TECHNIQUE 48 Work Cell Design

After processes are documented, they have to become as fast, efficient, and flawless as possible. This means you optimize the processes that generate all the value for your new solution. Several techniques will help you do this, but you should start with Measurement Systems Analysis, because it ensures the validity of any data you use in optimization studies (see the Design of Experiments, and Conjoint Analysis techniques). Then use Work Cell Design and Mistake Proofing to optimize the layout of people, machines, materials, and other factors in an office or factory. 

The steps that follow are a good start, but to take full advantage of work cell design you need to understand more about the principles and practices of Lean—an approach that increases the speed, efficiency, and value of operations while reducing waste in both product and service environments (see Resources in Technique 46). 

Scenario RayRay s House of Hair is a new chain of beauty salons that aims to reduce customer wait and servicing time. Let s see how RayRay uses the Work Cell Design technique to optimize the flow of the hair-cutting process. 

Coupled techniques have increased in popularity in recent years. Electrochemical techniques can be coupled to another characterization method to provide unique information. Many electrochemical techniques lend themselves well to coupling with other electrochemical or nonelectrochemical techniques. With these methods, cell design is often complex to allow simultaneous execution of both techniques. For example, optically transparent indium tin oxide is used as the working electrode with an optically transparent mesh electrode to allow for simultaneous electrochemical conversion and electronic absorption spectroscopy. For some techniques the sample is electrolyzed and then transferred under inert atmosphere for analysis. 

Spectroelectrochemistry has become a valued technique coupling spectroscopy and electrochemistry. Spectroelectrochemistry is a bulk electrochemical technique and as such many of the cell requirements discussed above that pertain to BE apply for spectroelectrochemistry. Often concentrations for spectroelectrochemistry are much lower than most electrochemical techniques due to the spectroscopic absorbance requirements. The bulk solution must still be oxi-dized/reduced in spectroelectrochemistry. Large surface area working and auxiliary electrodes are employed as in the bulk methods described above. Cells designed with optically transparent electrodes like thin films of Sn02 or In203 or optically transparent mesh electrodes are employed, otherwise the electrode must be manually removed to record spectra. Optically transparent electrodes can be constructed such that the solution volume to electrode surface area ratio is very small making the BE occm rapidly. 

Figure 1.3.11 Typical two- and three-electrode cells used in electrochemical experiments, a) Two-electrode cell for polarography. The working electrode is a dropping mercury electrode (capillary) and the N2 inlet tube is for deaeration of the solution. [From L. Meites, Polarographic Techniques, 2nd ed., Wiley-Interscience, New York, 1965, with permission.] (Jb) Three-electrode cell designed for studies with nonaqueous solutions at a platinum-disk working electrode, with provision for attachment to a vacuum line. [Reprinted with permission from A. Demortier and A. J. Bard, /. Am. Chem. Soc., 95, 3495 (1973). Copyright 1973, American Chemical Society.] Three-electrode cells for bulk electrolysis are shown in Figure 11.2.2.

The major sources of dilute, metal ion liquors are identified within the metals production/processing and chemical industries. Problems associated with traditional methods of metal ion removal are highlighted and the developing role of electrochemical techniques is discussed. Electrode and cell reactions are illustrated via typical examples from laboratory and industrial practice. The need to select an appropriate cell design and to control the reaction conditions is emphasised via consideration of the problems caused by secondary reactions. Important design criteria for electrochemical reactors are summarised. Available reactors are classified according to the nature of the product which may be metal flake or powder, a metal deposited onto a disposable substrate, a metal ion concentrate or an insoluble metal compound. The applications for electrochemical techniques in environmental treatment are illustrated by examples which show features of reactor construction and their typical performance. Current trends are summarised and recommendations are made for further work in critical areas. 

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