Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 970-975
Published Online October 2012 (
Production an d Characterization of Porous Insulating
Fired Bricks from Ifon Clay with Varied Sawdust
Fatai Olufemi Aramide
Department of Metallurgical and Materials Engineering, Federal University of Technology, Akure, Nigeria
Received August 2, 2012; revised September 5, 2012; accepted September 13, 2012
The effect of compositions of saw dust admixture on thermal conductivity and other mechanical/refractory properties of
Ifon Clay was investigated. The raw clay gotten from Ifon in Ondo state was first processed to very fine particles and
characterized using SEM/EDX, XRD and XRF. Sawdust from mahogany tree procured from a saw mill in Akure the
State capital of Ondo State was also dried to remove moisture present. A composite mixture of this dried saw dust with
the processed clay was made at various proportions of the saw dust, with a little addition of water for plasticity. Sam-
ples of cylindrical dimensions were then produced from the mounting press by the process of compaction with a very
high pressure. The samples were dried and then finally fired in the furnace at 1000˚C for a final curing. Properties
which include thermal shock resistance, bulk density, cold crushing strength, thermal conductivity and porosity were
obtained by the appropriate standard test methods. The microstructures of the fired samples were also characterized
with SEM using back scattered secondary imaging. The results show that the amount of sawdust admixture affects the
properties variously; porosity increases with percentage increase in sawdust admixture while the thermal conductivity
and other properties of the sample reduce with percentage increase in sawdust admixture. It was concluded that for
structural insulating bricks where compressive strength is important the sawdust admixture should not exceed 10 to 15
Keywords: Thermal Conductivity; Porosity; Insulating Brick; Ceramic
1. Introduction
Pores have traditionally been avoided in ceramic pro-
ducts to increase the crack resistan ce, but in the last dec-
ades an increasing number of applications that require
porous ceramics have emerged. Porous ceramic materials
have applications in many industrial areas, such as cata-
lyst supports for hetero geneous ch emical reactions , filters,
membranes, thermal insulators, and bioceramics.
These applications require an optimal pore-size distri-
bution, the porous microstructure, and other important
properties such as chemical inertia, and resistance to
thermal and/or mechanical shock [1]. The presence of
pores (holes) in a material can render itself all sorts of
useful properties that the corresponding bulk material
would not have [2]. Generally porous materials have po-
rosity (volume ratio of pore space to the total volume of
the material) between 0.2 - 0.95 [3]. Pores are classified
into two types: open pores which connect to the surface
of the material, and closed pores which are isolated from
the outside.
A thermal insulator is a poor conductor of heat and has
a low thermal conductivity. Insulation is used in build-
ings and in manufacturing processes to prevent heat loss
or heat gain. Although its primary purpose is an eco-
nomic one, it also provides more accurate control of pro-
cess temperatures and protection of personnel. It prevents
condensation on cold surfaces and the resulting corrosion.
Such materials are porous, containing large number of
dormant air cells.
This endeavour is focused on the production of effi-
cient thermal insulating bricks from local available clay
2. Materials and Methods
The materials used for this study include; dried saw dust,
Ifon clay as mined, water, wooden sieve, beaker, conical
flask and thermometer. The equipment used for this
study include; a furnace, mounting press, grinding mill,
pulverizer, seive shaker and set of sieves, and com-
pression strength tester. Dried saw dust from mahogany
tree acquired from a saw mill in Akure was sun dried
further to remove moisture present. Clay acquired from
Copyright © 2012 SciRes. JMMCE
Ifon, also in Ondo State was soaked in water for three
days to dissolve the clay and at the same time to form a
slurry. The resulting slurry was then sieved to remove
dirt and other foreign substances using a sieve. More
water was thereafter poured into the clay to form a slurry
once again . This is then allowed to settle down for seven
days. The floating clear liquid was decanted after the
seventh day. The settled fine clay was then poured into a
P.O.P mould and left undisturbed for three days in other
to allow the liquid still present to drain out completely.
The resulting clay was then sun dried for two days. This
was followed by grinding in a grinding mill to reduce the
particle sizes. A pulverizer was then used to reduce the
sizes of the clay particles further into still finer particles.
A final sieving of the pulverized sample was then carried
out. A sieve analysis of the clay and saw dust used in this
project is as stated: Clay; <850 µm, Saw dust; <1700 µm.
A mixture of clay and saw dust was made with the saw
dust in various propo rtions of 5%, 10%, 15%, 20%, 25%,
30% and 35%. Each mixture was made thoroughly with a
little addition of water to induce some plasticity and ho-
mogeneity of both the clay and saw dusts. The resulting
mixtures (for each proportions of saw dust), were then
compacted in a mounting press to obtain cylindrical
shaped samples. These samples were then placed in the
furnace and fired at 1000˚C (held at the temperature for 1
hour) such that the saw dust burns off leaving some ash
and pores. Series of tests were then performed on the
fired samples. These tests include; cold crushing strength,
bulk density, porosity, thermal shock resistance, perme-
ability and thermal conductivity.
