Microwave diagnosis of rubber compounds

The results of a study investigating the dielectric properties of rubber compounds and their constituents in the frequency range of 5 to 24 GHz are presented. A completely filled short circuited waveguide technique was used to conduct these dielectric measurements. The influence of carbon black content in rubber was investigated for carefully prepared rubber samples. The results showed that for all frequencies, the dielectric constant increases as a function of increasing carbon black content. The variation of dielectric constant values decreases as frequency increases. The presence of curatives in uncured rubber samples was also detected, which indicates the sensitivity of microwaves to the chemical reaction triggered by curatives     

Epoxy coating with self-healing capability based on a 2-mercaptobenzothiazole-loaded CeO2 nanocontainer

In this study, we demonstrated a facile approach for the synthesis of nanocontainers using the encapsulation of a 2-mercaptobenzothiazole (MBT) inhibitor; these nanocontainers were capable of responsively releasing a corrosion inhibitor and of self-healing performances. The anticorrosive performance of the CeO₂ nanocontainers was investigated with electrochemical impedance spectroscopy (EIS) measurement in a saline electrolyte via the incorporation of different weight percentages (0.5, 1, and 2 wt %) of synthesized nanocontainer in epoxy (EP) resin. The EIS results show that the loading of 1 wt % CeO₂ nanocontainer containing MBT inhibitor in the epoxy (EP) coating [EP/NC MBT–CeO₂ (1%)] provided the highest R_coat, the lowest constant phase element of coating, and the optimum release of MBT at different operating pHs. The highest coating resistance R_coat values of this coating (7.81 × 10⁷ Ω cm²) were about 12 and 8573 times greater than those considered for EP–CeO₂ and EP coatings, respectively. Different releases of the MBT inhibitor were detected at various pHs. We found that the coating operating in acidic media exhibited a better self-healing performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47297.     

Effect of Molybdenum on Metallurgical and Wear Properties of Fe–Cr–C Hard facing alloy

Protection of Metals and Physical Chemistry of Surfaces - In this research, Surface hardening was performed by two types of Flux Cored Arc Welding (FCAW) filler metals based on Fe–Cr–C...     

Oxygen adsorption and desorption characteristics of LSCF5582 membranes for oxygen separation applications

This study examines the oxygen adsorption and desorption characteristics of La_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (LSCF5582) membranes prepared at sintering temperatures of 1200–1300 °C, with the aim of gaining an insight into their performance in the surface reaction limited regime for oxygen separation applications. The findings of this work are then compared with our experimental data on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF5582) membranes. It is demonstrated that the adsorption rate constants of both membranes are two orders of magnitude greater than their respective oxygen desorption rate constants as the oxygen adsorption occurs in less than 24 s whilst the oxygen desorption takes approximately one hour to reach equilibrium. The activation energy for oxygen adsorption of LSCF5582 reduced to a quarter of its value with increasing the sintering temperature from 1200 °C to 1300 °C. This is attributed to the oxygen exchange occurring more rapidly along the grain boundaries resulting in a lower activation energy. The LSCF5582 grain sintered at 1200 °C is the optimum selection for oxygen separation applications at an operating temperature of 850 °C and oxygen partial pressure of 0.21 bar.     

Convenient method for preparation of a new absorbent based on biofunctionalized graphene oxide hydrogels using nitrene chemistry and click reaction

A new graphene oxide (GO)-based hydrogel was synthesized through cross-linking of biofunctionalized graphene oxide nanosheets by di-alkyne polyethylene glycol as cross-linking agent. In this respect, nitrene chemistry as a convenient and straightforward protocol was developed for biofunctionalization of GO using an azido-starch as an eco-friendly, biodegradable and cost-effective material. In the next step, 1,3-dipolar cycloaddition chemistry, a green and highly efficient approach was utilized in cross-linking of functionalized GO by PEG through click reaction between remaining azido groups of starch on the surface of GO sheets and terminal alkyne groups of polyethylene glycol. Formation of aziridine and triazole rings during functionalization and cross-linking in this method could evidently improve biological activities of the obtained hydrogel compared to the conventional methods. The antibacterial activity of the new compounds was explored. The synthesized hydrogel showed antibacterial properties against Gram-positive and Gram-negative bacteria due to the presence of triazole rings. Also, the resulting hydrogel exhibited high dye removal efficiency and it can be utilized in water treatment effectively. The adsorption kinetics was analyzed through the effects of adsorption time and the dye concentration on the adsorption capacity. Kinetic data were accurately described by a pseudo-second-order model.     

