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1 IntroductionQuite a number of extensive studies have been carried out on porcelain, a family of ceramic materials composed essentially of clay, feldspar and quartz, hence the name triaxial whitewares [1−6]. The triaxial com-position usually consists of 50 mass-% fine-grained clay called kaolin (Al2O3∙2SiO2∙2H2O); 25 mass-% flux as feldspar (K2O∙Al2O3∙6SiO2) and 25 mass-% filler as quartz (SiO2). The progression of the microstructure of porce-

lains to their final state is identified in that the clay provides plasticity, allowing easy shape formation as well as a binder for other components when in the green state [7]. Kaolin clay is very elastic and strong so that it holds the shape of the object during fir-ing. The quartz is to provide the mechani-cal strength while the feldspar is the fluxing material for porcelain [2]. A key advantage of porcelain is its chemical stability, and hence it provides excellent aesthetics that do not deteriorate with time as well as high compressive strength with good electrical insulating properties [8−9].Glass makes up a large component of house-hold and industrial waste and with this high generation, there is need for alternatives to the recycling option for cullet. The glass component in municipal waste is usually

made up of bottles and broken glassware, and compounding this waste problem is the fact that many manual methods of creating glass objects have a defect rate of forty per-cent, thereby increasing the percentage composition of cullet in the environment [10]. Approximately 13 million tons of glass waste is generated annually, and while food and beverage containers make up over 90 % of this amount the remaining 10 % comes from products like cookware and glassware, home furnishings and plate glass [11−12]. Glass is seen as a unique inert material that could be recycled many times without changing its chemical properties. The effi-ciency of this process depends on the meth-od of collecting and sorting glass of differ-ent colours (clear, green and amber) and has found use as aggregates for concrete [13−15].

1 Depart.ofIndustrialChemistry,CollegeofScienceandTechnology,CovenantUniversity,P.M.B.1023Ota(Nigeria)

2 RefractoryDivision,CSIR-CentralGlass&CeramicResearchInstitute,196RajaS.C.MullickRoad,Kolkata700032(India)

A.K. Oluseyi1, 2, M. Atul2, S.K. Das2

Effect of Substitution of Soda-Lime Scrap Glass for K-Feldspar in Triaxial Porcelain Ceramic Mix

Thestudywasdirectedtowardsutilizationofrecurrentlygeneratedsoda-limescrapglassandabundantlyavailableriversand,inaporcelainceramicmixbyreplacingK-feldsparandquartzfromstandardtriaxialporcelainbody(kaolin-quartz-feldspar).Fourbatchcompositionswerepreparedutilizingscrapglassintherangeof13−25mass-%,kaolinat50mass-%,feldsparat12−25mass-%andsandat20−25mass-%.The compactgreen sampleswereheated in the temperature rangeof1050–1250°C.Thephysico-mechanicalpropertiesi.e.linearshrinkage,bulkdensity,waterabsorption,apparentporosityandflexu-ralstrengthoftheheatedsamplesweredeterminedasperstandardtechniques.Thevariousphasesdevelopedinthevitrifiedsamplesandcrystalmorphologywereanalyzedbyx-raydiffractometryandScanningElectronMicroscopyrespectively.Re-sultsshowthatpartialreplacementofK-feldsparbysoda-limeglassscrapintriaxialporcelainmixbodywasfoundtobemorebeneficialthanitscompletereplacement,asthesampleswerevitrifiedat lowertemperature(~1200°C) incomparisontostandardK-feldsparcontainingporcelain(~1250°C).

The main author, Dr. Ajanaku Kolawole Oluseyi, is afacultymemberintheDepartmentofChemistry,CollegeofScienceandTechnology,CovenantUniversity,Canaan-land,Ota,Nigeria.HegainedaB.Sc., anM.Sc. andaPh.D.inIndustrialChemistryandhasbeenteachingIn-dustrialChemistryfor thepast18years.Recently,hewon the 2011 CSIR-TWAS Postdoctoral FellowshipAward for his research on “Development of Ceramic

MatrixCompositeforStructuralApplicationusingIndustrialWastes”.HejoinedtheCentralGlassandCeramicResearchInstitute,Refractorydivi-sionin2012andworkedunderthesupervisionofDr.SwapanKumarDas(ChiefScientist).Hisresearchinterestsincludewasteandenergymateri-als’managementaswellasmetal-environmentalimpactassessmentandcorrosionprevention.

