Materials Transactions, Vol. 50, No. 6 (2009) pp. 1448 to 1456
#2009 The Japan Institute of Metals
Effects of Basicity and FeO Content on the Softening
and Melting Temperatures of the CaO-SiO2 -MgO-Al2 O3 Slag System
Hsin-Chien Chuang1; *1 , Weng-Sing Hwang1; *2 and Shih-Hsien Liu2
1
Department of Materials Science and Engineering, National Cheng Kung University,
No. 1 Ta-Hsueh Road, Tainan 70101, Taiwan, R.O.China
2
Iron Making Process Development Section, Steel & Aluminum Research & Development Dept., China Steel Corporation,
No. 1 Chung Kang Road Hsiao Kang, Kaohsiung 81233, Taiwan, R.O.China
The effects of basicity (the ratio between CaO and SiO2 ) and FeO content on softening and melting temperatures of direct reduced iron
(DRI) residual, otherwise known as slag, were investigated.
Sample slag pellets were prepared for two target compositions, CaO-SiO2 -10%MgO-5%Al2 O3 and CaO-SiO2 -5%MgO-10%Al2 O3 . Two
sets of experiments were conducted on the pellets: one varied basicity values between 1.83 and 0.55, and the other varied the FeO contents
between 10% and 50% at constant basicity. The softening and melting process under elevated temperature was recorded using an optical
softening-melting temperature measuring device and the temperature points were recorded at the four distinct shape changes of the sample
pellets: initial deformation, sphere and hemisphere formation, and complete melting.
The lowest softening and melting temperatures of the CaO-SiO2 -5%MgO-10%Al2 O3 samples occurred at a basicity of 0.55 while for the
CaO-SiO2-10%MgO-5%Al2 O3 samples it occurred at 0.70. This corresponds to the liquidus temperatures on the CaO-SiO2 -MgO-Al2 O3
quaternary phase diagram. At constant basicity, the deformation temperature of CaO-SiO2 -10%MgO-5%Al2 O3 samples was found to be higher
than that of CaO-SiO2 -5%MgO-10%Al2 O3 samples. Lastly, the addition of FeO below 20% to the CaO-SiO2 -MgO-Al2 O3 system significantly
decreased the softening and melting temperatures of the slag samples. However, further addition of FeO beyond 20% produced inconclusive
results. [doi:10.2320/matertrans.MRA2008372]
(Received October 14, 2008; Accepted March 17, 2009; Published May 13, 2009)
Keywords: CaO-SiO2 -MgO-Al2 O3 , softening and melting temperatures, basicity, direct reduced iron
1.
Introduction
In integrated steel plants, dusts and sludges, commonly
called ‘‘residual materials’’, are inevitably generated during
steel production. The residual materials are composed
primarily of iron oxide and carbon, in addition to metallurgical slags, alkali oxides, and impurities such as chlorine,
phosphorus, and sulfur. The high iron oxide and carbon
content allows the residual materials to be converted into
direct reduced iron (DRI) by carbothermic reduction. The
reduction of iron oxide by carbon is performed with the
material agglomerated in the form of pellets. The advantage
of the agglomerate is a high reaction rate, due to a large
contact area between the reactants. In normal operation,
complete reduction is achieved in 10 to 20 min at temperatures between 1150 and 1250 C.
DRI can be charged into the blast furnace to produce
hot metal and to decrease fuel consumption. Mechanical
strength of DRI is essential to enable handling during
storage, transportation, and charging without crushing the
material.1) Meyer2) identified that the strength of a DRI pellet
depends upon bonds between metallic and slag phases.
Gupta3) found that adding slag-forming constituents such as
bentonite can offer more strength to DRI. Takano4) stated that
higher content of a binder, like Portland cement, could be
used to maintain the compressive strength of pellets after
heating.
The composition of slag affects the softening and melting
temperatures. When the deformation temperature of slag is
*1Graduate
Student, National Cheng Kung University
author, E-mail: [email protected]
*2Corresponding
low, the compressive strength of DRI is increased due to slag
bonding. Due to its complex composition, DRI does not
exhibit a discrete melting point, but rather softens and melts
gradually over a wide temperature range. Phase diagrams
only provide the liquidus temperature for specific slag
compositions. Dashed lines on phase diagrams are merely
predictive values.5) Moreover, relatively little research has
been conducted to investigate the softening and melting
temperatures of slag in the carbothermic process.
