Molecular Precursors to Boron Nitride Thin Films . 1 . Adsorption of Diborane on Ru ( 0001 ) , NH , / Ru ( 0001 ) , and O / Ru ( 0001 ) Surfaces

as berlinite. Therefore, the free energy of reaction 4 for AlP04-n molecular sieves can be estimated according to the available free energies of formation of dense AlP04 and SiOz phases, e.g., berlinite (AlP04) and quartz (SO2), which are structural analogues. For free energy calculations, we assume that AlC13 and PCls in reaction 4 are both gas-phase species since experimental reaction conditions employ high temperatures where these chlorides will be gas-phase species. As shown in Table IV, the free energy for the reaction of berlinite with SiCl, to form quartz at a temperature of 298 K is 301.5 kJ/mol. This value is very high compared to that observed for the reaction of an aluminosilicate zeolite with SiC14. The thermochemical properties of AlP04 berlinite at higher temperatures are not available to us. However, thermochemical data for the components in reaction 4 at different temperatures are available if we allow the AlP04 not to be berlinite.22 Using these data, it can be calculated that in a large temperature range the free energies do not significantly change