Proceedings of COBEM 2011 21

st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


EFFECT OF TEMPERATURE IN THE TUBULAR CERAMIC MEMBRANE
SINTERING OBTAINED WITH KAOLIN AND BALL CLAY

M. C. Silva, mirelecsilva@hotmail.com
R. C. Oliveira, rosacolima@yahoo.com.br
M. C. Silva, milecost@hotmail.com
H. L. Lira, heliolira@dema.ufcg.edu.br
F. A. Silva, falmeidasilva@gmail.com

Universidade Federal de Campina Grande, Unidade Acadmica de Engenharia de Materiais, Av. Aprgio Veloso 882, Bodocong
Caixa Postal: 10034 Campina Grande PB, 58109-970-Fone/Fax: (83)3310-1178.

N. L. Freitas, normanda@dema.ufcg.edu.br

Unidade Acadmica de Tecnologia do Desenvolvimento Universidade Federal de Campina Grande, Rua Luiz Grande, S/N, 58.540-
000, Sum PB

Abstract. Due to the increase in membrane technology in the last years and its applications are also widespread to
different areas of science, it become more important the studies of the parameters that affect its properties. In this way, the
aim of this work is to evaluate how the increase in sintering temperature changes structural and morphological
characteristics of the ceramic membrane obtained from raw materials: kaolin and ball clay. Ceramic membranes were
obtained from vacuum extrusion processing and sintering at temperatures of 900C, 1000C and 1100C.The ceramic mass
was characterized by thermogravimetric analysis, X-ray diffraction (DRX) and particle size distribution. The membranes
were also characterized by DRX and scanning electron microscopy. The results showed a total mass loss of 13.8% due to
water loss adsorbed on the surface of the particles, organic materials, hydroxyls from clay and from carbonates
decompositions. The value of particle size with 50% of accumulated mass was 3.52m. The crystalline phases present were
kaolinite, quartz and mica. After sintering at 900
o
C, the crystalline phases present were quartz; at 1000
o
C and 1100 present
quartz and mullite. After sintering the membranes presented the linear shrinking of 1.23%, 3% and 9.18%, to sintering
temperature of 900C, 1000C and 1100C, respectively. The images from microscopy showed porous membranes and with
the increase of sintering temperature it was observed an increase in the grain size and more homogeneous distribution of
them.

Keywords: ceramic membrane, sintering, kaolin, Ball clay.

1. INTRODUCTION

Membrane separation process are considered a clean technology and is each time more applied by the industry in
substituting conventional process, due to advantages, such as: make the separation without phase changing, appreciable
energy savings, are environmentally benign; the technology is clean and easy to operate; can replace conventional processes
like filtration, distillation, and ion exchange; produce high-quality products; and offer greater flexibility in system design
(Silva et al. 2005, Silva, 2002).
Among materials used to prepare inorganic membranes, ceramics are highlight. It can produce membrane with
tangential velocity, with turbulent flow to prevent the formation of fouling and maintain high permeate flow (Delcolle,
2010). Ceramic membrane properties include high temperature resistance, good biological resistance and allow sterilization
with vapor and its contamination with bacteria is less probably. This characteristic is very attractive to the food and
pharmaceutical industry (Chi-Sheng Wu and Lee, 1999, cited by Alicieo et al., 2008).
The first researches about ceramic membrane used -Al
2
O
3
as precursor, followed by -Al
2
O
3
, zirconia, titania and silica
were used to membrane preparation. Recently, some researchers start to work with raw materials of low cost, such as:
apatite, ash and kaolin, to reduce membrane cost (Jana et al. 2010).
Membranes can be classified into two geometrical shapes: plane and cylindrical. This later can be tubular, capillary and
hollow fiber. The tubular membrane present good resistance to fouling and are currently used when the feed contain high
amount of solids in suspension (Gea Filtration, 2010). Howell et al. (1993) describe a new application of tubular and plane
membrane to collect yeast. The research done by Ahn et al. (1998), showed the possibility to use ceramic membrane to
effluent treatment generated by the hotels and building and to reuse for secondary purposes.
The field of application of membrane technology has been expanded in the last years and the interest of the researchers
is to develop new methods with low cost to be applied in different membrane separation process.
Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


