Thermal Expansion of Sintered Glass Ceramics in the System BaO

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Thermal expansion of sintered glass ceramics in the system BaO-SrO-ZnO-SiO and its dependence on the particle size 2

Christian Thieme, Martin Schlesier, Christian Bocker, Gabriel Buzatto de Souza, and Christian Russel ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b07353 • Publication Date (Web): 19 Jul 2016 Downloaded from http://pubs.acs.org on July 21, 2016

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ACS Applied Materials & Interfaces

Thermal expansion of sintered glass ceramics in the system BaO-SrO-ZnOSiO2 and its dependence on the particle size Christian Thieme*, Martin Schlesier, Christian Bocker, Gabriel Buzatto de Souza, Christian Rüssel Otto-Schott-Institut für Materialforschung, Jena University, Fraunhoferstr. 6, 07743 Jena

Corresponding author: Christian Thieme email: [email protected] telephone: +49 (0) 3641 948525 fax: +49 (0) 3641 948502 email of Martin Schlesier: [email protected] email of Christian Bocker: [email protected] email of Gabriel Buzatto de Souza: [email protected] email of Christian Rüssel: [email protected]

Abstract The thermal expansion behavior of sintered glass-ceramics containing high concentrations of Ba1xSrxZn2Si2O7,

a phase with very low and highly anisotropic thermal expansion behavior was

investigated. The observed phase has the crystal structure of the high-temperature phase of BaZn2Si2O7, which can be stabilized by the introduction of Sr2+ into this phase. The high anisotropy leads to micro cracking within the volume of the samples, which strongly affects the dilatometric thermal expansion. However, these cracks also have an influence on the nominal thermal expansion of the as mentioned phase, which decreases if the cracks appear. Below a grain size of around 80 µm, the sintered glass-ceramics have almost no cracks and show positive thermal expansion. Hence, coefficients of thermal expansion in between -5.6 and 6.5·10-6 K-1 were measured. Besides dilatometric studies, the effect of the microstructure on the thermal expansion was also measured using in situ X-ray diffraction at temperatures up to 1000 °C.

Keywords glass-ceramics, sintering, high-temperature X-ray diffraction, negative thermal expansion, grain-size ACS Paragon Plus Environment


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Introduction Commercial glass-ceramics with low thermal expansion are commonly obtained from the Li2O · Al2O3 · SiO2 system in which crystalline phases with a structure similar or equal to β-quartz are formed.1–3 This high-temperature (HT) phase of quartz exhibits very low and depending on the temperature also negative thermal expansion and is in the case of pure quartz thermodynamically stable at temperatures above 573 °C.4 Below this temperature, the low-temperature (LT) phase (α-quartz) occurs, which has high thermal expansion and can be used in order to provide glass-ceramics with high coefficients of thermal expansion (CTEs).5 An even higher thermal expansion in a narrow temperature range can be achieved by the phase transition from low tetragonal cristobalite to cubic high cristobalite.6 However, the β-quartz structure can be stabilized also at room temperature or below by the formation of solid solutions in wide concentration ranges.7 Such glass-ceramic materials based on high- or low-quartz are hard to prepare especially because of the high melting temperatures, in most cases at least 1600 °C.8–10 A similar behavior to quartz can be found in BaZn2Si2O7, which has a much lower melting point than quartz-based materials.11 It has a very high CTE of around 17.6 ·10-6 K-1 up to the phase transition at 280 °C.12 At higher temperatures, the HT-phase with its very low and partially negative thermal expansion is stable.13 The phase transition temperature can be shifted to higher temperatures by the formation of solid solutions in which the Zn2+-sites are partially or fully replaced by ions with the same valence state and similar ionic radii.12,14 A stabilization of the HT-phase, i.e. a shift of the phase transition to lower temperatures was recently reported by the substitution of the Ba2+-sites with Sr2+ions.15 If a certain Sr2+-concentration is reached, the phase transition does not occur anymore and the HT-phase is stable at room temperature.15 As recently reported, solid solutions in the composition range Ba1-xSrxZn2Si2O7 with 0.1 ≤ x ≤ 0.9 exhibit the crystal structure of HT-BaZn2Si2O7 16 and show in a wide temperature range strongly negative coefficients of thermal expansion. Glasses and glass ceramics in the systems BaO-ZnO-SiO2 and SrO-ZnO-SiO2 are commonly known as materials, exhibiting very high thermal expansion.17,18 Furthermore, glasses from the as mentioned systems possess good sintering abilities, making them suitable for sealing applications.19 The phases crystallized from such glasses are high thermal expansion phases, with the exception of willemite (Zn2SiO4), showing coefficients of thermal expansion (CTEs) usually above 10·10-6 K-1.12,20–22 As

