Characterization of ceramic tiles containing LCD waste glass

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CERAMICS INTERNATIONAL

Ceramics International 42 (2016) 7626–7631 www.elsevier.com/locate/ceramint

Characterization of ceramic tiles containing LCD waste glass Kidong Kima,n, Kicheol Kima, Jonghee Hwangb a

Department of Materials Science and Engineering, Kunsan National University, Chunbuk, Republic of Korea b Korea Institute of Ceramic Engineering and Technology, Jinju, Republic of Korea Received 31 October 2015; received in revised form 14 January 2016; accepted 25 January 2016 Available online 2 February 2016

Abstract In the present work, the application of LCD waste glass as a flux material substituting for the traditional feldspar in ceramic tiles was studied. The viscosity of LCD glass at the sintering temperature of the ceramic tile was found to be optimal for the dense solid that is obtained from the sintering of the glass powder. The sintered body containing LCD waste glass showed a dense microstructure due to the rich liquid. Even for full replacement of feldspar, neither pyroplastic deformation nor liquid exudation was observed. Overall, properties such as water absorption and the thermal expansion coefficient were positively affected by LCD waste glass substitution. Moreover, the mullite content in the sintered body was almost unchanged. These results were discussed in terms of the apparent viscosity and glass composition. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: Ceramic tile; LCD waste glass; Feldspar; Viscosity; Glass composition

1. Introduction LCD glass is composed of SiO2, Al2O3, B2O3, and alkaline earth oxides. Because this glass is used for LCD panels, its homogeneity and the resulting physicochemical properties are very different from those of traditional glass [1]. A large amount of waste glass (hereafter designated as LPWG: LCD process waste glasses) equal to approximately 80 kt/y is currently produced by LCD panel manufacturers in four Asian countries. LPWG is contaminated by thin film transistors (TFT), indium tin oxide (ITO) conductors, polarizers and colour filters. Furthermore, the composition of LPWG occasionally exhibits considerable fluctuation because it consists of glass products from three different manufacturers. Therefore, unlike the LCD cullet recycled as a raw material in the E glass industry [2,3], the recycling of LPWG is difficult for an industry that is sensitive to compositional change. There have been several studies on LPWG recycling for use in clay ceramic tiles [4], glass–ceramics [5–7], foamed glass [8] and cement [9–11]. In particular, recently, the present authors have reported a full replacement of feldspar by LPWG n

Corresponding author. Tel.: þ82 63 469 4737; fax: þ 82 63 462 6982. E-mail address: [email protected] (K. Kim).

http://dx.doi.org/10.1016/j.ceramint.2016.01.172 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

in traditional porcelain sanitary ware [12]. It is well known that in porcelain ceramics such as vitreous white ware, the feldspar plays the role of a fluxing agent penetrating into the alumina silicate ceramic powders by viscous flow during sintering and the rest of the liquid phase is solidified without active crystallization during cooling. Therefore, several studies have investigated the use of soda lime silicate (SLS) glass [13–15] or alkali alkaline earth silicate CRT glass [16,17] derived from commercial products as a substitute for feldspar in conventional porcelain stoneware. However, because these glasses exhibit low viscosity at the sintering temperature, their content is limited to only 10–20 wt% of the total feldspar depending on body composition. In the present work, gradual replacement of feldspar by LPWG was examined for ceramic tiles, a typical application of traditional porcelain ceramics. The sintered specimens were characterized and the obtained results were discussed. 2. Materials and methods The ceramic floor tiles in the original batch obtained from a tile manufacturer consist of 36 wt% clay, 18 wt% quartz and 46 wt% feldspar. Up to 40 wt% of the 46 wt% concentration of

