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:

ragarcial@ufpso.edu.co 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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