Advanced Materials Research Vols. 79-82

Abstract: YAG crystal possesses chemical stability, mechanical intension, thermal conductivity and isotropy. These properties make it widely be used as functional and structural materials. YAG powder was successfully synthesized by gel solid-state reaction. AlOOH were reacted respectively with Y2(C2O4)3•10H2O (Route YІ) and Y2O3 (Route YІІ). The XRD indicated that the main phases were from YAM to YAP, finally to YAG with the increase of temperature in both routes, and YAG began to generate at 1250°C. The single-phase YAG generated after holding for 4h at 1450°Cin the YІ, but a little bit of YAP and Al2O3 was still remained in the YІІ. It was that Y2(C2O4)3•10H2O might be decomposed into high-activity, loose-structure yttrium oxide, which promoted the diffusion of Al3+ ion. According to XRD analysis, YAG generated slowly during 1250°C~1300°C and then fast during 1300°C~1450°C. The SEM images showed that the primary particles of YІ were 2-3µm, larger than that of YІІ. Particle distribution indicated that the average diameter is 18.68μm in the YІ and 9.35μm in the YІІ.

Abstract: Ultrafine MgAl2O4 powders have been successfully synthesized by solid-state reaction from the mixture of AlOOH and MgO at the lower temperature. The samples were investigated by DTA/TG、XRD and SEM analyses. The results showed that AlOOH can be decomposed into γ-Al2O3 from DG/TDA curves, which can improve the activity of Al2O3 and promote the process of solid-state reaction. The XRD analysis showed the single-phase MgAl2O4 was formed at 1400°C. Meanwhile it was detected by ICP-MS that the purity of powders was 99.995%. The SEM images showed that the mineralizer containing fluoride such as AlF3, NH4F can promote the resultant to grow into regular octahedrons and disperse the particles. The XRD analysis indicated the mixture containing 5% AlF3 can transform the integrated MgAl2O4 powders at 1200°C, nearly 200°C lower than general solid-state reaction. Furthermore, The SEM images showed that fluoride can crystal the fine particles into the larger MgAl2O4 crystals, about 0.5～1.5µm.

Abstract: Calcium chloride hexahydrate (CaCl2•6H2O) is an important inorganic phase change material used for thermal energy storage or discharge at lower storage temperature. Thermal energy discharge characteristics of a new type of PCM heat exchanger were investigated after thermal energy storage, in which its main body is based on the traditional structure of a shell-and-tube heat exchanger, and is full of PCMs (CaCl2•6H2O) in the tubes. The cold air of 16-17°C with different velocities flowed through the PCM heat exchanger, the temperature distributions of all the test points were measured by means of the experimetal system. The experimental results showed that, since the latent heat of phase transition in the tubes was so large during the process of thermal energy discharge, the time intervals of air temperature that maintained beyond 20°C at the outlet of the PCM heat exchanger were respectively 594min and 717min when the mass velocities of the cold air were 0.132 kg/s and 0.096kg/s, which is one of the important characteristics in the structure of this type of PCM heat exchanger. It can be used in the situations of temperature control or maintenance at the certain temperature, such as greenhouses, air conditioning etc.

Abstract: The influence of dispersant on sedimentation performance of ultrafine Al(OH)3 aqueous suspension was studied by the determination of settlement rate and Zeta potential. And the settlement rate formula of powder particle in water solution was modified. Results showed that 0.2% addition of DP-270 has better dispersion effect on Al(OH)3 aqueous suspension. As for spherical powder particle with electricity at size range 0.55~ 1.67μm, the settlement rate in aqueous solution can be calculated with modified formula: V=V0 [esp（ζn-ζ0）/ζ0]-1

Abstract: In this study, a novel green phosphor Ca2SrAl2O6:Ce3+,Tb3+ were prepared by solid state method. The crystal structure and particle morphology of phosphors were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result indicated that the phosphor belonged to a single Ca2SrAl2O6 phase and crystalline grain sizes were about 2.0~5.0 μm. The excitation and emission spectra were studied in this paper. Monitored at 545 nm, the excitation spectrum consisted of a broad band at UV region (320-400 nm), which was attributed to the abstract of Ce3+ and Tb3+ ions. Excited by 360 nm UV light, the emission spectrum was composed of four groups narrow band and the emission peaks located at 497, 545, 595 and 623nm, respectively. Luminescent intensity increased with Tb3+ and Ce3+ ions concentration and it would reach the maximum when the activator molar fraction was 0.04 for the highest emission intensity at 545 nm. Concentration quenching would occur if the activator concentration exceeded 0.04 mol-1. Li2CO3 could be used for flux and Li+ ion was used for charge compensation in this experiment. Thus, Ca2SrAl2O6:Ce3+, Tb3+ phosphor was a good candidate of green phosphor for UV based white LED.