2. MATERIALS AND METHODS

Raw materials used in the ceramic membrane preparation were: ball clay from Alhandra, Paraiba state, kaolin from
Junco do Serid, Paraiba and liquid additives. The raw materials were submitted to sieve ABNT 200 mesh (0.075mm) and
mixed in a blender METVISA model. The mixture was homogenized with water and additives to reach a plasticity fit to
extrusion. It was used a vacuum extruder Verds 051 model. The extruded parts in a tubular shape were dried and sintering
at 900
o
C, 1000
o
C and 1100
o
C, using an electrical oven JUNG model.
The ceramic mass was characterized by thermogravimetry, using a thermal analyzer, from BP Engenharia, RB-3000-20
model, with heating rate of 12.5oC/min and using nitrogen gas. It was used a platinum crucible and temperature range from
room temperature to 1000
o
C. Particle size analysis was done in diffraction laser particle size analyzer from Cilas, 1064 LD
model, with a measurement range from 0.04 to 500 m. To phase identification it was used a X-ray diffractometer from
Shimadzu, XRD-6000 model. Ceramic membranes were characterized also by scanning electron microscopy (SEM) from
Shimadzu, SSX-550 model. It was also calculated shrinking of the membranes after sintering with a digital caliper and
using the Eq. (1), where R means the shrinking, Da is the length of the membrane before sintering, in mm, and Dq is the
length of the membrane after sintering, in mm.

100% x
a
D
q
D
R
|
|
.
|

\
|
= 1 (1)


3. RESULTS AND DISCUSSION

Figure 1 shown the thermogravimetric curve of the ceramic mass before sintering. It was observed a first mass loss
(1.6%) starting at 25
o
C until 200
o
C related with adsorbed water on the surface. Between 200
o
C and 350
o
C the curve showed
another mass moss of 0.84% due to loss of organic matter. At 365
o
C it was observed the beginning of third mass loss that
finishes at 625C (10%) and is due to the elimination of hydroxyl groups from clay fraction. Between 630
o
C and 1000
o
C
there is a small mass loss of 1.32% due to the decomposition of carbonates. The total mass loss was 13.8%.

0 200 400 600 800 1000
86
88
90
92
94
96
98
100
102
W
e
i
g
h
t

l
o
s
s

(
%
)
Temperature (C)
TG


Figure 1. TG and DTG curves of ceramic mass before sintering.

Figure 2 present particle size distribution of the ceramic mass before sintering. The results showed a narrow distribution
of the particle with 50% of the accumulate average mass of 3.52m.

Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


0,1 1 10
0
20
40
60
80
100
D
everage
= 3,52 m
x (Diameter) / m
Q
3

(
C
u
m
u
l
a
t
i
v
e

v
a
l
u
e
s
)

/

%
0,0
0,5
1,0
1,5
2,0
2,5
3,0
q
3

(
H
i
s
t
o
g
r
a
m
)

/

%

[
x
2
4
]

Figure 2. Particle size distribution of ceramic mass before sintering.

Figure 3 present the results from X-ray diffraction of the mass before sintering and after sintering at 900
o
C, 1000
o
C and
1100
o
C. It was observed that the mass before sintering, Fig. 3(a), show the presence of crystalline phases such as kaolinite,
quartz and mica. The two main peaks are related to kaolinite.

10 20 30 40 50 60 70 80
I
n
t
e
n
s
i
t
y

(
a
.
u
)
Mu Mu Q
Mu
Q
Mu Q
Q
Q
Q
Q Mu
Mu
Mu
Mu
Mu
Mu Mu
Mu
Mu
Mu
Mu
Mu
Mu - MULLITE
Q - QUARTZ
(d)1100C
2(u)
Q
Q Q
Q
Q M
M M
M
M M
M
M
M
Mu
Mu
Mu
Mu
Mu
M - MICA
Mu - MULLITE
Q - QUARTZ
(c)1000C
Q
C C Q Q
Q Q Q Q
Q
Q
M - MICA
C - KAULINITE
Q - QUARTZ
M
M
M
M
M
M
M
M M
M M
(b)900C
C M Q C
M Q M
C C Q
C
Q
Q Q
C
C
C
M
C
M
Q
C
M
M
Q
M
C
M
C
M
M - MICA
C - KAOLINITE
Q - QUARTZ
(a)Mass before sintering


Figure 3. X-ray curves of (a) mass before sintering, (b) sintered at 900C, (c) sintered at 1000C e (d) sintered at 1100C.

