The reaction behavior of Si3N4/Al2O3 composite at 900–1500°C in dry O2 and Ar containing 20 vol.% H2O for 50 h was investigated using thermogravimetric method. The phase, microstructure and macroscopic cross sections of the products were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy as well as optical microscopy, respectively. Especially the morphological evolution of mullite, the main oxide product, was investigated. The results show that both the reaction atmosphere and temperature have significant influence on the morphology of the oxide product. Based on experimental results, the reaction kinetics of Si3N4/Al2O3 composite was discussed using the real physical picture model.
Special Article: The 71st CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Ionic conduction mechanisms in apatite-type lanthanum silicate and germanate studied by first-principles calculations were reviewed, along with the ones previously proposed by experiments and atomistic simulations. It was found that the most stable interstitial oxygen sites in La10(SiO4)6O3 are located at the vicinity of the O4 column and the metastable sites are present between SiO4 tetrahedra. In contrast, La10(GeO4)6O3 showed the most stable sites between GeO4 tetrahedra, forming Ge2O9 units. These can reasonably explain interstitial sites reported experimentally. The fundamental mechanism for ionic conduction in both systems is the interstitialcy mechanism, where interstitial oxygen ions and oxygen ions at regular lattice sites undergo cooperative motion through the lattices. In particular, the interstitialcy mechanism via Si/GeO4 tetrahedra takes place by sequential bond-forming and bond-breaking events between Si/Ge and oxygen ions, and play an important role to realize rapid ionic conduction.
Mo2FeB2-based cermets with Mn addition of 10 wt % were prepared by reaction sintering process. The effect of Mn addition on the microstructure and mechanical properties was investigated. It was found that the cermets with Mn addition exhibited relatively fine grain size and the transverse rupture strength obviously increased from 1750 to 2300 MPa, while the value for hardness decreased. Based on density functional theory and ultrasoft pseudopotentials, the first-principle calculations were carried out to investigate the bulk modulus B, Young’s modulus E, Poisson’s ratio υ and B/G of Mo2FeB2 and Mo2(Fe,Mn)B2 phase, and attempts were made to relate them to the mechanical properties.
In this study, we developed the low-temperature synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) using barium peroxide (BaO2) and strontium peroxide (SrO2) as starting materials of A-site elements in perovskite. The sintered bodies were obtained at a low temperature of 700°C by two approaches. One was a two-step sintering process, which included the preparation of fine hexagonal-phase BSCF powders with mean crystallite sizes of 20–30 nm by a novel low-temperature solid-state reaction before sintering. Another approach was a one-step sintering process using reactive sintering, which is the simultaneous reaction of BSCF synthesis and green body sintering from the starting material powders. For the sintered bodies obtained by the one- and two-step sintering processes, the relative density was ca. 50%. The reactive-sintered body of hexagonal-phase BSCF obtained by the one-step process showed higher electrical conductivity of 6.3 S cm−1 at 500°C than the BSCF sintered bodies obtained by the two-step process (4.1 S cm−1). Reactive sintering realizes good connectivity among BSCF particles, which enhances the electrical conductivity of porous BSCF bodies.
H2Ti12O25 (HTO) is a negative-electrode oxide materials used in Li-ion batteries that has higher capacity and repetition stability. We developed a new process for synthesizing Na2Ti3O7 by impregnation of Na2CO3 solution into porous titanium hydroxide and synthesized Na2Ti3O7 with higher anisotropic morphology. HTO with higher anisotropic morphology was synthesized by ion-exchange using soft-chemical synthesis and subsequent annealing. The HTO with higher anisotropic morphology was smaller and exhibited better performance in its Li insertion and extraction than that derived from Na2Ti3O7 synthesized by the solid-state method.
