Microwave-assisted wet chemical synthesis: advantages, significance, and steps to industrialization

Abstract

Previous research has revealed several advantages from microwave-assisted wet chemical synthesis in reaction acceleration, yield improvement, enhanced physicochemical properties and the evolvement of new material phases. The study present examples that demonstrate the significance of these advantages to industrial application. In order to achieve successful industrial application there is a need to distinguish between the microwave athermal (not excited by heat) effect from the microwave-induced thermal effect (temperature rise). The optimization of this new process has to be systematically investigated, so the advantages and benefits of this new technology can be fully exploited. Advantages and significance ?-Fe 2 O 3 based magnetic materials?-Fe 2 O 3 based magnetic materials have been extensively used as recording materials because of their good magnetic properties. The emergence of nanomagnetic technology has imposed new demands upon magnetic materials. To fabricate ultrahigh density and ultrahigh speed data storage devices, which work on the magnetic -spintronic concept, magnetic materials with nanoscale particles are highly preferred 1 . Conventionally, ? -Fe 2 O 3 powders with monodispersed particles are synthesized first by means of forced hydrolysis of ferric nitrate or ferric chloride in aqueous solutions, which produces α-Fe 2 O 3 , and then the α-Fe 2 O 3 are transformed into ?-Fe 2 O 3 in a high-temperature process 2,3 . To effectively control the particle shape and particle size, which are essential for achieving the desired magnetic properties, the hydrolysis solution must be very dilute. For producing micron-and submicron-sized particles, the concentrations of the ferric irons are generally within a range around 0.02M 2, 4, 5 and for producing nanosized powders, the ferric concentration should be much lower. In addition to dilute solutions, the conventional hydrolysis has to be carefully controlled and it generally requires 2-7 days. This means that, even based upon the shortest processing time and highest concentration, the rate for producing the nanosized iron oxide powders would be less than 0.014 gram per liter per hour. In order to use nanosized magnetic materials for industrial applications, appreciable acceleration of the process and an increase in the ferric concentration are required.Several researchers have attempted the iron oxide synthesis via microwave-assisted hydrolysis. Komarneni et al demonstrated that under otherwise identical processing conditions, synthesis of crystalline hematite by a microwave-hydrothermal approach was 36 times faster than by conventional hydrothermal methods 6 . Our study shows the capability of controlling the particle shape and particle size with this rapid synthesis approach. Rigneau et al further shortened the processing time to 30 minutes and also increased the ferric concentration to 0.05M 7 , which could increase the production rate over one hundred times. The even more striking finding from their results was that the microwave synthesized Fe 2 O 3 p...

Fast and Tunable Synthesis of ZrO2 Nanocrystals: Mechanistic Insights into Precursor Dependence

“…We transferred the conventional solvothermal synthesis of ZrO2 NCs in benzyl alcohol, described by Garnweitner et al 22,28 , to a microwave-assisted solvothermal synthesis to explore if the same results can be obtained in much shorter reaction times.…”

“…We explored if a microwaveassisted solvothermal treatment for ZrO2 NCs results in NCs with identical properties in terms of diameter and crystallinity, yet at much shorter reaction times, since microwaves directly heat the precursor solution, resulting in faster and more homogenous heating. [26][27][28] In the original benzyl alcohol synthesis, zirconium propoxide was used as a precursor to synthesize cubic ZrO2 NCs. However, it has been shown before that the use of different precursor types can lead to different formation reaction mechanisms.…”

Preparation of Selected Ceramic Compounds by Controlled Crystallization Under Hydrothermal Conditions

“…This situation, however, still cannot guarantee successful application of all these technologies to industries. Hence, much effort is needed to obtain a more comprehensive understanding of several physicochemical phenomena related to each of the new technologies hybridizing the conventional hydrothermal synthesis, in order to establish a relationship between science and technology that could lead to optimize these methods for their employment at a industrial scale (Shi & Hwang, 2003).…”

Chemical solution deposition of functional ceramic coatings using ink-jet printing

“…Microwaves directly couple with the precursor solution, resulting in an efficient energy transfer which leads to shorter reaction times. [12] As an example, TEM images of TiO2, ZrO2 and HfO2 nanoparticles synthesized via microwave methods are shown in Fig. 5.…”

“…This leads to a fast supersaturation, fast crystallization and shorter reaction times in comparison to conventional heating. [8][9][10][11][12][13] The as-synthesized nanoparticles can be stabilized in either polar or non-polar solvents, dependent on the processing requirements. [14] These nanoparticles containing inks can be deposited using ink-jet printing at ambient pressure.…”