Protocols for High Temperature Assisted-Microwave Preparation of Inorganic Compounds

Abstract

Assisted microwave heating involves the use of a susceptor to initially heat up reactants in a microwave reaction. Once hot, the reactants themselves become directly susceptible to microwave heating, and interdiffuse to form products. Assisted-microwave methods are appealing for a wide variety of high-temperature solid-state reactions, reaching reaction temperatures of 1500 • C and more. Among the many advantages are that the direct volumetric heating associated with microwaves allows for rapid reaction times while employing significantly less energy than conventional furnace-based preparation. Shorter reaction times and selective heating permit volatile reactants to be incorporated stoichiometrically in the product. Undesirable reactions with containers or enclosures are also minimized. The morphology of powders obtained through microwave reactions are also more uniform and comprise smaller particles than obtained conventionally. This Methods/Protocols article is presented as a user manual for carrying out assisted-microwave preparation of bulk complex oxides in air or reducing atmospheres, sol-gel based processing of complex oxides, air sensitive intermetallics, and transition metal chalcogenides.

On the underestimated influence of synthetic conditions in solid ionic conductors

“…Furthermore, the technique can heat samples fairly homogeneously, whereas a thermal gradient from the sample surface to the interior exists in classic solid-state syntheses, resulting in inhomogeneous heating. 143 For more detail on the mechanistic understanding of microwave methods in solid-state syntheses, we refer the readers to recent summaries by Kitchen et al, 152 Levin et al, 153 and Bhattacharya et al 154 The rst few successful uses of microwave-assisted synthesis for solid electrolytes have been demonstrated with Li-ion conducting oxides. Amores et al synthesized Li + conducting garnets (Li 6.5 Al 0.25 La 2.92 Zr 2 O 12 ) with a microwave method for the rst time in 2016.…”

“…Fig.5(a) Schematic of the heating profile of microwave (MW) susceptors, insulators, and the materials possessing critical temperature (T crit ) where the microwaves start coupling with the target sample 153. (b and c) show schematics of heating mechanisms of microwave-assisted synthesis.…”

Microwaves and Heterogeneous Catalysis: A Review on Selected Catalytic Processes

“…Almost simultaneously, Sheppard studied the microwave absorption by aluminosilicate gels, in which microwave energy was used for heating and sintering ceramics as well as in the fabrication of high-silica quartz fibers [38]. Microwave-assisted catalysts preparation is realizable with microwave susceptible materials; the materials are rapidly and homogeneously heated to enter into a reaction [39]. The susceptor may be the material that reacts, alternatively it is possible to use another material, inert towards the reaction, but susceptible to microwaves [40], such as silicon carbide [41] or activated carbon [42].…”

Investigation of the Thermal Properties of Electrodes on the Film and Its Heating Behavior Induced by Microwave Irradiation in Mounting Processes

“…(c) MW absorbers (high loss insulator such as dielectric materials); they take up the energy from the MW field and get heated up rapidly [14,17,18]. So far, MW dielectric heating has been used for inorganic/organic syntheses [19][20][21] and metal nanoparticle synthesis [22,23]. Bulk metals cannot be heated by an electric field because the spark phenomenon occurs as follows.…”

“…Due to low eddy current, which is induced by low magnetic field intensity, the generation of Joule heat is also low. Therefore, the △T (1,(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) would be also low. Figure 6 and Table S1 show the temperature difference ( T) between initial temperature (T 0 ) and arrived temperature (T) of the samples by the induction soldering of MW and T, as defined in the below equation:…”