Thecorrespondingauthor,Dr. Swapan Kumar Das,(Ph.D.inCeramicEngi-neering),hastotal33yearsofbasicandappliedresearchexperienceinthefieldoftraditionalceramic,refractoriesandwasteincorporationinceramiccomposition. Presently he is holding the post of Chief scientist at CSIR(CentralGlassandCeramicResearchInstitute),Kolkata(India).E-Mail: swapan@cgcri.res.in

The auThors

absTracT

glasscomposites,wasteglass,vitrifica-tion,porcelain,mulliteINTERCERAM62(2013)[4]

Keywords

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maximum for AP and ±0.5 to ±2.0 for flex-ural strength. It may be observed from Fig. 1a that the linear shrinkage increases with an increase in heating temperature for all compositions as it is commonly observed in normal triaxial porcelain systems. Be-tween 1200–1250 °C, the shrinkage values for glass cullet containing bodies are almost constant while AK-1, without glass cullet, shows some further increase in shrinkage at 1250 °C. The combined fluxing effect of alkaline earth oxides and alkali minerals in glass cullet bodies is reflected more at lower temperatures of heating towards shrinkage. The glass cullet containing bodies (AK-2, AK-3 and AK-4) showed higher shrinkage in the temperature range of 1050–1150 °C than the sample containing only K-(AK-1). Normal porcelain (AK-1) achieved the highest bulk density (2.44 g/cm3) at its vit-rification temperature (Fig. 1b). This is due to the difference in density of glass cullet (2.50 g/cm3) and feldspar (2.60 g/cm3) min-erals used in this study. The bulk density of

Fig. 1 (a) • Variation in linear shrinkage of experimental samples in relation to heating temperature, (b): variation in bulk density of experimental samples

in relation to heating temperature, (c): variation in apparent porosity of experimental samples in relation to heating temperature, (d): variation in flexural

strength of experimental samples in relation to heating temperature

1However, an interest in reformulating the body compositional mix of partial replace-ment of one of the natural raw materials with a readily available waste material in ceramic body becomes essential. Tucci and Esposito et. al. [16] studied the feasibility of using soda-lime scrap glass to the extent of 5−20 mass-% by replacing the same amount of Na-feldspar in a porcelain stoneware tile mix. The authors found a considerable de-crease in firing temperature and an increase in mechanical resistance. This process, being one of the concepts of zero emissions re-search and initiatives, has not been fully ex-ploited. In this paper, an attempt has been made to incorporate soda-lime scrap glasses in normal porcelain composition by replac-ing a part of K-feldspar, and to study the effect on physical, mechanical, phase evolu-tion and microstructural changes during heating.

2 Experimental Glass cullet and river sand were obtained from the inter-source of CGCRI, Kolkata; kaolin from Rajmahal, Bihar; and potash feldspar from Hyderabad A.P. in order to

prepare the batch compositions. The glass cullet used was pulverized in a high-energy ball milling system for 8 h at room tempera-ture. The milling speed was at 80 rpm with grinding media and a charge weight ratio of 2 : 1. The resulting powder was sieved through 100 mesh BS size and the sample was analyzed for its chemical composition. One kilogram each of four batches as per the composition provided in Table 1 were wet milled in a pot mill for 5 h. The milled mixtures in the form of slurry were passed through 100 mesh BS sieve. The resulting mixture was dried at 110 °C ± 5 K over-night using a laboratory oven, ground and passed through 60 mesh BS sieve. The dried mixture was thoroughly mixed with 10 % water and uniaxially compacted to 65 × 10 × 10 mm size dimension samples at ~400 kgcm–2 pressure using a Carver Labo-ratory press Model M. The compressed samples were first air-dried for 24 h fol-lowed by complete drying in oven at 110 °C ± 5 K for 12 h. The dried samples were then heated in the temperature range of 1050−1250 °C in an electrically operated high temperature furnace. The heating rate

