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Coloring and translucency mechanisms of Five dynasty celadon body from Yaozhou kiln
Ceramics International xxx (xxxx) xxx–xxx
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Coloring and translucency mechanisms of Five dynasty celadon body from Yaozhou kiln ⁎
Pei Shi, Fen Wang , Yi Wang, Jianfeng Zhu, Biao Zhang, Yuan Fang School of Materials Science and Engineering, Shaanxi University of Science & Technology, Xi'an 710021, PR China
A R T I C L E I N F O
A BS T RAC T
Keywords: Yaozhou kiln Five dynasty celadon body Coloring mechanism Translucency mechanism
This work takes the Five dynasty celadon body of Yaozhou kiln as the major study objects. Based on the analysis of XRF, XRD, SEM/EDS, UV/Vis/NIR spectrophotometers and XPS, the chemical compositions, microstructure and optical quality of the white and black bodies have been investigated. The results indicates that the Five dynasty celadon body has lower SiO2 content than that of the other dynasties, which provides an evidence for dating research on ancient celadon. Furthermore, the high Fe2O3 and TiO2 contents enhance the formation of 4+ 2+ 4+ Fe3+ 2 Ti O5 , Fe Ti2 O5 and Ti2O3 in the black body and deepen the coloring of Fe2O3. As a result, its color is darker than the white body. In addition, there are more crystal boundaries and residual micropores appeared in the black body. They serve as optical scattering centers and decrease the transmittance of incidence light. Therefore, the black body has much worse transmittance than that of the white body.
1. Introduction The central site of Yaozhou kiln is in the Huangpu town of Tongchuan city. As the Tongchuan city was affiliated with Yaozhou in Song dynasty, descendants called it “Yaozhou kiln”. It started from the Tang dynasty (618 AD–917 AD), passed through the Five dynasty (907 AD–960 AD), matured in the Song dynasty (960 AD–1279 AD) and stopped development in the Yuan dynasty (1279 AD–1368). The history of its continuous production had persisted for nearly 800 years [1,2]. At different times, the Yaozhou kiln had representative artistic achievements, such as the Tang dynasty black and tea dust wares, the Five dynasty sky-green ware, the Song dynasty olive-green ware and the Jin and Yuan dynasties moon-white ware. At first, the Yaozhou celadon was appreciated for the Song dynasty celadon with carved decoration [3]. Nevertheless, the awareness about the Five dynasty celadon had been going on for quite a long time. It was built on the accumulation of celadon shards excavated from kiln sites, city sites and tombs. At present, the Five dynasty sky-green ware is the most exciting and favorite celadon [4]. According to the body color, the Five dynasty celadon could be roughly divided into two groups: the white body and black body celadon (Fig. 1(a) and (b)). Most belong to the black body celadon, and the white body celadon is comparatively rare in the Five dynasty celadon shards excavated from kiln sites. In the beginning, due to a lot of over-firing bubbles in the early white body celadon, it did not draw a great deal of attention and interest. For the high quality white body celadon, the glaze color is green-blue and similar to that of Ru and
⁎
Guan kilns. It should be the oldest sky-green ware. The thin body celadon with carving patterns has the effect of the rice-pattern porcelain of Jingdezhen. The glaze surface is very bright and delicate as clearly as the day they are fired, and has very few cracks. Especially, the thickness of thinner body celadon is about 1 mm. It has high translucency, as well as the texture is pure and dense (Fig. 1(c)). The body color of the black body celadon is no less than the black-gray body celadon of Ge kiln, whereas it coats engobe. Furthermore, the decorative practices are mainly patternless and drawing flowers. Compared with the white body and black body celadon, the former has higher translucency and lighter body color than the latter. However, in addition to some archaeological reports, there is no special scientific research report about the formation mechanisms for the body color and translucency in the Five dynasty celadon of Yaozhou kiln [2]. In this paper, the chemical composition, firing condition and microstructure of the Five dynasty celadon body were studied, aiming at investigating the correlation between them and the body appearance. Based on that, the scientific rules behind the aesthetically pleasing appearance of the Yaozhou white body and black body celadon of Five dynasty was proposed. This work will throw some light on the better understanding of the coloring and translucency mechanisms about the Five dynasty celadon body. 2. Experimental procedure All of the celadon shards excavated from the Yaozhou kiln site of
Corresponding author. E-mail address: [email protected] (F. Wang).
http://dx.doi.org/10.1016/j.ceramint.2017.05.334 Received 17 May 2017; Received in revised form 27 May 2017; Accepted 27 May 2017 0272-8842/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Shi, P., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.05.334
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Fig. 1. Five dynasty celadon, (a) white body; (b) black body; (c) thin body.
Tongchuan were provided by the Yao kiln museum of Shaanxi province. The chemical compositions of shard bodies were determined by X-ray fluorescence (XRF, AXIOS, Netherlands). The phase compositions of the test pieces were identified by X-ray diffraction (XRD, D/ max 2200PC, Japan) with Co Kα radiation (λ = 1.7889 Å) and scanning from 10° to 70° under 40 kV and 100 mA. The chemical analysis was performed on the X-ray photoelectron spectrometer (XPS, AXIS Supra, UK) using Al Kα radiation. Microstructure and crystal composition were studied using scanning electron microscopy (SEM, S4800, Japan) equipped with an energy dispersive spectrometry (EDS). Before the testing, the fracture surfaces of the samples were etched using 1 vol% HF for 20 s to expose the crystals. Moreover, the in-line transmittance was obtained by using a UV/Vis/NIR spectrophotometers (Cary 5000, USA).
