UNITECR 2011 Kyoto FIRE Short Course

Evaluation of the Corrosion-Evaluation of the Corrosion-Resistance of RefractoriesResistance of Refractories

Experimental determination of Experimental determination of phase equilibria phase equilibria

Static methods• High temperature XRD• Quenching method• EMF measurements• Hot stage microscopy

Dynamic methods• Differential thermal analysis

(DTA)• Thermal gravimetry (TG)• Differential scanning

calorimetry (DSC) • Hot stage microscopy

Principles of Corrosion Testing: Principles of Corrosion Testing:

Static Tests • no relative movement

between refractory and corrosive-fluid

• change of slag-composition during tests

• no temperature gradient • Focus on thermodynamic

aspects of corrosion

Dynamic Tests• Forced relative movement

between refractory and corrosive-fluid

• Simulation of „real-life process“= renewed slag /removal of corrosion products / thermal gradient

• Focus on kinetic aspects of corrosion

Static Tests • button or sessile drop test• cup, crucible, brick or cavity

test• induction furnace test

Dynamic Tests• rotary slag test

„Hybrid“ – method of test: The static dipping/immersion or finger test

can be made dynamic by rotating the sample

Sessile Drop Test

Also: button test

• software helps with interpretation of recorded „motion pictures“, measuring the wetting-angle

• Knowing the wetting angle allows for interpretation of interface- and surface-energies

• strictly, the above is only valid for „non corrosive systems“ i. e. the fluids composition is not altered by any reaction with the substrate.

• e. g. slags or glasses on oxidic refractory material, only allow for comparative conclusions

Powders of the corrosive agents (e. g. slag, flux, ash, glass) are shaped into a small cylinder and placed on a substrate consisting of the refractory material of interest or a reference substrate.

These samples are heated up to certain temperatures or until complete melting of the corrosion agent in a furnace equipped with a camera for video documentation.

Characteristic Temperatures in the Sessile Drop Test

A cored out refractory brick is filled with the corrosive agent and exposed to high temperatures, to promote corrosive reactions. After cooldown, the crucibles are cut along the middle and pictures of both surfaces are taken. Depth of liquid-penetration into refractories or reduction of wall thickness (e. g. by spalling or dissolution) is measured. Evaluate samples optically as:A: Uneffected, B: lightly attacked, C: attacked or D: corroded (=sample destroyed)

Crucible Test

Also: Cup, Cavity or brick test

• Popular method, because many samples can be tested within a short time

• Limited conclusions, because: – Low slag/material rate leads to rapid

saturation of the slags composition with reaction products lowering the corrosive effect

– Sometimes all of the corrosive agent is absorbed into the brick

– no slag flow available (static method)

Evaluation of a Crucible Test

d: cut length = former diagonal of square crucible TL: Depth of dissolution TI: Depth of Infiltration RF: Remaining level of melt

Crucible, unaltered material

d

RF

Zone of Dissolution

Zone of Infiltration

Surface-level of melt after test

TI TL

Crucible, unaffected material

Induction Furnace Test

• Heating up the melt directly, allows to establish a temperature gradient between the inner and outer surface of the refractory bricks

• Temperature and atmosphere are easily controlled

• Observation of special corrosion effects at melt/slag line

• „Inductive stirring“ adds dynamic effect, leads to more realistic testing conditions, however uncontrolled

• Static method: no „flow“ of corrosive agents

Refractory bricks are combined to form a polygonal crucible within an induction furnace.Metal and slag are melted by induction in the crucible.

Induction Furnace Test

Pictures: DIFK, Bonn and RHI Refractories

1: heating coil 2: permanent lining 3: castable lining 4: insulating paper 5: thermocouple 6: tested segments 7: steel jig 8: melt 9: slag10: cover

5

Comparing samples

after Induction

furnace test

Dipping Test

Also: immersion or finger test

• Isothermal conditions within the refractory sample

• Possible use of a large volume of slag relative to the size of the sample limits the composition variation of the slag due to the solution of sample material

• The sample can be rotated in the liquid slag or melt, which removes boundary layers and thus increases any corrosive effect

• rotating finger test = dynamic method

Cylindrical or square pillar shaped samples are held in the corrosive liquid in a furnace. Immersion time, temperature and atmosphere can be varied.

Submerged Sample in Dipping Test

Rotary Slag Test • Heating the drum from the inside by a burner, establishes a temperature gradient within the refractory lining. The exact temperature however is difficult to control

• Rotating the drum and renewing the slag (and thus removing corrosion products) simulate conditions closer to industrial reality

• Many different materials can be tested simultaneously under the exact same conditions, but this test method also exceeds the laboratory scale

A cylindrical drum, heated by a burner, is lined with different refractory materials and rotated about a horizontal axis. To periodcally remove and renew the slag, the whole drum is tilted and after return to the horizontal position, new slag is applied.

Rotary Slag Test

Remaining thickness

parallel cracks

Sample-segmentsInsulating castable

flameFlue gas

Steel drum

Vertical cracks

Picture: Fundación ITMA (Materials Technological Institute), Spain

Determination of thermodynamic equlibrium using thermodynamic software packages

Example: Determination of the melt formation of the refractory/slag equilibrium(T=1250°C, pO2=10-10 bar)

Refractory oxide/species [wt.-%]

Amou

nt o

f mel

t [w

t.-%

]

V. Reiter, PhD thesis, MU Leoben, 2008

Determination of thermodynamic equlibrium using thermodynamic software packages

Example: Determination of solubility of refractory oxides in fayalite slags (T=1550°C, pO2=0,21 atm)