from room temperature to 800 °C was 5 K/min and then 3 K/min from 800 °C to the desirable temperatures for a soaking time of 30 min. The samples were first char-acterized with respect to their linear shrink-age (LS), bulk density (BD) and apparent porosity (AP) by standard a technique and flexural strength using an Instron-UTN 5500 R instrument coupled with blue hill software. The results reported here are the average of three samples. The polished 1250 °C heated vitrified sam-ples were used for morphological study. The polished samples were etched using 10 % HF solution for one minute, washed in water and acetone and subsequently coated with carbon to make the surface conduct-ing. The microstructural study was done by field emission scanning electron microscopy (FESEM), for which the images were taken with the help of a Gemini Zeiss Supra TM 35VP Model. The XRD pattern of the finely ground vitrified powdered was done using a Philips diffractometer (Model PW 1730) using nickel filtered CuKα radiation and a pattern recorded over a Braggs’ angle (2 θ) range of 5–70. Weight percentages of crys-talline phases were estimated for the selec-tive samples from X-ray diffraction line profile analysis with the Rietveld method [17–18] by “X” pert high score plus software (pAnalytical) [19].

3 Results and discussion3.1 Raw materialsThe chemical analysis of all the raw materi-als used in this study is provided in Table 2. It may be observed that kaolin and feldspar is of a common type used to make normal triaxial porcelain bodies. Glass cullet be-longs to the soda-lime-silica glass contain-ing 13.75 mass-% Na2O, 10.57 mass-% CaO and 69.55 mass-% SiO2. Hence, the com-bined fluxing effect of Na2O and CaO on vitrification of mix porcelain body is inter-esting to study with or without K-feldspar. River sand is relatively impure compared to quartz as it contains 4.31 mass-% of Al2O3, which may be beneficial to porcelain body, however the presence of Fe2O3 may impart some colour to the body. The oxide compo-sition of the experimental bodies is summa-rized in Table 3.

3.2 Physical and mechanical properties of fired test piecesThe behaviour of the linear shrinkage (LS), bulk density (BD), apparent porosity (AP) and flexural strength as a function of tem-perature are illustrated Fig. 1a−d respec-tively. The standard deviation is ±0.18 maxi-mum for LS, ±0.02 maximum for BD, ±0.80

Table 1 • Batch composition (mass-%)

Raw materials/blendAK-1

(standard)AK-2 AK-3 AK-4

Kaolin 50 50 50 50

Riversand 25 25 25 20

Feldspar 25 Nil 12 15

Scrapglass Nil 25 13 15

Table 2 • Chemical composition of raw materials used in the study

ConstituentsComposition / mass-%

Kaolin K-Feldspar Scrap glass River sandSiO2 55.90 66.81 69.55 89.50

Al2O3 30.28 18.08 1.42 4.31

Fe2O3 0.71 0.24 0.21 2.28

TiO2 0.86 – 0.13 0.18

CaO 0.13 1.03 10.57 0.71

MgO 0.07 0.23 3.53 0.49

Na2O 0.25 10.94 13.75 0.27

K2O 0.09 1.69 0.47 1.07

L.O.I.* 11.28 0.54 – 0.60

* Lossonignition

Table 3 • Oxide composition of the experimental bodiesConstituents / mass-% AK-1 AK-2 AK-3 AK-4SiO2 67.03 67.72 67.28 66.30