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recently reported, glasses in the quaternary system BaO-SrO-ZnO-SiO2 enable to crystallize Ba1xSrxZn2Si2O7

solid solutions and hence, lead to a strong decrease of the coefficients of thermal

expansion (CTE) of typical sealing glass compositions.23 However, glasses in this system from which high concentrations of Ba1-xSrxZn2Si2O7 as the only phase were crystallized are not known from the literature, to the best of our knowledge. These solid solution phases are some of the first mentioned Al2O3-free phases, which also exhibit negative thermal expansion and are precipitated from glasses also in high volume concentrations. Furthermore, such glasses should possess much lower processing temperatures than the commercial Al2O3 containing compositions. However, the as mentioned solid solutions exhibit a very high anisotropy of the CTEs, i.e. the CTEs of the different crystallographic axes can differ by more than 80 · 10-6 K-1.15 Such anisotropic phases often lead to micro cracking within the sample volume, which strongly decreases the overall thermal expansion and may lead also to large scattering of the CTE values as reported in the literature.24 This paper reports on the thermal expansion of sintered glass-ceramics based on the system BaO-SrOZnO-SiO2 considering the effect of the particle size. Special attention was also paid to the crystallization process as well as to the microstructure of the samples.

Materials and Methods A glass with the composition 8 BaO · 8 SrO · 35 ZnO · 45 SiO2 · 1 ZrO2 ·1 La2O3 · 2 B2O3 was melted in a batch of 200 g using the raw materials BaCO3 (> 98.5 %, Merck), SrCO3 (pure, VEB Laborchemie Apolda), ZnO (> 99 %, Carl Roth GmbH & Co. KG), SiO2 (>99 %, Carl Roth GmbH & Co. KG), ZrO2 (>99 %, Carl Roth GmbH & Co. KG), La2O3 · H2O (pure, VEB Laborchemie Apolda) and H3BO3 (> 99 %, Merck). The glass was melted at 1350 °C kept for 1 h under stirring in an inductively heated furnace using a platinum crucible. At first, the glass was characterized using thermal analysis techniques such as dilatometry, differential scanning calorimetry (DSC) and side-view hot-stage microscopy (HSM). The dilatometric measurements were performed with a NETZSCH Dil 402 PC on cylindrically shaped samples with a diameter of 8 mm and a length in between 15 and 25 mm. The applied heating rate was 5 K/min. DSC



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measurements were performed on a LINSEIS DSC Pt1600 with Pt/Rh10 crucibles and a heating rate of 10 K/min. A self-made HSM was used in order to measure the sintering behavior of the glass. Therefore, a rate of 5 K/min was applied. The error in the temperature of these three thermal analysis techniques is around ± 5 K. The thermal expansion behavior was also studied on powdered samples, which were subsequently sintered and crystallized. The powders were obtained by crushing the glass in a steel mortar. The resulting powder was sieved to different grain size fractions, which were afterwards given into a corundum boat where they were slightly compressed with a spatula. Very fine powder with a grain size of around 4 µm was obtained using a planetary mill with zirconia cups and spheres. The mean value of this powder was determined from slurry made of ethanol in which powder was dispersed using an optical microscope. Afterwards, the samples were pressureless sintered and crystallized inside the corundum boat. The resulting compact samples were used for scanning electron microscopy (SEM), dilatometry and bending strength measurements. The density was determined with a helium pycnometer MICROMERITICS AccuPyc 1330. The crystallization behavior was studied by X-ray diffraction with a RIGAKU Miniflex 300 and Ni-filtered Cu Kα radiation. The scanned 2θ-range was from 10° to 60°. Fine grained powdered samples with a grain size 10 µm in at least one direction). And there are two phases, which look like a brick wall. The microstructure and especially the micro cracks strongly influence the mechanical properties of sintered specimen, which is shown in Fig. 9, where the four-point bending strength is illustrated for different grain sizes as well as different sintering temperatures. It can be seen that the highest mean value of the bending strength was reached for the samples heat treated at 850 °C for 1 h. Higher temperatures as well as a higher grain size lead to a decrease in the bending strength, which is in the range of 30 MPa for the samples obtained from large grain sizes. In order to get chemical information on the appearing phases, elemental mappings using EDX were performed as illustrated in Fig. 10. In order to distinguish between Sr and Si which have an overlap of the emission lines of Si-Kα (1.74 keV) and Sr-Lα (1.81 keV), the excitation voltage was increased to 30 kV in order to detect the Sr-Kα transition at 14.16 keV (see the lower 6 EDX-scans in Fig. 10).



