Biomedical subjects

Malvina G Orkoula

Publications and source records attributed to Malvina G Orkoula.

2 recordsLinked to original sources

PubMed2003

Kinetics of dissolution of powdered Pentelic marble in under-saturated solutions: the role of particle characteristics.

In the present study, the effect of mesopore and particle size distributions on the kinetics of dissolution of powdered Pentelic marble was investigated. Powders obtained by grinding marble slabs in an agate mortar with a pestle (1-3.5 min) were found to be non-porous by nitrogen absorption measurements. These powders, upon dissolution under conditions of constant under-saturation, 25 degrees C, pH 8.25, showed that the kinetics in the absence of mesopores depended on the number of active sites on the exposed surface. Thus, powders consisting of smaller particles, having higher specific surface areas, yielded higher rates of dissolution. Powders, however, which were prepared by grinding marble slabs in a cylinder mill for time periods between 2.0 and 30.0 min, and which exhibited considerable mesoporosity, showed the opposite trend. The rates of dissolution measured for these powders in under-saturated solutions increased with increasing mean particle size and decreased with increasing specific surface area. This finding suggested that the presence of mesopores resulted in lower dissolution rates even though the exposed total surface area was larger. Furthermore, the larger the number of mesopores in a powder sample the slower the corresponding dissolution rates in under-saturated solutions.

Journal Article↗

PubMed2002

Variability of dissolution rates at constant undersaturation.

Dissolution processes play an important role in marble weathering. Investigation of the dissolution kinetics of powdered Pentelic marble, a calcitic natural stone, showed that the rates measured at constant undersaturation decreased with time. It was found that the rate of dissolution decreased sharply to about 50% of the initial value before 5% of the initially suspended powder was dissolved. Past a dissolution extent corresponding to 25% with respect to the suspended solid, the rates of dissolution at the same constant undersaturation reached a stable value corresponding to 20-25% of the initial rate measured. The reduction in the rates of dissolution up to 25% of mass loss was in agreement with the reduction in the total surface area exposed to the solution, suggesting a dependence of the rate on the number of active sites on the surface of the dissolving material. The decrease in the dissolution rates did not depend on the undersaturation of the solution or on the physical characteristics of the particles such as specific surface area, porosity, and particle size distribution. Equal mass losses, with respect to the initially suspended solid, of different samples exhibited the same relative decrease in rate regardless of the conditions of the aqueous solutions.

Journal Article↗