Electric field, and microwaves

Figure 1. Drawing showing how static electrical fields and microwave fields interact with the same electronic or ionic charge carriers and electrical dipoles.

Electric fields, and microwave fields, their interaction, 436... 

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. 

Scheme 3.7 The more polar TSn is more stabilized by dipole-dipole interactions with the electric field and therefore more prone to microwave effects.

The rate of phase separation after extraction in AOT-RMs is slow [167]. Keeping this in view, there is a need to study in detail the phase separation kinetics of this reverse micellar system in order to evolve means to enhance the phase separation rate. This is a very important aspect as far as industrial adaptability of RME is concerned, since the slower separation rate may become a bottleneck as in the case of ATPE. One possible approach to enhance phase separation is the application of external fields such as electric, acoustic, and microwave to reverse micellar systems. These are shown to enhance the phase separation rate in the case of ATPE [346-348]. Employing reverse micellar systems which phase separate quickly without the need for any external effort could also be a plausible solution. Some examples of such systems are DTDPA-RMs [237], sugar esters DK-F-110 RMs [239], and NaDEHP-RMs [167,243]. 

When a strongly conducting material (e.g., a metal) is exposed to microwave radiation, microwaves are largely reflected from its surface (Fig. 1.2a). However, the material is not effectively heated by microwaves, in response to the electric field of microwave radiation, electrons move freely on the surface of the material, and the flow of electrons can heat... 

Figure 10.73. Observed Zeeman pattern and theoretical reconstruction for a J = 3/2 —> 3/2 transition in HeAr+, with a rest frequency of 35 092.7 MHz [211]. The magnetic field was 4.85 G, using the TE10 mode with parallel ion beam and microwave propagation, but perpendicular microwave electric field and static magnetic field (AM/ = 1).

Leopold, J.G. and Percival, I.C. (1979). Ionization of highly excited atoms by electric fields III Microwave ionisation and excitation, J. Phys. B12, 709-721. 

Important structural information can be derived by an analysis of the microwave spectra of cyclopropanone along with the isotopic isomers C(1)- C(2) and 2,2-dideuteriocyclo-propanone. The rotational transitions were determined by an analysis of the Stark effect (the shifts and splittings of lines produced by an electric field) and the type of transition observed for cyclopropanone is considered to be consistent with C2 symmetry. The sum of... 

Dipole rotation refers to the alignment, by effect of the electric field, of molecules in the sample that have permanent or induced dipole moments. As the electric field of microwave energy increases, it aligns polarized molecules. As the field decreases, thermally induced disorder is restored. In fact, applied microwave fields cause molecules, on average, to temporarily spend very slightly more time pointing in one direction than in others. Associated with that very small fraction of preferred orientation there is another very small fraction of molecular order imposed and hence a tiny bit of energy. When the... 

The measured electric field wilt rise sharply as free solvent becomes exhausted and the microwaves attempt to couple with the ever-decreasing solvent load (or product load). At this time the temperature may also sharply rise. Therefore, it is imperative to cut back on the amount of microwave energy going into the chamber when the end of the steady state phase is reached. By proper instrumentation of the dryer careful monitoring of the drying process should allow the operator to prevent overheating of the product. The relationship between the electric field and temperature can be determined experimentally on small batches and ultimately be used to control the drying process. 

Electrons moving in both a magnetic and electric field generate microwaves. 

Physical agents in the environment that may cause illness include solar ultraviolet (UV) radiation, ionizing radiation (produced by radioactive materials and X-rays), extreme temperatures, noise, vibrations, and particulates. The most famous particulates inducing adverse health effects include asbestos and silica dust. Other physical agents, such as electric or magnetic fields and microwaves, may also cause adverse health effects, but there is of yet not enough solid evidence to support or refute this hypothesis. 

Molecules that have a permanent dipole moment (e.g., water) can rotate in a fast changing electric field of microwave radiation. Additionally, in substances where free ions or ionic species are present the energy is also transferred by the ionic motion in an oscillating microwave field. Owing to both these mechanisms the substance is heated directly and almost evenly. Heating with microwaves is therefore fundamentally different from conventional heating by conduction. The magnitude of this effect depends on dielectric properties of the substance to be heated. 

A plasma is an efficient way to dissociate gas molecules to produce non-equilibnum concentrations of gas-phase species, such as the high concentrations of atomic hydrogen needed for diamond growth. Plasmas can be generated by a number of energy sources (microwave, radio-frequency, or direct-current electric fields), and can be either cold (non-isothermal, or nonequilibrium plasmas) or hot (isothermal, or equilibrium plasmas). The major characteristics of these plasmas are summarized in Table 3. 

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