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Wettability at elevated temperatures

Wettability at elevated temperatures. FIRRE UNITECR 2011, October 30 – November 2, Kyoto Prof. C. G. Aneziris aneziris@ikgb.tu-freiberg.de. Topics. Surface and interfacial energies Gibbs equation Dupré equation Wetting behaviour of ideal solid surfaces Young equation

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Wettability at elevated temperatures

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  1. Wettability at elevated temperatures FIRRE UNITECR 2011, October 30 – November 2, Kyoto Prof. C. G. Aneziris aneziris@ikgb.tu-freiberg.de

  2. Topics • Surface and interfacial energies • Gibbs equation • Dupré equation • Wetting behaviour of ideal solid surfaces • Young equation • Microscopic and macroscopic contact angles • Effect of systemsize • High-temperature wettabilityof non ideal surfaces • Equipment • Microstructure-assisted • Electro-assisted • Contributionofwettability on meltcorrosionofrefractories • Penetration ofslagintorefractories • Dissolution ofrefractoriesintoslag • Moltenslagviscosity • Crystallitegrowthprocesses 2

  3. Surface and interfacial energies * Solid / Liquid / Vapour System:  the total free energy of the system F the surface area  defined by GIBBS (1961) for SOLIDS:  the work needed for reversible creation of a solid surface S at constant strain by breaking bonds to increase the number of solid atoms (or molecules) in contact with a vapour V, SV= solid surface energy T – temperature V – volume ni – number of moles of component i Creation of a solid surface (shaded) by cleavage * 3 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  4. Surface and interfacial energies * Solid / Liquid / Vapour System:  the total free energy of the system F the surface area  defined by GIBBS (1961) for SOLIDS:  the work needed for creation of a solid surface S without increasing the number of surface atoms by purely elastic strain of the solid in contact with a vapour V, SV= solid surface tension  = macroscopic elastic strain Creation of a solid surface (shaded) by elastic deformation* 4 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  5. Surface and interfacial energies Solid / Liquid / Vapour System:  the total free energy of the system F the surface area  Defined by GIBBS (1961) for LIQUIDS:  the work needed for reversible creation of additional surface of a liquid L in contact with a vapour V, LV= liquid surface energy  the reversible stretching of a liquid surface is identifical to a reversible creation of new surface; the liquid can increase its surface area only by the addition of new atoms to the surface, LV= liquid surface tension T – temperature V – volume ni – number of moles of component i 5

  6. Surface and interfacial energies * Solid / Liquid / Vapour System:  interface of two non-reactive phases = interfacial energy  Wc = the work of cohesion in a pure liquid or pure solid defined by DUPRÉ the work of adhesion (1869):  the reversible work needed for cleavage on the boundaries of two non-reactive phases (liquid and solid), Wa= the work of adhesion SL – solid/liquid interfacial energy 6

  7. Example: Meltfiltration a) Metalmeltwithoutfiltration b) Filtration c) Filtratedmetal 7 Aneziris, Jung, SFB 920 proposal 2011

  8. Janke, D.; Raiber, K.: Grundlegende Untersuchungen zur Optimierung der Filtration von Stahlschmelzen. Technische Forschung Stahl, Luxemburg: Amt für amtliche Veröffentlichungen der Europäischen Gemeinschaften, 1996. – ISBN 92-827-6458-3 8

  9. Equationsforfiltrationof non metallic inclusions (1) Work of adhesion to separate two phases Work of cohesion to create two new surfaces (2) (3) (5) (4) (5) 9

  10. Wetting behaviour of ideal solid surfaces (the solid surfaceisverticaland TL isperpendiculartothe plane ofthe fig. andassumetobe a straigthline; the total lengthof TL isconstantduringitsdisplacement, as in thecaseof a meniscusformed on a vertical plate) Displacement of a triple line around its equilibrium position that allows derivation of the Young equation.* 10 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  11. The surface free energy Fs of the system caused by a small displacement z of the solid/liquid /vapour triple line. The radius r of the triple line region is much larger than the range of atomic or molecular interactions in the system. For metallic and ionocovalent ceramics: The variation of interfacial free energy Fs per unit length of triple line (small linear displacement z): The equilibrium conditions: leads to Youngequation: Displacement of a triple line around its equilibrium position that allows derivation of the Young equation.* 11 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  12. Conditions: solid surface  flat, undeformable, perfectly smooth, chemically homogeneous liquid  non-reactive, does not completely cover the solid vapour phase contact angle  between liquid surface and solid surface, scale of wetting behaviour of the liquid The equilibrium value of the contact angle  obeys the classical equation of YOUNG (1805): LV 12

