Synthesis at several length scales of zeolite A membranes using a continuous flow method

Zeolite A membranes were synthesized in the inner side of porous TiO₂ and α-Al₂O₃ tubular supports by a continuous method. The methodology was then used at several scales for preparing membranes on TiO₂ and α-Al₂O₃ supports with lengths of 6, 12 and 25 cm. Formation of an homogeneous zeolite film was confirmed by XRD and SEM in all supports. Single-gas permeation experiments (He, H₂, N₂ and n-C₃H₈) indicated that Knudsen diffusion was the predominant mechanism in both supports. All the synthesized membranes present high flux and moderate selectivity to water in water–ethanol mixtures.     

A new synthetic route to molecularly imprinted ORMOSIL: Characterization and evaluation

A new strategy for synthesis of molecularly imprinted organically modified silica (MIORMOSIL) has been described. The MIORMOSIL was prepared by reacting vinyl acetate and 3-(trimethoxysilyl) propyl methacrylate, followed by condensation and hydrolysis with tetraethyl orthosilicate in the presence of caffeine. The ORMOSIL was characterized by SEM, FTIR, ²⁹Si MAS NMR, ¹³C MAS NMR, TGA, nitrogen adsorption/desorption and tested to extract analyte from coffee samples. The percentage recovery of caffeine 88 ± 5% (n = 9), limits of detection and quantification, 5.14 × 10^–4 and 1.71 × 10^?3 mmolL^?1 respectively, were achieved. Cross reactivity studies for theophylline and theobromine showed high recovery (77% and 82% respectively).

Abbreviations: HMIP: Molecularly Imprinted ORMOSIL; HNIP: non imprinted ORMOSIL; TMSPM: 3-(Trimethoxysilyl)propylmethacrylate     

Functionally Graded Ceramics Fabricated with Side‐by‐Side Tape Casting for Use in Magnetic Refrigeration

Functionally graded ceramic tapes have been fabricated by a side‐by‐side tape casting technique. This study shows the possibility and describes the main principles of adjacent coflow of slurries resulting in formation of thin plates of graded ceramic material. Results showed that the small variations of solvent and binder system concentrations have a substantial effect on slurry viscosity. Varying these parameters showed that side‐by‐side tape casting with a well‐defined interface area is possible for slurries with viscosities above 3500 mPa s at a casting shear rate of 3.3 s^?1. As it was expected, the choice of de‐bindering and sintering regimes significantly influences crack formation, and a three‐step heating programme was found to result in tapes of the highest quality. The interface regions of green graded tapes were investigated structurally by scanning electron microscopy; for a distinct identification of the interface region and analysing the degree of cross‐interface diffusion, the isothermal entropy change was measured by a vibrating sample magnetometer as the magnetic transition temperature (Curie temperature) is very sensitive to the dopant level in ceramics. Also the purpose of developing this graded ceramic tape casting was applications of these specific magnetocaloric properties within the magnetic refrigeration technology.     

Role of π-π interactions and chain flexibility in dispersion and dynamic-mechanical properties of nanocomposites with multiple wall carbon nanotubes

Two polymers of same functional group were used; one with greater chain flexibility, PA 6.6, and the other with two benzene rings in the main chain, PA 6I-6T (aPA), to evaluate how the structure influences on the nanoparticle dispersion homogeneity and on dynamic-mechanical properties. In the aPA nanocomposites, good dispersion and homogeneous distribution were observed for all CNT concentrations. However, PA 6.6 nanocomposites showed agglomerated regions in all formulations. The interfacial energy of the aPA/CNT was five times lower than that of PA6.6/CNT, resulting in greater compatibility in this nanocomposite. An increase of up to 26% was observed with 2.5% of CNT in aPA nanocomposites storage modulus. In the samples with PA 6.6, the increase was at most 5%. Even with greater flexibility of PA 6.6 macromolecules, the π-π interaction between the aPA aromatic rings and CNTs might be the decisive factor for dispersion improvement and positively influence on the dynamic-mechanical properties of these nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48195.     

Crack-free caustic magnesia-bonded refractory castables

A growing interest in designing high-alumina MgO-bonded refractory castables has been identified in recent years due to the magnesia ability to react: (i) with water at the initial processing stages of these materials (inducing the precipitation of brucite phase) or (ii) with alumina, giving rise to in situ MgAl₂O₄ generation at high temperatures. Nevertheless, despite the great potential of caustic magnesia to be used as a binder in such systems due to its high reactivity, it is still a challenge to control the hydration reaction rate of this oxide and the negative effects derived from the expansive feature of Mg(OH)₂ formation. Thus, this work evaluated the incorporation of different contents of aluminum hydroxyl lactate (AHL) into caustic magnesia-bonded castables, aiming to control the brucite precipitation during the curing and drying steps of the prepared samples, resulting in crack-free refractories. The designed compositions were characterized via flowability, setting behavior, X-ray diffraction, cold flexural strength, porosity, permeability and thermogravimetric measurements. According to the results, instead of Mg(OH)₂, hydrotalcite-like phases [Mg₆Al₂(OH)₁₆(OH)₂.4.5H₂O and Mg₆Al₂(OH)₁₆(CO₃)·4H₂O] were the main hydrated phases identified in the AHL-containing compositions. The addition of 1.0 wt% of aluminum hydroxyl lactate to the designed castable proved to be, so far, the best option for this magnesia source, resulting in the development of a crack-free refractory with enhanced properties and greater spalling resistance under heating.     

Mechanical and dynamical mechanical properties of chloroprene rubber and cellulose II composites

Vulcanized composites of chloroprene rubber (CR) with cellulose II (Cel II) as a filler were investigated. Cel II, obtained by the coagulation of cellulose xanthate, was incorporated in the rubber by the traditional method. The filler content varied from 0 to 30 phr. For comparison purposes, carbon black (CB)–CR composites were also studied. The CB amount varied from 0 to 45 phr. The mechanical and dynamic mechanical properties were determined, and the CR composite containing 20 phr of Cel II showed the best set of properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2425–2430, 2004     

Nuisance Operations of Distribution Fuse Links Due to Lightning-Induced Current Surges

The probability of nuisance operations of distribution fuse links due to lightning-induced current surges is the subject of much discussion today. This discussion is driven, in part, by the practice of moving the surge arrester to the transformer tank to improve overvoltage protection of the transformer. One consequence of this practice is that the probability of nuisance operation of the fuse link protecting the transformer will increase significantly unless larger fuse-link sizes are employed or unless high-surge-capacity fuse links are used. Section II of this paper describes a method for determining the probability of nuisance operations of fuse links under various conditions. Section III describes one utility's experience with moving the arrester to the transformer tank and also its success with high-surge-capacity fuse links