K. Kim et al. / Ceramics International 42 (2016) 7626–7631

3. Results and discussion The compositions and crystalline phases of the starting raw materials obtained by XRF and XRD analyses, respectively, are presented in Table 1. Andesine (Na0.7–0.5Ca0.3–0.5Al1.3– 1.5Si2.7–2.5O8: a kind of plagioclase minerals and mixture of albite and anorthite) and quartz are present, and no kaolinite was found in the clay used in the present work. In addition to the quartz, the raw quartz material contains magnesioferrite (MgFe2O4). The feldspar consists of albite (Na2OAl2O36SiO2) and quartz. Both clay and quartz supplied from local mines seem to be naturally contaminated with another mineral, leading to the presence of the unusual crystalline phases such as andesine and magnesioferrite. The three raw materials contain higher concentrations of Fe2O3 than LPWG. The normal sintered specimen therefore showed a deep reddish brown colour, which became less pronounced after the

Table 1 Compositions (wt%) and identified crystalline phases of raw materials. Component

Clay

Quartz

Feldspar

LPWG

SiO2 Al2O3 TiO2 B2O3 Na2O K2O MgO CaO SrO BaO Fe2O3 Crystalline phase

66.91 22.71 0.78 – 1.01 2.27 1.30 0.28 – – 4.43 Q, A

66.83 20.01 0.66 – 0.22 5.77 0.58 0.07 – – 5.38 Q, Ma

65.52 18.19 0.64 – 2.16 3.74 3.05 0.76 – – 5.41 Ab, Q

58–64 (60.1) 15–20 (16.8) – 7–11 (10.3) – – 0–4 (0.44) 3–8 (7.6) 0–8 (4.2) 0–5 (0.48) 0.025

Q: quartz, A: andesine, Ma: magnesio-ferrite, and Ab: albite. (): the average composition of LPWG used in the present work.

16

LCD glass SLS glass CRT glass

14

Viscosity (logη in dPas)

feldspar in the batch is replaced by LPWG powder fined partially via milling in a glass processing plant. LPWG is a waste glass generated from the edge trimming process of LCD and thus free from organic thin films; the number at the end of LPWG specimen code specifies wt% of LPWG in total batch. For all powders, the particle size was in the 5–50 μm range. To examine the effect of viscous flow due to glass powder during sintering, the temperature dependence of the LPWG viscosity was determined based on the DIN 52312 and ASTM C338 standards at high and low temperatures, respectively. The body mix of each batch composition was prepared by milling the three raw materials specified above and LPWG in a zirconia ball mill. Based on the actual ceramic tile production conditions, the disk-shaped green compacts prepared by uniaxial pressing with 500 kg/cm2 were heated at a rate of 5 1C/min in an electric box furnace and sintered for 1 h at 1100 1C or 1150 1C. After sintering the specimen was cooled naturally to room temperature. It took about 10 h for heating, isothermal sintering and cooling. All the sintered bodies showed neither pyroplastic deformation nor rough surfaces due to the rich liquid or the exudation of the glass phase. Properties such as bulk density, water absorption and thermal expansion coefficient were measured for the resulting sintered body according to ASTM C373 and E831, respectively. The bulk density was determined using special kit (P/N77402-00, Ohaus, USA) based on Archimedes principle. The water absorption was measured for the boiled specimen. Thermal mechanical analysis (TMA 4100S, Bruker AXS, Germany) was used to determine the thermal expansion coefficient. The details for some of the measurement procedures are described in the literatures [12,18,19,21]. The composition and crystalline phases of the raw materials and sintered bodies were analysed by XRF (ZSX Primus II, Rigaku, Japan) and HR-XRD (EMPYREAN, PANalytical, Netherlands), respectively. A quantitative analysis of the phases existing in the sintered body was carried out using the Rietveld-RIR method with PANalytical Highsco-plus in which a Si crystal was used as the standard phase. Data were recorded in the 2θ range of 5–751 under the condition of 0.0261 step size and 21/min step scan speed.

