Waterborne polysiloxane–urethane–urea for potential marine coatings

Waterborne polysiloxane–urethane–ureas (WBPSUU) were prepared through a prepolymer process using siloxane polyol, namely polydimethylsiloxane (PDMS) and polyether polyol, namely poly(tetramethyleneoxide glycol) (PTMG) as the soft segments. The goal of this study was to explore the potential use of polysiloxane–urethane–urea in marine coatings in order to boost the flexibility, adhesion, erosion, and foul-release property with respect to PDMS/PTMG ratio (PDMS wt%). The structural elucidation of the synthesized waterborne polyurethane and WBPSUU was carried out by FTIR, ¹H NMR, and ²⁹Si NMR spectroscopic techniques. The XPS and AFM analyses indicate that the polymer surface can be silicone enriched with the optimum PDMS content (15.76 wt%). The antifouling property of the coatings was investigated by the immersion test under a marine environment for 90 days. The fouled area was calculated for all the samples and the fouled area (%) decreased with increasing PDMS content. After 90 days the lowest fouled area (5%) was observed in the sample using WBPSUU4 (PDMS 15.76 wt%) among all of the samples.     

Cathodes for chlorate electrolysis with nanocrystalline Ti–Ru–Fe–O catalyst

Cathodes for chlorate electrolysis were prepared by mixing nanocrystalline Ti–Ru–Fe–O catalyst powder with small amounts of Teflon and subsequent hot pressing on a carbon–Teflon sublayer. Initially, the electrode materials were characterized by SEM, EDX, XRD and BET measurements. The behaviour of electrodes with catalyst loadings from 300 mg cm^–2 reduced to 10 mg cm^–2 was investigated in chlorate electrolyte with pH 6.5 and in part, for comparison, in 1 M sodium hydroxide solution at 70 C. Several methods have been used: cyclic voltammetry for the determination of double layer capacitance, Tafel plot analysis, cathodic potentiodynamic polarization and potentiostatic tests at i = –250 mA cm^–2. The as-milled catalyst powder electrodes showed a high activity for the HER in chlorate electrolyte particularly expressed in low overpotentials of about 580 mV at –250 mA cm^–2 for catalyst loadings down to 20 mg cm^–2 and high double layer capacitances in the freshly prepared state. These electrodes show increased activity at low polarization. The long-term stability during electrolysis was also analysed.     

Polyacryl–nanoclay composite for anticorrosion application

Polyacryl–nanoclay composites are new class of materials obtained by dispersing montmorillonite clay nanoplatelets (nanoclay) into the polymer matrix. In present work we investigate and confirmed that montmorillonite nanoclay significantly enhances barrier properties of acrylic composite. Two stage of dispersion process was used to prepare polyacry–nanoclay composites. Different percentages of montmorillonite clay nanolayers were added to polyacryl dispersion and applied on steel panel with 0% (w/w), 1% (w/w), 2% (w/w) and 4% (w/w) of nanoclay as composites. Performance of nanoclay intercalation in polyacryl composite was measured by X-ray diffraction (XRD) and the structure characteristics of samples were analyzed with transmission electron microscopy (TEM). The effectiveness of prepared nanocomposites was identified by the hardness measurements and mechanical properties. Further anticorrosion characteristics, especially barrier properties were indirectly detected by electrochemical impedance spectroscopy (EIS). This method was also used for the determination of montmorilonite nanoclay optimal concentration in acrylic composite where optimal barrier properties were achieved.     

Molded Glass–Ceramics for Infrared Applications

In this paper, the feasibility to make molded glass–ceramics transparent in the second and third atmospheric window has been investigated. The thermodynamical and viscosity properties of the base glass have been measured confirming the possibility of generating crystals during molding at different temperatures. ⁷¹Ga nuclear magnetic resonance confirms that gallium plays the role of nucleating agent of gallium in this glass. Examination of X-rays diffraction patterns and optical properties indicates that the generation of nanocrystals of GeGa₄Se₈ allows the glass–ceramics to keep a wide transparency in the infrared range from 2 to 15 μm. The crystallization of large GeSe₂ crystals of at higher temperature induces scattering and a reduced transparency window. The mechanical and structural properties of the as-prepared glass ceramics show an increase of toughness from 0.188 to 0.387 MPa m^1/2 and elastic modulus from 22.7 to 26.55 GPa while the number and size of crystals increase. As a result, the preparation of molded IR glass–ceramics with high resistance to thermal and mechanical shocks has been clearly demonstrated.     

