Kağan Kayacı (a), Ş. Can Genç (a,b), Yıldız Yıldırım (a), Aykut Keskin (a) (a) Kaleseramik, R&D Center, Çan, Çanakkale (b) Istanbul Technical University, Geology Department, Maslak, Istanbul email@example.com
Porcelain tiles are inorganic finishing materials that are starting to become prominent in our houses (both indoor and outdoor) in recent years. This group of tiles can be produced both glazed and unglazed, and in very large sizes (1.2 x 3.6 m) thanks to the developing technology. In this study, the usage possibilities of some feldspar resources especially granites in Biga and its vicinity in North West Anatolia, in porcelain tile bodies from 10 % to 40 % were investigated.
Geologically Biga peninsula has been scene of magmatic activities between 50 and 15 million years. The main products of these activities can be listed as granites, acidic and intermediate composition volcanic rocks. Of these, especially Oligo-Miocene aged granites are sometimes represented by light colored facies and pegmatites that do not contain dark colored minerals. While pegmatites are characterized by potassium-feldspars, granites are rich in sodiumfeldspar, potassium-feldspar and quartz. First chemical and minarelogical analyzes of granites which were considered to be used in porcelain tile bodies were conducted, later their technological properties were determined by firing at standard albite and potassium feldspar sources with porcelain tile firing temperatures (1200 ° C, 56 min.). In the light of these data, by adding 10 %, 20 %, 30 % and 40 % to the porcelain tile body, the bulk density of the bodies after firing, firing shrinkage (%), water absorption (%), firing strength (N / mm2) and L, a, b values were determined, and comparisons were made with the standard porcelain tile body accordingly. The sintering behaviors of the studied tile bodies were determined with a contactless dilatometer and phase analyzes were determined with XRD (X-ray diffraction). Microstructural investigations of all bodies were done with SEM (scanning electron microscope). As a result, it has been observed that the light colored granites of the Biga peninsula are good smelters and exhibit potential for use in porcelain tile bodiess.
Keywords: Porcelain tile, granite, additive, sintering, firing, microstructure
Along with glazed and unglazed, depending on technological developments, thin (3 mm) and very large sizes (1.2 x 3.6 m) have been started to be produced in recent years. Thanks to these features, they find use in composite form with some building materials both indoors and outdoors. With the development of decoration technologies in recent years, porcelain tiles are reaching new markets and new buyers with the advantages of rich texture, color and pattern diversity, aesthetic appearance, durability and sustainability, and their usage is increasing day by day.
By 2018, Turkey’s ceramic floor and wall tile production figure reached approximately 335 million m2, which corresponded to 6.3 million tonnes of raw materials. Considering that feldspar constituted approximately 40% of the said amount, it is understood that the annual feldspar demand was around 2.5 million tonnes. Feldspars needs of Turkish ceramic producers are met from Aydın-Milas-Çine region in Western Anatolia. Considering that in addition to the 2.5 million tonnes requirement, 6 million tonnes of exports were made from the region in 2018 (IMMIB, 2019), we can see that feldspar consumption has reached huge levels.
An important part of Turkish ceramic tile production has been established in Bilecik-Söğüt, Eskişehir-Bozüyük, Kütahya and Afyon Regions, along with İzmir and its immediate surroundings and Çan-Çanakkale regions. Almost all ceramic factories producing porcelain tiles in our country supply sodium feldspar from Çine-Aydın Region. Due to the increase in energy (electricity, natural gas) inputs, as well as high freight expenses, ceramic producers have sought to seek local and low-cost alternative raw materials. In this context, Çanakkale Ceramic Group has carried out a field and laboratory project to investigate the possibilities of using local smelting raw materials as a feldspar alternative. One part of the project is the geological characteristics, mineralogical-petrographic suitability and availability of reserve conditions of granitic rocks which are potential smelting raw material alternatives; the other part of the study has been planned to investigate their chemical, thermal and other technological properties on a laboratory scale. The project outputs revealed that some granitic rocks in the Biga peninsula are inconvenient due to their dense mafic mineral content, while others have the feature of alkali-melting raw materials, alternative to feldspar.
