UNITECR 2011 Kyoto
FIRE Short Course
Evaluation of the CorrosionResistance of Refractories
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)
• Hot stage microscopy
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
Dynamic Tests
• rotary slag test
• cup, crucible, brick or cavity
test
• induction furnace 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
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.
• software helps with interpretation of
recorded „motion pictures“, measuring
the wetting-angle
• Knowing the wetting angle allows for
interpretation of interface- and surfaceenergies
• 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
Characteristic Temperatures in the Sessile Drop Test
Crucible Test
Also: Cup, Cavity or brick 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 liquidpenetration 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)
• 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
Crucible,
unaffected
material
d
Crucible,
unaltered
material
d: cut length = former diagonal
of square crucible
Surface-level of
melt after test
TL
TI
RF
TL: Depth of dissolution
TI: Depth of Infiltration
RF: Remaining level of melt
Zone of
Dissolution
Zone of
Infiltration
Induction Furnace
Test
Refractory bricks are
combined to form a polygonal
crucible within an induction
furnace.
Metal and slag are melted by
induction in the crucible.
• 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
5
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
Comparing
samples
after
Induction
furnace test
Dipping Test
Also: immersion or finger test
Cylindrical or square pillar
shaped samples are held in
the corrosive liquid in a
furnace. Immersion time,
temperature and atmosphere
can be varied.
• 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
Submerged Sample in Dipping Test
Rotary Slag Test
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.
• 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
Rotary Slag Test
Sample-segments
Insulating castable
Flue
gas
Steel drum
flame
Remaining thickness
Vertical cracks
Picture: Fundación ITMA (Materials Technological Institute), Spain
parallel cracks
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)
Amount of melt [wt.-%]
V. Reiter, PhD thesis,
MU Leoben, 2008
Refractory oxide/species [wt.-%]
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)