Herein, a hybrid ZnO nanofiber/reduced graphene oxide (rGO) gas sensor is fabricated to detect acetone gas. Metal oxides, including ZnO, SnO2, and TiO2, have been widely used as gas sensors. This article investigates the implications of incorporating rGO into the network of ZnO nanofibers for the sensing characteristics of ZnO. Electrospinning, followed by a calcination treatment at 600 °C, is used to synthesize ZnO nanofibers. The synthesis is carried out with different ratios of zinc acetate (ZnAc) and GO. Scanning electron microscopy (SEM) is used to study the morphology of the nanofibers before and after calcination. Results show that the diameter of nanofibers before and after calcination is in the range of 400–650 and 190–480 nm, respectively. Results also confirm that rGO sheets are very well intermingled with ZnO nanofibers. It appear that the higher the weight fraction of ZnAc, the higher sensitivity to acetone can be attained. The addition of graphene to the ZnO‐based sensor is associated with an increase in the sensitivity of the fabricated sensor from 2.3 to 4 and a significant decrease in the operating temperature of the sensor from 400 to 200 °C.
Joining of stainless steel to carbon steel is widely used in various industries. Resistance spot welding (RSW) is a suitable process for joining steel sheets. Due to the complexity and importance of optimizing the parameters, numerical simulation of this process was considered. In this research, the electrical-thermal-mechanical simulation of RSW of 304 stainless steel to St37 carbon steel was performed using finite element method (FEM). Then, the simulated weld nugget size was compared with the experimental results of optical microscopy (OM). In addition, diffusion of metallic elements of the steels in the molten region was simulated using Fick’s equation and compared with experimental results of energy-dispersive X-ray spectroscopy (EDS). It was shown that diffusion of Cr and Ni through the weld nugget, would make a new stainless steel structure. Microstructure prediction of the heat affected zone (HAZ) was performed using Koistinen–Marburger and Leblond–Devaux equations to predict the percentage of martensite and ferrite-perlite phases during the heating and cooling stages of the specimens from room temperature to the peak temperature and cooling down under the Mf temperature. The results of this simulation were validated by scanning electron microscopy (SEM) images and shear tensile and micro-hardness test results. The simulation results showed that increasing the heat input from 1250 A during 0.5 s to 3750 A during 1.5 s, increases the percentage of martensite, from 40% to 80%, in the HAZ and widens the martensite region.
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