Comparison of pristine and polyaniline‐grafted MWCNTs as conductive sensor elements for phase change materials: Thermal conductivity trend analysis

Phase change materials (PCMs) function based on latent heat stored on or released from a substance over a slim temperature range. Multiwalled carbon nanotubes (MWCNTs) and polyaniline are important elements in sensor devices. In this work, pristine and polyaniline‐grafted MWCNTs (PANI‐g‐MWCNTs) were applied as conductive carbon‐based fillers to make PCMs based on paraffin. The attachment of PANI to the surface of MWCNTs was proved by Fourier transform Infrared analysis. Dispersion of MWCNTs in paraffin was studied by wide‐angle X‐ray scattering. Heating and solidification of PCM nanocomposites were investigated by differential scanning calorimetry, while variation in nanostructure of PCMs during heating/solidification process was evaluated by rheological measurements. It was found that after 30 min of sonication, the samples filled with 1 wt % MWCNTs have melting and solidification temperatures of 29 and 42 °C, respectively. It was also found that PANI attachment to MWCNTs significantly changes thermal conductivity behavior of PCM nanocomposites. The developed MWCNTs‐based sensor elements responded sharply at low MWCNTs content, and experienced an almost steady trend in conductivity at higher contents, while PANI‐g‐MWCNTs sensor followed an inverse trend. This contradictory behavior brought insight for understanding the response of PCMs against thermal fluctuations. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45389.     

Energy-saving transparent heat mirrors based on tungsten oxide–gold WO3/Au/WO3 multilayer structures

Transparent heat mirrors are multilayer structures that transmit visible light while reflecting infrared heat. Heat mirrors based on tungsten oxide and gold multilayers WO₃/Au/WO₃ were fabricated by thermal evaporation, and their performance was investigated as a function of the thickness of the gold layer. First, the properties of individual layers were investigated. Atomic force microscopy revealed that all layers possessed smooth surfaces that were suitable for optical applications. The transmittance of the gold layers was found to decrease as the thickness is increased, with an opposite trend followed by infrared reflectance. In the multilayers, the thickness of the WO₃ was fixed at 34 nm, whereas the thickness of the gold layers was varied in the range 20–44 nm. X-ray photoelectron spectroscopy was used to investigate the elemental diffusion among the various layers, and it revealed the presence of inter-diffusion of elements throughout the layers. The performance of the heat mirrors was evaluated on the basis of their optical behavior. The optimum thickness of the gold layer was found to be 36 nm, with a peak spectral transmittance of 84%.     

Dissimilar Joining of Pure Copper to Aluminum Alloy via Friction Stir Welding

In this study, the dissimilar friction stir welding(FSW) butt joints between aluminum alloy 5754-H114 and commercially pure copper were investigated. The thickness of welded plates was 4 mm and the aluminum plate was placed on the advancing side. In order to obtain a suitable flow and a better material mixing, a 1-mm offset was considered for the aluminum plate, toward the butt centerline. For investigating the microstructure and mechanical properties of FSWed joints, optical microscopy and mechanical tests(i.e., uniaxial tensile test and microhardness) were used, respectively.Furthermore, the analysis of intermetallic compounds and fracture surface was examined by scanning electron microscopy and X-ray diffraction. The effect of heat generation on the mechanical properties and microstructure of the FSWed joints was investigated. The results showed that there is an optimum amount of heat input. The intermetallic compounds formed in FSWed joints were Al4Cu9 and Al2Cu. The best results were found in joints with 1000 rpm rotational speed and100 mm/min travel speed. The tensile strength was found as 219 MPa, which reached 84% of the aluminum base strength.Moreover, maximum value of the microhardness of the stir zone(SZ) was attained as about 120 HV, which was greatly depended on the grain size, intermetallic compounds and copper pieces in SZ.     

Synthesis and Characterization of ZnO Nanoparticles via Thermal Decomposition of Two Zinc(II) Supramolecular Compounds

A new nano-sized Zn(II) complex, [Zn(5,5′-dtbu-2,2′-bipy)Cl₂] _n (1) was synthesized and its structure determined by X-ray crystallography. The new nano-sized complex was prepared at oleic acid as a surfactant at 280 °C and characterized by scanning electron microscopy, elemental analyses and IR spectroscopy. The ZnO nano-particles were synthesized from thermolysis of nano-compound 1 at 600 °C and similar compound, [Zn(5,5′-dimethyl-2,2′-bipy)Cl₂] _n (2), at two different methods. SEM images show the average size of ZnO nano-particles are 78 and 50 nm for the compounds 1 and 2, respectively.