Microstructure–Property Relationships for Low-Voltage Varistors

The low-voltage varistors with various layer thickness are prepared by laminating thin ZnO-based ceramic layers and AgPd electrodes together. The breakdown voltage dose not exhibit linear relationship with layer thickness. It is due to that the presence of the AgPd electrodes enhances the growth of ZnO grains. As some ZnO grains are large enough to touch the upper and lower electrodes, the breakdown voltage of the varistor is only 3.7 V. The nonlinear coefficient of the low-voltage varistor is 33. Such nonlinear current–voltage behavior is mainly contributed by the interface between the AgPd electrode and ZnO grains.     

A novel polyborosilazane for high-temperature amorphous Si–B–N–C ceramic fibres

Polyborosilazane synthesised from BCl₃, HMeSiCl₂, and Me₃SiNHSiMe₃ is easy to cross-link for dehydrogenation of Si–H and N–H, which limits its practical applications for Si–B–N–C fibres on an industrial scale. Therefore, in this context, MeSiCl₃ was used instead of HMeSiCl₂ to synthesise a novel polyborosilazane with limited cross-linking density to fabricate Si–B–N–C fibres. The polyborosilazane synthesised from BCl₃, MeSiCl₃, and Me₃SiNHSiMe₃ exhibits good melt-processability and 1 km long polyborosilazane fibre can be obtained by melt spinning. Prior to pyrolysis, chemical curing with vapour HSiCl₃ at 80 °C was utilised to make the λ green fibres infusible. The as-cured fibres were subsequently pyrolyzed at 1200 °C in nitrogen atmospheres to provide Si–B–N–C ceramic fibres with ca. 1.5 GPa in tensile strength, ca. 160 GPa in Young's modulus, ca. 12 μm in diameter and keeping amorphous up to 1700 °C, which makes them to be promising reinforcements in ceramic matrix composites for high temperature applications.     

Efficient La–Ba–MgO Supported Ru Catalysts for Ammonia Synthesis

Abstract  

Novel Ru-based catalysts were prepared by impregnating 2 wt% Ru₃(CO)₁₂ into rare earth (La, Sm, Ce) and barium doped nano-magnesia (RE–Ba–MgO) supports, which were originally prepared by chemical co-precipitation with ultrasonic treatment. The Ru/RE–Ba–MgO catalyst exhibits higher activity, more than three times of that of conventional Ba–Ru/MgO base on water impregnation. Characterization of this catalyst by various techniques reveals that the chemical and textural properties of nano Ba–MgO supports and formation state of barium in support are key factors responsible for the elevated activity of this catalyst.     

Comparison of Peel Tests for Metal–Polymer Laminates for Aerospace Applications

Standard peel tests for aerospace laminates based on metal–polymer systems, namely floating-roller and climbing-drum peel methods, have been accommodated in a unified theory of peeling. This theory also accommodates more basic peel tests such as T-peel and fixed-arm peel and also newer methods such as mandrel peel. These five methods have been applied to two aerospace laminate systems to critically examine their use in the determination of adhesive strength. The theory has been used to unify the outputs from the tests in terms of adhesive fracture toughness. In this way, the comparative merits of the methods can be commented on.

The validity of the standard methods has been put in doubt because of the absence of a correction for plastic bending energy and also because of the poor conformance of the peel arm to the roller system used in these methods. The unified theory and some measurements of peel-arm curvature help but not completely overcome some of these difficulties.

A further complication that arises in peel is a change in the plane of fracture. This reflects a transition from cohesive fracture in the adhesive to an adhesive fracture at the interfaces among adhesive, primer, and substrate. It is likely that such plane-of-fracture phenomena are intrinsic to evaluation of the laminate and that contemplation of cohesive fracture toughness for the adhesive cannot accommodate such events.     

