Lian Jun Wang

Preparation of Graphene Nanosheet/Alumina Composites

Graphene nanosheet (GNS)/ Al2O3 composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al2O3, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al2O3 composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al2O3 composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al2O3 particles and also the as-prepared GNSs/ Al2O3 composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Influence of Sintering Temperatures on Microstructures and the Thermal Conductivity of CuAlO2 Ceramics

Oxide ceramic is a kind of environmental friendly materials, which has attracted more and more interests for its bunch of advantages such as sound chemical, thermal stability, simple synthetic process, cheap price, harmless and safety. Therefore, Oxide ceramic will be a promising material in the future. In this work, polycrystalline samples of CuAlO2 were prepared by a solid state reaction method. The mixture of pure CuO and Al2O3 powders was firstly pressed under the pressure of 60 MPa, and then 200 MPa to prepare pellets of 5 mm thick and 10 mm in diameter. The green compacts were sintered at five different temperatures (1273 K, 1323 K, 1373 K, 1423 K, 1473 K) for various holding times (5 h, 10 h and 15 h) in the air and then the furnace cooled. The crystalline and microstructures of the sintered CuAlO2 bodies were detected by XRD and SEM. The properties of density, thermal conductivity were also investigated in detail. The experimental results show that CuAlO2 bodies were rhombohedral, belonging to R3m space group. It is found that the density and the thermal conductivity of CuAlO2 ceramics were significantly dependent on the sintering temperatures. The density and thermal conductivity increased with increasing the sintering temperatures. The thermal conductivity of samples sintered at 1273 and 1473 K with the same holding time (10 h) were 9.70 and 35.53 W/mk at the room temperature, 3.41 and 8.29 W/mk at 1100 K, respectively.

A Promising Energy-Saving and Environmental-Friendly Lighting Device: High CRI White LED with Phosphor Materials

Two kinds of commercial LED phosphors (green phosphor LuAG:Ce3+ and red phosphor CaAlSiN3:Eu2+) with polymethyl methacrylate (PMMA) powders were mixed to prepare film phosphors with tunable emission peak in photoluminescence spectrum by flat vulcanizing machine under the temperature of 170 oC and pressure of 2 MPa. The physical phase, surface morphology, transmittance, luminescence spectra of samples were characterized by means of X-ray diffraction (XRD), Environmental scanning electron microscopy (ESEM), Ultraviolet-Visible (UV-Vis) spectrophotometry and Fluorescence spectrometer. The results show that the film phosphors phase was consistent with raw phosphors, phosphor particles were uniformly distributed, and fluorescence spectra with different proportions of phosphors in different position can be adjusted. Tested by HSP 3000 spectrum analyzer, the white LEDs fabricated by blue chip and composite film phosphor containing 5 wt% green phosphor and 1.5 wt.% red phosphor, which refers to the remote excitation technique, possessed color coordinate of (0.3715, 0.3280) and color rendering index (CRI) of 87 when it was driven at power of 36 V/140 mA, reaching the international advanced level.

Preparation of Highly Transparent Silica Glass by SPS Sintering of SBA-15

Silica glass was prepared via the spark plasma sintering (SPS) method by using SBA-15 as the starting material. Five temperatures (1000, 1010, 1020, 1030 and 1040°C) were selected as the final sintering temperature above 600°C. The transparent silica glass was prepared by SPS sintering of mesoporous silica SBA-15 at 1040°C. The impact of temperature structure collapse of SBA-15, the structure and transmittance of the glass were studied using X ray diffraction, SEM, TEM, Infrared analysis, Raman analysis and UV-VIS spectrophotometer. Results show that SBA-15 collapsed completely at 1040°C, the sintered glass had high transmittance of above 90% in visible spectra, and its hardness was 6.96 Gpa, and that the sintered transparent sample was silica glass. The work demonstrated a novel strategy to use SPS to prepare highly transparent silica glass by sintering of SBA-15.

Variation of Transparency of Zeolite-Derived Silica Glass Prepared by Spark Plasma Sintering

A series of zeolite-derived silica glasses have been fabricated through the order-disorder transition process of zeolites using spark plasma sintering (SPS). The samples were characterized by UV-VIS-NIR transmittance, Raman spectra and Vicker’s hardness. Results showed that the transmittance of zeolite-derived silica glass samples increased with the sintering temperature increasing. The transmittance of the sample prepared at 1300°C was lower than 5%. The highly transparent samples could be obtained when the sintering temperature was above 1350°C. The transmittance of these samples was higher than 80% in the range of 780~1700nm and 60% in the UV-vis range of 250~780nm. One absorption band at 300nm can also be observed in the spectrum. The reason of this phenomenon could be ascribed to a few left crystallite fragments of ZSM-5. The Raman spectra showed that the bands at 378 and 292cm-1of ZSM-5 were significantly weakened and then disappeared with increasing the sintering temperature and the bands at 489 and 600cm-1 of silica glass became more apparent. The Raman spectra of the samples obtained above 1350°C were the same as that of the fused silica glass. The Vicker’s hardness of as-prepared samples increased with the rising of the sintering temperature. The maximum hardness of 7.31 GPa was achieved for the sample sintered at 1400°C. The fracture toughness of samples increased from 0.83 MPa·m1/2 to 2.37 MPa·m1/2 with the sintering temperature increasing.

