International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:20 No:05 225
Physical, chemical and thermal characterization of a
Colombian clay
R.A. García-León1-2, J.A. Gómez-Camperos2 & H.Y. Jaramillo2 1 Instituto Politécnico Nacional, SEPI-ESIME, U.P. Adolfo López Mateos, Zacatenco, Mexico city, 07738, Mexico. E-mail:
[email protected] 2 Facultad de Ingenierías, Programa de Ingeniería Mecánica y Civil, Universidad Francisco de Paula Santander Ocaña,
Colombia.
Abstract-- Clays are used as raw materials of the ceramic
industry for construction and other industries, which are
poorly understood to the laboratory level. The purpose of
this study was to obtain an optimal clay mixture for a
company localized in Ocaña, Norte de Santander,
Colombia. Initially, the physical characterization of five
different types of soil formations was developed to
determine the optimal clay mixture for the manufacture
of masonry products for construction. The granulometry,
hydrometry, and plasticity index results of the raw
material, based on the Winkler diagram, were analyzed
using ternary plots to select the m7 mixture. The behavior
of the mixture m7 obtained by mixture statistical design
was analyzed in all technological aspects considering
ideal test conditions and thus obtain a graph of the
behavior in cooking from the test of drying, water
absorption, flexural strength, XRD, XRF, SEM-EDS,
AFM, and thermogravimetry, and in this way control at
this important stage process. The alumina, iron oxide,
and silica oxide are the main compounds on the mixtures
and, therefore, the high dependence of the cooking
behavior due to chemical reactions of the clays and the
processing during the stages of the production process.
Index Term-- Clay; blocks; granulometry; hydrometry;
mineralogy; optimization.
1. INTRODUCTION
The manufacturing process of the ceramic (Figure 1) is
composed mainly of three stages, which are preparation of
the ceramic paste, molding, and cooking of the product [1].
Figure 1. Scheme of manufacture of the block
Source: [2, 3].
Clays are used as raw materials of the ceramic industry
for construction, but 90% is dedicated to the production of
construction materials and aggregates, and the remaining
10% is dedicated to other sectors in the manufacture of paper,
rubber, paints, absorbents, bleaches, molding sands,
agriculture, chemical, and pharmaceutical products [4-6]. Currently, soils are considered as clay, composed mainly
of a natural mixture of alumino-silicates and other organic
components [7]. The minerals present in clay are commonly
used at the construction level and other industrial processes,
classified according to mineralogy, chemical composition,
geological origin, physical properties, and geotechnical
behavior to determine the mechanical properties and
crystalline phases the different types of soils [8]. Therefore,
technological analyzes such as granulometry, hydrometry,
chemical composition, X-ray diffraction (XRD), X-ray
fluorescence (XRF), and differential thermal analysis are
used to characterize clays [9-11]. Viera et al. [12] analyzed clays from Rio de Janeiro,
Brazil, through the identification of phases, elemental
chemical composition, particle size distribution, thermal
analysis, plasticity index, and other physical tests to evaluate
the behavior during the production process. Also, some
studies related to the physical, chemical, physicochemical, or
technological tests were conducted to determine the optimum
mixture for the production of ceramic products based on their
properties [13-16].
The design of mixtures of experiments (M-DoE) is used
in this type of research to estimate the minimum number of combinations needed to estimate the technological properties
of the clays, considering chemical and mineralogical
compositions of the different mixtures, which provides a
semiquantitative approximation to the behavior on the
industrial level [17-25]. On the other hand, Colombian
technical standards NTC 4017 and 4205 has been used to
validate the behavior of clay-based raw materials and thus
achieve optimal quality mechanical properties in terms of the
final product [26, 27].
This work presents results on the behavior of clays using
experimental design to obtain an optimal quality of the final product with the clay soil raw materials used by a company
dedicated to the manufacture of masonry products for
construction in Ocaña, Norte de Santander, Colombia. For
this purpose, was used technological analyzes for the optimal
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clay-based m7 mixture using the design of experiments with
mixtures in statistical software, considering ideal test
conditions to evaluate the behavior at the laboratory level,
and thus, propose a right cooking curve according to the chemical composition of the m7 mixture, aiming to decrease
the losses of the products due to the bad quality.
