Refractory raw materials. Part VII. Raw Materials VII Refractory 1

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1 Refractory raw materials Part VII Raw Materials VII Refractory 1

2 Refractory raw materials Alumina Refractory silicates (alumino-silicates, mullite) Steatite (non-clay plastic) Magnetite Chrome Rutite Zirconia and zircon Raw Materials VII Refractory 2

3 Alumina (Al 2 O 3 ) Alumina, Sapphire, Corundum Gibbsite Al(OH) 3 and Boehmite AlO(OH) Bulk single crystal oxide α-al 2 O 3 stable Sapphire Polycrystalline form Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 3

4 Application of alumina refractory cements refractory blocks monolithic refractory materials alumina based ceramic fibers ceramic and other refractory products. refractories (50%), abrasive (20%), whiteware and spark plug (15%), engineering ceramic (10%) Figure from Ceramaret (Switzerland) Raw Materials VII Refractory 4

5 Diaspore Alumina Aluminum oxides ก ก ก silicates aluminum oxide ก Gibbsite Corundum, Al 2 O 3 Spinel, MgAl 2 O 4 Hercynite, FeAl 2 O 4 Galaxite, MnAl 2 O 4 Bauxite (alumina cement grade) Gibbsite, Al(OH) 3 Diaspore, AlO(OH) Boehmite, AlO(OH) Bayerite, Al(oH) 3 Raw Materials VII Refractory 5

6 Al 2 O 3 α-al 2 O 3 stable phase: Corundum structure, sapphire Meta-stable phases (γ,χ,η,δ,ε ) disordered crystal structures based on a close-packed oxygen sublattice with varying interstitial aluminum configurations Raw Materials VII Refractory 6

7 Spinel structure (from A.R. Von Hippel, Dielectrics and waves, wiley, New York, 1954) Raw Materials VII Refractory 7

8 Transformation of hydrated alumina on heating in air Bayerite Gibbsite > 150 C > 150 C γ (Gammar) δ (delta) θ (Theta) α (alpha) > 430 C Boehmite χ (Chi) κ (kappa) α (alpha) Diaspore > 450 C α (alpha) Ref: D. Ganguri and M. chatterjee, Ceramic powder preparation: a handbook, Kluwer academic publishers, 1997 Raw Materials VII Refractory 8

9 Bayer Process Al 2 O 3 + 2NaOH 2NaAlO 2 +H 2 O 2NaAlO 2 +3H 2 O +CO 2 Na 2 CO 3 +2Al(OH) 3 Al(OH) 3 Al 2 O 3 +3H 2 O Fe 2 O 3 red mud Bauxite NaOH autoclave 0.4 MPa at c NaAlO 2 + H 2 O CO 2 +H 2 O Na 2 CO 3 + Al(OH) 3 SEM image of Bayer process gibbsite (from southern, 1991) 20 µm ก ก Filter and wash Calcined > 1000 C Al 2 O 3 + H 2 O Raw Materials VII Refractory 9

10 Alkoxide hydrolysis method Metal aluminum alkoxide ก hydrolysis Al(OH) 3 Calcined Al 2 O 3 milling Reaction: alkoxide synthesis: Al + 3ROH Al(OR) 3 + 3/2H 2 Hydrolysis: Al(OR) 3 +3H 2 O Al(OH) 3 + 3ROH Calcination: 2Al(OH) 3 Al 2 O 3 + 3H 2 O Raw Materials VII Refractory 10

11 Typical chemical analyses of Bayer process alumina Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 11

12 Max.Na 2 O content and size for particular application (MacZura et.al.,1992) alumina Reactive Al 2 O 3 powder: Na 2 O ก MgO, CaO ก ก Effect of Na 2 O and surface area on reactivity (Souther, 1991) Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 12

13 Typical properties of alumina products Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 13

14 Fused and tabular refractory grades Tabular grade refractory: Al 2 O 3 99% ก Al 2 O 3 -graphite refractories, low-cement, ultre-low cement castable refractory mixes ก ก Fused Al 2 O 3 : white (Calcined bayer alumina) brown (Bauxite) Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 14

