Preparation and properties of multi-walled carbon nanotube/poly(organophosphazene) composites

Carbon nanotubes (CNTs) are promising materials because of their unique properties. However, the poor solubility in solvents limits the function of CNTs and hinders their applications in many fields. Surface modification of CNTs with polymers is an efficient method to solve this problem. Several polymers were tested for the preparation of CNT dispersions. In comparison with organic polymers, poly(organophosphazenes) are highly stable macromolecules with adjustable properties which depend on the side groups. This article is to describe the synthesis of thermally stable and soluble multi-walled CNT/poly(organophosphazene) composites. The poly(organophosphazene)s substituted with (a) 100 % quaternary protonated pyridinoxy (PPY), (b) 50 % quaternary protonated pyridinoxy and 50 % a long aliphatic chain alcohol (1-dodecanol) (PDK), and (c) 50 % quaternary protonated pyridinoxy and 50 % a glycol ether [(2-(2-methoxyethoxy)ethanol] (PET) have been synthesized. f-MWCNT/poly(organophosphazene) composites have been prepared by the treatment of the functionalized multi-walled carbon nanotubes (f-MWCNT) with the protonated polyphosphazenes (PPY, PDK, and PET) using different feed ratios [R _feed = 1:1, 1:3, 1:5, 1:10 (w:w)]. The thermal stability of prepared composites (f-MWCNT/PPY, f-MWCNT/PDK, and f-MWCNT/PET) have been investigated by TGA. By considering thermal stabilities and solubility of all prepared composites, f-MWCNT/PPY_1:5, f-MWCNT/PDK_1:5, and f-MWCNT/PET_1:5 have been chosen as optimum composite composition and characterized by ³¹P NMR, ¹H NMR, XRD, Raman spectroscopy, and EDX analysis. The morphologic characterizations of the f-MWCNT/PPY_1:5, f-MWCNT/PDK_1:5, f-MWCNT/PET_1:5 nanocomposites have been carried out by HRTEM. Excellent dispersions of the nanocomposites in water and common organic solvents have been achieved. The solubility and thermal stability of nanocomposites depend on the side groups on poly(organophosphazene).     

High-modulus steels reinforced with ceramic particles through ingot casting process

High Young's modulus steels can be fabricated based on the concept of metal matrix composites. In this paper, a number of reinforcing ceramic phases with high Young's modulus are assessed and selected to design compositions for high-modulus steels based on thermodynamic calculations. The steel matrix composites reinforced with boride and carbide phases are produced through ingot casting and are processed thermomechanically to strips following standard processing routes for automotive products. The results show that the Young's modulus of steels in the as-cast condition can be increased using borides and carbides. However, further down-stream processing via conventional thermomechanical processing leads to a gradual degradation of the Young's modulus due to extensive void formation. The opportunities and challenges of ceramic-reinforced high-modulus steels produced via conventional ingot casting and thermomechanical processing for the automotive market are discussed.     

Surface coating of polyamide reverse osmosis membranes with zwitterionic 3‐(3,4‐dihydroxyphenyl)‐l‐alanine (l‐DOPA) for forward osmosis

To overcome low permeability and fouling problems of membranes used in FO processes, modification is needed to improve the hydrophilicity, permeability and selectivity of membranes. In this work, thin film composite (TFC) commercial polyamide RO membranes (BW30‐LE, SW30‐HR, AG and AC) were functionalized with zwitterionic l ‐DOPA. The effect of l ‐DOPA on the morphology of membranes was determined via SEM, FT‐IR, AFM and contact angle analysis. The l ‐DOPA modified BW30‐LE membrane showed excellent properties with 46° contact angle and 3.8 L/m²hbar water permeability and 0.83 L/m²h salt permeability. Although, l ‐DOPA modified BW30‐LE membrane had the highest water flux and hydrophilicity, l ‐DOPA modified SW30‐HR membrane showed higher FO flux with 9.38 L/m²h than BW 30 membrane with 3.5 L/m²h at 50 g/L NaCl draw solution. Introducing hydroxyl and carboxyl ionic groups on the membrane surface with l ‐DOPA coating enhanced the FO performance and water permeability which provide a new insight in FO applications.     

Pull-out behavior of prestressing strands in steel fiber reinforced concrete

This paper presents the results of an experimental study investigating the effects of steel fibers on the mechanical properties of concrete and the enhancement of bond strength of prestressing strands in steel fiber reinforced concrete (SFRC). The first part of the experimental program consisted of compression, tension and flexural tests on SFRC. Two types of steel fibers with 30 mm and 60 mm fiber lengths were used with five different fiber contents. The second part of the study consisted of simple pull-out tests on 12.7 mm and 15.2 mm diameter seven-wire untensioned prestressing strands embedded in concrete blocks. The pull-out tests were conducted with two different fiber lengths and five different fiber contents for each strand diameter. The steel fibers were observed to improve the pull-out resistance of strands by controlling the crack growth inside concrete blocks.     