2. MATERIALS AND METHODS
2.1 Experimental design
In the development of the mixture design, the statistical
software Stargraphics Centurion was used with three
independent variables related to each other through the
multiple correlation coefficient, taking into account the
results of the physical characterization [28]. A cubic special
statistical and simplex lattice model was established with 3
factors and 3 response variables because none of the samples presented more than 20% dispersion [29]. The main objective
of this experimental design is to select an appropriate raw
material for the formulation of the optimal clay soil mixture,
using the methodology proposed in Figure 2.
Figure 2. Methodology applied in the selection of the raw material and
location.
Source: The authors.
2.2 Physical characterization
The granulometry and hydrometric tests were carried out
using five types of clay soils (M-1, M-2, M-3, M-4, and M-5) of the company object of study. The particles with a
diameter greater than 0.08 mm belong to sand, between 0.08
to 0.005 mm correspond to silt, and between 0.005 to 0 mm
correspond to clay. In the granulometry and hydrometric
tests, some appropriate samples of clays were selected. The
design of the experiment was estimated, taking into account
the physical properties of the clay soils, such as shown in
Table 1.
Table 1.
Preparation of the design of experiments obtained to the statistical model.
Sample
Mixture
M-1
(%)
M-2
(%)
M-5
(%) Total
1 100 0 0
30 Kg
2 0 100 0
3 0 0 100
4 50 50 0
5 50 0 50
6 0 50 50
m7 33.33 33.33 33.33
8 66.67 16.67 16.67
9 16.67 66.67 16.67
10 16.67 16.67 66.67
2.2.1 Granulometry and hydrometric tests
Granulometry tests were carried out according to the guidelines of NTC-1522 [30] and INV.E-123 [31] standard
procedures to determine the percentage of sands. The
samples were prepared using 200 g of the raw material of
each clay soil. During the tests, the following sieves were
used on dry samples ASTM 10 (2000 μm), ASTM 30 (600
μm), ASTM 60 (250 μm), ASTM 80 (180 μm), ASTM 100
(150 μm) y ASTM 120 (125 μm) and a collector for the
residual material.
The hydrometric test was performed according to the
guidelines of ASTM D422 [32] and INV.E-124 [33] standard
procedures to determine the percentage of fine particles (silts and clays) present in the samples of the clay soil. During the
test, around 50 g of dry material of each clay soil was sifting
by a sieve N°200 after were incorporate 200 ml of water and
50 mm of hexametafosfate (deflocculating agent). The
mixture was agitated using an automatic laboratory stirrer for
60 s and transferred to a hydrometer to obtain the
measurements 152H type [34].
On the other hand, physical tests for drying shrinkage,
water absorption, and flexural resistance of the m7 mixture
were performed according to the guidelines of NTC 4205 and
NTC 4017 standard procedures to evaluate the behavior of
the m7 mixture simulating the stages of the production process.
2.2.2 Ternary graphs
Triangular, ternary, or tri-linear graphs are used to
examine the relationships between three or more variables,
representing the components of a mixture. Therefore, the
interactions between them are limited in such a way that each
specific axis is 100% of each variable. A typical application
is when the measured response of an experiment depends on
the relative proportions of three components (e.g., sand, silt,
and clay), which are varied to find an optimal mixture or combination among the variables with which to control or
optimize the production process. In ternary graphs, triangular
coordinate systems are used to graph three variables and
obtain a response surface using a predetermined statistical
model. The graphics were obtained using the software
Statistica with an educational license.
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2.3 Chemical characterization
The samples were prepared according to the guidelines of
ASTM C323-56 standard procedure. 10 g of the dry mixture
m7 were recollected and sifting by a sieve N°400 until obtaining a particle size of 38 μm. After, 6 g were pressed in
a hydraulic machine at 15 tons for 1 min, which results in a
compacted sample of 30 mm of diameter.
2.3.1 X-ray fluorescence
Bruker/S4-Explorer equipment at 40 kV, and 25mA were
used to determine the presence in wt.% of the elements of the
m7 mixture. During this process, the m7 mixture was brought
to calcination at 1273 K for 1 h. Also, Loss of Ignition
(L.O.I.) is obtained to represents the number of elements that
react with the temperature, such as water, carbon, phosphorous, chlorine, sulfur, and material that cannot be
detected by the equipment.
2.3.2 X-ray diffraction
A Bruker/D4-Endeavor equipment with CuKα radiation
to 1.9 kW (λ =1.5406), Niquel filter, 40KV, 40mA and sweep
angle 2θ of 5° to 70° (m7 powder mixture) were used to
obtain the presence of characteristic phases.
