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Hisao Suzuki - One of the best experts on this subject based on the ideXlab platform.
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high thermal expansion polycrystalline Leucite ceramic
Journal of the American Ceramic Society, 1993Co-Authors: Toshitaka Ota, Minoru Takahashi, Iwao Yamai, Hisao SuzukiAbstract:A high-thermal-expansion ceramic consisting of Leucite crystals was prepared by sintering Leucite powder. The densification was promoted by adding Li 2 CO 3 or Na 2 CO 3 . The Leucite ceramic obtained had a thermal expansion coefficient of about 2.4 × 10 −5 /°C from room temperature to 600°C. Some of the Li + and Na + ions were incorporated into the Leucite crystal lattice to form solid solutions, and the characteristic tetragonal-cubic inversion point shifted from ca. 600° to 650°C
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High‐Thermal‐Expansion Polycrystalline Leucite Ceramic
Journal of the American Ceramic Society, 1993Co-Authors: Toshitaka Ota, Minoru Takahashi, Iwao Yamai, Hisao SuzukiAbstract:A high-thermal-expansion ceramic consisting of Leucite crystals was prepared by sintering Leucite powder. The densification was promoted by adding Li 2 CO 3 or Na 2 CO 3 . The Leucite ceramic obtained had a thermal expansion coefficient of about 2.4 × 10 −5 /°C from room temperature to 600°C. Some of the Li + and Na + ions were incorporated into the Leucite crystal lattice to form solid solutions, and the characteristic tetragonal-cubic inversion point shifted from ca. 600° to 650°C
C M B Henderson - One of the best experts on this subject based on the ideXlab platform.
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variable stoichiometry in tectosilicates having the Leucite pollucite type structure with particular emphasis on modelling the interframework cavity cation environment
Journal of Solid State Chemistry, 2017Co-Authors: Anthony M. T. Bell, C M B Henderson, K S KnightAbstract:Abstract Unit cell data for synthetic samples of I41/a or Ia-3d AAlSi2O6 (A=K,Rb,Tl,Cs) Leucite/pollucites are compared to those for feldspar-stoichiometry Leucite analogues (Rb,Tl,Cs)0.75□0.25Al0.75Si2.25O6. I41/a solid solutions between KAlSi2O6 and KAlSi3O8 (orthoclase feldspar, Or) and between K(Al0.85Fe0.15)Si2O6 and Or both show increasing volumes and decreasing c/a with increasing Or. Phase relations are given for KAlSi3O8-RbAlSi3O8; monoclinic feldspars occur at low temperatures and I41/a Leucites at higher temperatures; volumes of Leucite solid solutions increase with increasing Rb. The cell volume of Rb0.75□0.25Al0.75Si2.25O6 Leucite is larger than that of RbAlSi2O6 Leucite. Published Leucite/pollucite structures belonging to different Space Group symmetries are treated as having the cubic Ia-3d topology with a ‘pseudocell’ edge V1/3 (V = unit cell volume); inequivalent site bond lengths and angles provide mean structural parameters for the cubic ‘pseudocells’. Multivariant linear regression equations using mean A – O distances as the independent variable were obtained using other structural parameters as dependent variables. Only two independent variables (V and mean tetrahedral ionic radius) are required to account for >90% of the variation. These regression equations can be used to predict the sizes of the cavity cation sites in Leucite/pollucite-type phases of any stoichiometry.
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complex impedance spectroscopy and ionic transport properties of natural Leucite k0 90na0 08 al0 98si2 02 o6 as a function of temperature and pressure
Mineralogical Magazine, 2010Co-Authors: R L Jones, C M B Henderson, M ThrallAbstract:The temperature ( T ) and pressure ( P ) dependence of dielectric and conductivity properties of natural Leucite were determined using complex impedance spectroscopy at frequencies from 10 3 to 10 6 Hz. Experiments were carried out in a Walker multi-anvil cell at 1 atm and P from 2.5 to 6 GPa and at T from 350 to 800°C. At pressure >6 GPa and temperature >790°C the Leucite broke down to kalsilite+sanidine and dielectric properties for this phase assemblage are given at 6.0–7.0 GPa and T to 1050°C. Leucite conductivity increases with increasing T and decreases with increasing P reflecting their different effects on migration of K cations within the channels in the Leucite aluminosilicate framework. Activation energies for K + migration in Leucite increase with increasing pressure (0.74–0.97 eV; 70.0–93.2 kJ/mol) and activation volumes for Leucite increase with increasing T (6.42–9.51 cm 3 /mol; 400–700°C). The latter data provide model K + cation diameters increasing from 2.7 A at 400°C to 3.2 A at 700°C. These values are consistent with the earlier suggestion of Palmer and Salje that the ionic mobility mechanism consists of diffusion along rather than along the main channels parallel to .
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Revision of the structure of Cs2CuSi5O12 Leucite as orthorhombic Pbca.
