A typical scientific MW apparatus normally works at a frequency of 2.45 GHz. It consists of a magnetron that generates the MW and introduces it into the cavity, where samples to be treated are placed. Figure 6.1 shows the typical apparatus for MW experiments (Ethos, Milestone Co. Ltd.). The MW power is programmable from 0 to 1000 W. In this apparatus, the temperature, time, and MW power output can be monitored and automatically controlled.

The reactors being used in the experiments are usually made of MW transparent materials such as glass or Teflon. However, for high-temperature experiments, high — pressure build-up inside the reactor is expected and specially designed reactor should be used. For this purpose, tough material such as those made from poly-ether ether ketone (PEEK) could serve as a casing for the reactor to resist high pressure. Till date, reactors made for use up to a maximum temperature of 250 °C and maximum pressure of 2.5 MPa are readily available but demand high costs.

Another commercially available laboratory scale MW apparatus for high — temperature and high-pressure experiments is the MW Accelerated Reaction System (MARS-5, CEM Corporation). This apparatus, comparable with the one shown in Fig. 6.1, can be operated at a programmable MW power up to 1250 W at 2.45 GHz

О о

Reactor components
Tmax = 250°C, Pmax = 2.5 MPa

Microwave Oven

Fig. 6.1 Typical microwave apparatus for high temperature and high pressure experiments (Ethos, Milestone Co. Ltd.) frequency. This is equipped with fiber optic temperature and pressure probes within the cavity and a turning carousel with a maximum of 14 pressure sealed 100 mL vessels (XP-1500), which can be used up to a maximum temperature of 260 °C and maximum pressure of 3 MPa. This equipment operates with a focused MW irradiat­ing beam and is capable of heating and holding at desired cooking (or temperature ramp) rates and holding times.