  13. Wetting liquid –  < 90° Non-wetting liquid –  > 90° drop Perfect wetting liquid –  = 0° Non-wetting liquid –  = 180° 13

  14. local nanometric (microscopic) contact angle   macroscopic contact angle M * The energyof an atomlying on a giveninterfaceinside a sphereofradiusrcis different totheenergyof an atomatthe same interfacefarfromthetripleline. The three relevant interfacialenergiesSV, SL, LVclosetoandfarfromthetriplelineare different andthisdifferenceincreasewiththerangeatomic interactions. 14 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  15. Sessile drop configuration during wetting:  effect of system size * drop size r increase with rc the relevant contact angle is no longer Young contact angle Y but the microscopic contact angle concept of line energy  the increase R of the drop base radius R leads to an increase of the triple line length  the triple line can be treated as an equilibrium line defect with a specific excess free energy  The variation of interfacial free energy during wetting in the sessile drop configuration is: The equilibrium conditions: leads to: for R < 100 nm Top view of a sessile drop during spreading.* 15 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  16. Solid / Liquid / Vapour System:  effect of the curvature of the liquid/vapour surface * defined by LAPLACE (1805) for LIQUIDS and VAPOURS:  the curvature at each point Q of the Liquid / Vapour surface in the gravitational field PLQ – pressure on the liquid side of the surface PVQ– pressure on the vapour side of the surface LV–liquid surface energy R1, R2– principal radii at point Q The principal radii of curvature R1 and R2 at a point Q on a curved liquid surface. * 16

  17. The total free energy change F can be calculated when a liquid surface initially in a horizontal position (z* = 0,  = 90°) is raised (or depressed) to form a meniscus of height z*, corresponding to a contact angle . The contact angle  can be determined by minimizing F as a function of z*. For a triple line of unit length, the total free energy change F is (Neumann and Good, 1972): – A0    90° + A 90    180° vapour solid liquid vapour solid liquid 17 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all. Meniscus rise on a vertical wall when  < 90° (a) and depression when  > 90° (b).*

  18. The total free energy change F can be calculated when a liquid surface initially in a horizontal position (z* = 0,  = 90°) is raised (or depressed) to form a meniscus of height z*, corresponding to a contact angle . The contact angle  can be determined by minimizing F as a function of z*. For any rise z*of the meniscus, z* and  are related by: + z*0    90° – z* 90    180° The capillary length lc is the maximum rise of a liquid on a perfectly wetted vertical plate. • lc – capillary length • – liquid density • g – gravity vapour solid liquid vapour solid liquid 18 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all. Meniscus rise on a vertical wall when  < 90° (a) and depression when > 90° (b).*

  19. Solid / Liquid / Vapour System:  metastable and stable equilibrium contact angles * After spreading of a liquid droplet:  (a) metastable equilibrium: Young angle Y conditions: only displacements of the triple line parallel to an undeformable Solid / Vapour surface  (b) stable equilibrium: dihedral angles 1, 2, 3 conditions: deformation of the solid close to triple line as displacement h defined by SMITH (1948):  (c) total equilibrium: equilibrium at the triple line and along the whole Solid / Liquid interface are attained conditions: unchanging curvature at any point of the Solid / Liquid interface (a small liquid droplet on the surface of another immiscible liquid) (a)* (b)* (c)* 19 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  20. Solid / Liquid / Vapour System:  metastable and stable equilibrium contact angles * The stable equilibrium in terms of the three dihedral angles 1, 2, 3can be obtained by regarding the displacement h of the triple line as two elementary displacements, one perpendicular to the intersections of the Liquid / Vapour surface (h1) and one perpendicular to the intersection of the Solid / Liquid interface (h2). Assuming isotropic Solid / Vapour and Solid / Liquid surface and interfacial energies, the interfacial free energy change Fsfor the displacements h1and h2 is: The equilibrium conditions: , leads to: and defined by SMITH (1948): Displacement of the triple line around ist equilibrium position when the solid is deformable.* 20