Fig. 2. Two dimensional corresponding chemical compositions analysis of the Yaozhou celadon bodies from different dynasties.
weakened the coloring of impurities. Moreover, it also showed that the black ones were added in purple clay. The high K2O in white-body ones might reveal the raw materials contained abundant feldspar. Whereas, the high TiO2 content in the black body might be connected with the body color. Comparing the chemical compositions of W1-W7 bodies, the Fe2O3 content of the black ones was higher than white-body one. On the basis of verification testing, 3% of Fe2O3 was the dividing line for black and white body colors. The content of Fe2O3 in the white-body samples was below 2%, causing the body color was light. In addition to the chemical compositions, the body appearance variations also came from the fluctuation of firing conditions such as firing temperature, time and atmosphere in the horse-shoe kilns with wood as fuel [6]. Combining the color and performance of bodies, the
3. Results and discussion Table 1 lists the chemical compositions of celadon bodies from the Tang, Five dynasty, Song, Jin and Yuan dynasty. By comparison, the Al2O3, SiO2, K2O and TiO2 contents had significant difference. In order to further analysis their characteristic, the two-dimension chart of these celadon bodies from different dynasties is shown in Fig. 2. As being observed, the Five dynasty celadon body had lower SiO2 content than that of other dynasties, which provided an evidence for dating research on ancient celadon [5]. Furthermore, there were obvious differences in K2O, Al2O3 and TiO2 contents between the white body and black body. The higher K2O and lower Al2O3 contents in white body helped to form more glass phase and melt with impurities so that Table 1 Chemical compositions of the shard bodies from different dynasties (wt%). Number
Dynasty
Na2O
MgO
Al2O3
SiO2
K2O
CaO
TiO2
Fe2O3
T1 T2 T3 W1 W2 W3 W4 W5 W6 W7 S1 S2 S3 J1 J2 J3 Y1 Y2 Y3
Tang
0.57 0.35 0.31 0.16 0.47 0.17 0.39 0.23 0.25 0.25 0.53 0.98 0.38 0.17 0.45 0.28 0.07 0.43 0.22
0.95 0.98 1.11 0.46 0.62 0.79 0.76 0.88 1.07 1.05 0.84 0.93 0.90 0.86 0.81 0.89 1.15 0.87 0.76
20.39 25.82 27.44 22.98 22.67 18.90 22.41 28.78 29.35 29.53 24.33 23.28 24.42 20.29 19.81 21.39 18.83 22.38 19.89
71.83 66.33 64.12 66.60 67.63 72.18 67.19 62.81 62.67 61.78 67.65 68.23 68.05 71.58 72.21 71.13 73.49 68.92 72.12
2.29 1.77 1.97 6.17 5.09 4.59 5.37 1.84 1.84 1.97 2.25 2.08 2.11 2.38 2.23 2.38 2.29 2.35 2.55
0.41 0.50 0.44 0.67 0.63 0.50 0.98 1.01 0.34 0.32 0.51 0.57 0.32 0.83 0.62 0.39 0.79 1.07 0.54
0.65 1.08 0.99 0.22 0.22 0.49 0.25 1.11 1.19 1.29 0.76 0.78 0.85 0.67 0.61 0.68 0.62 0.71 0.77
1.90 2.18 2.63 1.74 1.66 1.38 1.65 2.34 2.30 2.83 2.13 2.15 1.98 2.22 2.26 1.86 1.76 2.27 2.14
(W) (W) (W) (W) (B) (B) (B)
Five dynasty
Song
Jin
Yuan
Note: W-white body; B-black body.
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Fig. 3. (a)-(b) Appearance of the Five dynasty celadon shards; (c)-(d) low power SEM images of the W3 and W6 fracture surfaces.
W3 and W6 needed to be further researched. The appearance of the typical celadon shards and bodies are shown in Fig. 3(a) and (b). Fig. 3(c) and (d) present the low power SEM pictures of the W3 and W6 fracture surfaces. Apparently, the white and black bodies were all quite porous, whereas the pore sizes were different. The pore sizes of the white bodies were larger than the black body, which was ascribed to the difference of firing temperatures. In a relative low temperature, as the water in clay was evaporated and glass phase was formed, the clay became more and more dense. In a higher temperature, some high temperature stable minerals like iron oxides began to decompose and release gas (O2). So in this stage, the clay matrix became porous again. Accordingly, the white-body one should have been fired at a higher temperature. Since the crystallization behavior of body was greatly influenced by the firing temperature, it was necessary to clarify the formation of various crystalline phases created in the white and black bodies, which could influence the physical properties of body. Fig. 4 shows the XRD patterns of the W3 and W6 bodies. The characteristic amorphous hump could be seen within the 2θ ≈ 15–40° range in all samples, which were associated to the existence of glass phase. The enlarged figure of the range showed that the intensity of glass phase hump was stronger in W3. It further proved the firing temperature of W3 was higher than the W6. Meanwhile, the main crystalline phases of the samples were all quartz (SiO2, PDF#86-2237), mullite (3Al2O3·2SiO2, PDF#83-1881) and cristobalite (SiO2, PDF#82-0512). Among them, the quartz was mainly from the original composition. The cristobalite came from the transformation of quartz (thermal polymorphism), and the mullite were probably crystallized from the decomposition of clay (first mullite) and the precipitation of feldspar (secondary mullite). The refractive index of mullite was more different from that of the glass phase than the refractive index of quartz and cristobalite, so mullite crystals influenced the opacity more than quartz and cristobalite [7]. As a result, the presence of mullite was only considered.
