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Oxide nanofibers are widely used in several applications, including thermal insulation, fuel cells, flexible sensors, and catalyst support. Fiber morphology significantly affects their application performance. In this work, alumina-based nanofibers were successfully prepared using a sol-gel combined with an electrospinning method. The electrostatic polarity effects on fiber morphology were investigated. When fibers were electrospun by negative polarity at elevated voltages, the fibers retained uniform and smooth morphology, with a slightly increased average diameter and diameter uniformity. In contrast, ultra-thin nanofibers were generated when electrospinning was done under positive polarity. The strong charge repulsion by the agminated cations in the precursor caused bifurcations, finally forming ultra-thin nanofibers. At increased voltages, the electrospun fibers with positive polarity exhibited a distinctly increased average diameter and decreased diameter uniformity. This was attributed to the increased fiber whip scope, increasingly robust nonaxisymmetric whip behaviors, and fiber bifurcation during the jet whipping process. The results showed that the electrostatic polarities can affect the morphology of oxide fibers. This study provides guidance to prepare oxide nanofibers with desired morphology and specific requirements. [ABSTRACT FROM AUTHOR]

Yttrium oxide (Y 2 O 3) nanoparticles have critical applications in many industries, including ceramics, optics, and biomedicine. However, conventional synthesis methods are typically cumbersome and time-consuming. Herein, a novel emulsion detonation method successfully achieved the one-step synthesis of Y 2 O 3 nanoparticles. In this method, yttrium nitrate hexahydrate was uniformly dispersed in the emulsion explosive as a precursor and an auxiliary oxidizer. After the emulsion explosive was detonated in a detonation chamber, the detonation products were collected, purified and characterized by X-ray diffraction, Fourier transform infrared spectrometer, Raman spectrometer, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, field emission transmission electron microscopy, and ultraviolet spectrophotometer. The results show that the as-synthesized powders are high-purity cubic phase yttrium oxide nanoparticles with a spherical-like morphology and an average particle size of approximately 30 nm. These Y 2 O 3 nanoparticles have a wide (5.53 eV) energy band gap, close to the conventional methods. Based on detonation theory, thermochemical theory, and characterization results, this text discussed the mechanism of the Y 2 O 3 nanoparticles synthesized by the emulsion detonation method. During detonation, the formation of the Y 2 O 3 nanoparticles underwent three stages: the formation of the Y 2 O 3 molecules by the collision of Y and O ions, the formation of the crystal nucleus at supersaturation concentration, and crystal growth. This study provides a novel, cost-effective method for efficiently synthesizing Y 2 O 3 nanoparticles. [ABSTRACT FROM AUTHOR]

Transparent sapphire and magnesium aluminum spinel (MgAl 2 O 4) ceramic was first brazed using La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 (LSBN) or La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 -MgO (LSBNM) glass filler. The Al 2 O 3 layer was formed at MgAl 2 O 4 /LSBN interface or sapphire/LSBNM interface, which caused the decrease of light transmission of joints. To avoid the formation of this interface layer, sapphire/LSBN/LSBNM/MgAl 2 O 4 joints with double glass interlayers were fabricated by using a two-step joining method consisting of high-temperature coating and low-temperature bonding. After the first step of high-temperature coating, no interfacial layer was observed in sapphire/LSBN glass and MgAl 2 O 4 /LSBNM glass samples. During the bonding process, low bonding temperature (750 °C) resulted in cracks and unbonding, while high bonding temperature (950 °C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 °C, the in-line transmission and shear strength of the sapphire/MgAl 2 O 4 joints reached 78.3% and 52 MPa, respectively. [ABSTRACT FROM AUTHOR]

Transparent sapphire and magnesium aluminum spinel (MgAl 2 O 4) ceramic was first brazed using La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 (LSBN) or La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 -MgO (LSBNM) glass filler. The Al 2 O 3 layer was formed at MgAl 2 O 4 /LSBN interface or sapphire/LSBNM interface, which caused the decrease of light transmission of joints. To avoid the formation of this interface layer, sapphire/LSBN/LSBNM/MgAl 2 O 4 joints with double glass interlayers were fabricated by using a two-step joining method consisting of high-temperature coating and low-temperature bonding. After the first step of high-temperature coating, no interfacial layer was observed in sapphire/LSBN glass and MgAl 2 O 4 /LSBNM glass samples. During the bonding process, low bonding temperature (750 °C) resulted in cracks and unbonding, while high bonding temperature (950 °C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 °C, the in-line transmission and shear strength of the sapphire/MgAl 2 O 4 joints reached 78.3% and 52 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this work, crystallization, thermal expansion and wetting behavior of ZnO–Al 2 O 3 –SiO 2 (ZAS) glass were first investigated. The results showed that ZnAl 2 O 4 was precipitated from ZAS glass after crystallization treatment. Crystallization increased the coefficient of thermal expansion (CTE) of ZAS glass ceramic due to the high CTE of ZnAl 2 O 4. In addition, ZAS glass exhibited good wettability on the surface of MgAl 2 O 4 substrate. On this basis, ZAS glass was used to join MgAl 2 O 4 ceramic, and the microstructure and mechanical properties of joints obtained with different cooling methods were investigated. The flexural strength of joints was related to the content of ZnAl 2 O 4 crystals in the brazing seams. Additional nucleation and crystallization treatment during cooling process improved the crystallinity of brazing seam, resulting in better matching of the CTE of brazing seam with that of MgAl 2 O 4 ceramic. The maximum flexural strength of joints reached 201 MPa, which was equivalent to the strength of MgAl 2 O 4 ceramic. [ABSTRACT FROM AUTHOR]

