Carbon–Nitrogen Pyrolyzates: Attempted Preparation of Carbon Nitride

Precursors for the preparation of carbon nitride were selected from a number of relatively high nitrogen content organic materials. The precursors were pyrolyzed in a closed system at 700°C under 225 MPa. The resulting residues showed little nitrogen loss, but were amorphous with relatively low densities. Raman spectroscopy and ¹³C NMR indicate the presence of trigonal carbon.     

自组装膜材料偶氮苯硫醇衍生物的合成

运用一种方便有效的方法合成一新型自组装膜材料,其末端为巯基的偶氮苯衍生物,以对氨基苯磺酸为起始原料,经重氮化反应苯酚偶合反应,得中间产物NaO3SAzoOH。再经Williamson醚化反应,使其与1,3-二氯丙烷在甲醇中反应,得到反应产物NaO3SAzo(CH2)3Cl。最后,与硫脲在乙醇中反应,碱性条件下水解,以较高的收率获得偶氮苯衍生物NaO3SAzo(CH2)3SH。此种新化合物的结构可经红外光谱鉴定。     

Review: Polymers,Surface-Modified Polymers,and Self Assembled Monolayers as Surface-Modifying Agents for Biomaterials

Biocompatibility and nontoxicity of biomaterials are of utmost importance when foreign bodies come in contact with a biological system. Irrespective of the nature of material, nonspecific protein adsorption is the first process observed at surface–biological system interfaces followed by cellular processes. Nonspecific protein adsorption leads to deleterious cellular processes such as biofouling and finally immunological host response. Hence, surface modification becomes mandatory for preventing undesirable implant failure and inflammatory responses. Various polymers, surface-modified polymers and surfaces withself assembled monolayers, have been tested to tune surface properties for a given application. Surface functional groups and surface structures of polymers and copolymers regulate surface hydrophobicity, nonspecific protein adsorption, biomaterial stability, and antifouling property, etc. Self assembled monolayers are formed by covalent linkage with more controlled surface structure and smoothness. Mixed and hybrid self assembled monolayers containing both hydrophilic and hydrophobic groups result in moderate wettability. Further, we have discussed different methods of surface modification using polymers, modified polymers, and self assembled monolayers for improved surface biocompatibility and nonfouling properties.     

Electrochemical impedance spectroscopy of carboxylic-acid terminal alkanethiol self assembled monolayers on GaAs substrates

Adsorbate-induced charge depolarization can influence the organization of self assembled monolayers (SAMs) on semiconductor surfaces, especially as a function of the SAM functional group, SAM length and substrate dopant level and type. Based on systematic differences in the frequency response of the electrochemical impedance and phase data for carboxylic acid (COOH) terminal alkanethiol monolayers of varying alkane chain length assembled on GaAs substrates of different dopant level and type, we assessed the relative monolayer quality through fits to an appropriate equivalent circuit analog to compare the proportion of defects and SAM-induced semiconductor depolarization. At the open circuit potential in the NaCl-phosphate buffer, while SAMs on p+ GaAs were of marginally better quality than those on p GaAs, SAMs on n+ GaAs exhibited a far superior quality than those formed on n GaAs. COOH-terminal SAMs of longer chain lengths formed higher quality monolayers at all the substrate doping levels. COOH-terminal SAM modified n and n+ GaAs surfaces were passivated and stable over a wider voltage range than SAM modified p and p+ GaAs surfaces, from cyclic voltammetry. The poorer quality of COOH-terminal SAMs formed on GaAs substrates at the lower doping levels is attributed to the disorder as a result of the enhanced degree of charge depolarization at these surfaces, as substantiated by systematic variations in the space charge capacitance upon SAM modification that suggest a negative surface dipole.     

The effect of interfacial chemistry on coating adhesion and performance: A mechanistic study using aminobutylphosphonic acid

Failure of adhesion of organic coating (paints) to steel and other metallic substrates is one of the key mechanisms for local coating failure and for consequent restriction of coating lifetime. This study thus focuses on modification to the chemistry of the metal interface in order to promote enhanced (dry and wet) coating adhesion. The work uses an appropriate bi-functional amino alkyl phosphonate to provide the desired interfacial properties. The study uses X-ray photoelectron spectroscopy and water contact angle measurement to examine changes in the interfacial surface chemistry and electrochemical impedance spectroscopy and cathodic disbonding to determine improvements to the anti-corrosion performance. Choosing 4-amino-butyl-phosphonic acid as the surface modifier a significant influence on its efficiency as an adhesion promoter was observed as a function of pH. Thus, when the amino group was protonated at a pH of 5.3, the molecule demonstrated attachment to carbon steel at both ends with no significant improvement in performance. However at pH 8 the molecule demonstrated greatly improved surface packing density with the amino group outwards from the surface in the preferred orientation. In this condition, an epoxy coating demonstrated substantial resistance to interfacial hydrolysis with overall improved adhesion and reduced cathodic disbondment rate.     

