ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

PHYSICAL BEHAVIOR AT NANO-SCALESProbably molecular hydrogen (H 2 ) is the most obvious candidate to replace the fossil fuels as an energy vectorenvironmentally neutral. A safe and efficient H 2 storage presents, however, a series of unsolved technologicalchallenges. One possible solution is the adsorption of H 2 at low temperatures in light nanostructured materials.However, practical limitations impose a minimum temperature of 77 K (air liquid temperature) and a maximumpressure around 50 atmospheres. These are very challenging thermodinamical conditions. Above 33 K molecularhydrogen is in a supercritical state, that is, it is a fluid than cannot be condensed. In other words, the thermodynamicstate is such that weak (dispersive) interactions, i.e., interactions comparable to those acting between the moleculesthemselves so that there is not a breakdown of the chemical molecular bond (chemisorption), it is not possible toretain a substantial quantity of molecules on the adsorvent substrate. Since the retention of the molecules by meansof chemical bonding (chemisorption) implies temperatures for the hydrogen release too high for the practicalapplications, it is compulsory to find microscopic mechanisms of molecular trapping going beyond those present inconventional sorbents.By means of a concurrent use of neutron scattering techniques and adsorption measurement, we have been able toidentify novel mechanisms that contribute to a substantial increase of the hydrogen storage capacity of thecorresponding substrates. More specifically, we have observed a kinetic trapping process of the H 2 molecules incertain carbonaceous tubular bundles. During the filling process, the structure expands so that on one hand itsnominal capacity increases as the pressure increases, while, on the other hand, the molecules get kinetically trappedin the structure so that an excess of particles are retained in the structure when the pressure is decreased, giving riseto a hysteresis loop in the adsorption/desorption process.Following the same rational we started to study materials based in graphite oxide. We have succeeded in theintercalation of simple molecules so that it is possible to “tune” the interlayer space as well as the tortuosity of thepores among the “pillars”. We hope in such a way to develop efficient materials in trapping interesting molecularspecies, in particular H2.MICROSOCPIC STRUCTURE AND DYNAMICS OF DISORDERD CONDENSED MATTERThe wealth of microscopic structures of condensed matter goes far beyond traditional crystalline phases (orderedsolid), glass (disordered solid) and liquid (fluid). Even simple molecular substances such as small chain monohydricalcohols (methanol, ethanol, propanol ...) have phases with different types of spatiotemporal order in differentdegrees of freedom. Probably, the most notable example is the ethanol in which apart from the conventional crystal,glass and liquid phases, can take a orientational glass phase with translational degrees of freedom arranged in a bcccrystal while the orientational ones are in a disordered glassy phase. These orientational degrees may in turn "fuse"at a certain temperature and rotate around the molecular centers of mass ordered in the crystalline structure. In thiscontext, making recourse of the neutron diffraction techniques, we are studying the kinetic of the transition betweenthe bcc rotator phase (plastic crystal) and the conventional monoclinic crystal as a function of temperature.ADVANCED INSTRUMENTATION DEVELOPMENT FOR NEUTRON SOURCESIn recent years much of the work in this area developed by the group has been focused on the Spanish candidature tothe European Spallation Neutron Source (ESS-Bilbao). Within this respect, on May 2009 an inflexion point wasreached after an informal agreement in Bruxels in favor of the Swedish site proposal (Lund) and the subsequentagreement between the Spanish Science and Innovation Ministry and the relevant Swedish. As a consequence theESS-Bilbao Consortium (Central Administration / Basque Country Government) has refocused its activities nowunder the direction of Prof. Javier Bermejo. More specifically, the ongoing activities are aimed at building a localinfrastructure based on a high power light ion accelerator in order to provide service to advanced experimentalprograms not only in the production of neutron beams by nuclear fragmentation processes (spallation) but in areas asdiverse as particle physics, the study of materials for nuclear fusion, unstable isotopes production for nuclear physicsstudies or possible applications of this kind accelerators in radiation oncology. Three are the main objectives thecenter:- To serve as a center for design, development and prototyping of some acceleration structures responsible for theneutron beam energy gain up to about 2.5 GeV.- To nucleate in our system of Science-Technology-Innovation, a laboratory specializing in science and technologyof high power accelerators, comparable with those in the surrounding countries involved in the development andcoordination of international large facilities.- To provide to our industrial sectors tools to position themselves advantageously in areas requiring the use of lightion beams (high power semiconductors, aerospatial industry, lithography, ultra-hard materials).60