Fig. 4. XRD patterns of W3 and W6 bodies.
Fig. 5 displays the SEM images of the etched W3 and W6 fracture surfaces. Due to the acid treatment, a large number of crystals were observed on the bodies. It can be clearly seen that some lamellar and needle-shaped crystals were disorderly distributed in glass phase of W3 and W6 bodies (Fig. 5(a) and (c)). Additionally, from Fig. 5(b) and (d), the size of crystals in the W3 body was larger than that of W6 body. In order to determine the types of crystals, the SEM/EDS elemental analysis of the W3 body is shown in Fig. 6. As shown in Fig. 6(a)-(c), strong Al and weak Si signals were detected from the aggregate crystals, indicating that these crystals might be mullite rather than quartz and cristobalite. Fig. 6(d) and (e) displays the enlarged image and EDS analysis, measured on the microspots denoted by the numbers 1. Apparently, the crystals in position 1 were rich in Al, Si and O. 3
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Fig. 5. SEM micrographs and enlarged images of bodies on the fracture surfaces, (a)-(b) W3; (c)-(d) W6.
respectively in the W3 and W6 bodies. It could be seen that more crystal boundaries appeared in the W6 body. As a result, the transmittance of the black body was less than the white body [9]. Furthermore, there were still some residual micropores remained in the W6 body (Fig. 5(c)). These residual micropores served as optical scattering centers and further decreased the transmittance of incidence light [8]. The XPS technique is especially powerful for elemental analysis, as the binding energy values of core levels are, to a certain extent dependent on the molecular environment. Hence, XPS was carried out to identify the chemical status of the Ti and Fe elements in the Five dynasty celadon bodies. Typical Ti 2p spectrums of the W3 and W6 within the binding energy range of 470–448 eV are illustrated in Fig. 8(a). As being observed, there was no obvious peak in the W3 spectrum, whereas three peaks appeared in the W6 spectrum. The reason was that the W3 sample had only 0.49 wt% TiO2 (Table 1) so that the intensity of Ti 2p peak was very low. Fig. 8(b) shows the fitted Ti 2p spectrum of the W6 sample. In the fitted spectrum, five peaks of 452.5, 457.3, 458.2, 459.3 and 464.3 eV were observed, which were ascribed to Ti 2p3/2(0), Ti 2p3/2(III), Ti 2p3/2(IV) and Ti 2p1/2. Accordingly, the Ti atom in the celadon body was in both metallic (Ti°) and oxidized state (Ti3+, Ti4+) [10,11]. Fig. 8(c) presents the fitted Fe 2p XPS spectrum of W6 with the Fe 2p3/2(II), Fe 2p3/2(III) and Fe 2p1/2 peaks located at the binding energy positions of 709.9, 714.1 and 724.0 eV, respectively. In addition, the Fe 2p3/2 peak at 718.2 eV was associated with satellite peaks [12,13]. Based on the ratio of relative peak areas, the Fe2+ to Fe3+ atomic rations was 63.6/36.4. The Ti and Fe atoms behave as electron acceptors in the 3d levels, so they could replace each other in the high temperature melt [14,15]. Kim et al. [16] found that the ratio of Fe2+ to Fe3+ was related to the amount of TiO2 in the glaze. This is probably related to the effect of Ti4+ on the stability of Fe3+ relative to Fe2+ in the glaze. Dondi et al. investigated that the yellow color of some modern ceramics was attributed to the formation of pseudobrookite (Fe2TiO5) phase during firing process. It was obtained from a titanium-rich clay preparation.
Combining with the XRD analysis in Fig. 4, the lamellar and needleshaped crystals were inferred as mullite. The lamellar mullite belonged to first mullite, and needle-shaped mullite was the secondary mullite. At about 1200 °C, the alkali ion in feldspar melt diffused to the decomposition area of clay, which contributed to the formation of lamellar mullite. When the firing temperature was increased to 1200– 1250 °C, the precipitated mullite increased dramatically. In addition, with the decreasing of the K2O content, the chemical compositions of the feldspar center area changed towards the crystallization area of mullite, caused the formation of secondary mullite in feldspar melt. At 1200–1400 °C, the liquid phase promoted the diffusion process and the growth of the secondary mullite. Fig. 7 presents the transmittance spectra of the W3 and W6 (the thickness of 3 mm). It was obviously seen that the optical transmittance of W3 kept nearly unchanged at 380–480 nm, but rised significantly as the wavelength was 480–700 nm and declined at 700–760 nm. And yet, the W6 always kept optical transmittance close to 0 at 380–780 nm. The optical transmittance of the ceramic was affected by the reflection of surface, scattering of crystal boundaries and pores as well as absorption of coloring ions [8,9]. Since the surfaces of the W3 and W6 were all celadon glazes, the amount of reflected light had no much difference. However, the amount of absorption and scattering light in the W3 was obviously different from the W6 sample. Based on the analysis of chemical compositions, there were more color oxides in the W6, so the amount of absorption light was more than that of W3. Meanwhile, due to a large number of mullite distributed in the white and black bodies (Fig. 5(a) and (c)), the optical quality of the bodies was affected by the boundaries between mullite and glass phase. They refracted the incidence light and decreased the transmittance of bodies. From Fig. 4, the content of mullite had no much difference in the W3 and W6 bodies, while its size was the major factor of optical transmittance. Based on the SEM analysis in Fig. 5(b) and (d), the average sizes of mullite were 140.2 nm and 63.4 nm 4
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Fig. 6. SEM/EDS elemental analysis of the W3 body, (a)-(c) SEM images and elemental mapping images of Al K and Si K edges; (d)-(e) the enlarged images of (a) and EDS spectra.