DRI pellets produced by the carbothermic process are
composed of four main oxides: CaO, SiO2 , MgO, and Al2 O3 .
In industry, MgO and Al2 O3 typically account for approximately 15% of the material by mass. This will be reproduced
in the experiment by using two combinations; one with
10 mass% of MgO and 5 mass% of Al2 O3 , the other with
5 mass% of MgO and 10 mass% of Al2 O3 . Moreover, since
FeO is one of the main components in the residual materials
the effects of varying its composition will be examined.
This study investigates the effects of basicity and FeO
content on the softening and melting temperatures of CaOSiO2 -MgO-Al2 O3 slag. This is the primary slag system used
for the production of DRI from the residual material of steel
plants. Two variations on this slag system are analyzed,
using the compositions of MgO and Al2 O3 described above.
The softening and melting temperatures of interest are the
deformation, spherical, semi-spherical, and flow temperatures.
2.
Experimental Method
Slag pellets with basicity (B2 = CaO (mass%)/SiO2
(mass%)) ranging from 0.55 to 1.83 were prepared using a
Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO2 -MgO-Al2 O3 Slag System
Table 1 Compositions of the quaternary slag CaO-SiO2 -MgO-Al2 O3
system.
1449
Table 2 Compositions of the quinary slag CaO-SiO2 -MgO-Al2 O3 -FeO
system.
No.
CaO
(mass%)
SiO2
(mass%)
MgO
(mass%)
Al2 O3
(mass%)
B2
No.
CaO
(mass%)
SiO2
(mass%)
MgO
(mass%)
Al2 O3
(mass%)
FeO
(mass%)
B2
1
55
30
10
5
1.83
2
50
35
10
5
1.43
3
45
40
10
5
1.13
4
40
45
10
5
0.89
5
35
50
10
5
0.70
1-1
2-1
3-1
4-1
5-1
6-1
49.5
45.0
40.5
36.0
31.5
27.0
27.0
31.5
36.0
40.5
45.0
49.5
9.0
9.0
9.0
9.0
9.0
9.0
4.5
4.5
4.5
4.5
4.5
4.5
10
10
10
10
10
10
1.83
1.43
1.13
0.89
0.70
0.55
6
30
55
10
5
0.55
7
55
30
5
10
1.83
8
50
35
5
10
1.43
9
45
40
5
10
1.13
10
40
45
5
10
0.89
11
12
35
30
50
55
5
5
10
10
0.70
0.55
7-1
8-1
9-1
10-1
11-1
12-1
49.5
45.0
40.5
36.0
31.5
27.0
27.0
31.5
36.0
40.5
45.0
49.5
4.5
4.5
4.5
4.5
4.5
4.5
9.0
9.0
9.0
9.0
9.0
9.0
10
10
10
10
10
10
1.83
1.43
1.13
0.89
0.70
0.55
1-2
2-2
3-2
4-2
5-2
6-2
44.0
40.0
36.0
32.0
28.0
24.0
24.0
28.0
32.0
36.0
40.0
44.0
8.0
8.0
8.0
8.0
8.0
8.0
4.0
4.0
4.0
4.0
4.0
4.0
20
20
20
20
20
20
1.83
1.43
1.13
0.89
0.70
0.55
7-2
8-2
9-2
10-2
11-2
12-2
44.0
40.0
36.0
32.0
28.0
24.0
24.0
28.0
32.0
36.0
40.0
44.0
4.0
4.0
4.0
4.0
4.0
4.0
8.0
8.0
8.0
8.0
8.0
8.0
20
20
20
20
20
20
1.83
1.43
1.13
0.89
0.70
0.55
1-3
2-3
3-3
4-3
5-3
6-3
38.5
35.0
31.5
28.0
24.5
21.0
21.0
24.5
28.0
31.5
35.0
38.5
7.0
7.0
7.0
7.0
7.0
7.0
3.5
3.5
3.5
3.5
3.5
3.5
30
30
30
30
30
30
1.83
1.43
1.13
0.89
0.70
0.55
7-3
8-3
9-3
10-3
11-3
12-3
38.5
35.0
31.5
28.0
24.5
21.0
21.0
24.5
28.0
31.5
35.0
38.5
3.5
3.5
3.5
3.5
3.5
3.5
7.0
7.0
7.0
7.0
7.0
7.0
30
30
30
30
30
30
1.83
1.43
1.13
0.89
0.70
0.55
1-4
2-4
3-4
4-4
5-4
6-4
33.0
30.0
27.0
24.0
21.0
18.0
18.0
21.0
24.0
27.0
30.0
33.0
6.0
6.0
6.0
6.0
6.0
6.0
3.0
3.0
3.0
3.0
3.0
3.0
40
40
40
40
40
40
1.83
1.43
1.13
0.89
0.70
0.55
7-4
8-4
9-4
10-4
11-4
12-4
33.0
30.0
27.0
24.0
21.0
18.0
18.0
21.0
24.0
27.0
30.0
33.0
3.0
3.0
3.0
3.0
3.0
3.0
6.0
6.0
6.0
6.0
6.0
6.0
40
40
40
40
40
40
1.83
1.43
1.13
