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New Energy Materials Based on Non-Molecular Nitrogen

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Search for New Energy Materials based on Metastable Cluster and Polymeric Forms of Non-Molecular Nitrogen by Means of Computer Modeling from the First Principles, and Experimental Researches

Tech Area / Field

  • PHY-SSP/Solid State Physics/Physics
  • CHE-THE/Physical and Theoretical Chemistry/Chemistry
  • NNE-MEC/Miscellaneous Energy Conversion/Non-Nuclear Energy

Status
3 Approved without Funding

Registration date
25.08.2006

Leading Institute
MIFI, Russia, Moscow

Collaborators

  • Max-Planck-Institut für Chemie, Germany, Mainz

Project summary

The goal of the Project is the elaboration of physical foundation for development of novel energy materials based on the cluster and polymeric forms of non-molecular nitrogen which are capable to accumulate the energy 3-4 times greater than the energy accumulated in familiar “chemical” energy materials as well as to release entire accumulated energy in a time of the order of one picosecond.

There are several reasons that we choose to study the nitrogen structures as a promising element for the synthesis of high energy density materials (HEDM). First, it is well known that nitrogen does not form the condensed matter in normal conditions but exists in the form of diatomic molecules N2. In a N2 molecule, the nitrogen atoms are bound to each other by a very strong triple covalent bond NN. This bond is one of the strongest in Nature, its energy equals to 4.95 eV/atom. In cluster and polymeric nitrogen structures, the interatomic bonds are either double or single, and hence their energies are lower than that of the triple bond. The energy of the double bond NN equals to 2.17 eV/atom, while the single bond N-N is even more weaker, its energy equals to 0.87 eV/atom. So, for nitrogen, the sum of the energies of three single bonds is much less than the energy of a triple bond. This fact gives an opportunity to accumulate energy in a matter that contains nitrogen atoms coupled to each other by double or single bonds. Such a relation between the bond energies is not a characteristic one for other elements. So, for carbon, the energy of three single bonds is somewhat greater than the energy of one triple bond (we recall that three single bonds per atom are characteristic for graphite layers). Second, such probable nitrogen structures should release the energy upon their fission into stable nitrogen molecules.

Theoretical investigations aimed at the study and synthesis of polymeric non-molecular nitrogen are carried out in USA, France, Germany, and other countries. In 1985, McMahan et al. had predicted the transition of the molecular ε-phase of nitrogen into the monoatomic simple cubic structure at a pressure of the order of 100 GPa. It was also shown that the transition from the molecular ε-phase to the diamond structure and to the face-centered cubic structure should take place at the pressure of 200 GPa and
300 GPa, respectively. In the subsequent papers, a new structure had been suggested and named the cubic gauche (CG) structure. That structure is the most energetically favorable polymeric form of nitrogen among those studied under pressure. The equilibrium transition from the molecular ε-phase of nitrogen into the predicted CG structure should take place at the pressure of (50 ± 15) GPa, being accompanied by 17% change in the volume. The polymeric nitrogen structures analogous to the arsenic (A7) and black phosphorous (BP) structures were studied as well. In the later works, several other novel polymeric phases of nitrogen were found theoretically. In all those works, the transition of nitrogen into metastable polymeric structures with the single bonds was predicted at high pressure.

For more than twenty years, experimental efforts aimed at the synthesis of non-molecular nitrogen were unsuccessful. In recent 3 years, the first successful experimental results were obtained at extremely high pressure of 100-200 GPa. The parent material to be compressed was pure molecular nitrogen. The leader in the experimental studies of non-molecular nitrogen is the scientific group from Max Planck Institute fur Chemie (Mainz, Germany). The basic idea of those experiments was that the molecules N2 get closer to each other upon strong compression, resulting in formation of non-molecular structures.

In the pioneering paper published in 2001, the experimental results on transformation of molecular nitrogen into some non-molecular phase were presented. That phase was shown to be semiconducting and had a huge transformation hysteresis on pressure. No marked features in Raman and IR spectra were detected. The new phase was suggested to be amorphous and consist of both nitrogen molecules and clusters.

