This paper presents an analytical solution to predict the transient temperature distribution in fillet arc welding, including the effect of the molten metal generated from the electrode. The analytical solution is obtained by solving a transient three-dimensional heat conduction equation with convection boundary conditions on the surfaces of an infinite plate with finite thickness, and mapping an infinite plate on to the fillet weld geometry, including the molten metal with energy equation. The electric arc heat input on the fillet weld and on the infinite plate is assumed to have a travelling bivariate Gaussian distribution. To check the validity of the solution, flux cored arc (FCA) welding experiments were performed under various welding conditions. The actual isotherms of the weldment cross-sections at various distances from the arc start point are compared with those of the simulation result. As the result shows a good accuracy, this analytical solution can be used to predict the transient temperature distribution in the fillet weld of finite thickness under a moving bivariate Gaussian distributed heat source. The simplicity and short calculation time of the analytical solution provides the rationale for using the analytical solution to model the welding control systems or to obtain an optimization tool for welding process parameters.
The influence of the phase shift between rf voltages applied to the powered electrodes on plasma parameters and etch characteristics was studied in a very high-frequency ͑VHF͒ capacitively coupled plasma ͑CCP͒ triode reactor. rf voltages at 100 MHz were simultaneously applied to the top and bottom electrodes having a controlled phase shift between them, which could be varied between 0°and 360°. Several plasma and process characteristics were measured as a function of the phase shift: ͑i͒ radial profiles of plasma-emission intensity, ͑ii͒ line-of-sight averaged plasma-emission intensity, and ͑iii͒ radial profiles of blanket SiO 2 etching rate over a 300 mm wafer. Radial profiles of plasma emission were obtained using the scanning optical probe. It has been shown that all the measured characteristics strongly depend on the phase shift: ͑i͒ plasma-emission intensity is minimal at phase shift equal to 0°and maximal at 180°for all radial positions, while the emission radial profile changes from bell-shaped distribution with considerable nonuniformity at 0°to a much more flattened distribution at 180°; ͑ii͒ line-of-sight averaged plasma-emission intensity shows a similar dependence on the phase shift with minimum and maximum at 0°and 180°, respectively; and ͑iii͒ the etch-rate radial profile at 180°shows a much better uniformity as compared to that at 0°. Some of these results can be qualitatively explained by the redistribution of plasma currents that flow between the electrodes and also from the electrodes to the grounded wall with the phase shift. We suggest that the phase-shift effect can be used to improve the plasma and etch-rate spatial uniformity in VHF-CCP triode reactors.
Electrocatalysts
with dramatically enhanced water splitting efficiency,
derived from controlled structures, phase transitions, functional
activation, etc., have been developed recently. Herein,
we report an in situ observation of graphene-based
self-healing, in which this functional activation is induced by a
redox reaction. Specifically, graphene on stainless steel (SUS) switches
between graphene (C–C) and graphene oxide (C–O) coordination
via an electrical redox reaction to activate water splitting. A heterostructure
comprising Pt-NiO thin films on single-layer graphene directly grown
on a SUS substrate (Pt-NiO/Gr-SUS) was also synthesized by electrodeposition.
Pt-NiO/Gr-SUS exhibited water splitting activity with low Pt loading
(<1 wt %). The findings provide valuable insight for designing
robust electrodes based on reversible redox-induced self-healable
graphene to develop more efficient catalysts.
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