The color of pure pseudobrookite was relatively dark and went to brown. One could not exclude the presence of a small amount of Fe2+ in the pseudobrookite structure, because there was a solid state solution 4+ 2+ 4+ between Fe3+ 2 Ti O5 (pseudobrookite) and Fe Ti2 O5 (ferropseudobrookite) [17,18]. However, the presence of Fe2+ and Fe3+ in the same structure increased highly the optical absorption and led to dark colors. Therefore, the coloring mechanism of the black body might be the presence of pseudobrookite and ferropseudobrookite in the Five dynasty celadon [19]. Chen et al. [20,21] reported that titanium suboxide (TiO, Ti2O3 and TinO2n-1 (1 ≤ n ≤ 10)) was a black pigment with pure color and good thermal stability. According to the XPS analysis in Fig. 8(b), there was probably the Ti2O3 in the W6. Fig. 9 shows the SEM/EDS analysis of the W6 surface. It could be clearly seen that the crystal in position 2 was rich in Ti except for Al, Si, O and Fe. By computation, the atomic ratio of Ti/O was 1 : 1.3, which was consistent with the atomic ratio of Ti2O3. As a result, the body color of W6 got black.
Fig. 7. Optical transmittance of the W3 and W6.
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Fig. 8. XPS spectrums of the Ti 2p and Fe 2p, (a) XPS spectrums of Ti 2p with W3 and W6; (b)-(c) fitting XPS spectrum of Ti 2p and Fe 2p with W6.
Fig. 9. SEM image and EDS spectra of crystal on the W6 surface.
Fe2+Ti24+O5 and Ti2O3) and deepened the color of body. The translucency of celadon body was related to the scattering light of crystal boundaries and residual micropores. The microstructure analysis by SEM showed that the average sizes of mullite were 140.2 nm and 63.4 nm respectively in the white and black bodies, causing more crystal boundaries appeared in the black body. In addition, there were also more residual micropores in the black body. Therefore, the black body had much worse transmittance. These results could thus potentially help researchers imitate the translucent and white celadon body of Yaozhou kiln.
4. Conclusion The Five dynasty celadon shards of Yaozhou kiln excavated from the Yaozhou kiln site of Tongchuan were adopted as test samples. According to the XRF and XPS results, the Five dynasty celadon body had lower SiO2 content than that of other dynasties, which provided an evidence for dating research on ancient celadon. Furthermore, there were obvious differences in K2O, Al2O3, Fe2O3 and TiO2 contents between the white body and black body. The white body had higher K2O and lower Al2O3 contents than the black body, which helped to form more glass phase and melt with impurities so that weakened the coloring of impurities. Meanwhile, the high Fe2O3 and TiO2 contents in the black body contributed to the iron 4+ titanium compounds and titanium suboxide formation (Fe3+ 2 Ti O5 ,
Acknowledgements This work was supported by the National Foundation of Natural 6
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[10] M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J.J. Niu, M. Heon, L. Hultman, Y. Gogotsi, M.W. Barsoum, Two-dimensional nanocrystals produced by exfoliation of Ti3AlC2, Adv. Mater. 23 (2011) 4248–4253. [11] M.C. Biesinger, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn, Appl. Surf. Sci. 257 (2010) 887–898. [12] T. Yamashita, P. Hayes, Analysis of XPS spectra of Fe2+ and Fe3+ ions in oxide materials, Appl. Surf. Sci. 254 (2008) 2441–2449. [13] M. Omran, T. Fabritius, A.M. Elmahdy, N.A. Abdel-Khalek, M. El-Aref, A. Elmanawi, XPS and FTIR spectroscopic study on microwave treated high phosphorus iron ore, Appl. Surf. Sci. 345 (2015) 127–140. [14] O. Lobacheva, Y.M. Yiu, N. Chen, T.K. Sham, L.V. Goncharova, Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3, (001), Appl. Surf. Sci. 393 (2016) 74–81. [15] V. Bilovol, S. Ferrari, D. Derewnicka, F.D. Saccone, XANES and XPS study of electronic structure of Ti-enriched Nd-Fe-B ribbons, Mater. Chem. Phys. 146 (2014) 269–276. [16] J.Y. Kim, H. No, A.Y. Jeon, U. Kim, J.H. Pee, W.S. Cho, K.J. Kim, C.M. Kim, C.S. Kim, Mössbauer spectroscopic and chromaticity analysis on colorative mechanism of celadon glaze, Ceram. Int. 37 (2011) 3389–3395. [17] T. Wang, C. Sanchez, J. Groenen, P. Sciau, Raman spectroscopy analysis of terra sigillata: the yellow pigment of marbled sigillata, J. Raman Spectrosc. (2016). [18] W.Q. Guo, S. Malus, D.H. Ryan, Z. Altounian, Crystal structure and cation distributions in the FeTi2O5-Fe2TiO5 solid solution series, J. Phys. Condens. Mater. 11 (1999) 6337. [19] X.Q. Chen, J.Z. Li, R.F. Huang, S.P. Chen, Z.X. Zhuo, B.R. Du, Tang dynasty Yaozhou celadon and black glazed wares, Chin. Ceram. (1990) 57–62. [20] X.B. Chen, L. Liu, P.Y. Yu, S.S. Mao, Increasing solar absorption for photocatalysis with black hydrogenated titanium dioxide nanocrystals, Science 331 (2011) 746. [21] M.C. Pan, Y.N. Wang, H.Q. Xu, Y.X. Yang, X.N. Liu, Preparation and characterization of black titanium oxides with large surface area, J. Inorg. Mater. 29 (2013) 1345–1354.