Preparation and Properties of Up-Conversion Luminescent NaYF 4 :Yb 3+ , Er 3+ Ceramics

A series of ytterbium and erbium co-doped sodium yttrium fluoride (NaYF4:Yb3+, Er3+) ceramics have been successfully prepared by pressureless sintering. The ceramic samples were characterized by X-ray diffraction (XRD), photoluminescence (PL), density and field emission scanning electron microscope (FESEM). The results showed that the phases of the NaYF4:Yb3+, Er3+ ceramic samples transformed when the sintering temperature was changed. The ceramic samples sintered below 600 oC contained both cubic α-NaYF4:Yb3+, Er3+ and hexagonal β-NaYF4:Yb3+, Er3+. The sample sintered at 600oC is the pure hexagonal β-NaYF4:Yb3+, Er3+. When the sintering temperature is above 600 oC, the ceramic samples present the α-NaYF4:Yb3+, Er3+ again. The fluorescence intensity increased firstly and then decreased with the sintering temperature increasing. The luminous intensity of the sample sintered at 600 oC was the highest. The densities of as-prepared ceramic sample increased with the sintering temperature rising. The samples sintered at 600 oC with different holding time possessed the similar crystal phases (β-NaYF4:Yb3+, Er3+) and fluorescence intensity. As the holding time increased, the densities of the samples increased. To obtain more dense ceramics, the ceramics using β-NaYF4:Yb3+, Er3+ powders were prepared by spark plasma sintering (SPS). The maximum relative density reached 97%.

Mechanism of Self-Propagating High-Temperature Synthesis of MoSi2

The reaction mechanism of self-propagating high-temperature synthesis of MoSi2 was investigated by means various methods. The result of activation energy calculation indicates that the synthesis reaction is controlled by a single mechanism. Analysis on the microstructure of Mo/MoSi2 and Si/MoSi2 interfaces reveals that Mo reacts with Si to directly form MoSi2 without any transient product (s). Morphology comparison between the reactants and the product demonstrates that the reaction mechanism is not reactive diffusion. Microstructural observation on the materials from quenched zone shows MoSi2 particles precipitate from liquid phase. A mechanism may be proposed based on the above results: Mo particles are covered by molten Si and dissolve into the melt, and then MoSi2 particles precipitate from the melt due to super saturation.

Comparison of the Luminescence Properties of PbS Quantum Dots Prepared by Different Methods

PbS quantum dots (QDs) were prepared through a two-phase approach and an aqueous method respectively. The reaction conditions of the two-phase approach were mild and highly controllable, but the as-prepared QDs were capped with oleic acid. Although the PbS QDs prepared by the aqueous method did not exhibit excellent photoluminescence properties, it was more facile and environmentally friendly, and furthermore the resulting PbS QDs were more promising in biological labeling without ligand exchange. We have investigated the absorption and luminescent properties of QDs prepared by the two methods. The results showed that the absorption shoulder of oil soluble PbS QDs was at 580nm and water soluble PbS QDs was at 600~700nm. And the emission peaks in the photoluminescence spectra were at 755nm and 970nm, respectively. XRD analysis confirmed that the PbS QDs were cubic phase. The TEM results showed that the size of both types of PbS QDs was smaller than the excitons Bohr radius (18nm).

Preparation and Thermoelectric Properties of Polyaniline Doped with Protonic Acids

Hydrochloric acid doped polyaniline and camphor sulfonic acid doped polyaniline were prepared by oxidative chemical polymerization and grinding, respectively. The structures of polyaniline samples were measured by Fourier transform infared spectroscopy. The Seebeck coefficient and electrical conductivity of the composites were investigated as protonic acid content in the temperature range from room temperature to 380K. The highest electrical conductivity of the 1M hydrochloric acid doped polyaniline reaches 5.57×102S/m at 320K, and the mass ratio of 1:1 camphor sulfonic acid doped polyaniline reaches 5.97×102S/m at 380K. This work suggests that a new method improves the thermoelectric properties of conducting polymers.

Preparation of Stable Pt Nanoparticles Supported by Mesoporous Silica SBA-15

A simple two-step procedure towards the Pt nanoparticles and mesoporou silicate SBA-15 composite was developed in this work. The ultrasonic irradiation and the calcinations involved in the preparation did not destroy the size and morphology of prepared Pt nanoparticles, and no agglomeration of Pt nanoparticles was observed, thus stable Pt nanoparticles supported by SBA-15 host were formed. The hexagonal ordered structure of SBA-15 also remained. This stable composite are mainly used as the starting material in fabricating stable Pt nanoparticles doped glass.