Microwaves energy considerations

With conductive heating, several factors militate against efficient distillation. Transferal of heat to the liquid usually occurs from the inner surfaces of the vessel. Vaporization from the surface and convection preclude a uniform temperature within the liquid. To achieve distillation under those circumstances, the pot temperature must be considerably higher than that of the distillate. With microwaves, energy is absorbed more uniformly, a larger volume of the sample in the pot is heated simultaneously, convection is reduced and distillation is more rapid. 

On the other hand, solvents usually show a decrease in dielectric constant with temperature. Efficiency of microwave absorption diminishes with temperature rise and can lead to poor matching of the microwave load, particularly as fluids approach the supercritical state. Solvents and reaction temperatures should be selected with these considerations in mind, as excess input microwave energy can lead to arcing. If allowed to continue unchecked, arcing could result in vessel rupture or perhaps an explosion, if flammable compounds are involved. Therefore it is important in microwave-assisted organic reactions, that the forward and reverse power can be monitored and the energy input be reduced (or the load matching device adjusted) if the reflected power becomes appreciable. 

Energy Considerations Microwaves, Ultrasound, Electricity and Light... 

Microwave-assisted sample digestion has its own safety requirements. As a result of the direct energy absorption and rapid heating, microwave techniques introduce unique safety considerations that are not encountered in other methods. Differences in conditions between traditional laboratory practices and microwave-implemented methods should be examined before microwave energy is used to heat reagents or samples. An excellent suimnary of this aspects is given in the literature [18, 19, 175]. 

Nickel-mesoporous silicon structures are of considerable industrial interest for various applications. Anisotropy of magnetic properties of the nickel nanowires inside porous silicon conditioned by their high aspect ratio is applicable for the magnetic store production [1], Moreover, these structures offer much promise for the rectenna (a special type of antenna that is used to directly convert microwave energy into DC electricity) fabrication. So, it is of value to study in detail the process of the nickel electrodeposition into pores of porous silicon and elaborate control methods for pore filling with metal. 

Illite, a mineral that forms in alkaline solutions (15), is more stable than kaolinite in 30% NaOH. The experiments (Table II) in which illite was reacted either at room temperature or at 105 C with 30% NaOH showed that no discernible reaction took place. In the microwave irradiated experiments, however, considerable changes occurred. Illite strongly absorbed the microwave energy, causing considerable heating of the sample. When illite was irradiated for... 

However, most cosmetic samples require a pretreatment like complete acid digestion or leaching of the analytes, which may or may not be relatively difficult depending on how efficiently the analytes are extracted from the matrix. Microwave energy permits rapid heating of samples, which considerably reduces pretreatment time. For example, heavy metals have been determined in some cosmetics (lipsticks, powders) using different atomic spectroscopic techniques after acid treatment assisted by micro-wave irradiation. 

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