Study on the Hydrogenated Diamond-Like Carbon Films Synthesized by RF-PECVD from n-decane

Using a mixture of n-decane and hydrogen, diamond-like carbon thin films (DLCTFs) with high growth rate of 35?nm/min are deposited by radio frequency plasma enhanced chemical vapor deposition. We show that n-decane can be considered as a promising carbon source in DLCTF deposition. The properties of the deposited films such as structure, hydrogen content, deposition rate and refractive index are studied for 20, 50 and 100?sccm hydrogen flow rates (HFRs). It is shown that the deposition rate has a maximum of 35?nm/min for HFR?=?20?sccm and by increasing hydrogen concentration, deposition rate drops to 19?nm/min for HFR?=?100?sccm. The Raman spectra reveal that the films represent hydrogenated diamond-like carbon features. The photoluminescence background of the Raman spectra is used as a measure for hydrogen content of the films. The hydrogen content varies from 29 to 46% which yields a various amount of sp³ fraction. The results of the spectroscopic ellipsometry indicate that by increasing HFR, refractive index decreases from 2.1 to 1.9 at 632?nm. The aforementioned trends are attributed to the increase of hydrogen content in DLCTFs which is in very good agreement with enhancing of the photoluminescence background of the Raman spectra.     

Sintering Behavior and Machinability of Phlogopite Glass Ceramics Containing Fe2O3

Mica-based glasses in the SiO₂-Al₂O₃-MgO-K₂O-F system were prepared by a sintering method to investigate the effects of different amounts of hematite (Fe₂O₃) on thermal and sintering behaviors besides machinability of the glasses by means of differential thermal analysis (DTA), X-ray diffraction, and scanning electron microscope techniques. DTA analysis on fine and coarse glass powders indicated that the main crystallization mechanism in this system occurred in the bulk rather than the surface. Increasing Fe₂O₃ content to 5 wt.% improved machinability of the glass ceramic. Fe₂O₃ led to the disruption of the glass matrix and facilitated the nucleation of the crystalline phase. Precipitation of sellite (MgF₂) crystals as heterogeneous nucleating sites for potassium phlogopite crystals acted as a second contribution to the machinability of the 5 wt.% Fe₂O₃-containing sample. However, introducing more than 5 wt.% Fe₂O₃ to the base glass prohibited the nucleation of MgF₂, and as a result, large micas formed within the glass. This together with precipitation of cordierite aggregates in highly doped glass with Fe₂O₃ led to lower machinability in these samples.     

Continuous devulcanization of waste tires by using a Co‐rotating twin screw extruder: Effects of screw configuration,temperature profile,and devulcanization agent concentration

Recently, for reasons both economical and environmental, recycling of waste tires based on (styrene butadiene rubber)/(natural rubber) (SBR/NR) has been widely considered. Response surface methodology (RSM) has been used to predict SBR/NR devulcanization behavior in a co‐rotating twin screw extruder. In this study, variable parameters were barrel temperature, screw configuration, and content of devulcanization agent. A Box‐Behnken design for the three variables, at three levels, was chosen. The sol fraction of devulcanized rubber, Δtorque (difference between maximum and minimum curing torque), and mechanical properties of revulcanizate samples were considered as the responses. The results indicated that an increase of devulcanization agent content at a certain temperature caused the sol fraction to increase. Samples including a higher sol fraction showed a lower cross‐link density. Sol fraction for high shear rate screw configuration was lower than that for other screw configurations. Tensile strength of revulcanized rubber showed a decrease with a rise of devulcanization temperature. Moreover, a relationship connecting the residence time in the extruder with stagger angle and length of different kneading blocks were obtained. J. VINYL ADDIT. TECHNOL., 19:65–72, 2013. © 2013 Society of Plastics Engineers     

Synthesis,characterization, and optimization of α‐Fe2O3/silica nanocomposites using homogenous precipitation method

The purpose of this study was to systematically synthesize and characterize the high surface area 10 wt% nanocomposites of α‐Fe₂O₃ (hematite)/silica using a simple and economically effective homogenous precipitation (HP) route via Response Surface Method combined with Central Composite Design (CCD). Accordingly, the RSM‐CCD approach including 20 experiments was designed to investigate the effects of three factors including concentration of iron chloride solution, pH and calcinations temperature on the final surface area of α‐Fe₂O₃/silica nanocomposites. The optimum surface area was 373 m²/g at the condition including iron chloride concentration of 0.018 mol/L, pH=8.95, and calcination temperature of 573°C.     

Ternary solubility of mono- and di-tert-butyl ethers of glycerol in supercritical carbon dioxide

Using a continuous flow apparatus, the ternary solubility of mono- and di-tert-butyl ethers of glycerol (MTBG and DTBG, respectively) in supercritical carbon dioxide was measured at the temperatures of 313.15, 333.15, and 348.15 K; a pressure range of 80-200 bar; and an expanded gas flow rate of 180 ± 10 mL min⁻¹ at average laboratory temperature of 300.15 K and pressure of 0.89 bar. The ternary solubility of the ethers at the constant temperatures of 333.15 and 348.15 K increased with increasing pressure up to the crossover point (i.e., 152 bar for MTBG and 170 bar for DTBG). MTBG exhibited a higher solubility than DTBG in scCO₂. The experimental data for the ternary solubility of MTBG and DTBG were correlated using the Bartle equation.     

