Silica-Alumina Refractory Synthesisbased on

Silica-Alumina Refractory Synthesisbased on

D
J. Chem. Chem. Eng. 7 (2013) 132-136
DAVID
PUBLISHING
Silica-Alumina Refractory Synthesis based on Moroccan
Granitic Geo-Materials
Chaouki Sadik1*, Iz-Eddine El Amrani 2 and Abderrahman Albizane1
1. Department of Chemistry, Faculty of Science and Technology, University Hassan II, Casablanca 20650, Morocco
2. Geomaterials and Geoenvironment Team (GeoM&E), Department of Earth Sciences, Scientific Institute, University Mohammed V
Agdal, Rabat 703, Morocco
Received: December 20, 2012 / Accepted: January 10, 2013 / Published: February 25, 2013.
Abstract: Andalusite rich schist until now has not been utilized to produce refractory. In this work, refractory materials were
elaborated from alumina-silica geomaterials related to granitoids and their direct surrounding rocks (kaolin clay and andalusite riche
schist). Characterization evolution on heating was investigated in a composition (80% kaolinitic clay, 20% andalusite rich schist).
The evolution of mullite was examined by SEM (scanning electron microscopy) and XRD (X-ray diffraction). The thermal shock test
showed that the refractory sample has a good thermal shock resistance.
Key words: Kaolin mullite, alusite firing.
1. Introduction
Alumina silicate refractories are extensively used in
the metallurgical, ceramic and glass industries,
representing an important material in the overall
refractory market. These materials are made primarily
from refractory and kaolinitic clays, which are used
both in crude and grog forms. Silica-alumina
refractory materials generally have a heterogeneous
microstructure with a large grain size distribution and
high porosity [1-3].
The mineralogical composition of refractory
materials based on kaolinitic clays consists of mullite
(3Al2O3·2SiO2) and silica, both in crystalline form
(quartz or cristobalite) and in the amorphous phase.
The mullite phase results from the transformation of
kaolinite [Al2O3·2SiO2·2H2O] during high temperature
thermal cycle [4-10]. Mullite-based ceramics have
important chemical physical properties, including
*
Corresponding author: Chaouki Sadik, Student Ph.D.,
research
field:
ceramics
and
refractory.
E-mail:
[email protected].
good resistance to corrosion and creep, are high
temperature materials and exhibit a low thermal
expansion coefficient [11]. These advantages confer to
mullite-based refractories the ability to bear severe
service conditions encountered in a variety of
applications. The vitreous phase resulting from the
reactions between free silica and alkalines governs the
thermo-mechanical behavior of alumina-silicate
refractory materials, limiting their use at high
temperatures [1, 2]. The content of the vitreous phase
varies according to the raw materials, chemical
compositions and firing temperature [2].
This work is therefore aimed at developing
silica-alumina refractory bricks from granitic kaolin
clay deposits using andalusite rich schist as
aggregates.
2. Materials and Experimental Procedure
Raw materials used in the present investigation
were kaolinitic clay and andalusite rich schist.
Chemical and mineralogical compositions of all raw
materials were given in Tables 1 and 2.
133
Silica-Alumina Refractory Synthesis Based on Moroccan Granitic Geo-Materials
Table 1
ArgK
SchA
Table 2
Chemical analyzes of the raw material.
SiO2
57.20
63.40
TiO
0.08
1.13
Al2O3
29.40
21.70
Fe2O3
4.50
6.00
MgO
0.65
1.59
CaO
0.26
0.12
Na2O
1.55
0.30
K2O
3.08
3.36
P2O5
0.00
0.11
PF
3.28
2.29
Total
100.0
100.0
Mineralogical composition of kaolin clay and andalusite rich schist.
Raw material
ArgK
SchA
Major minerals
Kaolinite, muscovite, quartz
Quartz, muscovite
2.1 Granitic Kaolin (ArgK)
It is rich kaolin clay resulting from hydrothermal
alteration of alkali granite of Oulmès. This
late-Hercynian granitic pluton (290 MPa), located in
the center of the Moroccan Meseta, is affected at its
SW border, in contact with the schistic surrounding
rocks, by an intense hydrothermal alteration. This
alteration caused the kaolinization of alkali-feldspar
of the granitic rock and gave a friable material, rich
in kaolin clay with an appreciable quantity of quartz,
flakes of muscovite, and chloritized biotite. The
sample used in this study (ArgK) comes from the
great clay quarry, which is located on the road
towards the village of Oulmès; (X: 33°26'19.14''N; Y:
06°02'58.83''W; Alt: 1,095 m).
2.2 Andalusite-Rich schist (SchA)
They correspond to a schistose rock of upper Visean
age (330 Ma), which constitutes the surrounding rock
of the Oulmès granite. The shistose rock, of a
gray-black color with a shiny and spotted surface, is
affected by a high grade of contact metamorphism
related to the emplacement of Oulmès granite. This
metamorphism is responsible for the development of a
rich andalusite zone. The sample used for this study
(SchA) comes from the schist rich in andalusite,
located near to the contact with the Oulmès granite, at
approximately 1.2 km far from the great quarry of
kaolinic
clay.
(X:
33°26'21.37''N;
Y:
06°03'44.04''O;Alt: 1,052 m).
The chemical compositions of the geomaterials,
performed by X-ray Fluorescence, are shown in Table
1. The kaolin clay has less iron and magnesium but it
Minor minerals
Feldspar
Montmorillonite, kaolinite
is more aluminous and potassic. Andalusite rich schist
has a siliceous composition with a low content of
alumina compared to kaolin clay. The mineralogical
composition of the kaolin clay is composed of
kaolinite, quartz, and small amounts of feldspar (Table
2). The particle size distribution of this clay is
composed of particles of size in the range (0.1 and 1
mm]). Andalusite rich schist is mainly composed of
quartz and muscovite, beside a small amount of
montmorillonite and kaolinite.
