Lithium Perchlorate‐Catalyzed Boc Protection of Amines and Amine Derivatives

A new mild and chemoselective method for mono‐N‐protection of amines and amine derivatives as tert‐butoxycarbonyl derivatives is reported. The reaction proceeds with lithium perchlorate (20 mol %) and pyrocarbonates, and shows general applicability. The catalytic action of LiClO₄ is specific for the activation of Boc₂O, thus acid‐sensitive functionalities of the starting materials remain unchanged in the protection process. This procedure works well for sterically hindered primary amine as well as electron‐deficient primary arylamines, primary and secondary amino alcohols, α‐amino acid esters, hydroxylamines, hydrazines and sulfonamides.     

The comparison between the effects of solvent casting and melt intercalation mixing processes on different characteristics of polylactide‐nanographite platelets composites

This study investigates the influence of enhanced dispersion of nanographite platelets (NGP) fillers through solvent casting mixing process on rheological, electrical and thermal properties of polylactide (PLA)/NGP composites. PLA/NGP composites were fabricated at 1 to 5 wt% filler contents by means of three processing techniques: (i) dry mixing and melt intercalation; (ii) solvent casting using dichloromethane organic solvent; and (iii) combination of solvent casting and melt intercalation techniques. The extent of dispersion of nanofillers within polymer matrix was evaluated through X‐ray diffraction and transmission electron microscopy analysis of the composites. Morphological studies of the samples revealed that the maximum extent of dispersion of NGP fillers within PLA matrix was achieved when the combination of solvent casting and melt intercalation processes occurred. Rheological analyses of the samples were indicative of deterioration in the composites produced through solvent casting mixing process. Despite of initial reduction in electrical resistivity of the composites after the addition of 1 wt% of NGP fillers, further addition of nanofillers did not exhibit a considerable enhancement in their electrical conductivity of the composites. Thermogravimetric analysis of the composites was demonstrative of enhancing impact of nanofiller loading, along with detrimental effect of solvent casting on the thermal stability of the PLA matrix. POLYM. ENG. SCI., 55:1560–1570, 2015. © 2014 Society of Plastics Engineers     

The effect of agarose content on the morphology,phase evolution,and magnetic properties of CoFe2O4 nanoparticles prepared by sol‐gel autocombustion method

Hard‐magnetic CoFe₂O₄ nanoparticles were produced with the sol‐gel autocombustion route using agarose and citric acid as a neutral organic gel and combustion agent. For this purpose, the obtained gel is annealed at 800°C for 3 hours and then the spinel structure of the samples was confirmed by X‐ray diffraction (XRD). In addition, the existence of metal‐oxygen complexes in the gel and nanoparticles was investigated by Fourier transformation infrared (FTIR) spectra. Furthermore, FESEM images showed that semispherical and rod‐like particles were obtained by variation in agarose contents. For the rod‐like sample with 2.5 g agarose, the saturation magnetization and coercivity were measured equal to 71.7 emu/g and 10076.84 Oe, respectively.     

Effect of TGO thickness on the thermal barrier coatings life under thermal shock and thermal cycle loading

Effect of thermally grown oxide (TGO) thickness on thermal shock resistance of thermal barrier coatings (TBCs) and also their behavior under a cyclic loading (including aging at maximum temperature) was evaluated experimentally. In order to form different thicknesses of TGO, coated samples experience isothermal loading at 1070?°C for various periods of times. Heat-treated samples were heated to 1000?°C and cooled down rapidly in water from the substrate side using a mechanical fixture. The life of samples was investigated as a function of TGO thickness. Furthermore, by performing an experiment the simultaneous effect of the TGO growth and thermal expansion mismatch– on the failure of thermal barrier coatings was evaluated. The results demonstrated that the presence of TGO with a thickness of 2–3?µm has a positive effect on the resistance against thermal shock.     