  21. The actual triple line configuration observed after certain time of contact between the solid • and liquid phases depends on the scale of observation and on the relative rates of two processes: • the movement of triple line over large distances to satisfy the YOUNG equation •  the distortion of triple line to satisfy locally the more general SMITH equation • Non-reactive Solid / Vapour couples • (molten metals, certain oxide melts at high temperature): • the lateral movement of the triple line is • very fast (< 10-1 sec. for mm-size-droplets) • the high of wetting ridge h can attain • several tens of nm or µm and increase • continuously with time (several hours or • tens of hours) Formation of a wetting ridge h at the triple line.* 21 Eustathopoulos, N. et all (1999): Wettability at high temperatures. Pergamon: Amsterdam et all.

  22. A. Non-reactive Solid / Vapourcouples • The wetting of low viscosity liquid drops on solid substrates can occour in 3 stages: •  rapid stage: the macroscopic contact angle approaches the YOUNG angle Y, the area of the Solid / Liquid interface and the Liquid / Vapour surface are determined • slower stage: the stable local equilibrium according to the SMITH equation • much longer time stage: the total equilibrium i.e., a constant curvature on the whole Solid / Liquid interface is obtain • The rapid and the slower stages will take several minutes or hours. 22

  23. B. Reactive Solid / Vapourcouples Chemical dissolutionwithlowinfluence on SL– solid/liquid interfacial energy LV– liquid surfaceenergy + • firststage: 10-2 s spreadingwithoutreaction; themacroscopiccontact angle approaches • the YOUNG angle Y, • secondstage: thechemicaldissolutionisaffectingthemacroscopiccontact angle; in caseof • liquid Sn / solid Bi remainstheinterface solid/liquid in thefirst 5 s • macroskopic flat andthenarisesatthetriplepoint; diffusionistakingplace, • themeltvolumeisincreasingandthespreadingdiameterisincreasing. (Gibbs-Thomson-EquationwithCiequilibriumconcetrationwithcurvature, Ceq equilibriuemconcetrationof a flat interface, k curvatureandVm molar volumeof solid) 23

  24. B. ReactiveSolid / Vapourcouples Chemical dissolutionwithlowinfluence on SL– solid/liquid interfacial energy LV– liquid surfaceenergy + • thirdstage: the total equilibrium i.e., a constantcurvature on the • whole Solid / Liquid interfaceisobtained. • In caseof liquid Sn/Bi solid at 245 °C thechemicalequilibrium • isreached after 100 s with 7 % changeofthespreadingradius. 24

  25. C. Reactive Solid / Vapourcouples Chemical dissolutionwithhighinfluence on SL– solid/liquid interfacial energy LV– liquid surfaceenergy + (Momentary wetting angle) 25

  26. High-temperature wettability(B) Wetting behaviour for real, microstructuredsurfaces 26

  27. 27

  28. Wetting behaviour for real, microstructured surfaces: the apparent contact angle W • on a rough surface • Defined by WENZEL (1936): • For a smooth surface: • For a rough surface: W – apparent contact angle r – roughness ratio Y– macroscopic YOUNG contact angle The roughnessleadstomorewettingof a goodwettedsurface andlesswettingof a „bad“ wettedsurface Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 28

  29. On real surfaces may exist a wide range of practically stable apparent contact angles: • „Advancing contact angle“: when the drop volume , • the contact line appears to be pinned •  W = maximum • „Receding contact angle“: when the drop volume , • the contact line appears to be pinned •  W = minimum • „Contact angle hysteresis“: difference between „advancing“ and „receding“ • contact angle Influenceofroughnessof solid surfacetowetting:  increaseoftheactualsurfaceand  pinningofthetriplelineby sharp edges On rough, hydrophilicsurfaces:  in contactwith large dropsthe WENZEL equationismainlyfulfill 29

