Examination of organosilicon impregnating mixtures by static SIMS and diffuse reflectance FT-IR

Results of an extensive examination concerning effectiveness and durability of two different commercial organosilicon impregnating mixtures applied to Obernkirchener sandstone are presented briefly. Hygric tests and contact angle measurements prior to spectroscopic surface investigations of a propyl/octylsilane mixture and a methyl/octylsiloxane mixture reveal different long-term stability of the protective organosilicon coatings. General surface characteristics of the coatings were elucidated by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The measurements on freshly soaked stone slabs give evidence of spherical silsesquioxanes and their homoderivatives only of the precursor compound with the shorter alkyl chain. Investigations on the weathered coatings (8 years) show the presence of silsesquioxanes only in case of the silane system. Additional DRIFT (diffuse reflectance FT-IR) measurements on both freshly soaked and exposed material confirm the presence of the coating in case of the silane mixture, but not in case of the siloxane mixture.