Advanced Materials Research Vols. 55-57

Abstract: This research article reports a development on green pigments having high reflectance of NIR radiation from the sun. The aim of the development is to use the green pigments as a component of building paint to reduce heat penetrating into the building. Cr2O3, a green pigment oxide, was used as the host component and the mixtures of Al2O3, V2O5 and TiO2 were used as the guest components. Al2O3, V2O5 and TiO2 were mixed at different 36 compositions according to triaxial diagram. For each sample preparation, 80% wt Cr2O3 was mixed with 20%wt of guest component for each composition. Then the mixed sample were calcined at 1150 °C for 4 hours and were ground with an agate ball mill for 7 minutes at a speed of 250 rev/min. Finally, the pigments were sieved to obtain the particle sizes of 0.5 - 2.0 µm. The pigment powders were compressed in a mold to get samples in the form of thin disks, each one with a diameter of 2.7 cm and a thickness of 4 mm. The reflectance for all samples was measured using a spectrophotometer in the wavelength ranging from 300 – 2100 nm in accordance with ASTM E891. It was found that the maximum reflectance, in the wavelengths ranging from 780 – 2100 nm, of 82.83% was obtained from the sample with a composition of 80%Cr2O3, 14%Al2O3, 4%TiO2 and 2% V2O5.

Abstract: Nanopowders of n-type (Bi0.95Sb0.05)2(Te0.95Se0.05)3 and p-type (Bi0.2Sb0.8)2Te3 have been synthesized by laser fracture of micron-sized powders in water. These alloys are the best conventional thermoelectric materials for use in room temperature applications. The nanopowders have been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanopowders have been mechanically mixed in different ratios with the micron sized powders. These mixtures have then been cold pressed in order to perform thermoelectric characterization and to see the influence of nano-particle inclusions on the transport properties.

Abstract: The short-time-consumption melting and hot pressing processes were used to synthesize n-type and p-type Bi-Sb-Te thermoelectric materials. The synthesis materials were characterized and used for the module fabrication. The aluminium substrate was used instead of alumina substrate because it is easy to cut and to avoid fragility of the module. The performance of 20 x 20 mm2 prototype thermoelectric module consists of 7 pairs of n-type and p-type Bi-Sb-Te thermoelectric materials was investigated and then compared its performance to 40 mm x 40 mm commercial module. The output power densities as a function of temperature difference across the devices and open circuit voltages from the module are reported.

Abstract: One of the critical issues in designing a planar solid oxide fuel cell (SOFC) is the development of materials to hermetically seal the metal (430 series stainless steel) or ceramic interconnector with the ceramic electrolyte of the cell. The main objective of this sealing material is to achieve a low leak rate, long-term stability at operating temperature and chemical compatibility with other components. One of the compositions has been operated in an SOFC in excess of 30 minutes over the range of 600, 700, 800, and 900°C. The seal is a composition of polymer blend and glass of 1:3, 1:1 and 3:1 by weight. The leakage rate of each seal was measured simultaneously under the compressive force of 100 N, 2 bar Helium. The seal was characterized using a thermogravimetric analysis. The effect of glass composition on operating temperature and compressive forces on the leakage rate have been discussed and correlated.

Abstract: Highly luminescence lattice-matched InxGa1-xP1-yNy/GaP single quantum wells (SQWs) on GaP (001) substrates were successfully grown by metalorganic vapor phase epitaxy (MOVPE). High-resolution X-ray diffraction measurements established that the lattice-matched InxGa1-xP1-yNy/GaP SQWs with various In (x = 0.050, 0.080, 0.135) and N (y = 0.025, 0.048, 0.071) contents were realized with excellent crystal quality and fairly flat interfaces. The results of photoluminescence (PL) and PL-excitation (PLE) showed the strong visible light emission (yellow to red emission) from the SQWs. With increasing In and N contents, the PL peak position and the PLE absorption edge exhibited the red-shift to lower energy, indicating the lowering of the InGaPN conduction band edge. The conduction band offset (∆Ec) of the InGaAPN/GaP quantum structure was estimated to be as high as 270 to 480 meV, which depends on the In and N contents in the well. Our results demonstrate that this novel InGaPN/GaP SQW system appropriates for the fabrication of light-emitting and laser diodes.