After sintering at 900
o
C it also observed peaks related with quartz and mica and traces of kaolinite. Due to the increase
in temperature during the sintering process there is a reaction between silica (SiO
2
) and alumina (Al
2
O
3
) present in the raw
materials, to produce mullite (3Al
2
O
3
2SiO
2
) that appear when the membrane was sintering at 1000
o
C.
Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


For the sintering temperature of 1100C, it was presented also two crystalline phases, quartz and mullite, with more
intense and defined peaks when compared with the temperature of 1000
o
C.

Figure 4 present the shrinking of the ceramic membranes before and after sintering at 900C, 1000C e 1100C.

84%
86%
88%
90%
92%
94%
96%
98%
100%
102%
100C 900C 1000C 1100C
Shrinking
-1,23%
-3%
-9,18%


Figure 4. Linear shrinking of the ceramic membrane before and after sintering at 900
o
C, 1000
o
C and 1100
o
C.

After sintering process membranes present a shrinking in relation to the initial length and diameter. The shrinkage
increase with the increase of sintering temperature, that is, to the ceramic membrane sintering at 900
o
C, 1000
o
C and 1100
o
C
presented shrinkage of 1.23%, 3% and 9.18%, respectively.
In relation to the color, it was observed that the increase in sintering temperature cause a change in color intensity and
became more light, probably due to the small amount of iron present in the ceramic mass.
Figure 5 show the SEM images for the membrane sintering at 900
o
C. It was observed a porous structure, with presence
of grains with irregular shape and distribution, also with some agglomerates with different sizes and plate shape. This
temperature was not enough to promote a good sintering of the particles. Although a porous structure, from the image it was
not possible to estimate with precision the pore size as well as the porosity of the membranes.

Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


Figure 5. SEM images for the tubular ceramic membrane sintering at 900
o
C. (a
1
and b
1
) transversal section of the membrane
and (a
2
and b
2
) longitudinal section of the membrane. Magnification of (a)1000 times and (b) 5000 times, respectively.

Figure 6 presents images for membrane sintering at 1000
o
C. It can be observed that an increase in sintering temperature
of 100
o
C produced an increase in grain size. Also it was observed the presence of agglomerates with different geometries
and improperly distributed on the membrane surface. In the image a
1
it was observed a porous structure of the membrane
and in b
1
it was observed an increase in particle sintering. As also mentioned to Figure 5, from Figure 6 images it was not
possible to estimate the pore size of the membranes.

(a
1
) (a
2
)
(b
2
)
(b
1
)
(b
1
)
(a
2
) (a
1
)
(b
1
) (b
2
)
Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil




Figura 6. SEM images for the tubular ceramic membrane sintering at 1000C. (a
1
and b
1
) transversal section of the
membrane and (a
2
and b
2
) longitudinal section of the membrane. Magnification of (a)1000 times and (b) 5000 times,
respectively.


Figure 7 showed the SEM images from ceramic membrane sintering at 1100
o
C. From these images it can be
observed an changin the the surface aspect of the membrane when compared with Figure 5 and 6. In spite of the
presence of sintering grains, still possible to see a more distributed and homogeneous particles on the membrane
surface. Also with these images it was not possible to estimate the pore size.

(a
2
)
(a
1
) (a
2
)
(b
1
) (b
2
)
Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil





Figura 7. SEM images for the tubular ceramic membrane sintering at 1100C. (a
1
and b
1
) transversal section of the
membrane and (a
2
and b
2
) longitudinal section of the membrane. Magnification of (a)1000 times and (b) 5000 times,
respectively.

4. CONCLUSIONS

After this study it can be concluded that:
Tubular ceramic membranes were produced with success. The ceramic mass used to produce membrane presented a total
mass loss of 13.8%. The particle size distribution presented 50% of the mass with size of 3.52m. After sintering at 1000
o
C
it was observed the presence of quartz and mica and trace of kaolinite and at 1100
o
C it was observed the presence of mullite
and quartz. The membranes presented shrinkage from 1.23% (900
o
C) to 9.18% (1100
o
C) and presented a porous structure
with changing in aspect when sintering at different temperature.

5. ACKNOWLEDGEMENTS

The authors thanks to CNPQ for the financial support and to the Programa de Pos-Praduao em Engenharia de
Materiais, Federal Uninversity of Campina Grande.

6. REFERENCES

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1
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Proceedings of COBEM 2011 21
st
Brazilian Congress of Mechanical Engineering
Copyright 2011 by ABCM October 24-28, 2011, Natal, RN, Brazil


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The authors M. C. Silva, R. C. O. Lima, M. C. Silva, H. L. Lira, F. A. Silva, N. L. Freitas, are the unique responsible for the
press material included in this work.