Thermal decomposition properties of guanidine nitrate and basic cupric nitrate

Characterized with a large gas production and low combustion temperature, the guanidine nitrate (GN) gas-generating agents are studied and applied widely. The determination factors of thermal decomposition properties of guanidine nitrate and basic cupric nitrate (GN/BCN) gas-generating agents for airbag application was investigated by the thermogravimetry–differential scanning calorimetry–mass spectrmetry–Fourier transform infrared spectroscopy (TG-DSC-MS-FTIR) and automatic calorimeter. Five different mass ratios were concerned. Our study showed that the onset reaction temperatures of GN/BCN mixtures were lower than that of individual GN and BCN. The thermal decomposition of GN/BCN mixtures could be divided into three stages, including the dissociation and escape of crystal water, solid (GN)-solid (BCN) phase reaction, and liquid (GN)-solid (BCN) phase reaction. When mass ratio of GN/BCN was 62.24/37.73, the largest value of the reaction heat was measured to 3152.7 J g^?1, with N₂ and H₂O as the major gases during thermal decomposition.     

Evaluating a four-directional benzene-centered aliphatic polyamine curing agent for epoxy resins

A four-directional benzene-centered aliphatic polyamine, MXBDP, with high functionality and low volatility, is used to cure epoxy resin (DGEBA). Herein we originally report the isothermal cure kinetics and dynamic mechanical properties of DGEBA/MXBDP. Differential scanning calorimetry confirms that MXDBP is more reactive than commercial linear metaxylenediamine and branched Jeffamine T-403 and the isothermal curing reaction is autocatalytic. The Kamal model is found to be able to well describe the curing rate up to the onset of diffusion control, and the excellent match over the whole conversion range is achieved using the extended Kamal model. Interestingly, the isoconversional kinetic analysis indicates that the effective reaction activation energy (E _α ) changes substantially with conversion, and ultimately decreases to a very small value (<10 kJ mol^?1) because of the diffusion-controlled reaction kinetics. Then, dynamic mechanical analysis reveals that DGEBA/MXBDP exhibits the higher α- and β-relaxation temperatures and the much higher crosslink density than DGEBA/metaxylenediamine. Our experiment results support that MXBDP has the high reactivity and improved thermal resistance in combination with the advantages of the high functionality, low volatility and decreased CO₂ absorption. Therefore, MXBDP may be especially suitable for room temperature-cure epoxy coatings and adhesives.     

Electrodeposited nanogold decorated graphene modified carbon ionic liquid electrode for the electrochemical myoglobin biosensor

In this paper, a carbon ionic liquid electrode (CILE) was fabricated using ionic liquid 1-hexylpyridinium hexafluorophosphate as modifier, which was further in situ electrodeposited with graphene (GR) and gold nanoparticles step by step to get an Au/GR nanocomposite modified CILE. Myoglobin (Mb) was further immobilized on the Au/GR/CILE surface with Nafion film to get the modified electrode denoted as Nafion/Mb/Au/GR/CILE. Cyclic voltammetric experiments indicated that a pair of well-defined quasi-reversible redox peaks appeared in pH 3.0 phosphate buffer solution with the formal potential (E ^0′) located at ?0.197 V (vs. saturated calomel electrode), which was the typical characteristics of Mb heme Fe(III)/Fe(II) redox couples. Thus, the direct electron transfer rate between Mb and the modified electrode was promoted due to the high conductivity and increased surface area of Au/GR nanocomposite present on electrode surface. Based on the cyclic voltammetric data, the electrochemical parameters of Mb on the modified electrode were calculated. The Mb-modified electrode showed excellent electrocatalytic activities towards the reduction of trichloroacetic acid and H₂O₂ with wider linear range and lower detection limit. Using GR and Au nanoparticles modified CILE, a new third-generation electrochemical Mb biosensor was constructed with good stability and reproducibility.     

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li₂FeSiO₄/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li₂FeSiO₄/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li₂FeSiO₄ nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li₂FeSiO₄/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g^?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li₂FeSiO₄/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.     

Phase Stability and Elastic Properties of Chromium Borides with Various Stoichiometries

Phase stability is important to the application of materials. By first‐principles calculations, we establish the phase stability of chromium borides with various stoichiometries. Moreover, the phases of CrB₃ and CrB₄ have been predicted by using a newly developed particle swarm optimization (PSO) algorithm. Formation enthalpy–pressure diagrams reveal that the MoB‐type structure is more energetically favorable than the TiI‐type structure for CrB. For CrB₂, the WB₂‐type structure is preferred at zero pressure. The predicted new phase of CrB₃ belongs to the hexagonal P‐6m2 space group and it transforms into an orthorhombic phase as the pressure exceeds 93 GPa. The predicted CrB₄ (space group: Pnnm) phase is more energetically favorable than the previously proposed Immm structure. The mechanical and thermodynamic stabilities of predicted CrB₃ and CrB₄ are verified by the calculated elastic constants and formation enthalpies. The full phonon dispersion calculations confirm the dynamic stability of WB₂‐type CrB₂ and predicted CrB₃. The large shear moduli, large Young’s moduli, low Poisson ratios, and low bulk and shear modulus ratios of CrB₄? PS_C and CrB₄? PS_D indicate that they are potential hard materials. Analyses of Debye temperature, electronic localization function, and electronic structure provide further understanding of the chemical and physical properties of these borides.     

Copper-and Silver-Mediated Cyanation of Aryl Iodides Using DDQ as Cyanide Source

A new copper and silver‐mediated cyanation of aryl iodides with DDQ as a cyanide source is achieved, providing nitriles with good yields. This new approach represents a safe method leading to aryl nitriles.     

Preparation of Polymer-Functionalized Iron Oxide Nanoparticles and Their Biomedical Properties

Superparamagnetic iron oxide nanoparticles with narrow size distributions were successfully prepared in large scale by a facile one‐pot synthetic method in the presence of hydrophilic polymers, such as polyethylene glycol diacid (HOOC‐PEG‐COOH) and poly(acrylic acid) (PAA). The as‐prepared products were investigated in detail by powder X‐ray diffraction (XRD), thermogravimetric analyses (TGA), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), and vibrating sample magnetometer (VSM). The interaction between polymers and iron oxide nanoparticles was investigated using Fourier transform infrared spectrometry (FT‐IR). The results show that polymers can be attached onto the surface of iron oxide nanoparticle by bridging coordination and monodentate fashion, respectively. The interaction affects iron oxide nanoparticle properties significantly, such as XRD diffraction intensity, hydrodynamic diameter, isoelectric point, and saturation magnetization. Furthermore, the results of in vitro experiments indicated that iron oxide‐PEG‐COOH nanoparticle is more cytotoxic than iron oxide‐PAA nanoparticle due to different coordinating modes.     

离子色谱法测定甲醇和噻吩中硫、氯含量

建立了测定工业用甲醇和噻吩中硫、氯含量的离子色谱检测方法。样品经(700±25)℃灼烧后,残留物用蒸馏水洗涤,利用离子色谱仪进行分析。甲醇和噻吩中硫、氯检测结果的相对标准偏差为1.04%~1.26%,加标回收率为99.2%~101.2%。该方法操作简单,精密度和准确度高,可用于大部分可燃性有机化合物中硫、氯含量的检测。