Evolution of calcite surfaces upon thermal decomposition, characterized by electrokinetics, in-situ XRD, and SEM

The present study analyses transformation pathways of pristine and thermally treated porous limestone and dense marble surfaces by means of time-resolved streaming current and potential measurements coupled with scanning electron microscopy and in-situ X-ray diffraction. The results reveal that under nonequilibrium conditions the zeta potential (zeta) of natural carbonates may exhibit positive and negative signs and zeta drifts in opposite directions. Sample surface roughness influences zeta because it contributes to dissolution, as observed particularly in the initial period of time-resolved measurements. Thermal treatment causes a temporary charge reversal from negative to positive. The reactivity of calcium hydroxide on calcite surfaces governs the net electrokinetic potential and isoelectric point (IEPpH), even at low surface coverage, as cross-validated by in-situ XRD. It was also found that pore conductivity may lead to similar to 90% underestimation of zeta when assessed by streaming potential. SEM studies revealed micro cracks inducement on marble after thermal treatment, which can result in underestimation of zeta up to the same extent as for the porous limestone. When an asymmetric cell configuration involving calcite and polypropylene surfaces is used, the fractional contribution of polypropylene to the IEPpH is 0.3 and to the overall determined zeta up to 0.5. Our findings contribute to the understanding of nonequilibrium and timedependent electrokinetic potential modifications associated with the reactivity of porous surfaces. This study highlights the effectiveness of the streaming potential technique for monitoring such changes further supported by the use of ancillary techniques to analyze the extend of chemo-mineralogical and physical alterations.

Automated summary

This study analyzes the transformation pathways of porous limestone and dense marble surfaces using a combination of techniques and reveals the influence of factors such as surface roughness, thermal treatment, and chemical reactions. It found that pore conductivity may lead to a significant underestimation of zeta potential.