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12 10 8 Sintering range of

to a solid body

glass powder

6 4 2 400

600

800

1000

1200

1400

1600

o

Temperature ( C) Fig. 1. Temperature dependence of the viscosity of LPWG inclusive of conventional two glasses (SLS and CRT) and a description of the sintering range of glass powder only.

introduction of LPWG containing approximately 250 ppm Fe2O3. The viscosity curves of LPWG and the conventional SLS and CRT glasses in Fig. 1 show different temperature dependences. The LPWG is an alkali-free alumino-borosilicate glass, and its viscosity is therefore much higher than those of SLS and CRT glasses that include alkali oxide, alkaline earth oxide and silica. For LPWG, the temperature corresponding to 106 dPas, where a dense microstructure can be obtained by sintering the glass powder [20], lies in the 1080–1120 1C range. Moreover, the viscosity behaviour in this range is similar to that of Na feldspar suggested by Andreola et al. [21]. On the other hand the corresponding temperature for SLS and CRT glass is 840 1C, which is much lower than the normal sintering temperature. The ceramic tile sintering range of 1100–1150 1C corresponds to 105–105.6 dPas for LPWG. Therefore, it is expected that compared to SLS and CRT glass, LPWG can be an excellent substitute for feldspar. The bulk density (D) of the specimens sintered at 1100 1C and 1150 1C as a function of LPWG content is shown in Fig. 2. Irrespective of the sintering temperature, similar dependences of

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K. Kim et al. / Ceramics International 42 (2016) 7626–7631 2.6 o

1100 C o 1150 C

3

D (g/cm )

2.4

2.2

2.0

1.8 0

10

20

30

40

LPWG Content (wt%)

Fig. 2. Bulk density (D) of the sintered specimens.

14

o

1100 C o 1150 C

12

WA (%)

10 8 6 4 2 0 0

10

20

30

40

LPWG Content (wt%)

6.0

o

1100 C o 1150 C

5.8

-6

TEC (10 /?C)

5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 0

10

20

30

40

LPWG Content (wt%)

Fig. 3. (a) Water absorption (WA) and (b) thermal expansion coefficient (TEC) of the sintered specimens.

D on the LPWG content are obtained. The D values show an overall decrease with increasing LPWG content. At the initial introduction of LPWG, D shows an approximately constant value, but an abrupt decrease in D is observed in the 10–15 wt% range. D values are again constant for LPWG contents greater than 25 wt%. Two factors contributing to the change in D upon

substitution for feldspar by LPWG can be suggested: one is the volume shrinkage difference that increases D, and the other is the density difference between LPWG (2.45 g/cm3) and feldspar (2.55–2.76 g/cm3) that decreases D. A viscous flow of LPWG during sintering strongly affects the volume shrinkage. Nevertheless, the results in Fig. 2 imply that the latter factor is dominant. Fig. 3 shows the results of the water absorption (WA) and the thermal expansion coefficient (TEC) measurements. While at 1100 1C, the obtained WA is greater than 0.5 up to LPWG35, at LPWG40 it approaches the 0.5 value, which is marked by an arrow in Fig. 3. By contrast, at 1150 1C, all specimens except LPWG0 show almost 0 WA, satisfying the requirement (ISO 13006) of WAo0.5 for the dry-pressed ceramic tiles Group Bla. Regarding the TEC, unlike the alkali aluminosilicate feldspar, LPWG is an alkali-free glass, and its TEC under the glass transition temperature is 32–36  10  7/1C, which is much lower than those of the feldspar glasses [22]. This is the origin for the decrease in the TEC of the sintered specimen with increasing LPWG content. Therefore, better thermal shock resistance is expected for the ceramic tiles containing LPWG. Analysis of SEM micrographs of samples with increasing LPWG contents (Fig. 4) demonstrates the behaviour observed in a previous study of porcelain sanitary ware [12]. Comparison of the micrographs shows that the evolution of the microstructure depends on the LPWG content. The sintered body with LPWG shows a soft and dense microstructure due to the rich liquid phase derived from the pure glass. Such a tendency is clearly shown by LPWG40, which is sintered at 1150 1C but exhibits large closed pores. Conversely, the LPWG0 has a rough microstructure due to a small quantity of liquid phase derived from the partially melted feldspar. Fig. 5 shows the shapes of the sintered specimens consisting of only flux with feldspar and LPWG:feldspar ¼ 1:1; the results confirm that differences between feldspar and LPWG affect the sintering of the green compact. The differences in the sintering mechanisms of feldspar and LPWG in the green compact can be described as follows: while for the feldspar (LPWG0), the sintering may proceed by diffusion via slightly viscous flow of the partially melted feldspar, for the LPWG, diffusion via full viscous flow of the glass may be dominant. Finally, the sintering reaction results in the formation of a quasi-liquid consisting of a liquid and non-melted crystalline phase. Because the fluidity of a quasi-liquid depends on the content of the crystalline phase [23], its apparent viscosity at the sintering temperature decreases with increasing LPWG content. The constant D in the 30–40 wt% range shown in Fig. 2 may be due to the large closed pores trapped in the quasi-liquid with low viscosity obstructing body shrinkage [13,14]. XRD patterns of some specimens sintered at 1100 1C are shown in Fig. 6. In addition to quartz and mullite, the presence of andesine derived from the clay was observed in these sintered specimens. The contents of these three crystalline phases and the glass phase in the body sintered at 1100 1C are quantitatively described as a function of LPWG content in Fig. 7. The contents of the four phases are almost constant for all sintered specimens containing LPWG. In particular, the

