Optimizing Bi2O3 and TiO2 to achieve the maximum non-linear electrical property of ZnO low voltage varistor

In fabrication of ZnO-based low voltage varistor, Bi2O3 and TiO2 have been used as former and grain growth enhancer factors respectively. Therefore, the molar ratio of the factors is quit important in the fabrication. In this paper, modeling and optimization of Bi2O3 and TiO2 was carried out by response surface methodology to achieve maximized electrical properties. The fabrication was planned by central composite design using two variables and one response. To obtain actual responses, the design was performed in laboratory by the conventional methods of ceramics fabrication. The actual responses were fitted into a valid second order algebraic polynomial equation. Then the quadratic model was suggested by response surface methodology. The model was validated by analysis of variance which provided several evidences such as high F-value (153.6), very low P-value (<0.0001), adjusted R-squared (0.985) and predicted R-squared (0.947). Moreover, the lack of fit was not significant which means the model was significant

Response surface methodology for optimization of sintering process for preparation of ZnO low voltage varistor

Optimization of variables in order to maximize an electrical non-linear coefficient (α) of varistor ceramics by traditional method is a daunting and time-consuming task. The objectives of the present work are optimization of sintering temperature and holding time as input variables, and secondly the cooling and heating rates of the sintering process in order to maximize an electrical non-linear coefficient (α) of varistor ceramics. It was achieved by designing the varistor ceramic fabrication using the central composite design (CCD) of four levels of variables, sintering temperature, holding time, cooling rate and heating rate, and a response. Then the varistor ceramics was fabricated in laboratory according to the design to achive actual responses, α. The responses were used for modeling in optimizing the above factors by response surface methodology (RSM). The actual responses were fitted into a valid second order algebraic polynomial equation as quadratic model. The quadratic model was suggested to investigate by analysis of variance (ANOVA) based on some statistical conformation such as lowest standard deviation, P-value, PRESS and the highest Radj, Rpred values. The validated model optimized the above factors by either canonical equation or by 3D plots as optimum point on the surface area. Results indicated that the maximum electric property of the varistor was at temperature 1260°C and holding time of 60 minutes that maximized the nonlinear value around 13. Also, the optimum area is around 5.5 for both cooling rate and heating rate which the maximum α was around 12. Moreover, the model suggested a high desirable solution in special condition to predict the optimum amount of the factors. The condition was including minimum standard error and maximum nonlinearity. The predicted solution included standard error, 0.096, sintering temperature, 1253°C, holding time, 53 min, and α, 11.2. The optimized sample tested by further experiments confirmed that the obtained α value (11) was very close the model predicted value. Then this information was used in optimizing the cooling and heating rates and the predicted solution has standard error of 0.038, cooling rate of 4.65, heating rates of 4.8, and α value of 10.96. The optimized sample tested by experiments, confirmed that the obtained α value is 11.4 was very close the model predicted value. Therefore, RSM was succeeded in modeling of the sintering profile in fabrication of zinc oxide based low voltage varistor

Functionalized cellulose beads with activated carbon Fe3O4/CoFe2O4 for cationic dye removal

Modified regenerated cellulose beads functionalized with activated carbon (AC), as well as magnetic cellulose beads of AC-Fe3O4 and AC-CoFe2O4, were synthesized. The AC was further used as adsorbent for the removal of cationic methylene blue (MB) dye from aqueous solution. The magnetic cellulose beads possessed a high magnetic response to an external magnetic field and their ease of recovery could be facilitated with the aid of a magnetic field. The synthesized adsorbents were characterized using a Field Emission Scanning Electron Microscope (FESEM), as well as by energy dispersive X-ray (EDX) spectrometry and thermogravimetric analysis (TGA). In comparison with the synthesized magnetic cellulose beads, the maximum adsorption capacity of the adsorbent beads assisted with AC, AC-Fe3O4 and AC-CoFe2O4 was of 54, 53 and 50 mg/g, respectively. The kinetic study of the adsorption of MB dye onto the adsorbents was performed at different parameters (initial dye concentration and temperature). The kinetics of the adsorption fit well with the pseudo-second-order model. © 2019 Editura Academiei Romane. All rights reserved

