Synthesis microwaves

The sample absorbs microwave radiation and converts the absorbed electromagnetic radiation to heat that the sample retains. Hence, the sample can be brought to a very high temperature without needing to heat the surroundings. Not all materials absorb microwave radiation. As with any matter-electromagnetic radiation interaction, three possibilities exist. The material can (1) reflect the radiation, (2) transmit the radiation with minimal attenuation, or (3) absorb the radiation. 

The dielectric constant is part of a more complicated parameter, the complex 

The square of the electric field is a measure of how much energy the sample will aborb. At a given frequency, which will determine e, the power absorbed is 

Angelici, R. J. Synthesis and Technique in Inorganic Chemistry, 2nd ed., University Science Books, Mill Valley, CA, 1986, pp. 33-38. 

Bushma, A. I. Krivtsun, I. V. Laser Treat. Mater. (Pap. Eur. Conf.). 1992, 719-23. Cauchetier, M. Musset, E. Luce, M. Herlin, N. Armand, X. Mayne, M. Nanostruct. 

The standard microwave frequency used for synthesis is 2450 MHz. At this frequency, molecular rotation occurs as molecular dipoles or ions try to align with the alternating electric field of the microwave by processes called dipole rotation or ionic conduction [24, 25). On the basis of the Arrhenius equation, (k = g-Ka/j r j the reaction rate constant depends on two factors, the frequency of collisions between molecules that have the correct geometry for a reaction to occur, A, and the fraction of those molecules that have the minimum energy required to overcome the activation energy barrier, 

Although there is some speculation that microwaves can reduce activation energy by dipolar polarization, this has yet to be proven. Microwave energy will affect the temperature of the system, however. In the Arrhenius equation, T measures the average bulk temperature of all components of the system. It is known that for a given temperature the molecules in the system are at a range of temperatures as shown in the Boltzmann equation, F( ) = Because not all compo- 

The N-terminus amine group and the backbone in peptides are polar, which 

Some laboratories have reported that use of simultaneous cooling with micro-wave irradiation leads to improvements in reaction rates compared with micro-waves alone [26-28]. This strategy enables greater amounts of microwave energy to be delivered to a sample while keeping the bulk of the solution at a lower temperature. 

This is not exactly referring to a synthesis procedure, as the role of microwaves (MW) is merely to increase the rate of the solid-solid reaction and the diffusion rate no other difference exists with the conventional ceramic method. 

When using MW, heat energy is directly transferred to the material through the interaction with the electromagnetic field at the molecular level. MW reduce the processing time, but can lead to formation of hot spots, with non-homogeneous temperature profiles. Not all materials are sensitive to micro-waves, but these can heat selectively a given material within a mixture of several components. 

Direct MW irradiation of solid reactants has been used to prepare solids. MW can also be used as an aging source in hydrothermal synthesis (see below). MW heating can also be combined with other synthesis procedures, for instance, with sol-gel procedures to prepare solid oxide fuel cells such as Lai ,Sr ,Fe03+5 and Lai Sr Fe eCoi j,03+5 [6], or in a MW-induced autocombustion to produce LaMnOs [7]. The application of MW to synthesize perovskites has been recently reviewed [8]. MW-assisted synthesis of YBa2Cu307 e can be achieved by 

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Hayes BL (2002) Microwave synthesis chemistry at the speed of light. CEM Publishing, Matthews... 

The feasibility of synthesizing oxovanadium phthalocyanine (VOPc) from vanadium oxide, dicyanobenzene, and ethylene ycol using the microwave synthesis was investigated by comparing reaction temperatures under the microwave irradiations with the same factors of conventional synthesis. The efficiency of microwave synthesis over the conventional synthesis was illustrated by the yield of crude VOPc. Polymorph of VOPc was obtained ttough the acid-treatment and recrystallization step. The VOPos synthesized in various conditions were characterized hy the means of an X-ray dif actometry (XRD), a scanning electron microscopy (SEM), and a transmission electron Microscopy (TEM). 

Fig. 1. The yield of the crude VOPcs obtain at various temperatures for 4 h by (a) conventional and (b) microwave synthesis.