自组装单层膜技术及其在制备功能薄膜领域中的应用

自组装单层膜技术应用于薄膜制备领域越来越受到研究人员的关注。详细地介绍了自组装单层膜技术的发展历程,综述以有机硅烷类自组装单层膜制备功能陶瓷薄膜的反应机理,论述自组装单层膜在制备功能陶瓷薄膜领域中的应用,并对自组装单层膜技术及其应用做了一定的展望。     

Preparation and Properties of Oxynitride Glasses Made from Potassium Metaphosphate

Potassium phosphate oxynitride (KPON) glasses were made by heating crystalline KPO₃ at 702^° to 775^°C in dry ammonia. The softening temperature, thermal expansion coefficient, refractive index, and dissolution rate in water were measured as a function of nitrogen content and compared with the properties of oxynitride glasses made from LiPO₃ and NaPO₃.     

Elastic Moduli and Hardness of Cubic Silicon Nitride

The bulk modulus B ₀= 290(5) GPa and its first pressure derivative B '₀= 4.9(6) were obtained for c -Si₃N₄ from volume versus pressure dependence. Measurements were performed under quasi-hydrostatic conditions in a diamond anvil cell to 53 GPa using synchrotron radiation and energy dispersive X-ray powder diffraction. This combined with nanoindentation measurements determined the shear modulus G ₀ of c -Si₃N₄ to be 148(16) GPa. The Vickers microhardness H _V(0.5) for dense, oxygen-free c -Si₃N₄ was estimated to be between 30 and 43 GPa. Both the elastic moduli and microhardness of c -Si₃N₄ exceed those of the hexagonal counterparts, α- and β-phases.     

氮化硅陶瓷的制备及性能研究进展

氮化硅陶瓷是一种具有广阔发展前景的高温、高强度结构陶瓷,它具有强度高、抗热震稳定性好、疲劳韧性高、室温抗弯强度高、耐磨、抗氧化、耐腐蚀性能好等高性能,已被广泛应用于各行业。本文介绍了氮化硅陶瓷的基本性质．综述了氮化硅陶瓷的制备工艺和提高其高温性能的方法以及增韧的途径,并展望了氮化硅陶瓷的发展前景。     

Mn-P共掺杂氮化碳的制备及其光催化性能研究

采用四水氯化锰、磷酸氢二铵和三聚氰胺为原料制备了Mn-P共掺杂的石墨相氮化碳(g-C3 N4).使用X射线衍射光谱(XRD)、扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、光致荧光光谱(PL)、紫外-可见漫反射光谱(UV-Vis DRS)、电化学阻抗谱(EIS)、瞬态光电流响应等分析测试手段对制备的催化剂...     

原位聚合法制备PET/纳米氮化钛改性材料及其性能

通过原位聚合法制备纳米氮化钛改性PET材料.利用差式扫描量热仪(DSC)研究纳米氮化钛改性PET材料结晶行为和在不同降温速率下的非等温结晶动力学,用Jeziorny方程对非等温结晶过程进行分析;同时利用热重分析仪(TGA)和万能试验机等研究改性材料的热性能和力学性能.结果表明:纳米氮化钛粒子的加入,起到了异相成核作用,改变了PET的成核机理,提高了PET的结晶度和结晶速率;改善了PET材料的热稳定性和力学性能.     

Theoretical Prediction of the Structure and Properties of Cubic Spinel Nitrides

The structure and properties of cubic spinel nitrides were investigated based on first-principles theoretical calculations. The lattice constants, bulk moduli, band structures, electronic bonding, and lattice stability of thirty-nine single and double nitrides were studied. The single spinel nitrides of the form c -A₃N₄ (where A is a Group IVA element), except c -Hf₃N₄, are all semiconductors with band gaps ranging from an indirect gap of 0.07 eV in c -Ti₃N₄ to a direct gap of 3.45 eV in c -Si₃N₄. For double nitrides of the form c -AB₂N₄ (where A and B are Group IVA (Ti, Zr, Hf) or IVB (C, Si, Ge, Sn) elements), both metallic and insulating band structures are possible. The stability of the double spinel nitrides, relative to single nitrides, is dependent on the optimal cation radii and polyhedral volumes at the tetrahedral A sites and the octahedral B sites. Of the thirty-two double nitrides, only nine are predicted to be energetically favorable. Among the potentially stable phases, the most interesting ones are c -CSi₂N₄ (which has an exceptionally strong covalent bonding and large bulk modulus), c -SiGe₂N₄ (which has an energetically favorable direct band gap of 1.85 eV), and c -SiTi₂N₄ (which is metallic).     