2.3.3 Scanning electron microscopy
Quanta/200-r equipment under different magnifications
at 20KV was used to obtain the microstructure on the surface of the m7 mixture at high magnifications. SEM-EDS
technique provides qualitative and quantitative information
on the elemental chemical compositions (EDS) [16, 35].
2.3.4 Atomic force microscopy
Veeco/V-Model equipment and the Nanoscope/7.3
software was applied to obtain information from the
characteristic topographic and roughness in 3D on the m7
mixture surface.
2.4 Thermal characterization
2.4.1 Differential analysis “DTA” and
Thermogravimetric analysis “TA” techniques
A solid sample formed by the extrusion molding method
of the m7 mixture was used in a temperature range between
20°C and 1,200°C in an oxygen atmosphere with a thermal
cycle of 5°C/min with the aid of a Q600/thermobalance of
high sensitivity and the Data Analysis software. The DTA
and TA curves allow observed the behavior in endothermic
and exothermic peaks due to the chemical reactions,
accompanied by the weight losses generated by the material
due to the influence of the temperature and the thermal decomposition of the m7 mixture [36, 37].
3. RESULTS AND DISCUSSIONS
The use of technological analyzes of the physical,
chemical, and thermal behavior of clays is essential in the
ceramic industry due to providing an approximation of the
performance of the clay soils during the stages of the
production process. Also, aid in the exploitation of other
types of soils to obtain optimal mixtures to the raw material
for the companies, and as a consequence, achieve an optimal final product with the required quality by the current
standards procedures.
3.1 Physical characterization results
The m7 mixture is composed of three samples of clay
soils (M-1, M-2, and M-5). During the characterization,
granulometry and hydrometric tests were performed to
calculate percentages of sand, silt, and clay of the m7 mixture
(Figure 3), summarized in Table 2, similar to [38].
Figure 3. Plot Granulometry and Hydrometry test for the optimal mixtures
m7.
Source: The authors.
Table 2.
Hydrometry and granulometry values for the samples and mixture selected.
Sample
% SAND
Sieve: 100 mm
– 0.08 mm
% SILT
Sieve: 0.08 mm
– 0.005 mm
% CLAY
Sieve: 0.005
mm – 0 mm
M-1 58.0 18.0 24.0
M-2 61.0 17.8 21.2
M-3 56.3 38.1 5.9
M-4 59.7 31.1 4.6
M-5 58.0 27.0 15.0
m6 59.5 22.5 18.0
m7 58.5 21.0 20.5
m8 58.0 20.0 22.0
m9 60.0 19.5 20.5
m10 58.5 24.5 17.5
On the other hand, ternary graphs were obtained to
evaluate the behavior granulometry and hydrometry
composition of the samples (M-1, M-2, M-3, M-4, and M-5)
on the m7 mixture (Figure 4).
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Figure 4. Ternary graphs obtained for the overall experimental set for a)
Liquid limit “LL”, b) Plastic limit “PL”, c) Plasticity index “IP”, d) Optimal
mixture, e) Type of soil sample, and f) Type of product can be manufactured.
Source: The authors.
The behavior of each ternary graph is presented in Table
3 through the use of specific Equations. The variables LL and IP are influenced by the amount of sand in the clay soils
mixture, while the LP variable shows a tendency towards
clay and silt, such as shown in Figure 4.
Table 3.
Predicted behavior of the ternary graphs.
Variable Equation
Liquid Limit - LL R=(35.8828×S)+(11.6649×L)+(16.7148×C)
Plastic Limit - LP R= (11.0157×S)+(37.9098×L)+(34.5665×C)
Plasticity Index - IP R= (24.8671×S)–(26.245×L)-(17.8517×C)
Note: S=Sands, L=Silts, and C=Clays
The extrusion process of the block becomes complex due
to the lower clay content and plasticity index. Table 4 present a CL-ML zone for the m7 mixture, due to is located in the
ideal zone for the production of H-10 blocks in the company,
note that also ML, represent inorganic silts and fine sands,
clean silts, fine sands, silty or clayey, or clayey-silts with
slight plasticity and CL, represent inorganic clays of low to
medium plasticity, gravel-clays, sandy-clays, silty-clays.
Also, the m7 mixture presents a Franco-Clays-Silts soil type,
optimal for the manufacture of perforated blocks, in the
ranges of the Winker diagram for the production of ceramic
products [39].
Table 4.
