MET 130 Slag_Fundamentals_2011_March

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FUNDAMENTALS OF SLAG
Paulo Santos Assis
[Full Prof. by UFOP and Prof by REDEMAT
Honorary Prof. by Hebei University, China]
Colaborators
Álvaro Martins Júnior, M.Sc.
Adriano Ferreira da Cunha, M.Sc.
M.Sc and Dr. Student of Prof. Assis
INTRODUCTION
Inorganic;
Non-metallic;
Crystalline and amorphous regions;
Generated or incorporated in metallurgical processes.
SLAG
Figure 1 - Photo of slags being flowed out from two ladles.
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TOP SLAG/SYNTHETIC SLAG
Steel refining
Thermal protection
Capture of inclusions
Ladle protection.
MANUFACTURE
Fusion
Pelletizing
Sintering
Mixture of raw materials
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PROPERTIES
1) Optical basicity
2) Desulfurization
3) Dephosphorization
4) Viscosity
5) Thermal conductivity
6) Electrical conductivity
7) Surface tension
8) Interface tension
9) Liquidus temperature
10) Density
Figure 2 - Slag formation during oxygen injection.
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OPTICAL BASICITY (N) 
 2
1
k
k
N



 Concept of basicity refers to the relation between basic and acid oxides;
 This information enables to predict about viscosity of slags;
 In microstructure aspects, basic oxides have elements which are
breaking agents of nets;
 Optical basicity concept is quite actual and was initially developed
for vitreous materials;
 It basically measures how much is the oxygen linked (O, O-, O-2);
The formula showed below represents the value of N
[where k1 = 10,74 and k2 = 0,26]
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Figure 3 - Variation of optical basicity from different oxides.
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DESOXIDATION
 Depends on oxygen potential;
 Depends on basicity of slags which normally is between 2 to 3,5;
 Presence of lime helps to take out the phosphorous oxidised (P2O5);
 Oxygen rate in the bath has such a relevance because this parameter
is related to inclusions index of steel.
Figure 4 - Relationship between the inclusions index and the total oxygen in the bath.
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DESULFURIZATION
 Capacity of absorbing sulphur (S) from the bath;
1/2 S2 (g) + O
-2 1/2 O2 (g) + S
-2
Figure 5 - Ternary diagram showing the dependence of 
desulfurization rate with CaO content.
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Figure 6 - Variation of desulfurization capacity according to the 
amount and sort of oxide mixed with CaO. 
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DEPHOSPHORATION
Capacity of absorbing phosphorous (P) from hot metals.
P2 (g) + 5/2 O2 (g) + 3 O
-2 2 PO4
-3
A good basicity is also required (CaO);
 But, opposite to desulfurization process, the oxygen rate must be higher
and the lowest possible temperature;
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Figure 7 - Relationship between the desphosphoration rate and FeO content 
for several percentages of CaO.
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VISCOSITY
 Defined as the shearing strength;
 Influences in the kinetic of reactions
slag/metal;
Main parameters that affect slag
viscosity are:
1) Temperature
2) Composition.
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Figure 8 - Viscosity versus temperature for a slag 
(50% CaO, 7% MgO, 30 % Al2O3, 13 % SiO2).
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Figure 9 - Variation of viscosity according to CaO and MgO content.
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THERMAL 
CONDUCTIVITY
 Capability of keeping heat;
 Some works show that thermal conductivity presents a little increase
as the temperature increases until 1100K;
 On the other hand, above this temperature, the thermal conductivity
decreases according to its enhancement.
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Figure 10 - Conductivity versus temperature for two different slags.
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ELECTRICAL 
CONDUCTIVITY
 Measures the ability of conducting when a
material is submitted to a electric field;
 In some mills carried out with glasses show
that electric conductivity increases according 
to enhancement of temperature;
 This event can be associated to improvement
of mobility of ions presented in slags.
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Figure 11 - Electrical conductivity versus temperature for a synthetic slag.
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SURFACE TENSION
 Free energy per area unit;
 Necessary work to alter the surface area in 1 cm2;
 Refers to the wettability degree of slag in the bath;
 High surface tension implies on low degree of 
wettability (slag does not mix to the bath);
 Low surface tension enables a higher rate of mass
transfer (to take the impurities out from the hot
metal)
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Figure 9 - Surface tension versus MgO content for the system 
(Al2O3 - CaO - MgO - SiO2).
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DENSITY
 Parameter which varies according to the
composition and temperature;
 It allows to make adjustments on the amount of
slag to be employed;
 Small quantity of slag can let the refractory
exposed to the electric arc (occurring a bigger wear
of it);
 Big amount of slag demands more operational
costs (like more energy consumption and additional
work to take the slag out).
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MANUFACTURE 
PROCESSES
R
e
l
a
t
i
v
 