Al2O3 20.74 16.57 18.57 18.93

Fe2O3 0.99 0.98 0.98 0.88

TiO2 0.48 0.51 0.49 0.49

(CaO+MgO) 0.72 3.93 2.38 2.64

(K2O+Na2O) 3.67 4.06 3.87 4.47

LOI 5.93 5.79 5.85 5.84

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maximum for AP and ±0.5 to ±2.0 for flex-ural strength. It may be observed from Fig. 1a that the linear shrinkage increases with an increase in heating temperature for all compositions as it is commonly observed in normal triaxial porcelain systems. Be-tween 1200–1250 °C, the shrinkage values for glass cullet containing bodies are almost constant while AK-1, without glass cullet, shows some further increase in shrinkage at 1250 °C. The combined fluxing effect of alkaline earth oxides and alkali minerals in glass cullet bodies is reflected more at lower temperatures of heating towards shrinkage. The glass cullet containing bodies (AK-2, AK-3 and AK-4) showed higher shrinkage in the temperature range of 1050–1150 °C than the sample containing only K-(AK-1). Normal porcelain (AK-1) achieved the highest bulk density (2.44 g/cm3) at its vit-rification temperature (Fig. 1b). This is due to the difference in density of glass cullet (2.50 g/cm3) and feldspar (2.60 g/cm3) min-erals used in this study. The bulk density of

the glass cullet containing bodies varies in the range of 2.25 to 2.35 g/cm3. Full replace-ment of feldspar by glass cullet (AK-2) achieved the lowest density (2.25 g/cm3) compared to part replacement for the same reason as explained above depending upon the proportion of glass cullet and feldspar. Another phenomenon is observed in AK-3 and AK-4 with glass cullet and feldspar mix, which showed a decrease in bulk density at 1250 °C, while AK-1 and AK-2 follow the trend of an increase in density with heating temperature unttil vitrification occurs. More of the glassy phase formation in AK-3 and AK-4 at 1250 °C due to the combined pres-ence of glass cullet and feldspar mix is prob-ably the reason for this decrease in density. Figure 1c represents the variation in appar-ent porosity with an increase in heating temperature. As normally observed, the po-rosity decreased with an increase in heating temperature. However, it may be interesting to note that AK-3 and AK-4 (mix of glass cullet and feldspar) achieved less than 5 %

porosity at 1200 °C, while samples AK-1 with only feldspar and AK-2 with only glass cullet possess around 8 % porosity at this temperature. This observation implies the effectiveness of soda-lime scrap glass and K-feldspar mix in achieving the vitrification of porcelain samples, unlike the observation of Tucci et. al. [16] that an increase in the percentage of soda-lime cullet caused a general increase in porosity in porcelain materials. From Fig. 1d, it may be observed that there is not much variation in flexural strength value between samples. All the vitrified samples possess flexural strength between 50−55 mPa. Full or partial substitution of feldspar in the triaxial porcelain composi-tion did not deteriorate the strength, which is one of the prime requirements of such products. In fact, AK-2 (full replacement of feldspar) showed the highest strength (ap-proximately 55 mPa) compared to the full feldspar containing body (approximately 50 mPa).

Fig. 1 (a) • Variation in linear shrinkage of experimental samples in relation to heating temperature, (b): variation in bulk density of experimental samples

in relation to heating temperature, (c): variation in apparent porosity of experimental samples in relation to heating temperature, (d): variation in flexural

strength of experimental samples in relation to heating temperature

1from room temperature to 800 °C was 5 K/min and then 3 K/min from 800 °C to the desirable temperatures for a soaking time of 30 min. The samples were first char-acterized with respect to their linear shrink-age (LS), bulk density (BD) and apparent porosity (AP) by standard a technique and flexural strength using an Instron-UTN 5500 R instrument coupled with blue hill software. The results reported here are the average of three samples. The polished 1250 °C heated vitrified sam-ples were used for morphological study. The polished samples were etched using 10 % HF solution for one minute, washed in water and acetone and subsequently coated with carbon to make the surface conduct-ing. The microstructural study was done by field emission scanning electron microscopy (FESEM), for which the images were taken with the help of a Gemini Zeiss Supra TM 35VP Model. The XRD pattern of the finely ground vitrified powdered was done using a Philips diffractometer (Model PW 1730) using nickel filtered CuKα radiation and a pattern recorded over a Braggs’ angle (2 θ) range of 5–70. Weight percentages of crys-talline phases were estimated for the selec-tive samples from X-ray diffraction line profile analysis with the Rietveld method [17–18] by “X” pert high score plus software (pAnalytical) [19].