Science, China (51472153), the Key Project of State Administration of Culture Heritage, China (20120218), Shaanxi Science & Technology Co-ordination & Innovation Project, China (2015KTTSGY02-03, 2017TSCXL-GY-08-05) and the Graduate Innovation Fund of Shaanxi University of Science and Technology. References [1] J.Z. Li, History of Ancient Science and Technology (Ceramics Part), Science Press, Beijing, 1998. [2] F. Wang, Pottery and Porcelain of Yaozhou kiln, Shaanxi Science and Technology Press, Xi'an, 2000. [3] T.Q. Zhu, H. Huang, H.M. Wang, L.M. Hu, X.B. Yi, Comparison of celadon from the Yaozhou and Xicun kilns in the Northern Song Dynasty of China by X-ray fluorescence and microscopy, J. Archaeol. Sci. 38 (2011) 3134–3140. [4] P. Shi, F. Wang, J.F. Zhu, B. Zhang, T. Zhao, Y. Wang, Y. Qin, Study on the Five dynasty sky-green glaze from Yaozhou kiln and its coloring mechanism, Ceram. Int. 43 (2017) 2943–2949. [5] G.Z. Li, P.Y. Guan, A study on Yaozhou celadon, J. Chin. Ceram. Soc. 4 (1979) 360–369. [6] W.D. Li, J.Z. Li, J. Wu, J.K. Guo, Study on the phase-separated opaque glaze in ancient China from Qionglai kiln, Ceram. Int. 29 (2003) 933–937. [7] L. Pagliari, M. Dapiaggi, A. Pavese, F. Francescon, A kinetic study of the quartzcristobalite phase transition, J. Eur. Ceram. Soc. 33 (2013) 3403–3410. [8] J.W. Dai, M.Q. Cao, H.M. Kou, Y.B. Pan, J.K. Guo, J. Li, Fabrication and properties of transparent Tb:YAG fluorescent ceramics with different doping concentrations, Ceram. Int. 42 (2016) 13812–13818. [9] W. Guo, J.Q. Huang, Y. Lin, Q.F. Huang, B.J. Fei, J. Chen, W.C. Wang, F.Y. Wang, C.Y. Ma, X.Y. Yuan, Y.G. Cao, A low viscosity slurry system for fabricating chromium doped yttrium aluminum garnet (Cr:YAG) transparent ceramics, J. Eur. Ceram. Soc. 35 (2015) 3873–3878.
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Coloring and translucency mechanisms of Five dynasty celadon body from Yaozhou kiln ⁎
Pei Shi, Fen Wang , Yi Wang, Jianfeng Zhu, Biao Zhang, Yuan Fang School of Materials Science and Engineering, Shaanxi University of Science & Technology, Xi'an 710021, PR China
A R T I C L E I N F O
A BS T RAC T
Keywords: Yaozhou kiln Five dynasty celadon body Coloring mechanism Translucency mechanism
This work takes the Five dynasty celadon body of Yaozhou kiln as the major study objects. Based on the analysis of XRF, XRD, SEM/EDS, UV/Vis/NIR spectrophotometers and XPS, the chemical compositions, microstructure and optical quality of the white and black bodies have been investigated. The results indicates that the Five dynasty celadon body has lower SiO2 content than that of the other dynasties, which provides an evidence for dating research on ancient celadon. Furthermore, the high Fe2O3 and TiO2 contents enhance the formation of 4+ 2+ 4+ Fe3+ 2 Ti O5 , Fe Ti2 O5 and Ti2O3 in the black body and deepen the coloring of Fe2O3. As a result, its color is darker than the white body. In addition, there are more crystal boundaries and residual micropores appeared in the black body. They serve as optical scattering centers and decrease the transmittance of incidence light. Therefore, the black body has much worse transmittance than that of the white body.
1. Introduction The central site of Yaozhou kiln is in the Huangpu town of Tongchuan city. As the Tongchuan city was affiliated with Yaozhou in Song dynasty, descendants called it “Yaozhou kiln”. It started from the Tang dynasty (618 AD–917 AD), passed through the Five dynasty (907 AD–960 AD), matured in the Song dynasty (960 AD–1279 AD) and stopped development in the Yuan dynasty (1279 AD–1368). The history of its continuous production had persisted for nearly 800 years [1,2]. At different times, the Yaozhou kiln had representative artistic achievements, such as the Tang dynasty black and tea dust wares, the Five dynasty sky-green ware, the Song dynasty olive-green ware and the Jin and Yuan dynasties moon-white ware. At first, the Yaozhou celadon was appreciated for the Song dynasty celadon with carved decoration [3]. Nevertheless, the awareness about the Five dynasty celadon had been going on for quite a long time. It was built on the accumulation of celadon shards excavated from kiln sites, city sites and tombs. At present, the Five dynasty sky-green ware is the most exciting and favorite celadon [4]. According to the body color, the Five dynasty celadon could be roughly divided into two groups: the white body and black body celadon (Fig. 1(a) and (b)). Most belong to the black body celadon, and the white body celadon is comparatively rare in the Five dynasty celadon shards excavated from kiln sites. In the beginning, due to a lot of over-firing bubbles in the early white body celadon, it did not draw a great deal of attention and interest. For the high quality white body celadon, the glaze color is green-blue and similar to that of Ru and
⁎
Guan kilns. It should be the oldest sky-green ware. The thin body celadon with carving patterns has the effect of the rice-pattern porcelain of Jingdezhen. The glaze surface is very bright and delicate as clearly as the day they are fired, and has very few cracks. Especially, the thickness of thinner body celadon is about 1 mm. It has high translucency, as well as the texture is pure and dense (Fig. 1(c)). The body color of the black body celadon is no less than the black-gray body celadon of Ge kiln, whereas it coats engobe. Furthermore, the decorative practices are mainly patternless and drawing flowers. Compared with the white body and black body celadon, the former has higher translucency and lighter body color than the latter. However, in addition to some archaeological reports, there is no special scientific research report about the formation mechanisms for the body color and translucency in the Five dynasty celadon of Yaozhou kiln [2]. In this paper, the chemical composition, firing condition and microstructure of the Five dynasty celadon body were studied, aiming at investigating the correlation between them and the body appearance. Based on that, the scientific rules behind the aesthetically pleasing appearance of the Yaozhou white body and black body celadon of Five dynasty was proposed. This work will throw some light on the better understanding of the coloring and translucency mechanisms about the Five dynasty celadon body. 2. Experimental procedure All of the celadon shards excavated from the Yaozhou kiln site of
Corresponding author. E-mail address: [email protected] (F. Wang).