Many researchers have previously supported alternative sources that can be used instead of sodium feldspar with some studies. (Kayacı and Genç 2009, Dias et al. 2017; Dondi, 2018). These materials are generally of acidic composition, high silica, alumina and alkali content, igneous rocks such as low iron oxide, titanium oxide and alkaline earth granite, volcanic rocks such as syenite, ingneous rocks such as as dacite, rhyolite and their pyroclastic equivalents. Related rocks tend to be smelting materials with partially high alkaline contents (Kingery and Bowen, 1976; Enrique et al. 1985; Klein, 2001; Sacmi, 2005; Salmang et al. 2007; Dias et al. 2017; Dondi, 2018; Zanelli et al. 2018). The low Fe2O3 and TiO2 content provides a light (high L value) firing color for ceramic bodies. Therefore, it can be used instead of traditional feldspars.
2. GEOLOGICAL SITUATION
There are two major geological units on the Biga peninsula. The first of these is Triassic and older metamorphic rocks, and the other is the Jura-Quaternary aged sedimentary and volcanic rocks, which are the top cover of this foundation. In the Eocene-Miocene range, a severe magmatic activity took place in the region and formed mainly plutonic / depth magma rocks and their surface equivalents (Genç, 1998; Yılmaz et al. 2001; Ersoy et al. 2017) (Figure 1). Oligo-Miocene old plutonic rocks from igneous rocks constitute the main subject of this study. These granitic rocks, whose locations are shown in Figure 1, are epizonal bodies located in shallow depths (~ 5 km) in the shell. Volcanic rocks developed in relation to plutonic/depth rocks are mainly acidic and intermediate rocks. All of these igneous rocks were formed in NW Turkey during the tensiontectonic regime that occurred between the late Oligocene-early Miocene (Okay and Satır, 2000).
Figure 1. Distribution of Oligo-Miocene old plutonic rocks in the Biga peninsula (red areas; Simplified from Ersoy et al. 2017) and map showing the locations of the granitic rocks that are the subject of this study (green stars).
3. MATERIAL AND METHOD
A total of 30 samples from Biga Peninsula granites and pegmatitic rocks were collected and analyzed in the laboratory. All experiments except electron microscopy (SEM-EDX) were carried out in the R&D Center Laboratories of Çanakkale Seramik Company. Samples were dried in the oven for 6 hours at 105 ° C before the characterization processes and milled smaller than 63µm. Chemical compositions of raw materials were analyzed by X-ray fluorescence spectrometry (XRF, Panalytical Axios). For structural analysis, Panalytical X’Pert Pro MPD diffractometer (XRD) CuKα (1.5406 ° A) radiation and X’Celerator detector were used. X-Ray diffractions scanned between 0.02 ° increments and 3-70 ° 2α were evaluated using the peak identifier and auto-match features of the High Score Plus (v.4.6) program. Quantitative mineralogical analyzes were done with the Rietveld and Reference Intensity Ratio (R.I.R) method (Young, 1995). Thermal analyzes were carried out with Seteram Labsys Brand Evo Model STA device by heating up to 1200 ° C with a heating rate of 10 ° C / min.
Technological tests were conducted on the samples to investigate their sintering behavior. After the rocks were grinded under porcelain tile conditions in the laboratory, they were turned into granules by filtering with a sieve with an interval of 0.500 mm, giving 6% moisture. Then the granules were shaped as 5 cm diameter tablets with 325 kg/cm2 press pressure. The tablets were then dried and fired in an industrial oven at 1200 ° C peak temperature for 56 minutes. After firing, water absorption (ISO 10545-3), cooking shrinkage (ISO 105452) and post-firing color values were measured with Minolta 3600 d Colorimeter device.
Instead of albite, new body recipes were created by using different granites and pegmatites at the values of 10, 20, 30 and 40%. Technological properties such as water absorption, shrinkage and color (L, a, b) values were determined after firing these recipe mixes. In addition to the double-camera non-contact dilatometry Misura ODHT HSM 1600/80 (Expert SystemSolutions, Italy) brand and model for the detection of sintering behaviors, new phases occurring in fired bodies and research of developing new microbodies, XRD and Zeiss Supra 50 VP brand scanning electron microscopy (SEM-EDX) devices were used.
