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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

Wettability at elevated temperatures

FIRRE

UNITECR 2011,

October 30 – November 2, Kyoto

Prof. C. G. Aneziris

aneziris@ikgb.tu-freiberg.de

topics
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

slide3

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.

slide4

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.

slide5

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

slide6

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

slide7

Example: Meltfiltration

a) Metalmeltwithoutfiltration

b) Filtration

c) Filtratedmetal

7

Aneziris, Jung, SFB 920 proposal 2011

slide8

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

slide9

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

wetting behaviour of ideal solid surfaces
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.

slide11

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.

slide12

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

slide13

Wetting liquid –  < 90°

Non-wetting liquid –  > 90°

drop

Perfect wetting liquid –  = 0°

Non-wetting liquid –  = 180°

13

slide14

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.

slide15

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.

slide16

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

slide17

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).*

slide18

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).*

slide19

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.

slide20

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

slide21

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.

slide22

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

slide23

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

slide24

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

slide25

C. Reactive Solid / Vapourcouples

Chemical dissolutionwithhighinfluence on

SL– solid/liquid interfacial energy

LV– liquid surfaceenergy

+

(Momentary wetting angle)

25

slide26

High-temperature wettability(B)

Wetting behaviour for real, microstructuredsurfaces

26

slide28

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

slide29

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

slide30

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

slide31

s 0.64

s 0.05

s 0.25

Bico, J., Marzolin, C., Quere, D., „Perl drops“, Europhysics Lett., 47 (2), (1999)

31

slide32

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

slide34

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

slide35

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

slide36

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

slide37

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

slide38

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

slide39

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

slide40

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

slide41

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

slide42

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

slide43

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

slide44

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

slide45

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

slide46

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

slide47

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

slide48

Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

48

slide49

Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

49

slide50

Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

50

slide51

Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

51

slide52

Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

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Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

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Sobczak, N., Nowak, R., Radziwill, W., Budzioch, J., Glenz, A., Experimental complex

ofhigh-temperature behaviourofmoltenmetals in contactwithrefractorymaterials,

Mat. Sc. Techn., 2007

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ContributionofWetting on MeltCorrosionofRefractories

  • Penetration of slag into refractories
  • Dissolution of refractories into slag
  • Molten slag viscosity
  • Crystallite growth processes

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Penetration of slag into refractories:

  •  capillaries (open pores, microcracks) = initial
  •  the penetration rate dl/dt of slag into a capillary expressed by POISEULLE:
    •  brick temperature has a large effect on the penetration depth l trought is effect on 
    • influence of the cristallite shape and crystallite growth (microstructure) during penetration by a liquid
    •  influence of the microstructure (grain size, porosity) during penetration by a liquid:
  • r – capillary radius
  • P – capillary sucking pressure
  • – dynamic viscosity of the slag
  • l – slag penetration depth
  • t – time

gb – grain boundary interface energy

SL – Solid / Liquid interface energy

 – dihedral angle

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Penetration of slag into refractories: influence of the microstructure (grain size, porosity)

    • the liquid can penetrate into grain boundaries:
    • the liquid can appear along all three grain edges
    • as a continously connected phase:
    •  liquid can only partially penetrate along grain
    • boundaries:
    •  no penetration:

gb – grain boundary interface energy

SL – Solid / Liquid interface energy

 – dihedral angle

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Penetration of slag into refractories: influence of the brick temperature

  • the temperature decrease away from the hot face
  • the slag viscosity increase
  • the slag is to viscous to penetrate
  • the slag penetration can be suppressed by increasing slag viscosity or contact angle or by decreasing the surface tension:
  • a temperature gradient from a cool outside surface to the hot (contact) face can limit penetration

Schematic diagramm of liquid (slag) penetration in typical kiln lining.**

  •  – slag surface tension t – time
  • – wetting or contact angle r – capillary radius
  • – dynamic viscosity of the slag
  • l – slag penetration depth

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Penetration of slag into refractories: influence of the slag viscosity

    •  diffusive mass transport within the liquid slag after penetration into the refractory
    • by STOKES-EINSTEIN:
                  • changes in slag composition (dissolution of the solid)
                  •  slag viscosity , transport in the slag 
                  • accelerated degradation processes dependent on diffusive mass transport
                  •  and  vary with time
                  • reaction products: solid, liquid, gas
                  • remain attached to the solid (a)
                  • are fugitive (b)
                  • are a combination of (a) and (b)

