Glasses
Building materials
Oxides (SiO2, Al2O3)
Carbide tools
Compressive strength is typically ten times the tensile strength. This makes ceramics good structural materials under compression (e.g., cement, bricks in building apartments, stone blocks in the pyramids).
Graphite
Diamond
Carbide tools

10. Engineering Materials Ceramic and Glasses materials
Charge Neutrality:
--Net charge in the crystal structure should be zero.

11. Engineering Materials
Ceramic and Glasses materials

12. Engineering Materials Ceramic and Glasses materials
Coordination number (CN):- the number of equidistant nearest neighbors to an ion in a unit cell of a crystal structure. For example, in NaCl, CN=6 since six equidistance Cl- anion surround a central Na+ cation.
Radius ratio (for ionic solid):- the ratio of the radius of the central cation to that of the surrounding anions.
Critical (minimum) radious ratio- the ratio of the central cation to that of the surrounding anions when all the surrounding anions just touch each other and the central cation.

13. Engineering Materials Ceramic and Glasses materials
For a specific coordination number there is a critical or minimum cation/anion radius ratio rC/rA for which this contact can be maintained.

14. Engineering Materials
Ceramic and Glasses materials

15. Engineering Materials
Ceramic and Glasses materials

16. Engineering Materials Ceramic and Glasses materials
EX1: PREDICTING STRUCTURE OF FeO
On the basis of ionic radii, what crystal structure would you predict for FeO?
based on this ratio,
--CN = 6
--structure = NaCl (rocksalt)
FCC; other examples are MgO, MnS, LiF….

17. Engineering Materials
Ceramic and Glasses materials

18. Engineering Materials
Ceramic and Glasses materials

19. Engineering Materials Ceramic and Glasses materials
Example: ZnS – Zinc Blende Structure
Zn2+ + S2-
What is the CN ?
What should be the structure ?

20. Ceramic Density Computations
Engineering Materials
Ceramic and Glasses materials
Ceramic Density Computations
VC: volume of the unit cell
NA: Avogadro’s number, X 1023 (formula units)/mol

21. Ceramic Density Computations
Engineering Materials
Ceramic and Glasses materials
Ceramic Density Computations
Example 1: Calculate the density of NaCl, from a knowledge of its crystal structure, the ionic radii of Na+ and Cl-, and the atomic masses of Na and Cl. The ionic radius of Na+=0.102 nm and that of Cl-=0.181 nm. The atomic mass of Na=22.99 g/mol and that of Cl=35.45 g/mol. Ans=2.14 g/cm3)
Cl 1- occupy the FCC in the unit cell 4 ions and because of the neutrality Na+ must be 4.

22. Ceramic Density Computations
Engineering Materials
Ceramic and Glasses materials
Ceramic Density Computations
Example 2: calculate the density of zinc blende (ZnS). Assuming the structure to consist of ions and that the ionic radius of Zn2+= 0.060nm and that of S2-=0.174nm. The atomic weight of Zn=65.37 g/mol and that of S=32.06 g/mol. (Ans=4.10 g/cm3)
S 2- occupy the FCC in the unit cell 4 ions and because of the neutrality Zn 2+ must be 4.

23. Ceramic Density Computations
Engineering Materials
Ceramic and Glasses materials
Ceramic Density Computations
Example 3: calculate the density of Uranium oxide (UO2). Which has the calcium fluoride (CaF2) structure. (Ionic radii: U4+=0.105 nm and O2-=0.132 nm). The atomic mass of U=238 g/mol and that of O=16 g/mol.
(Ans=10.9 g/cm3)
U 4+ occupy the FCC in the unit cell 4 ions and because of the neutrality O 2- must be 8.