4. FINDINGS AND DISCUSSION
4.1 RAW MATERIAL CHARACTERIZATION (PETROGRAPHY, XRD, XRF, HEAT MICROSCOPE)
Biga peninsula Oligo-Miocene granites consist of a series of plutonic / depth magma rocks. Some of these are granite and granodiorites containing biotite and hornblende, and their high content of dark minerals (mica and amphibole), as well as high iron and magnesium content cause some problems for ceramic production. In contrast, light colored granitic rocks (leucogranites) with little or no mafic mineral content are suitable for ceramic production. Accordingly, this study is focused on such light colored granites and some pegmatites. In Figure 2, light colored granites and pegmatites are classified in Streckeisen (1967) and TAS (Total Alkali versus Silica; Le Bas et al. 1986) diagrams combined with each other. As can be seen from the figure, the samples are classified in different areas from monzonite to granite. Rarely, they are classified in the granodiorite region. The silica diagram (TAS) versus total alkalis also confirms this classification (Figure 2). The main mineral composition of the samples examined is Quartz + K-Feldspar + Plagioclase (albite - oligoclase) ± microcline ± mica. They are defined in usual textural terms as leukogranite, granofir, aplogranite, aplite and pegmatite.
Figure 2. Classification of granites and pegmatites of Biga peninsula, mineralogical (QAP; Streckeisen, 1967 diagram) and chemical (Total AlkaliSilica diagram; Le Bas et al. 1986).
In addition to petrographic (QAP) and chemical (XRF, TAS) classifications, samples were analyzed mineralogically with XRD. XRD results showed that there are fewer muscovite-like mica and chlorite in addition to orthoclase (K-Feldspar) and albite (Na-Feldspar) (Figure 3). The results of the chemical (XRF) and XRD analysis are summarized in Table 1.
Figure 3. XRD analysis results of Karadoru, Soğucak, Namazgah granite and Sazoba pegmatite (M: Mica, Ch: Chlorite, Ort: Orthoclase, Q: Quartz, Alb: Albite).
Table 1. Chemical (XRF) and modal mineralogical (XRD, Rietveld) analysis results of Biga peninsula granites and pegmatites (Q: Quartz, Or: Orthoclase, Alb: Albite, Musc: Muscovite, Il: Illite, Chl: Chlorite, Mica: unseperated mica) (AK: Fire loss).
All the raw materials examined were fired in industrial ovens in order to reveal the water absorption, shrinkage and color qualities. The results are given in Table 2. Accordingly, Soğucak granite has the highest shrinkage rate with 6% and lowest water absorption rate with 5.34%. Water absorption values of Karadoru, Namazgah granites and Sabzoba pegmatite ranged between 15.38-18.51% and shrinkage rate between 2.37-3.23%.
Table 2. Technological properties of Biga Peninsula granitic rocks
In order to test the smelting of Aydın-Çine albite and Biga peninsula alternative raw materials, heat microscopy experiments were conducted on the samples. As a result, the closest sintering point to albite was seen in Sazoba pegmatite at 1235 ° C. After Sazoba pegmatite, Soğucak granite shows 1240 ° C, Namazgah granite 1245 ° C and Karadoru granite shows the highest value with 1260 ° C. A difference of 40 ° C was observed between the minimum sintering (Albite: 1220 ° C) and the maximum sintering point (Karadoru granite: 1260 ° C) (Figure 4).
Figure 4. Aydın-Çine sodium feldspar and Biga peninsula granite and pegmatites thermal microscopic behavior.
4.2 STRUCTURE FORMATIONS
During the body development activities, Istanbul Şile clay, Çanakkale kaolinite and fired fracture values were kept constant. In the recipes of the bodies, new compositions were obtained by using granitic rocks in different proportions instead of AydınÇine albite (Table 3).
According to the recipe values created, the raw materials were weighed by calculating the moisture values. The raw material mixtures were milled with the addition of water and 0.8% sodium silicate in laboratory-type ball mills until the 45 µm sieve balance reached 2-2.5%. The density (g / lt) and sieve balance (+45 µm) of the muds obtained were measured and later they were dried at 110 ° C in a laboratory type kiln. For the pressing process, the dried muds were ground into mortar and powdered into granules and dampened up to 5-6%. The granules prepared to obtain a homogeneous moisture distribution were kept for a day. These samples were formed by pressing the granules at 50x50 mm dimensions with 400 kg / cm2 pressure and dried in a kiln at 110 ° C for 1 hour. These samples were sintered at the Kaleseramik Granite Factory at 1200 ° C for 56 minutes of firing time.
Table 3. Porcelain tile body recipes prepared with Soğucak (S), Karadoru (K), Namazgah granites (N) and Sazoba pegmatite (P) (Std: Standard Structure).