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Because the emission lines of Si-Kα and Sr-Lα cannot be separated reliably, Sr is not displayed for an acceleration voltage of 15 kV. However, the spatial resolution is better at 15 kV (because of the smaller excitation volume in the sample) and four phases can be clearly distinguished in Fig. 10. (i) The black appearing phase is strongly enriched in Si and depleted in all other elements. (ii) La and Zr appear at the same areas and form a second phase. (iii) Regions strongly enriched in Zn and depleted in Ba, La, and Zr are observed. (iv) Ba-enriched regions, depleted in La and Zr are found while Sr is enriched alongside Ba.

Discussion The thermal properties of the glass summarized in Table 1 explain the good sintering behavior of fine glass powders. At the supplied conditions sintering is completed at 757 °C, whereas the crystallization starts at 772 °C. Hence, the two processes occur at well separated temperatures and sintering is not hindered by simultaneously occurring crystallization processes, which would hamper further densification. However, if too high crystallization temperatures are applied, foaming starts, which is a known problem of alkaline earth zinc silicate glasses.17,26 Hence, the crystallization temperature should not be too high. The upper temperature limit is at around 950 °C in the case of the studied glass composition. Some pores were also found in the glass-ceramics. However, this closed porosity does not influence the thermal expansion of the samples below the glass transition temperature of the residual glassy matrix. Above, the pores might slightly affect the thermal expansion. The crystallization leads to the formation of crystals with the structure of HT-BaZn2Si2O7 (see Fig. 3). Due to the studied glass composition, the crystal phase can be assumed to be Ba0.5Sr0.5Zn2Si2O7 because no other Ba- or Sr-containing phases could be detected, neither with XRD nor with EDX. At temperatures of around 900 °C, the formation of willemite starts, which has a higher coefficient of thermal expansion than crystals with the structure of HT-BaZn2Si2O7.25,27 From the diffractograms recorded at room temperature the lattice parameters were also determined (see Fig. 4) as a function of the particle size of the starting powder. It can be seen that the volume of the unit cell is much smaller in the case of the samples prepared from small grain sizes, i.e. the crack free samples. This can be explained as follows: During cooling from the crystallization temperature, the phase with negative


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thermal expansion expands while the residual glassy matrix with its positive thermal expansion contracts and hence, radial compressive stresses are applied to the crystal phase leading to a smaller volume of the unit cell in comparison to the case of the cracked samples. The latter show almost the same volume of the unit cell than the stress-free powders. An analogous behavior was found in the case of the lattice parameters b and. The b parameter is also compressed in the case of crack free materials with small starting grain sizes which is due to the strongly negative thermal expansion in this direction of the unit cell. In the case of the c parameter it is the other way around because of the very high CTEs in this crystallographic direction. And the a parameter scatters around a mean value due to its positive thermal expansion, which is not very high and should therefore be in the same order of magnitude as the residual glassy matrix. The compressed unit cell as well as the non-compressed one also shows different thermal expansion. The in situ XRD measurements, illustrated in Fig. 6, show that the phase embedded in a crack free material has a higher thermal expansion than the same phase in a material containing micro cracks. The dependency of the thermal expansion as a function of the preparation method as well as the pressure was recently reported in Ref.

