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Contents
8.4.1 Mechanism of Control Protection ..................................... 281
8.4.1.1 Zinc Coatings ........................................................ 281
8.4.1.2 Corrosion of Zinc Coatings ................................. 283
8.4.1.3 Zinc-5% Aluminum Hot Dip Coatings ............. 285
8.4.1.4 Zinc-55% Aluminum Hot Dip Coatings ........... 286
8.4.1.5 Zinc-15% Aluminum Thermal Spray ................ 287
8.4.1.6 Zinc-Iron Alloy Coatings .................................... 288
8.4.1.7 Aluminum Coatings ............................................ 289
8.4.1.8 Cadmium Coatings .............................................. 289
8.4.1.9 Manganese Coatings ............................................ 290
8.5 Mixed Control Protection ................................................................ 290
8.5.1 Phosphate Coatings ............................................................. 291
8.5.2 Chromate Coatings .............................................................. 292
8.5.3 Oxide Coatings ..................................................................... 294
8.5.4 Anodized Coatings .............................................................. 295
8.6 Eclipse Molding Framework (EMF) Control Protection.............. 296
9 Cathodic Protection .................................................................................... 297
9.1 Background ........................................................................................ 297
9.2 Theory ................................................................................................. 298
9.2.1 Sacrificial Anodes ................................................................300
9.2.1.1 Anode Requirements ...........................................300
9.2.1.2 Anode Materials and Backfill ............................. 303
9.2.2 Impressed Current Systems ............................................... 303
9.2.2.1 Current Requirements .........................................304
9.2.2.2 Anode Materials and Backfill .............................304
9.2.2.3 Testing for Completeness of Protection ............305
9.3 Use with Coatings .............................................................................306
9.4 Economics .......................................................................................... 307
10 Corrosion Inhibitors ..................................................................................309
10.1 Inhibitor Evaluation .......................................................................... 310
10.2 Classification of Inhibitors ............................................................... 311
10.2.1 Passivation Inhibitors .......................................................... 311
10.2.1.1 Mechanism of Passivation .................................. 311
10.2.2 Organic Inhibitors................................................................ 315
10.2.3 Precipitation Inhibitors (Cathodic Inhibitors) .................. 317
10.2.4 Vapor-Phase Inhibitors ........................................................ 317
10.3 Inhibition in Acid Solution .............................................................. 318
10.3.1 Physical Adsorption ............................................................ 319
10.3.2 Chemisorption ..................................................................... 320
10.3.3 Interactions between Adsorbed Inhibitors ...................... 321
10.3.4 Relationships between Inhibitor Reactivity and
Efficiency ............................................................................... 321
10.4 Inhibition of Near-Neutral Solutions ............................................. 321