Oxidation Kinetics of an Amorphous Silicon Carbonitride Ceramic

The oxidation kinetics of amorphous silicon carbonitride (SiCN) was measured at 1350°C in ambient air. Two types of specimens were studied: one in the form of thin disks, the other as a powder. Both specimens contained open nanoscale porosity. The disk specimens exhibited weight gain that saturated exponentially with time, analogous to the oxidation behavior of reaction-bonded Si₃N₄. The saturation value of the weight gain increased linearly with specimen volume, suggesting the nanoscale pore surfaces oxidized uniformly throughout the specimen. This interpretation was confirmed by high-resolution electron microscopy and secondary ion mass spectroscopy. Experiments with the powders (having a particle size much larger than the scale of the nanopores) were also consistent with measurements of the disks. However, the powder specimens, having a high surface-to-volume ratio, continued to show measurable weight gain due to oxidation of the exterior surface. The wide range of values for the surface-to-volume ratio, which included all specimens, permitted a separation of the rate of oxidation of the free surface and the oxidation of the internal surfaces of the nanopores. Surface oxidation data were used to obtain the rate constant for parabolic growth of the oxidation scale. The values for the rate constant obtained for SiCN lay at the lower end of the spectrum of oxidation rates reported in the literature for several Si₃N₄ and SiC materials. Convergence in the behavior of SiCN and CVD-SiC is ascribed to the purity of both materials. Conversely, it is proposed that the high rates of oxidation of sintered polycrystalline silicon carbides and nitrides, as well as the high degree of variability of these rates, might be related to the impurities introduced by the sintering aids.     

On Structural,Optical, and Electrical Properties of Chromium Oxide Cr2O3 Thin Film for Applications

Protection of Metals and Physical Chemistry of Surfaces - Chromium oxide thin films were grown on Al2O3 substrates by ablating a pure Cr2O3 target using a KrF excimer laser. The energy density on...     

Highly luminescent film functionalized with CdTe quantum dots by layer‐by‐layer assembly

Robust and facile strategies are required to fabricate film with high luminescence for application in the fields of biomaterials. In this study, the luminescent electrospinning cellulose fibrous mats were decorated with CdTe quantum dots (QDs) and poly(diallyl dimethyl ammonium chloride) (PDDA) using layer by layer (LBL). The characterizations of the LBL films coated mats were executed by X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, fluorescent spectroscopy, X‐ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. The luminescent intensities were linearly increased with adding the amount of deposited bilayers. The green fabricated (QDs/PDDA)_n coated mat through physical interactions is a promising luminescent material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41893.     

A new method for evaluating sulfur dioxide tolerance of certain trees

The paper proposes a new method for evaluating the tolerance of trees to SO₂ pollution stress, and grouping plants as indicators and controllers by tolerance index values. The index is calculated by a new arithmetic formula. The developed model is useful in identifying tolerant and susceptible plants to SO₂.     

Aspects of varying crosslinker and catalyst concentrations on tear strength of silicone polymer networks: Comparison of tear strengths using samples of different geometries

Crosslinker and catalyst concentrations have been varied to prepare different hydroxyfunctional poly(dimethylsiloxane) (HOPDMS) polymer network compositions. The tear strengths of these silicone polymer networks have been measured using different geometries, as trouser, crescent, and Graves (angled) specimens. It has been observed that the results of tear strength of Graves and crescent‐shaped specimens do not show a constant ratio with the concentration of crosslinker used for curing of HOPDMS networks. Instead, it has been observed and reported for the first time that the tear strengths of Graves and crescent‐shaped samples show a crossover at about 1.2% crosslinker. The observation of this crossover pattern for different compositions of silicone networks show that it is difficult to compare the results of the tear test of the same polymer performed on samples of different geometries with one another. The crossover pattern of the tear energy results for the test specimens of two different geometries has been explained in the light of essential work facture theory based on the geometry of the testing sample, crosslinking, and testing that alters the distribution of force over the width of the specimen. It was shown that the change in composition of the HOPDMS networks changes the order of ranking of Graves and crescent tear tests. With varying catalyst concentration in the silicone network composition, the tear property differences between the Graves and crescent‐shaped specimens are not significant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43115.     