3 Results and discussion3.1 Raw materialsThe chemical analysis of all the raw materi-als used in this study is provided in Table 2. It may be observed that kaolin and feldspar is of a common type used to make normal triaxial porcelain bodies. Glass cullet be-longs to the soda-lime-silica glass contain-ing 13.75 mass-% Na2O, 10.57 mass-% CaO and 69.55 mass-% SiO2. Hence, the com-bined fluxing effect of Na2O and CaO on vitrification of mix porcelain body is inter-esting to study with or without K-feldspar. River sand is relatively impure compared to quartz as it contains 4.31 mass-% of Al2O3, which may be beneficial to porcelain body, however the presence of Fe2O3 may impart some colour to the body. The oxide compo-sition of the experimental bodies is summa-rized in Table 3.

3.2 Physical and mechanical properties of fired test piecesThe behaviour of the linear shrinkage (LS), bulk density (BD), apparent porosity (AP) and flexural strength as a function of tem-perature are illustrated Fig. 1a−d respec-tively. The standard deviation is ±0.18 maxi-mum for LS, ±0.02 maximum for BD, ±0.80

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4 ConclusionsThe present investigation widens the scope of utilizing soda-lime scrap and abundantly available river sand as a fluxing agent in kaolin-quartz-feldspar bound triaxial por-celain. The results showed that the replace-ment of 15 mass-% of K-feldspar by soda-lime scrap has decreased the firing temper-ature considerably. The presence of well- developed needle-shaped mullite crystals support higher strength. The densification was not detrimentally affected by the blend, rather the introduction of the waste glass led to the formation of new phases in the non-equilibrum microstructure of porcelain stoneware.

AcknowledgementsThe authors are very grateful to CSIR-TWAS for the fellowship support and also to the Director, CSIR-Central Glass & Ceramic Research Institute, for the equipment and laboratory support for this work.

References [1] Kamseu, E., Leonelli, C., Boccaccini, D.N., Veronesi,

P., Miselli P., Pellacani G., Chinje Melo, U.:Charac-terizationofporcelaincompositionsusingtwochi-na clays fromCameroon. Ceram. Inter.33 (2007)851−852

[2] Carty, W.M., Senapati, U.:Porcelain-rawmaterial,processing, phase evolution, and mechanical be-haviour.J.Am.Ceram.Soc.81(1998) [1]3−20

[3] Klein, A.A.:Constitutionandmicrostructureofpor-celain. National Bureau of Standards Tech. PaperNo.3–38,1916–1917

[4] Rado, P.:Thestrangecaseofhardporcelain.Trans.andJ.Brit.Ceram.Soc.70(1971)131–39

[5] Vazquez, S.B., Velazquez, J.C.M., Gasga, J.R.:Alu-minaadditionsaffectelasticpropertiesofelectricalporcelains. Bull. Am. Ceram. Soc. 77 (1998) [4]81–85

Fig. 6 • (a) Microstructure of etched AK-4 fired at 1250 °C, (b): microstructure from the same sample

showing the mullite crystals formed

(b)(a)

5 µm 1 µm

3.3 XRD AnalysisFrom the XRD pattern (Fig. 2), it may be observed that the crystalline phases present in all the vitrified samples are mainly quartz and mullite with the dominant phase being quartz. The mullite formation signifies the vitrification of the samples during firing. The X-ray diffraction pattern of the samples containing soda-lime scrap glass indicated the formation of a new phase, cristobalite, at position 23 (2 θ) which is absent in the

AK-1 sample. The highest amount of cristo-balite was observed in the batch containing largest amount of glass waste (AK-2). The relative intensity of this peak is different than that obtained in AK-3 and AK-4. The presence of more CaO in AK-2 might have acted as a mineralizer and converted a part of the quartz into cristobalite. The mass percentage of crystalline and glassy phases of AK-1 and AK-2 are provided in Table 4.

