نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 64 (بهار 1402)

In this study the effect of UTP 2535 Nb and UTP 3545 Nb filler metals on the microstructure and oxidation resistance of the weld metal of GTAW welded 35Cr-45Ni alloy have been investigated. According to the results, microstructure of the weld metals includes Cr and Nb Carides precipitating along the grain boundaries of austenitic matrix. Weld metal of the sample welded with UTP 3545 Nb filler metal showed denser and more continuous carbides which arises from higher Cr content in this filler metal. According to the XRD analysis of the oxidized weld metals at 1000 ℃ for 96 h, all samples represent an external oxide layer, mostly consist of Cr oxide and an internal oxide layer, mostly composed of Si oxide. Weld metal of the sample welded with UTP 2535 filler metal showed the highest weight gain (4.3 mg/cm2) and oxide thickness (20 μm). For the weld metal of the other sample, these values were 3.6 mg/cm2 and 11 μm, respectively. It can be attributed to the higher Cr and Si in the UTP 3545 Nb filler metal. The first element results in a resistant, continuous, and defect free external oxide on the surface, and the latter one leads to formation of a resistant internal oxide, both strongly effective in improving the oxidation resistance of the weld zone.

To solve the problems caused by the use of chemical solvents such as amine solutions and caustic solution, a single bubble adsorption tower was used to investigate the effect of water-based nanofluids with nickel oxide nanoparticles on the CO2 adsorption process. CO2 was introduced as single bubbles from the end of a column, and the mass transfer coefficients and adsorption rates were investigated. The results showed that nickel oxide nanoparticles are hydrophobic and the addition of surfactant to nanofluid increases the surface electric charge of nickel oxide nanoparticles and increases the surface polarity for gas absorption. In this way, carbon dioxide gas is absorbed on the surface of nanoparticles due to its very polar nature, and this phenomenon increased the amount of gas absorption in the nanofluid by 270% compared to the base fluid.The maximum mass transfer flux for adsorption of CO2 with nanofluids containing nickle oxide nanoparticles was observed in the weight fraction of nanoparticles of 0.1%. To investigate the effect of important parameters on the mass transfer process in a single bubble tower, the parameters of nanoparticle weight fraction, gas injection nozzle diameter, with different levels were investigated. Finally, an experimental relationship was presented to estimate the mass transfer coefficient of CO2 gas, which is a function of the flow regime and microscopic structure of nanoparticles. The results showed that the amount of computational error for the proposed model is less than 20% and this model can estimate the laboratory results with a suitable approximation.

The aim of this research is to fabricate a moisture sensor based on porous nanostructure of pure tungsten trioxide (WO3) and doped with silver nanoparticles (SN), and to use the properties of ohmic changes, capacitance and impedance versus moisture as output. The structural characteristics of the prepared nanocomposite were examined by a scanning electron microscope and X-ray diffraction spectroscopy. The results showed that synthetic WO3 is in the form of spheres with dimensions of 3 to 7 μm, with a surface porous structure in size of 10 to 60 nm. To fabricate the sensors, first the materials were mixed and dispersed, then coated on the interdigitated electrode by sedimentation method. The investigation showed that the doped sensor with SN have a better performance in comparison with WO3 sample. Its sensitivity was obtained 4.4 and 0.68 MΩ/%RH for the relative humidity range of 20-50% and 50-90%, respectively, improved 7 and 5% compared to similar previous samples. The response and recovery time of this sensor was measured approximately 2 and 7 seconds, which is 37.5 and 41.4 times smaller than available samples, respectively. Decreasing the capacitance of the sensor to 3800 Pf by increasing the relative humidity to 90% is another finding. Significant impedance changes of the sensor versus the humidity alternations is other important result, showing that the impedance can be considered as a sensor output by compensating for errors of ohmic changes and capacitance.

