Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 863-868
Published Online September 2012 (
Characterization of Sintered Ceramic Tiles Produced
from Steel Slag
Benneth C. Chukwudi1*, Patrick O. Ademusuru1, Boniface A. Okorie2
1Department of Mechanical Engineering, Imo State University, Owerri, Nigeria
2Department of Materials and Metallurgical Engineering, Enu gu State University of Science and Technology, Enugu, Nigeria
Email: *
Received March 15, 2012; revised April 21, 2012; accepted May 7, 2012
Ceramic tiles were processed in this present work using clay mineral and steel slag. Steel slag in the range of 0 - 100
wt% was added to kaolinite clay. The blended samples were hydraulic pressed into rectangular moulds, oven dried and
sintered to 1200˚C. Linear shrinkage, apparent porosity, water absorption, bulk density, and modulus of rupture of sin-
tered specimens were examined. Phases present in the sintered products were identified using X-ray Diffractometer
(XRD), while the microstructural examination was conducted using Scanning Electron Microscopy (SEM). The ele-
ments present in the sintered products were identified using Energy Dispersive X-ray (EDX). Phases like quartz, wol-
lastonite, anorthite and enstatite were identified in the sintered products. The SEM revealed crystals embedded in the
glassy matrix. EDX studies detected Aluminum (Al), Silicon (Si), Magnesium (Mg) and Calcium (Ca) as the major
metal ions. Results obtained showed that samples containing 20 - 60 wt% steel slag have very good usable ceramic tile
Keywords: Sintering; Phases; Pig Iron; Mineral
1. Introduction
Slag is a major by-product in the iron and steel making
industry [1]. It may be classified into two main catego-
ries namely—blast furnace slag and steel slag. Blast fur-
nace slag is produced during pig iron production in the
blast furnace, while steel slag is generated at the steel
melting shop during steel manufacturing. It is well
known that removal of excess silicon and carbon from
iron is necessary in order to produce steel. This is
achieved through oxidation by adding limestone and
coke [2].
Steel slag has higher amount of iron and its physical
characteristics are similar to air-cooled iron slag. Iron
content of steel slag is the major difference between blast
furnace slag and steel slag. Slag, 2009 reported that the
iron content of blast furnace slag is about 0.5% against
10% - 23% for steel slag. Emery, 2004 observed that
blast furnace utilization in many industrial applications is
well known compared to steel slag. Furthermore, the
practice of incorporating industrial waste in tile produc-
tion is gaining ground in many ceramic industries all
over the world. Consequently, several studies have been
carried out on the production of ceramic products using
both organic and inorganic waste like sewage sludge,
natural stone waste, fly ashes, and metallurgical waste
[3]. The need to characterize ceramic bodies from such
combinations is not only justified, but imperative. This
study is a contribution in that regard.
2. Experimental Procedure
Steel slag used in this work was collected from Delta
Steel Company, Ovwian Aladja, Delta State. Kaolinite
sample was collected from Agbaghara Nsu in Ehime
Mbano Local Government Area of Imo State. Both sam-
ples were separately crushed, ground and sieved using
ASTM sieve to obtain 100% passing 200 mesh. The ag-
gregates obtained from sieving were batched and blended
in the range of 0 - 100 wt%. Water was added to temper
and the mixture thoroughly worked into a paste. The
paste was introduced into fabricated mild steel mould
measuring approximately 90 mm × 70 mm × 10 mm. The
required quantity of batch mixtu re (paste) was introd uced
into the fabricated metal mould and pressed under a pre-
ssure of 40 MPa using hydraulic pressing machine. The
formed products were allowed to air dry for two days,
followed by oven drying for 1 hour at 105˚C. It was then
sintered to 1200˚C, with 30 minutes soaking time, using
GK4 1300˚C Electric Furnace. Then the sintered prod-
ucts were furnace-cooled to ambient conditions. Standard
methods were applied to determine the linear shrinkage
*Corresponding author.