Grain-Boundary-Phase Crystallization and Strength of Silicon Nitride Sintered with a YSlAlON Glass

Densifying silicon nitride with a YSiAlON glass additive produced 99% dense materials by pressureless sintering. Subsequent heat-treating led to nearly complete crystallization of the amorphous intergranular phase. Transmission electron microscopy revealed that for heat treatments at 1350°C, only β-Y₂Si₂O₇ was crystallized at the grain boundaries. At a higher temperature of 1450°C, primarily YSiO₂N and Y₄Si₂O₇N₂ in addition to small amounts of Y₂SiO₅ were present. Al existed only in high concentrations in residual amorphous phases, and in solid solution with Si₃N₄ and some crystalline grain-boundary phases. In four-point flexure tests materials retained up to 73% of their strengths, with strengths of up to 426 MPa, at 1300°C. High-strength retention was due to nearly complete crystallization of the intergranular phase, as well as to the high refractoriness of residual amorphous phases.     

Patterned self-assembled monolayers: efficient, chemically defined tools for cell biology

Self-assembled monolayers (SAMs) of alkanethiolates on gold can be used to carefully probe immobilized biomolecule interactions with cell-surface receptors. However, due to a lack of experimental throughput associated with labor-intensive production, specialized fabrication apparatus, and other practical challenges, alkanethiolate SAMs have not had widespread use by biological researchers. In this Minireview, we investigate a range of techniques that could enhance the throughput of SAM-based approaches by patterning substrates with arrays of different conditions. Here we highlight microfluidic, photochemical, localized removal, and backfilling techniques to locally pattern SAM substrates with biomolecules and also describe how these approaches have been applied in SAM-based screening systems. Furthermore we provide perspectives on several crucial barriers that need to be overcome to enable widespread use of SAM chemistry in biological applications.     

Hydrotreating of heavy vacuum gas oil (HVGO) on molybdenum and tungsten nitrides catalytic phases

A series of supported and unsupported Mo₂N and W₂N phases were synthesized by means of the treatment under ammonia atmosphere at 700°C of Mo and W oxides. The X-ray diffraction and electron microscopy techniques verified the formation of the Mo₂N and W₂N ceramic phases, while the N₂ adsorption (BET) was used to determine the surface areas, between 46–133 m²/g for Mo₂N (unsupported) and 81–101 m²/g for W₂N (unsupported). The supported phases had surface areas between 109–113 and 109–122 m²/g, for Mo₂N/Al₂O₃ and W₂N/Al₂O₃, respectively. The catalytic hydrotreating of a heavy vacuum gas oil (HVGO) derived from Maya crude (i.e. 2.21 wt.% S, 0.184 wt.% N₂) was performed on both, supported and unsupported Mo nitrides and W nitrides, which promoted the HDN reaction preferentially, up to 26.6% on Mo₂N/Al₂O₃ and up to 22.3% on W₂N/Al₂O₃, against 3.26% on the reference catalyst, i.e. CoMo/Al₂O₃ at 350°C and 80 kg/cm². Also, the rates for HDN increased with the crystallite size in the unsupported W₂N series. Also, the pore volume and mean pore diameters of the Mo₂N/Al₂O₃ and W₂N/Al₂O₃ series improve substantially with respect to the pure ceramic phases.     

Variation of Width and Composition of Grain-Boundary Film in a High-Purity Silicon Nitride with Minimal Silica

Contrary to the widely accepted observation that grain-boundary amorphous films for a given Si₃N₄ composition have common (equilibrium) widths and compositions, a significant variation for both parameters from film to film was observed in an undoped high-purity Si₃N₄ prepared using a hot isostatic pressing method. This material previously has been reported to have an equilibrium film width of 0.6 nm, as measured using a high-resolution electron microscopy (HREM) method; this value is significantly different from that which is typical for other high-purity Si₃N₄ ceramics (1.0 nm). A total of four boundaries were analyzed, using spatially resolved electron energy-loss spectroscopy methods, which can give the chemical width and composition for the film. Widths of these grain-boundary films were substantially different from each other; only the thinnest matches the previous HREM observations. The nitrogen content in the film decreased concurrently as the film thickened. This material had many cavities and complicated configurations at triple pockets, because of the very low total-SiO₂ content (0.55 vol%). They created locally different equilibrium conditions for grain-boundary films, in comparison with other fully densified Si₃N₄, causing such strong variation in both film structure and chemistry. This observation reveals the importance of triple pockets in equilibrium film structures, providing new insight in evaluating the absorption and wetting models. The thinnest film may correspond to the amorphous structure that is required to bind two randomly oriented Si₃N₄ grains under greater local stress.     