The aim of this research is to improve the corrosion resistance and create the active inhibitory in hybrid-silane coatings. Therefor the graphene oxide (GO) nano-sheets and the methylene triphosphonic acid (ATMP) were used as a protective pigment and organic inhibitor carrier in the coating, respectively. The peaks appearing in 1059, 1380, 1730, and 3430 cm-1 belong to hydroxyl stretching, carbonyl, hydroxyl bending, and epoxide groups confirmed the successful synthesis of GO nanoparticles by infrared transfer spectroscopy (FTIR). The displacement of two peaks of 230 and 250 nm in GO to 261 and 360 nm in GO-ATMP represent the successful reduction of graphene oxide by ATMP molecules. Then, the corrosion resistance of GO-ATMP coating was evaluated using electrochemical impedance spectroscopy (EIS) and polarization tests. The results showed that the ATMP inhibitor improves the corrosion resistance properties of the coating, and the corrosion current density is reduced as 50%. After successfully inhibiting adsorption on GO plates, the coating (GO-ATMP) was applied on 2024 aluminum alloy sheets. The results of EIS and salt-spray tests showed that the corrosion resistance properties of GO-ATMP coatings improved due to restrict the access of corrosive environment to the metal surface. The intelligent releasing of the inhibitor during electrolyte penetration in scratched area of the coating was confirmed by the formation of a protective film in the scratch area in the electron microscope image of the sample. This caused to restrict the electrochemical reactions.

Polyethylene terephthalate is used in various industries, but due to the lack of functional groups on the surface, it is limited in use and needs surface modification to improve the application. In this study, the surface of PET fibers was first functionalized with carboxylic acid groups. Then, in an alkaline medium, gold nanoparticles were synthesized sonochemically on their surface, and the effect of parameters affecting the size and density of nanoparticles was investigated and optimized (temperature, power of ultrasonic device, and pH). The ability of PET-AuNPs nanocomposites to remove industrial dyes from the environment was used, and the removal and measurement of methyl orange dye from aqueous media were used. The effect of initial dye concentration, time, and pH was investigated and optimized. In quantitative electrochemical dye measurements, the modified AuNPs-PET / CNT / Au electrode had a linear response in the range of 20 to 60 μM. The detection limit of this electrode was 55 μM, and the effect of potential scanning speed on peak flow and the effect of solution pH were investigated. Adsorption equation studies have shown that adsorption follows the obedience isotherm.

The purpose of this research is synthesis of nanocomposite with high photocatalyst property and magnetic separation ability in order to degradation of organic pollutants and reusability, respectively. Therefore, Eu doped ZnS - Fe3O4 nanocomposite is synthesized via sonochemical method which this method is easy and low cost. The synthesized photocatalyst is investigated with X-ray Diffraction Pattern (XRD), Energy Dispersive X-ray Spectroscopy (EDS), Photoluminescence Spectroscopy (PL), UV-Vis Spectrophotometry. As a consequence of testing the capability of magnetic separation, the high amount of photocatalyst attracted by the magnet guarantees the property of recyclability. Photocatalytic application in presence of synthesized nanocomposite for degradation of Rhodamine-B dye under UV-C and visible lamp is studied and results showed 81% and 78% degradation efficiency under UV-C lamp for 3 hours and visible lamp for 1 hour, respectively. In addition, stability and reuse investigation showed that the nanocomposite still remains its photocatalytic capacity after 3 cycles test.

In this research, the effect of electric discharge machining input parameters on the surface roughness of A413 composite reinforced with 2.5% Al2O3, in two cases with the presence of a magnetic field and without a magnetic field was investigated and compared. The research presented with Taguchi experiment design approach which is based on L9 orthogonal array and iterative surface technique. The input parameters of these experiments include voltage (two levels), current intensity (three levels), pulse on-time (three levels) and pulse off-time (three levels). Experiments results show machined surface roughness reduction in presence of magnetic field up to 32 percent. The analysis of the results included the determination of signal-to-noise ratio diagrams corresponding to each of the input parameters and analysis of variance by Minitab software. The results show that the surface quality of the workpiece improves in the presence of a magnetic field compared to machining conditions without a magnetic field. Also, based on the results of analysis of variance in both cases, the current intensity is the most effective input parameter on the surface roughness of the workpiece made of A413 composite reinforced with 2.5% Al2O3.