Repercussions of size heterogeneity on the measurement of specific surface areas of colloidal minerals: Combination of macroscopic and microscopic analyses
Résumé
The nature and the extent of reactive crystalline surfaces for colloidal particles is an essential factor
for understanding of reactions at the solid-liquid interfaces. The measurement of this specifi c surface
area for colloidal mineral particles is usually obtained from gas-adsorption isotherms. This measurement,
based on adsorbate-adsorbent interactions, yields overall weight-averaged values that fail to display the
distribution of geometrical specifi c surface areas of individual particles. The present work proposes to use
three dimensional atomic force microscopy (AFM) images to characterize the distribution of geometrical
features of hexagonal plate-like gibbsite [Al(OH)3] particles without microporosity. This sub-micrometer
approach, which requires minute quantities of solids (picograms), demonstrates the broad distribution
of specifi c surface areas (lateral, basal, and total) determined for each individual particle in our sample.
The resulting weight-averaged specifi c surface area values of basal and lateral surfaces, calculated from
this distribution, agree with values measured by Kr-adsorption isotherms. The lateral specifi c surface
area values thus obtained confi rm the estimates given by and are correlated with the infrared spectrum
analysis proposed in our previous papers. Moreover, these results reveal the importance of the smallest
particles in the overall distribution, whereas the weight-averaged value is monitored by high-mass particles
that are few in number. This kind of specifi c surface area heterogeneity must be taken into account
in describing the reactivity of anisotropic shaped mineral particles.