Table of Contents Table of Contents I. Materials Properties and Cathode Construction 1 I. Materials Properties and Cathode Construction 1 INTRODUCTION 1 INTRODUCTION 1 THE CARBON LINING 4 THE CARBON LINING.. 4 Anthracite 5 5 Natural graphite 12 12 Syntetic graphite 12 12 Binders Binders 15 15 Ramming pastes 17 Ramming pastes 17 Cathode blocks 21 Classification Cathode blocks of Cathodes block 2621 Choice Classification of bottom of block cathode materials blocks 3526 Sidewall Choice blocks of bottom block materials 3635 Carbon Sidewall glues blocks and cements 4336 REFRACTORIES AND INSULATION. 48 Carbon glues and cements 43 Thermal insulation 52 REFRACTORIES Alumina powder AND INSULATION 5348 Dense Thermal refractory insulation materials 5452 Composite Alumina powder or sandwich insulation 5453 PROPERTIES Dense refractory OF REFRACTORY materials AND INSULATION MATERIALS 55 54 DIFFUSION AND PENETRATION BARRIERS.. 63 Composite or sandwich insulation 54 Steel plates 64 PROPERTIES Graphite foil OF REFRACTORY AND INSULATION MATERIALS 6555 DIFFUSION Glass AND PENETRATION BARRIERS 6563 Bricks Steel and plates tiles 6664 Monolithic Graphite castables foil 68 65 Dry barrier materials 69 Glass 65 STEEL SHELLS AND SUPPORTS.. 71 INSTALLATION Bricks and tiles 7466 Refractories Monolithic and castables insulation 7468 Collector Dry barrier materials installation 7769 STEEL Bottom SHELLS block AND installation SUPPORTS 83 71 Sidewall 86 INSTALLATION Rammed parts 88 74 CATHODE Refractories MODEL COMPUTATIONS and insulation 9374 WETTABLE Collector CATHODES bar installation 9677 Introduction Bottom block installation 9683 Properties of TIB2 Sidewall materials 97 86 Industrial trials 100 REFERENCES.. Rammed parts 106 88 CATHODE MODEL COMPUTATIONS 93 WETTABLE CATHODES 96 II.PREHEATING, START AND OPERATION.. 107 Introduction 96 PREHEATING Properties AND of STARTUP.. TIB2 materials 107 97 Preheating Industrial methods trials 108 100 REFERENCES Ramming paste 108 106 Liquid metal 111 Anode bake-out 115 Resistive preheating 115 Flame preheating 125 V
II. PREHEATING, START AND OPERATION 111 PREHEATING AND STARTUP 111 Preheating methods 112 Ramming paste 112 Liquid metal 115 Anode bake-out 119 Resistive preheating 119 Flame preheating 129 Electrical panels 140 Liquid bath (cold start) 140 Comparision of preheat methods 141 Conclusions concerning preheat methods 144 Displacements of lining materials 147 THE STARTUP AND BATH SOAKING PERIOD 149 EARLY OPERATION 159 NORMAL OPERATION 162 Temperature and bath ratio 162 Heat balance and ledge formation 167 Potholes and cracks 170 POT LIFE PREDICTION 170 REFERENCE 180 III. CHEMICAL REACTIONS AND WEAR 183 GASIFICATION AND OTHER SURFACE REACTIONS 183 Carbon lining oxidation 183 Oxidation and exfoliation of steel shell 186 FORMATION OF ALUMINIUM CARBIDE 189 LABORATORY WEAR EXPERIMENTS 193 WEAR IN INDUSTRIAL CELLS 205 Bottom wear mechanism 210 CHEMICAL REACTIONS WITHIN THE CARBON LINING 211 Sodium and melt penetration 211 Reaction thermodynamics 220 Experimental verification of the penetration/reaction model 223 Electrolyte penetration and reactions in carbon cathodes during industrial aluminium electrolysis 225 Sodium reactions in carbonaceous sidewall blocks 231 Lithium and potassium in the cathode 232 NaCN formation 234 REACTIONS WITH THE COLLECTOR BAR 235 REACTONS IN REFRACTORIES AND INSULATION 236 Penetration of bath components into the refractory layer 236 Reactions between electrolyte and aluminosilicate refractories 238 Reactions between sodium vapor and aluminosilicate refractory 243 Combined reaction of bath and sodium 248 VI
Reactions with other refractories 249 Reactions with aluminium 251 Reactions with ceramic sidewall materials 253 REFERENCES 257 IV. PHYSICAL CHANGES DURING CELL OPERATION 261 THERMAL EXPANSION AND SHRINKAGE 261 Cathode blocks 262 Ramming paste 262 Collector bar and steel shell 267 Combined thermal dilations 269 Refractories and insulation 272 ELECTRICAL PROPERTIES 273 Electrical properties of virgin lining materials 274 Changes of electrical properties over time 278 THERMAL CONDUCTIVITY 297 Thermal conductivities of virgin cathode block materials 297 Changes of thermal conductivities of carbon block materials with time 298 Correlation of the electrical and thermal conductivity of carbon block materials. 298 Thermal conductivity of refractory materials 300 SODIUM EXPANSION 302 Free expansion 302 Expansion with pressure 305 CATHODE HEAVING 311 Vertical expansion gradients 311 Salt crystallization 313 Material conversion 314 Movement restraints 315 MECHANICAL STRENGTH 319 REFERENCES 325 V. CHARACTERIZATION OF CATHODE MATERIALS 329 INTRODUCTION 329 STANDARD CHARACTERIZATION OF CARBONACEOUS MATERIALS 330 Survey of ISO Test Methods for cathodes, ramming paste and refractories 330 Sampling (ISO 8007-1: 1999 331 Apparent density (ISO 12985-1, 2 :2000) 334 Open porosity (ISO 12985-2:2000) 336 Real density (ISO 9088:1997, ISO 21687:2007) 336 Total porosity 338 Electrical resistivity at ambient temperature (ISO 11713: 2000) 338 Thermal conductivity (ISO 12987:2004) 339 VII