0.89
0.70
0.55
1-5
2-5
3-5
4-5
5-5
6-5
27.5
25.0
22.5
20.0
17.5
15.0
15.0
17.5
20.0
22.5
25.0
27.5
5.0
5.0
5.0
5.0
5.0
5.0
2.5
2.5
2.5
2.5
2.5
2.5
50
50
50
50
50
50
1.83
1.43
1.13
0.89
0.70
0.55
7-5
8-5
9-5
10-5
11-5
12-5
27.5
25.0
22.5
20.0
17.5
15.0
15.0
17.5
20.0
22.5
25.0
27.5
2.5
2.5
2.5
2.5
2.5
2.5
5.0
5.0
5.0
5.0
5.0
5.0
50
50
50
50
50
50
1.83
1.43
1.13
0.89
0.70
0.55
mixture of high purity reagent grade CaO, SiO2 , MgO,
and Al2 O3 powder to achieve the compositions shown in
Table 1. For each of the CaO-SiO2 -10%MgO-5%Al2 O3 and
CaO-SiO2 -5%MgO-10%Al2 O3 slag systems, six compositions were investigated. Each of these twelve powder
mixtures was placed in a graphite crucible and pre-melted
at 1450 C for one hour. After cooling to room temperature,
the synthetic slag was ground and sized for subsequent
investigation.
FeO was added to each slag mixture in amounts ranging
between 10 and 50 mass%, while the four basic oxides were
maintained in the ratios described above. This produces sixty
different compositions for investigation, as shown in Table 2.
FeO was obtained from reagent grade Fe2 O3 powder with a
purity of 95% or higher and poured into a low carbon steel
crucible. It was heated gradually and held at 1200 C for 24 h
under a 1 : 1 CO and CO2 atmosphere. The crucible and FeO
sample were then quenched in a water bath under high argon
atmosphere to prevent oxidation of the FeO sample due to
contact with air. The FeO was then pulverized in an agate
mortar filled with alcohol.
Both the quaternary (CaO-SiO2 -MgO-Al2 O3 ) and the
quinary (CaO-SiO2 -MgO-Al2 O3 -FeO) slag were mixed uniformly with light starch water and then pressed into
cylindrical pellets (5 mm diameter 5 mm height). These
pellets were made using a steel die, punched with a constant
impact, and then left to dry at room temperature. An optical
softening and melting temperature measuring device, as
shown in Fig. 1, was employed in this study. The apparatus
consists of three principal units mounted on an optical bench:
a light source to illuminate the specimen, an electric furnace
with an alumina tube for heating the specimen and introducing various gases, and a video camera unit for recording the
shape change of the specimen. The specimen was placed on a
ceramic plate and placed in the middle of the alumina tube.
The tip of a B-type thermocouple was placed close to the
specimen to measure the in-situ temperature. The specimen
temperature was controlled by a programmable temperature
control unit. The heating rate was set at 20 C/min. for
heating from room temperature to 1000 C, and subsequently
decreased to 5 C/min. to continue heating until 1600 C was
1450
H.-C. Chuang, W.-S. Hwang and S.-H. Liu
high purity
alumina tube
1600
gas outlet
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
gas inlet
Temperature
controller
electric furnace
1550
Temperature (°C)
video system
sample and ceramic plate
thermocouple
stainless steel
flange with water
cooling jacket
light
source
power
1500
1450
1400
1350
1300
Fig. 1 A schematic diagram of the optical softening-melting temperature
measuring device employed in this study.