2.1. Apparent Porosity
Test samples from each clay/saw dust blend (for varying
proportions) were dried for 12 hours at 110˚C. The dry
weight of each fired sample was taken and recorded as D.
Each sample was immersed in water for 6 hrs to soak and
weighed while been suspended in air. The weight was
recorded as W. Finally, the specimen was weighed when
immersed in water. This was recorded as S. The apparent
porosity was then calculated from the expression:
2.2. Cold Compression Strength
Cold compression strength test is to determine the com-
pression strength to failure of each sample, an indication
of its probable performance under load. The shaped sam-
ples of clay blends with saw dust were dried in an oven
at a temperature of 110˚C, allowed to cool and then
placed between two plates of the compression strength
tester. This was followed by the application of a uniform
load to it. The load at which a crack appears on the sam-
ple was noted and the cold compression strength (CCS) is
calculated from the equation:
Load to FractureKG cm
Surface Area ofSample
2.3. Thermal Shock Resistance
Each sample of the clay/saw dust blend was placed in an
electrically heated furnace to attain the test temperature
of 1000˚C for over 3 hours. Each sample was then with-
drawn from the furnace and held for 10 minutes. The
procedure was repeated until an appearance of a crack
was visible. The number of cycles necessary to cause a
crack was recorded for each of the samples and taken as
a measure of its thermal shock resistance.
2.4. Bulk Density
The test specimens were dried at 110˚C for 12 hours to
ensure total water loss. Their dry weights were measured
and recorded. They were allowed to cool and then im-
mersed in a beaker of water. Bubbles were observed as
the pores in the specimens were filled with water. Their
soaked weights were measured and recorded. They were
then suspended in a beaker one after the other using a
sling and their respective suspended weights were mea-
sured and recorded. Bulk densities of the samples were
calculated using the fo rmula:
bulk densityg
where: D = Weight of dried specimen, S = Weight of
dried specimen suspended in water, and W = Weight of
soaked specimen suspended in air
2.5. Thermal Conductivity Test (Using Ibrahim’s
Thermal Conductivity Apparatus; the Steam
Test specimens of area 0.002 m2 and thickness of 0.01 m
were cut from their respective mother bricks. The test
specimens were tested one after the other. Each specimen
was fixed between two copper discs provided within the
equipment. A conical flask containing 50 ml of water
was placed directly above and in contact with the speci-
men. A cork having a thermometer passing through it
was used to cork the mouth of the conical flask. The
thermometer reads the temperature changes of the water
in the flask. The test section was then closed and the ini-
tial water temperature was noted. A second thermometer
with the aid of a cork was inserted into the steam outlet
pipe offset to monitor the steam temperature so as to en-
sure a constant base temperature of 100˚C.
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mass of water in conical flask k (kg), C = specific heat
capacity of water in conical flask (J/kgk), L = thickness
of specimen (m), θ1 = T1 - Ti, θ2 = T1 - T4.
The boiler water outlet valve was closed while 5 litres
of water was measured and poured into the boiler. The
steam inlet valve, outlet valve, and condensate outlet
valve were all closed. With the boiler cover remaining
opened, the boiler was switched on. Immediately the
water started boiling, the boiler cover was closed, while
the steam inlet valve was fully opened with all the re-
maining valves closed. Timing commenced with the aid
of a stopwatch immediately the steam inlet valve was
opened. The testing was timed in each case for 10 min-
utes and final temperature of the water in the beaker was
noted at the end of time. Each specimen was tested (ex-
perimented) twice and a mean temperature value was
obtained. At the end of each experiment, the steam outlet
valve was opened to release steam. The water in the
boiler was refilled to maintain 5 litres and the ex periment
was repeated as stated above for other specimens. The
value of the thermal conductivity, K for each of the
specimen was determined using the formula [4,5];
3. Results and Discussion
Figures 1 and 2 respectively shows the XRD result the
SEM/EDX analysis of the raw clay sample. Tables 1 and
2 also respectively shows the XRD and XRF analysis
results of the raw clay sample. These show the various
phases present in the raw clay sample. It can be seen
from Table 1 that the overall feldspar conten ts of the raw
clay samples is high (35.2% microcline and 12.07%
Plagioclase Albite). It has been noted that feldspars
favour liquid phase formation and densification at low
temperature [6-11], this will disqualify the utilization of
the clay in refractory (high temperature) applications
except if subjected to serious purification process to re-
duce or eliminate the feldspar content.
