INCORPORATION OF QUARTZITE RESIDUE IN CERAMIC MASS … · ceramic tiles, specifically porcelain...

INCORPORATION OF QUARTZITE RESIDUE IN CERAMIC MASS FOR PORCELAIN TILE PRODUCTION

K. R. Silva1*, L. F. A. Campos2, L. N. L. Santana1

1Academic Unit of Materials Engineering, Federal University of Campina Grande

Av. Aprígio Veloso, No. 882, Bodocongo, Campina Grande, PB 58109-970, Brazil 2Department of Materials Engineering, Federal University of Paraiba

Cidade Universitária, Conj. Pres. Castelo Branco III, João Pessoa, PB 58051-900,

Brazil

*[email protected]

Abstract

The objective of this work was to evaluate the potentiality of using quartzite residue,

as an alternative raw material, in the composition of a ceramic mass used for

production of porcelain tile. Raw materials were subjected to chemical, physical and

mineralogical characterizations. Central composite design was used to analyze the

effects of firing temperature (1143, 1160, 1200, 1240 and 1257ºC) and residue

content (1.76, 3, 6, 9 and 10.24%) on the physical-mechanical properties of the

material: linear shrinkage, water absorption, apparent porosity and flexural strength.

The elevation of firing temperature levels presented a positive and statistically

significant effect on the investigated response variables. On the other hand, the

increase of the residue content had no significant effect on the studied properties.

Finally, ceramic pieces containing quartzite residue, up to 10.24 wt.%, sintered at

1240 and 1257ºC, can be classified as porcelain tile, according to the international

standard ISO 13006.

Keywords: Ceramics, Porcelain tile, Quartzite residue, Central composite design.

7th International Congress on Ceramics & 62º Congresso Brasileiro de CerâmicaJune 17-21, 2018, Foz do Iguaçu - PR - Brazil

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Introduction

The growing need for higher productivity indices in industries around all the

world has led to a decrease in available natural resources and the generation of a

large volume of waste or by-products. In this sense, the ornamental rock industry

presents itself as a major producer of solid waste, which is usually disposed in

landfills or discarded directly into the environment without previous treatment [1, 2].

Considering that many of the raw materials used in the traditional ceramic

industry derive from the decomposition of rocks, it is expected considerable

similarities between their compositions and mineral residues. It means that residues

from ornamental rock extractive activity present themselves as good substitutes for

raw materials used in the manufacture of traditional ceramics [3 – 5].

Quartzite is a metamorphic rock, composed almost entirely of quartz grains.

The techniques used in the extraction and processing of quartzite result in high

generation of residues, which are non-toxic and non-hazardous, but are classified as

non-inert. Chemically, it is composed mostly of silicon oxide (SiO2), but also of

aluminum oxide (Al2O3), calcium oxide (CaO) and alkaline oxides (K2O and Na2O)

[4, 6].

Over the past few years, the use of quartzite residue as an alternative raw

material in the manufacture of various ceramic products has been investigated [4, 6,

7]. However, the introduction of this type of residue in compositions used to produce

ceramic tiles, specifically porcelain tiles, need to be further analyzed.

Therefore, the main objective of this work was to verify the potential of using

quartzite residue, as an alternative raw material, in the composition of a ceramic

mass used for industrial production of porcelain tile. Using central composite design,

it was statistically evaluated the effects of residue content and firing temperature on

the physical-mechanical properties of the material: linear shrinkage, water

absorption, apparent porosity and 3-point flexural strength.

Materials and methods

For this work, an industrial ceramic mass for porcelain tile production and

quartzite residue were used as raw materials. The mass was supplied by a ceramic


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tiles company, and the residue was supplied by a quartzite processing unit, both

located in the State of Paraiba, Brazil.

Central composite design was used to evaluate the effect of firing temperature

(1143, 1160, 1200, 1240 and 1257ºC) and residue content (1.76, 3, 6, 9 and 10.24

wt.%) on the physical-mechanical properties of the material. Table 1 presents the

complete design matrix.

Table 1 – Central composite design matrix.

Experiment Firing temperature (oC) Residue content (%)

1 1160 3,00

2 1160 9,00

3 1240 3,00

4 1240 9,00

5 1143 6,00

6 1257 6,00

7 1200 1,76

8 1200 10,24

9 1200 6,00

10 1200 6,00

First, the quartzite residue was ground in a ball mill to reduce its particles size.