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
B2
Fig. 3 Relationship between B2 and softening and melting temperatures
for the CaO-SiO2 -10%MgO-5%Al2 O3 slag system.
3.
3.1
(a)
(b)
(c)
(d)
Fig. 2 A typical series of photographs showing the evolution of a slag
pellet during heating, which corresponds to (a) deformation temperature,
(b) spherical temperature, (c) semi-spherical temperature, and (d) flow
temperature.
achieved. The atmosphere around the specimen was controlled by a flow of argon of one normal liter per minute.
In addition, each slag system is repeatedly tested to ensure
accuracy.
In this investigation, the shape change of the slag pellet as
it is heated is used as an indicator for assessing the physical
changes occurring in the material (softening and melting).
The different stages of the process were recorded photographically or by means of a video camera. Figure 2 shows
a typical series of photographs that illustrate the stages of
shape change, defined in accordance with German standard
DIN 51730.6) These stages correspond to the deformation,
spherical, semi-spherical, and flow temperatures of the
sample. At the deformation temperature the sample shows
the first signs of softening; the rounding of the edges is
complete and the sample starts to fill out the gas volume
between the particles. The spherical and semi-spherical
temperatures correspond to the stages where the cylinder
acquires approximate spherical and semi-spherical forms
respectively. At the flow temperature, the solid sample has
been melted to the liquid state.
Results and Discussion
Effects of basicity on the softening and melting
temperatures of the quaternary slag CaO-SiO2 MgO-Al2 O3 system
Figure 3 shows the relationship between B2 and softening
and melting temperatures in the quaternary slag CaO-SiO2 10%MgO-5%Al2 O3 system. It shows that in the CaO-SiO2 10%MgO-5%Al2 O3 slag system the trends exhibited by the
deformation, spherical, semi-spherical, and flow temperatures with changing B2 are similar. The deformation,
spherical, semi-spherical, and flow temperatures decrease
substantially as B2 of the quaternary slag is reduced from
1.83 to 0.70. Minimum deformation, spherical, semi-spherical, and flow temperatures are recorded when B2 is 0.70.
However, when B2 keeps decreasing to 0.55, the softening
and melting temperatures inversely rise. Figure 4 is the phase
diagram of the CaO-SiO2 -MgO with 5% Al2 O3 slag system.7)
When MgO content is fixed at 10%, the liquidus temperature
of the slag gets lower as B2 is reduced from 1.83 to 0.70. This
trend corresponded closely with the softening and melting
temperatures in Fig. 3. In addition, the liquidus temperatures
when B2 values are 0.70 and 0.55 cannot be clearly
differentiated in the phase diagram.
The relationship of B2 and softening and melting temperatures in the quaternary slag CaO-SiO2 -5%MgO-10%Al2 O3
system is shown in Fig. 5. It shows that in the CaO-SiO2 5%MgO-10%Al2 O3 slag system the trends exhibited by the
deformation, spherical, semi-spherical, and flow temperatures with changing B2 are also similar. The deformation,
spherical, semi-spherical, and flow temperatures decrease
substantially as B2 of the quaternary slag is reduced from
1.83 to 0.55. Minimum deformation, spherical, semi-spherical, and flow temperatures are recorded when B2 is 0.55.
Figure 6 is the phase diagram of the CaO-SiO2 -MgO with
10% Al2 O3 slag system.7) When MgO content is fixed at 5%,
the liquidus temperatures of the slag gets lower as B2 is
reduced from 1.83 to 0.55. When B2 is 0.55, the liquidus
temperature has the lowest value. This trend corresponds
very well with the softening and melting temperatures in
Fig. 5.
