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  • Publication
    Experimental and economic study of aluminium-gallium alloys as a fuel/catalyst for hydrogen propulsion
    An investigation was carried out into the feasibility of using Al-Ga alloys as a renewable agent to produce hydrogen from water, following positive claims from a research group in the USA. The hypothesis was that pellets of Al-Ga would oxidise in water, resulting in hydrogen evolution which could be directly used in a fuel cell to power a vehicle. This paper reports on new experiments on the reaction of a range of compositions of binary Al-Ga pellets in contact with water. It was found that the reaction does not go to completion, resulting in only a fraction of theoretical hydrogen evolution, and that – contrary to research findings of others – gallium is not a passive catalyst and is also partially oxidised in water. A new proposal on the reaction mechanism is presented. Even if theoretical H2 output was achieved, we show that the aluminium cycle is uneconomic and impractical, and that total CO2 emissions per km travelled are significantly higher than those from an equivalent petrol engine. Guidelines for improved alloy design and optimum microstructure for renewable hydrogen production from water are suggested.
  • Publication
    Domain size as a parameter for studying the potential alkali-silica reactivity of chert-bearing aggregates
    The presence of chert or flint in aggregates used for concrete manufacture has long been a source of concern in the context of alkali-silica reactivity. The global in-service performance of chert and flint-bearing aggregates, however, varies from innocuous to deleterious. This could be due to variations in the degree of crystallinity of the silica, which influences potential reactivity. Chert occurs in significant Irish sources of aggregate used for concrete, yet no cases of deleterious expansion have been reported in the Republic of Ireland to date. Many of these sources fail to conclusively demonstrate innocuous behaviour in the laboratory expansion tests despite satisfactory in-service behaviour. A previous X-ray diffraction study, employing quartz crystallinity index, had indicated a significant difference between Irish Carboniferous cherts and English Cretaceous flints. This paper reports a further study of crystallinity, correlated with mortar bar expansion tests, but employing both quartz crystallinity index and domain size in the characterisation of crystallinity. The influence of chert content was also studied. Twenty-three Irish aggregate sources were sampled, and petrographic analysis revealed that 17 of these contained chert. Three flint-bearing aggregates, from sources in England that had demonstrated alkali-silica reactivity, were also sampled. Chert and flint were extracted from the aggregate samples by a petrographer experienced in the field of concrete technology. Twenty-six distinct samples were successfully extracted from 13 of the Irish and the three English sources. X-ray diffraction testing confirmed the previous findings (using the quartz crystallinity indices) that the Irish cherts are,more crystalline than the English flints. Domain size determination, however, showed that the difference in crystallinity of the national sets was less than that anticipated. The influence of chert content is advanced as a hypothesis to explain the apparent reactivity of Irish cherts in screening tests. The potential value of combining domain size and chert content determination in helping to classify aggregate reactivity is advanced for cases where in-service behaviour is in significant conflict with findings from standard laboratory tests.
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