Acta crystallographica. Section B Structural science, 2010Co-Authors: A M T Bell, C M B Henderson, K S Knight, A N FitchAbstract:The crystal structure of a hydrothermally synthesized Leucite analogue Cs(2)CuSi(5)O(12) has been determined and refined using the Rietveld method from high-resolution synchrotron X-ray and neutron powder diffraction data. This structure is based on the topology and cation-ordering scheme of the Pbca Leucite structure of Cs(2)CdSi(5)O(12), and exhibits five ordered Si sites and one ordered Cu tetrahedrally coordinated (T) site. This structure for Cs(2)CuSi(5)O(12) is topologically identical to other known Leucite structures and is different from that originally proposed by Heinrich & Baerlocher [(1991), Acta Cryst. C47, 237-241] in the tetragonal space group P4(1)2(1)2. The crystal structure of a dry-synthesized Leucite analogue Cs(2)CuSi(5)O(12) has also been refined; this has the Ia3d cubic pollucite structure with disordered T sites.
Atsushi Kyono - One of the best experts on this subject based on the ideXlab platform.
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synthesis of thallium Leucite tlalsi 2 o 6 pseudomorph after analcime
Mineralogical Magazine, 1999Co-Authors: Atsushi Kyono, Mitsuyoshi Kimata, Norimasa Nishida, Masahiro Shimizu, S. Saito, T. HattaAbstract:Thallium Leucite, TlAlSi 2 O 6 , has been synthesized at 450 degrees C for 7 days, under ambient conditions, by the transformation of dehydrated analcime NaAlSi 2 O 6 in the presence of excess T1C1. This substitution of T1 for Na leads to confirmation of a thallium-Leucite pseudomorph after analcime. Their optical properties, X-ray powder diffraction patterns, electron microprobe analysis, infrared spectra, and X-ray photoelectron spectroscopy have characterized the synthetic T1-Leucites. The IR spectra show that the mid-IR modes T-O stretching and T-O-T bending vibrations for TlAlSi 2 O 6 are more resemblant of those for analcime than for Leucite, KAlSi 2 O 6 . This resemblance implies that T1 cation enters the W-site rather than the S-site in the analcime structure: Na (S)+H 2 O (W) []+K (Leucite) +[]Tl (Tl-Leucite), where [] represents an S-site vacancy. The mechanism of this substitution is supported by the crystal chemical constraints: inasmuch as the S-site is smaller than the W-site, Tl (super +) cations being larger than Na (super +) plainly prefer the latter site to the former. One inference from the binding energy for Tl (super +) by XPS is that Tl (super +) occupies the extra-framework site in synthetic Leucite pseudomorph, rather than the smaller tetrahedral site. The difference in A1/Si disordering between analcime and Leucite and the nonstoichiometry due to the solid solution of the []Si 3 O 6 component into the Leucite structure may provide a fundamental insight into understanding why TlAlSi 2 O 6 deviates from the trend defined by K-, Rb- and CsAlSi 2 O 6 Leucite series on the a-c parameter diagram, inasmuch as these three cations in the Leucite structure occupy the W-sites. Finally, synthesis of TlAlSi 2 O 6 Leucite has an implication for the existence of other polymorphs due to different degrees of Al/Si disordering, except for high- and low-temperature Leucites already known: natural Leucites crystallized directly through igneous processes are different from those formed by substitution of K for Na in analcimes.
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synthesis of thallium Leucite tlalsi2o6 pseudomorph after analcime
Mineralogical Magazine, 1999Co-Authors: Atsushi KyonoAbstract:Thallium Leucite, T1A1Si206, has been synthesized at 450~ for 7 days, under ambient conditions, by the transformation of dehydrated analcime NaA1Si206 in the presence of excess T1C1. This substitution of TI for Na leads to confirmation of a thallium-Leucite pseudomorph after analcime, Their optical properties, X-ray powder diffraction patterns, electron microprobe analysis, infrared spectra, and X-ray photoelectron spectroscopy have characterized the synthetic Tl-Leucites. The IR spectra show that the mid-lR modes T-O stretching and T-O-T bending vibrations for TIA1Si206 are more resemblant of those for analcime than for Leucite, KA1Si206. This resemblance implies that TI cation enters the W-site rather than the S-site in the analcime structure: Na (S) + H20 (W) ~[] + K (Leucite) ~ [] + T1 (T1Leucite), where [] represents an S-site vacancy. The mechanism of this substitution is supported by the crystal chemical constraints: inasmuch as the S-site is smaller than the W-site, T1 + cations being larger than Na + plainly prefer the latter site to the former. One inference from the binding energy for T1 + by XPS is that T1 + occupies the extra-framework site in synthetic Leucite pseudomorph, rather than the smaller tetrahedral site. The difference in A1/Si disordering between analcime and Leucite and the nonstoichiometry due to the solid solution of the []Si306 component into the Leucite structure may provide a fundamental insight into understanding why T1A1Si206 deviates from the trend defined by K-, Rband CsA1Si206 Leucite series on the a-c parameter diagram, inasmuch as these three cations in the Leucite structure occupy the W-sites. Finally, synthesis of T1A1Si206 Leucite has an implication for the existence of other polymorphs due to different degrees of A1/Si disordering, except for highand low-temperature Leucites already known: natural Leucites crystallized directly through igneous processes are different from those formed by substitution of K for Na in analcimes.
