Crystal Structure and Optical Performance of Al3+ and Ce3+ Codoped Ca3Sc2Si3O12 Green Phosphors for White LEDs

Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce) green phosphors used for white light‐emitting diodes (LEDs) are synthesized and codoped with Al³⁺ via a solid‐state reaction method. The crystal structure and vibrational modes are analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman scattering spectroscopy. The energy transfer behavior and optical performance are characterized by photoluminescence and excitation spectra, quantum efficiency, and time‐resolved photoluminescence. The incorporation of Al³⁺ into CSS:Ce can inhibit the formation of the impurity phases Sc₂O₃ and CeO₂, improve crystallinity, and enhance the photoluminescence intensity as well as quantum efficiency. The substitution of Sc³⁺ with Al³⁺ increased the crystal field splitting of Ce³⁺ and resulted in the red shift of photoluminescence. The results show that Ca₃Sc_2?xAl_xSi₃O₁₂:Ce³⁺ has high quantum efficiency, making it a promising green phosphor that can be collocated with a commercial 450 nm blue LED and a red phosphor for solid‐state lighting applications.     

Structural Optimization and Improved Discharged Energy Density for Niobate Glass‐Ceramics by La2O3 Addition

The structural and dielectric properties were investigated in the La₂O₃ added glass‐ceramics based on complex niobates. With the addition of La₂O₃, the optimization of microstructure was observed which resulted in the improvement of breakdown strength for the glass‐ceramics. Besides, the dielectric constant was drastically enhanced because of the doping effect of La³⁺ in the A‐sites of both crystallographic structures. Due to the combined effects of both high breakdown strength and polarization difference, the maximum discharged energy density of 1.2 J/cm³ was achieved in the niobate glass‐ceramics with 2 mol% La₂O₃, suggesting dielectric glass‐ceramics of this composition could be the most attractive candidate for high‐energy density capacitors.     

Preparation and Mechanical Properties of Cross-Linked Polyphosphazene Elastomers Based on Urethane Oligomers

Linear poly [bis-(phenoxy)_1.8 (4-hydroxybutaneoxy)_0.2 phosphazene] (PPHBP) was synthesized and characterized by FTIR, NMR and GPC. Then, PPHBP was cross-linked by different ratio of toluene diisocyanate and 1, 4-butanediol mixtures at mild temperature to prepare PPHBP elastomers. The FTIR spectral analysis demonstrated that the elastomers' chemical composition was the same with our expectations. Tensile testing results indicated that the tensile strength increased from 0.053 to 7.9 MPa and the break elongation approached from 1.82 to 68.7%. The novel cross-linked method might open a simple and economic route to preparing polyphosphazene elastomers.     

Influence of Process Variables on the Reactivity of Low Formaldehyde Emission Urea-Formaldehyde Resin

One of the important characteristics of the thermosetting resins such as urea-formaldehyde resin is the cure property. This is an invaluable characteristic for determining the processing capabilities of the resin. Differential scanning calorimetry (DSC) measurements are ideally suited to achieve this end. This paper presents the results of the effect of process variables on the enthalpy of cure of a low formaldehyde emission UF resin prepared by a four-stage process as described in the text. Response surface methodology (RSM) was used to design and the analyze the experiments. Urea (U) was added to the reaction mixture according to a pre-determined program of varying the number of additions and the duration between the additions during the second stage of the process. A mathematical relationship between the process variables and enthalpy of cure was established. The urea-formaldehyde (UF) resin was prepared under optimum conditions. Experiments were performed with the resin so prepared to determine the energy of activation of the curing reaction catalyzed by ammonium chloride.     

The Friction and Wear of Aramid Fiber-Reinforced Polyamide 6 Composites Filled with Nano-MoS2

The friction and wear behaviors of aramid-filled PA 6 composites filled with and without nano-MoS₂ were investigated on an end-face tribometer through rubbing against ASTM 1045 steel under dry friction. The experimental results indicated that the wear rate and the friction coefficient of PA 6 decreased with the addition of nano-MoS₂. The friction coefficients of PA 6 composites filled with aramid fiber are lower than those without nano-MoS₂. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing. For best combination of friction coefficient and wear rate, the optimal volume content of MoS₂ in the composites appears to be 10 vol %.     

SOME OBSERVATIONS FROM STUDIES OF RF PLASMA PYROLYSIS OF WASTE TIRES

Pyrolysis treatment of waste tires was studied in a capacitively-coupled radio frequency (RF) plasma reactor. Using RF input power between 1600 and 2000 W and a reactor pressure between 3000 and 8000 Pa, a reactive plasma environment with a temperature between 1200 and 1800 K can be reached. Under these conditions, pyrolysis experiments with tire powder showed that two product streams were obtained: a combustible gas and a pyrolytic char. The main gaseous components were H₂, CO, and CH₄. When adopting double sets of electrodes in this plasma reactor, the gas yield and concentrations of H₂ and CO can be enhanced. The energy utilization efficiency of this RF plasma pyrolysis reactor system was also analyzed.     