Abstract: The GaAs1-xNx alloy semiconductor has been grown on GaAs (001), (111)A and (011) substrates by metalorganic vapor-phase epitaxy. High resolution X-ray diffraction and Raman scattering were employed to examine the effective N content and the growth rate, as a function of the substrate-surface orientation. The growth rate, which was assessed though the clear Pendellösung fringes, and the N content were found to change dramatically with the substrate-surface orientations. The N content was determined in the order (111)A > (001) > (011). While, the growth rate is in the order, (001) > (011) > (111)A. The effect of substrate-surface orientation on the N incorporation found in the present study is interpreted in terms of the difference in the growth rate on each surface orientation and the number of dangling bonds with which the N atoms can be trapped on the growing surface. Our results show that controlled nitrogen incorporating for GaAsN is successfully achieved and can be applied to the fabrication of some novel structures such as a spontaneous N content modulated structure, which is applicable to high performance long wavelength laser diodes.

Abstract: Te-doped CoSb3 was prepared by the encapsulated induction melting, and its doping effects on the thermoelectric properties were investigated. Single phase d-CoSb3 was successfully obtained by the subsequent annealing at 773K for 24 hours. Tellurium atoms acted as electron donors by substituting antimony atoms. Thermoelectric properties were remarkably improved by the appropriate doping. Dimensionless figure of merit was obtained to be 0.83 at 700K for the CoSb2.8Te0.2 specimen.

Abstract: Handmade mulberry paper was coated with flame retardants reagent: ammonium sulphate, at the various concentrations. The properties of mulberry paper, i.e. rate of water absorption, rate of flammability, flash point and mechanical properties expressed as Young’s modulus were studied. Mulberry paper coated with sulphate-based compound was not flammable and the rate of water absorption was decreased, while the elasticity was increased.

Abstract: This study investigated fundamental of phase formation, crystal structure and calcination process for bismuth dysprosium titanate (Bi4-xDyxTi3O12; BDT) powders when x = 0, 0.25, 0.5, 0.75 and 1.0. BDT powders were prepared using a simple solid-state reaction on mixtures of reagent grade Bi2O3, Dy2O3 and TiO2 powders. The mixtures were calcined at temperature in the range of 500-800°C for 4 h at a heating/cooling rate of 5°C/min. Thermal characteristics of powders were studied using thermogravimetric/differential thermal analyses which indicated that the formation of Bi4Ti3O12 and Bi3Dy1Ti3O12 powders occurred at ~500oC. Effect of Dy3+ concentration on phase and crystal structure was investigated using X-ray diffractometry. The results revealed that at small concentration of Dy dopant (x £ 0.25), optimum calcination temperature for providing bismuth titanate-based phase was 650oC. Increasing content of Dy dopant seemed to reduce calcination temperature to 600oC. This study suggested the alternative environmental friendly BDT materials which may be used as starting powders for production of high quality BDT ceramics.

Abstract: This research studied the effects of sintering temperature and La3+ doping content on phase, microstructure and densification of bismuth lanthanum titanate (Bi4-xLaxTi3O12; BLT) ceramics when x = 0, 0.25, 0.5, 0.75 and 1.0, respectively. The BLT powders were prepared using a mixed-oxide method. The mixtures were calcined at 750°C for 4 h before being pressed and sintered at 1000-1150°C for 4 h. The result of phase analysis by X–ray diffraction (XRD) indicated the existence of orthorhombic phase for all sintering temperatures. The XRD peak intensities of the ceramics showed preferred orientation of a particular set of {00l}-type planes. The ceramics mainly composed of plate-like grains. Increasing the sintering temperature increased grain size and increased preferred grain orientation. The present of La3+ in BLT ceramics reduced preferred orientation especially at higher sintering temperature. Results of microstructural investigation agreed well with X-ray diffraction patterns.