Xinglong Duan - One of the best experts on this subject based on the ideXlab platform.
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relationship between Leucite content and compressive strength of k2o al2o3 sio2 system dental glass ceramics
Journal of Wuhan University of Technology-materials Science Edition, 2009Co-Authors: Biao Zhang, Fatang Qian, Xinglong DuanAbstract:Relationship between Leucite content and compressive strength of K2O-Al2O3-SiO2 system dental glass ceramics were investigated. 10 groups of feedstock powder with different compositions were treated according to the same thermal treatment system of Leucite micro-crystallization reported in some primary studies. The products of each group were analyzed by X-ray diffractometer, polaring microscope and scanning electronic microscope (SEM), and then the compressive strength was tested by a material testing machine. A direct proportion was found between Leucite content and the compressive strength when Leucite content was less than 50 vol%, and compressive strength decreased with the increasing of Leucite micro-crystals when Leucite content was more than 50vol%, The Leucite content has a notable influence on the compressive strength of K2O-Al2O3-SiO2 system dental glass ceramics.
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Study on thermal treatment schedule of Leucite microcrystallization to reinforce dental glass ceramics
Zhonghua kou qiang yi xue za zhi = Zhonghua kouqiang yixue zazhi = Chinese journal of stomatology, 2003Co-Authors: Biao Zhang, Fatang Qian, Xinglong DuanAbstract:Objective To explore the thermal treatment schedule of Leucite microcrystallization to reinforce dental glass ceramics. Methods After component analysis and selection, the raw material were treated by different temperature schedules. The products were analyzed by polaring microscope and X-ray diffractometer to determine the appropriate thermal treatment schedule. Results The temperature of melting, nuclearing and crystalizing was 1,600 degrees C, 1,200 degrees C and 1,500 degrees C. Leucite microcrystals dispersed in the glass matrix evenly and the size of Leucite particle was about 0.8 micro m. Conclusion Leucite can be microcrystalized according to an appropriate thermal treatment schedule.
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Study on some mechanism of Leucite microcrystallization to reinforce dental glass ceramics.
Zhonghua kou qiang yi xue za zhi = Zhonghua kouqiang yixue zazhi = Chinese journal of stomatology, 2002Co-Authors: Biao Zhang, Fatang Qian, Xinglong DuanAbstract:OBJECTIVE To research the influence of K(2)O composition in the raw material on Leucite microcrystallization and to study the effect of Leucite content on compressive strength of the dental glass ceramics reinforced by Leucite microcrystallization. METHODS The raw materials with different K(2)O content were treated by a decided thermal treatment system. The products were analyzed by polaring microscope and X-ray diffractometer, and their compressive strength was also tested. RESULTS The microstructure of products from high K(2)O component was remarkably good, at microcrystal size of 0.8 micro m and the compressive strength was 206.6 MPa. A positive correlation was found between Leucite volume and the compressive strength when Leucite volume was less than 50% (Vol%). CONCLUSIONS The component of K(2)O has a great effect on the microstructure and the properties of the Leucite-microcrystal-reinforced dental glass ceramics and the content of Leucite microcrystals has a notable influence on the compressive strength of the dental glass ceramics.
Toshitaka Ota - One of the best experts on this subject based on the ideXlab platform.
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high thermal expansion polycrystalline Leucite ceramic
Journal of the American Ceramic Society, 1993Co-Authors: Toshitaka Ota, Minoru Takahashi, Iwao Yamai, Hisao SuzukiAbstract:A high-thermal-expansion ceramic consisting of Leucite crystals was prepared by sintering Leucite powder. The densification was promoted by adding Li 2 CO 3 or Na 2 CO 3 . The Leucite ceramic obtained had a thermal expansion coefficient of about 2.4 × 10 −5 /°C from room temperature to 600°C. Some of the Li + and Na + ions were incorporated into the Leucite crystal lattice to form solid solutions, and the characteristic tetragonal-cubic inversion point shifted from ca. 600° to 650°C
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High‐Thermal‐Expansion Polycrystalline Leucite Ceramic
Journal of the American Ceramic Society, 1993Co-Authors: Toshitaka Ota, Minoru Takahashi, Iwao Yamai, Hisao SuzukiAbstract:A high-thermal-expansion ceramic consisting of Leucite crystals was prepared by sintering Leucite powder. The densification was promoted by adding Li 2 CO 3 or Na 2 CO 3 . The Leucite ceramic obtained had a thermal expansion coefficient of about 2.4 × 10 −5 /°C from room temperature to 600°C. Some of the Li + and Na + ions were incorporated into the Leucite crystal lattice to form solid solutions, and the characteristic tetragonal-cubic inversion point shifted from ca. 600° to 650°C