Thermal transformation and ionic conductivity of ammonium ion-exchanger prepared from Na-4-mica

Ammonium ion exchange of Na-4-mica and thermal transformation of the ion-exchanger were investigated and the conductivities of the heated ion-exchangers were estimated. More than 95.4% of Na+ ions in the interlayer of the Na-4-mica could be substituted by NH4+ ions after repeating ion exchange four times. Almost of NH4+ ions remained in the interlayer at 700 degrees C and they were completely decomposed into protons at 900 degrees C. The conductivities of the ion-exchangers heated at 700-900 degrees C were 10(-7)-10(-6) S/cm at 700 degrees C. The conduction mechanism of the ion-exchangers heated at 700 and 800 degrees C was NH4+ ion migration in the interlayer and that of the ion-exchanger heated at 900 degrees C was proton migration. However, the contribution of residual Na+ ions to the conduction cannot be excluded. (C) 2010 Elsevier B.V. All rights reserved.ArticleMaterials Science and Engineering: B. 173(1-3):271-274 (2010)journal articl

Influence of Cu2O Addition on Crystallization Process and Microstructure of Transparent Mica Glass-Ceramics

ArticleKey Engineering Materials. 617: 209-212 (2014)journal articl

Morphology control and interlayer pillaring of swellable Na-taeniolite mica crystals

Na-taeniolite (NaMg2LiSi4O10F2) mica crystals were synthesized from nonstoichiometric raw batches containing NaCl as a flux, in order to control the morphology of mica crystals. Swellable Na-taeniolite was obtainable from both stoichiometric and nonstoichiometric batches although small amounts of different products were coprecipitated, depending on the composition of the raw batches. Samples obtained from raw batches containing <= 1 mol NaCl consisted of a single-phase swellable mica. The addition of a small amount of NaCl was effective in controlling the morphology of the mica crystals. Raw batches containing 1 mol NaCl yielded mica crystals having a hexagonal, plate-like morphology with a larger aspect ratio. Alumina-pillared micas prepared from host micas thus obtained from raw batches containing NaCl had larger specific surface areas than those obtained from stoichiometric batches. This suggests that the swellability of mica crystals is also affected by the addition of NaCl.ArticleMATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS. 177(7):524-527 (2012)journal articl

Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol-gel route under seeding

Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl(3) Solutions under alpha-alumina (similar to 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 degrees C under 5 mass % alpha-alumina seeding, consisted of similar to 80-nm alpha-alumina particles and gamma-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 mu m could be obtained at 1400 degrees C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 mu m at 1400 degrees C. (C) 2009 Elsevier B.V. All rights reserved.ArticlePOWDER TECHNOLOGY. 193(1):26-31 (2009)journal articl

Low-temperature formation of alpha-alumina from various polyhydroxoaluminum-hydroxy acid composite gels

Low-temperature alpha-alumina formation was attempted using various polyhydroxoaluminum (PHA)-hydroxy acid composite gels, which were prepared from PHA solutions containing different amounts of hydroxy acids, such as lactic acid, glycolic acid, malic acid, citric acid or mandelic acid. The composite gels began to transform into alpha-alumina when heated at lower temperatures of around 500 degrees C and the alpha-alumina fraction of the heat-treated products increased with increasing temperature. The alpha-alumina fraction was also dependent on both the type and amount of hydroxy acid additive. Among the composite gels studied, significant low-temperature alpha-alumina formation was observed for the PHA-mandelic acid, PHA-citric acid and PHA-lactic acid series. Low-temperature alpha-alumina formation was further promoted by employing a two-step heat-treatment method. The interaction between the functional groups of PHA and hydroxy acid and the seeding effect appear to play important roles in the course of the gelation and calcination processes for low-temperature alpha-alumina formation.ArticleCERAMICS INTERNATIONAL. 37(1):201-206 (2011)journal articl

Fabrication of submicron alumina ceramics by pulse electric current sintering using M(2+) (M = Mg, Ca, Ni)-doped alumina nanopowders

Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering (PECS) using M(2+)(M: Mg, Ca, Ni)-doped alumina nanopowders at 1250 degrees C under a uniaxial pressure of 80 MPa. The M(2+)-doped alumina nanopowders (0-0.10 mass%) were prepared through a new sol-gel route using high-purity polyhydroxoaluminum (PHA) and MCl(2) solutions as starting materials. The composite gels obtained were calcined at 900 degrees C and ground by planetary ball milling. The powders were re-calcined at 900 degrees C to increase the content of a-alumina particles, which act as seeding for low-temperature densification. Densification and microstructural development depend on the M(2+) dopant species. Dense alumina ceramics (relative density >= 99.0%) thus obtained had a uniform microstructure composed of fine grains, where the average grain size developed for non-doped, Ni-doped, Mg-doped and Ca-doped samples was 0.67, 0.67, 0.47 and 0.30 mu m, respectively, showing that Ca-doping is the most promising method for tailoring of nanocrystalline alumina ceramics. (c) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.ArticleCERAMICS INTERNATIONAL. 35(5):1845-1850 (2009)journal articl

Preparation and luminescent properties of Eu-doped transparent mica glass-ceramics

Eu-doped transparent mica glass–ceramics were prepared, the influence of Eu-doping on the crystallization of the parent glasses was investigated and the luminescent properties of the parent glasses and the glass–ceramics were estimated. A small additive amount of Eu element was very effective in preparing transparent mica glass–ceramics. However, the excess addition led to the coarsening of phase separation in the glass phase and the separation of unidentified crystal phases and β-eucryptite during heating of the parent glasses, which caused white opaque at lower heating temperatures. When mica crystals were separated, Eu ions entered the interlayers of mica crystals. The observed emission and excitation spectra showed that parts of Eu³⁺ ions which were added as Eu₂O₃ were reduced to Eu²⁺ ions during melting of the starting materials and heating the parent glasses in air and the energy transfer from Eu²⁺ to Eu³⁺ ions occurred.ArticleCeramics International. 36(4):1303-1309 (2010)journal articl

Deposition of boehmite on carbon nanofibers using aluminum alkoxide and its thermal transformation

We attempted to prepare carbon nanofibers (CNFs) bonded chemically with alumina particles using acid-treated CNFs and aluminum secbutoxide. The structure and morphology of the boehmite deposited on the CNFs, the boundary between the CNFs and the deposited boehmite, and the thermal transformation of the deposited boehmite were investigated using Raman spectroscopy, X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The boehmite deposited not only particulately on the CNFs but also in a film-like manner on parts of the CNFs. In addition, the boehmite could deposit not only on the disordered inner walls of the CNFs but also on the ordered inner walls. By heating at 1200 degrees C, the boehmite on the CNFs was transformed into alpha-alumina and theta-alumina. At this time, some alumina particles, particularly those formed on the ordered inner walls of CNFs, fell out of the CNFs, and only those alumina particles which might chemically bond with CNFs remained on the CNFs. Finally, CNFs dotted with alumina particles with a size of <50 nm were obtained. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.ArticleCERAMICS INTERNATIONAL. 41(10):13171-13178 (2015)journal articl

Fabrication and Fracture Toughness of CNTs/Alumina Composites with Fine Microstructures

ArticleKey Engineering Materials. 617: 205-208 (2014)journal articl

Deposition of Apatite on Carbon Nanofibers in Simulated Body Fluid

Carbon nanofibers (CNFs) were soaked in 1.5 simulated body fluid (1.5 SBF) in which inorganic ion concentrations are 1.5 times as high as those in the standard SBF. The influence of the CNFs content in 1.5 SBF and pretreatment of the CNFs on the biomimetical deposition of apatite were investigated. The spherical bone-like apatite particles were deposited on the pristine CNFs soaked in 1.5 SBF. Amount of deposited apatite per a unit of CNFs increased with a decrease in the CNFs content in 1.5 SBF, and it decreased markedly when the CNFs were pretreated with concentrated sulfuric acid/nitric acid (3 : 1 v/v) mixture for longer periods. Such results suggest that too many nucleation sites of apatite, which were functional groups, such as carboxyl and hydroxyl groups, existed on the CNFs in the 1.5 SBF, and most embryos formed on the sites could not grow to critical nuclei and furthermore did not grow to apatite.ArticleJOURNAL OF NANOMATERIALS. 2011:935320 (2011)journal articl