15 Al 2 O 3 ก Emery: ก Corundum, spinel, feldspar ก Magnetite Al 2 O % 25%. ก. Sillimanite: Al 2 O % ก ก emery ก Pyrophyllite Al Si 2 4 O 10 (OH OH) 2 Al 2 O % ก.. ก. ก. ก Laterite Al2O3 ~ 25% ข นก บแหล งท ก าเน ด. Raw Materials VII Refractory 15

16 Refractory silicates Aluminasilicate Sillimanite Kyanite Andalusite 3Al 2 SiO C 3Al 2 O 3.2SiO 2 + SiO 2 (mullite 88% total mass) Mullite (3Al 2 O 3.2SiO 2 ) Al 2 O 3 72% Application: high refractoriness Chemical resistance Thermal stability Medium heat conductivity Raw Materials VII Refractory 16

17 Action on heat 1545 C Sillimanite minerals mullite-forming material (mullite + vitreous silica, vol. expand 5-6%) Application: for refractories, porcelain slowly heat C Kyanite 17 % expansion Application: ceramic body (high strength) C Andalusite vol. expansion 5-6% Application: spark plug Mullite: interlocking crystal Raw Materials VII Refractory 17

18 Properties of Alumino-silicate (N.F.Norton) Raw Materials VII Refractory 18

19 Magnesium oxide MgO Raw Materials VII Refractory 19

20 Magnesium oxide (MgO) : High thermal conductivity Refractoriness (> 2750 C) Resistance to basic slag : High ionic crystal with Mg-O bonds having about 80% ionic character. Rock salt structure Raw Materials VII Refractory 20

21 ก MgO Magnesite (MgCO 3 ) Dolomite (Mg,Ca)CO 3 ก ก MgO 1 ก ก 500 MgCl 2 Raw Materials VII Refractory 21

22 Dolomite CaMg(CO 3 ) 2 CaO:MgO Rock salt or periclase structure 54.35% CaCO 3, % MgCO C CaCO 3.MgCO 3 MgO + CaCO 3 + CO C CaO + CO 2 Application: glaze and body > 1000 C : flux < 1000 C : appear pores Raw Materials VII Refractory 22

23 Sea-water magnesite Sea water contains sulphates and chlorides of sodium, potassium, calcium and magnesium. heated 1000 C H 2 O CaMg(CO 3 ) 2 CaO + MgO Ca(OH) 2 + Mg(OH) 2 Dolomite Mg(OH) 2 + MgCl 2 2Mg(OH) 2 + CaCl 2 Ca(OH) 2 MgSO 4 CaSO 4 slaked dolomite sea water magnesium hydroxide by-product Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 23

24 Physical properties of calcium and Magnesium Carbonates (N.F. Norton) Raw Materials VII Refractory 24

25 Secondary phases commonly formed in MgO refractories Raw Materials VII Refractory 25

26 Physical properties of raw materials used in refractory production (Brown and White, 1986) Raw Materials VII Refractory 26

27 Chromium Oxide (Cr 2 O 3 ) Raw Materials VII Refractory 27

28 Chromium Oxide (Cr 2 O 3 ) กก ก (Mg,Fe)O Mg,Fe)O.. (Cr,Fe,Al) 2 O 3.,., ก ก., ก.. Specification: Spinel group Hardness 5.5 Density g/cm 3 Cr 2 O % Melting point C Fe 2 O 3 ก Purification: Na CO 2 3 flux sulfur/carbon Chromite NaCrO, NaCr 3 2 O 3 Na SO Cr 2 O 3 Raw Materials VII Refractory 28