An Experience in Testing an Object-Oriented Satellite Control System

This paper presents our experience in testing an object-oriented software: the Telemetry and Telecommand System (TMTC). The TMTC runs along a distributed architecture comprising microcomputers plus a Data Base server inter-connected via LAN under TCP/IP protocol. This in-house developed software was designed according to the Object Modelling Technique (OMT). TMTC's software components represent clusters of classes related to functionality and building blocks of generic services. In order to establish a systematic way for the testing activities we have adapted the Hierarchical Approach (HA), proposed by Shel Siegel, to the experience and culture of the team. The HA, focusing on object-oriented testing, has fitted well with the aim of detecting as many faults as possible in the early phases of the development. In the HA almost all classes are individually tested before being gradually integrated into groups. Groups of classes are defined according to the scenarios specified in the system design phase. This has considerably reduced the testing effort. This paper also discusses the system class number in comparison with the number of stubs and drivers generated for testing. The difficulties to test a distributed application for satellite controlling and monitoring are likewise examined.     

Herringbone nanofiber CVD synthesis and high pressure hydrogen adsorption performance analysis by molecular modelling

In order to interpret adsorption results of hydrogen storage by adsorption in graphite nanofiber (GNF) materials at molecular scale and to propose optimized structures of graphitic materials, we have realized both experimental and numerical studies of gas adsorption in GNF. The porous materials have been synthesized by CVD method. The adsorption experiments were performed at 293 K by a volumetric method at high pressure until 40 MPa. We completed the surface reactivity analysis by performing structural characterizations of the samples using different structural techniques and numerical modelling computed in the grand canonical Gibbs ensemble. Within the cell, stacks of plans of graphite are arranged periodically using boundary conditions. The present numerical approach enables to interpret the results based on the solid–gas molecular interactions reactivity analysis.     

Arc magmatism as a window to plate kinematics and subduction polarity: Example from the eastern Pontides belt, NE Turkey

The Eastern Pontides orogenic belt in the Black Sea region of Turkey offers a critical window to plate kinematics and subduction polarity during the closure of the Paleotethys.Here we provide a brief synthesis on recent information from this belt.We infer a southward subduction for the origin of the Eastern Pontides orogenic belt and its associated late Mesozoic-Cenozoic magmatism based on clear spatial and temporal variations in Late Cretaceous and Cenozoic arc magmatism,together with the existence of a prominent south-dipping reverse fault system along the entire southern coast of the Black Sea.Our model is at variance with some recent proposals favoring a northward subduction polarity,and illustrates the importance of arc magmatism in evaluating the geodynamic milieu associated with convergent margin processes.     

Osteogenic activities of polymeric soybean oil-g-polystyrene membranes

A novel biocompatible copolymer membrane was synthesized and characterized for use in guided bone regeneration using polymeric soybean oil-g-polystyrene (PSO-g-PS) graft copolymer which was successfully obtained by free radical polymerization of styrene initiated by PSO peroxide as a macroinitiator at 80 °C. Osteoblastic cellular activities of MC3T3-E1 cells on PSO-g-PS membranes with different soybean oil composition (PSO-g-PS1, PSO-g-PS2, and PSO-g-PS3) were evaluated. Nuclear magnetic resonance (¹H NMR) spectra showed that PSO inclusion (mol%) was found to be 27, 69, and 51 % for PSO-g-PS1, PSO-g-PS2, and PSO-g-PS3 membranes, respectively. Superior biocompatibility of the PSO-g-PS membranes was determined compared to polystyrene tissue culture plates (TCPS) as positive control. Cell proliferation was enhanced on PSO-g-PS2 and PSO-g-PS3 membranes compared to PSO-g-PS1 membranes (p < 0.001), and a statistically significant higher ALP value of MC3T3-E1 cells on PSO-g-PS2 membranes (p < 0.05) suggested that proliferation and differentiation of preosteoblastic on PSO-g-PS membranes were enhanced with regard to soybean oil content within the membranes. Thus, the present study suggests that PSO-g-PS2 membranes, which showed a favorable biological environment for the preosteoblastic cells, can be well suited for bone tissue engineering applications.     

Optimization of the Wet Mechanochemical Process Conditions of SrSO4 to SrCO3 and (NH4)2SO4 by Using Response Surface Methodology

The wet mechanochemical process was optimized for insoluble SrCO₃ and soluble (NH₄)₂SO₄ formation from celestite (SrSO₄)-(NH₄)₂CO₃-H₂O mixtures in a planetary ball mill by Box-Behnken design (BBD). The products formed during wet milling were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. For converting to SrCO₃ of celestite (SrSO₄) and to (NH₄)₂SO₄ of (NH₄)₂CO₃, a hydrometallurgical process optimization via the wet mechanochemical conversion using (NH₄)₂CO₃ was developed the first time in this work using response surface methodology. The wet mechanochemical conversion was carried out by varying ball to grinding material mass ratio, (NH₄)₂CO₃ to SrSO₄ mole ratio and the rotational speed of mill in a planetary mill. Under the optimum experimental conditions (9.24 of ball to grinding material mass ratio, 1.86 of (NH₄)₂CO₃ to SrSO₄ mole ratio and 400 rpm of the rotational speed of mill), the conversion of SrCO₃ was 99.08 pct. The (NH₄)₂SO₄ obtained as byproduct was crystallized.