Then, the ceramic mass and the ground residue were sifted through an ABNT No.

200 sieve (0.075 mm) and subjected to chemical, mineralogical and physical

characterization by the following techniques: (a) X-ray fluorescence, using a

Shimadzu EDX-720 energy dispersive X-ray fluorescence spectrometer; (b) X-ray

diffraction, using a Shimadzu Lab XRD-6000 X-ray diffractometer equipped with a

CuKα radiation tube, operating at a 2θ scan angle of 5-40º, scan speed of 2º/min and

step size of 0,02º; (c) particle size analysis, using a Cilas 1064-LD particle size

analyzer; (d) differential thermal analysis and thermogravimetric analysis, using a TA

Instruments SDT thermal analyzer, at a maximum temperature of 1270ºC and

heating rate of 12.5ºC/min.

After complete homogenization via dry process, the mixtures had the adjust of

their moisture contents (~ 6%) for the pressing process. They were passed through


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an ABNT No. 40 sieve (0.425 mm) and then remained at rest for 24 hours.

Compositions were shaped into rectangular test specimens (20 mm x 7 mm x 60

mm) under a pressure of 50 MPa, using a Marcon MPH-30 uniaxial hydraulic press.

The specimens were oven-dried at 110ºC for 24 hours and then heat-treated in a

Flyever FE50RPN conventional electric furnace, applying a heating rate of 49oC/min

and a 2-min hold time at the maximum firing temperature. Chosen parameters for

laboratory-scale firing cycle were adapted from industry parameters.

Finally, the sintered specimens were submitted for tests of linear shrinkage,

water absorption, apparent porosity and 3-point flexural strength. The mechanical

tests were performed using a Shimadzu AG-X 10 kN universal test machine,

operating at 0.5 mm/min speed of applied force.

Results and discussion

Table 2 presents the chemical composition of the ceramic mass and quartzite

residue. As it can be seen, the ceramic mass is composed mostly of silica (SiO2) and

alumina (Al2O3), but also presents a significant amount of fluxing oxides (K2O, Na2O,

CaO, MgO, Fe2O3). The high content of SiO2 in the ceramic mass is due to the

strong presence of silicates and also to the free silica. Silica is commonly found in

several mineralogical clayey and non-clayey phases, such as kaolinite, mica,

feldspar and quartz, which corresponds to its purest natural form. Alumina is also

usually associated with some of these mineralogical phases [6]. Potassium (K2O)

and sodium (Na2O) oxides generally come from feldspars and micas, while calcium

(CaO) and magnesium (MgO) oxides may be associated with minerals such as

dolomite. The small content of iron oxide (Fe2O3) is fundamental for the production of

white ceramics, since it can develop a reddish colour in products during sintering [8].

As well as the ceramic mass, the quartzite residue is also composed mostly by silica

and alumina. The high SiO2 and Al2O3 contents are typical of ornamental

metamorphic rocks [9]. In smaller proportions, there are fluxing oxides, normally

present in quartzite residues as impurities in the form of feldspar and micaceous

mineral [9]. In general, a great similarity is observed between the chemical

compositions of both raw materials.


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Table 2 - Chemical composition of the raw materials (%).

Raw material SiO2 Al2O3 K2O CaO MgO Fe2O3 Na2O Outros

Ceramic Mass

67.75 23.82 3.28 1.48 1.08 0.62 1.35 0.62

Quartzite Residue

67.71 18.50 7.80 1.23 1.78 1.96 - 1.02

Figure 1 shows the XRD spectra of the raw materials. For the ceramic mass, it

is observed the presence of the following mineralogical phases: kaolinite (JCPDS:

89-6538), dolomite (JCPDS: 89-5862), feldspar (JCPDS: 89-8574), mica (JCPDS:

83-1808) and quartz (JCPDS: 46-1045). Kaolinite is an important component of a

ceramic mass, since it acts in the conformation favoring the workability of the

material [6]. Feldspar and mica act as fluxes, favoring the formation of the first liquid

phases during the sintering. Quartz, due to its high melting point, ensures thermal

and dimensional stability [10, 11]. For the quartzite residue, it is verified the presence

of the mineralogical phases: quartz (JCPDS: 46-1045), mica (JCPDS: 83-1808) and

microcline (JCPDS: 19-0932), which is a potassic feldspar. All minerals that were

detected in the quartzite residue are present in the raw materials used for the

manufacture of porcelain tiles, which makes possible its incorporation.