A typical refractory composition was prepared by
mixing 80% kaolinitic clay and 20% andalusite rich schist.
Batches (100 g each) were prepared by mixing the
constituents
with
a
granulometric
distribution
composed of the fine fraction (grain size < 100 μm)
and the coarse fraction (grain size 1,000-2,000 μm).
The bricks were produced in steps as the flowchart in
Fig. 1.
3. Results and Discussions
The measurement of technological parameters of the
refractory was conducted according to ASTM [12-14].
Andalusite rich schist:
coarse fraction F3:
1,000 to 2,000 μm
Granitic Kaolin:
fine fraction F1 < 100 μm
coarse fraction F2: 1,000 to 2,000
μm
Mixing: (F1 + F2) = 80%, (F1 =
30%, F2 = 70%). F3 = 20%.
10% of the dry matter
Drying 105 °C / 24 h
calcinations at 600 °C
/1h
Firing at 1,500 °C / 1 h
(1 °C/min)
Fig. 1
Pressing at 30 MPa into molds of
10 × 5 × 2 cm3
Refractory elaboration flow chart.
134
Silica-Alumina Refractory Synthesis Based on Moroccan Granitic Geo-Materials
3.1 Technological and Mineralogical Characteristics
Several studies on refractory materials in clays [1, 2,
4, 6] have shown that the characteristics of the bricks
are influenced by the mineralogical composition of the
raw material. In general, the porosity increases with
increasing granulometry of the grains, while the linear
shrinkage, decreases. The firing temperature improves
the densification due to the formation of a liquid phase
[1, 2]. For the coarse microstructure refractory, no
distortion, no color change and especially no linear
shrinkage were observed (Table 3).
The refractory sample shaped by dry pressing and
fired during 1h at 1,400 °C was analyzed by XRD.
The obtained spectra are shown in Fig. 2. The results
reveal that elaborated refractory contains mullite and
silica [1].
The results are shown in Fig. 4. It is well known that
the reactions between free silica and alkaline, in
particular potassium oxide that is present in excess in
the kaolin and schist, lead to the formation of a
vitreous phase that governs the thermo-mechanical
behaviour of the materials [2].
Refractory materials inevitably contain some flaws
in the form of porosity, micro cracks and impurities.
3.2 Textural Characteristics
Fig. 3
3.3 Thermal Characteristics
The cyclic thermal shock tests were performed
according to DIN 51068 [1]. The samples were heated
for 15 min at 950 °C, and immediately immersed in
the cooling water at 25 °C for 3 min. After drying for
2 h at 110 °C, the flexural strength is measured [15].
Table 3
SEM micrographs of refractory.
Flexural strength (MPa)
The SEM Image shows that, at the maximum
temperature of 1,400 °C, the briquette presents a
homogeneous texture (Fig. 3). The image shows
furthermore a more important development of mullite.
The mullite is present as very fine needles of 10
microns long, oriented in all directions.
60
55
50
45
40
0
20
40
60
80
Cycles number
Fig. 4 Flexural strength vs. thermal shock cycle for the
sample fired at 1,400 °C (∆T = 925 °C).
Technological parameters for studied refractory fired at 1,400 °C.
Flexural strength
(MPa)
55.34
100
Open porosity (%)
Density (g/cm3)
Water absorption (%)
Linear shrinkage (%)
17.8
2.91
11.2
no shrinkage
Fig. 2 X-ray diffraction patterns of refractory synthesized at 1,400 °C.
Silica-Alumina Refractory Synthesis Based on Moroccan Granitic Geo-Materials
135
valorization of Moroccan geomaterials and leads to
the local synthesis of refractories, which the national
need is mainly imported from abroad.
Acknowledgments
This study was conducted in the laboratory of
Geomaterials and Geoenvironment (Geo M&E) of the
Scientific Institute (University Mohammed V-Agdal,
Rabat, Morocco). The authors acknowledge support
Fig. 5 Fracture surface of sample fired at 1,400 °C and
underwent 100 cycles of thermal shock with a temperature
difference of 925 °C.
When containing inherent flaws ceramics are
subjected to severe thermal shock, damage
concentrated at tips of those preexisting flaws will be
generated leading to higher number of micro cracks
and hence the fracture strength is degraded [15]. The
image of Fig. 5, illustrates the heterogeneous character
of the sample microstructure, subjected to 100 cycles
of thermal shock with a temperature difference of
925 °C. The authors observe andalusite crystals
plunged in the refractory matrix. Cracks and elongated
pores are observed at interfaces between coarse grains
and the matrix. The average length of the cracks is
about 1 cm.
4. Conclusions
Refractory sample based on Moroccan geomaterials
have been improved through the use of andalusite rich
schist as aggregates with granulometric distribution
composed of coarse fraction (mean grain size:
1,000-2,000 mm). From these studies, the conclusions
were drawn:
At 1,400 °C, no cracks, no distortion, no color
change and especially no linear shrinkage were
observed for the sample.
The thermal shock test showed that the refractory
sample has a good thermal shock resistance
investigated by destructive tests (flexural strength).
On the other hand, the results of this study have a
double economic interest: it contributes to the
from National Center for Scientific and Technical
Research (CNRST) (research unite URAC 46) and
Hassan II Academy for Sciences and Techniques
(Project V2GV). The first author thanks the laboratory
of the Ceramic Industrial Unit “FACEMAG” for the
achievement of the cyclic thermal shock tests.
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