26

for crystals with the same structure. It should be mentioned

that the error bars of the HT-XRD measurements shown in Fig. 6 are comparatively high because no internal standard could be used. However, both measurements were performed under the same measuring conditions and the same sample shape was used for both measurements and hence the differences in the thermal expansion curves are real effects. The micro cracking leads to a smaller CTE of the main crystal phase, but also strongly affects the dilatometric thermal expansion as illustrated in Fig. 5. The larger the grain size of the starting powder, the smaller is the CTE. This is due to micro cracking, which becomes stronger with increasing grain size of the starting powder. This effect is already known from highly anisotropic phases, for instance Al2TiO5.28 However, in the case of phases with the structure of HT-BaZn2Si2O7 reported here, the micro cracking influences the thermal expansion not only by a contraction of the cracks with increasing temperature. The thermal expansion of the crystal phase itself is also affected by the stresses. The CTE is lower in the case of samples containing micro cracks with a microstructure almost free of stresses.



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The as described micro cracks are also seen in the micrographs shown in Fig. 8, where a bulk glass was crystallized. These cracks cannot be found in the samples crystallized from fine glass powder, which is due to the smaller crystal size of fine powdered samples. Even in the bulk sample, no volume crystals were found, which leads to the growth of large size crystals starting from the surface and hence, micro cracking. These cracks also influence the mechanical properties of the glass-ceramics, i.e. the more cracks occur, the lower is the strength. If the grain size is adjusted accurately, a thermal expansion near zero can be obtained supposed simultaneously with reasonable strength values. However, this will be the focus of future work. The crystal phases identified with XRD agree with the elemental distribution obtained from EDX analyses. Additionally, a phase highly enriched in SiO2 was found (see Fig. 10). This phase was not detected by XRD. This is an indication of an amorphous residual glassy phase. This phase seems to appear in larger concentrations if a larger grain size of the starting powder is used. Besides the Si-rich phase, a Zn-rich phase, which according to the XRDs should be willemite was found. Furthermore, the Ba1-xSrxZn2Si2O7 solid solutions can be attributed to the areas in which Ba as well as Sr is strongly enriched. In between the as mentioned phases, Zr and La are enriched, which should be incorporated into a residual glassy matrix. It should be noted, that boron was detected qualitatively using a wavelength dispersive spectrometer (WDX). However the spatial resolution is not sufficient for elemental mapping in this case. The signal of boron in EDX is too low for a reliable quantitative analysis. However, it can be assumed that the B2O3 is incorporated into the residual glassy matrix because it cannot be incorporated in any other of the appearing phases. Possibly, the boron might also be enriched in the Si-rich phase. The small black areas, observed in Figs. 7 and 8 might also be due to phase separated areas, which might appear during the crystallization process. Such a residual glassy matrix should have a highly positive thermal expansion and should hence, lead to stresses during cooling from the crystallization temperature. However, a stoichiometric glass with the composition of Ba0.5Sr0.5Zn2Si2O7 would solve this problem but it cannot be obtained using conventional melt quenching techniques. Much higher cooling rates would be required in order to obtain such a glass from the melt. But this glass is not suitable to be sintered due to the high crystallization tendency.


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From the XRD, SEM and dilatometry studies, the thermal expansion of the appearing phase can be summarized as follows: Densification of the pressed powder samples takes place by viscous flow of the glass. At the crystallization temperature (Tcryst), the sample is dense, stress- and crack-free. During cooling to room temperature, radial compressive stresses appear on the crystals, which lead to a contraction of the unit cell. If the grain size of the starting powder exceeds 80 µm, cracks appear during cooling, which enable stress relaxation. This relaxed phase shows its negative thermal expansion. However, this effect is overlapped by the contraction of the cracks during reheating. If a grain size below around 80 µm is used, no cracks or only few cracks will appear and the compressive stresses still occur at room temperature and hence the phase is strongly compressed. Negative thermal expansion of this compressed structure is not observed because the volume of the unit cell cannot further decrease. Hence, this phase exhibits positive thermal expansion if it is reheated. Even this positive thermal expansion is much lower than that of conventional glass-ceramics obtained from alkaline earth zinc silicate glasses. The Ba1-xSrxZn2Si2O7 solid solutions hence enable the formation of glass-ceramics with comparatively small CTE by a sintering route.