K. Kim et al. / Ceramics International 42 (2016) 7626–7631

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LPWG0

LPWG20

LPWG40

LPWG0

LPWG20

LPWG40

Fig. 4. SEM micrographs of specimens (  1000) at (a) 1100 1C and (b) 1150 1C.

100

Glass phase Mullite Quartz Andesine

90

(a)

Content of Phase, wt%

80

(b)

70 60 50 40 30 20 10

Fig. 5. Shape of the sintered specimens of (a) feldspar only and (b) LPWG: feldspar¼ 1:1 at 1150 1C.

0 0

5

10

15

20

LPWG Content, wt% Fig. 7. Dependence of the phase content of the sintered specimens on the LPWG content at 1100 1C.

M Q

A

Intensity (arbitrary)

Q

Table 2 Mullite content (wt%) of specimens sintered at 1100 or 1150 1C determined by the Rietveld-RIR method and its resulting range of numerical statistical indicators (Rwp, Rp) and goodness-of-fit (s) showing the quality of refinement.

LPWG0

M Q

A

LPWG5

A

LPWG10

A

LPWG15

A

LPWG20

Q M Q Q M Q Q M Q Q

0

10

20

30

40

50

60

70

80

2θ Fig. 6. XRD patterns of specimens sintered at 1100 1C. Q: Quartz, M: Mullite, and A: Andesine.

Item

LPWG0

LPWG5

LPWG10

LPWG15

LPWG20

1100 1C 1150 1C Rwp (%) Rp (%) s

4.6 5.2 3.0–9.5 2.1–3.8 4.1–7.4

4.1 5.3

4.2 5.3

4.5 5.4

4.5 5.9

mullite content for LPWG5–LPWG20 is approximately 4– 6 wt%, which is nearly the same as that of LPWG0 at each sintering temperature, as shown in Table 2. In other words, there is no significant change in the mullite content despite the replacement of the feldspar by LPWG. It is well known that

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Table 3 Average compositions of several sintered bodies (wt%). Component

