Contribution to the study of the band structure of amorphous selenium

From a study of the conductivity and photoconductivity of amorphous Se layers we are able to propose a model for the electronic states in the band gap.     

The determination of the amount of bound water within cellulosic gels by NMR spectroscopy

It has been shown that the NMR spectrum of moist cellulose is consistent with the idea that part of the water within the gel is destructured and bound to the accessible surfaces. A method for calculating the amount of bound water is presented, but because of experimental difficulties in obtaining an exact value for the spin-spin relaxation time of the protons in the bound water, only upper limits can at present be obtained for the amount of bound water. Accordingly, it is estimated that the amount of bound water does not exceed the following values: wood, 0.23 g/g; cotton, 0.15 g/g; two wood pulps, 0.30 and 0.33 g/g. The amount of bound water appears to approximate to a monomolecular layer upon all accessible surfaces, which suggests that the NMR technique might be used to determine the surface areas of the gels in the wet state.     

Plasma-enabled healing of graphene nano-platelets layer

Graphene platelet networks (GPNs) were deposited onto silicon substrates by means of anodic arc discharge ignited between two graphite electrodes.Substrate temperature and pressure of helium atmosphere were optimized for the production of the carbon nanomaterials.The samples were modified or destroyed with different methods to mimic typical environments responsible of severe surface degradation.The emulated conditions were performed by four surface treatments,namely thermal oxidation,substrate overheating,exposition to glow discharge,and metal coating due to arc plasma.In the next step,the samples were regenerated on the same substrates with identical deposition technique.Damaging and re-growth of GPN samples were systematically characterized by scanning electron microscopy and Raman spectroscopy.The full regeneration of the structural and morphological properties of the samples has proven that this healing method by arc plasma is adequate for restoring the functionality of2D nanostructures exposed to harsh environments.     

Speciation of the gaseous phase of the HI section of the iodine sulphur thermochemical cycle by modeling and inversion of FTIR spectra

This paper presents a laboratory experiment for the study of the liquid–vapor equilibrium of HI–I₂–H₂O ternary mixtures that are involved in the iodine sulphur thermochemical cycle for the production of hydrogen. The apparatus is based on a heated tantalum pressurized vessel equipped with temperature and pressure transducers and carrying windows for optical soundings. It enables recordings of the infrared transmission of the vapor with a Fourier Transform Spectrometer (FTS). The spectra show the signatures of HI and H₂O through rovibrational absorption transitions in both the 4200–5800 cm⁻¹ (1.7–2.4 μm) and 6200–7800 cm⁻¹ (1.3–1.6 μm) regions. In order to analyze the FTS recordings, a spectra calculation software and a dedicated database of spectroscopic parameters have been built. Using these tools, the HI and H₂O amounts in the vapor are determined from least square fits of the experimental spectra in both regions. It is first shown that the measured and the calculated transmissions are in good agreement. Furthermore, the species amounts determined independently in the two spectral regions are very consistent, confirming the quality of the optical soundings.     

Distributed parameter model simulation tool for PEM fuel cells

In this work, a simulation tool for proton exchange membrane fuel cells (PEMFC) has been developed, based on a distributed parameter model. The tool is designed to perform studies of time and space variations in the direction of the gas channels. Results for steady-state and dynamic simulations for a single cell of one channel are presented and analyzed. Considered variables are concentrations of reactants, pressures, temperatures, humidification, membrane water content, current density, among others that have significant effects on the performance and durability of PEMFC.     

Environmental aspects of ethanol-based fuels from Brassica carinata: A case study of second generation ethanol

One of the main challenges faced by mankind in the 21st century is to meet the increasing demand for energy requirements by means of a more sustainable energy supply. In countries that are net fossil fuel importers, expectation about the benefit of using alternative fuels on reducing oil imports is the primary driving force behind efforts to promote its production and use. Spain is scarce in domestic energy sources and more than 50% of the energy used is fossil fuel based. The promotion of renewable energies use is one of the principal vectors in the Spanish energy policy. Selected herbaceous crops such as Brassica carinata are currently under study as potential energy sources. Its biomass can be considered as potential feedstock to ethanol conversion by an enzymatic process due to the characteristics of its composition, rich in cellulose and hemicellulose. This paper aims to analyse the environmental performance of two ethanol-based fuel applications (E10 and E85) in a passenger car (E10 fuel: a mixture of 10% ethanol and 90% gasoline by volume; E85 fuel: a mixture of 85% ethanol and 15% gasoline by volume) as well as their comparison with conventional gasoline as transport fuel. Two types of functional units are applied in this study: ethanol production oriented and travelling distance oriented functional units in order to reflect the availability or not of ethanol supply. E85 seems to be the best alternative when ethanol production based functional unit is considered in terms of greenhouse gas (GHG) emissions and E10 in terms of non-renewable energy resources use. Nevertheless, E85 offers the best environmental performance when travelling distance oriented functional unit is assumed in both impacts. In both functional unit perspectives, the use of ethanol-based fuels reduces the global warming and fossil fuels consumption. However, the contributions to other impact indicators (e.g. acidification, eutrophication and photochemical oxidants formation) were lower for conventional gasoline.Life Cycle Assessment (LCA) procedure helps to identify the key areas in the B. carinata ethanol production life cycle where the researchers and technicians need to work to improve the environmental performance. Technological development could help in lowering both the environmental impact and the prices of the ethanol fuels.     

Life-cycle assessment of electricity from biomass: Case studies of two biocrops in Spain

Through the Renewable Energies Plan 2000–2010, Spain has fixed the objective of covering 12% of the primary energy demand from renewable sources. The achievement of this objective implies an annual increase of 22.4% of the energy produced from renewable sources. In this context, the objective of this study is to determine if the electricity from biomass produced in Spain would be environmentally competitive with electricity from natural gas or from the Spanish electricity mix. For that, the environmental impacts associated to the whole life cycle of two energetic crops in Spain, Poplar and Ethiopian mustard, used for power generation were evaluated. The overall assessment includes the cultivation and collection of biomass, its transport and the processes of its energetic transformation. We calculated different scenarios of electricity production from biomass in different capacity power plants (10, 25 or 50 MW), different transport scenarios and different productivities for biomass production. Our results show that, given the assumptions of this study, Ethiopian mustard is more impacting than Poplar when used for electricity production. Also, the transportation of biomass from the field to the power plant is an important stage that has to be carefully planned in order to get the maximum amount of electricity with a minimum environmental impact. Compared to electricity from natural gas or the Spanish electricity mix, the electricity obtained from biomass is more impacting in three from six impact categories we present here.