Optimization of Bi2O3, TiO2, and Sb2O3 doped ZnO-based low-voltage varistor ceramic to maximize nonlinear electrical properties

In ZnO-based low voltage varistor, the two essential features of microstructure determining its nonlinear response are the formation Bi-enriched active grain boundaries as well as a controlled ZnO grain size by secondary spinel-type phases. Besides, the microstructure and phase composition are strongly affected by the dopant concentration during sintering process. In this study, the optimal dopant levels of Bi2O3, TiO2, and Sb2O3 to achieve maximized nonlinear electrical property (alpha) were quantified by the response surface methodology (RSM). RSM was also used to understand the significance and interaction of the factors affecting the response. Variables were determined as the molar ratio of Bi2O3, TiO2, and Sb2O3. The alpha was chosen as response in the study. The 5-level-3-factor central composite design, with 20 runs, was used to conduct the experiments by ball milling method. A quadratic model was established as a functional relationship between three independent variables and alpha. According to the results, the optimum values of Bi2O3, TiO2, and Sb2O3 were obtained 0.52, 0.50, and 0.30, respectively. Under optimal conditions the predicted alpha (9.47) was calculated using optimal coded values from the model and the theoretical value is in good agreement with the value (9.43) obtained by confirmation experiment

Effect of Temperature, Syngas Space Velocity and Catalyst Stability of Co-Mn/CNT Bimetallic Catalyst on Fischer Tropsch Synthesis Performance

The effect of reaction temperature, syngas space velocity, and catalyst stability on Fischer-Tropsch reaction was investigated using a fixed-bed microreactor. Cobalt and Manganese bimetallic catalysts on carbon nanotubes (CNT) support (Co-Mn/CNT) were synthesized via the strong electrostatic adsorption (SEA) method. For testing the performance of the catalyst, Co-Mn/CNT catalysts with four different manganese percentages (0, 5, 10, 15, and 20%) were synthesized. Synthesized catalysts were then analyzed by TEM, FESEM, atomic absorption spectrometry (AAS), and zeta potential sizer. In this study, the temperature was varied from 200 to 280 °C and syngas space velocity was varied from 0.5 to 4.5 L/g.h. Results showed an increasing reaction temperature from 200 °C to 280 °C with reaction pressure of 20 atm, the Space velocity of 2.5 L/h.g and H2/CO ratio of 2, lead to the rise of CO % conversion from 59.5% to 88.2% and an increase for C5+ selectivity from 83.2% to 85.8%. When compared to the other catalyst formulation, the catalyst sample with 95% cobalt and 5% manganese on CNT support (95Co5Mn/CNT) performed more stable for 48 h on stream

Effect of Pressure, H2/CO Ratio and Reduction Conditions on Co–Mn/CNT Bimetallic Catalyst Performance in Fischer–Tropsch Reaction

The effects of process conditions on Fischer&ndash;Tropsch Synthesis (FTS) product distributions were studied using a fixed-bed microreactor and a Co&ndash;Mn/CNT catalyst. Cobalt and Manganese, supported on Carbon Nanotubes (CNT) catalyst were prepared by a Strong Electrostatic Adsorption (SEA) method. CNT supports were initially acid and thermally treated in order to functionalize support to uptake more Co clusters. Catalyst samples were characterized by Transmitted Electron Microscope (TEM), particle size analyzer, and Thermal Gravimetric Analysis (TGA). TEM images showed catalyst metal particle intake on CNT support with different Co and Mn loading percentage. Performance test of Co&ndash;Mn/CNT in Fischer&ndash;Tropsch synthesis (FTS) was carried out in a fixed-bed micro-reactor at different pressures (from 1 atm to 25 atm), H2/CO ratio (0.5&ndash;2.5), and reduction temperature and duration. The reactor was connected to the online Gas Chromatograph (GC) for product analysis. It was found that the reaction conditions have the dominant effect on product selectivity. Cobalt catalyst supported on acid and thermal pre-treated CNT at optimum reaction condition resulted in CO conversion of 58.7% and C5+ selectivity of 59.1%