Thermal expansion (ISO 14420: 2005) 340 Mechanical properties and geometry 341 Compressive strength (ISO 18515 : 2007) 341 Bending strength (ISO 12986-1:2000, ISO 12986-2:2005) 342 Tensile strength (ASTM C 651) 345 Young s modulus (DIN 51915) 346 Expansion of carbon due to sodium penetration (ISO 15379-1, 2: 2004), 348 Ash content (ISO 8005:2007) 350 Sampling of cold and tepid ramming paste (ISO 14422:1999 350 Binder and aggregate content and aggregate size distribution (ISO/TC 14423 : 99, ISO 2591-1: 1988) 350 Volatile matter content of unbaked paste (ISO/TS 14425: 1999) 352 Compaction characteristics of ramming paste (ISO 17544: 2004) 353 Preparation of unbaked paste specimens and determination of apparent density after compaction (ISO 14427: 2004) 356 Thermal expansion and shrinkage of ramming paste during baking (ISO 14428: 2004 356 Preparation of baked test pieces and determination of baking loss (ISO 20202: 2004) 358 Properties of baked ramming paste 358 STANDARD TESTS FOR REFRACTORIES AND INSULATION BRICKS 360 Introduction 360 Sampling and acceptance testing for shaped refractory products (ISO 5022: 1979) 361 Bulk density and true porosity (porosity > 45%) (ISO 5016: 1997) 361 Bulk density, apparent porosity and true porosity (porosity < 45%) (ISO 5017: 1998 361 Real or true density (ISO 5018: 1983 362 Gas permeability of refractory products (ISO 8841: 1991) 362 Cold crushing strength (ISO 8895: 2004, ISO 10059-1: 1992) 364 Thermal conductivity. Part 1. Hot wire method (cross array) (ISO 8894-1: 1987) 364 Cryolite resistance for dense refractory bricks (ISO 20292: 2009) 364 NON-STANDARD CHARACTERIZATION 365 High temperature electrical resistance 366 Thermal conductivity at elevated temperatures 369 Thermal shock 370 Fracture mechanics 373 Crack detection 375 High temperature strength testing 375 Density control during installation 377 Abrasion resistance of carbon during electrolysis 378 Oxidation resistance of carbon 378 Rate of sodium penetration in carbon 378 VIII
Chemical resistance of carbon towards sodium 379 Characterization of graphitization by X-ray diffraction 381 Characterization of graphitization by intercalation 383 Microscopy and image analysis 384 Nuclear magnetic resonance (NMR) 392 Refractory testing under combined bath and sodium attack 393 Testing of SiC-containing materials under electrolysis conditions 394 OVERVIEWS 396 Test methods 396 REFERENCES 405 VI. CATHODE FAILURES 409 INTRODUCTION 409 CATHODE AUTOPSIES 411 UNEVEN HEATING AND THERMAL SHOCK 418 INSTALLATION DAMAGE OF RAMMED PARTS 423 SHRINKAGE OF RAMMING PASTE 431 COLLECTOR BAR INDUCED FAILURES 434 INTERATIONS BETWEEN POT SHELL AND LINING 447 CAUSTIC OOZE 463 SHELL DAMAGE 465 TRANSIENT TEMPERATURES AND INFILTRATION 471 SIDE LEDGE DYNAMICS 490 OVER-INSULATION OF CATHODES 498 SODIUM SWELLING AND EXFOLIATION 507 AIR OXIDATION OF SIDEWALLS 512 SIDEWALL EROSION 519 OXIDATION DAMAGE OF BOTTOM BLOCKS 524 BOTTOM EROSION 527 POTHOLE FORMATION 544 ALUMINOTHERMIC REACTIONS IN SUB-CATHODIC PARTS 550 TEMPORARY POT SHUTDOWN AND RESTART 560 POT REPAIR 584 REFERENCES 585 VII. SPENT POTLINING DISPOSAL 589 SPENT POTLINING MATERIAL 589 Background 589 Handling of SPL 592 Watering reactions 593 TREATMETN OVERVIEW 594 DISPOSAL; RECOVERY OR RECYCLING TECHNIQUES 595 Combustion for power-generating purposes 595 IX
Slag and metal additives in iron- and steel-industry 596 Fuel and mineral supplement in cement manufacture 597 Conversion to inert landfill materials 599 Red brick ceramic products 611 Rockwool 612 Fluoride recovery from leaching processes 612 Pyrohydrolysis 616 Portland Ausmelt Technology 619 Elkem spent potlining and cast iron process 621 Pyrosulpholysis 624 Silicopyrohydrolysis 625 Graphite recovery 626 Cathode carbon additives 626 Anode carbon additives 627 Selective recovery of aluminium metal 630 FUNDAMENTAL VIEWPOINTS ON SPL DISPOSAL 631 Landfill 631 Transport 631 Removal from pot and sorting 632 Direct recycling 632 Recent process development 632 REFERENCES 633 VIII. TRENDS AND DEVELOPMENTS 637 GENERAL TRENDS 637 CATHODE CARBON MATERIALS 638 RAMMING PASTE 638 GLUING 639 SIDEWALL MATERIALS 640 REFRACTORIES 640 STEEL SHELL 640 WASTE PRODUCTS 640 MATHEMATICAL MODELS 641 WETTABLE CATHODE 641 REFERENCES 642 INDEX 643 X