Riassunto analitico
1. The crystallography of ice formed on the moon is contingent upon the cooling rate. Additionally, due to the general principle that heterogeneous nucleation necessitates half the energy of homogeneous nucleation, the crystallography is influenced by the properties of pre-existing substrates. This thesis discusses the experiments and results conducted on ice samples maintained in a cryogenic state, aimed at elucidating the potential structure of moon ice. The primary objective of this 6-months study was to investigate the crystal structure of ice under conditions similar to those present on the
moon, as well as to analyze the effects of contaminating the ice with various species of regolith. X-ray diffraction (XRD) was employed to investigate the ice structure. Cooling stage faced problems to keep the temperature at a desired value, while the pressure used was different base on the vacuum pump setup. The results predominantly revealed hexagonal and cubic ice structures, with no evidence of amorphous ice.
2. The use of Pb-free alloys is common in the commercial electronics and in automotive, but are not yet used in high reliability application as defense and aerospace. The experience of the commercial and automotive electronics has lead to development of many alloys in the last 15 years and currently a third generation of alloys starts to be used. Pb free alloys have very different metallurgy, aging mechanisms and failure mechanisms than the traditional SnPb alloys used in space application. In this study a preliminary characterization of the microstructure and intermetallic compounds evolution of solder alloys applied on an ENIG substrate when submitted to isothermal aging at 100°C, was done. The study has also investigated reversible transformation that might take place in these alloys in the typical thermal cycling regime used for accelerated reliability testing of solder connections confirming the importance understanding the metallurgy of the alloy in order to define representative accelerated test regime for the different alloy systems. Due to the test conducted with the XRD and SEM, a new set of temperature will be used for the LMPA-Q alloy and a better understanding of how to prepare the samples was gained.
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