The Role Of Graphite In Refractories Such As Al2O3/MgO/C

The Role of Graphite in Refractories such asAl2O3/MgO/C by Graphit KropfmuehlRFpage 116.10.13

OverviewAMG Mining – Short introductionHistory of refractory production in EuropeCruciblesRefractoriesHigh alumina refractoriesAl2O3-MgO-CMgO-CSummery of the graphite role in refractoriesPage 210/22/2013

AMG Mining - Company 22012 GraphitKropfmühlKropfmuehl by GraphitAGStart of industrial Graphite mining in KropfmühlPatent for a „Method to purify Graphite“Change into a public companyFirst deliveries to the pencil industryDevelopment of water based Graphite-DispersionsUF Graphite: Standard in PM IndustryAcquisition of RW silicium GmbHStart of expandable Graphite production in TýnIntroduction of SGB Graphite80% of GK shares were bought by AMGFirst increase to 93,59 %, then squeeze outRestart of mining in KropfmühlRFpage 322.10.2013 Page 516.10.13

Worldwide companies AMG GraphitKropfmühlKropfmuehl by GraphitAGRFpage 422.10.2013 Page 616.10.13

Turnover AMG Mining 2012 GraphitKropfmühlKropfmuehl by GraphitAGRFpage 522.10.2013 Page 616.10.13

RefractoriesHistory – graphite in cruciblesThe melting of metals in crucibles has a long history, beginning in ancient Egypt and stillcontinuing it s traditions in today s modern world. The first crucibles in the very advancedcivilisation made in Egypt were based on silicates free of graphite.It is not clear when people first found out the advantagesof mixing clay with graphite for crucibles. The Germanscientist Georgius Agricola was the first who made areport on the Passauer / Hafnerzeller crucibles formelting metals before the year 1556.The addition of graphite to pottery made it water proofeven without glaze and better heat conductive. We canassume that the very first production of clay boundedgraphite crucibles had taken place in the “Kropfmühl”area.In history, the celtics used graphite for production ofceramics already 2500 years ago. by Graphit KropfmuehlRFpage 616.10.13

RefractoriesMarket Size for Graphite in Refractories2011: About 485,000 t graphite for 3.2 Mio t C-containing refractories2 main groups at the center of attention:A) Crucibles:Main parts: Clay/tone, graphiteB) Refractory stones (magnesite carbon stones)Main parts: Magnesite coal materials by Graphit KropfmuehlRFpage 716.10.13

RefractoriesGraphite containing cruciblesSpecs: Good thermal and el. conductivityUsed in furnaces fired with fuel, electricity or induction, mostly for light non-ferrous metalsService temperature up to 1600 CRaw materials used in mixes for crucibles:Clay bondedCarbon bonded22-28% binder (refractory clays)12-25% binder (refractory clays,pitch/phenolic resin)6-10% Si3-5% Si15-25% SiC38-45% SiC40-50% Graphite25-35% GraphiteIsostatic pressing or screw-in (plastic) processGlaze formation during service protects graphite against oxidation by Graphit KropfmuehlRFpage 816.10.13

RefractoriesGraphite containing cruciblesSpecification for mostly used natural graphite:C 85-94%, other important parameters: crystallite size, flake size and thickness , BET- relative fraction of edge sites strongly influences oxidationAsh composition and melting point“thick” graphite flakes from Zimbabwe by Graphit Kropfmuehl“thin” flakes from MadagaskarRFpage 916.10.13

RefractoriesAl2O3-C (AC) high alumina refractories with ZrO2Widely used as the lining materials in blast furnaces and electric furnacesImportant spec:Corrosion behavior in the melts of smelting reduction with the iron bathThermal shock during filling and emptyingStudied compositions:Cold crushing strengthModulus of ruptureLIU Qing-cai et al., Journal of Materials Science and Engineering 2(12) (2008) 49-53. by Graphit KropfmuehlRFpage 1016.10.13