Figure 7 shows the relationship between B2 and deformation temperature for the CaO-SiO2 -10%MgO-5%Al2 O3 and
1451
Ma
ss
Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO2 -MgO-Al2 O3 Slag System
Ma
ss
B2 = 0.55
B2 = 0.70
B2 = 0.89
B2 = 1.13
B2 = 1.43
B2 = 1.83
Mass
Fig. 4 Phase diagram of CaO-SiO2 -MgO with 5% Al2 O3 .7)
1500
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
Temperature (°C)
1450
1400
1350
1300
1250
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
B2
Fig. 5 Relationship between B2 and softening and melting temperatures
for the CaO-SiO2 -5%MgO-10%Al2 O3 slag system.
CaO-SiO2 -5%MgO-10%Al2 O3 slag systems. The deformation temperature of the CaO-SiO2 -10%MgO-5%Al2 O3 slag
system can be seen to be consistently higher than that of the
CaO-SiO2 -5%MgO-10%Al2 O3 system. For the quaternary
slag CaO-SiO2 -10%MgO-5%Al2 O3 system the deformation
temperature substantially decreases as B2 decreases, reaching
a minimum of 1303 C when B2 is 0.70. Likewise, the
deformation temperature of the quaternary slag CaO-SiO2 5%MgO-10%Al2 O3 system substantially decreases as B2
decreases, reaching a minimum of 1255 C when B2 is 0.55.
3.2
Effects of FeO on the softening and melting temperatures of the quaternary slag CaO-SiO2 -MgO-Al2 O3
system
Figure 8 shows the relationship between FeO content and
softening and melting temperatures in CaO-SiO2 -10%MgO5%Al2 O3 slag system when B2 is equal to 1.83. From this it
can be seen that increasing the FeO content of the quaternary
slag CaO-SiO2 -10%MgO-5%Al2 O3 system causes a de-
crease in the deformation, spherical, semi-spherical, and flow
temperatures of the slag. The initial addition of 10 mass%
FeO is found to lower the softening and melting temperatures
of the slag most drastically. The softening and melting
temperatures of the slag continue to decrease as the addition
of FeO is increased to 50 mass%. Figures 9 through 13 show
the relationship between FeO content and softening and
melting temperatures in the CaO-SiO2 -10%MgO-5%Al2 O3
slag system for B2 equal to 1.43, 1.13, 0.89, 0.70, and 0.55,
respectively. Again, the addition of the first 10 mass% of FeO
most drastically lowers the softening and melting temperatures of the slag. The softening and melting temperatures
continue to decrease as the FeO content is increased to
50 mass%, with the exception in some cases of a slight
increase in these values at high FeO.
The effect of FeO content on the deformation temperature
of the CaO-SiO2 -10%MgO-5%Al2 O3 slag system for different values of B2 is shown in Fig. 14. From the figure, it can be
seen that the deformation temperature has no clear relations
with B2 for any given FeO content ranging from 0 to 50%.
However, the deformation temperature is seen to decrease
as FeO content increases for all the B2 values ranging from
0.55 to 1.83 except for the B2 value of 0.89. It can be clearly
seen that the addition of 20 mass% of FeO to CaO-SiO2 10%MgO-5%Al2 O3 slag system with a B2 value of 0.89
yields the minimal deformation temperature, of approximately 1175 C. This peculiar phenomenon for the B2 value
of 0.89 deserves some attention and a possible explanation is
proposed as the following.
As described in Section 2, the samples of the CaO-SiO2 10%MgO-5%Al2 O3 slag system were pre-melted at 1450 C
for one hour, then cooled and ground into powder. The free
oxides in the samples have in fact formed minerals after the
pre-melting treatment. Generally, the softening and melting
behaviors of the minerals are very complicated. According to
Fig. 4, the formed minerals are shown in Table 3 and their
H.-C. Chuang, W.-S. Hwang and S.-H. Liu
Ma
ss
1452
B 2 = 0.55
B2 = 0.70
Ma
ss
B 2 = 0.89
B2 = 1.13
B2 = 1.43
B 2 = 1.83
Mass
Fig. 6 Phase diagram of CaO-SiO2 -MgO with 10% Al2 O3 .7)
1500
CaO-SiO2-10 % MgO-5 % Al2O3
1500
1480
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1460
1450
1440
1420
Temperature (°C)
Deformation Temperature (°C)
CaO-SiO2-5 % MgO-10 % Al2O3
1400
1350
1400
1380
1360
1340
1320
1300
1300
1280
1250
1260
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0
10
B2
20
30
40
50
B2 = 1.43 FeO content (mass%)
Fig. 7 Relationship between B2 and deformation temperature for the CaOSiO2 -10%MgO-5%Al2 O3 and CaO-SiO2 -5%MgO-10%Al2 O3 slag systems.