http://dx.doi.org/10.1016/j.ceramint.2017.05.334 Received 17 May 2017; Received in revised form 27 May 2017; Accepted 27 May 2017 0272-8842/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Shi, P., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.05.334
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Fig. 1. Five dynasty celadon, (a) white body; (b) black body; (c) thin body.
Tongchuan were provided by the Yao kiln museum of Shaanxi province. The chemical compositions of shard bodies were determined by X-ray fluorescence (XRF, AXIOS, Netherlands). The phase compositions of the test pieces were identified by X-ray diffraction (XRD, D/ max 2200PC, Japan) with Co Kα radiation (λ = 1.7889 Å) and scanning from 10° to 70° under 40 kV and 100 mA. The chemical analysis was performed on the X-ray photoelectron spectrometer (XPS, AXIS Supra, UK) using Al Kα radiation. Microstructure and crystal composition were studied using scanning electron microscopy (SEM, S4800, Japan) equipped with an energy dispersive spectrometry (EDS). Before the testing, the fracture surfaces of the samples were etched using 1 vol% HF for 20 s to expose the crystals. Moreover, the in-line transmittance was obtained by using a UV/Vis/NIR spectrophotometers (Cary 5000, USA).
Fig. 2. Two dimensional corresponding chemical compositions analysis of the Yaozhou celadon bodies from different dynasties.
weakened the coloring of impurities. Moreover, it also showed that the black ones were added in purple clay. The high K2O in white-body ones might reveal the raw materials contained abundant feldspar. Whereas, the high TiO2 content in the black body might be connected with the body color. Comparing the chemical compositions of W1-W7 bodies, the Fe2O3 content of the black ones was higher than white-body one. On the basis of verification testing, 3% of Fe2O3 was the dividing line for black and white body colors. The content of Fe2O3 in the white-body samples was below 2%, causing the body color was light. In addition to the chemical compositions, the body appearance variations also came from the fluctuation of firing conditions such as firing temperature, time and atmosphere in the horse-shoe kilns with wood as fuel [6]. Combining the color and performance of bodies, the
3. Results and discussion Table 1 lists the chemical compositions of celadon bodies from the Tang, Five dynasty, Song, Jin and Yuan dynasty. By comparison, the Al2O3, SiO2, K2O and TiO2 contents had significant difference. In order to further analysis their characteristic, the two-dimension chart of these celadon bodies from different dynasties is shown in Fig. 2. As being observed, the Five dynasty celadon body had lower SiO2 content than that of other dynasties, which provided an evidence for dating research on ancient celadon [5]. Furthermore, there were obvious differences in K2O, Al2O3 and TiO2 contents between the white body and black body. The higher K2O and lower Al2O3 contents in white body helped to form more glass phase and melt with impurities so that Table 1 Chemical compositions of the shard bodies from different dynasties (wt%). Number
Dynasty
Na2O
MgO
Al2O3
SiO2
K2O
CaO
TiO2
Fe2O3
T1 T2 T3 W1 W2 W3 W4 W5 W6 W7 S1 S2 S3 J1 J2 J3 Y1 Y2 Y3
Tang
0.57 0.35 0.31 0.16 0.47 0.17 0.39 0.23 0.25 0.25 0.53 0.98 0.38 0.17 0.45 0.28 0.07 0.43 0.22
0.95 0.98 1.11 0.46 0.62 0.79 0.76 0.88 1.07 1.05 0.84 0.93 0.90 0.86 0.81 0.89 1.15 0.87 0.76
20.39 25.82 27.44 22.98 22.67 18.90 22.41 28.78 29.35 29.53 24.33 23.28 24.42 20.29 19.81 21.39 18.83 22.38 19.89
71.83 66.33 64.12 66.60 67.63 72.18 67.19 62.81 62.67 61.78 67.65 68.23 68.05 71.58 72.21 71.13 73.49 68.92 72.12
2.29 1.77 1.97 6.17 5.09 4.59 5.37 1.84 1.84 1.97 2.25 2.08 2.11 2.38 2.23 2.38 2.29 2.35 2.55
0.41 0.50 0.44 0.67 0.63 0.50 0.98 1.01 0.34 0.32 0.51 0.57 0.32 0.83 0.62 0.39 0.79 1.07 0.54
0.65 1.08 0.99 0.22 0.22 0.49 0.25 1.11 1.19 1.29 0.76 0.78 0.85 0.67 0.61 0.68 0.62 0.71 0.77
1.90 2.18 2.63 1.74 1.66 1.38 1.65 2.34 2.30 2.83 2.13 2.15 1.98 2.22 2.26 1.86 1.76 2.27 2.14
(W) (W) (W) (W) (B) (B) (B)
Five dynasty
Song
Jin
Yuan
Note: W-white body; B-black body.