Conclusions The grain size of glass powder used for sintering strongly influences the dilatometric thermal expansion behavior of the glass-ceramics from the system BaO-SrO-ZnO-SiO2. The main phase appearing in the investigated glass-ceramics has negative and anisotropic thermal expansion. Hence, a grain size above around 80 µm leads to the formation of micro cracks, which strongly affect the thermal expansion behavior, i.e. the cracks will close at higher temperatures leading to a shortening of the sample. These cracks are also responsible for the lower thermal expansion of the appearing phase, which was proved by high temperature X-ray diffraction. The combination of these two effects leads to negative coefficients of thermal expansion below -5·10-6 K-1. Besides the mechanical properties, e.g. the bending strength, also the microstructure depends on the size of the glass powder.



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References (1)

Roy, R.; Agrawal, D. K.; McKinstry, H. A. Very Low Thermal Expansion Coefficient Materials. Annu. Rev. Mater. Sci. 1989, 19, 59–81.

(2)

Arnault, L.; Gerland, M.; Rivière, A. Microstructural Study of Two LAS-Type Glass-Ceramics and Their Parent Glass. J. Mater. Sci. 2000, 35, 2331–2345.

(3)

Evans, J. S. O. Negative Thermal Expansion Materials. J. Chem. Soc., Dalton Trans. 1999, 3317–3326.

(4)

Ackermann, R. J.; Sorrell, C. A. Thermal Expansion and the High–low Transformation in Quartz. I. High-Temperature X-Ray Studies. J. Appl. Crystallogr. 1974, 7, 461–467.

(5)

Dittmer, M.; Müller, M.; Rüssel, C. Self-Organized Nanocrystallinity in MgO–Al2O3–SiO2 Glasses with ZrO2 as Nucleating Agent. Mater. Chem. Phys. 2010, 124, 1083–1088.

(6)

Hunger, A.; Carl, G.; Gebhardt, A.; Rüssel, C. Ultra-High Thermal Expansion Glass–ceramics in the System MgO/Al2O3/TiO2/ZrO2/SiO2 by Volume Crystallization of Cristobalite. J. NonCryst. Solids 2008, 354, 5402–5407.

(7)

Ray, S.; Muchow, G. M. High-Quartz Solid Solution Phases from Thermally Crystallized Glasses of Compositions Li2O,MgO).Al2O3,nSiO2. J. Am. Ceram. Soc. 1968, 51, 678–682.

(8)

Beall, G. H.; Duke, D. A. Transparent Glass-Ceramics. J. Mater. Sci. 1969, 4, 340–352.

(9)

Guo, X.; Yang, H.; Han, C.; Song, F. Crystallization and Microstructure of Li2O–Al2O3–SiO2 Glass Containing Complex Nucleating Agent. Thermochim. Acta 2006, 444, 201–205.

(10)

Karmakar, B.; Kundu, P.; Jana, S.; Dwivedi, R. N. Crystallization Kinetics and Mechanism of Low-Expansion Lithium Aluminosilicate Glass-Ceramics by Dilatometry. J. Am. Ceram. Soc. 2002, 85, 2572–2574.

(11)

Segnit, E. R.; Holland, A. E. The Ternary System BaO-ZnO-SiO2. Aust. J. Chem. 1970, 23, 1077–1085.

(12)

Kerstan, M.; Müller, M.; Rüssel, C. Thermal Expansion of Ba2ZnSi2O7, BaZnSiO4 and the Solid Solution Series BaZn2−xMgxSi2O7 (0≤x≤2) Studied by High-Temperature X-Ray Diffraction and Dilatometry. J. Solid State Chem. 2012, 188, 84–91.


Page 12 of 30

Page 13 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13)

Lin, J. H.; Lu, G. X.; Du, J.; Su, M. Z.; Loong, C.-K.; Richardson Jr, J. W. Phase Transition and Crystal Structures of BaZn2Si2O7. J. Phys. Chem. Solids 1999, 60, 975–983.

(14)

Thieme, C.; Rüssel, C. High Thermal Expansion in the Solid Solution Series BaM2-xNixSi2O7 (M = Zn, Mg, Co) - The Effect of Ni-Concentration on Phase Transition and Expansion. J. Mater. Sci. 2015, 50, 3416–3424.

(15)

Thieme, C.; Rüssel, C. Very High or Close to Zero Thermal Expansion by the Variation of the Sr/Ba Ratio in Ba1-xSrxZn2Si2O7 - Solid Solutions. Dalton Trans. 2016, 45, 4888–4895.