Palm date fibers: analysis and enzymatic hydrolysis

Waste palm dates were subjected to analysis for composition and enzymatic hydrolysis of their flesh fibers. The fruit contained 32% glucose and 30% fructose, while the water-insoluble fibers of its flesh consisted of 49.9% lignin and 20.9% polysaccharides. Water-insoluble fibers were settled to 55% of its initial volume in 12 h. The presence of skin and flesh colloidal fibers results in high viscosity and clogging problems during industrial processes. The settling velocity of the fibers was improved by enzymatic hydrolysis. Hydrolysis resulted in 84.3% conversion of the cellulosic part of the fibers as well as reducing the settling time to 10 minutes and the final settled volume to 4% of the initial volume. It implies easier separation of the fibers and facilitates fermentation processes in the corresponding industries. Two kinds of high- and low-lignin fibers were identified from the water-insoluble fibers. The high-lignin fibers (75% lignin) settled easily, while the low-lignin fibers (41.4% lignin) formed a slurry suspension which settled very slowly. The hydrophilicity of these low-lignin fibers is the major challenge of the industrial processes.     

Constitutive modeling of isotropic hyperelastic materials using proposed phenomenological models in terms of strain invariants

Rubber‐like materials deform largely and nonlinearly under loading and preserve their initial configuration after removal of the load. These materials are usually modeled as being homogeneous, isotropic, and incompressible elastic solids that are supported by experimental data. In this article, a general form for the strain energy density of these materials is assumed as the sum of two independent functions of the first and second strain invariants. Applying the essential requirements on the form of the strain energy density, the mathematical form of these functions is obtained as polynomial, logarithmic, and exponential. Then a general form is derived for the strain energy density of compressible materials and its effectiveness is evaluated for hydrostatic compression and uniaxial tension tests. The determination of material parameters and the evaluation of effectiveness of models are done based on the correlation between the values of the strain energy density (rather than the stresses) cast from the theory and the test data. Comparison of the theoretical predictions with the experimental data indicates that the represented models can achieve a satisfactory agreement with the behavior of different materials. POLYM. ENG. SCI., 56:299–308, 2016. © 2015 Society of Plastics Engineers     

Preparation of Nanostructured ZnO Thin Films Using Magnetron Sputtering for the Gas Sensors Applications

ZnO is one of the most promising transparent conducting oxide materials, which widely used in thin film gas sensors. In this research, the dependence of the thermal oxidation time on structural, morphological and gas sensing properties of ZnO thin films is investigated. ZnO nanostructures are synthesized by using DC magnetron sputtering for deposition of pure zinc layers on glass substrates and then thermal oxidation of deposited zinc layers to produce zinc oxide (ZnO) thin films. Obtained results from X-ray diffraction revealed that the degree of crystallinity and the average grain size of the ZnO deposited thin films enhance with increasing the thermal oxidation time. Surface topography and growth behavior of ZnO thin films have important role in optimization of gas sensing properties of these films. In this study, scanning electron microscopy and atomic force microscopy have been used to investigate the effective parameters related to the surface topography of the films. Obtained results from these analyzes revealed that the surface topography of ZnO deposited samples strongly depend on thermal oxidation time. Also the effect of thermal oxidation time on the performance of ZnO gas sensors is investigated. The results indicated that the ethanol gas sensing properties of ZnO samples improve with decreasing the size of grains.     

Effects of peroxide and phenolic cure systems on characteristics of the filled ethylene–propylene–diene monomer rubber (EPDM)

The effects of three curing systems, peroxide, peroxide–phenolic combination, and phenolic on selected properties of cured carbon black‐filled ethylene–propylene–diene monomer rubber (EPDM) were investigated. The cured rubbers immersed in hot amine solution to evaluate their suitability for seal and gasket industry at elevated temperature and amine environments. These tests were essential for evaluating the durability of the gasket in a gas refinery. The Fourier transform infrared spectroscopy spectrums revealed that the phenolic crosslink was constructed between rubber macromolecules during the curing process. The changing curing system from peroxide to peroxide–phenolic and phenolic increased the glass transition temperature of the filled cured rubbers between 3 and 5 °C. There was not any significant difference between thermogravimetric analysis thermographs of the selected cured rubbers with various cure systems and the residues ranged between 45% and 47%. Unlike of peroxide curing system, a dual phase was observed from scanning electron microscopy micrographs for peroxide–phenolic and phenolic cure systems. The phenolic cure system was not beneficial for rubber curing although, it reduced scorch time of the curing process. For the most studied mechanical properties, phenolic cure system deteriorated mechanical properties for both, aged and unaged cured rubbers. Increasing the amount of diene monomer in EPDM structure was beneficial for phenolic rubber cure system. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46213.     

Supporting QoS in IEEE 802.11e wireless LANs over fading channel

Transferring real-time traffic such as voice and video over wireless LAN networks (WLAN) requires stringent delay and jitter requirements. Recently IEEE 802.11e standard has been emerged to support QoS in WLAN. One of the methods to provide QoS in this standard is Enhanced Distributed Channel Access (EDCA) which benefits form the concept of traffic categories. However, EDCA is a contention based method; therefore it can not guarantee strict QoS required by real-time services without proper network control mechanisms. In this paper, we analyze the effect of loss and delay caused by fading channel on EDCA performance. Then, we propose a modification to the media access scheme, called CAFD (Collision Avoidance with Fading Detection) to elevate the performance against channel failures. Moreover an adjustment for the maximum number of retransmissions is proposed to maintain the delay and jitter requirements of the real-time traffic. The performances of the proposed methods are evaluated by simulations.