RefractoriesAl2O3-C (AC) high alumina refractories with ZrO2TestingCorrosion behaviors: rotary immersion and quasi-static immersion in electric resistance furnaceExperimental temperatures were between 1400 C and 1650 C.The atmosphere above the molten bath was maintained at 30% CO, 60% N2 and 10% CO2 byvolume.Slag composition: 10.0% FeO, 35.3% CaO, 33.2% SiO2, 8.0% MgO, 11.0% Al2O3, 2.5% TiO2. Ironbath formed by pig iron scrap, 4.16% C, 0.53% Si, 0.32% Mn, 0.10% P and 0.034% S.C 7.2%, ZrO2 0.51%C 9.8%, ZrO2 6%C 9.8%, ZrO2 9% by Graphit Kropfmuehl-Dependence of the corrosion rate of refractories onthe FeO content in melts , test temperature 1500 C- The refractories containing ZrO2 exhibit a goodanti-corrosion characteristic, especially in the melts ofFeO concentration above 6%.- Graphite carbon contained in the refractory is anactive reducing agent of the iron oxides. The graphiteof theAl2O3-C refractories was oxidized by the ironoxides of the melts. Pores and cracks are formed inthe reaction zone.RFpage 1116.10.13

RefractoriesAl2O3-C (AC) high alumina refractories with ZrO2SEM: AC2, immersed in slag and iron bath, test temperature 1773 K, rotary speed of refractory inmelts 15 r/min.Al2O3-C refractories are composed ofcorundum, mullite, Al2O3 and graphite.EDS data: graphite carbon was oxidized over 90% and no graphitecarbon was found in the interface between deteriorative layer of therefractory and slag film.Corrosion mechanism of AC refractories in the smelting reductionmelts with iron bath:1. graphite oxidization2. deteriorative layer formation.The deteriorative layer of Al2O3-C refractory was corroded greatly bythe smelting reduction melts.Lot of new compounds formed by reaction with slag, such as CaSiO3,TiO2, FeSiO3, Al2SiO5 and Fe3C by Graphit KropfmuehlRFpage 1216.10.13

RefractoriesAl2O3-MgO-C (AMC) refractories for steel ladle liningImportant spec:Residual expansion during the usageTemperatures from 1600 to 1750 C, resistance against turbulence of steel bath duringheating/purgingThermal shock during filling and emptyingCorrosion contact with basic steel ladle slagsAMC: Superior chemical and thermodynamic stability characteristics when compared to highalumina and doloma steel laddle refractories, but also excellent thermal and mechanicalproperties.Influence of alumina/carbon ratio and magnesia / silica contents on the refractories corrosionresistance.The carbon bond enables combinations of raw materials with varying expansion coefficientUsual compositions: 50-70% Al2O3 ,15-30% MgO, 2-15% C, 0.3-3% others (SiO2, Fe2O3, TiO2) by Graphit KropfmuehlRFpage 1316.10.13

RefractoriesAl2O3-MgO-C (AMC) refractories for steel ladle liningImportant spec: Residual expansion during the usage. responsible for the formation of amonolithic refractory lining resulting in a decreased steel penetration through the refractory joints.Al2O3/C (A/C) 12.9Higher corrosion resistance for highest C contentand smallest SiO2 contentPresent phases:corundum Al2O3mullite 3Al2O3 2 SiO2periclase MgOSeparate graphite phase with high refractoriness, λ,low thermal expansion, low wettability by slagWear results with rotary slag attackHigh mullite conc. promotes Ca-aluminosilicatformation (eutectic at 1265 C)Periclase consumes mullite and contributescorrosion resistance to high basicity slagsW. S. Resende et al., Journal of the European Ceramic Society20 (2000) 1419-1427. by Graphit KropfmuehlRFpage 1416.10.13

RefractoriesAl2O3-MgO-C (AMC) refractories for steel ladle liningRefractoriness under loadA/C 12.9Better packing of microstructure, smallerpore sizeHigher conc. of graphite lead to bestpackingHot modulus of raptureCold crushing strengthApp. porosityLin. dim. changebulk density by Graphit KropfmuehlRFpage 1516.10.13