3.4 SEM/EDX microstructure analysisThe microstructures of the samples fired at 1250 °C are presented in Fig. 3, 4, 5 and 6 for AK-1, AK-2, AK-3 and AK-4 respectively. The SEM pictures in Fig. 3a show the for-mation of scaly mullite and granular mullite in the pure triaxial mixtures at 5 μm with quartz particles very visible as well as albite. A closer view at 2 μm reveals the needle-like structure of the mullite with a higher aspect ratio (Fig. 3b), similar to a normal porcelain microstructure observed by another authors [7]. This structure was not prominent in Fig. 4a and 4b due to full replacement of feldspar by glass cullet as seen in the batch composition (Table 1) which gave a lower level of mullite and quartz relicts in the microstructure. Also, the mullite clinkers are not uniformly distributed, rather present as isolated clusters. A close observation also indicated regions of cracks and pores, sug-gestive of full replacement being a dreadful compositional mix. The microstructure of AK-3 looks like similar to AK-2 and AK-4 (Fig. 5 and 6) but Fig. 6b shows good devel-opment of mullite crystals surrounded by a glassy matrix as seen in Fig. 3b. Tucci et al. [16] observed different microstructural fea-tures with soda-lime scrap and in Na-feld-spar containing stoneware mix and mostly it was characterized by the presence of in-terconnected small pores with enhanced homogeneity.

Table 4 • Mass percentage of different phases present in the bodyCrystalline phase / mass-%

Glassy phase / mass-%Body Mullite Quartz CristobaliteAK-1 26.6 19.4 Nil 54.1

AK-2 18.6 9.1 29.9 42.4

Fig. 2 • XRD patterns

of the samples

(AK-1, AK-2, AK-3 &

AK-4) fired at 1250 °C;

M=Mullit, Q=Quartz,

C=Cristobalite

2 Ɵ / °

Inte

nsity

/ a

. u.

2

Fig. 3 • (a) Microstructure of etched AK-1 fired at

1250 °C showing granular mullite, (b): microstruc-

ture from the same sample showing mullite crys-

tals formed in the matrix mixture

(a)

(b)

5 µm

1 µm

3

Fig. 4 • (a) Microstructure of etched AK-2 fired at

1250 °C, (b): microstructure from the same sample

showing the mullite crystals formed

(b)

(a)

5 µm

1 µm

4

Fig. 5 • (a) Microstructure of etched AK-3 fired at

1250 °C, (b): microstructure from the same sample

showing the mullite crystals formed

(a)

(b)

5 µm

1 µm

5

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4 ConclusionsThe present investigation widens the scope of utilizing soda-lime scrap and abundantly available river sand as a fluxing agent in kaolin-quartz-feldspar bound triaxial por-celain. The results showed that the replace-ment of 15 mass-% of K-feldspar by soda-lime scrap has decreased the firing temper-ature considerably. The presence of well- developed needle-shaped mullite crystals support higher strength. The densification was not detrimentally affected by the blend, rather the introduction of the waste glass led to the formation of new phases in the non-equilibrum microstructure of porcelain stoneware.

AcknowledgementsThe authors are very grateful to CSIR-TWAS for the fellowship support and also to the Director, CSIR-Central Glass & Ceramic Research Institute, for the equipment and laboratory support for this work.

References [1] Kamseu, E., Leonelli, C., Boccaccini, D.N., Veronesi,

P., Miselli P., Pellacani G., Chinje Melo, U.:Charac-terizationofporcelaincompositionsusingtwochi-na clays fromCameroon. Ceram. Inter.33 (2007)851−852

[2] Carty, W.M., Senapati, U.:Porcelain-rawmaterial,processing, phase evolution, and mechanical be-haviour.J.Am.Ceram.Soc.81(1998) [1]3−20

[3] Klein, A.A.:Constitutionandmicrostructureofpor-celain. National Bureau of Standards Tech. PaperNo.3–38,1916–1917

[4] Rado, P.:Thestrangecaseofhardporcelain.Trans.andJ.Brit.Ceram.Soc.70(1971)131–39

[5] Vazquez, S.B., Velazquez, J.C.M., Gasga, J.R.:Alu-minaadditionsaffectelasticpropertiesofelectricalporcelains. Bull. Am. Ceram. Soc. 77 (1998) [4]81–85

[6] Kobayashi, Y., Kato, E.: Lightening of alumina-strengthened porcelain by controlling porosity. J.Ceram.Soc.ofJap.106 (1998)[9]938–941

[7] Iqbal, Y., Lee, W.E.:Firedporcelainmicrostructurerevisited.J.Am.Ceram.Soc.82 (1999)[12]3584–3590