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and modulus of rupture of sintered products. Apparent
porosity, bulk density, and water absorption of the sin-
tered products were determined following ASTM C 373
standard procedure. Phases present in the sintered speci-
mens were identified using X-ray Diffractormeter (XRD),
while the microstructural examination was conducted
using Scanning Electron Microscopy (SEM). The ele-
ments present in the sintered products were identified
using Energy Dispersive X-ray (EDX).
3. Results and Discussion
3.1. Linear Shrinkage
The average total (drying and sintered shrinkage) values
are presented in Table 1 It is shown that the highest
shrinkage of 19.28% was obtained for sample (tile 1)
sintered to 1200˚C, followed by 9.09% record ed by tile 2.
This shows that steel slag gave some level of dimen-
sional stability to the tiles since tile 1 without steel slag
recorded very high shrinkage values compared to tiles
with steel slag compositions. In the production of stand-
ard size ceramic tiles, it is not desired to have a high fir-
ing shrin kage.
Figure 1 shows that the values of firing shrinkage de-
creased with increase in steel slag addition. Apart from
tile 1, linear shrinkage of the tested tiles, compared well
with values recorded by [4]. Generally, firing shrinkage
values increased with higher sintering temperatures due
to the densification of samples as a result of sintering.
Again, linear shrinkage affects porosity as higher shrink-
age resulted to the closure of pores thus leading to reduc-
tion in porosity.
Table 1. Results of tested parameters.
Sintered at 1200˚C
Description Tile 1 Tile 2 Tile 3 Tile 4Tile 5
Apparent porosity, AP (%) 31.32 15.38 11.29 14.0614.24
Water absorption, WA (%) 17.12 7.66 5.61 6.977.04
Linear shrinkage (L S) 19.28 9.09 8.18 7.556.36
Bulk density, BD (g/cm3) 1.82 2.01 2.01 2.012.00
MOR (MPa) 2 25 38 55 58
Figure 1. Firing shrinkage against steel slag addition at
(1200˚C) sintering temperature.
3.2. Apparent Porosity and Bulk Density
Results obtained are shown in Table 1 and Figure 2. Tile
1 sintered to 1200˚C with the highest porosity of 31.32%
also recorded the lowest bulk density of 1.82 g/cm3. Tile
3 sintered to 1200˚C with the lowest porosity of 11.29%
recorded the highest bulk density of 2.01 g/cm3. Similar
observations were observed for other samples though the
bulk densities seem to remain constant as porosity in-
creased. This is in agreement with the fact that densifica-
tion reduces pore spaces and hence volume upon which
density depends.
3.3. Water Absorption
Water absorption is commonly referred to as an indicator
of porosity value of wall and floor tiles. Table 1 shows
the results obtained. Tile 1 sintered to 1200˚C with the
highest water absorption of 17.12% also recorded the
highest porosity of 31.32%. Tile 3 sintered to 1200˚C
with the lowest water absorption of 5.61% also recorded
the lowest porosity of 11.29%. Therefore, it can be said
that water absorption d irectly varies with apparent poros-
ity; hence both properties showed similar trend in the
overall steel slag additions. Figure 3 shows that water
absorption of samples sintered to 1200˚C decreased with
increasing steel slag addition down to 40 wt% before
slightly increasing with further additions. Romero et al.,
2008, suggested that closed porosity dominates at high
Figure 2. Apparent porosity (AP) and bulk density (BD)
against steel slag addition (1200˚C).
Figure 3. Water absorption against steel slag addition sin-
tering temperature (1200˚C).
Copyright © 2012 SciRes. JMMCE
temperatures hence justifying apparent porosity values
recorded in this work. Apart fro m tile 1, water absorp tion
values recorded by other tiles compared well with values
recommended by EN 14411 [5], which stipulated 10% to
18% and 6% to 10% for wall tiles and floor tiles respec-
tively. Water absorption requirements for floor tiles are
much lower; therefore samples generated from this work
could be suitable for floor tiles purposes.
3.4. Modulus of Rupture (MOR) Result
MOR is the measurement of the transverse strength of
tile. The higher the value, the stronger the tile. The re-
sults obtained are shown in Table 1 and Figure 4. It
shows that the addition of steel slag drastically increases
the strength of tiles. MOR of normal floor tiles varies
from 20 MPa to 35 MPa [5].