(a)**

  • D – ionic diffusivity
  • k – Boltzmann‘s constant
  • T – absolute temperature
  • r – radius of the diffusing species
  • –dynamic viscosity of the slag

(b)**

(c)**

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Crystallite growth processes: precipitation and growth from satured solution

  • = reverse process to corrosion  indirect dissolution
  • Phases form from the liquid at temperature or on cooling:
    •  analysis via thermodynamic calculations (GIBBS energy minimisation modules)
  • Tend to high dissolution rate:
  •  components of a solid with the highest solubility
  •  particles with high specific surface area (small radius of curvature, angular shaped protuberances)
  •  pressure at particles/particles contact (necks)
  • … leads to a general rounding of the microstructur.
  • Equilibrium shap of the crystals:
  • - considering their interfacial energies with the liquid phase
  •  isotropic interfacial energy  spherical shap
  •  anisotropic interfacial energy  shaps by the WULFF construction
  • For example: MgO – spheres Mullite – needle like or cuboidal
  • Al2O3 – prismatic CA6 – elongated tabular

Dissolution and redeposition leads to general rounding of angular crystals.**

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Crystallite growth processes: precipitation and growth from satured solution

  • = reverse process to corrosion  indirect dissolution
  • Effect of local composition changes (phase separation, impurity segregation)
  • lead to changes in the equilibrium form of the crystal morphology so that these
  • shapes may not necessarily occur for these phases in complex refractory-slag systems.
  •  Cr2O3 liquid into solid MgO: angular MgO(-Cr2O3) crystal morphologies
  • Crystallite growth processes tend to bee defined by the rate determinig step:
  •  growth of Al2O3: controlled by the rate of reaction at the liquid/alumina interface
  • growth of MgO: controlled by mass transport diffusion through the boundary layer phase
  • Slag penetration into a refractory can lead to (subsatured slag species at lower temperature):
  •  solid state diffusion of slag species into a grain phase
  •  exsolution (precipitation) on cooling
  • For example: exsolved precipitation in refractories include Cr2O3 in MgO grains in MgO-Cr2O3 bricks
  • and (Mg, Fe, Mn)O in MgO grains in doloma

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Thankyouverymuchfortheattention

WettingandMicro-hydrodynamics

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Appendix

  • Penetration of slag into refractories:rate of corrosion
  • Corrosion rate = f (T, refractory/liquid/interface composition, liquid density, viscosity, diffusivity, degree of agitation, …)
  • Active corrosion: - reaction product is soluble or dissociates directly in the liquid slag
  •  destruction of the refractory
  • Passive corrosion: - reaction product is a solid phase forms a layer on the refractory
  •  reduce the overall rate of corrosion of the refractory
  • - possible corrosion rate steps:
  • - chemical reactions forming the layer,
  • - diffusion through the layer, or
  • - diffusion through the slag
          • For example: - formation of a dense MgO layer in MgO-graphite refractories
          • - formation of a MgAl2O4 spinel layer in alumina refractories by MgO containing slags
          • - formation of a dicalcium silicate C2S layer on MgO-dolomite refractories by silica containing slags
          • Selective corrosion: - only certain phases in the solid are attacked
          • For example: - decarburisation of carbon containing refractories
          •  dissolution of carbon in the molten steel
          •  decarburised refractory layer is wetted by the slag
          •  penetration and spalling of the decarburised layer

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Penetration of slag into refractories: other physiochemical effects
  • microstructural effects where a smooth surface and material:
      • dens material may resist
      • porous material may not resist
  • slag line attack
  • velocity of slag flow (Marangoni effect):
      • turbulent flow tends to pull out the fine grains in the brick by erosion
      • (physical wear)

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Dissolution of refractories into slag:
          • Types of dissolution:
            • interface controlled  chemical reactions (or solution) at the interface
            •  direct process
            • diffusion controlled  transport (or diffusion) of reacting species through the liquid
                  •  direct or indirect process
          • Refractory and liquid in contact should be of similar nature:
            • SiO2 are acidic  high silica refractories are used with acid liquids
            • (some steelmaking, coal gasifiers, glassmelts)
            • MgO, CaO are basic  used in contact with basic melts
            • (basic oxygen steelmaking, cement production)
            • MgCr2O4, carbon are neutral  resisting acid and basic slags to a similar degree
          • Important in refractories corrosion:  solubility of refractory oxides in molten slag
          •  saturation concentration at the interface between refractory and slag