It is also observed from Figure 3 that the thermal con-
ductivity of the samples decreases with increased saw-
dust admixture. This should be expected; as the samples
were fire, the sawdust admixture got burnt off, leaving
pores (compare with Figure 4) which are empty spaces
within the solid-bodied samples. This is supported by
Figure 8 (compared with Figure 9) which show the
SEM micrographs of the various samples with different
percentages sawdust admixture.
2.303 log
where, K = thermal conductivity of the specimen, Tl =
temperature of steam k, Ti = Initial temperature of water
in conical flask, T4 = Final temperature of water in coni-
cal flask, τ = Time (s), A = Specimen area, (m2), M =
Figure 1. X-ray diffraction pattern (phase analysis) of the ifon clay sample.
Figure 2. Typical SEM/EDX of ifon clay sample; showing the morphology of the minerals and its chemical composition.
Table 1. XRD result of the ifon clay sample showing the
quantity of different phases.
Phases identified Weight%
Kaolinite 10.21
Microcline 35.2
Muscovite/illite 4.7
Plagioclase albite 12.07
Quartz 37.78
Table 2. XRF Semi-quantitative analysis of the elements of
Ifon clay sample (weight %).
Phases A
Al2O3 22.42
SiO2 63.35
Fe2O3 6.109
K2O 2.878
MgO 1.351
Ba 0.092
CaO 0.689
Cl -
Co -
Cr2O3 0.046
Cu 0.021
MnO 0.117
Na2O 0.789
Ni 0.064
P2O5 0.109
SO3 0.047
Sr 0.019
TiO2 0.923
Zr 0.045
Total 99.1
Figure 3. Effect of percentage saw dust admixture on the
thermal conductivity of the sample .
It could be noticed that the pores in the micrographs
increases with sawdust admixture. These empty spaces or
voids (though may contain air) insulate the thermal flow
hence, the reduction in thermal conductivity of the sam-
ples as the percentage sawdust admixture increases. The
same explanation is applicable to Figure 4, where the
porosity of the samples increases with increased per-
centage sawdust admixture. When the samples were fired,
the sawdust admixture got burnt off, leaving pores. As
the percentage sawdust admixture increased it leads to
increased percentage pores when the samples were fired
The influence of texture and porosity may be con-
sidered together because; the principal effect on the ther-
mal conductivity is the relation between the amount of
solid and of air which the heat has to transverse in
passing through the material. Since air is a much better
insulator than any solid material, the larger the propor-
tion of air the greater will be the thermal insulation
power of the material. Hence, a fine grained, closed-
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Figure 4. Effect of percentage saw dust admixture on the
porosity of the sample.
textured material has a much greater thermal condu-
ctivity than one with a co arser open texture. The relation
between insu lation power and texture or porosity cannot,
however be expressed in very simple terms. The thermal
conductivity of ceramic materials will, in fact, not only
depend on the total void space but also the size and the
nature of the voids i.e. to whether the voids are closed or
Furthermore, from Figure 5, it is observed that the
bulk density of the various samples reduced with in-
creased percentage sawdust admixture. This is because
firing the samples, burn off the sawdust admix tures lead-
ing to increased porosity while at th e same time results in
reduced matter contents of the samples. From Figure 6,
it is also observed that the cold crushing strength of the
samples reduced with increased percentage sawdust
admixture [14]. This is because as explained above, the
increased percentage sawdust admixture leads to reduced
matter content of the sample; less matter are available to
bear the applied load. A brick of high porosity will have
lower load bearing capacity than one of the same mate-
rial with lower porosity, since th ere is less material in the
brick to carry the load in the former case. Porous bricks
are lighter and therefore unlikely to carry heavy load
Moreover, from Figure 7, it is observed that the ther-
mal shock resistance of the samples reduces with in-
crease in the percentage saw dust admixture; this could
be attributed to increase in the amount of open porosity
in the sample which acts as ‘notch’ which is a stress
(both mechanical and thermal) concentrator. Also highly
porous insulating materials have been noted show little
stability due to their high porosity [16, 17 ]
4. Conclusions
From the discussion so far it can be concluded that;
Figure 5. Effect of percentage saw dust admixture on the
bulk density of the sample.
Figure 6. Effect of percentage saw dust admixture on the
cold crushing strength of the sample
Figure 7. Effect of percentage saw dust admixture on the
thermal shock resistance of the sample.
Figure 8. Scanning electron micrographs of the morphology
of the various samples with sawdust admixture: Top, left to
right; 5%, 10% and 15% sawdust; while Bottom left to
right; 20%, 25% and 30% sawdust respectively.
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Figure 9. Scanning electron micrographs of the morphology
of the samples with no sawdust admixture (0% sawdust).
Porosity of the samples considered varies inversely as
the thermal conductivity, cold crushing strength and
bulk density of the samples
The porosity of the sample could be controlled by
varying the percent a ge s awdust admixtu re
For structural insulating fired brick where the com-
pressive strength is also important, the percentage
sawdust admixture should not exceed 10 to 15 per-
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