3.5. XRD Result
XRD results of sintered samples are shown in Figures
5-8. Results of all the tested sintered products (tiles 2 - 5)
indicated the presence of quartz (SiO2) as expected. From
the XRD images, quartz particles have diffraction peaks
at 4.24, 2.45, 2.23, 2.12 and 1.37 as observed by [6],
2010). XRD pattern of (tiles 2 - 5) also showed the
Figure 4. Modulus of rupture against steel slag addition.
Figure 5. XRD patterns (intensity (cps) vs. degrees 2Θ) for
the tile 2 sintered to 1200˚C.
Figure 6. XRD patterns (intensity (cps) vs. degrees 2Θ) for
the tile 3 sintered to 1200˚C.
Figure 7. XRD patterns (intensity (cps) vs. degrees 2Θ) for
the tile 4 Sintered to 1200˚C.
Figure 8. XRD patterns (intensity (cps) vs. degrees 2Θ) for
the tile 5 sintered to 1200˚C.
presence of enstatite (MgOSiO2). The XRD images
showed that enstatite particles have diffraction peaks at
3.17, 2.54, and 1.48 as indicated by Mineral Data, 2001.
The formation of enstatite phase may be attributed to
the increasing amount of MgO in the ceramic tile body
[7]. The presence of Anorthite (CaO·Al2O3·2SiO2) and
Wollastonite (CaOSiO2) phases were detected in (tiles 3 -
5). From the XRD images, anorthite particles have dif-
fraction peaks at 4.07, 3.67, 3.62, 3.60, 3.18, and 3.12;
while wollastonite particles have diffraction peaks at
3.32, 1.98, 1.97, 1.87, 1.83, 1.75, 1.53 and 1.45 as indi-
cated by [6,8,9]. The presence of anorthite and wollaston-
ite is supported by the increasing amount of Calciu m Ox-
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ide (CaO) in tiles 3 - 5, as high CaO content favours the
formation of both phases [7]. Wollastonite crystallisation
gives high mechanical resistance to tile products and a
high content of this phase in a sintered body will imply
higher strength of the final product [10]. This justifies the
MOR values recorded by tiles 3 - 5.
visible However, some elongated grains could be seen in
tiles 3 - 4, which may be responsible for the good streng -
th of the tiles. The presence of pores (dark holes) was
also indicated. Images from SEM revealed that at 1200˚C,
considerable degree of vitrification took place as evi-
denced by the formation of glassy phases embedded in
the small crystals.
3.6. SEM Result
3.7. EDS Result
The SEM results are shown in Figures 9-12. Results
showed the pr esence of fine gr ained microstru cture along
with relatively small pores originating most likely from
the removal of volatile compounds. Tiles 2 - 5 show the
presence of vitreous (glassy) phases which are evident in
several zones where the microstru ctures are not perfectly
The EDX results are shown in Figures 13-16. The results
show that Aluminium (Al), Silicon (Si), Magnesium (Mg)
and Calcium (Ca) were detected as the major metal ions.
Other elements detected include Potassium (K), Iron (Fe),
Titanium (Ti) etc.
Figure 10. SEM image of tile 3 sintered to 1200˚C.
Figure 9. SEM image of tile 2 sintered to 1200˚C.
Figure 12. SEM image of tile 5 sintered to 1200˚C.
Figure 11. SEM image of tile 4 sintered to 1200˚C.
Figure 13. EDS result of tile 2 sintered to 1200˚C.
Figure 14. EDS result of tile 3 sintered to 1200˚C.
Figure 15. EDS result of tile 4 sintered to 1200˚C.
Figure 16. EDS result of tile 5 sintered to 1200˚C.
4. Conclusion
The production of ceramic tiles using kaolinite clay and
steel slag has been investigated in this present work. The
results obtained indicated the formation of phases like
quartz, wollastonite, enstatite, anorthite which is very
useful in the formation of high quality ceramic tile prod-
ucts. However, physical, service and mechanical proper-
ties tested confirmed that samples developed in this study,
possessed qualities that are good for use as floor tiles.
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