In this paper, to save energy and reduce consumption in building ceramic process, the low temperature porcelain building tiles were prepared by fast firing process using two kinds of “K2O–Na2O” feldspar with different amounts of alkaline and alkaline earth oxides fluxing agents, Si/Al ratio and melting point. The sintering properties of the samples were evaluated by linear shrinkage, water absorption and bulk density. The crystalline phase and microstructure of the samples were characterized by X-ray diffraction and scanning electron microscope. The results showed that the optimum linear shrinkage of 7.55%, water absorption of 0.03% and bending strength of 78.3–85.8 MPa can be achieved for the sample fired at 1170–1190°C, which is attributed to the effect of the combined “K2O–Na2O” feldspar flux system.
Pseudobrookite-type titanate has two types of oxide octahedra for different cation types. The cation distributions in the octahedra of three pseudobrookite type oxides, Al2TiO5, MgTi2O5 and Fe2TiO5, and in a solid solution of 0.5Al2TiO5–0.5MgTi2O5 were studied by the Rietveld method. The analysis revealed that the cation distributions of Al2TiO5 and Fe2TiO5 did not depend on the annealing temperature, whereas that of MgTi2O5 depended on the annealing temperature. The estimated cation distributions determined by the Rietveld method agreed with those determined by bond valence sum estimation. The configuration entropies of Al2TiO5 and Fe2TiO5 were almost the same as that of the maximum value of the random distribution of cations. Although the configuration entropy stabilized Al2TiO5 thermodynamically, the decomposition of Al2TiO5 should be attributed to the stable nature of corundum, and the rather “stretched” structure of Al2TiO5 would also cause its instability at low temperature.
We report the synthesis of spherical cobalt oxide nanoparticles by a polyol method. To obtain spherical nanoparticles, water, polyvinylpyrrolidone (PVP), and cobalt acetate tetrahydrate were mixed in diethylene glycol and refluxed at 200°C. Spherical particles were not obtained in the absence of water or PVP, or when the mixture was refluxed at 180°C. The spherical nanoparticles were found to be composed of cobalt (II) oxide (CoO) with a small amount of cobalt oxyhydroxide (CoOOH). The synthesized spherical nanoparticles had good dispersibility in water, and Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis measurements indicated that the nanoparticles had a core–shell structure, with a core of CoO and a polymer shell.
Er3+/Yb3+ co-doped transparent niobosilicate glass-ceramics with main crystalline phase NaNbO3 were prepared by crystallization of glass. The heat treatment temperature, crystalline phase composition, microstructure, optical transmittance and up conversion luminescence of the samples were investigated using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, Ultraviolet-Visible-Near Infrared spectrophotometer and fluorescence spectrometer. The results show that the optimum crystallization temperature is 700°C, the optimal heat treatment time is 2 h and the transmittance of the sample in the near infrared region at 850 nm is up to 79% under the condition of Yb3+/Er3+ molar ratio of 7.5:1. The influence of different Yb3+/ Er3+ doping concentration on the luminescent properties of glass-ceramics and the up-conversion luminescence mechanism was discussed. It was found that the luminescence intensity was the highest when the Yb3+/Er3+ doping molar ratio was 7.5:1.
Smectite containing Zn2+ or Mg2+ ions was synthesized by a solution process. The X-ray diffraction patterns of the synthesized smectite powder corresponded to those of previous studies. In bacterial adsorption tests, smectite containing Zn2+ or Mg2+ ions was found to exhibit bacterial adsorption properties which were greater for smectite containing Zn2+ ion than for smectite containing Mg2+ ion. By observation, using the fluorescent staining method, the bacteria adsorbed on the smectite powder were confirmed as live bacteria. These results suggested that the bacterial adsorption can reduce bacterial infection.
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Edited and published by : The Ceramic Society of Japan Produced and listed by : Komiyama Printing Co., Ltd.(Vol.115 No.1344-Vol.116 No.1351, Vol.118 No.1376-) Letterpress Co., Ltd.(Vol.116 No.1352-Vol.118 No.1375)