29 Chrome Basic rock: Cr, Fe, Al, Mg, O Spinel A IV B 2 VI O 4 RO.R 2 O 3 = AO.B 2 O 3 A = divalent cation (e.g. Fe 2+,Mg 2+, Cu 2+, Mn 2+ ) B = trivalent cation (e.g. Cr 3+, Fe 3+, Al 3+ ) Ex. Chromite FeCr 2 O 4, MgCr 2 O 4 Inversed spinel B IV (AB) VI O 4 Ex. Magnetite Fe IV Fe 2 VI O 4 Chrome ore: mixed spinel A Fe 2+, Mg 2+ B Cr 3+, Al 3+, Fe 3+ Softening temp C Melting point 2180 C Application: refractories (Chromemagnesite) neutral zone Normal spinel Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 29

30 Chrome bricks Cr 2 O % SiO % Al 2 O % Fe 2 O 3 3.6% Melting point C Slag resistance Raw Materials VII Refractory 30

31 Chrome Magnesium Bricks SiO 2 2-6% Cr 2 O % Fe 2 O % (< 18% ก ) Al 2 O % MgO 38-52% CaO % (<1% ) Melting point > 2100 C (high refractoriness) Good thermal shock resistance Slag resistance High strength at high temperature Raw Materials VII Refractory 31

32 Rutite, TiO 2 A form of titanium dioxide, TiO 2, is a mineral associated with sands and sandstones. Relatively inert and insoluble in water and acids (except sulfuric acids) but is soluble in caustic alkalis. Raw Materials VII Refractory 32

33 Zirconia ZrO 2 Raw Materials VII Refractory 33

34 Zirconia ก ก ก ก Raw Materials VII Refractory 34

35 Zirconia (ZrO 2 ) ZrO 2 ceramics Application: kiln linings (refractories) kiln furniture, furnace elements Dispersion, grinding media Heating tubes solid electrolyte in Oxygen sensors Fuel cells in glaze: opacifier, control texture and crazing increase mechanical stability in mullite china Netural minerals: baddeleyite hafnium oxide 1-1.5% Zircon sand (ZrO 2.SiO 2 ) ZrO %, SiO %, Fe 2 O 3 3-5% S.G Hardness 6.5 M.P. of Zirconia C insoluble Raw Materials VII Refractory 35

36 Crystal systems of zirconia Monoclinic 1150 C, vol. expansion = 3-5 % Tetragonal 2370 C Cubic s.g. = 5.6 g/cm C s.g. = 6.1 g/cm 3 s.g.= g/cm C Liquid (melting) Raw Materials VII Refractory 36

37 Thermal expansion of ZrO 2 (a) unstabilized ZrO 2 (b) stabilized ZrO 2 Linear expansion % (From E. Tyshkewitch and D.W. Richerson, 1985) Raw Materials VII Refractory 37

38 Physical properties of single crystal zirconia Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 38

39 Zirconia Unstabilized ZrO 2 Partially stabilized ZrO 2 : Mixing of Monoclinic and tetragonal/cubic Tetragonal Zirconia Polycrystals TZP Fully Stabilised Zirconia FSZ: tetragonal or cubic Transformation Toughened Ceramics TTC Zirconia Toughened Alumina ZTA Transformation Toughened Zirconia TTZ From Azom.com Raw Materials VII Refractory 39

40 Physical properties of partially stabilized zirconia (PSZ) Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 40

41 ZTA (Zirconia toughened alumina) Backscattered SEM image of a ZTA The alumina-zirconia binary phase diagram. Raw Materials VII Refractory 41

42 Stabilizer Zirconia Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 42

43 L +CaZrO 3 Temperature C Cubic +CaZrO 3 CaZr 4 O 9 +CaZrO 3 M +CaZr 4 O 9 ZrO 2 -MgO ZrO 2 -CaO Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 43

44 TEM image of the Mg-PSZ (courtesy of A.H. Heuer, CWRU) Tetragonal precipitates in a cubic matrix Raw Materials VII Refractory 44

45 ZrO 2 -Y 2 O 3 ZrO 2 -CeO 2 Ref. R.W. Cahn et.al., Materials Science and Technology, Vol. 11, 1994 Raw Materials VII Refractory 45

46 Zircon ZrO 2.SiO 2 (Zircon sand) Baddeleyite ก ก ก ZrO 2 ก ZrO 2 > 65.0% TiO 2 < 1.0% ก ZrO 2 > 60.0% TiO 2 < 1.0% Raw Materials VII Refractory 46

