Microwave heating is now an established method for stimulating chemical reactions. For chemists it provides drastically reduced reaction times, the potential for higher yields and a simple, clean and efficient alternative to traditional heating methods.
Shorter reaction times are a well-documented advantage of using microwave energy to heat samples. In addition to reducing the reaction times themselves, the set-up times are often shorter, there is no delay in waiting for heaters to reach a specified temperature and the reactants can reach the required temperature in seconds. Compared with traditional heating blocks or hot plates, microwave irradiation can reduce reaction times from hours to minutes, or even seconds - allowing you to do more reactions in a fraction of the time, and often with a better yield.
All readily available commercial laboratory systems operate at the standard 2.45GHz frequency. Many academic and industrial chemists have been searching for a cost-effective, low power, higher frequency microwave source, but without significant investment and custom development there simply isn't anything available.
Working closely with leading Microwave Chemistry expert Dr Gavin Whittaker, of Tan Delta Microwaves, Emblation can offer turnkey solutions at 915MHz, 2.45GHz, 5.8GHz and 8GHz to meet the demand and requirement for novel, economical organic synthesis apparatus.
There is an almost infinite variety of applications available to chemists when considering microwave chemistry. As in any field of conventional synthetic chemistry, the reactions may take place in open or closed vessels or in flow systems; at elevated or reduced pressure; and under any chosen atmosphere. It is impossible to describe all the possible chemical applications in a brief overview, but example areas are:
The popularisation and widespread growth of microwave induced chemistry started with organic reactions, and microwave reactors are commonplace in synthetic organic laboratories. Microwave heating has provided a clean, efficient and fast alternative to conventional heating methods, and with high intensity microwave fields in modern applicators, there is seldom any need to change the preferred conditions to polar solvents. Microwaves may heat up samples far faster than conventional heating, allowing novel kinetic pathways to be exploited and leading directly to shorter reaction times.
These are examples of areas of chemistry that have so far underexploited the use of microwave heating, despite a number of interesting and novel results. The ready availability and fast creation of hydrothermal reaction conditions in microwave reactors, for example, has permitted the synthesis of numerous polymetallic complexes at rates far in excess of those seen using conventional hydrothermal methods.
With more convincing evidence for microwave specific effects than in any other area of chemistry, microwave-induced solid state chemistry remains an interesting area of research. Because solid state reactions rely on thermal conduction to get energy to the core of a sample, it is an area that strongly benefits from the direct volumetric heating that characterises microwave heating. It is even possible to exploit the different microwave properties of the components in inhomogeneous mixtures to heat components in the sample at different rates.
The properties of nanomaterials are intimately linked with their physical dimensions and morphology. Their successful production is therefore critically linked to temperature homogeneity within the reactant materials; small temperature differences within the reactants lead to differing growth rates and lead to an undesirable increase in the product particle size distribution (PSD). The direct, volumetric, heating that results from microwave irradiation can readily generate homogeneous temperature profiles, even in the absence of unwanted agitation or stirring of the reaction solution. Microwave heating in these syntheses therefore leads to a better, controllable, PSD within the product, and better-defined product properties.
The availability of a source operating at a higher frequency such as 5.8GHz or 8GHz affords chemists the opportunity to take advantage of higher microwave frequency effects and to investigate novel chemical processing regimes. In most common solvents, for example, the penetration depths at higher frequencies are normally much shorter than at 2.45GHz. As a result, it is possible to impart greater energies into small volumes, and this is particularly important where small, but valuable, samples are being used in miniature vessels. The consequence of this, and other effects, is up to 4 fold increases in yields when compared to 2.45GHz or oil bath heating under otherwise equivalent conditions.