Ionic interdiffusion as interaction mechanism between Al and Si3N4

Al-Si₃N₄ couples were heat-treated at 850-1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre-coefficient of 5 × 10⁻⁹ m²/s, indicating that the interaction is diffusion-dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al-Si transfer through the solid solution (Si_3-xAl_xN_4-y) at the interface of Al alloy and β-Si₃N₄ grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al_1-xSi_xN_1+y (viz., AlN). Next, the Al_1-xSi_xN_1+y grains detach from the β-Si₃N₄ grains and subsequently new Al-Si₃N₄ interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics.     

Mullite‐glass and mullite‐mullite interfaces: Analysis by molecular dynamics (MD) simulation and high‐resolution TEM

The properties of mullite‐glass and mullite‐mullite interfaces have been investigated at 1800 K by molecular dynamics (MD) simulation and high‐resolution TEM. The simulation showed that mullite‐glass interfaces typically have much lower interfacial energies than mullite‐mullite interfaces, which results from the structural flexibility of the glass and associated accommodation of interfacial mismatch. The (110)‐glass interface has the lowest energy of all interfaces studied, which is consistent with the observed dominance of this interface in experimental mullite‐glass samples examined by TEM. The simulation shows that the interfacial energies of the (100)‐glass and (010)‐glass interfaces are higher than that those of the (001)‐glass interface, so [100] and [010] would be expected to be the dominant growth directions. However, the growth of mullite in glass occurs predominantly in the [001] direction. This apparent discrepancy can be explained by the fact that growth in the [100] and [010] directions is limited by the slow growth of (110) plane (i.e., [110] direction), which facilitates [001] growth, which is confirmed by the TEM data.     

Designing dual-mode luminescence in Er3+ doped Y2WO6 microparticles for anticounterfeiting and temperature measurement

In recent years, rare earth ions doped optical materials have been extensively utilized in anticounterfeiting, temperature measurement, and other fields. However, it is difficult for single-mode photoluminescence to meet the increasingly complex anticounterfeiting needs in practice. In this article, Yb³⁺/Er³⁺ codoped Y₂WO₆ multifunctional microparticles have been designed and prepared, which can emit multimode luminescence and are used for anticounterfeiting and temperature measurement. Under excitation at 254, 365, and 980 nm, Y₂WO₆:Yb³⁺/Er³⁺ microparticles can emit blue, green, and yellow-green luminescence, respectively. The multicolor emission is helpful to improve the security of anticounterfeiting in multimode. In addition, the upconversion, downconversion luminescence, and downconversion lifetime attenuation of this material can be used for fast responsive and noncontact temperature measurement. Among the three temperature measurement methods, the material has the highest sensitivity under the downconversion temperature measurement method, which is 1.25 × 10^–2 K^–1 (at 303 K). The results suggest that the Y₂WO₆:Yb³⁺/Er³⁺ microparticles have excellent applications in the domain of multimode anticounterfeiting and temperature measurement.     

Synthesis of mesoporous nanocrystalline MgAl2O4 spinel via surfactant assisted precipitation route

In this research, mesoporous nanocrystalline MgAl₂O₄ spinel powders were synthesized with a facile synthesis method by co-precipitation route using CTAB as surfactant. The prepared samples were characterized by X-ray diffraction, N₂ adsorption, thermal gravimetric and differential thermal analyses, Fourier transform infrared spectroscopy and transmission electron microscope. The effects of surfactant to metal molar ratio on the structural properties of the samples were investigated. The obtained results showed that the sample prepared without addition of surfactant presented a lower specific surface area and bigger crystallite size compared with those obtained for the samples prepared by CTAB/metal molar ratio of 0.3. The results showed that the sample prepared by CTAB/metal molar ratio of 0.3 has the highest specific surface area and the smallest crystallite size. Moreover, the CTAB/metal molar ratio higher than 0.3 led to a decrease in the specific surface area, due to destruction of the pore walls.