Calculation of the physical properties for the selected mixture.
Calculation m7 Mixture (%)
Liquid Limit - LL 26.85
Plastic Limit - LP 21.21
Plasticity Index - IP 5.640
A ceramic paste can be defined as a combination of clay
soils and other minerals substances, which are mixed to
achieve a product with excellent physical and mechanical
properties. Generally, three components are used in the mixture that is plastic, non-plastic, and inert materials. The
first is the clay, which provides adequate plasticity and
facilitates the molding and handling of the product, the
second is the alumina, which is used as a flux, and the third
is the silica, which provides the mechanical stabilization of
the product [40]; besides, some feldspars [(K, Na, Ca, Ba,
NH4)(Si, Al)4O8] aim in the homogenization of the clay
mixture.
Shrinkage to drying: The m7 mixture presented values of
around 6.05±0.25% for this test, revelating shrinkage drying and losses for calcination less than 2.0% and 10%,
respectively, which restricts the formation of fractures,
cracking, and deformations on the cooking stage. Also, it is
evident the contribution of the temperature around 900°C,
where the drying is accelerated with positive values causing
the stabilization of the clay sample (Figure 5).
Figure 5. Shrinkage to drying versus temperature.
Source: The authors.
Water absorption: This parameter is evaluated according
to the guidelines of NTC 4205 standard procedure; for raw
materials of structural use, values of water absorption are
13% and 13.5% for indoor and outdoor use, respectively.
Figure 6. Water absorption versus temperature.
Source: The authors.
The results of water absorption are shown in Figure 6; the
decreases in water absorption are evident whit the increased
temperature due to the internal chemical reactions and
evaporation of residual water. This test revelated values
above 19%, and thus, none of the samples comply with the
specification of the NTC 4205 standard procedure for the
experimental conditions used. This behavior is attributable to the presence of big sand particle sizes (greater than 2 mm)
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and mischaracterization during the stages of the manufacture
of blocks that do not comply with the minor specifications to
obtain optimum product quality.
Flexural strength: This test is used as quality control of
the manufactured samples; norms do not present values to
compare the quality of the samples under this test [41], but
Figure 7 shows the results obtained, which are above typical
mechanical strength values for structural masonry products,
according to [10].
Figure 7. Flexural strength versus temperature.
Source: The authors.
3.2 Chemical characterization results
X-ray fluorescence: The results obtained for the mixture
m7 are shown in Table 5:
Table 5.
X-ray fluorescence for the m7 mixture.
Element Composition %
Chemical Equation Name
Al2O3 Aluminum oxide 20.67
Ba Barium 0.071
CaO Calcium oxide 1.845
Co Cobalt 0.000
Cr Chrome 0.002
Cu Copper 0.001
Fe2O3 Iron oxide 6.567
K2O Potassium Oxide 2.926
MgO Magnesium oxide 0.898
Mn Manganese 0.052
Na2O Sodium Oxide 0.626
Ni Nickel 0.001
P2O5 Phosphorus Oxide 0.448
Pb Lead 0.000
Rb Rubidium 0.063
SiO2 Silica oxide 54.70
Sr Strontium 0.074
TiO2 Titanium oxide 0.871
V Vanadium 0.009
Zn Zinc 0.063
Zr Zirconium 0.059
LOI Lost by Ignition 9.187
SiO2/Al2O3 Molar Relationship 2.646
Total 100.00
The current industrial use of clays is for masonry products
for construction, and therefore, the suggested chemical
values around 50-60% for SiO2 and of 20-30% for Al2O3,
according to [42]. Also, the optimum mixture has the
following composition SiO2 of 54.70%, Al2O3 of 20.67%,
and Fe2O3 of 6.56% obtained by FRX. The high Fe2O3
contents are typical for clays with values no more than 10%,
which confer a red color after cooking [43]. The high wt.%
of SiO2 causes a quick-drying process during cooking and a
decrease in shrinkage; also, the Al2O3 in a high percentage
provides resistance to high temperatures (Table 5). The low
contents of alkaline oxides (Na and K) and natural alkaline oxides (Mg and Ca) make to generate the vitreous phase at
relatively high temperatures (<900°C), conferring semi-
refractive properties, as it could be seen on the physical-
ceramic test. The presence of high content of K2O with 2.926
wt.% above other alkaline and alkaline-natural oxides is
classified as an illitic clay soil material; the other elements
are in low proportions that do not affect the structure of the
final product due to weak chemical reaction on the cooking
stage [23].