Fig. 9 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 1.43.
1600
1550
1500
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1440
1420
Temperature (°C)
Temperature (°C)
1460
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1450
1400
1400
1380
1360
1340
1320
1300
1350
1280
1300
1260
1240
0
10
20
30
40
50
B2 = 1.83 FeO content (mass%)
Fig. 8 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 1.83.
0
10
20
30
40
50
B2 = 1.13 FeO content (mass%)
Fig. 10 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 1.13.
Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO2 -MgO-Al2 O3 Slag System
1400
1340
B2=1.83
B2=1.43
1450
Deformation Temperature (°C)
1360
Temperature (°C)
1500
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1380
1320
1300
1280
1260
1240
1220
1200
1180
1453
B2=1.13
B2=0.89
1400
B2=0.70
B2=0.55
1350
1300
1250
1200
1160
0
10
20
30
40
50
1150
0
10
B2 = 0.89 FeO content (mass%)
Fig. 11 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 0.89.
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1340
40
50
Fig. 14 Effects of FeO content on the deformation temperature for CaOSiO2 -10%MgO-5%Al2 O3 slag system.
CaO-SiO2 -10%MgO-5%Al2 O3
B2 Primary phase
1320
Temperature (°C)
30
Table 3 Primary phase of CaO-SiO2 -MgO-Al2 O3 after pre-melting in this
study.
1380
1360
20
FeO content (mass%)
CaO-SiO2 -5%MgO-10%Al2 O3
B2 Primary phase
1300
0.55 pyroxene
0.55 wollastonite
1280
0.70 wollastonite
0.70 pseudowollastonite
1260
0.89 melilite
0.89 pseudowollastonite
1240
1.13 merwinite
1.13 melilite
1220
1.43 2CaOSiO2
1.43 2CaOSiO2
1200
1.83 2CaOSiO2
1.83 2CaOSiO2
1180
0
10
20
30
40
50
B2 = 0.70 FeO content (mass%)
Table 4
Fig. 12 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 0.70.
Mineral
pyroxene
wollastonite
1400
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1380
1360
Temperature (°C)
1340
1320
melilite
Formula of the various minerals.
Formula
MgOSiO2 (clinoenstatite)
CaOMgO2SiO2 (diopside)
-CaOMgOSiO2
2CaOMgO2SiO2 (akermanite)
2CaOAl2 O3 SiO2 (gehlenite)
merwinite
3CaOMgO2SiO2
pseudowollastonite
-CaOSiO2
1300
1280
1260
1240
1220
1200
1180
1160
0
10
20
30
40
50
B2 = 0.55 FeO content (mass%)
Fig. 13 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -10%MgO-5%Al2 O3 slag system as B2 equals
to 0.55.
formulas are listed in Table 4. The information for the phase
diagram of CaO-SiO2 -MgO-Al2 O3 -FeO is absent so the
limited reference is utilized to explain the phenomenon.
Firstly eliminating FeO effect, the primary mineral phases
such as pyroxene (CaOMgO2SiO2 ), wollastonite (CaOSiO2 ), and melilite have liquidus temperatures lower
than 1400 C as can be seen in Fig. 4. Melilite8,9) is a solid
solution of akermanite (2CaOMgO2SiO2 ) and gehlenite
(2CaOAl2 O3 SiO2 ). In this case, the content percentage of
akermanite is higher than that of gehlenite because
MgO content is higher than Al2 O3 . Subsequently, the
effect of FeO is taken into consideration. Figure 15 shows
the phase diagram of CaO-SiO2 -FeO system.10) It shows
that the addition of FeO lowers the liquidus temperature for all the B2 values ranging from 1.83 to 0.55.
