CORROSION OF REFRACTORIES IN LEAD SMELTING REACTORS By LINGXUAN WEI B.Sc, Wuhan University of Science & Technology, China 1986 M.Sc, University of Science & Technology Beijing, China 1997 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF METALS AND MATERIALS ENGINEERING We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH .UMB1A DECEMBER 2000 ©Lingxuan Wei, ZO0O UBC Special Collections - Thesis Authorisation Form http://www.library.ubc.ca/spcoll/thesauth.html In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. v 3 The University of British Columbia Vancouver, Canada Date lof 1 3/19/01 2:36 PM ABSTRACT Corrosion of refractories by slag is a complex phenomenon which, depending on the particular system, involves many processes, such as chemical wear (corrosion) and physical or mechanical wear (erosion), which may act synergistically. No single model can explain all cases of corrosion nor can it explain all corrosion mechanisms of a particular refractory in different environments, but the knowledge of the microstructure combined with the chemistry of the systems are necessary to understand the corrosion mechanism of a refractory material. There is no systematic study on the corrosion of refractories used in lead smelting reactors (KIVCET furnace and TBRC) in literature so far. In the present work, the available literature concerning corrosion of refractories in lead-smelting reactors was reviewed. By using different analytical methods such as sessile drop technique, SEM/EDS and XRD, the interfacial phenomena at the slag-refractory interfaces were investigated, and microstructural studies on different refractory specimens were carried out. It was observed that above 1150° C, the KIVCET slag tends to separate into two phases: a liquid and a solid. The liquid mainly consists of S1O2, CaO and PbO, while the solid primarily contained Fe2C«3 and ZnO in the form of zinc ferrite (ZnFe204) spinel. It was proposed that ZnO from the KIVCET slag could also react with Cr203 and Fe203 from the magnesite-chrome brick and reacted slag to form spinel-type phases: zinc chromite ii (ZnCr204) and zinc ferrite (ZnFe2C>4) respectively. The volume changes accompanying these reactions could lead to microcracks in the matrix of the brick, and eventually cause the failure of the brick. Laboratory evaluation of the corrosion behavior of various refractory materials against industrial slags from KIVCET and TBRC furnaces was performed using both dynamic and static corrosion tests. The corrosion rating on nine different magnesite-chrome bricks was estimated, and the possible corrosion mechanism was discussed. It was found that the rebonded fused grain type of magnesite-chrome bricks have superior performance compared with direct bonded type when used in contact with KIVCET slag and the alumina-chromia bricks performed better than magnesite-chrome bricks under similar conditions. iii Table of Content Abstract » List of Tables ; vii List of Figures viii List of Abbreviations and Symbols xi Acknowledgements xiii 1 Introduction , 1 2 Literature Review 6 2.1 Refractory Materials Used in Lead-Smelting Reactors 6 2.1.1 Magnesite-Chrome and Chrome-Maghesite Bricks 6 2.1.2 Alumina-Chromia Bricks 7 2.2 Corrosion of Refractories by Molten Slags 7 2.2.1 Theoretical Aspects Regarding Corrosion of Refractories 10 2.2.2 Corrosion of Refractories in Contact With Various Slags.. 16 2.2.2.1 MagnesiteRefractories 16 2.2.2.2 Alumina-Chromia Refractories 18 2.2.2.3 Magnesite-Chrome Refractories 20 2.3 Wetting Behaviors of Refractories 22 2.3.1 Wettability 22 2.3.2 Wetting Behaviors of Refractories at High-Temperature 24 iv 2.4 Mechanisms of Refractory Corrosion in Nonferrous Smelting Environments 26 3. Scope and Objectives of this Work 29 4. Experimental Procedures 30 4.1 Contact Angl e Measurements 30 4.2 Corrosion Tests 31 4.2.1 Dynamic Corrosion 31 4.2.2 Static Corrosion 33 4.3 Sample Preparation 35 4.3.1 Samples for Contact Angle Measurements. 