(16)

Thieme, C.; Görls, H.; Rüssel, C. Ba1-xSrxZn2Si2O7 - A New Family of Materials with Negative and Very High Thermal Expansion. Sci. Rep. 2015, 5, 18040.

(17)

Lara, C.; Pascual, M. J.; Durán, A. Glass-Forming Ability, Sinterability and Thermal Properties in the Systems RO–BaO–SiO2 (R = Mg, Zn). J. Non-Cryst. Solids 2004, 348, 149–155.

(18)

Tiwari, B.; Dixit, A.; Kothiyal, G. P. Study of Glasses/glass-Ceramics in the SrO–ZnO–SiO2 System as High Temperature Sealant for SOFC Applications. Int. J. Hydrogen Energy 2011, 36, 15002–15008.

(19)

Lara, C.; Pascual, M. J.; Prado, M. O.; Durán, A. Sintering of Glasses in the System RO– Al2O3–BaO–SiO2 (R=Ca, Mg, Zn) Studied by Hot-Stage Microscopy. Solid State Ionics 2004, 170, 201–208.

(20)

Kerstan, M.; Rüssel, C. Barium Silicates as High Thermal Expansion Seals for Solid Oxide Fuel Cells Studied by High-Temperature X-Ray Diffraction (HT-XRD). J. Power Sources 2011, 196, 7578–7584.

(21)

Kerstan, M.; Thieme, C.; Grosch, M.; Müller, M.; Rüssel, C. BaZn2Si2O7 and the Solid Solution Series BaZn2−xCoxSi2O7 (0≤x≤2) as High Temperature Seals for Solid Oxide Fuel Cells Studied by High-Temperature X-Ray Diffraction and Dilatometry. J. Solid State Chem. 2013, 207, 55–60.

(22)

Thieme, C.; Rüssel, C. Thermal Expansion Behavior of SrSiO3 and Sr2SiO4 Determined by High-Temperature X-Ray Diffraction and Dilatometry. J. Mater. Sci. 2015, 50, 5533–5539.

(23)

Thieme, C.; de Souza, G. B.; Rüssel, C. Glass-Ceramics in the System BaO-SrO-ZnO-SiO2 with Adjustable Coefficients of Thermal Expansion. J. Am. Ceram. Soc. 2016.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(24)

Chu, C. N.; Saka, N.; Suh, N. P. Negative Thermal Expansion Ceramics: A Review. Mater. Sci. Eng. 1987, 95, 303–308.

(25)

Thieme, C.; Waurischk, T.; Heitmann, S.; Rüssel, C. New Family of Materials with Negative Coefficients of Thermal Expansion: The Effect of MgO, CoO, MnO, NiO, or CuO on the Phase Stability and Thermal Expansion of Solid Solution Phases Derived from BaZn2Si2O7. Inorg. Chem. 2016, 55 (9), 4476–4484.

(26)

Kracker, M.; Thieme, C.; Häßler, J.; Rüssel, C. Sol–gel Powder Synthesis and Preparation of Ceramics with High- and Low-Temperature Polymorphs of BaxSr1-xZn2Si2O7 (x=1 and 0.5): A Novel Approach to Obtain Zero Thermal Expansion. J. Eur. Ceram. Soc. 2016, 36, 2097–2107.

(27)

Kerstan, M.; Müller, M.; Rüssel, C. Binary, Ternary and Quaternary Silicates of CaO, BaO and ZnO in High Thermal Expansion Seals for Solid Oxide Fuel Cells Studied by HighTemperature X-Ray Diffraction (HT-XRD). Mater. Res. Bull. 2011, 46, 2456–2463.

(28)

Parker, F. J. Al2TiO5-ZrTiO4-ZrO2 Composites: A New Family of Low-Thermal-Expansion Ceramics. J. Am. Ceram. Soc. 1990, 73, 929–932.

(29)

Klaska, K. H.; Eck, J. C.; Pohl, D. New Investigation of Willemite. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 1978, 34, 3324–3325.


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Figure captions Figure 1

Thermal analysis of the glass. On the left side, results from dilatometry (bulk sample), DSC (< 40 µm) and HSM (< 40 µm) are shown. The DSC-curve was baselinecorrected. On the right side, results from DSC using different particle sizes are shown. The temperatures given inside the graphs are the respective onsets of the crystallization.

