Facile synthesis of nanosized sodium magnesium hydride, NaMgH₃

The ternary magnesium hydride NaMgH3 has been synthesised via reactive milling techniques. The method employed neither a reactive H2 atmosphere nor high pressure sintering or other post-treatment processes. The formation of the ternary hydride was studied as a function of milling time and ball:powder ratio. High purity NaMgH3 powder (orthorhombic space group Pnma, a=5.437(2) Å, b=7.705(5) Å, c=5.477(2) Å; Z=4) was prepared in 5 h at high ball:powder ratios and characterised by powder X-ray diffraction (PXD), Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). The products formed sub-micron scale (typically 200–400 nm in size) crystallites that were approximately isotropic in shape. The dehydrogenation behaviour of the ternary hydride was investigated by temperature programmed desorption (TPD). The nanostructured hydride releases hydrogen in two steps with an onset temperature for the first step of 513 K

On the independence of hydrogen production from methanogenic suppressor in olive mill wastewater

Anaerobic degradation of olive mill wastewater (OMW) at concentrations ranging from 2 to 100 g/L of chemical oxygen demand (COD) was assessed in batch assays. Methane was the main final product obtained for the lower concentrations tested. For 25 g COD/L, H2 was temporarily produced, albeit H2 depletion occurred, likely due to homoacetogenesis, since acetate was formed concomitantly. Hydrogen was produced and accumulated permanently in the assays containing 50 g COD/L of OMW. Methanogenesis and homoacetogenesis were naturally inhibited, suggesting that hydrogen recovery from OMW can be performed without the addition of methanogenic suppressors such as 2-bromoethanosulfonate. This fact opens new perspectives for the utilization of high OMW concentrations in a two-stage valorisation process combining biohydrogen and biomethane production.The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013, the FCT Project RECI/BBB-EBI/0179/2012, the Project "BioEnv - Biotechnology and Bioengineering for a sustainable world", REF. NORTE-07-0124-FEDER-000048, co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER. Also through the project PTDC/ENR/69755/2006 and grants given to Marta Goncalves SFRH/BD/40746/2007, Jose Carlos Costa SFRH/BDP/48962/2008 and Angela A Abreu SFRH/BPD/82000/2011

Ionic conductivity and the formation of cubic CaH₂ in the LiBH₄-Ca(BH₄)₂ composite

Transient absorption spectroscopy is used to follow the reactive intermediates involved in the first steps in the photochemistry initiated by ultraviolet (266-nm wavelength) excitation of solutions of 1,5-hexadiene, isoprene, and 2,3-dimethylbut-2-ene in carbon tetrachloride or chloroform. Ultraviolet and visible bands centered close to 330 and 500 nm in both solvents are assigned respectively to a charge transfer band of Cl-solvent complexes and the strong absorption band of a higher energy isomeric form of the solvent molecules (iso-CCl3–Cl or iso-CHCl2–Cl). These assignments are supported by calculations of electronic excitation energies. The isomeric forms have significant contributions to their structures from charge-separated resonance forms and offer a reinterpretation of previous assignments of the carriers of the visible bands that were based on pulsed radiolysis experiments. Kinetic analysis demonstrates that the isomeric forms are produced via the Cl–solvent complexes. Addition of the unsaturated hydrocarbons provides a reactive loss channel for the Cl–solvent complexes, and reaction radii and bimolecular rate coefficients are derived from analysis using a Smoluchowski theory model. For reactions of Cl with 1,5-hexadiene, isoprene, and 2,3-dimethylbut-2-ene in CCl4, rate coefficients at 294 K are, respectively, (8.6 ± 0.8) × 109, (9.5 ± 1.6) × 109, and (1.7 ± 0.1) × 1010 M–1 s–1. The larger reaction radius and rate coefficient for 2,3-dimethylbut-2-ene are interpreted as evidence for an H-atom abstraction channel that competes effectively with the channel involving addition of a Cl-atom to a C═C bond. However, the addition mechanism appears to dominate the reactions of 1,5-hexadiene and isoprene. Two-photon excited CCl4 or CHCl3 can also ionize the diene or alkene solute