X-ray diffraction: Mixtures of clays have mostly a composition of fifty percent of kaolinite, thirty percent of
quartz, and twenty percent of potassium feldspar [44]. These
compositions were identified in m7 mixture by XRD (Figure
8), considering the diffraction profiles on the PDF-2
database, and the results are summarized in Table 6.
Figure 8. XRD pattern for the m7 mixture.
Source: The authors.
Table 6.
Mineralogical structures from XRD analysis for the selected mixture (m7).
ICDD Mineral Chemical
Equation (%) Crystal
000-
89-
8934
Quartz SiO2 38.1
Hexagonal Crystal System
A=4.915
B=4.915
C=5.406
α=90
β=90
φ=120
P(154)
000-
86-
1385
Muscovite
K0.86Al1.94(Al0,9
65Si20.895
O10)((OH)1.744
F0.256)
19.1
Monoclinic Crystal System
A=5.208
B=8.989
C=20.084
α=90
β=95.868
φ=90
C12/C-1
000-
78-
1996
Kaolinite Al2(Si2O5)(OH
)4 16.2
Triclinic Crystal System
A=5.259
B=8.982
C=7.477
α=90.410
β=106.14
φ=91.100
C-1
000-
70-
3752
Albite (Na0.98Ca0.02)(
Al1.02Si2.98 O8) 13.7
Triclinic Crystal System
A=8.143
B=12.797
α=94.220
β=116.59
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C=7.157
φ=87.890
C-1
000-
77-
0135
Microcline K(Si0.75Al0.25)4
O8 10.3
Triclinic Crystal System
A=8.617
B=12.976
C=7.209
α=89.905
β=115.76
φ=90.432
C-1
000-
13-
0135
Montmoril
lonite
Ca0.2(AlnMg)2
Si4 O10(OH)2
!4 H2O
2.6
Triclinic Crystal System
A=6.562
B=9.895
C=15.610
α=87.889
β=78.044
φ=78.044
C-1
The phases presence and clay soil composition are
constituent by feldspars, which correspond to a ternary
system of Quartz-Moscovite-Kaolinite, due to the high presence on the m7 mixture; also, the clays can be present the
same behavior independent of the type of soil.
The m7 mixture is constituted by muscovite or illite in a
high proportion (the second most important mineral after
quartz), with silica and hydrated aluminosilicates and some
impurities (e.g., Na, Fe, K, and Ca). Also, XRD pattern
reflects the high content of Microcline and Muscovite, which
justifies its yellow color of the samples [42]. In this way, the
mineralogical composition consisted of quartz 38.1%, albite
13.7%, microcline 10.3%, montmorillonite 2.6%, Muscovite
19.4%, and kaolinite 16.2%. Table 7 shows some properties of the elements identified in the XRD pattern. Díaz and
Torrecillas [45] report that the main type of clays is kaolin,
illite, and montmorillonite. Also, some peaks contain
smectites but in a similar proportion to kaolinite. Clays find
can be used in the absorbent sector because they can retain
water or other molecules in the interlaminar space (smectites
in the form of montmorillonite), which have properties of
hydration and dehydration of the interlaminar spaces [46].
Table 7.
Properties of the constituent phases.
Element Category Properties
Kaolinite Phyllosilicates It is hygroscopic. Low plasticity.
It resists high temperatures.
Moscovite
or Illite Phyllosilicates
Unstable. Inexpansible. Average
plasticity
Montmorill
onite Phyllosilicates Expansive. Tiropoxico. Unstable.
Quartz Tectosilicates Shrinkage decreases. Easy
fusion. Stable
Microstructural analysis: SEM micrographs for the m7
mixture allowed to verify the laminar texture and the layout
in sheets of the natural aggregates of clay materials, such as
shown in Figure 9.
Figure 9. Micrographs obtained via SEM for m7 mixture. a) 500X, b)
1,000X, c) 2,000X, d) 5,000X, and e) 10,000X.
Source: The authors.
The m7 mixture presents crystalline structures of
different elements such as Al₂Si₂O₅(OH)₄ (Kaolinite), KO2
(Potassium oxide), Fe2O3 (Iron oxide) y Al2O3 (Alumina)
mainly, according to the micrographs obtained at different
magnifications [47]. Likewise, EDS results (Figure 10) for the points selected on the surface revealed the presence of
elements that compose the m7 mixture.
