Hot Corrosion Behavior and Microstructural Change of Al-Gradient CoNiCrAlYSi Coatings, Produced by LVPS and Diffusional Processes

Conventional and gradient CoNiCrAlYSi coatings were produced by using low vacuum plasma spray and an additional step of diffusional over aluminizing (pack cementation) techniques on an Inconel-738 substrate. Hot corrosion of these coatings was investigated using Na₂SO₄–20wt%NaVO₃ molten salt at 880?°C for 800?h. Hot corrosion rate was determined by measuring the weight gain of the specimens at regular intervals for a duration of 20?h. X-ray diffraction, field emission scanning electron microscopy and electron probe micro analysis techniques were used to determine the nature of phases, investigation of the thermally grown oxide, examination of the surface attack and determination of the elemental distribution. The gradient coating showed better performance by re-healing alumina scale due to its possession of more β phase as Al reservoir. Results indicated that pack cementation process caused an increase in amount of aluminum-rich β phase and better hot corrosion properties of gradient coatings owing to the Al enrichment in the outer layer and rapid formation of protective oxide on the surface.     

Investigation of local thermal nonequilibrium effects on oil in situ combustion simulation

In the models developed for oil in situ combustion so far, local thermal equilibrium (LTE) was assumed between reservoir rock and fluids without being validated. As presence of a combustion zone makes the validation of this assumption questionable, in this study a new two-energy equations model is developed describing the temperature fields of rock and fluids separately. Investigating the effect of local thermal nonequilibrium between rock and fluids indicates that LTE will fail if the grain's diameter size order exceeds a millimeter. In this case, using LTE will lead to overestimating the heat and mass transfer rates.     

Compressive and flexural properties of novel polylactic acid/hydroxyapatite/yttria-stabilized zirconia hybrid nanocomposite scaffold

The mechanical property is a crucial factor in the design of bone tissue engineering scaffolds. In the current study, novel PLLA (Poly-L-lactic acid)–Hydroxyapatite (HA)–yttria-stabilized zirconia (YSZ) nanocomposite scaffold with various compositions was prepared and characterized. The effect of HA and YSZ contents on the mechanical behavior of the resultant composites was investigated. TEM micrograph revealed that HA particles are needle-like in shape and nano in size. Scanning electron microscopy (SEM) micrograph also showed that YSZ powder is in granule form and submicron size. SEM disclosed that all scaffolds had a highly interconnected porous structure and X-ray diffractometry revealed that there were some molecular interactions between PLA (Polylactic acid), HA, and YSZ in the composites. The results depicted that introducing YSZ to the nanocomposite leads to a significant increase in compressive strength, modulus, and densification strain. In addition, flexural strength and modulus showed an upward trend by adding YSZ particles to scaffolds. It should be noted that PLA–20%HA–20%YSZ indicates the highest strength and modulus in both compression and bending tests, though, it did not demonstrate the proper strain compared to other scaffolds. Thus, PLA–15%HA–15%YSZ has been reported as the best candidate due to appropriate strength and strain. Also, energy absorption in nanocomposites showed an upward trend by increasing the amount of YSZ particles. It was found that the strength of samples was declined after being soaked in simulated body fluid. However, scaffolds with HA underwent more decrease in strength compared to samples containing YSZ.     

A system-level design method for RF receiver front-end with low power consumption

Analog Integrated Circuits and Signal Processing - Due to wireless communication’s rapid growth, the need for low power integrated transceivers is increasing. The receiver power is a major...     

An experimental investigation on the effect of pH variation of MWCNT–H2O nanofluid on the efficiency of a flat-plate solar collector

The effect of pH variation of MWCNT–H₂O nanofluid on the efficiency of a flat-plate solar collector was investigated experimentally. The experiments were carried out using 0.2 wt.% MWCNT with various pH values, 3.5, 6.5, and 9.5, and Triton X-100 as additive. The procedure of ASHRAE standard was used for testing the thermal performance of flat-plate solar collector. Results show that by increasing or decreasing the pH values with respect to the pH of isoelectric point, the positive effect of nanofluid on the efficiency of solar collector is increased.     

A high flux graphene oxide nanoparticles embedded in PAN nanofiber microfiltration membrane for water treatment applications with improved anti-fouling performance

A high flux and anti-fouling graphene oxide (GO) nanoparticles embedded in polyacrylonitrile (PAN) nanofiber microfiltration membranes (PANGMs) were fabricated through the facile electrospinning method and were characterized by water treatment applications. The synthesized GO nanoparticles and GO nanoparticles embedded in PAN nanofiber membranes were characterized by FESEM, FTIR, and EDS. SEM images showed that the PANGMs possessed randomly overlaid fibers with a network-like highly porous structure similar to the pristine PAN nanofiber membrane, while agglomeration of GO nanoparticles was observed at high GO concentration. The introduction of GO nanoparticles into the PAN polymeric matrix significantly increased the permeation flux of the resulting membrane in both dead-end and cross-flow filtration systems. A high flux recovery ratio of 96.6% and a low irreversible fouling ratio of 3.4% were obtained at 2% (wt.) GO nanoparticles. More importantly, a high flux recovery ratio of GO nanoparticles embedded in PAN nanofiber membrane was retained after 20 repeated cycles of activated sludge suspension filtration. Therefore, it can speculate that the incorporation of GO nanoparticles into the PAN nanofibers could efficiently improve the anti-fouling ability of membranes which had opened up an alternative for the preparation of high flux and anti-fouling microfiltration membranes in practical water treatment applications such as membrane bioreactors.

     

Effects of chitosan and zirconia on setting time,mechanical strength,and bioactivity of calcium silicate‐based cement

In this research, we aimed at improving the setting properties and biocompatibility of the mineral trioxide aggregate‐like cements while maintaining the main chemical formula. Consequently, chitosan and zirconium oxide were added to the cement instead of bismuth oxide to improve the mechanical behavior, limit the possible toxicity, and enhance the bioactivity of the cements. Adding zirconia resulted in a shorter setting time and adding chitosan contributed to the setting time, mechanical strength, and biocompatibility at the same time. Thus, cements containing both chitosan and zirconia had the shortest setting time, highest compressive strength, and apatite‐forming ability.     

Hydrophilic goethite nanoparticle as a novel antifouling agent in fabrication of nanocomposite polyethersulfone membrane

The goethite nanoparticle was used as a multifunctional additive to fabricate antifouling polyethersulfone (PES) nanofiltration membranes. The goethite/PES membranes were synthesized via the phase inversion method. The scanning electron microscopy (SEM) photographs showed an increase in pore size and porosity of the prepared membranes with blending of the goethite. The static water contact angle measurements confirmed a hydrophilic modification of the prepared membranes. With increase in the goethite content from 0 to 0.1 wt %, the pure water flux increased up to 12.7 kg/m² h. However, the water permeability decreased using high amount of this nanoparticle. Evaluation of the nanofiltration performance was performed using the retention of Direct Red 16. It was observed that the goethite/PES membranes have higher dye removal capacity (99% rejection) than those obtained from the unfilled PES (89%) and the commercial CSM NE 4040 NF membrane (92%). In addition, the goethite/PES blend membranes showed good selectivity and antifouling properties during long‐term nanofiltration experiments with a protein solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43592.