Metal hydrides for concentrating solar thermal power energy storage

The development of alternative methods for thermal energy storage is important for improving the efficiency and decreasing the cost for Concentrating Solar-thermal Power (CSP). We focus on the underlying technology that allows metal hydrides to function as Thermal Energy Storage (TES) systems and highlight the current state-of-the-art materials that can operate at temperatures as low as room-temperature and as high as 1100 oC. The potential of metal hydrides for thermal storage is explored while current knowledge gaps about hydride properties, such as hydride thermodynamics, intrinsic kinetics and cyclic stability, are identified. The engineering challenges associated with utilising metal hydrides for high-temperature thermal energy storage are also addressed

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed

Råvarornas inverkan på ljusbågsugnsslaggens egenskaper

Validerat; 20101217 (root

Biogeochemical Effects of Particle Filters in Forest Drainge Ditches

In Sweden and in Finland large forest areas have been ditched to increase forestproductivity. In Sweden more than 1.5 million ha forest have been ditched with a total lengthof about 220 000 km ditches for the last 100 years. Forest drainage ditching results in theerosion of minerals and humus from the ditch slopes and further transport of the erodedmaterial with the ditch water. This probably affects the biological and ecological conditions inthe ditches and brooks due to increased turbidity and sedimentation. Such adverse effects canpotentially be prevented by particle filters. In 2005-2007, the Swedish Forestry Board built ca80 particle filters in Northern Sweden. The effects of these particle filters on water quality arehowever unknown. If ditching is done in acid sulphate soils in areas of for example isostaticland uplift there is also a risk of acidification, which potentially can lead to leakage of metals.The aim of the study was to evaluate if particle filters in forest drainage ditches improve waterquality.The study was performed in a ditch in Alvik, Luleå municipality, during May toNovember 2007 and in three ditches in Tärendö, Pajala municipality in October 2007. TheAlvik catchment is characterized by sulphide soils. In Alvik, only suspended materialdecreased significantly after the second particle filter during the study period. All otherinvestigated elements were unaffected by the particle filters. There were no differences in thewater levels before and after the particle filters, which indicates that the particle filters weretoo loosely packed. The effect of the ditches in Tärendö was difficult to assess. In one ditchboth of the particle filters were flooded and in another ditch, two of three particle filters wereflooded. In the third ditch there was almost no flow. On the basis of this study it is hard to saywhich benefit the particle filters constitute. The construction of the particle filters seams to becritical for their function. In Alvik, the particle filters probably were too loosely packed and inTärendö the particle filters were too small for working satisfactorily.The influence of the acid sulphate soil was significant in the Alvik ditch. The pH waslowest during May (mean 4.5), at the same time sulphur and metal concentrations were high(S mean 17 mg/l, Al mean 2464 μg/l and Zn mean 41 μg/l). During summer (June-September)the pH increased and sulphur and metal concentrations decreased (pH mean 6.2, S mean 10mg/l, Al mean 950 μg/l and Zn mean 15 μg/l). In November the trend reversed again, pHdecreased and sulphur and metal concentrations increased again to the highest values for someelements (pH mean 4.8, S mean 24 mg/l, Al mean 2880 μg/l and Zn mean 47 μg/l). pH wassignificantly negatively correlated with S and with several metals (Al, Cd, Co, Mg, Mn, Niand Zn). Sulphur and the metals were significantly correlated to each other. These resultssuggest that sulphate oxidation occurred in the soil which affected the geochemistry in theditch water. After drainage ditching the groundwater level sinks and the sulphate soils areoxidised. After oxidation, hydrogen ions and metal ions leach from the soils when the soilsagain are saturated by melt water. Because of this, the pH will decrease and further metal ionsare leaching from the soils. The leaching and transport of metals from the ditch in Alvik wassignificant. The transport of S in November was estimated to be ca. 11 kg/day. The annualaverage transport of S was ca. 2200 kg/year from the ditch in Alvik. The transport of metals inNovember in Alvik was for Al ca. 1 kg/day, for Zn 22 g/day and for Cd 64 mg/day. Theresults suggest that drainage ditching in areas containing acid sulphate soils should beavoided.Validerat; 20110630 (anonymous