Preparation and Electrocatalytic Application of Composites Containing Gold Nanoparticles Protected with Rhodium-Substituted Polyoxometalates

Substitution of a metal center of phosphomolybdate, PMo₁₂O₄₀³⁻ (PMo₁₂), or its tungsten analogue with dirhodium(II) and subsequent stabilization of gold nanoparticles, AuNPs, with Rh₂PMo₁₁ are demonstrated. The AuNP-Rh₂PMo₁₁ mediates oxidations but adsorbs too weakly for direct modification of electrode materials. Stability in quiescent solution was achieved by modifying glassy carbon (GC) with 3-aminopropyltriethoxysilane (APTES) and then electrostatically assembling AuNP-Rh₂PMo₁₁. At GC|APTES|AuNP-Rh₂PMo₁₁, cyclic voltammetry showed the expected set of three reversible peak-pairs for PMo₁₁ in the range −0.2 to 0.6 vs. (Ag/AgCl)/V and the reversible Rh^II,III couple at 1.0 vs. (Ag/AgCl)/V. The presence of AuNPs increased the current for the reduction of bromate by a factor of 2.5 relative to that at GC|Rh₂PMo₁₁, and the electrocatalytic oxidation of methionine displayed characteristics of synergism between the AuNP and Rh^II. To stabilize AuNP-Rh₂PMo₁₁ on a surface in a flow system, GC was modified by electrochemically assisted deposition of a sol–gel with templated 10-nm pores prior to immobilizing the catalyst in the pores. The resulting electrode permitted determination of bromate by flow-injection amperometry with a detection limit of 4.0 × 10⁻⁸ mol dm⁻³.     

Thermodynamic and kinetic aspects of the electron transfer reaction of bovine cytochrome c immobilized on 4-mercaptopyridine and 11-mercapto-1-undecanoic acid films

Bovine cytochrome c (cyt c) was adsorbed on a polycrystalline gold electrode coated with 4-mercaptopyridine and 11-mercapto-1-undecanoic acid self-assembled monolayers (SAMs) and the thermodynamics and kinetics of the heterogeneous protein-electrode electron transfer (ET) reaction were determined by cyclic voltammetry. The E°′ values for the immobilized protein were found to be lower than those for the corresponding diffusing species. The thermodynamic parameters for protein reduction ( and ) indicate that the stabilization of the ferric state due to protein–SAM interaction is enthalpic in origin. The kinetic data suggest that a tunneling mechanism is involved in the ET reaction: the distance between the redox center of the protein and the electrode surface can be efficiently evaluated using the Marcus equation.     

Large-Scale Fabrication of Boron Nitride Nanotubes via a Facile Chemical Vapor Reaction Route and Their Cathodoluminescence Properties

Cylinder- and bamboo-shaped boron nitride nanotubes (BNNTs) have been synthesized in large scale via a facile chemical vapor reaction route using ammonia borane as a precursor. The structure and chemical composition of the as-synthesized BNNTs are extensively characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and selected-area electron diffraction. The cylinder-shaped BNNTs have an average diameter of about 100 nm and length of hundreds of microns, while the bamboo-shaped BNNTs are 100–500 nm in diameter with length up to tens of microns. The formation mechanism of the BNNTs has been explored on the basis of our experimental observations and a growth model has been proposed accordingly. Ultraviolet–visible and cathodoluminescence spectroscopic analyses are performed on the BNNTs. Strong ultraviolet emissions are detected on both morphologies of BNNTs. The band gap of the BNNTs are around 5.82 eV and nearly unaffected by tube morphology. There exist two intermediate bands in the band gap of BNNTs, which could be distinguishably assigned to structural defects and chemical impurities.     

Nanocrystalline Aluminum Nitride: II, Sintering and Properties

Nanocrystalline aluminum nitride powders obtained from gas condensation and in situ nitridation in a forced-flow reactor have been sintered successfully without pressure or additives. The resulting densified pellets showed good thermal conductivity and low oxygen content. A comparison of the improvement in densification with micrometer-size and nanocrystalline yttria additives was undertaken and it was found that the nanocrystalline yttria decreased the sintering temperature significantly. Besides spherical nanoparticles, needle-shaped nanocrystalline aluminum nitride particles that resulted in highly textured compacts when hot pressed could also be produced.