Figs. 2 and 3 shows typical SEM pictures and XRD patterns of crude VOPcs obtained at ISO °C for 4 h in the amventional and microwave synthrais. As shown in Fig. 2, the smaller particle size and nairowra size distribution are obtained in the microwave synthesis, compared to conventional one. From XRD results in Fig. 3, it can be c culated that the crystallite sizes of onde VOPcs obtained by the conventional and microwave synthesis are about 44 nm and 48 nm, respectively. Thus, the tact that particle size is snutller and crystallite size is larger in microwave sample, compared to conventional sample is probably caused by the microwave non-thramal eflfect [3]. 

To prepare the charge generation material of photoreceptor used in xerography, the crude VOPc synthesized at 150 °C for 4 h in the microwave synthesis was acid-treated, and then recrystallized. As shown in Fig. 4, the amorphous VOPc can be obtainol from crude VOPc by acid-treatment and the fine crystal VOPc can he obtained fixim amorphous VOPc by recrystallization. From XRD results, it can be calculated that the crystallite size of fine crystal VOPc is about 18 nm. As shown in Fig. 5, the fine crystal VOPc is well dispersed with uniform size. It indicates that this fine crystal VOPC can be probably used as the chaige generation material of photoreceptor. Thus, further research will be required to measure the electrophotographic properties of fine crystal VOPc. 

The microwave synthesis described in the present paper has proven to be quite eifective due to its intense internal heating, compffl ed to conventional syndesis. The yield of crude VOPc increased with increasing the reaction temperature under both synthetic methods. Fine crystal VOPc was prepared successfiiUy from the crude VOPc obtained by microwave synthesis through the acid-treatment and recrystallization step. 

In this study we show that the Pd/C catalyzed Suzuki-Miyaura coupling reaction can be performed in a microwave oven. Overall the microwave synthesis is faster than comparable thermal methods and the combination of the ease of use of the microwave oven and the facile work-up with Pd/C makes this a very efficient method for performing coupling reactions. 

Doping is important for semiconductors in order to tune their optical and electrical properties for the potential applications in biotechnology and solar cells [65]. Ag-doped hexagonal CdS nanoparticles were successfully obtained by an ultrasound-assisted microwave synthesis method. Here, the doping of Ag in to CdS nanoparticles induced the evolution of crystal structure from cubic to hexagonal. Further support from photocatalytic experiment also clearly indicates the doping of Ag clusters into the CdS matrix. 

A review on microwave synthesis of electrode materials for lithium-ion batteries. Ionics, 15, 765-777. 

Li, Y. and Yang, W. (2008) Microwave synthesis of zeolite membranes a review. Journal ofMemhrance Science, 316, 3-17. 

Nyutu, E.K., Chen, C., Sithambaram, S., Crisostomo, V.M.B. and Suib, S.L. (2008) Systematic control of particle size in rapid open-vessel microwave synthesis of K-OMS-2 nanofibers. Journal of Physical Chemistry C, 112, 6786-6793. 

Keywords Microwave synthesis Mesoporous zeolite Carbon template Sn-MFI Baeyer-Villiger Oxidation... 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

B. L. Hayes, Microwave Synthesis Chemistry at the Speed of Light, CEM Publishing, Matthews, NC, 2002. 

Since the early days of microwave synthesis, the observed rate accelerations and sometimes altered product distributions compared to oil-bath experiments have led to speculation on the existence of so-called specific or non-thermal microwave effects. Historically, such effects were claimed when the outcome of a synthesis per-... 

Another unusual phenomenon in microwave synthesis was described by Ley and coworkers. In several examples [45, 46], the authors found that pulsed microwave... 

The MARS Microwave Synthesis System (Fig. 3.12 and Table 3.2) is based on the related MARS 5 digestion instrument and offers different sets of rotor systems with several vessel designs and sizes for various synthesis applications. 

Table 3.2 MARS Microwave Synthesis System — General Features...

Table 3.4 MARS Microwave Synthesis System - Features of Parallel Pressure Rotors. ...

In modern microwave synthesis, a variety of different processing techniques can be utilized, aided by the availability of diverse types of dedicated microwave reactors. While in the past much interest was focused on, for example, solvent-free reactions under open-vessel conditions [1], it appears that nowadays most of the published examples in the area of controlled microwave-assisted organic synthesis (MAOS) involve the use of organic solvents under sealed-vessel conditions [2] (see Chapters 6 and 7). Despite this fact, a brief summary of alternative processing techniques is presented in the following sections. 

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