c
o
s
t
Mixture Sinter Briquetted Pellet Fused
Figure 12 - Graph of the related cost for several manufacture 
processes of synthetic slags.
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INDUCTION FURNACE
Example: Producing a SS
 Electric furnace which shows some
advantages comparing it with other electric
equipments:
4) High heating rate (1300oC in 20 minutes).
3) Metal has an uniform composition due to 
electromechanical mix;
2) Metal is not carbonized;
1) Lost by oxidising of metal is lower;
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Figure 13 - a) Scheme of working 
of a simplified induction furnace; 
b) Photo of a bobbin (spark coil).
A)
a)
b)
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SYNTHETIC SLAG 
MANUFACTURE
Objectives:
 Estimate production cost
 Characterization of the manufactured material;
 Manufacture synthetic slag through fusion process;
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METHODOLOGY
Furnace wall
Pieces of graphite
Slag level
Tube of Al for Ar injection
2 a 3 cm
Figure 14 - Scheme of the crucible used in the fusions.
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Slag Groups Athmosfer used Sample number 
PF1 - Natural 1 
PF2 - Natural 1 
PF1 1 Air 5 
PF1 2 Argon 5 
PF2 3 Ar 5 
PF2 4 Argon 5 
 
Table 1 - Division of samples according to the chemical composition 
and atmosphere employed.
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RESULTS
 
Slag SiO2 Al2O3 Fe2O3 CaO MgO CaF2 PPC Others 
PF1 3,0 36,1 0,26 27,5 1,0 27,1 3,19 1,67 
PF2 5,0 21,5 0,38 16,7 1,0 50,3 4,53 0,59 
 
 
Slag Arithmetic Media Standard Deviation Tmédia ± 2σ 
Group 1 1356 21 1314 – 1398 
Group 2 1373 27 1319 – 1427 
Group 3 1296 22 1252 – 1340 
Group 4 1249 23 1203 – 1295 
 
Table 2 - Chemical composition from synthetic slag 
manufactured.
Table 3 - Range of fusion temperatures for the slags manufactured
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CONCLUSIONS
 The range of fusion temperature for slags PF1
was higher than slags PF2;
 The energy consumption was lower for
slags PF2;
 The atmosphere employed had not influence in
the fusion temperature and the chemical
composition of slags;
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 There was no important changes in the 
chemical composition of slag's before 
and after the melting process
 The estimated cost for production was: 
PF1 (US$ 634) and PF2 (US$ 556).
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ACKNOWLEDGMENTS
FAPEMIG, CAPES and CNPq for helping the 
researches conducted by Prof. Assis
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You are all invited to come to one 
of the best University in Brazil and 
to do one of Engineering Course 
given by this University
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Muito obrigado
Thank you
Merci Bien
Gracias
Grato
Shieshie
Namaste
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Chapters 4 and 11.
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Janvier, 2001. N. 3. p. 41-53.
[13] DA SILVA, I. A; DA SILVA, C. A; CANDIDO, L. C. Fisico-Química Metalúrgica. V. 1. Apostila no 55. Departamento de
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