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Fig. 3. (a)-(b) Appearance of the Five dynasty celadon shards; (c)-(d) low power SEM images of the W3 and W6 fracture surfaces.
W3 and W6 needed to be further researched. The appearance of the typical celadon shards and bodies are shown in Fig. 3(a) and (b). Fig. 3(c) and (d) present the low power SEM pictures of the W3 and W6 fracture surfaces. Apparently, the white and black bodies were all quite porous, whereas the pore sizes were different. The pore sizes of the white bodies were larger than the black body, which was ascribed to the difference of firing temperatures. In a relative low temperature, as the water in clay was evaporated and glass phase was formed, the clay became more and more dense. In a higher temperature, some high temperature stable minerals like iron oxides began to decompose and release gas (O2). So in this stage, the clay matrix became porous again. Accordingly, the white-body one should have been fired at a higher temperature. Since the crystallization behavior of body was greatly influenced by the firing temperature, it was necessary to clarify the formation of various crystalline phases created in the white and black bodies, which could influence the physical properties of body. Fig. 4 shows the XRD patterns of the W3 and W6 bodies. The characteristic amorphous hump could be seen within the 2θ ≈ 15–40° range in all samples, which were associated to the existence of glass phase. The enlarged figure of the range showed that the intensity of glass phase hump was stronger in W3. It further proved the firing temperature of W3 was higher than the W6. Meanwhile, the main crystalline phases of the samples were all quartz (SiO2, PDF#86-2237), mullite (3Al2O3·2SiO2, PDF#83-1881) and cristobalite (SiO2, PDF#82-0512). Among them, the quartz was mainly from the original composition. The cristobalite came from the transformation of quartz (thermal polymorphism), and the mullite were probably crystallized from the decomposition of clay (first mullite) and the precipitation of feldspar (secondary mullite). The refractive index of mullite was more different from that of the glass phase than the refractive index of quartz and cristobalite, so mullite crystals influenced the opacity more than quartz and cristobalite [7]. As a result, the presence of mullite was only considered.
Fig. 4. XRD patterns of W3 and W6 bodies.
Fig. 5 displays the SEM images of the etched W3 and W6 fracture surfaces. Due to the acid treatment, a large number of crystals were observed on the bodies. It can be clearly seen that some lamellar and needle-shaped crystals were disorderly distributed in glass phase of W3 and W6 bodies (Fig. 5(a) and (c)). Additionally, from Fig. 5(b) and (d), the size of crystals in the W3 body was larger than that of W6 body. In order to determine the types of crystals, the SEM/EDS elemental analysis of the W3 body is shown in Fig. 6. As shown in Fig. 6(a)-(c), strong Al and weak Si signals were detected from the aggregate crystals, indicating that these crystals might be mullite rather than quartz and cristobalite. Fig. 6(d) and (e) displays the enlarged image and EDS analysis, measured on the microspots denoted by the numbers 1. Apparently, the crystals in position 1 were rich in Al, Si and O. 3
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Fig. 5. SEM micrographs and enlarged images of bodies on the fracture surfaces, (a)-(b) W3; (c)-(d) W6.
respectively in the W3 and W6 bodies. It could be seen that more crystal boundaries appeared in the W6 body. As a result, the transmittance of the black body was less than the white body [9]. Furthermore, there were still some residual micropores remained in the W6 body (Fig. 5(c)). These residual micropores served as optical scattering centers and further decreased the transmittance of incidence light [8]. The XPS technique is especially powerful for elemental analysis, as the binding energy values of core levels are, to a certain extent dependent on the molecular environment. Hence, XPS was carried out to identify the chemical status of the Ti and Fe elements in the Five dynasty celadon bodies. Typical Ti 2p spectrums of the W3 and W6 within the binding energy range of 470–448 eV are illustrated in Fig. 8(a). As being observed, there was no obvious peak in the W3 spectrum, whereas three peaks appeared in the W6 spectrum. The reason was that the W3 sample had only 0.49 wt% TiO2 (Table 1) so that the intensity of Ti 2p peak was very low. Fig. 8(b) shows the fitted Ti 2p spectrum of the W6 sample. In the fitted spectrum, five peaks of 452.5, 457.3, 458.2, 459.3 and 464.3 eV were observed, which were ascribed to Ti 2p3/2(0), Ti 2p3/2(III), Ti 2p3/2(IV) and Ti 2p1/2. Accordingly, the Ti atom in the celadon body was in both metallic (Ti°) and oxidized state (Ti3+, Ti4+) [10,11]. Fig. 8(c) presents the fitted Fe 2p XPS spectrum of W6 with the Fe 2p3/2(II), Fe 2p3/2(III) and Fe 2p1/2 peaks located at the binding energy positions of 709.9, 714.1 and 724.0 eV, respectively. In addition, the Fe 2p3/2 peak at 718.2 eV was associated with satellite peaks [12,13]. Based on the ratio of relative peak areas, the Fe2+ to Fe3+ atomic rations was 63.6/36.4. The Ti and Fe atoms behave as electron acceptors in the 3d levels, so they could replace each other in the high temperature melt [14,15]. Kim et al. [16] found that the ratio of Fe2+ to Fe3+ was related to the amount of TiO2 in the glaze. This is probably related to the effect of Ti4+ on the stability of Fe3+ relative to Fe2+ in the glaze. Dondi et al. investigated that the yellow color of some modern ceramics was attributed to the formation of pseudobrookite (Fe2TiO5) phase during firing process. It was obtained from a titanium-rich clay preparation.
