Papers by Author: Yan Gai Liu

Abstract: Tourmaline has characteristics of repeatedly producing electric dipole polarity transformation. Using FTO glass substrate coated with conductive films as raw materials, the research aims to prepare functional glass materials, which have spontaneous polarization effect, absorption of wideband electromagnetic radiation and high visible light transmittance. This paper applied Magnetron Sputtering deposition technique, studying on tourmaline as target, sputtering on conductive FTO glass, using multiple means to measure and analyze the surface morphology, component, structure, electrical and magnetic properties. And the functions of tourmaline as composite electromagnetic shielding films are also discussed in the paper.

Abstract: Doping perovskite structure ceramics constitute an important type of solid oxides fuel cell (SOFC) cathode materials. In this study, BaCe1-xTaxO3+δ powders were prepared by solid state reaction at 1500oC for 4h. BaCe1-xTaxO3+δ ceramics were pressureless sintered at 1600oC for 5h. The results indicated that the relative density of BaCe1-xTaxO3+δ ceramics reached the range of 84.15 - 90.88%. At the frequency of 1Hz, the conductivity of BaCe0.65Ta0.35O3+δ ceramic samples varied greatly, when the testing temperature rose from room temperature to 900oC in increments of 100oC. The highest conductivity was obtained at 600oC with the value of 6.74×10-5 S/cm.

Abstract: Silicon nitride (β-Si₃N₄) nano-belts had been synthesized by used silica bricks and carbon powder as raw materials through carbothermal reduction nitridation. The morphology and microstructure of β-Si₃N₄ nano-belts were characterized by scanning electron microscopy (SEM/HRSEM), energy disperse spectrum (EDS) and X-ray diffraction (XRD). Results showed that the well-crystallized β-Si₃N₄ nano-beltes were grown with thinness of 50-150nm and width of 3-5μm. The relatively purer β-Si₃N₄ were prone to be thin films with thinness of 150nm, while the as-grown SiCN (impurityβ-Si₃N₄with C elements) were presented as nanorods with cross section length of 150*150nm. Orientation growth mechanism by grain dislocation and vapor-solid (VS) mechanism were both involved in the growth of nanostructures of β-Si₃N₄ nano-beltes and SiCN nanorods.

Abstract: Mullite with puncheon-like grains was synthesized by sintering the mixtures of coal gangue and γ-Al₂O₃ at 1400 °C~1550 °C for 4 h. The phase and microstructure evolution of the mullitization behavior were investigated by XRD, SEM and EDS. Phases of the sintered specimens were mullite, corundum and cristobalite at 1400 °C to 1450 °C. Arise of temperature would enhance mullitization, and total consumption of cristobalite occurred from 1500 °C upward. The in-situ produced primary mullite from gangue upon heating may be seeds for the growth of enenly dispersed mullite puncheons. Specimen sintered at 1550 °C consists of puncheons with an aspect ratio of 2~4, regionally forming an interlocking structure.

Abstract: Lanthanum magnesium hexaaluminate (LaMgAl11O19, LMA) has attracted much interest as its widely used in solid state lasers, TV phosphors and fluorescent lamps. In this paper, LaMgAl11O19 ceramic was pressureless sintered at 1650 °C for 10 h in air atmosphere using LaMgAl11O19 powders prepared by solid-state reaction at 1500 °C for 4 h. The result indicated that the synthesis temperature of LaMgAl11O19 powders was about 1500 °C. The LMA ceramic sample was dense and had a microstructure of platelet-like gains. The excitation spectrum shows two wide bands with the peaks at about 254 nm and 265 nm by monitoring the strongest 362 nm emission, and the emission spectra is consisted of a broad band emission with their peaks near 362 nm with a half-width about 5 nm exciting with 265 nm wavelength.

Abstract: Doped ceria-based (Gd0.2Ce0.8O1.9, GDC) solid electrolytes were prepared by Solid-phase synthesis method. The effect of doping bismuth oxide and samarium oxide on the phase and microstructure of GDC was investigated. The phase composition was analyzed by the X-ray diffraction (XRD).The single cubic fluorite structure was observed after doping these oxides. Appearance and microstructure of doped ceria-based solid electrolytes were analyzed by the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM). The results showed that the doped trivalent cations had entered into the ceria structure uniformly. The density, porosity rate and water absorption of GDC were measured by Archimedes principle. It indicated that the density of doped GDC solid electrolyte increased with the rising of sintering temperature.