5 10 15 20 25 30 35 40

FFKKMK

QMK

QKDF

Q

K

FF

KM

2θ

M K

Q

F

Ceramic Mass

5 10 15 20 25 30 35 40

MiMi M MiMiMiMi

Mi

Mi Q QM

Q

M

2θ

M

Q

Quartzite Residue

Figure 1 - XRD spectra of the raw materials. D – Dolomite; F – Feldspar; K –

Kaolinite; M – Mica; Mi – Microcline; Q – Quartz.


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Table 3 describes the particle size distribution of the raw materials. It is

presented the average diameter and the volumetric fraction for diameters (D) below 2

µm, between 2 and 20 µm and above 20 µm. As it can be seen, the clay fraction (D <

2 µm) present in the ceramic mass is 23.06%, while the silt (2 µm < D < 20 µm) and

sand (D > 20 µm) fractions correspond respectively to 59.61 and 17.33%. In relation

to the quartzite residue, it is observed that the clay fraction corresponds to only

5.87%, while the silt and sand fractions correspond respectively to 36.27 and

57.86%. The particle size distribution of the residue is quite distant from the mass

distribution, presenting an average diameter 2.63 times higher.

Table 3 – Particle size distribution of the raw materials.

Raw Material Average

diameter (µm) D<2µm

(%)

2µm<D<20µm

(%)

D>20µm

(%)

Ceramic Mass 10.56 23.06 59.61 17.33

Quartzite Residue 27.78 5.87 36.27 57.86

Figure 2 shows the thermal analysis (TGA - thermogravimetric analysis and

DTA - differential thermal analysis) of the ceramic mass. The DTA curve presents five

endothermic peaks and two exothermic peaks. The first two endothermic peaks

occur at ~50ºC and ~160ºC and correspond to the release of the free and adsorbed

water, resulting in a mass loss of approximately 1.20 wt.%. The third peak occurs at

~512ºC and is attributed to the dehydroxylation of clay minerals present in the

sample [12], such as kaolinite, resulting in a mass loss of approximately 5 wt.%. The

discrete endothermic peak at ~576oC is associated to the polymorphic transformation

of α – β quartz [13, 14]. The last endothermic peak, at ~670ºC, possibly refers to the

dehydroxylation of mica [15, 16]. The two small exothermic peaks, at ~990ºC and

~1055ºC, correspond to the spinel formation and mullite nucleation [4, 12, 13].


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0 200 400 600 800 1000

8

6

4

2

0

Temperatura (ºC)

TG (%

)

~1.20%

~5%

-10

0

10

20

~160ºC

Ceramic Mass

~512ºC

~50ºC

DTA

(µV)

~576ºC

~670ºC

~990ºC

~1055ºC

Figure 2 – TGA and DTA of the ceramic mass for porcelain tile production.

From the experimental results observed for linear shrinkage (LS), water

absorption (WA), apparent porosity (AP) and 3-point flexural strength (FS), it was

built mathematical models correlating these dependent variables with the firing

temperature (FT) factor. The residue content (RC) factor does not appear in the

models, since it did not present statistically significant effects on the studied

variables, at 95% confidence level. The mathematical models are presented by

Equations (A) to (D).

LS (%) = - 702.1958(±153.5375) + 1.1221(FT)(±0.2560) – 0.0004(FT)2

(A)

WA (%) = 1691.7703(±160.2797) – 2.7060(FT)(±0.2673) + 0.0011(FT)2

(B)

AP (%) = 3008.1019(±317.7879) – 4.7853(FT)(±0.5300) + 0.0019(FT)2

(C)

LS (MPa) = - 445.9800(±41.1569) + 0.4095(FT)(±0.0343) (D)

The most relevant statistical parameters of the mathematical models - F-test, p-

value and coefficient of determination R2 - are presented in Table 4. As it can be

seen, all proposed models have statistical significance, at 95% confidence level,

since the p-value < 0.05 and F-test > F-table for each of them [17]. The values of R2,


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quite close to 1, indicate that the adjusted models do not present considerable

variability.

Table 4 - Relevant statistics for the analysis of variance of the mathematical models.

