Browsing by Issue Date, starting with "2010-09-27"
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- Hydrogen production by catalytic hydrolysis of sodium borohydride in batch reactors: new challengesPublication . Ferreira, M. J. F.; Rangel, C. M.; Pinto, A. M. F. R.The present manuscript faces the study of H2 generation and storage from catalytic hydrolysis of sodium borohydride (NaBH4) under pressure. We revisit several works on this topic developed (or under development) by our team in the last four years on some of the most critical issues in this research area, namely catalyst durability/reutilization, gravimetric hydrogen storage density and recyclability. New results are also presented. Hydrogen generation rates and yields and hydrogen storage capacities can be augmented to reach 6 wt%, by adding small amounts of an organic polymer (CMC) to the classic NaBH4 hydrolysis, performed with stoichiometric amount of water in a batch reactor with a conical bottom shape and in the presence of Ni-Ru based catalyst, reused from 300 times. Sodium tetrahydroxoborate, NaB(OH)4), was produced in the presence of CMC additive, and did not show crystalline water in its crystal structure. This latter finding has potential to reduce recycling costs of NaBO2 back to NaBH4 and also increase the overall storage density of systems based on NaBH4 as hydrogen carrier.
- Microstructural characterization of the ODS Eurofer 97 EU-batchPublication . Mateus, R.; Carvalho, Patricia Almeida; Nunes, D.; Alves, L. C.; Franco, N.; Correia, J.B.; Alves, E.Four as-processed forms (Plate 16, Plate 6, Rod 20 and Rod 12.5) of the ODS Eurofer 97 EU-batch produced under different thermomechanical conditions have been investigated by scanning nuclear microprobe, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, electron backscattered diffraction, hightemperature X-ray diffraction and microhardness measurements. The materials presented a ferritic microstructure with a homogeneous distribution of Y. The thicker plate presented a fine carbide dispersion while the other forms showed carbide morphologies corresponding to pseudo-pearlitic and pseudo-bainitic transformations with wellmatched hardness values. Hot rolling induced crystallographic textures of the {101}<101> type, rotary swaging resulted in a complex texture, and extrusion produced a strong <101> fiber texture. X-ray diffraction experiments at high temperature showed that at a cooling rate of 5 ºC/min the complete austenite-to-ferrite transformation occurs between 760 and 750 ºC compromising the material quenchability.
- Production of Cu/Diamond composites for first-wall heat sinksPublication . Nunes, D.; Correia, J.B.; Carvalho, Patricia Almeida; Shohoji, Nobumitsu; Silva, C.; Fernandes, H.; Alves, L. C.; Hanada, K.; Osawa, E.Due to their suitable thermal conductivity and strength copper-based materials have been considered appropriate heat sinks for first wall panels in nuclear fusion devices. However, increased thermal conductivity and mechanical strength are demanded and the concept of property tailoring involved in the design of metal matrix composites advocates for the potential of nanodiamond dispersions in copper. Copper-nanodiamond composite materials can be produced by mechanical alloying followed by a consolidation operation. Yet, this powder metallurgy route poses several challenges: nanodiamond presents intrinsically difficult bonding with copper; contamination by milling media must be closely monitored; and full densification and microstructural homogeneity should be obtained with consolidation. The present line of work is aimed at an optimization of the processing conditions of Cu-nanodiamond composites. The challenges mentioned above have been addressed, respectively, by incorporating chromium in the matrix to form a stable carbide interlayer binding the two components; by assessing the contamination originating from the milling operation through particle-induced X-ray emission spectroscopy; and by comparing the densification obtained by spark plasma sintering with hot-extrusion data from previous studies.