BaTiO3–Epoxy Composites for Electronic Applications

A brief review related with dielectric properties of BaTiO₃/epoxy composites is presented. The composites were obtained using the dipping technique. To facilitate the mixing and modify the filler surface, a solvent and a surface coupling agent were used. Intermediate and low concentrations of solvent and silane improved microstructure and dielectric properties of the composite material, whereas higher concentrations led to composites of poor quality. Finally, a model using finite elements was used, in order to predict the composite permittivity in relation to the percentage of filler. Model results were compared with the effective medium theory and experimental results.     

Structure–property relationships for partially aliphatic polyimides

The structure–property relationship was studied for partially aliphatic polyimides containing alicyclic dianhydride and aromatic diamine unit. Rel-[1S,5R,6R]-3-oxabicyclo[3,2,1]octane-2,4-dione-6-spiro-3′-(tetrahydrofuran-2′,5′-dione) (DAn) was used as an unsymmetrical spiro dianhydride, and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA) and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BOCA) were used as symmetrical non-spiro dianhydrides. The dianhydrides were polymerized with two aromatic diamines, 4,4′-oxydianiline (ODA) and 4,4′-(hexafluoroisopropylidene)dianiline (FDA), using a conventional two-step chemical imidization method. Structures of the PAl-PIs prepared were confirmed by ¹H-NMR and FT-IR spectroscopy. Solubility of the polyimides was tested in various organic solvents. Thermal properties of the PAl-PIs were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV-visible spectroscopy was performed to evaluate the optical transparency of the polyimides. The effect of monomer structure on the properties was studied. The PAl-PIs prepared from DAn showed improved solubility, thermal properties, and transparency when compared with PAl-PIs derived from CPDA and BOCA. It is considered that the rigid, unsymmetrical spiro structure of DAn leads to rigidity, bulkiness, irregularity, and non-linearity of the polyimide chains, resulting in the enhanced properties of DAn polyimides. The molecular arrangement in the polyimides has also been studied by wide-angle X-ray diffraction (WAXD) and was correlated with the properties.     

Ignition Delay Time for Hydrogen–Silane–Air Mixtures at Low Temperatures

A modified physicomathematical model of ignition of hydrogen–silane–air mixtures is applied to calculate the ignition delay time for these mixtures at low initial temperatures (300–900 K) and pressures (0.4–1 atm) of the mixture. It is shown that the diagram of the ignition delay time as a function of temperature contains a region of the so-called negative temperature coefficient. The influence of the pressure in the mixture and of the silane fraction on the length of this region is studied. It is found that an increase in both factors (silane concentration and pressure in the mixture) leads to an increase in the length of the negative temperature coefficient region.     

Co/SiO2 Sol–Gel Catalysts for Fischer–Tropsch Synthesis

Six catalysts with a different cobalt content were prepared following the sol–gel method. The samples were tested by the Fischer–Tropsch synthesis performed both at low and high temperature and pressure. All the catalytic performances are well correlated with the characterization results which highlighted the good metal distribution and the presence of a large amount of metallic cobalt (but not the whole) on the surface of both 10 and 30% Co catalysts. As a result, high CO conversions were observed with a particular sensitivity to the reaction pressure and also the limitation of the produced hydrocarbons fraction to C₆ or C₉ at low or high pressure, respectively.     

Shape- and Composition-Controlled Pt–Fe–Co Nanoparticles for Electrocatalytic Methanol Oxidation

We report the preparation of several shape and composition-controlled platinum-based nanoparticles: Pt–Fe nanocubes, Pt–Fe–Co nanocubes, Pt–Fe–Co branched nanocubes, Pt–Fe–Co nanoparticles with low cobalt content, and Pt–Fe–Co nanoparticles with high cobalt content. Pt–Fe–Co branched nanocubes, in particular, showed the best activity and durability for electrocatalytic methanol oxidation.     

Reactive Phosphazene–Siloxane Polymers for Materials Chemistry

Catenapoly(dimethyl-⁵-phosphazene-co-methylphenyl-⁵-phosphazene) functionalized by electrophilic substitution of a methyl hydrogen atom with reactive Si(OMe)₃ groups grafts easily to glass or cross-links to free-standing films by hydrolysis and further condensation of the silicon functional group. The manufactured films exhibit a high gas permeability.