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  • In this regard http www apexbt


    In this regard, some attempts have been made to reduce the presence of those radicals. In presence of fluorine source, it seems that the fluorine atoms can substitute the hydrogen atoms linked to silicon atoms, forming Si-F bonds with a higher bonding (+)- Corydaline (536 kJ mo1−1) than the Si-H bonding energy (295 kJ mol−1) [23]. In addition, fluorine atoms saturate the extra silicon dangling bonds in the film, which prevent the formation of traps in the nitride and also decrease the surface state density. Kinetics of Si3N4 film depositions from various gaseous systems with ammonia shows that kinetic constant for formation of Si3N4 at normal pressure deposition systems increase in the order K SiC14< K SiH2CI2 < KSiH4. The fact that silane is more thermally unstable than SiCI4, while SiH2C12 shows an intermediate stability, explains this tendency. The lowest activation energy is for SiH4 whilst the highest one is for SiCI4, keeping SiH2C12 as the precursor with an intermediate value [24]. In this contribution, the hybrid system chemical vapor deposition and infiltration (HYSY-CVD and HYSY-CVI) methods were used [25]. In order to promote wetting of RHA by two Al alloys, a three-fold objective has been established for this investigation. The first objective consisted of depositing Si3N4 on RHA, via the thermal decomposition of Na2SiF6 in nitrogen containing atmospheres. The second objective was to establish the optimum processing conditions for maximizing the amount of silicon nitride deposited into porous silica (RHA) preforms by studying the quantitative effect of time and temperature, gas flow rate and nitrogen precursor (N2 or N2-5 vol. % NH3) on the amount of Si3N4 formed. Using the sessile drop method, the third objective was to conduct a comparative study of the wetting of Si3N4 coated silica, reagent-grade Si3N4 and SiO2 (RHA) substrates with two experimental Al-Si-Mg alloys, with the final aim of optimizing the wetting conditions.
    Results and discussion
    Conclusions Based on the results and discussion, within the framework of the experimental design, in the range of parameters and levels established for this study, it can be concluded that: