Potential control difficulties

These remarks must be balanced by some characteristic difficulties of using the electrochemical path. Sometimes, and in spite of tight potential control, two or more reactions take place at the same time and give not one product but a mixture. Correspondingly, overoxidation may occur the intended oxidation may continue to a further step by means of a chemical driving force outside the control of the potentiostat. 

Potential Technical Difficulties in Applying Lipoxygenases for the Controlled Blogeneratlon of Fresh Fish Aromas... 

Emersion of the electrode in transfer systems has relied on either the use of a completely volatile electrolyte (normally aqueous HF [17, 19]) whose residue adhering to the electrode can be pumped off, or a washing procedure in which the electrolyte is replaced by the (volatile) solvent [14]. In either case, it is necessary to consider what processes can occur as potential control is lost when the electrode breaks contact with the solution. The resistance measurements mentioned above suggest that no substantial changes occur provided that no faradaic processes are possible. Traces of oxygen in the ambient gas above the electrolyte can also cause oxidation of surface species and great care is essential to use purified gas when the surface species are susceptible. For example, sub-monolayer deposits of non-noble metallic atoms are readily oxidized and so are observable ex-situ with difficulty [42],... 

The foregoing sections have outlined the principles of potential control. Here we examine some of the difficulties that can arise in measurements with real systems. 

Another difference between classical electrochemistry and electrochemical engineering lies in the size of the electrode. Conventional electrochemistry most commonly employs micro electrodes of well defined area operating under carefully controlled current and mass transfer conditions. Conversely, electrochemical engineering typically employs large surface area electrodes, where, moreover, the surface area and electrode activity varies constantly as metal is deposited. In addition, there are usually difficulties in maintaining uniform potential control and current distribution over the electrode surface. It is also necessary to consider the reverse stripping process of recovering the metal after collection. 

It is important that the formaldehyde addition rate be balanced with the alkali content of the system and the engineering control capability. At high alkali contents, the exotherm will be more vigorous and create more load on the heat exchangers. At low alkali contents, the reaction rate may be quite slow. While this temporarily reduces the difficulty in instantaneous heat load, it may permit potentially hazardous levels of unreacted formaldehyde to accumulate. Such accumulations could become dangerous as batch temperature rises. In both cases. 

The sometimes contradictory results from different workers in relation to the elements mentioned above extends to other elements . Some of these differences probably arise from variations in test methods, differences in the amounts of alloying additions made, variations in the amounts of other elements in the steel and the differing structural conditions of the latter. Moreover, the tests were mostly conducted at the free corrosion potential, and that can introduce further variability between apparently similar experiments. In an attempt to overcome some of these difficulties, slow strain-rate tests were conducted on some 45 annealed steels at various controlled potentials in three very different cracking environments since, if macroscopic... 

Continuous conductivity measurement controlled with the electrode placed in the boiler. This method is not recommended because of potential safety and liability issues. In addition, there are difficulties with cleaning and maintaining the electrode, and the intense heat to which the electrode is constantly subjected may cause failure. FT boiler installations generally provide for the electrode to be placed above the first set of tubes but 4 to 6 inches below the waterline. 

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