In 2004, the results on the synthesis of a polymeric phase of nitrogen with single bonds were presented. That phase has a cubic gauche structure predicted earlier by McMahan and identified experimentally by means of X-ray diffraction and Raman spectroscopy. It is important that the synthesized non-molecular phases were broken down upon partial decompression. This was accompanied by the energy release.

In recent years, a great number of theoretical works were concerned with the search for the structures of separate clusters, ranging from N4 to N60. However, we are not aware of works aimed at the study of ensembles of such clusters. Extraordinary capability of those clusters to release the energy much higher than the energy released from the most powerful (at present and in the forecast future) high-energy materials stimulated the fancy of engineers and technologists specialized in the field of propellants. Studies on a possibility of existence of other perspective poly-nitrogen compounds are carried out in numerous scientific centers. Recently, important key blocks were revealed: Mg(N5)2, N51+ Sb F61-, N51+ Sb F11, N51+, N51+ Sn F6 и N51+ Sn(CF3)4. After their detection, the scientific community working in the field of high energy density materials is close to the discovery of even greater number of poly-nitrogen compounds. The scientists all over the world ambitiously plan for the synthesis of N60. If synthesized, this molecule will accumulate a huge energy, being ecologically harmless.

The main result of our theoretical investigations started in 1997 is the prediction of a possibility of the existence of ensembles composed of N8 clusters (so-called “boats”), i.e., a condensed phase formed from the N8 clusters as from “bricks”. We have shown that this new nanomatter can accumulate the energy 3-4 times greater than the best “chemical” energy materials; it can be stable under normal pressure and heating up to 800 K.

We have also found that the energy release from nitrogen clusters upon their fission into N2 molecules occurs completely and in a very short time. We have shown that the process of the energy release from non-molecular nitrogen is fundamentally different from the process of the energy release from “chemical” energy carriers where it takes place upon synthesis of fuel and oxidant.

Thus our theoretical approach, i.e., the fabrication of the ensembles of nitrogen clusters which are stable under normal pressure, can be tested experimentally. Furthermore, we plan to study the ways of synthesis of non-molecular nitrogen under reduced pressure. We suppose to obtain the following theoretical results: determination of the structure and stability of ensembles of the nitrogen clusters; optimization of pressure and temperature for the synthesis of such ensembles; calculation of Raman, infra-red, and X-ray spectra in order to confirm the presence of the cluster ensembles in non-molecular nitrogen phases.

The experimental researches will be made of nitrogen phases at high hydrostatic pressure by methods of optical spectroscopy and X-ray diffraction with using synchrotron radiation. The local structure of high pressure phase of CsN3 by EXAF spectroscopy method with use synchrotron radiations will be investigated. The comparison of the received experimental and theoretical results is seemed as one of the key elements of the forthcoming works.

Except for the above-mentioned basic interest (the synthesis of a fundamentally new high energy density material and development of a new knowledge on its physical characteristics), the Project is also of a great practical interest since it opens a way to the synthesis of a novel fuel.

Submitted project allows a full-scale realization of the ISTC aims and problems including:

  • the supporting of efforts in the field of the energy production;
  • the consolidation of efforts of experts on development of alternative energy sources;
  • the developing of scientifically valid recommendations on the synthesis of metastable non-molecular form of nitrogen capable to accumulate a high energy;
  • the using of knowledge and research experience accumulated at the development of scientific and technical products for the defensive purposes.

We have developed the methods and software for calculation of characteristics of nitrogen clusters and their ensembles from the first principles, and accumulated a great experience. Our group includes highly qualified physicists-theoreticians and programmers, candidates and doctors of sciences, associate professors and professors known worldwide in the field of physics of nanostructures, as well as young scientists and post-graduate students.

Thus there emerges an opportunity to synthesize a novel matter that can be used in practice as a perspective HEDM.


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