Intermittent microwave heating

Intermittent microwave heating has been used for enhancing FISH signals in the paraffin-embedded tissue sections of gastrointestinal neoplasia (see page 458) (Kitayama et al., 2000). The processing of these tumors is known to be particularly difficult because of the presence of necrosis and contamination with inflammatory and normal stroma cells and poor attachment of paraffin sections to the slide. 

In recent years, tungsten carbide was reported as a Pt support for PEFC cathode [63, 64]. Nie et al. prepared Pt on a tungsten carbide nanocrystalline support (Pt-WC/C) by the direct reduction of a platinum salt precursor combined with intermittent microwave heating [64]. The Pt-WC/C catalyst showed the onset potential for the ORR of 1.05 V vs. SHE, which was over 150 mV more positive compared to that of a commercial Pt/C. Zhu and coworkers also synthesized tungsten carbide-modified mesoporous carbon with uniform dispersion of Pt nanoparticles [63]. Both an enhanced thermal stability and a good electrochemical stability were observed. It might be necessary to pay attention to the stability of these materials. More details can be found in Chap. 24. 

Moreover, Yin et al. [57] developed WC on carbon surface by intermittent microwave heating method to support other Pt-free catalyst, such as Pd-Fe (catalyst noted as Pd-Fe/WC/C). According to TEM images, a good dispersion was obtained with particle sizes in the range of 4 nm for Pd-Fe/WC/C and 2.8 nm for the... 

Shen s group focused on flie studies of the Pt-free catalysts preparation and the effect of the CL structure on fuel eell performance. They developed oxide-promoted Pd catalysts prepared by a novel intermittent microwave heating technique [56, 96, 97]. All flie oxide-Pd catalysts on carbon showed higher catalytic activities than those of Pt/C or Pt-Ru/C catalysts. The Pd-NiO/C eatalyst... 

In a typical experiment, benzaldehyde (106 mg, 1 mmol) was added to the finely powdered paraformaldehyde (60 mg, 2 mmol). To this mixture, powdered barium hydroxide octahydrate (631 mg, 2 mmol) was added in a glass test tube and the reaction mixture was placed in an alumina bath (neutral alumina 125 g, mesh 150, Aldrich bath 5.7 cm diameter) inside a household microwave oven and irradiated for the specified time at its full power of 900 W intermittently or heated in an oil bath at 100-110 °C. On completion of the reaction, as indicated by TLC (hexane-EtOAc, 4 1, v/v), the reaction mixture was neutralized with dilute HC1 and the product extracted into ethyl acetate. The combined organic extracts were dried over anhydrous sodium sulfate and the solvent removed under reduced pressure. The pure benzyl alcohol (99 mg, 91%), however, is obtained by extracting the reaction mixture with ethyl acetate prior to neutralization and subsequent removal of the solvent under reduced pressure. 

In an utmost simplistic approach, an unmodified household microwave oven has been used in this study with excellent results and the generation of higher temperatures is simply avoided by intermittent heating [35]. 

Microwave-expedited condensation reactions using montmorillonite KIO clay or Envirocat reagent, EPZG , have yielded a rapid synthesis of imines and enamines via the reactions of primary and secondary amines with aldehydes and ketones, respectively (Scheme 2.2-32) [97,98]. In these reactions, the generation of polar transition-state intermediates that readily couple to microwaves is probably responsible for the rapid imine or enamine formation. The use of a MW oven at lower power levels or intermittent heating has been used to prevent the loss of low-boi-Hng reactants. 

Use of superheated steam in direct dryers Increased use of indirect (conduction) heating Use of combined (or integrated) heat transfer modes Use of volumetric heating (microwave [MW]/radio-frequency [RF] fields) in specialized situations Use of two-stage (or multistage) dryers Use of intermittent heat transfer Use of novel combnstion technologies (e.g., pulse combustion for flash drying)... 

The main drawback of the methods usually employed to produce chitosan is that they involve long processing times and expend large amounts of alkali. In order to overcome this, a number of unconventional deacetylation methods, such as thermomechanical processes using a cascade reactor operating under alkali conditions [22], flash treatment undo" saturated steam [23], microwave dielectric heating [14] and intermittent water washings [ 17], have been developed... 

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