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Dissolution of refractories into slag:
          • Direct dissolution: - atoms from the solid dissolve directly into the liquid melt
          • - can be reaction or interface controlled
          •  the diffusivity of reaction products is faster then the rate of chemical reaction at the interface
          • Rate of corrosion:
          •  crystal orientation, grain boundary phases, grain shape are neglected
          •  stirring of the melt has no apparent effect on dissolution rate

J – dissolution rate [g/cms]

K – rate constant

Ac – actual area of refractory [cm²]

Ao – apparent area of refractory [cm²]

Cm – concentration of reactant in the melt [g/cm³]

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Dissolution of refractories into slag:
          • Direct dissolution: - atoms from the solid dissolve directly into the liquid melt
          • - can be transport or diffusion controlled
          •  the diffusivity of reaction products is slower the rate of chemical reaction at the interface
    • Rate of corrosion
    • by NERNST:
    • Boundary layer thickness:
    •  if the solid is unsaturated with component of the liquid then solid solution may occur
    •  the liquid phase diffusion of the product through the melt boundary layer is consitered

J – dissolution rate [g/cms]

D – diffusion coefficient [cm²/s]

Cs – saturation concentration of refractory in the melt [g/cm³]

Cm – concentration of reactant in the melt [g/cm³]

 – effective boundary layer thickness [cm²]

dc/dx – concentration gradient over the interface

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Dissolution of refractories into slag:
          • Indirect dissolution: - growth of solid interlayer between refractory and slag
          • - can be transport or diffusion controlled
          •  stirring the melt or rotating the refractory sample (slab), enhances the rate of indirect dissolution by reducing the thickness of liquid boundary layer
          • For laminar conditions the rate of corrosion:
          • A flat slab held vertically in the melt:
          • the rate of corrosion depends on the
          • boundary layer thickness
          • the boundary layer thickness is limited by:
          • degree of convective flow, liquid viscosity,
          • mean diffusion coefficient, container size

J – dissolution rate [g/cms]

D – diffusion coefficient [cm²/s]

Cs – saturation concentration of refractory in the melt [g/cm³]

Cm – concentration of reactant in the melt [g/cm³]

 – density difference between saturated and bulk melt [g/cm³]

 – dynamic viscosity [poise]

g – gravitational constant [cm/s²]

x – distance from the leading edge of the slab [cm]

Growth of solid interlayer between refractory and slag leads to indirect dissolution; t1<t2.**

Lee, W.E., Zhang, E.: Melt corrosion of oxide and oxide-carbon refractories. International Materials Reviews, Vol. 44, No. 3, 1999, pp. 77-104

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Appendix

  • Dissolution of refractories into slag:
          • Indirect dissolution: - growth of solid interlayer between refractory and slag
          • - can be transport or diffusion controlled
          •  stirring the melt or rotating the refractory sample (slab),
          • enhances the rate of indirect dissolution by reducing the thickness of liquid boundary layer
          • For forced convection
          • rate of corrosion:
          •  J=0, if the refractory oxid has been saturated in the slag
          •  to minimise J  (Cs-Cm) must be minimised,
          • For example: if the MgO content in the slag,
          • the corrosion of periclas -refractories
          •  Cm=0  (Cs-Cm) = maximum, J= maximum
  • J – dissolution rate [g/cms]
  • D – diffusion coefficient [cm²/s]
  • Cs – saturation concentration of refractory in the melt [g/cm³]
  • Cm – concentration of reactant in the melt [g/cm³]
  • U – bulk velocity of the fluid [cm/s]
  • – kinematic viscosity [cm²/s]
  • =3,09(x/U)1/2(D/)1/3 – effective boundary layer thickness
  • x – distance from the leading edge of the slab [cm]

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Appendix

  • Molten slag viscosity: with more fluid slag  the slag penetration  and
  • the refractories dissolution 
  • If dissolving refractory in the liquid slag:  increasing the slag viscosity
  •  slower mass transport through the melt layer
  •  progressively saturation of the melt layer
          • Viscosity measurements for molten slag:  oscillation method
                  •  falling body method
                  •  concentric cylinder method
          • difficult, time intensive, expensive
          • Theoretical models for molten slag viscosity: on the basic of composition
          • by FRENKEL:
  • – viscosity
  • T – absolute temperature
  • A, B – parameters depending only on the melt
  • composition

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