Abstract: Ta-doped Li3V2(PO4)3 cathode material coated by carbon was synthesized via a sol-gel method. Effects of Ta5+ doping on the physical structure and electrochemical performances of the Li3V2(PO4)3/C cathode materials were investigated. Compared with the undoped sample, the Ta-doped samples had no excess peaks but the larger particle size and the narrower distribution of the particle size, indicating that Ta5+ entered into the structure of (Li1-5xTax)3V2(PO4)3/C rather than forming any impurities. When x was up to 0.01, the best electrochemical properties of the Ta-doped cathode materials had been displayed at the charge and discharge rate of 0.1C with the voltage of 3.0～4.8V. The analysis of cyclic voltammetry revealed that the polarization of the Li3V2(PO4)3/C cathode materials could be effectively decreased by Ta5+ doping(x=0.01), mainly resulting from the better electronic conductivity.

Abstract: The erosion wear resistance of YSZ ceramics is worth studying because solid particle erosion is one of the main causes of destroying the materials and apparatuses. In this paper, 8YSZ ceramics reinforced by NiCr alloy and Al2O3 particles were pressureless sintered at an optimized sintering condition. The facture toughness reached a maximum value of 4.6 MPa•m ^1/2 when the addition of NiCr alloy is 12 vol.%, which was much higher than that of the pure 8YSZ ceramic (2.0 MPa•m ^1/2) fabricated in the same condition. Solid particle erosion wear behavior of NiCr-Al₂O₃-ZrO₂ (8Y) ceramics composites was performed by self-designed sand blasting type solid particle erosion wear equipment, using 36# SiC particles as abrasive particles with the 90o erosion angle. The effect of the volume addition of NiCr alloy on the erosion wear of NiCr-Al₂O₃-ZrO₂ (8Y) ceramic composites at room temperature was investigated. The results show that the volume erosion rate of the ceramic composites decreased as the volume addition of the NiCr alloy increasing. Crossing cracks, plastic deformation and minor chipping are the major erosion mechanisms.

Abstract: The utilization of lightweight refractories plays an important role in reducing the energy consumption of industrial furnaces. In this paper, MgAl₂O₄-CaA1₁₂O₁₉ high temperature composite was synthesized via solid state reaction using magnesite, dolomite and industrial alumina as raw materials. The influences of raw materials and reaction temperature on phase compositions and microstructure of the composite were investigated by XRD and SEM，respectively. The parameters to prepare MgAl₂O₄-CaA1₁₂O₁₉ high temperature composite were optimized. The results show that the optimum reaction conditions for synthesizing MgAl₂O₄-CaA1₁₂O₁₉ composite is the CA₆/MA weight ratio of 2:3, and the reaction temperature of 1500°C for 4h. The CaA1₁₂O₁₉ crystals showed laminated or plate-like structure, and the MgAl₂O₄ showed spherical morphology. The reaction temperature had little effect on the phase compositions of MA-CA₆ composite in this experiment. The content of Al₂O₃ in the raw material affected the phase composition of MA-CA₆ composite.With the increase of the CaA1₁₂O₁₉ amount, the bending strength of the composite decreased.

Abstract: ZrO₂ ceramics have been widely used to many fields with its excellent physical and chemical properties, but the mechanical properties of YSZ ceramics, especially the fracture toughness, decline caused by the failure of the phase transformation toughening at high temperature. In this investigation, plate-like LaMgAl₁₁O₁₉ toughened ZrO₂ ceramics were prepared by pressureless sintering at 1550 °C for 3h in air . The bulk density of the sintered samples are between 5.5 to 6.0 g/cm³, and the relative density are above 93%. The mechanical properties of the ZrO₂-LaMgAl₁₁O₁₉ ceramics were studied systematically at room temperature. The flexure strength and fracture toughness of ZrO₂-LaMgAl₁₁O₁₉ ceramic are 811.8 MPa and 13.9 MPa•m^½ with the LMA addition of 2wt%.