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Tungsten-bearing molybdenite from Borralha
Publication . Silva, Teresa; Figueiredo, M. Ondina; Veiga, JP; de Oliveira, Daniel Pipa Soares; Batista, Maria Joao; Noronha, Fernando
Mechanical activation of pre-alloyed NiTi2 and elemental Ni for the synthesis of NiTi alloys
Publication . Zhao, X.; Neves, Filipe; Correia, J.B.; Liu, K.; Fernandes, F. M. Braz; Koledov, V.; von Gratowski, S.; Xu, S.; Huang, J.
ABSTRACT: This work reports on an efficient powder metallurgy method for the synthesis of NiTi alloys, involving mechanical activation of pre-alloyed NiTi2 and elemental Ni powders (NiTi2-Ni) followed by a press-and-sinter step. The idea is to take advantage of the brittle nature of NiTi2 to promote a better efficiency of the mechanical activation process. The conventional mechanical activation route using elemental Ti and Ni powders (Ti-Ni) was also used for comparative purposes. Starting with (NiTi2-Ni) powder mixtures resulted in the formation of a predominant amorphous structure after mechanical activation at 300 rpm for 2 h. A sintered specimen consisting mainly of NiTi phase was obtained after vacuum sintering at 1050 degrees C for 0.5 h. The produced NiTi phase exhibited the martensitic transformation behavior. Using elemental Ti powders instead of pre-alloyed NiTi2 powders, the structural homogenization of the synthesized NiTi alloys was delayed. Performing the mechanical activation at 300 rpm for the (Ti-Ni) powder mixtures gave rise to the formation of composite particles consisting in dense areas of alternate fine layers of Ni and Ti. However, no significant structural modification was observed even after 16 h of mechanical activation. Only after vacuum sintering at 1050 degrees C for 6 h, the NiTi phase was observed to be the predominant phase. The higher reactivity of the mechanically activated (NiTi2-Ni) powder particles can explain the different sintering behavior of those powders compared with the mechanically activated (Ti-Ni) powders. It is demonstrated that this innovative approach allows an effective time reduction in the mechanical activation and of the vacuum sintering step.
Investigation of single phase Cu2ZnSnxSb1-xS4 compounds processed by mechanochemical synthesis
Publication . Neves, Filipe; Stark, A.; Schell, N.; Mendes, Manuel Joao; Aguas, H.; Fortunato, Elvira; Martins, Rodrigo; Correia, J.B.; Joyce, A
ABSTRACT: The copper zinc tin sulfide (CZTS) compound is a promising candidate as an alternative absorber material for thin-film solar cells. In this study, we investigate the direct formation of Cu1.92ZnSnx(Sb1-x)S-4 compounds [CZT(A)S], with x = 1, 0.85, 0.70, and 0.50, via a mechanochemical synthesis (MCS) approach, starting from powders of the corresponding metals, zinc sulfide, and sulfur. The thermal stability of the CZT(A)S compounds was evaluated in detail by in situ synchrotron high-energy x-ray diffraction measurements up to 700 degrees C. The CZT(A)S compounds prepared via MCS revealed a sphalerite-type crystal structure with strong structural stability over the studied temperature range. The contribution of the MCS to the formation of such a structure at room temperature is analyzed in detail. Additionally, this study provides insights into the MCS of CZTS-based compounds: the possibility of a large-scale substitution of Sn by Sb and the production of single phase CZT(A)S with a Cupoor/Zn-poor composition. A slight increase in the band gap from 1.45 to 1.49-1.51 eV was observed with the incorporation of Sb, indicating that these novel compounds can be further explored for thin-film solar cells.
New WC-Cu composites for the divertor in fusion reactors
Publication . Dias, Marta; Pinhão, N.; Faustino, R.; Martins, Ricardo; Ramos, A. S.; Vieira, M. T.; Correia, J.B.; Camacho, E.; Fernandes, F. M. Braz; Nunes, B.; Almeida, Amélia; Mardolcar, U. V.; Alves, E.
ABSTRACT: The requirements for the divertor components of future fusion reactors are challenging and therefore a stimulus for the development of new materials. In this paper, WC-Cu composites are studied for use as thermal barrier between the plasma facing tungsten tiles and the copper-based heat sink of the divertor. Composite materials with 50% vol. WC were prepared by hot pressing and characterized in terms of microstructure, density, expansion coefficient, elastic modulus, Young's modulus and thermal diffusivity. The produced materials consisted of WC particles homogeneously dispersed in a Cu matrix with densifications between 88% and 98%. The sample with WC particles coated with Cu evidenced the highest densification. The thermal diffusivity was significantly lower than that of pure copper or tungsten. The sample with higher densification exhibits a low value of Young's modulus (however, it is higher compared to pure copper), and an average linear thermal expansion coefficient of 13.6 x 10(-6) degrees C-1 in a temperature range between 100 degrees C and 550 degrees C. To estimate the behaviour of this composite in actual conditions, a monoblock of the divertor in extreme conditions was modelled. The results predict that while the use of WC-Cu interlayer leads to an increase of 190 degrees C on the temperature of the upper part of the monoblock when compared to a pure Cu interlayer, the composite will improve and reduce significantly the cold-state stress between this interlayer and the tungsten.
Ultrafast low-temperature crystallization of solar cell graded formamidinium-cesium mixed-cation lead mixed-halide perovskites using a reproducible microwave-based process
Publication . Brites, Maria João; Barreiros, M. Alexandra; Corregidor, V.; Alves, L. C.; Pinto, Joana V.; Mendes, Manuel Joao; Fortunato, Elvira; Martins, Rodrigo; Mascarenhas, João
ABSTRACT: The control of morphology and crystallinity of solution-processed perovskite thin-films for solar cells is the key for further enhancement of the devices’ power conversion efficiency and stability. Improving crystallinity and increasing grain size of perovskite films is a proven way to boost the devices’ performance and operational robustness, nevertheless this has only been achieved with high-temperature processes. Here, we present an unprecedented low-temperature (<80 °C) and ultrafast microwave (MW) annealing process to yield uniform, compact, and crystalline FA0.83Cs0.17Pb(I(1–x)Brx)3 perovskite films with full coverage and micrometer-scale grains. We demonstrate that the nominal composition FA0.83Cs0.17PbI1.8Br1.2 perovskite films annealed at 100 W MW power present the same band gap, similar morphology, and crystallinity of conventionally annealed films, with the advantage of being produced at a lower temperature (below 80 °C vs 185 °C) and during a very short period of time (∼2.5 min versus 60 min). These results open new avenues to fabricate band gap tunable perovskite films at low temperatures, which is of utmost importance for Mechanically flexible perovskite cells and monolithic perovskite based tandem cells applications.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
5876
Funding Award Number
UID/CTM/50025/2013