Temperature scale current definition

The current definition of the temperature scale is based on one fixed point, the triple point of water. The absolute temperature of that point is defined arbitrarily as 273.16 K exactly. (The triple point of water is that temperature at which pure liquid water is in equilibrium with ice and water vapor.) This definition fixes the size of the kelvin, the degree on the thermodynamic scale. The size of the Celsius degree is defined to be equal to one kelvin exactly and the origin of the Celsius scale of temperature is defined as 273.15 K exactly. 

Figure 7.17 shows a summary of the available conditions of water electrolysis [72]. For each configuration there exists a range of performance. Conventional electrolyzers, which nevertheless are still the most common in the current production of H 2 on the intermediate and small scale, show high overpotential and a relatively small production rate. Membrane (SPE) and advanced alkaline electrolyzers show very similar performance, with somewhat lower overpotential but a much higher production rate. Definite improvements in energy consumption would come from high temperature (steam) electrolysis, which is, however, still far from optimization because of a low production rate and problems of material stability. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

For the optimisation work, the deposition time was increased to 24 h, which would normally give a good indication of the performance at the industrial scale. The previous testing period was so short that the effect of additives could not be properly demonstrated. The level of additives was then included in the optimisation work. Current density was definitely to be tested on a 24-h time period, considering the major impact it had on all responses. A new factor, not tested before, was the catholyte recirculation rate. A new series of optimisation tests with a five level central composite design of experiments was initiated to obtain more precise results on the effects of four factors ([HCl], [TBACl], current density and catholyte recirculation flowrate) on zinc electrowinning. The temperature was fixed at 35°C, the concentration of zinc chloride in solution was maintained at 50 g/L and the concentration of sodium chloride was fixed at 0.25 M. 

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