Improving properties of silicone rubber composites using macromolecular silane coupling agent (MMSCA)

Two types of vinyl silicone oil (VSO), allyl‐capped hyperbranched polycarbosilane (HBP), and triethoxysilane (TES) were employed to synthesize macromolecular silane coupling agent (MMSCA) by hydrosilylation. VSOs, HBP, and the hydrosilylated products were used as crosslinker, respectively, to improve weak mechanical properties of silicone rubber (SR). Structures of the crosslinkers were studied by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Crosslinking density test and scanning electron microscope (SEM) observation showed an increased interaction between silicone rubber and fumed silica by the use of MMSCA. Mechanical properties of the resulted composites using MMSCAs were increased to varying degrees compared with those possessing crosslinkers without ethoxy group. MMSCAs were effective for further property enhancements of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43415.     

Boron nitride based polyaniline nanocomposite: Preparation,property, and application

In this study, we report first time the electrical properties and photocatalytic activity of HCl doped polyaniline (Pani) and Pani/boron nitride (Pani/BN) nanocomposite prepared by in situ polymerization of aniline using potassium persulfate (K₂S₂O₈) in the presence of hexagonal boron nitride (h‐BN). The prepared Pani and Pani/BN nanocomposite were characterized by Fourier transform infrared, X‐ray diffraction, Thermogravimetric analysis, Scanning electron microscope, and Transmission electron microscope. The stability of the Pani/BN nanocomposite in comparison of Pani in terms of the DC electrical conductivity retention was investigated under isothermal and cyclic aging conditions. The Pani/BN nanocomposite in terms of DC electrical conductivity was observed to be comparatively more thermally stable than Pani. The degradation of Methylene blue (MB) and Rhodamine B (RhB) under UV‐light irradiation were 50 and 56.4%, respectively, over Pani and 65.7 and 71.6%, respectively, over Pani/BN. The results indicated that the extent of degradation of MB and RhB was greater over nanocomposite material than Pani, which may result due to high electron–hole pairs charge separation under UV light. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43989.     

Ultra-high strength Mg-9Gd-4Y-0.5Zr alloy with bi-modal structure processed by traditional extrusion

It is usual to observe that multi-scale structures can lead to combined strength and ductility both in aluminum alloys and steels, but related research has been seldom reported yet in magnesium alloys. In this study, applying traditional one step extrusion, we have successfully obtained a bimodal (Mg-9Gd-4Y-0.5Zr) alloy capable of ultra-high strength. The characterized sample reveal a bi-modal microstructure with two constitutions, i.e. stretched coarse-grain region with strong basal fiber texture and recrystallization fine-grain region. The bi-modal structured sample exhibit excellent mechanical properties with an ultimate strength 508 MPa and elongation 8% via 400 °C extrusion and subsequently 200 °C-60 h peak aging process. Ultra-high strength can be attributed to its strong extrusion texture in stretched coarse grains and dispersed nano-scale precipitates. This unique bimodal structure could be produced easily by one step extrusion, which is quite reliable and low costs in industrial applications of magnesium alloys with ultra-high strength as well as ideal ductility.     

Accelerated Design of Eutectic High Entropy Alloys by ICME Approach

Eutectic high entropy alloy with seven components is designed based on the integrated computational materials engineering (ICME) framework. The framework includes thermodynamic prediction using calculation of phase diagrams (CALPHAD), microstructure simulation using phase-field method, and experimental validation. The designed alloy shows the eutectic structure consisting of FCC and laves phase in the composition range from 8.25 to 10 at. pct Ta. The simulation and experimental results are co-related and a framework is proposed that can be used for high entropy alloy design subjected to various manufacturing processes.