47 Synthesis of Zirconia Zircon decomposition Alkaline breakdown Chlorination or chemical decomposition Lime fusion Plasma decomposition Raw Materials VII Refractory 47

48 Zircon decomposition ZrSiO 4 ก > 6000 C ก ก ZrO 2, SiO 2 ก Na 2 O ก ก sulfuric acid Raw Materials VII Refractory 48

49 Alkaline breakdown ZrSiO 4 ก basic flux (NaOH, Na 2 CO 3 ) Na 2 ZrSiO 5, Na 2 SiO 3, Na 2 ZrO 3, NaOH, Na 2 ZrO 3 wash Na 2 SiO 3, NaOH ก Na 2 ZrO 3 + H 2 O Zr(OH) 2 + 2NaOH ZrO 2 + H 2 O Na 2 ZrSiO 5 + 4HCl ZrOCl 2 + SiO 2 + 2NaCl + 2H 2 O NaOH Na 2 ZrO 3 + 2HCl Raw Materials VII Refractory 49

50 Chemical decomposition: chlorination ZrSiO 4 ZrSiO 4 + C + 4Cl 2 Reaction coke and Cl 2 at temp C ก gas ZrCl C SiCl 4-10 C Bubbled in the water ZrOCl 2 (zirconium oxychloride) Reaction ก NaOH Na 2 CO 3 at high temp. Sodium zirconate (Na 2 ZrO 3 ), sodium silicate ก Zirconate ions hydrolyze + H 2 O Form hydrated hydroxide Zr(OH) 2 ZrO 2 + H 2 O Raw Materials VII Refractory 50

51 Chlorination >1000 C ZrSiO 4 + C + 4Cl 2 ZrCl 4 + SiCl 4 +4CO ZrCl 4 + H 2 O ZrOCl 2 + 2HCl ZrOCl NaOH Na 2 ZrO 3 + 2HCl Alkaline C ZrSiO 4 + 4NaOH Na 2 ZrO 3 + Na 2 SiO H 2 O ZrSiO 4 +2NaOH Na 2 ZrSiO 5 + H 2 O C ZrSiO Na 2 CO 3 Na 2 ZrO 3 + Na 2 SiO CO ZrSiO 4 + Na 2 CO 3 Na 2 ZrSiO 5 + CO 2 Raw Materials VII Refractory 51

52 Preparation of ZrO 2 powder Chlorination and thermal decomposition C in a shaft furnace or fluidized bed ZrSiO 4 + 4C + 4Cl 2 ZrCl 4 + SiCl 4 + 4CO ZrCl 4 condensed at C เพ อแยกส งเจ อปน hydrolysis zirconium oxychloride or zirconyl chloride (ZrOCl 2 ) ZrO 2 Raw Materials VII Refractory 52

53 Preparation of ZrO 2 powder ( ) Lime fusion C ZrO 2.SiO 2 + CaO CaZrSiO C ZrO 2.SiO 2 + 2CaO ZrO 2 + CaSiO 3 (trated with HCl) C /3-9 h ZrSiO 4 + CaCO 3 ZrO 2 + CaSiO 3 + CO 2 Leaching with HCl at 90 C and treatment with NaOH at 15 C Raw Materials VII Refractory 53

54 Preparation of ZrO 2 powder ( ) Plasma decomposition: Zircon Argon plasma reactor C quenching ZrO 2 and SiO 2 The decomposed mass is treated with NaOH or H 2 SO 4 Raw Materials VII Refractory 54

55 Application of ZrO 2 Figures from SPI supplies, Refractron Technologies corp. Raw Materials VII Refractory 55

56 Raw Materials VII Refractory 56

57 Question: Homework To stabilize zirconia to cubic structure, 6.5 mol% of Y 2 O 3 was added in ZrO 2. Calculate the wt% of ZrO 2 and Y 2 O 3 to prepare a 500 g. batch of powder. Raw Materials VII Refractory 57