1. UNITECR 2011 Kyoto FIRE Short Course Evaluation of the Corrosion-Resistance of Refractories

2. Experimental determination of 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)

3. Principles of Corrosion Testing:
Static Tests
Dynamic Tests
no relative movement between refractory and corrosive-fluid
change of slag-composition during tests
no temperature gradient
Focus on thermodynamic aspects of corrosion
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

4. Static Tests Dynamic Tests
button or sessile drop test
cup, crucible, brick or cavity test
induction furnace test
rotary slag test
„Hybrid“ – method of test:
The static dipping/immersion or finger test
can be made dynamic by rotating the sample

5. 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.

6. Characteristic Temperatures in the Sessile Drop Test

7. 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)
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)

8. Evaluation of a Crucible Test
Crucible, unaffected material

9. 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.

10. Induction Furnace Test5
Induction Furnace Test
1: heating coil
2: permanent lining
3: castable lining
4: insulating paper
5: thermocouple
6: tested segments
7: steel jig
8: melt
9: slag
10: cover
Pictures: DIFK, Bonn and RHI Refractories

11. Comparing samples after Induction furnace test

12. 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.

13. Submerged Sample in Dipping Test

14. 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.

15. Rotary Slag Test Sample-segments Insulating castable Steel drum
flame
Flue gas
Steel drum
Vertical cracks
Remaining thickness
parallel cracks
Picture: Fundación ITMA (Materials Technological Institute), Spain

16. 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.-%]
Amount of melt [wt.-%]
V. Reiter, PhD thesis, MU Leoben, 2008

17. 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)