Figure 2

Side-view hot-stage microscopy of glass with a particle size < 40 µm. (A) Sintering; (B) Foaming; (C) Melting.

Figure 3

XRD-patterns of the glass, crystallized at different temperatures kept for 1 h. Most of the observed peaks are attributed to Ba0.5Sr0.5Zn2Si2O7 with HT-BaZn2Si2O7-structure. All other peaks belong to Zn2SiO4. In the lower part, theoretical peak positions taken from Refs. 16,29 are illustrated.

Figure 4

Lattice parameters of sintered glass-ceramics prepared by pressureless sintering of glass powders, which were heated with 5 K/min to 950 °C for 1 h. The lattice parameters were determined using sintered samples, which were not milled before the XRD scans were performed. The lattice parameters of the samples denoted as “stressfree” were taken from Ref. 25, where fine grained powders from solid state reaction, i.e. without a glassy matrix, were characterized.

Figure 5

Dilatometry of samples with different grain sizes. The values are given in units of [µm]. All the samples were heat treated at 950 °C kept for 1 h. The applied heating rate was 5 K/min. The sample denoted as “63-100/100-200” is made of a 1:1 mixture of powders with the particle size 63-100 µm and 100-200 µm. The same was done for the sample “~ 4/100-315”.

Figure 6

Thermal expansion of the unit cell of Ba0.5Sr0.5Zn2Si2O7 between room temperature and 1000 °C. The sintered bulk samples were obtained by heating different glass powders with a rate of 5 K/min to 950 °C kept for 1 h. Plates with a thickness of 1 mm were measured. The data of the powder from the solid state reaction are shown for comparison and were taken from Ref. 25.



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Figure 7

Fine grained powder heat treated at different temperatures.

Figure 8

Bulk glass sample heated with 5 K/min to 950 °C kept for 1 h.

Figure 9

Four-point bending strength of samples sintered at different temperatures using different grain sizes of the starting powders. The values next to the triangles are the respective mean values in units of [MPa].

Figure 10

EDX analyses with 15 kV (upper 6 images) and 30 kV (lower 5 images) acceleration voltage of a sintered sample (grain size 100 - 315 µm), heat treated at 950 °C kept for 1 h. The numbers on the right of each micrograph are given in units of counts.


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Tables Table 1: Properties of the glass. Property

Method

Unit

Value

Glass transition temperature

Dilatometry

°C

654

Measuring error 5

DSC

°C

646

5

Density

Pycnometry

g/cm³

4.00

0.01

DSC

°C

876

5

DSC

°C

772

5

Softening point

Dilatometry

°C

690

5

Coefficient of thermal expansion

Dilatometry

10-6/K

7.3

0.1

°C

714

5

°C

757

5

Onset of crystallization (bulk sample) Onset of crystallization (fine powder)

Onset of sintering End of sintering

Hot-stage microscopy Hot-stage microscopy



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Table 2: Technical coefficients of thermal expansion of sintered and crystallized samples heat treated at 950 °C for 1 h using different starting particle sizes. The values are given for different temperature ranges and in units of [10-6 K-1]. particle size [µm]

100-600 °C

100-800 °C

300-500 °C

~4

4.2

5.1

4.4

< 80

5.5

5.6

6.4

63-100

4.5

6.5

3.9

80-125

1.9

3.4

1.6

125-200

-5.1

-5.8

-2.1

100-315

-5.2

-2.1

-5.6

~4/100-315

4.4

5.5

4.4

63-100/100-200

-2.9

-0.7

-2.3

bulk

0.1

1.0

2.3


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Table 3: Lattice parameters of Ba0.5Sr0.5Zn2Si2O7 obtained via sintering and crystallization of glasses with different starting powders as a function of the temperature. ~ 4 µm

125-315 µm

T [°C] a [Å]

b [Å]

c [Å]

a [Å]

b [Å]

c [Å]

30

12.9960(36)

7.5568(20)

6.6215(14)

13.0021(39)

7.5962(21)

6.6110(17)

100

12.9974(37)

7.5526(20)

6.6244(15)

12.9999(42)

7.5844(24)

6.6180(18)

