Friday, December 24, 2010

Working with some nitrogen compounds

I always laugh whenever I see a new paper (JACS or Angewandte Chemie notwithstanding) describing the synthesis of and/or new/novel nitrogen compounds that are either some kind of superfuel (read: large ∆G) or so rare that precious little previous literature can be found on them.

There are reasons why you hardly read about them or why they are not in widespread use in industry already.

The reason that one gets our attention is that compounds with lots of nitrogens in them – more specifically, compounds with a high percentage of nitrogen by weight – are a spirited bunch. They hear the distant call of the wild, and they know that with just one leap of the fence they can fly free as molecules of nitrogen gas. And that’s never an orderly process.

...And thermodynamically, there aren't many gently sloping paths down to nitrogen gas, unfortunately. Both enthalpy and entropy tilt things pretty sharply.
- Derek Howe

I like Ancient Hacker's summary on slashdot:

Rocket fuel was a big research area in the 1950's. Dozens of very good chemists spent a whole load (hundreds of millions of 1950-size dollars) trying to make better rocket fuels.

( One of them wrote a informative and funny book about that time and place ).

The short summary is: Yes, you can make higher oomph rocket fuels and oxidizers with more oxygen in them.

But a lot of the formulas are impractical as:

(0) They were already discovered years ago, and discarded, but chemists don't like to write up their failures, and researchers don't like to read old moldy research summaries anyway.

(1) They're waaay too expensive to make, even for military uses.

(2) They are highly toxic, even more toxic than the widely-used hydrazines, which can kill you in several interesting ways.

(3) They're so unstable, you have to keep them under impossible conditions, like no sound, no vibrations, no light, and under a part per million of crud in the perfectly-smooth and unscratched nickel-plated tanks.

(4) They can't be stored for more than a day or so before the fuel or oxidizer starts decomposing itself or the tank walls.

(5) Too many of the researchers were vaporized while handling the stuff. Literally. Truly. Completely. That tends to make it hard to find substitute researchers to continue working with the same stuff.

(6) For military applications, you need a fuel that can be handled by raw recruits, stored for many months, be pumped quickly into not always totally clean rocket tanks, kept in those loaded rockets for days to months, and tolerate wide temperature swings. These requirements alone disqualify a large percentage of really zippy fuels and oxidizers.

The odds are pretty high against this "new" compound being all that new, or it passing the basic requirements for fuel or oxidizer.

One of my side projects in Grad School was funded by NASA and we were handling hydrazine to test their viability for use in micro-reactors. That was one nasty little guy to deal with on a daily basis, and we all had to wear dosimeter badges on our lab coats in addition to two layers of gloves, sleeve protectors and rubber boots. And yes, the whole setup was inside a fume hood with the sash lowered all the time.

Be grateful this isn't your PhD project.

Oh, and Merry Christmas to those of you celebrating the Yuletide holiday. Stay warm and safe!

Edit (25 Dec): A nice youtube video of shock sensitive nitroglycerin:

Thursday, December 16, 2010

Paper by SMA researchers gets retracted due to self-plagiarism

First time I have seen this happen to the SMA folks.

Of course it will not be reported on the SMA homepage, or will it?

The above article, published in Applied Physics Letters, has originally reported the growth of ZnO nanorods on GaN using hydrothermal synthesis without any catalyst. Some initial results, including scanning electron microscopy, x-ray diffraction, photoluminescence, and transmission electron microscopy were also discussed in the article. After a few months, we wrote another paper, i.e., Ref. 1. In this paper, we explored in more detail the properties of ZnO nanorods. However, there are some overlapping parts which included the introduction and Figs. (4 out of 12 figures). This unintentional negligence in repetitive data extraction and omission of cross reference to the published experimental results, leading to the unexpected ambiguities and inconveniences to the readers, have constituted the authors full obligation to apologize and to spontaneously retract the above article to uphold the publication protocol.

It took them five years to retract their 2005 publication.

Tuesday, December 07, 2010

Arsenic-based life forms: Fact or fiction?

The biggest science news of the past week probably has to be NASA's press release claiming to have isolated a bacterium that substitutes arsenic for phosphorus on its macromolecules and metabolites. (Wolfe-Simon et al. 2010, A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus.)

As things stand, many scientists are openly skeptical of the claims made in the paper.

That is understandable, given the potential impact on biology. If the results are shown to be right, this might open a whole new field of research on arsenic-based life forms (and possibly the Nobel Prize in the near future). E.g. The discoverers of graphene were awarded the 2010 Physics Nobel a mere six years after their publication in Science.

And the authors' response to the online critics?

"If we are wrong, then other scientists should be motivated to reproduce our findings. If we are right (and I am strongly convinced that we are) our competitors will agree and help to advance our understanding of this phenomenon. I am eager for them to do so." - Ronald Oremland, US Geological Survey.

Heh, the scientific method is at work here.

This whole episode reminded me of a question back in the days of my JC S-paper chemistry class where we were asked to suggest alternative elements that could potentially replace those currently in use by nature. Can we substitute carbon with silicon? Phosphorous with arsenic? Would there be any problems with these changes under earth's atmosphere and conditions?

Maybe I should revisit my old A level notes (if I still have them somewhere) to look for old theories to test. Maybe I can get something useful (like a Science publication) out of them. Like the SN2 reaction mechanism. Who could have thought there would be an unexpected 'roundabout' mechanism in addition to the traditional 'inverted umbrella' pathway?