Athermal effects

The objective of this first part of the book is to explain in a chemically intelligible fashion the physical origin of microwave-matter interactions. After consideration of the history of microwaves, and their position in the electromagnetic spectrum, we will examine the notions of polarization and dielectric loss. The orienting effects of the electric field, and the physical origin of dielectric loss will be analyzed, as will transfers between rotational states and vibrational states within condensed phases. A brief overview of thermodynamic and athermal effects will also be given. 

The essential questions raised by the assumption of athermal or specific effects of microwaves are, then, the change of these characteristic terms (free energy of reaction and of activation) of the reaction studied. Hence, in relation to previous conclusions, five criteria or arguments (in a mathematical sense) relating to the occurrence of microwave athermal effects have been formulated by the author [25], More details can be found in comprehensive papers which analyze and quantify the likelihood of nonthermal effects of microwaves. This paper provides guidelines which clearly define the character of nonthermal effects. 

In conclusion, is it necessary to obtain a microwave athermal effect to justify microwave chemistry Obviously not - it is not necessary to present microwaves effects in a scientific disguise. There are many examples in which microwave heating results in specific time-temperature histories and gradients which cannot be achieved by other means especially for solid materials. Hence, rather than claiming nonther-mal effects it is better to claim a means or a tool which induces a specific thermal history. 

Stuerga, D.A.C. and Gaillard, R, Microwave athermal effects in chemistry a myth s autopsy 2. Orienting effects and thermodynamic consequences of electric field, J. Microw. Power Electromagn. Energy, 1996, 31, 101. 

However, there have been a number of reports of athermal effects in processing ceramic materials, where the sintering rate or the microstructure evolution (grain size and/or porosity) resulting from microwave heating differed from that obtained by a conventional heat treatment at the same temperature. Thus, athermal effects refer to mechanisms that operate in addition to the conventional thermal effects and may be a function of, for example, the electric field intensity or the frequency. 

The origin of confusion between the behavior of a single species and a collection, or the difference between dilute and condensed phases, is the most important problem and the source of illusions within microwave athermal effects. 

After a brief overview of the thermal conversion data (thermal dependence of dielectric properties, electric field focusing effects, hydrodynamics) thermodynamic aspects and athermal effects of electric fields will be examined. Next, the effects of thermal path and hot spots induced by microwave heating will be analyzed in term of kinetic effects. 

In conclusion, is it necessary to obtain a microwave athermal effect to justify mi-... 

In the other case, the preliminary precaution principle was respected regarding the evaluation of risk acceptability. For that, action values of dosimetric quantities Sr or, if need be, Er defined by the Directive (EUPC. 2004) were used. An rmcertainty related to the existence of athermal effects during the exposure to NIEMF was incorporated using the uncertainty factor UF = 10 and an rmcertainty related to the individual differences in sensitivity was incorporated in the form of the uncertainty factor UFsd = 2. 

However, it is possible to draw entirely different conclusions if the preliminary precaution principle is respected with regard to the athermal effects of longterm exposures to NIEMF, even if of imder-limit levels. As a basis for risk assessment a current effective action value of the electric field strength Er was selected here since it better captures the affection of hmnan tissue by NIEMF in comparison with power density. For radar transmitting frequencies, Er = 137Vm is determined. The imcertainties from the sphere of the... 

It always depends on the top-management of an entity which method for risk assessment will be selected. The use of the other method is based on the fact that if action values were derived without NIEMF athermal effects, first of all it should have been proved that these effects don t exist more importantly than to he satisfied only with the statement that the abovemen-tioned effects were not proved on a sufficient level of statistical significance. 

Nevertheless, it is still required first of all to submit quantifiable and reproducible findings with a higher level of statistical reliability including the possibility of their independent confirmation to he capable of considering athermal effects proven and to take them into accoimt when setting hygienic limits (ICNIRP. 1994, ICNIRP. 1998). 

We assiune that if action values are derived without NIEMR athermal effects, first of all, it should be proved that these effects do not exist and not conversely to be satisfied only with the statement that the mentioned effects were not proved reliably. With the existing approach it can be presumed that hygienic limits are defined rather according to the requirements of transnational companies operating information and communications networks. 

Significantly enhanced densification has been reported in plasma sintering for a variety of ceramics but the mechanisms are not clear. In microwave-induced plasma sintering of AI2O3, Su and Johnson (57) found significantly enhanced densification rates when compared to conventional sintering under the same time-temperature schedule. These results indicate that, besides the rapid heating rate achievable in a plasma, an athermal effect caused by the plasma itself also... 

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