High temperature corrosion of calcium hexaaluminate with biomass slag Von der Fakultät für Georessourcen und Materialtechnik der Rheinisch -Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades einer Doktorin der Ingenieurwissenschaften genehmigte Dissertation vorgelegt von Dipl.-Ing. Lise Rebecca Loison aus Schiltigheim Berichter: Univ.-Prof. Dr.rer. nat. Rainer Telle Univ.-Prof. Dr.-Ing Jacques Poirier Tag der mündlichen Prüfung: 07.12.2018 Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar Chapter 1: Introduction .............................................................................................................. 1 1. 1. Research question ........................................................................................................... 1 1. 2. Objectives ....................................................................................................................... 3 1. 3. Acknowledgements ........................................................................................................ 4 Chapter 2: Bibliography ............................................................................................................. 5 2. 1. Industrial context ............................................................................................................ 5 2. 1. 1. Biomass as alternative combustible for the energy production .............................. 5 2. 1. 2. Ash related issues at high temperature ................................................................... 6 2. 1. 3. Refractory lining in biomass incinerators .............................................................. 7 2. 2. Degradation mechanisms of refractory lining in contact with biomass slag .................. 8 2. 2. 1. Molten slag infiltration ........................................................................................... 8 2. 2. 2. Refractory dissolution ............................................................................................ 9 2. 2. 3. Structural spalling ................................................................................................ 10 2. 3. Calcium hexaaluminate as refractory component ........................................................ 11 2. 3. 1. Properties of calcium hexaaluminate ................................................................... 11 2. 3. 2. Refractory applications ........................................................................................ 12 2. 3. 3. Stability with alkaline ........................................................................................... 13 Chapter 3: Materials ................................................................................................................. 14 3. 1. Presentation of the system ............................................................................................ 14 3. 1. 1. Refractory castables ............................................................................................. 14 3. 1. 2. Al2O3-SiO2-CaO-K2O phase diagrams ................................................................. 16 3. 1. 3. Slag structure ........................................................................................................ 21 3. 2. Refractory samples ....................................................................................................... 23 3. 2. 1. Powder .................................................................................................................. 24 3. 2. 2. Matrix ................................................................................................................... 25 3. 2. 3. Castables ............................................................................................................... 30 3. 3. Slag samples ................................................................................................................. 32 3. 3. 1. Wood ash .............................................................................................................. 33 3. 3. 2. CaO-SiO2-K2O ternary slag ................................................................................. 34 3. 3. 3. CaO-SiO2 binary slag ........................................................................................... 35 3. 4. Conclusion .................................................................................................................... 37 Chapter 4: Identification of reactive mechanisms .................................................................... 39 4. 1. Theory .......................................................................................................................... 39 4. 1. 1. Gibbs’energy ........................................................................................................ 39 4. 1. 2. Local thermodynamic equilibrium ....................................................................... 40 4. 1. 3. Dissolution in the system Al2O3-SiO2-CaO ......................................................... 40 4. 2. Method ......................................................................................................................... 41 4. 2. 1. Generation of reactive interface ........................................................................... 41 4. 2. 2. Characterization techniques ................................................................................. 42 4. 2. 3. Thermodynamic calculations ............................................................................... 42 4. 3. Results .......................................................................................................................... 43 4. 3. 1. Solubility limit and thermodynamic equilibriums ............................................... 43 4. 3. 2. Phase identifications ............................................................................................. 47 4. 3. 3. Post-mortem microstructures ............................................................................... 49 4. 4. Conclusion .................................................................................................................... 58 Chapter 5: Determination of kinetics ....................................................................................... 61 5. 1. Theory .......................................................................................................................... 61 5. 1. 1. Regime of kinetics ................................................................................................ 61 5. 1. 2. Transport of species ............................................................................................. 62 5. 1. 3. Influence of viscous boundary layer .................................................................... 63 5. 2. Method ......................................................................................................................... 63 5. 2. 1. Reaction couple specimens .................................................................................. 63 5. 2. 2. Quantitative X-Ray Diffraction ............................................................................ 64 5. 2. 3. Corrective factors ................................................................................................. 67 5. 3. Results and discussion .................................................................................................. 68 5. 3. 1. Liquid phase formation ........................................................................................ 68 5. 3. 2. Matrix reaction ..................................................................................................... 72 5. 3. 3. Phases identification in the microstructure .......................................................... 75 5. 4. Conclusion .................................................................................................................... 78 Chapter 6: Microstructural considerations ............................................................................... 80 6. 1. Theory .......................................................................................................................... 80 6. 1. 1. Microstructural properties influencing the corrosion resistance .......................... 80 6. 1. 2. Microstructure development of calcium hexaaluminate ...................................... 81 6. 1. 3. Expansive reactions .............................................................................................. 81 6. 2. Method ......................................................................................................................... 82 6. 2. 1. Characterisation of the porous network................................................................ 82 6. 2. 2. Corrosion tests ...................................................................................................... 83 6. 2. 3. XRD measurements .............................................................................................. 83 6. 3. Results and discussion .................................................................................................. 83 6. 3. 1. Resistance to structural spalling ........................................................................... 83 6. 3. 2. Influence of the porosity ...................................................................................... 86 6. 3. 3. Morphology of calcium hexaaluminate ...............................................................