LPWG0

LPWG10

LPWG20

LPWG30

LPWG40

SiO2 Al2O3 B2O3 Na2O K2O MgO CaO SrO BaO TiO2 Fe2O3

66.25 20.14 – 1.39 3.58 1.98 0.46 0.04 0.06 0.69 5.05

65.65 19.95 1.05 1.18 3.20 1.71 1.16 0.50 0.10 0.63 4.51

65.04 19.84 2.09 0.96 2.82 1.43 1.86 0.96 0.15 0.56 3.96

64.44 19.70 3.14 0.75 2.45 1.16 2.57 1.43 0.20 0.50 3.42

63.84 19.55 4.18 0.53 2.07 0.89 3.27 1.89 0.24 0.44 2.88

mullite strongly influences the maintenance of the mechanical strength of the final ceramic body. Therefore, the mullite content is very important in these ceramics. There could be several possible explanations for the lack of dependence of mullite content on the LPWG content. Comparison of the present results with those of other studies using waste glass such as SLS [13] and CRT glasses [16] shows that LPWG exhibits two remarkable differences from other waste glasses: (1) the Al2O3-rich composition and (2) viscosity with optimal fluidity at sintering temperature. Table 3 shows the average compositions of several selected sintered bodies. Because the Al2O3 content of LPWG is similar to that of the feldspar, as shown in Table 1, the replacement of the feldspar by LPWG hardly influences the Al2O3 concentration of the final sintered specimens. As indicated above based on Fig. 5, the apparent viscosity at the sintering temperature will decrease with the replacement of feldspar by LPWG because the viscosity of LPWG is smaller than that of feldspar. Therefore, active diffusion of the corresponding components of LPWG via viscous flow during sintering can be expected. These two features of LPWG are certainly contributing factors for the maintenance of the mullite content [12]. Normally, the green bodies of ceramic tile prepared from the present batch are sintered at 1150 1C during industrial production. However, the results of the present work show that depending on LPWG content the required ceramic tile properties can be achieved even at 1100 1C. This means that the energy consumption and the feldspar usage in the tile industry can be reduced by the introduction of the LPWG.

4. Conclusions In the present study, the effects of feldspar substitution by LPWG in ceramic tiles on some properties of the sintered body were investigated. The properties such as WA and TEC including microstructure showed a positive tendency for ceramic tile up to almost complete replacement of feldspar by LPWG. Moreover, there was no significant change in the mullite content in the sintered body containing LPWG. It can be concluded that the viscosity and composition of LPWG

play decisive roles in determining the properties of the final product. However, the present positive results for LPWG are not valid for the current end LCD waste glasses generated from the end-of-life LCD devices. Such end waste glasses derived from the glass product before 2010 contain mostly toxic components such as As2O5 and Sb2O5 [24] that preclude their active recycling. From the perspective of the WEEE directives of the EU [25], various attempts for positive use of the end LCD waste glasses are necessary. Acknowledgements This study was supported by the R&D Center for Valuable Recycling in the Institute for Advanced Engineering (GlobalTop Environmental Technology Development Program) and was funded by the Ministry of Environment, Republic of Korea (Project no. 2014001170002). References [1] A. Ellison, I.A. Cornejo, Glass substrate for liquid crystal displays, Int. J. Appl. Glass Sci. 1 (2010) 87–103. [2] K. Kim, J. Hwang, Recycling of TFT-LCD cullet as a raw material for fibre glasses, Glass Technol. : Eur. J. Glass Sci. Technol. A 52 (2011) 181–184. [3] K. Kim, K. Kim, J. Hwang, TFT-LCD cullet: a raw material for production of commercial soda lime silicate glasses, J. Clean. Prod. 79 (2014) 276–282. [4] K.L. Lin, Use of thin film transistor liquid crystal display (TFT-LCD) waste glass in the production of ceramic tiles, J. Hazard. Mater. 148 (2007) 91–97. [5] K.L. Lin, W.K. Chang, T.C. Chang, C.H. Lee, C.H. Lin, Recycling thin film transistor liquid crystal display (TFT-LCD) waste glass produced as glass–ceramics, J. Clean. Prod. 17 (2009) 1499–1503. [6] C.S. Fan, K.C. Li, Production of insulating glass ceramics from thin film transistor-liquid crystal display (TFT-LCD) waste glass and calcium fluoride sludge, J. Clean. Prod. 57 (2013) 335–341. [7] C.S. Fan, K.C. Li, Glass-ceramics produced from thin-film transistor liquid-crystal display waste glass and blast oxygen furnace slag, Ceram. Int. 40 (2014) 7117–7123. [8] C.T. Lee, Production of alumino-borosilicate foamed glass body from waste LCD glass, J. Ind. Eng. Chem. 19 (2013) 1916–1925. [9] K.L. Lin, W.J. Huang, J.L. Shie, T.C. Lee, K.S. Wang, C.H. Lee, The utilization of thin film transistor liquid crystal display waste glass as a pozzolanic material, J. Hazard. Mater. 163 (2009) 916–921. [10] H.Y. Wang, The effect of the proportion of thin film transistor-liquid crystal display (TFT-LCD) optical waste glass as a partial substitute for cement in cement mortar, Constr. Build. Mater. 25 (2011) 791–797. [11] K.L. Lin, S. Shiu, J.L. Shie, T.W. Cheng, C.L. Hwang, Effect of composition on characteristics of thin film transistor liquid crystal display (TFT-LCD) waste glass-metakaolin-based geopolymers, Const. Build. Mater. 36 (2012) 501–507. [12] K. Kim, K. Kim, J. Hwang, LCD waste glass as a substitute for feldspar in the porcelain sanitary ware production, Ceram. Int. 41 (2015) 7097–7102. [13] A. Tucci, L. Esposito, E. Rastelli, C. Palmonari, E. Rambaldi, Use of soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix, J. Eur. Ceram. Soc. 24 (2004) 83–92. [14] A.P. Luz, S. Ribeiro, Use of glass waste as a raw material in porcelain stoneware tile mixture, Ceram. Int. 33 (2007) 761–765. [15] E. Rambaldi, W.M. Carty, A. Tucci, L. Esposito, Using waste glass as a partial flux substitution and pyroplastic deformation of a porcelain stoneware tile body, Ceram. Int. 33 (2007) 727–733.

