Silica-Metal Composite for Hydrogen Storage Applications
In spite of their favourable chemical characteristics, using AB5 alloys as fixed bed for hydrogen storage devices requires proper management of a number of technological aspects. Among these, the mechanical stability of metal particle grains under hydrogen cycling and the overall thermal conductivity of the material bed constitute crucial features. We developed by High Energy Ball Milling HEBM a mechanically stable silica-based AB5 composite with enhanced thermal conductivity. Here, focusing on the material’s physical-chemical properties, we report on the silica-AB5 composite development and characterization. Particularly, we studied the material consolidation process, the resulting composite morphology and the system behaviour under hydrogen loading/unloading cycling.
AB5/ABS composite material for hydrogen storage
Abstract AB5 metal hydride (MH) particles were polymer dispersed in order to entrap the micro and nanoparticles produced by repeated fragmentations of the metal phase during the hydrogen charging/discharging cycles. Acrylonitrile-butadiene-styrene copolymer (ABS) was selected as a matrix on the basis of its physical and chemical properties. AB5/ABS composite pellets were obtained by using a dry mechanical particle coating approach in a tumbling-mill apparatus and successive consolidation by uniaxial hot pressing. A number of characterization techniques were used to assess the morphological, chemical and structural properties of the composites. High pressure DSC measurements, conducted at different pressure values, were used to assess the H2 absorption properties and profile the Van't Hoff plots of the material. The overall results indicated that the AB5/ABS composite well tolerated the hydriding effects on metal particles, with no losses in hydriding kinetics. The material characteristics were found to be compatible with its application in developing MH-based H2 storage devices.
Exposure to violence in incarcerated youth from the city of São Paulo.
OBJECTIVE
This study aimed to determine the extent of exposure to community violence among delinquent Brazilian youth in the 12-month period prior to their incarceration and to identify factors associated with this exposure.


METHOD
With an oversampling of girls, a cross-section of youth under 18 years of age from juvenile detention units in the city of São Paulo, Brazil completed a structured interview. Key items related to exposure to violence (witnessed and experienced) were drawn from the Social and Health Assessment questionnaire to cover the 12-month period prior to incarceration.


RESULTS
Participants (n = 325, 89% boys) reported high rates of exposure to violence with largely similar levels for boys and girls. Being threatened with physical harm, being beaten or mugged and/or shot at were the most common forms of violence experienced. After controlling for demographic and family variables, the fact of having peers involved in risk behavior, easy access to guns and previous involvement with the justice system were associated with witnessed violence; whereas having slept on the street was the only variable associated with experienced violence.


CONCLUSION
This group of youth was exposed to high levels of violence and other adverse experiences. Future research should examine the effectiveness of strategies aimed at reducing the exposure to violence of high-risk youth.