Adding 10 mass% FeO significantly reduces the liquidus
temperature of CaO-SiO2 -FeO. Further increasing the FeO
content to 40 mass%, the liquidus temperature is reduced
even further. Because pyroxene (CaOMgO2SiO2 ) and
melilite (2CaOMgO2SiO2 ) both consist of MgO. Also, the
mass percentage of MgO is higher than that of Al2 O3 in FeOCaO-SiO2 -10%MgO-5%Al2 O3 system. Thus, the quaternary
system CaO-SiO2 -MgO-FeO is considered as can be seen in
ss
Ma
B2 = 0.55
ss
H.-C. Chuang, W.-S. Hwang and S.-H. Liu
Ma
1454
B2 = 0.70
B2 = 0.89
B2 = 1.13
B2 = 1.43
B2 = 1.83
Mass
Fig. 15 Phase Diagram of CaO-SiO2 -FeOn with various FeO contents and B2 values depicted on the diagram.10)
Fig. 16 Diagram representing the CaO–SiO2 –FeO–MgO system. W =
wollastonite, pseudowollastonite (CaOSiO2 ); Mo = monticellite
(CaOMgOSiO2 ); Fe-Mo = iron-monticellite (CaOFeOSiO2 ); Ak =
akermanite (2CaOMgO2SiO2 ); Fe-Ak = iron-akermanite (2CaOFeO
2SiO2 ).11)
Fig. 16.11) Figure 17 shows an enlargement of the portion
CaOSiO2 –CaOMgOSiO2 –FeO within the CaO-SiO2 MgO-FeO system.11) The liquidus temperature of mineral
phase declines with the increase of FeO between 0 and 50%.
As for the melilite, its minimum liquidus temperature is
1255 C as FeO content is around 24%. Furthermore, the
phase area of pseudowollastonite (-CaOSiO2 ) and olivine
trend to low FeO side due to MgO addition. Reconsidering
the phase diagram of CaO-SiO2 -FeO in Fig. 15, it is
suspected that the primary phase area of Wollastonite also
Fig. 17 Phase diagram of CaOSiO2 –CaOMgOSiO2 –FeO.11)
tends to low FeO side and that of Rankinite tends to high
SiO2 side. Due to the above resultant effects, the minimum
temperature of slag, which is the eutectic point at the
intersection of Wollastonite and Rankinite, appears at a
composition around 20% FeO content.
Figure 17 shows the relationship between FeO content and
softening and melting temperatures in CaO-SiO2 -5%MgO10%Al2 O3 slag system when B2 is equal to 1.83. The initial
addition of 10 mass% FeO is found to drastically lower the
softening and melting temperatures of the slag. The softening
and melting temperatures of the slag continue to decrease as
the addition of FeO is increased to 50 mass%. Figures 18
Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO2 -MgO-Al2 O3 Slag System
1520
1340
1500
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1480
1460
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1320
1300
Temperature (°C)
1440
Temperature (°C)
1455
1420
1400
1380
1360
1340
1280
1260
1240
1220
1320
1300
1200
1280
1180
1260
1240
1160
0
10
20
30
40
50
0
10
B2 = 1.83 FeO content (mass%)
Fig. 18 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 1.83.
30
40
50
Fig. 21 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 0.89.
1340
1420
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1400
1380
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1320
1300
1280
1360
Temperature (°C)
Temperature (°C)
20
B2 = 0.89 FeO content (mass%)
1340
1320
1300
1260
1240
1220
1200
1180
1280
1160
1260
1140
1240
1120
0
10
20
30
40
0
50
Fig. 19 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 1.43.
1380
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1360
Temperature (°C)
1340
1320
1300
1280
1260
1240
1220
1200
0
10
20
30
40
10
20
30
40
50
B2 = 0.70 FeO content (mass%)
B2 = 1.43 FeO content (mass%)
Fig. 22 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 0.70.
melting temperatures of the slag. The softening and melting
temperatures continue to decrease as the FeO content is
increased to 50 mass%, with the exception in some cases of
a slight increase in these values at high FeO. The trend
exhibited in the softening and melting temperatures of the
slag is not consistent for B2 lower than 0.89, as shown in
Figs. 20–22. The effect of FeO content on the deformation
temperature of the CaO-SiO2 -5%MgO-10%Al2 O3 slag system for different values of B2 is shown in Fig. 23. It shows
that as B2 decreases, the deformation temperature of the
CaO-SiO2 -5%MgO-10%Al2 O3 -FeO slag system decreases.