K. Kim et al. / Ceramics International 42 (2016) 7626–7631 [16] F. Andreola, L. Barbieri, E. Karamanova, I. Lancellotti, M. Pelino, Recycling of CRT panel glass as fluxing agent in the porcelain stoneware tile production, Ceram. Int. 34 (2008) 1289–1295. [17] E. Bernado, L. Esposito, E. Rambaldi, A. Tucci, ‘Glass based stoneware’ as a promising route for the recycling of waste glasses, Adv. Appl. Ceram. 108 (2009) 2–8. [18] E. Suvaci, N. Tamsu, The role of viscosity on microstructure development and stain resistance in porcelain stoneware tiles, J. Eur. Ceram. Soc. 30 (2010) 3071–3077. [19] A. Bernasconi, N. Marinoni, A. Pavese, F. Francescon, K. Young, Feldspar and firing cycle effects on the evolution of sanitary-ware vitreous body, Ceram. Int. 40 (2014) 6389–6398.

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[20] T. Wallenberger, A. Smrcek, The liquidus temperature; its critical role in glass manufacturing, Int. J. Appl. Glass Sci. 1 (2010) 151–163. [21] F. Andreola, L. Barbieri, F. Bondioli, I. Lancellotti, P. Miselli, A. M. Ferrari, Recycling of screen glass into new traditional ceramics materials, Int. J. Appl. Ceram. Technol. 7 (2010) 909–917. [22] P.J. Vergano, D.C. Hill, D.R. Uhlmann, Thermal expansion of feldspar glasses, J. Am. Ceram. Soc. 50 (1967) 59–60. [23] K. Kim, S. Lee, Prediction of viscosity in the two-phase range of a ternary glass-forming system, J. Mater. Sci. 32 (1997) 6561–6565. [24] K. Kim, Fining behavior in alkaline earth aluminoborosilicate melts doped with As2O5 and SnO2, J. Am. Ceram. Soc. 96 (2013) 781–786. [25] WEEE, 〈http://ec.europa.eu/environment/waste/weee/index_en.htm〉, 2012.