| Abstract: | Silica gel has been modified by successive gas reactions with (SiCl4-NH3) and (BCl3-NH3) in order to obtain Si-N and B-N preceramic polymers, which are chemically bound to the substrate surface. The effect of the polymer synsthesis on the porosity characteristics of the substrate is determined as a function of the number of applied modification cycles, using N2 adsorption-desorption isotherms recorded at 77 K. The elemental analysis data in combination with the adsorption isotherms yield a more detailed picture of the density and the homogeneity of the coatings. Using the pore size distributions, the contribution of pore blocking and pore narrowing can be calculated as a function of the amount of reaction cycles. A new calculation method for the pore blocking and pore narrowing, which is not based on any pore shape model, is also presented and compared with the former calculation method. |