50
B2 = 1.13 FeO content (mass%)
Fig. 20 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 1.13.
through 22 show the relationship between FeO content and
softening and melting temperatures in the CaO-SiO2 5%MgO-10%Al2 O3 slag system for B2 equal to 1.43, 1.13,
0.89, 0.70, and 0.55, respectively. The addition of the first
10 mass% of FeO most drastically lowers the softening and
4.
Conclusions
The effect of B2 and FeO content on softening and melting
temperatures of CaO-SiO2 -10%MgO-5%Al2 O3 and CaOSiO2 -5%MgO-10%Al2 O3 slag systems were investigated in
this study. The following conclusions can be drawn:
(1) The softening and melting temperatures of CaO-SiO2 5%MgO-10%Al2 O3 slag system were found to reach a
minimum when B2 was 0.55. However, for the CaOSiO2 -10%MgO-5%Al2 O3 slag system the minimum
occurred when B2 was 0.70.
1456
H.-C. Chuang, W.-S. Hwang and S.-H. Liu
1340
Flow Temp.
Semi-spherical Temp.
Spherical Temp.
Deformation Temp.
1320
1300
Temperature (°C)
1280
1260
1240
1220
1200
1180
1160
1140
1120
1100
1080
0
10
20
30
40
50
B2 = 0.55 FeO content (mass%)
Fig. 23 Relationship between FeO content and softening and melting
temperatures for CaO-SiO2 -5%MgO-10%Al2 O3 slag system as B2 equals
to 0.55.
for a given value of B2 .
(3) The trends in the softening and melting temperatures of
the slag systems closely correspond to the changes in
liquidus temperature predicted by the phase diagrams of
the quaternary slag CaO-SiO2 -MgO-5%Al2 O3 and
CaO-SiO2 -MgO-10%Al2 O3 systems.
(4) The addition of FeO up to 20 mass% to the CaO-SiO2 MgO-Al2 O3 system significantly decreases the softening and melting temperatures of the slag system.
However, further addition of FeO does not produce
consistent results.
(5) The CaO-SiO2 -10%MgO-5%Al2 O3 slag system with a
B2 value of 0.89 and the addition of 20 mass% of FeO
produced the minimum deformation temperature of
approximately 1175 C.
Acknowledgements
1450
B2=1.83
Deformation Temperature (°C)
1400
B2=1.43
B2=1.13
1350
The authors are grateful to the supports of China Steel
Corporation for this study. The assistance from Mr. ChingHo Chen is also greatly appreciated.
B2=0.89
B2=0.70
B2=0.55
1300
1250
1200
1150
1100
0
10
20
30
40
50
FeO content (mass%)
Fig. 24 Effects of FeO content on the deformation temperature for CaOSiO2 -5%MgO-10%Al2 O3 slag system.
(2) The deformation temperature of the CaO-SiO2 10%MgO-5%Al2 O3 system was found to be higher
than that of the CaO-SiO2 -5%MgO-10%Al2 O3 system
REFERENCES
1) B. Anameric and S. K. Kawatra: Miner. Process. Extr. Metall. Rev. 28
(2007) 59–116.
2) K. Meyer: Pelletizing of Iron Ores, (Springer-Verlag, Berlin, 1980)
p. 292.
3) R. C. Gupta and J. P. Gautam: ISIJ Int. 43 (2003) 1913–1918.
4) C. Takano and M. B. Mourao: ISIJ Int. 41 (2001) S22–S26.
5) F. Dahl, J. Brandberg and D. Sichen: ISIJ Int. 46 (2006) 614–616.
6) A. R. Boccaccini and B. Hamann: J. Mater. Sci. 34 (1999) 5419–5436.
7) V. D. Eisenhüttenleute: Slag Atlas, (Verlag Stahleisen GmbH,
Düsseldorf, 1981) p. 81.
8) E. F. Osborn, R. C. DeVries, K. H. Gee and H. M. Kraner: J. Met. 6
(1954) 33–45.
9) A. R. Lee: Blastfurnace and Steel Slag, (John Wiley & Sons, New
York, 1974) p. 26.
10) V. D. Eisenhüttenleute: Slag Atlas, (Verlag Stahleisen GmbH,
Düsseldorf, 1981) p. 68.
11) J. F. Schairer and E. F. Osborn: J. Am. Ceram. Soc. 33 (1950) 160–
167.