I find the work being done on the materials — especially the inorganic design work, to be extremely fascinating. Started thinking about this with all of the excitement when catalysts were shown to superheat in organic mediated reactions and the abundance of literature on catalyst design. Moving over to a new group of people I found that the traditional parr bomb and high-temp sintering, grinding and additional solid-state techniques for making specialized inorganic structures a CRAZY world indeed. Just to give an example — for a conventional hydrothermal reaction to work, a temperature has to be reached by adding heat across a volume of material from the outside in, and depending on the phases and nucleation, the desired material is formed. Well — what a set up for the microwave — heat dissipated from the contents and not the vessel…and when we have something to absorb the microwave energy we have the possibility to reach temperatures not used in conventional approaches (alas, we are still measuring the bulk temperature of the event, so there is still some handwaving — that’s my favorite part because it means we can conjecture over a few beers at the pub).

In a recent report, some solution phase chemistry was performed by Antonino Rezzuti and Christina Leonelli and compared with traditional high temperature ceramic methods. This group has contributed an number of research publications utilizing microwave technology over the years (so a good group to look at when thinking of your own research). In this report, the research centered around the preparation of perovskite ceramics, specifically, strontium-doped lanthanum manganites with different stoichiometric ratio of the three oxides, La1-x SrxMnO3(x = 0.3, 0.5, 0.6). Normally I wouldn’t go into the specific notebook reaction but in this case indulge me, because if you read through the article you will realize that compared to the high-temp conventional reaction, they are going from 24 hrs to 1 h total time…….that can sure take years off a Ph.D., don’t you think?

As an example, using a microwave-assisted hydrothermal method, 1.95 ml of 0.350 M lanthanum nitrate 1.95 ml of 0.350 M strontium nitrate and 2.73 ml of manganese(II) nitrate were mixed together in a 100 ml Teflon vessel. To this was added 1.17, ml of 0.350 M potassium permanganate and a suitable amount of potassium hydroxide (as mineralizer). The reaction mixture was sealed and placed in a multi-mode microwave reactor using 2.45 GHz frequency with maximum power of 1000 W. The power of microwave oven was automatically adjusted (variable power PID feedback) in such a way to reach the temperature of 240°C in 15 minutes, with a hold time of 30 minutes. After the reaction was cooled to room temperature, the solid product was washed several times with deionized water and 1 M nitric acid solution and then dried at 50°C.

Screen Shot 2013-10-19 at 1.45.32 PM

Several compounds made using the microwave method

Screen Shot 2013-10-19 at 1.45.45 PM

SEM of PVK03

Screen Shot 2013-10-19 at 1.45.57 PM

XRD PVK05

Screen Shot 2013-10-19 at 1.46.09 PM

SEM PVK05

Confirmation versus conventionally prepared compounds indicated the morphologies were the same. The newer approach provided easy access with gentle conditionals to narrowly dispersed doped perovskite particles.

Advertisements