  30. On microstructuredhydrophobicsurfaces (surfacepattern):  themainparameterthatdetermainesthecontact angle is thefractionof solid sactually in contactwiththe liquid (not thesurfaceroughness) (Cassie and Baxter equation) (Bico, Marzolinand Quere equation) Cassie, A., Baxter, S., Trans. Farraday Soc, 40, (1944) 546 Shinozaki, N., Kaku, H., Mukai, K., “ Influence of pores on wettability of zirconia ceramic by molten manganese”, Trans. JWRI, Vol 30 (2001) 30

  31. s 0.64 s 0.05 s 0.25 Bico, J., Marzolin, C., Quere, D., „Perl drops“, Europhysics Lett., 47 (2), (1999) 31

  32. Effect of an electrical potential on the wettability: corrosion resistance of refractories • Applications of electrical voltage: •  at room temperature: – Electro Wetting on Dielectric (EWOD) • – the movement of a microdroplet with reducing contact angle • based on the YOUNG-LIPPMANN equation: •  the shape of a liquid drop on a surface is determined by: • the composition of the liquid and • the composition and morphology of the surface •  anelectric potential is applied across the liquid drop and the solid substrate: • ions and dipoles redistribute in the liquid, in the solid, or in both depending on the • relative material properties • hydrophobic surface to behave an a hydrophilic manner • V– contact angle at a voltage V • Y– macroscopic YOUNG contact angle • 0 – dielectric constant in vakuum • – dielectric constant of the layer • V – the voltage • d – the thickness of layer • LV – the Liquid/Vapour surface tension Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 32

  33. 33

  34. Kinetic quantification of the wetting process: between silicate slag and silicate refractories Kinetic equation:  activation energy for three kinetic stages: (a) initiation of wetting stage (b) development and spreading stage (c) penetration and reaction stage Liquid drops on vertical an inclined surface: (at room temperature)  B0 = ratio of gravitional to surface tension forces:  B0 indicates D and/or   d – diameter of the slag wetting area t – time K0– constant Q – activation energy R – gas constant T – absolute temperature – liquid density g – acceleration of gravity D – equivalent drop diameter  – surface inclination angle LV – Liquid/Vapour surface tension Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 34

  35. Kinetic quantification of the wetting process: between silicate slag and silicate refractories Static work of adhesion of surface inclination: Dynamic work of adhesion of surface inclination: (at room temperature)  a high work of adhesion = good wetting  a low work of adhesion = poor wetting Inclination constant k:  k at the  is directly proportional to WLV, R– reciding contact angle at  A – advancing contact angle at   – surface inclination angle LV – Liquid/Vapour surface tension m – mass of the liquid r* – radius of the base of the droplet g – acceleration of gravity Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 35

  36. Experimental: sample preparation •  Raw material: - commercially fused magnesia • (bulk density= 3,52 g/cm³, grain size > 100 µm, d50= 25 µm) • - temporary pressing additive (1wt% liquid ligninsulfonate) •  Mixing: - at room temperature • Forming: - uniaxial pressing at 150 MPa • - cylindrical sampels (d= 50 mm, h= 25 mm) •  Sintering: - electrical furnace in air • - 1.700 °C, 6 h •  Grinding: - surface roughness for samples • Microstructuring: - CO2 laser (laser pulse energy 20 mJ, 100 ms laser pulse duration) • - three different stripe pattern • - distance of laser beam 150 µm, 300 µm Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 36

  37. Experimental: influence of the roughness of MgO-surfaces of the contact angle  ground-MgO surface  laser-treated MgO-surface pores between 5 and 30 µm XRD-Analysis: MgO Ca3Mg(SiO4)2 pores stripe area XRD-Analysis: MgO Ca3Mg(SiO4)2 Ground-MgO surface.*** Laser-treated MgO surface, distance of laser beam 300 µm.*** Cross-section of laser-treated MgO surface, distance of laser beam 300 µm.*** Cross-section of MgO-ground surface.*** 37

  38. Experimental: influence of the roughness of MgO-surfaces of the contact angle • Heating microscope: - sessile drop method • - amorphous slag based on Fayalite (2FeOSiO2) • in contact with MgO surface • - as a function of time, temperature and voltage • in argon atmosphere: •  macroscopic YOUNG contact angle Y •  advancing and receding contact angle •  adhesive work as a function of the inclination angle •  spreading diameter Heating microscope, IKGB TU Bergakademie Freiberg 38