Abstract: ZnO/Zn3N2 multilayer films were synthesized on slide glass substrates by radio-frequency (RF) magnetron sputtering technology with RF powers of 100 W. After annealing in oxygen atmosphere for 3 hours at the temperature changed from 473 K to 873 K, the multilayer films were changed to be single-layer films of nitrogen doped ZnO dilute ferromagnetic semiconductor. The structural, elementary constituents, carrier concentration and magnetic properties of the films were investigated with X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), hall-effect measurements and vibrating sample magnetometer (VSM) magnetization measurements, respectively. The XRD measurements revealed that the nitrogen doped ZnO films had a wurtzite structure with their crystal (002) directions oriented along the c-axis of the substrate. Hall-effect measurements indicated that nitrogen doped ZnO thin film, annealed at 673 K for 3 hour, had the best p-type properties. Carrier concentration and resistivity of the film was 3.12 × 1017 cm-3 and 93 Ωcm, respectively. A Lakeshore 7407 vibrating sample magnetometer was employed for magnetization (M) versus applied field strength (H) investigations of these thin films. A typical hysteresis loop was found in the observed M–H curve of the samples, demonstrated that the films annealed at 673 K for 3 hour were ferromagnetic at 300 K. The XPS analysis revealed the presence of Zn-N chemical bonding in the films. It suggested that nitrogen atoms are substituted at the oxygen sites of the ZnO films and mediate the ferromagnetic properties of the films.

Abstract: Two-dimensional iron polyphthalocyanine(PPcFe) was synthesized by heating iron (II) phthalocyanine tetracarboxylic acids at 400°C in argon atmosphere. The polymer was characterized and analyzed by UV-Vis, FT-IR, XRD and TG. UV-Vis absorption spectra of iron phthalocyanine showed that absorption bands appeared at higher wavelengths than monomer phthalocyanine. The result of IR indicated that the absorption peaks corresponding to the carboxylic acid groups decreased and the characteristic phthalocyanine ring absorption bands were observed. The DTA data for PPcFe showed exceptional thermal stability. PPcFe, monomer phthalocyanine(PcFe) and dinuclear iron phthalocyanine(DPcFe) were adsorbed on the Vulcan XC-72 carbon and then heat-treated at 400°C in argon atmosphere to prepare catalyst. The electrocatalytic activity was investigated using linear scan voltammetry(LSV) in 0.5M H2SO4. The polarisation curve of oxygen reduction on the FePPc/C catalyst in O2-saturated H2SO4 was compared to that obtained on PcFe, DPcFe and platinum catalysts. Results showed that it possessed higher catalytic activity than PcFe and DPcFe catalysts. LSV at different electrode rotation rates led to determine the Koutecky-Levich plots from which it was shown that the kinetic parameters for the ORR at FePPc/C electrodes are similar to those obtained at 30wt% Pt/C.

Abstract: Three non-destructive test (NDT) methods were used to detect the two dimensional C/SiC specimens after low velocity impact (LVI) of various energies. The damage areas characterized by these methods were very different. Both ultrasonic and thermographic images reveal the LVI damages, while X ray is non-sensitive to the interior damage. However, small delaminations were not found by thermography and accurate judgment depends on the experience and the resolution of the infrared camera. And the result acquired from the higher frequency transducer was very confused because of the inherent defects. It is suggested that using both ultrasonic C-scan and thermography to evaluate the LVI damage of C/SiC. It is also suggested using the transducer of low frequency to perform the ultrasonic C-scan.

Abstract: Nanodiamonds coated with polystyrene were prepared by in-situ latex polymerization using azobisisobutylonitrile as initiator in alcohol-water solution. The products were characterized by transmission electron microscope, X-ray diffraction, thermo-gravimetric and differential thermal analysis and Fourier transformation infrared spectrum. A possible formation mechanism and the structure of products were proposed. The experimental evaluation of wettability performance showed that the hydrophobicity of nanodiamond have been enhanced with the wrapping of polystyrene films on the surface of nanodiamond particles.

Abstract: Double-layer cementitious plates with absorbing microwave properties were designed, based on the impedance matching theory and electromagnetic wave propagation laws. The reflectivity of cementitious composites was measured in the frequency ranges from 8 GHz to 18GHz, and the influence of silica fume on the impedance of the composites surface was studied. Meanwhile, absorbing properties of cementitious plates, which used ferrite and carbon fiber composited ferrite as microwave absorbers, were also investigated respectively. It is shown that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Compared with the single-layer structure, the reflectivity of the double-layer cementitious plates decreased around 6 dB ~ 8 dB. The maximum reflection loss of double-layer cementitious plate employing carbon fiber and ferrite reached -16.2dB, while the absorption bandwidth under – 10 dB was from 9.6 to 18 GHz.