Characterization of adsorption sites on a quartz powder from ESCA analysis of an adsorbed fatty diamine

摘要

In this report we describe a method to estimate the amount of adsorption sites on mineral surfaces by means of ESCA analysis. This is obtained from quantification of the adsorbed amount of a test molecule on a mineral surface. The approach is based on chemical derivatization of mineral powders followed by extraction in solvents of different polarities. This procedure also provides information on whether the adsorption sites on the mineral surfaces are of different or similar nature. The system studied was a fatty diamine adsorbed on quartz powder from a non-polar medium, n-octane, with subsequent desorption by extraction in pure n-octane and ethanol. This model system has application in asphalt systems, where fatty amines often are added to strengthen adhesion between bitumen and stone aggregates. Desorption was followed by surface analysis (ESCA) of the quartz powder to detect the fatty diamine remaining on the surface. Further analysis, using equations based on a substrate/overlayer model for flat and spherical particles, provided information on the adsorbed layer thickness and the adsorbed amount. After extraction with n-octane, a monolayer of the fatty diamine remains on the quartz surface. More fatty diamine can be removed by changing the extraction medium to a more polar solvent such as ethanol. This result demonstrates that this particular quartz powder has adsorption sites of differing nature on the surface.