EXAMINATION OF ORGANOSILICON IMPREGNATING MIXTURES BY STATIC SIMS ANDDIFFUSE-REFLECTANCE FT-IR

Results of an extensive examination concerning effectiveness and durab ility of two different commercial organosilicon impregnating mixtures applied to Obernkirchener sandstone are presented briefly. Hygric test s and contact angle measurements prior to spectroscopic surface invest igations of a propyl/octylsilane mixture and a methyl/octylsiloxane mi xture reveal different long-term stability of the protective organosil icon coatings. General surface characteristics of the coatings were el ucidated by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The measurements on freshly soaked stone slabs give evidence of spher ical silsesquioxanes and their homoderivatives only of the precursor c ompound with the shorter alkyl chain. Investigations on the weathered coatings (8 years) show the presence of silsesquioxanes only in case o f the silane system. Additional DRIFT (diffuse reflectance FT-IR) meas urements on both freshly soaked and exposed posed material confirm the presence of the coating in case of the silane mixture, but not in cas e of the siloxane mixture.