RefractoriesAl2O3-MgO-C (AMC) refractories for steel ladle liningA/C 12.9Slag test at 2.74 bin. basicity2h / 1750 CA/C 12.9A/C 19.2A/C 19.2SEM before test (20x)SEM after rotary slag test by Graphit KropfmuehlRFpage 1616.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesImportant spec:Used in basic furnance, electric arc furnance, and steel ladlesRole of graphiteCarbon specs:- macrocrystalline flakes with 90-96% C, -100 to 50 mesh, 3-25%- carbon black for optimal pore filling 1-2%)- pitch / phenolic resin for coaked binders (3%)Negative effects of oxidation of graphite: spalling and pore generation- addition of antioxidants necessaryEven better protection is possible by coating the antioxidant on top of the graphite particles by Graphit KropfmuehlRFpage 1716.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesRole of graphiteCorrosion resistance by less wettability with a molten metalExcellent thermal shock resistance by low thermal expansion & high thermal conductivityLow elasticity, due to the presence of graphiteStructure-flexible bond characteristic – C-bond usually forms in serviceCarbon changes the infiltration depth from cm to the mm range by:Reduction of Fe2O3 in the infiltrating slag to Fe - increase of the eutectic temp. from 1300 C to 1600 CNon wetting behaviour between oxidic slag and brick carbonT. Ayashi : Recent Trends in Japanese RefractoryTechnology, Transactions ISIJ, V21, 1981R. Engel, The Refractories Engineer, (2013) 20-23 by Graphit KropfmuehlRFpage 1816.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesSEM: Anisotropy of thermal conductivity by flake orientationGraphite flake alignment in MgO-C bricks, perpendicular (left) and parallel (right) to the bricks longdimensionW.E. Lee, http://core.materials.ac.uk by Graphit KropfmuehlRFpage 1916.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesSEM:Hot face – slagDense zoneUnreacted brickI. Strawbridge, D.G. Apostolopoulos: High PurityMagnesias and Graphites in MagnesiaCarbon Refractories, Stahl und Eisen, Special, 1994Formation of a dense zone due to reduction of MgO with C at high T which vaporized the Mgand precipitated it in the dense zone. by Graphit KropfmuehlRFpage 2016.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesProtection of the graphite in the dense zone: additions of metals like Mg, Al, SiAl additionTT. Rymon-Lipinski: Reaktionen von Metallzusätzen in MagnesiaKohlenstoffsteinen in einem Sauerstoffkonverter, Teil 1, p 1049 (47),Teil 2, p 1055 (53), Stahl u. Eisen, V. 108, # 22, 1988K. Ichikawa, et al., “Suppression Effects of Aluminumon Oxidation of MgO-C Bricks, Taikabutsu Overseas,V 15, #2, 1995Example of reactions inside different zones of the basic oxygen furnace with Al addition by Graphit KropfmuehlRFpage 2116.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesProtection of the graphite in the dense zone: additions of metals like Mg, Al, SiYAMAGUCHI, A. Self-repairing function in the carboncontaining refractory, Int J Applied Ceramic Technology,vol. 4, no. 6, 2007, pp.490–495.Typical microstructure of a MgO-C brick which contains Al and Si as antioxidants.A MgO; B aluminium; C silicon;D merwinite (Ca3MgSi2O8) by Graphit KropfmuehlRFpage 2216.10.13

RefractoriesMgO-C (MC) refractories for basic/electric arc furnacesFurther protection of the graphite particles by coating with AlZ. Ali Nemati et al., Tehran InternationalConference on Refractories , 4-6 May 2004 by Graphit KropfmuehlShrinking – Core Model (SCM)The shrinking core model for an isothermal sphericalgraphite particle (B) which reacts with gas (A)There is a sharp boundary (the reaction surface)between the no reacted core of the graphite and theporous outer shell (ash layer).The gas film reflected the resistance to mass transfer ofgas (A) from the bulk gas to the exterior surface of theparticle.As time passes, the reaction surface movesprogressively toward the center of the particle.According to the SCM model, three processes involvingmass transfer of gas in gas film, diffusion of gas inporous layer and reaction of gas with solid (B) atreaction surface, are rate controlling steps.RFpage 2316.10.13