  39. Experimental: influence of the roughness of MgO-surfaces of the contact angle Heating microscope:  macroscopic YOUNG angle Y as a function of temperature  the roughness , the contact angle   higher wetting of the microstructured samples at lower temperature leads to higher adhesive work Contact angles as a function of temperature.*** Contact angles at 1116 °C.*** 39

  40. Experimental: influence of the applied voltage of the contact angle Heating microscope:  macroscopic YOUNG angle Y as a function of temperature and voltage Assumption: The dielectric constant and the thickness of the electro formed layers have the same value for two different applied voltages. 0– contact angle with no voltage 1 – contact angle at the applied voltage V1 2 – contact angle at the applied voltage V2 -35 V 57,8 ° Contact angles at 1116 °C.*** +35 V 87,4 ° Heating microscope images of MgO samples with applied voltages, above -35 V (contact angle 57,8 °1,5 °), below +35 V (87,4 °1,7 °), 1116 °C, 30 s).*** 40

  41. Experimental: influence of the applied voltage of the phases of slag Heating microscope:  phase formation of the slag in air and in argon atmosphere Applying positive voltage:  change of the slag phase composition with insitu formation of MgFe2O4 Applying negative voltage:  formation of the interface layer between slag drop and the MgO slag layer MgO XRD, X-ray diffraction of the frozzen slag.*** SEM-image, -35 V, 1116 °C, 6.000s, slag, interface layer, MgO.*** 41

  42. Experimental: influence of the applied voltage of the interface layer Heating microscope:  thickness and phase evolution of the interface layers between MgO and slag The phase composition of the interface layers is a function of the applied voltage. Applying negative voltage:  the voltage , the thickness of interface layer  XRD, X-ray diffraction.*** *** Aneziris, C. G.; Hampel, M.: Microstructured and Electro-Assisted High-Temperature Wettability of MgO in Contact with a Silicate Slag-Based on Fayalite. Int. J. Appl. Ceram. Technol., Vol. 5, No. 5, 2008, pp. 469-479 42

  43. Experimental: influence of the roughness and the applied voltage of the contact angle Heating microscope:  macroscopic YOUNG angle Y as a function of time and voltages at high temperature With increasing of time:  contact angles  Applying voltage („+“ or „-“):  higher contact angles after 6.000 s of all „electro-assisted“ samples Contact angles as a function of time.*** 43

  44. Experimental: influence of the roughness of MgO-surfaces of the activation energy Q Heating microscope:  spreading diameters of the slag as a function of temperature, time and voltages  low contact angle (high spreading diameter) leads to a low activation energy Q  the porous stripes of the „300 µm laser“sample contribute to lowest activation energy Q Q– activation energy d1– spreading diameter at temperature T1 and time t1 d2 – spreading diameter at temperature T2 and time t2 Kinetic stages: (a) initiation of wetting stage (b) development and spreading stage (c) penetration and reaction stage Spreading diameters as a function of temperature and time, activation energies and kinetic stages.*** 44

  45. Experimental: influence of the roughness of the MgO-surfaces on inclined surfaces Heating microscope:  advancing A and receding Rangles of the slag as a function of inclination; inclination constant k Laser microstructured MgO surface, 300 µm:  rolling angle * 24,3 °  advancing angle A99,9 °  receding angle R22,2 ° 1116 °C; 24,3 ° 1116 °C; 99,9 ° Rolling angle at 24,3 °, advancing angle at 99,9 °, and receding angle at 22,2 ° of a laser-treated MgO surface with a laser beam distance of 300 µm.*** 1116 °C; 22,2 ° 45

  46. Experimental: influence of the roughness of the MgO-surfaces on inclined surfaces Heating microscope:  advancing A and receding Rangles of the slag as a function of inclination; inclination constant k Roughness of the laser-treated samples:  highest inclination constant k  high adhesion work Young contact angles, advancing (A) and receding (R) angles as a function of inclination angle (), rolling angles (*) as well as calculated inclination constant k. *** 46

  47. High-temperature wettability (C) Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials, Mat. Sc. Techn., 2007 47

  48. Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials, Mat. Sc. Techn., 2007 48

  49. Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials, Mat. Sc. Techn., 2007 49

  50. Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials, Mat. Sc. Techn., 2007 50

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