4.3 TECHNOLOGICAL CHARACTERISTICS
As a result of firing different recipes, it was observed that no significant incompatibility occurred in the ceramic tile formulation by adding the Biga peninsula granites and pegmatites. It has been determined that the water absorption and shrinkage values required for porcelain tiles are close to the standard in the areas where Soğucak and Namazgah granites and Sazoba pegmatites are used by 20% and Karadoru granite is used by 10%. However, when these materials are used above 20% instead of albite, water absorption values increased and shrinkage decreased visibly. With the increase in the usage rate of granites and pegmatites of Biga peninsula, an increase in color values (whitening) was observed. (Table 4.)
Table 4. Firing characteristics of porcelain tiles prepared with different ratios of alkaline raw material (granite and pegmatite) (maximum firing temperature is 1200 °C, and firing time is 56 min.) (STD: standard structure , S: Soğucak granite, K: Karadoru granite, N: Namazgah granite, P: Sazoba pegmatite; 10, 20, 30, 40: % shows usage values).
Non-contact dilatometry analyzes were carried out on the 16 new recipes prepared, the maximum degree of sintering rate (Flex point) and expansion value were determined as 1202 ° C / -3.77 (%) especially for the K-40 formulation. The minimum sintering rate and expansion values were determined as 1176 ° C / -3.02 (%) for the P-20 recipe. The results of the analysis revealed that the increase of granitic raw material ratios used as an alternative to Na-feldspar and the temperature values at the maximum sintering points show an increase trend (Table 5).
Table 5. Sintering behavior of different body formulations (values of standard porcelain tile: flex: 1169 ° C, expansion: -3.25%).
4.4 PHASE AND MICROSTRUCTURE ANALYSIS
XRD and electron microscopy (SEM-EDX) methods were used to examine the phases developed in different formulations cooked in a laboratory environment. XRD analysis on the baked bodies revealed the presence of a small amount of newly crystallized mulite phases with residual quartz, albite and orthoclase (Figure 5).
Albite phase is prevalent in the structure as residual phase. Since porcelain tile bodies are fired in fast firing cycles, some of the albite phase remains unmelted after firing (Esposito et al. 2005, Küçüker 2009, Xian et al. 2015). A decrease in albite phase has been observed with the increase of different granite sources. When the comparative XRD patterns of K-10, S-20, N-20 and P-20 bodies, especially the ones in which granite and pegmatites were used instead of sodium feldspar, are examined, a significant decrease in the peak intensity of the albite phase is clearly observed. Using granites with a 20% ratio has especially increased the sintering of the bodies. This increase in sintering caused more albite phase smelting in these bodies, reducing the amount of residual albite phases. In higher rates of granite and pegmatite use (30% and 40%), the quartz peak intensity increased, which caused the water absorption values to rise above 0.5%, especially in the bodies. There was no significant difference observed in the mullite phase quantity that developed in the bodies. In the porcelain tile body composition, the glassy phase formation limit is located in the mullite phases. Therefore, the excess alumina in the structure crystallizes into mullite from glassy structure. In these bodies, two types of properties develop; primary and secondary.
Figure 5. XRD analysis and the determined mineral phases of the prepared recipes and standard fired bodies (M: mullite, Q: Quartz, Alb: Albite, Ort: Orthoclase).
SEM-EDX analysis performed in granite/pegmatite bodies prepared as an alternative to standard porcelain body with albite content showed the presence of newly developed mullite phases together with residual feldspar and quartz (Figure 6a-f), and the data supported XRD results. In addition, in the SEM-EDX analysis of the body prepared with Soğucak granite, a small amount of anortite development was observed in addition to the phases mentioned above (6d).
Figure 6 a-f. Phases determined by SEM-EDX analysis in bodies prepared with standard porcelain body (a, b), Karadoru (c), Soğucak (d) and Namazgah (e) granites, along with Sazoba pegmatite (f) (In (d), the spherical phases in the central part of the image are anortic).
As a result of the findings obtained in the researches, Biga granite and pegmatites can be used as alternative resources for porcelain tile production in certain ratios and conditions instead of Na-feldspar (albite). The use of these and similar local raw materials will reduce the high freight expenses from AydınÇine-Milas region. In addition, these raw materials will be an alternative to feldspar resources that are consumed rapidly and will increase the use of raw materials that are idle in local areas.
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