200

13.0065(37)

7.5549(20)

6.6324(14)

13.0071(42)

7.5795(24)

6.6266(18)

300

13.0074(36)

7.5537(19)

6.6375(14)

13.0156(39)

7.5652(21)

6.6321(16)

400

13.0154(36)

7.5481(18)

6.6420(14)

13.0195(37)

7.5607(20)

6.6406(15)

500

13.0189(34)

7.5453(17)

6.6480(13)

13.0273(43)

7.5588(22)

6.6460(17)

600

13.0303(39)

7.5444(20)

6.6532(14)

13.0271(35)

7.5486(18)

6.6517(14)

700

13.0311(39)

7.5417(20)

6.6559(14)

13.0307(36)

7.5419(18)

6.6571(14)

800

13.0353(36)

7.5449(19)

6.6629(14)

13.0389(36)

7.5432(18)

6.6682(14)

900

13.0504(37)

7.5403(18)

6.6756(13)

13.0532(35)

7.5383(17)

6.6753(13)

1000

13.0569(41)

7.5339(25)

6.6824(18)

13.0584(33)

7.5297(18)

6.6821(14)



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Table of Contents


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Figure 1: Thermal analysis of the glass. On the left side, results from dilatometry (bulk sample), DSC (< 40 µm) and HSM (< 40 µm) are shown. The DSC-curve was baseline-corrected. On the right side, results from DSC using different particle sizes are shown. The temperatures given inside the graphs are the respective onsets of the crystallization. 150x93mm (300 x 300 DPI)



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Figure 2: Side-view hot-stage microscopy of glass with a particle size < 40 µm. (A) Sintering; (B) Foaming; (C) Melting. 221x214mm (300 x 300 DPI)


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Figure 3: XRD-patterns of the glass, crystallized at different temperatures kept for 1 h. Most of the observed peaks are attributed to Ba0.5Sr0.5Zn2Si2O7 with HT-BaZn2Si2O7-structure. All other peaks belong to Zn2SiO4. In the lower part, theoretical peak positions taken from Refs. 16,29 are illustrated. 172x243mm (300 x 300 DPI)



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Figure 4: Lattice parameters of sintered glass-ceramics prepared by pressureless sintering of glass powders, which were heated with 5 K/min to 950 °C for 1 h. The lattice parameters were determined using sintered samples, which were not milled before the XRD scans were performed. The lattice parameters of the samples denoted as “stress-free” were taken from Ref. 25, where fine grained powders from solid state reaction, i.e. without a glassy matrix, were characterized. 247x200mm (300 x 300 DPI)


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Figure 5: Dilatometry of samples with different grain sizes. The values are given in units of [µm]. All the samples were heat treated at 950 °C kept for 1 h. The applied heating rate was 5 K/min. The sample denoted as “63-100/100-200” is made of a 1:1 mixture of powders with the particle size 63-100 µm and 100-200 µm. The same was done for the sample “~ 4/100-315”. 259x196mm (300 x 300 DPI)



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Figure 6: Thermal expansion of the unit cell of Ba0.5Sr0.5Zn2Si2O7 between room temperature and 1000 °C. The sintered bulk samples were obtained by heating different glass powders with a rate of 5 K/min to 950 °C kept for 1 h. Plates with a thickness of 1 mm were measured. The data of the powder from the solid state reaction are shown for comparison and were taken from Ref. 25. 240x181mm (300 x 300 DPI)


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Figure 7: Fine grained powder heat treated at different temperatures. 26x12mm (300 x 300 DPI)



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Figure 8: Bulk glass sample heated with 5 K/min to 950 °C kept for 1 h. 132x89mm (300 x 300 DPI)


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Figure 9: Four-point bending strength of samples sintered at different temperatures using different grain sizes of the starting powders. The values next to the triangles are the respective mean values in units of [MPa]. 238x188mm (300 x 300 DPI)



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Figure 10: EDX analyses with 15 kV (upper 6 images) and 30 kV (lower 5 images) acceleration voltage of a sintered sample (grain size 100 - 315 µm), heat treated at 950 °C kept for 1 h. The numbers on the right of each micrograph are given in units of counts. 91x180mm (300 x 300 DPI)


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Thermal Expansion of Sintered Glass Ceramics in the System BaO

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