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Title: Mitigating Chemical Degradation of Magnesia-chromite Bricks in Contact With a PbO Based Slag
Other Titles: Mitigatie van de chemische degradatie van magnesia-chromiet refractair in contact met een PbO houdende slak
Authors: Scheunis, Lennart
Issue Date: 22-Dec-2014
Abstract: Vessel integrity is a vital aspect in the production of metals, determining the efficiency and feasibility of pyrometallurgical production processes. The linings in the reactors are made of refractory bricks, ceramic materials used for their excellent chemical and thermo-mechanical properties at the operational temperature. Nevertheless, failure of the lining occurs over time due to a combination of thermal, mechanical and chemical stresses, requiring a timely and costly replacement of the lining. Reducing the refractory wear would lead to less standstills and thus a more cost efficient production process. The objective of this work is to investigate the in-situ formation of phases by reaction with the slag as a method to limit the chemical refractory degradation caused by PbO-SiO2 based slags. The chemical degradation of porous magnesia-chromite bricks by PbO-SiO2 based slags is caused by (1) liquid infiltration into the porous refractory brick and (2) dissolution of MgO from the refractory into this liquid slag. Slag engineering is successfully used to form a protective layer between the liquid and the refractory brick sample, slowing down the dissolution rate as the refractory components have to diffuse through this new layer. For deep infiltration slags, the liquid composition, and thus the chemical corrosion, changes inside the refractory brick and the protective layer no longer forms. The formation of in-situ phases is used to seal off the open pores in the refractory. This has been tested for refractory brick under isothermal conditions and under a temperature gradient. The latter uses a newly designed experimental setup. The ability to seal off the pores before complete infiltration depends on the ratio between the growth rate of the new phases and the infiltration rate of the liquid.
Table of Contents: Voorwoord I
Abstract III
Samenvatting V
List of minerals and symbols VII
Table of content IX
Chapter 1 General introduction 1
1.1 Research objectives 3
1.2 Outline of the text 3
Chapter 2 Magnesia-chromite bricks 7
2.1 Production of magnesia-chromite bricks 8
2.2 Behavior in use 13
2.2.1 Thermo-mechanical degradation 13
2.2.2 Chemical degradation 14
2.3 Identification of degradation 16
2.4 Conclusion 17
Chapter 3 Mitigating the chemical wear 23
3.1 Viscosity of the slag 23
3.2 Changing the solubility of refractory components in the slag 23
3.3 Direct-indirect dissolution 26
3.4 Infiltration 28
3.4.1 Fundamentals of infiltration 28
3.4.2 In-situ measurements 29
3.4.3 Changes in slag composition 30
3.4.4 Predicting the slag changes 30
3.4.5 Methods to stop infiltration 34
3.5 Conclusions 37
Chapter 4 Slag engineering for PbO slags 43
4.1 Introduction 43
4.2 Materials and methods 43
4.3 Results 45
4.3.1 Slag S1 47
4.3.2 Slag S2 51
4.4 Discussion 55
4.5 Conclusion 56
Chapter 5 The influence of slag compositional changes on the chemical degradation of magnesia-chromite refractories exposed to PbO-based non-ferrous slag saturated in spinel 57
5.1 Introduction 58
5.2 Experimental procedure 59
5.3 Results 61
5.3.1 Microstructure 61
5.3.2 Composition of the slag inside the sample 69
5.4 Discussion 71
5.5 Effect on the overall degradation of a refractory lining 74
5.6 Conclusions 77
5.7 Acknowledgement 79
Chapter 6 The effect of phase formation during use on the chemical corrosion of magnesia-chromite refractories in contact with a non-ferrous PbO-SiO2 based slag 85
6.1 Introduction 86
6.2 Experimental procedure 89
6.3 Results and discussion 90
6.3.1 Reacted brick 90
6.3.2 Slag-refractory interaction 98
6.4 Conclusion 108
6.5 Acknowledgement 109
Chapter 7 The effect of a temperature gradient on the phase formation inside a magnesia-chromite refractory brick in contact with a non-ferrous PbO-SiO2-MgO slag 113
7.1 Introduction 114
7.2 Experimental procedure 116
7.3 Results 119
7.3.1 Temperature measurements 119
7.3.2 Microstructure 121
7.3.3 Slag composition as a function of position 125
7.4 Discussion 129
7.4.1 Local temperature 130
7.4.2 Slag composition 130
7.4.3 Infiltration behavior 131
7.4.4 Effect of external cooling on chemical degradation 134
7.5 Conclusion 136
Chapter 8 Conclusions and future work 141
8.1 Conclusions 141
8.2 Future work 143
ISBN: 978-94-6018-933-3
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Sustainable Metals Processing and Recycling

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