Process Biotechnology

Engineering Materials Corrosion Types of corrosion Corrosion can be classified according to the appearance of the corroded metal; 1. 2. 3. 4. 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. 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. 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.

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. Engineering Materials Corrosion Methods of corrosion control or prevention: Metallic Nonmetallic Materials selection Coating

Design Corrosion control or prevention Metallic Inorganic Organic Avoid excessive stresses Avoid dissimilar metal contact Avoid crevices Exclude air Cathodic & anodic protection Environmental control

Temperature Velocity Oxygen Concentration Inhibitors Cleaning Engineering Materials Corrosion Cathodic protection 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 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 Furnace Lining brick Ceramic tiles porcelain 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). Diamond Graphite Carbide tools Engineering Materials Ceramic and Glasses materials 1.

Charge Neutrality: --Net charge in the crystal structure should be zero. CaF 2: Ca2+ + cation Fanions F- Engineering Materials Ceramic and Glasses materials

- + - - - - stable + -

- - - stable + - unstable 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. - +

- - - - stable + - - -

- stable + - unstable 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. Engineering Materials

Ceramic and Glasses materials rcation ranion < .155 Coord # 2 .155-.225 3 .225-.414 4 .414-.732 6 .732-1.0 ZnS (zincblende) 8

NaCl (sodium chloride) CsCl (cesium chloride) Engineering Materials Ceramic and Glasses materials 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?

CationIonic radius (nm) rcation ranion Al 3+ 0.053 Fe 2+ 0.077 Fe 3+ 0.069 Ca2+ 0.100 Anion O2ClF- 0.077 0.140 0.550

based on this ratio, --CN = 6 --structure = NaCl (rocksalt) 0.140 0.181 0.133 FCC; other examples are MgO, MnS, LiF. Engineering Materials Ceramic and Glasses materials Engineering Materials Ceramic and Glasses materials

Engineering Materials Ceramic and Glasses materials Example: ZnS Zinc Blende Structure Zn2+ + S2What is the CN ? What should be the structure ? Engineering Materials Ceramic and Glasses materials Ceramic Density Computations Density ( )

( No. cations per unit cell atomic mass No. anions per unit cell atomic mass) Vc N A VC: volume of the unit cell NA: Avogadros number, 6.023 X 1023 (formula units)/mol 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. 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. for Zinc blende (ZnS) a 4 (r R ) 3 Engineering Materials Ceramic and Glasses materials Ceramic Density Computations

Example 3: calculate the density of Uranium oxide (UO 2). 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.

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