Electron-based economy

Particularly desirable among film deposition processes are solution-based techniques, because of the relative simplicity and potential economy of these approaches. However, the covalent character of the metal chalcogenides, which provides the benefit of the desired electronic properties (e.g., high electrical mobility), represents an important barrier for solution processing. Several methods have been developed to overcome the solubility problem, including spray deposition, bath-based techniques, and electrochemical routes, each of which will be discussed in later chapters. In this chapter, a very simple dimensional reduction approach will be considered as a means of achieving a convenient solution-based route to film deposition. 

Atom economy is high. As a reagent, no compounds are needed and consequently none are produced as the electron is immaterial. This results in a greater advantage of electrochemical reactions compared to chemical conversions, namely, an effective contribution to pollution control. The direct ET from the electrode to the substrate avoids the problem of separation and waste treatment of the, frequently, toxic end products of chemical reductions or oxidations. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of, for example, sulfuric acid or... 

The environmental impact of waste disposal and of chemical use in Europe has led to three legislative actions that, in today s global economy, greatly affect flame-retardant use and research. These actions go by the acronyms of RoHS (Reduction of Hazardous Substances), WEEE (Waste Electrical and Electronic Equipment), and REACH (Registration, Evaluation, Authorisation, and Restriction of Chemical substances). These actions are discussed in detail in Chapter 22, but need to be mentioned here as they are clear examples of how changing regulations affect flame-retardant use, selection, and new fire-safety developments. The first one, RoHS, refers to how new items are manufactured, and specifically bans chemicals and elements of environmental and toxicological concern in Europe. One fall-out item of RoHS is the move from a lead-based solder on circuit... 

The motivation for constructing the effective Hamiltonian is one of economy and perhaps even of feasibility. It reproduces the eigenstates of the vibronic state of interest but with a much smaller representation than that of the Ml Hamiltonian. The effective Hamiltonian provides a naMal resMg poM in the journey from experiment to theory. It permits data to be Med in an unprejudiced fashion, the parameters being determined by statistical criteria only. These parameters in turn can be interpreted in terms of various theoretical models for the electronic states, and provide a point of comparison for ab initio calculations. A soundly based effective Hamiltonian makes allowance for all possible admixtures of electronic states the relative importance of the perturbations by these different states is determined by a detailed comparison of the parameter values with theoretical predictions. In this way, the task of data fitting is clearly separated from that of theoretical interpretation. 

For example, one criterion is based on heats of adsorption chemisorption has high heats while physical adsorption has low heats. We know of chemisorption phenomena in which the heats of adsorption are probably zero and some that are endothermic. Another criterion is based on rates of adsorption, fast for physical, slow for chemical. There are chemisorption phenomena that are too fast to be measured, and also some physical adsorption phenomena are too slow to be measured. If 1 understand Dr. Hauffe, his criterion would be that physical adsorption does not perturb the electronic economy of the solid while chemisorption does.. Mignolet [Rec. tray, chlm., 74, 685 (1955)] found that noble gases adsorbed on evaporated metal films changed the work function by approximately one volt. 

To see that, let us focus on a couple of factors that mainly determine the economy of the EB remediation process i.e. a high power (by which high volumes of water can be rehabilitated daily), and the efficiency (which establishes the transfer rate ofthe accelerator nominal power into useful energy). To this respect, it is instructive to learn from Table 2 that DC and UHF machines (Chapter 2) best match with these requirements. In the DC type machines, electrons are accelerated by a direct-current field, while in the UHF type, acceleration occurs across an electromagnetic field oscillating at few hundreds MHz. These accelerators achieve high powers coupled with moderately-high efficiencies, and therefore represent the best choice for wastewater treatment. At present, the linear accelerators, which are based on a microwave field, show efficiencies and power below the others, such that they are not suitable for environmental purposes. 

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