Oxidizing compounds physical techniques

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

Among the physical techniques, reactive sputtering is used most frequently because it produces films of high purity with relative ease and good reproducibility. In addition, many compound types can be prepared (carbides, nitrides, oxides, carbonitrides, oxicarbonitrides) including metastable phases. 

There are many other kinds of reactive intermediates, which do not fit into the previous classifications. Some are simply compounds that are unstable for various possible reasons, such as structural strain or an unusual oxidation state, and are discussed in Chapter 7. This book is concerned with the chemistry of carbocations, carbanions, radicals, carbenes, nitrenes (the nitrogen analogs of carbenes), and miscellaneous intermediates such as arynes, ortho-quinone methides, zwitterions and dipoles, anti-aromatic systems, and tetrahedral intermediates. This is not the place to describe in detail the experimental basis on which the involvement of reactive intermediates in specific reactions has been estabhshed but it is appropriate to mention briefly the sort of evidence that has been found useful in this respect. Transition states have no real hfetime, and there are no physical techniques by which they can be directly characterized. Probably one of the most direct ways in which reactive intermediates can be inferred in a particular reaction is by a kinetic study. Trapping the intermediate with an appropriate reagent can also be very valuable, particularly if it can be shown that the same products are produced in the same ratios when the same postulated intermediate is formed from different precursors. 

Other techniques include oxidative, steam atmosphere (33), and molten salt (34) pyrolyses. In a partial-air atmosphere, mbber pyrolysis is an exothermic reaction. The reaction rate and ratio of pyrolytic filler to ok products are controlled by the oxygen flow rate. Pyrolysis in a steam atmosphere gives a cleaner char with a greater surface area than char pyroly2ed in an inert atmosphere however, the physical properties of the cured compounded mbber are inferior. Because of the greater surface area, this pyrolytic filler could be used as activated carbon, but production costs are prohibitive. Molten salt baths produce pyroly2ed char and ok products from tine chips. The product characteristics and quantities depend on the salt used. Recovery of char from the molten salt is difficult. 

Inorganic Compounds. Inorganic selenium compounds are similar to those of sulfur and tellurium. The most important inorganic compounds are the selenides, haUdes, oxides, and oxyacids. Selenium oxidation states are —2, 0, +1, +2, +4, and +6. Detailed descriptions of the compounds, techniques, and methods of preparation, and references to original work are available (1—3,5,6—10, 51—54). Some important physical properties of inorganic selenium compounds are Hsted in Table 3. 

Elemental composition Sn 78.77%, 0 21.23%. Tin(IV) oxide can be identified by physical properties and x-ray diffraction. Tin content may be determined by various instrumental techniques in an acid solution of the oxide (See Tin). The compound is solubilized by digestion with nitric acid or aqua regia and diluted appropriately. 

Manoyl oxide (4), Fig. (7), has been isolated as a pure compound or identified via analytical techniques, in several plant species [33,44,63,137, 138,139]. Ohloff has shown that manoyl oxide can be prepared from sclareol [140]. The physical and chromatographic data of the synthetic and of the natural manoyl oxides have been compared and discussed [141]. Hodges and Reed have substantially contributed to the knowledge of the stereochemistry of manoyl oxide [141]. 

HPLC-based electrochemical detection (HPLC-ECD) is very sensitive for those compounds that can be oxidized or reduced at low voltage potentials. Spectrophotometric-based HPLC techniques (UV absorption, fluorescence) measure a physical property of the molecule. Electrochemical detection, however, measures a compound by actually changing it chemically. The electrochemical detector (ECD) is becoming increasingly important for the determination of very small amounts of phenolics, for it provides enhanced sensitivity and selectivity. It has been applied in the detection of phenolic compounds in beer (28-30), wine (31), beverages (32), and olive oils (33). This procedure involves the separation of sample constituents by liquid chromatography prior to their oxidation at a glassy carbon electrode in a thin-layer electrochemical cell. 

The difficulties created by stopcocks and valves can usually be minimized. However, it is occasionally necessary to completely eliminate these sources of leakage and contamination by the use of break-seals and vacuum seal-offs. Typical situations in which sealed tube techniques are widely used are quantitative hydrolysis and oxidation reactions which require elevated pressures and temperatures, precise physical measurements on highly reactive organometallic compounds, long-term storage of reactive samples, and nonaqueous reactions under high pressure (for example, SO2 or NH3 at room temperature). Each piece of apparatus must be constructed to meet a specific need, so it is not possible to outline an apparatus which is of general use. Nevertheless, several examples will be presented here which serve to indicate the approach. 

Chemical/physical treatment processes are those in which a chemical reaction is used to alter or destroy a hazardous waste component. Chemical treatment techniques can be applied to both organic and inorganic wastes, and may be formulated to address specific target compounds in a mixed waste. Typical chemical treatment processes include oxidation-reduction reactions such as ozonation, alkaline chlorination, electrolytic oxidation and chemical dechlorination. Physical treatment processes separate waste component by either applying physical force or changing the physical form of the waste. Various physical processes include adsorption, distillation, or filtration. Physical treatment is applicable to a wide variety of waste streams but further treatment is usually required. 

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