[8] Biscard, C., Hseuh, H., Mapes, M.:Applicationsofporcelainenamelasanultra-high-vacuum-compat-ibleelectricalinsulator.J.VacuumSci.andTechnol.A18(2000) [4]1751−1754

[9] Sedghi, A., Hamidnezhad, N., Noori, N.R.:Theef-fectoffluxesonaluminasilicateporcelaininsula-torpropertiesandstructures.Proc.Inter.Conf.onEcological, Environmental and Biological sciences(Dubai)7−8January2012,343–345

[10] Glass. Region 7 solid waste. http://www.epa.gov/region7/waste/solidwaste/glass.htm – accessedSeptember26,2012

[11] Casehistory:Thetruthaboutrecycling. http://www.economist.com/ode/9249262?story_

id=9249262–accessedSeptember26,2012[12] Waste Glass recycling: An effective way to save

energyandenvironment. http://saferenvironment.wordpress.com/2009/06/04/waste-glass-recycling-%E2%80%93-an-effective-way-to-save-energy-and-environment/–accessedSeptember26,2012

[13] Johnson, C.D.: Waste glass as coarse aggregatefor concrete. J. Testing and Evaluation 2 (1998)344–350

[14] Masaki, O.:Studyonthehydrationhardeningchar-acterofglasspowderandbasicphysicalpropertiesofwasteglassasconstructionmaterial.AsahiCer-am.FoundationAnn.Tech.Rep.(1995)143–147

[15] Park, S.B.:Developmentofrecyclingandtreatmenttechnologies for constructionwastes.Ministry ofConstructionandTransportation,Tech.Rep.,Seoul(2000)

[16] Tucci, A., Esposito, L., Rastelli, E., Palmonari, C., Rambaldi, E.: Use of soda-lime scrap-glass as afluxing agent in a porcelain stoneware tile mix.JournaloftheEuropeanCeramicSociety24(2004)83−92

[17] Rietveld, H.M.: A profile refinement method fornuclear and magnetic structures. J. Appl. Crystal-lography2(1969)65−71

[18] Young, R.A.: The Rietveld Method, ed. By R.A.Young.OxfordUniversityPress,Oxford,U.K.(1995)1−38.ISBN-13:978-0198559122

www.PANalytical.com.–accessedFebruary14,2013

Received: 14.02.2013

Fig. 6 • (a) Microstructure of etched AK-4 fired at 1250 °C, (b): microstructure from the same sample

showing the mullite crystals formed

(b)(a)

5 µm 1 µm

6

3.4 SEM/EDX microstructure analysisThe microstructures of the samples fired at 1250 °C are presented in Fig. 3, 4, 5 and 6 for AK-1, AK-2, AK-3 and AK-4 respectively. The SEM pictures in Fig. 3a show the for-mation of scaly mullite and granular mullite in the pure triaxial mixtures at 5 μm with quartz particles very visible as well as albite. A closer view at 2 μm reveals the needle-like structure of the mullite with a higher aspect ratio (Fig. 3b), similar to a normal porcelain microstructure observed by another authors [7]. This structure was not prominent in Fig. 4a and 4b due to full replacement of feldspar by glass cullet as seen in the batch composition (Table 1) which gave a lower level of mullite and quartz relicts in the microstructure. Also, the mullite clinkers are not uniformly distributed, rather present as isolated clusters. A close observation also indicated regions of cracks and pores, sug-gestive of full replacement being a dreadful compositional mix. The microstructure of AK-3 looks like similar to AK-2 and AK-4 (Fig. 5 and 6) but Fig. 6b shows good devel-opment of mullite crystals surrounded by a glassy matrix as seen in Fig. 3b. Tucci et al. [16] observed different microstructural fea-tures with soda-lime scrap and in Na-feld-spar containing stoneware mix and mostly it was characterized by the presence of in-terconnected small pores with enhanced homogeneity.

Fig. 5 • (a) Microstructure of etched AK-3 fired at

1250 °C, (b): microstructure from the same sample

showing the mullite crystals formed

(a)

(b)

5 µm

1 µm

5

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