35 4.3.2 Samples for Corrosion Tests 37 4.4 Slag Compositions 39 4.5 Testing Methods 40 5 Results and Discussion 41 5.1 Characterization of KIVCET Slag 41 5.2 Interaction Between KIVCET Slag and Various Substrates 53 5.3 Postmortem Analysis of Used MC Bricks from the KIVCET Furnace 58 5.4 Results of Corrosion Tests 67 5.4.1 Magnesite-Chrome (MC) Bricks with KIVCET Slag 67 5.4.2 Alumina-Chromia (AC) Bricks with KIVCET Slag 79 5.4.3 Magnesite-Chrome Bricks with TBRC Slag 82 5.5 Summary 86 6 Conclusions 89 V 7 Future Work 91 8 References 92 vi LIST OF TABLES Table 1. Substrates used in the contact angle measurements 35 Table 2. Characteristics of the magnesite-chrome (MC) and alumina-chromia (AC) brick samples 38 Table 3. Chemical composition of slags 39 Table 4. Results of EDS analyses of KS slag in Figure 19 48 Table 5. Elemental compositions of KS slag in Figure 21a and 21b 51 Table 6. Calculated compositions of KS slag based on EDS analyses in Table 5 51 Table 7. Slag compositions on the used MC brick from KIVCET furnace by EDS analyses 59 Table 8. Results of corrosion tests of the magnesite-chrome bricks with KS slag 68 Table 9. EDS analyses of MCI brick after RSF test with KS slag 79 Table 10. Results of corrosion tests of alumina-chromia (AC) bricks with KS slag 80 Table 11. Results of corrosion tests of MC and AC bricks with TBRC slag 83 Table 12. Results of EDS analyses of MC4 brick after RSF test with TBRC slag ...85 LIST OF FIGURES Figure 1. Schematic diagram of typical refractory microstructure 2 Figure 2. KIVCET flash smelting furnace arrangement 5 Figure 3. Top blown rotary converter (TBRC) arrangement 5 Figure 4. Phase diagram of the MgO-Cr203 system 8 Figure 5. Phase diagram of the MgO-Al203-Cr203 system 8 Figure 6. Phase diagram of the MgO-Al203-Si02 system 9 Figure 7. Phase diagram of the Al203-Cr203 system 9 Figure 8. Equilibrium forces at the solid-liquid-vapor interface for an (a) acute contact angle and (b) obtuse contact angle 23 Figure 9. Schematic diagram of a sessile drop on a surface 23 Figure 10. Schematic diagram of contact angle measurements at high temperatures 30 Figure 11. Schematic Diagram of the Rotary Slag Furnace (RSF) 32 Figure 12. Schematic diagram of the slag cup test (SCT) 34 Figure 13. Flow chart of the refactory substrate preparation for contac angle measurements 36 Figure 14. Wetting behavior of KS slag on pure A1203 and MC2 substrates at different temperarues 42 Figure 15. Wetting behavior of KS slag on pure A1203 and MC2 substrates at different soaking times 43 Figure 16. Contact angle versus temperature for KS slag 44 viii Figure 17. Contact angle versus soaking time at 1250° C for KS slag 44 Figure 18. XRD patterns of residual slag on MC2 substrate (top) and original slag (bottom) 46 Figure 19. SEM images of residual slag on MC2 substrate 47 Figure 20. XRD paterns of the KS slag after 3h at 1250° C in zero porosity alumina crucible 49 Figure 21a. SEM image of KS slag at the top of the alumina crucible, 3hat 1250°C 50 Figure 21b. SEM images of KS slag at the bottom of the alumina crucible, 3h at 1250° C 50 Figure 22. Schematic phase separation of the KS slag on porous refarctory substrates 54 Figure 23 a. XRD patterns of KS slag impregnated areas of AC4 substrate and its original 54 Figure 23b. XRD patterns of KS slag impregnated areas of MC2 substrate and its original 55 Figure 24. Phase diagram of the AbCVSiCVPbO system 57 Figure 25. Phase diagram of a) CaO-Cr203 system b) PbO-Cr203 system 57 Figure 26. Analyzed areas of the used MC brick from KIVCET furnace 59 Figure 27a. SEM image of the used MC brick from KIVCET furnace (interface).... 60 Figure 27b. SEM image of the used MC brick from KIVCET furnace (brick) 60 Figure 28. XRD patterns of the used MC brick from KIVCET furnace 62 Figure 29. Elemental distribution versus distance from the interface in the used MC brick from KIVCET furnace 63 Figure 30. Ternary phase diagrams of a) ZnO-Cr2C>3-Yb203 and b) ZnO-Fe203-Yb203 66 Figure 31a. Corroded MC specimens after SCT with KS slag, 24 hours at 1350°C. 69 Figure 31b. Corroded AC specimens after SCT with KS slag, 24 hours at 1350°C .. 70 Figure 32a. Corroded MC specimens after RSF 5 hour tests with KS slag at 1350°C 71 Figure 32b. Corroded MC specimens after RSF 5 hour tests with TBRC slag at 1075°C 72 Figure 33. Corroded specimens after SCT with KIVCET slag, 24h at 1350° C 76 Figure 34a. SEM image on MCI brick after RSF test with KS slag 77 Figure 34b. SEM image on MCI brick after RSF test with KS slag (Field 01) 77 Figure 34c. SEM image on MCI brick after RSF test with KS slag (Field 02) 78 Figure 34d. SEM image on MCI brick after RSF test with KS slag (Field 03) 78 Figure 35.