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Figure 10. Micrograph obtained by SEM-EDS techniques.
Source: The authors.
The presence of the elements that make up the m7 mixture
along the analyzed area can be identified in points with the
higher intensity of the oxygen that reacts to Aluminum
Oxide, Iron Oxide, and Silicon Oxide mainly, also there are
other elements such as Potassium, Manganese, and Calcium,
which are validated in the phases obtained by XRD.
Figure 11. AFM images of different areas on the surface of the m7 mixture.
a) Alumina, b) Kaolinite, c) and d) Iron oxide.
Source: The authors.
Figure 11 showed AFM images on different areas of the
surface for m7 mixture, identifying mainly in Figure 11a
Alumina [Al2O3], Figure 11b Kaolinite [Al₂Si₂O₅(OH)₄], Figure 11c and Figure 11d Iron oxide [Fe2O3], due to de high
percentage of these elements validate by XRF and SEM-
EDS. These elements present a morphologic in flat plates and
a spheroidal form of around 10 nm. However, the presence
of aluminum-silicates is characteristic of materials base clays
[47-49].
3.3. Thermal results
The samples were formed by the extrusion molding
method to obtain a solid sample of the m7 mixture. The DTA
and TA curves were obtained using the Data Analysis software at a thermal cycle of 5°C/min and a temperature
range between 20°C and 1,200°C in a controlled atmosphere
of oxygen. The endothermic and exothermic peaks
accompanied by the weight losses suffered for the material
were obtained, such as shown in Figure 12, and the behavior
is described in Table 8.
Figure 12. Thermal analysis of DTA and TA, for the m7 mixture.
Source: The authors.
Table 8.
Analysis of the DTA and TA graphs for the m7 mixture.
Temperature
°C
Curve
DTA (Blue line) TA (Green line)
0-50
Endothermic change,
associated with desorption
or drying processes.
Between points O-A
Weight loss of 2.60%
related to the loss of
hygroscopic, free water,
or the residual humidity
of the sample. A II type
characteristic curve is
presented.
50-200
Between the O-A points, a
slight stabilization is
observed due to the fact
that chemical reactions are
not generated.
There is a loss of mass of
2.40%, product of the
evaporation of water,
linked to the structures
of the samples. A typical
III type curve is
presented.
200-450
Between points A-B, an
exothermic reaction
occurred. For the
oxidative dissociation of
iron hydroxides (Fe2O3).
A mass loss of 7.5% is
presented. Between
440°C appears the
characteristic curve VII
type related to the
presence of
montmorillonite
(desorption of water).
400-650
At point B, an
endothermic reaction is
initiated with a small jump
related to the allotropic
transformation of α to β
quartz, typical at
temperatures of 573°C.
The expulsion of the
crystallized water is
presented, as well as the
characteristic curve IV
and VII type, with a
weight loss of 11%
600-1050
At point C at
approximately 950°C, the
endothermic reaction
occurs; this effect could
correspond to the
The curve presents a
gradual and progressive
decrease, with
characteristic curves of
V and VI types, with a
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dehydroxylation (dilution
of the combustible gases
by the formed water) of
the clay that would last up
to the melting
temperature.
weight loss of 12%
where the release of CO2
could have been
presented.
1050-1250
Between the C-D points,
the constant progressive
descent of the curve is
observed, probably
because the material has
already merged, which
does not stabilize because
the phase found for sample
m7 is at approximately
1500°C, which is where
you get mullite, which
begins to form at around
980°C.
A weight loss of 7% is
presented.
In total, you get at this
temperature a weight
loss of 37%
Note: For characteristic curves [50].
The beginning of the vitrification increases the
mechanical resistance of the samples; this phase is obtained
from 1,200 °C [23]. Besides, do not exist stabilization of the
DTA curve because the mullite phase is achieved at the firing
contractions for the clay are high and have a marked increase
at 1,050ºC, without finishing to contract at 1,200ºC [51].
3.4 Determination of the ideal cooking curve for the
mixture studied.
The optimization of the cooking process can be improved
with the establishment of the ideal temperature curve, which
allows avoiding breakages of preheating, cooking, or cooling
of masonry products for construction that mainly are H-10
blocks. Therefore, the block interacts with the cooking
temperatures deforming elastically, and heating or abrupt
cooling must be avoided. At other times, if the stresses are
higher than the resistance of the material, cooking cracks can
be generated. With the values of strength and elasticity of the
sample at each cooking temperature, a heating speed could be established such that the stresses derived from the
indicated factors were always lower than the resistance of the
block. At the moment, the research on ceramic materials, do
not have precise data on the values pointed due to that the
behavior of the clays in all their production process is
complicated.