In this study, dysprosium-aluminosilicate (DAS) and neodymium-aluminosilicate (NAS) glasses with high softening temperature were used as fillers to join alumina ceramics. The similarities and differences in the interfacial microstructure and flexural strength of the joints were investigated. Results showed that the glass fillers both could infiltrate into alumina ceramics during the joining process. However, excessive infiltration at high joining temperatures led to the formation of pore defects in the brazing seam. An interfacial reaction layer composed of Dy 3 Al 5 O 12 was formed at the DAS glass/alumina interface. In contrast, no interfacial reaction was observed between the NAS glass and alumina ceramic. Slower cooling rate promoted the crystallization of Dy 2 Si 2 O 7 and Al 2 O 3 in the Al 2 O 3 /DAS/Al 2 O 3 joints, and only Nd 2 Si 2 O 7 in the Al 2 O 3 /NAS/Al 2 O 3 joints. The flexural strength at room temperature of both joints first increased and then decreased with the increased of joining temperature, and showed a declined tendency with the decrease in cooling rate. The flexural strength at 900 °C of Al 2 O 3 /DAS/Al 2 O 3 joints reached 245 MPa, which is higher than that of Al 2 O 3 /NAS/Al 2 O 3 joints. [ABSTRACT FROM AUTHOR]

Effects of ZrO 2 content on the crystallization kinetics, formation mechanism of voids and mechanical property of Dy 2 O 3 –Al 2 O 3 –SiO 2 glass were studied. The crystallization method of DAS glasses transforms from surface crystallization into bulk crystallization with an increase in ZrO 2 content from 0-3% to 6–9%. When ZrO 2 content is 0–3%, the crystalline phases of DAS glass ceramics are Dy 2 Si 2 O 7 and Al 2 O 3 , accompanied by formation of voids. When ZrO 2 content is 6–9%, the DAS glass ceramics consist of Dy 2 Si 2 O 7 , Al 2 O 3 and ZrO 2. At the same time, no voids are found in the glass ceramics. Therefore, formation of voids during crystallization can be attributed to combined effect of the crystallization method and the density difference before and after crystallization. In addition, for glassy samples, the flexural strength increases from 80.4 MPa to 219.3 MPa with an increase in ZrO 2 content from 0% to 9%. Moreover, crystallization further improves the mechanical properties of the DAS glass ceramics with bulk crystallization method. [ABSTRACT FROM AUTHOR]

Y 2.94 (Al 1−x Ga x ) 5 O 12 :0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were prepared by conventional solid-state reaction. Phosphor films are prepared from the synthesized Y 2.94 (Al 1−x Ga x ) 5 O 12 :0.06Ce phosphors by a simple spin coating method. The influence of different content of Ga 3+ doping on the photoluminescence (PL) spectra, thermal stability and reliability of prepared Y 2.94 (Al 1−x Ga x ) 5 O 12 :0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films were investigated. The emission peak of the Y 2.94 (Al 1−x Ga x ) 5 O 12 :0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films shifted from 545 nm to 520 nm with the Ga 3+ content(i.e. the value of x) increasing from 0.05 to 0.3 excited at 460 nm. The phosphor films have excellent thermal stability, and the intensities of PL spectra decrease by about 2%, 5%, 20% and 50% at 373 K, 423 K, 473 K and 523 K, respectively. The xenon lamp aging test show that the relative PL spectra intensity of the phosphor films decreases to 95.55%, 96.24%, 96.05%, 97.67%, 95.96% and 93.22% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the xenon lamp aging test for 168 h. The high temperature and high humidity test show that the relative PL spectra intensity of the phosphor films decreases to 94.36%, 95.6%, 95.26%, 96.87%, 95.28% and 93.1% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 85 ℃/RH85% for 168 h. The thermal cycling test show that the relative PL spectra intensity of the phosphor films decreases to 90.6%, 91.4%, 93.76%, 94.38%, 91.84% and 88.81% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 120 ℃ for 1 h and −40 ℃ for 1 h by turns for eight times. So, it can be generalized that low level of Ga 3+ doping can enhance the thermal stability and reliability of Y 2.94 (Al 1−x Ga x ) 5 O 12 :0.06Ce phosphor films. [ABSTRACT FROM AUTHOR]

Well-crystallized NaGd(MoO 4 ) 2 :Sm 3+ microcrystals with different morphologies were successfully prepared via a facile hydrothermal method without any additives and characterized by an X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The morphologies of the samples evolved from truncated octahedrons, through tetragonal plates and square sandwiches without filling, to elongated bipyramids by simply altering pH values from 3.5 to 7.0. According to the time-dependent experiments, a possible formation mechanism of the tetragonal plate was proposed. Moreover, the luminescent properties of NaGd(MoO 4 ) 2 :Sm 3+ phosphors with different morphologies and Sm 3+ concentrations were investigated. The sample with the morphology of tetragonal plates obtained under the pH value of 4.5 presented the stronger red-emitting than others. Moreover, the optimal concentration ( x ) of Sm 3+ was confirmed to 0.03. The concentration quenching of Sm 3+ was mainly attributed to dipole-dipole interaction. [ABSTRACT FROM AUTHOR]