Variable Model F-Test F-Table p-value R2

LS Quadratic 143.49 3.35 0.00 0.91

WA Quadratic 479.64 3.35 0.00 0.97

AP Quadratic 472.41 3.35 0.00 0.97

FS Linear 142.69 4.20 0.00 0.89

Figure 3 presents the response surfaces of the variables LS (a), WA (b), AP (c)

and FS (d), obtained from Equations (1) to (4).

(a) (b)


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Figure 3 – Response surfaces of the variables LS (a), WA (b), AP (c) and FS (d).

The linear shrinkage indicates the degree of densification during sintering and is

very important for the dimensional control of the finished ceramic products [9]. In

Figure 3(a), it can be noticed that the elevation of firing temperature, from 1143 to

1257ºC, caused an increase of approximately 6% in the linear shrinkage of the

pieces. This increase was more pronounced at temperatures above 1200ºC. This

behavior is related to the sinterability of the pieces [6, 9] or, in other words, the ability

of the material in form of powder to absorb thermal energy and diffuse, favoring the

formation of liquid phase and the consequent compaction.

Water absorption is related to the microstructure of the sintered ceramic matrix

and determines the open porosity level of the pieces [13]. In Figure 3(b), it is verified

that the elevation of firing temperature caused a great decrease in the water

absorption values. The pieces sintered at 1143 and 1160ºC presented water

absorption of approximately 12 and 9%, respectively. These values indicate a high

level of porosity in the microstructure of the material. However, when the pieces were

sintered at 1200ºC, the water absorption decreased to approximately 2%. At this

temperature, the flux oxides present in the mass already are an abundant liquid

phase that, through the action of capillarity and surface tension, infiltrates the open

pores causing the densification of the ceramic bodies [6, 9, 18]. Finally, for the pieces

subjected to sintering at temperatures of 1240 and 1257ºC, water absorption values

were very close to zero. It is believed that in this temperature range the pores have

already been filled, almost completely, by the liquid phase formed during the process.

(c) (d)


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In Figure 3(c), it can be observed that the elevation of firing temperature, from

1143 to 1257ºC, caused a decrease of almost 25% in the apparent porosity of the

material. The pieces sintered at 1143 and 1160ºC presented apparent porosity

values slightly lower than 25 and 20%, respectively. However, when they were

sintered at 1200ºC, porosity decreased to approximately 5%. This behavior is due to

the mechanism of densification, previously explained [6, 9, 18]. Finally, for the pieces

subjected to sintering at temperatures of 1240 and 1257ºC, apparent porosity values

were very close to zero, which means that the maximum densification of the material

has been reached. These results are in full agreement with those for LS and WA.

In Figure 3(d), it is verified that the flexural strength of the ceramic bodies

increases linearly according to the elevation of the firing temperature. This behavior

can be attributed to the volume and morphology of the mullite formed for each firing

temperature. Studies carried out by Martín-Márquez et al. [19] suggest that the

mechanical strength of porcelain tile is related to the formation of mullite during

sintering. Specifically, the larger the mullite volume and the higher the interaction

force between its needle structures, greater will be the flexural strength of the

material. In this sense, the mechanical strength of the porcelain tiles depends on

factors that affect the volume and size of mullite structures, such as the firing

temperature [20]. Martín-Márquez et al. [19] also show that the elevation of flexural

strength of porcelain tiles is related to the reduction of their porosity.

Conclusions

Quartzite residue has adequate chemical and mineralogical properties so that it

can be incorporated in a industrial ceramic mass for porcelain tile production.

According to the international standard ISO 13006 (1998), porcelain tiles are

ceramic tiles with water absorption equal to or less than 0.5% (WA ≤ 0,5%) and

flexural strength equal to or greater than 35 MPa (FS ≥ 35 MPa). Thus, in the present

study, pieces containing up to 10.24 wt.% of quartzite residue, which were sintered at

1240ºC and 1257ºC, can be classified as porcelain tiles.

The results showed that the use of quartzite residue as an alternative raw

material in a ceramic mass for porcelain tile production is a sustainable solution for


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this type of waste, bringing many benefits to the environment, to the industry and

also to the population.

Acknowledgments

Authors acknowledge financial support received from CAPES and CNPq (proc.

447881/2014-0 and 308912/2016-0), Brazil.

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