Figure 13 showed the cooking curve proposed at the
laboratory level for the m7 mixture, taking into account the
technological analysis developed.
Figure 13. The optimal cooking curve proposed.
Source: The authors.
In the optimum cooking curve, was proposed during the
preheating stage at the beginning of the thermal cycle it will
reach a temperature of 170°C with a heating rate of
approximately 1.3°C/min of 2.5 h to help the loss of water hygroscopic (evaporation of water) and avoid cracks because
the samples have large particles of sand. Then, when the
temperature of 170°C is reached, it is the stage where the
residual humidity has evaporated; from this point, a heating
speed of 3.83°C/min is proposed until reaching a temperature
of 400°C where it will remain for 20 min (Evaporation of
bound water). It is needed to reach a temperature of 550°C
with a speed of 2.5°C/min with the purpose of decomposing
and dissociating the iron hydroxides. Then until reaching
1,000°C, a heating rate of 6.4°C/min is proposed because at
573°C, is an exothermic reaction related to the allotropic transformation of quartz α to β, with the curve characteristic
type VII. Subsequently, an ideal temperature of 1,000°C was
proposed, which is where the DTA and TA curves stabilize
for the m7 mixture, where it will be maintained for 4.6 h to
guarantee the fusion of the particles and obtain at
temperatures of approximately 1,500°C, mullite phase for
blocks with refractory characteristics with better properties.
Finally, in the cooling stage, a speed of 2.3°C/min was
proposed in a time of 7.2 h approximately so that the product
does not have thermal shocks and, consequently, cracks and
deformations.
Also, the products of the ceramic industry can be classified according to several criteria, separated into two
groups: Porous paste, which is sewn at less than 1200°C, and
short pasta, which are cooked to more than 1200°C to obtain
a fusion that agglomerates all the particles of the mixture.
Because of this, it is concluded that the oven for cooking the
company does not reach a curve with which the quality of the
final product is guaranteed, using its clay soils as raw
material.
5. CONCLUSIONS
The company uses natural soils that can be considered as
useful to prepare masonry products for construction with adequate properties. Therefore, the m7 mixture selected
present good properties related to the chemical composition
due to the excellent behavior of the soil and the physical
properties such as medium quality plastic clays.
The results found in this work demonstrate the possibility
of using clay evaluated as raw material for the manufacture
of reddish colored bricks. The physical, chemical, and
thermal characterization allowed to identify an elementary
composition and the existence of crystalline phases.
Results of XRD measurements showed a sequence of
chemical and structural modifications, such as the decomposition and formation of new phases, in clay samples
subjected to thermal treatment. The components of the
samples were determined, identifying quartz in 38.1%, albite
in 13.7%, microcline in 10.3%, montmorillonite in 2.6%,
Muscovite in 19.1% and kaolinite in a 16.2%.
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:20 No:05 233
203905-4646-IJMME-IJENS © October 2020 IJENS I J E N S
From XRF, the presence of montmorillonite clays was
obtained because the chemical composition is SiO2=48-56%,
Al2O3=11-22%, MgO=0.3-0.8%, taking into account the
values for the m7 mixture of SiO2=54.743%, Al2O3=20.670, MgO=0.898, CaO=1.845, Fe2O3=6.567 y K2O=2.926, as the
most important. Also, the morphology was identified on
different surface areas of the m7 mixture by SEM-EDS and
AFM.
The thermal analyzes present information according to
the phases found; the behavior at high temperatures proved
impossible to fuse the clay at temperatures higher than
1000°C due to the characteristics of the raw material, while
at temperatures of 950°C the sintering phenomena
predominated and the integrity of the material was not
affected, validated with the ternary diagrams and the physical ceramic analysis made to the possible two optimal mixtures
found at the experimental level.
Maintain an optimal cooking curve is of great importance
to ensure the homogenization of the fusion of the particles as
well as reducing the imperfections that may occur at the time
of not reaching the temperatures established in the literature.
ACKNOWLEDGMENTS
The authors thank the Research and Extension Division
“DIE” of the Francisco de Paula Santander University Ocaña, Colombia. This work was supported by the research grand
158-08-021.
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