THE PREDICTION OF NOx FORMATION FOR THE COMBUSTION OF NITROGEN-DOPED DROPLETS OF HEXANE INSIDE A REFRACTORY TUBE

The detailed kinetic model developed by Tang and Churchill for the prediction of the combustion of premixed-gaseous or evaporated-liquid hydrocarbon fuels in a refractory plug flow burner has been extended to account for nitrogen compounds in the fuel. In the modified model the nitrogen compounds are postulated to decompose thermally to HCN in the flame front prior to oxidation. The concentrations of NO₂ computed from this model for 0.795% wt. nitrogen in hexane are found to be in excellent agreement with measured values for fuel-lean mixtures doped with diethylamine, isobutylamine, pyridine and piperidine, and in fair agreement for fuel-rich mixtures up to an equivalence ratio of 1.3. The formation of NO₂ from fuel-nitrogen is found to be essentially complete after 1 ms in the postflame zone. All nitrogen-containing species except N₂ and NO are computed to be in negligible concentration for fuel-lean mixtures. Significant concentrations of HCN, NH₃ and HN₂ are predicted for the combustion of very fuel-rich mixtures. The computed concentrations of O, OH and CO are not changed significantly by the addition of fuel-nitrogen.     

The surface condition effect of Cu2O flower/grass-like nanoarchitectures grown on Cu foil and Cu film

Cu₂O flower/grass-like nanoarchitectures (FGLNAs) were fabricated directly on two category specimens of Cu foils and Cu film using thermal oxidation method. The FGLNAs are approximately 3.5 to 12 μm in size, and their petals are approximately 50 to 950 nm in width. The high compressive stress caused by a large oxide volume in the Cu₂O layer on the specimen surface played an important role in the growth of FGLNAs. The effects of surface conditions, such as the surface stresses, grain size, and surface roughness of Cu foil and Cu film specimens, on the FGLNA growth were discussed in detail.

PACS

81. Materials science; 81.07.-b Nanoscale materials and structures: fabrication and characterization; 81.16.Hc Catalytic methods     

Morphological evolution,growth mechanism,and magneto-transport properties of silver telluride one-dimensional nanostructures

Single crystalline one-dimensional (1D) nanostructures of silver telluride (Ag₂Te) with well-controlled shapes and sizes were synthesized via the hydrothermal reduction of sodium tellurite (Na₂TeO₃) in a mixed solution. The morphological evolution of various 1D nanostructures was mainly determined by properly controlling the nucleation and growth process of Ag₂Te in different reaction times. Based on the transmission electron microscopy and scanning electron microscopy studies, the formation mechanism for these 1D nanostructures was rationally interpreted. In addition, the current–voltage (I-V) characteristics as a function of magnetic field of the highly single crystal Ag₂Te nanowires were systematically measured. From the investigation of I-V characteristics, we have observed a rapid change of the current in low magnetic field, which can be used as the magnetic field sensor. The magneto-resistance behavior of the Ag₂Te nanowires with monoclinic structure was also investigated. Comparing to the bulk and thin film materials, we found that there is generally a larger change in R (T) as the sample size is reduced, which indicates that the size of the sample has a certain impact on magneto-transport properties. Simultaneously, some possible reasons resulting in the observed large positive magneto-resistance behavior are discussed.     

Paclitaxel-loaded nanoparticles of star-shaped cholic acid-core PLA-TPGS copolymer for breast cancer treatment

A system of novel nanoparticles of star-shaped cholic acid-core polylactide-d-α-tocopheryl polyethylene glycol 1000 succinate (CA-PLA-TPGS) block copolymer was developed for paclitaxel delivery for breast cancer treatment, which demonstrated superior in vitro and in vivo performance in comparison with paclitaxel-loaded poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles and linear PLA-TPGS nanoparticles. The paclitaxel- or couramin 6-loaded nanoparticles were fabricated by a modified nanoprecipitation method and then characterized in terms of size, surface charge, surface morphology, drug encapsulation efficiency, and in vitro drug release. The CA-PLA-TPGS nanoparticles were found to be spherical in shape with an average size of around 120 nm. The nanoparticles were found to be stable, showing no change in the particle size and surface charge during 90-day storage of the aqueous solution. The release profiles of the paclitaxel-loaded nanoparticles exhibited typically biphasic release patterns. The results also showed that the CA-PLA-TPGS nanoparticles have higher antitumor efficacy than the PLA-TPGS nanoparticles and PLGA nanoparticles in vitro and in vivo. In conclusion, such nanoparticles of star-shaped cholic acid-core PLA-TPGS block copolymer could be considered as a potentially promising and effective strategy for breast cancer treatment.