Combining with the XRD analysis in Fig. 4, the lamellar and needleshaped crystals were inferred as mullite. The lamellar mullite belonged to first mullite, and needle-shaped mullite was the secondary mullite. At about 1200 °C, the alkali ion in feldspar melt diffused to the decomposition area of clay, which contributed to the formation of lamellar mullite. When the firing temperature was increased to 1200– 1250 °C, the precipitated mullite increased dramatically. In addition, with the decreasing of the K2O content, the chemical compositions of the feldspar center area changed towards the crystallization area of mullite, caused the formation of secondary mullite in feldspar melt. At 1200–1400 °C, the liquid phase promoted the diffusion process and the growth of the secondary mullite. Fig. 7 presents the transmittance spectra of the W3 and W6 (the thickness of 3 mm). It was obviously seen that the optical transmittance of W3 kept nearly unchanged at 380–480 nm, but rised significantly as the wavelength was 480–700 nm and declined at 700–760 nm. And yet, the W6 always kept optical transmittance close to 0 at 380–780 nm. The optical transmittance of the ceramic was affected by the reflection of surface, scattering of crystal boundaries and pores as well as absorption of coloring ions [8,9]. Since the surfaces of the W3 and W6 were all celadon glazes, the amount of reflected light had no much difference. However, the amount of absorption and scattering light in the W3 was obviously different from the W6 sample. Based on the analysis of chemical compositions, there were more color oxides in the W6, so the amount of absorption light was more than that of W3. Meanwhile, due to a large number of mullite distributed in the white and black bodies (Fig. 5(a) and (c)), the optical quality of the bodies was affected by the boundaries between mullite and glass phase. They refracted the incidence light and decreased the transmittance of bodies. From Fig. 4, the content of mullite had no much difference in the W3 and W6 bodies, while its size was the major factor of optical transmittance. Based on the SEM analysis in Fig. 5(b) and (d), the average sizes of mullite were 140.2 nm and 63.4 nm 4
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Fig. 6. SEM/EDS elemental analysis of the W3 body, (a)-(c) SEM images and elemental mapping images of Al K and Si K edges; (d)-(e) the enlarged images of (a) and EDS spectra.
The color of pure pseudobrookite was relatively dark and went to brown. One could not exclude the presence of a small amount of Fe2+ in the pseudobrookite structure, because there was a solid state solution 4+ 2+ 4+ between Fe3+ 2 Ti O5 (pseudobrookite) and Fe Ti2 O5 (ferropseudobrookite) [17,18]. However, the presence of Fe2+ and Fe3+ in the same structure increased highly the optical absorption and led to dark colors. Therefore, the coloring mechanism of the black body might be the presence of pseudobrookite and ferropseudobrookite in the Five dynasty celadon [19]. Chen et al. [20,21] reported that titanium suboxide (TiO, Ti2O3 and TinO2n-1 (1 ≤ n ≤ 10)) was a black pigment with pure color and good thermal stability. According to the XPS analysis in Fig. 8(b), there was probably the Ti2O3 in the W6. Fig. 9 shows the SEM/EDS analysis of the W6 surface. It could be clearly seen that the crystal in position 2 was rich in Ti except for Al, Si, O and Fe. By computation, the atomic ratio of Ti/O was 1 : 1.3, which was consistent with the atomic ratio of Ti2O3. As a result, the body color of W6 got black.
Fig. 7. Optical transmittance of the W3 and W6.
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Fig. 8. XPS spectrums of the Ti 2p and Fe 2p, (a) XPS spectrums of Ti 2p with W3 and W6; (b)-(c) fitting XPS spectrum of Ti 2p and Fe 2p with W6.
Fig. 9. SEM image and EDS spectra of crystal on the W6 surface.
Fe2+Ti24+O5 and Ti2O3) and deepened the color of body. The translucency of celadon body was related to the scattering light of crystal boundaries and residual micropores. The microstructure analysis by SEM showed that the average sizes of mullite were 140.2 nm and 63.4 nm respectively in the white and black bodies, causing more crystal boundaries appeared in the black body. In addition, there were also more residual micropores in the black body. Therefore, the black body had much worse transmittance. These results could thus potentially help researchers imitate the translucent and white celadon body of Yaozhou kiln.
4. Conclusion The Five dynasty celadon shards of Yaozhou kiln excavated from the Yaozhou kiln site of Tongchuan were adopted as test samples. According to the XRF and XPS results, the Five dynasty celadon body had lower SiO2 content than that of other dynasties, which provided an evidence for dating research on ancient celadon. Furthermore, there were obvious differences in K2O, Al2O3, Fe2O3 and TiO2 contents between the white body and black body. The white body had higher K2O and lower Al2O3 contents than the black body, which helped to form more glass phase and melt with impurities so that weakened the coloring of impurities. Meanwhile, the high Fe2O3 and TiO2 contents in the black body contributed to the iron 4+ titanium compounds and titanium suboxide formation (Fe3+ 2 Ti O5 ,
Acknowledgements This work was supported by the National Foundation of Natural 6
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