Statistical Characterization of Heterogeneous Dissolution Rates of Calcite from In situ and Real-Time AFM Imaging

Abstract The evolution of the surface topography of a calcite crystal subject to dissolution is documented through in situ real-time imaging obtained via atomic force microscopy (AFM). The dissolution process takes place by exposing the crystal surface to deionized water. AFM data allow detection of nucleation and expansion of mono- and multilayer rhombic etch pits and are employed to estimate the spreading rate of these structures. Spatially heterogeneous distributions of local dissolution rate are evaluated from the difference between topographic measurements taken at prescribed time intervals. We rest on a stochastic framework of analysis viewing the dissolution rate as a generalized sub-Gaussian (GSG) spatially correlated random process. Our analysis yields: (i) a quantitative assessment of the temporal evolution of the statistics of the dissolution rates as well as their spatial increments; (ii) a characterization of the degree of spatial correlation of dissolution rates and of the way this is linked to the various mechanisms involved in the dissolution process and highlighted through the experimental evidences. Our results indicate that the parameters driving the statistics of the GSG distribution and the spreading rate of the multilayer pits display a similar trend in time, thus suggesting that the evolution of these structures imprints the statistical features of local dissolution rates. Article Highlights We investigate dynamics of dissolution patterns on a calcite crystal in contact with deionized water via AFM imaging Temporal behavior of parameters of our statistical model is consistent with surface pattern evolution A nested model for the spatial correlation of rates embeds multiple mechanisms driving dissolution rate

A Combined Raman Spectroscopy and Atomic Force Microscopy System for In Situ and Real-Time Measures in Electrochemical Cells

: An innovative and versatile set-up for in situ and real time measures in an electrochemical cell is described. An original coupling between micro-Raman spectroscopy and atomic force microscopy enables one to collect data on opaque electrodes. This system allows for the correlation of topographic images with chemical maps during the charge exchange occurring in oxidation/reduction processes. The proposed set-up plays a crucial role when reactions, both reversible and non-reversible, are studied step by step during electrochemical reactions and/or when local chemical analysis is required

Evolution of the graphite surface in phosphoric acid: an AFM and Raman study

Phosphoric acid is an inorganic acid used for producing graphene sheets by delaminating graphite in (electro-)chemical baths. The observed phenomenology during the electrochemical treatment in phosphoric acid solution is partially different from other acidic solutions, such as sulfuric and perchloric acid solutions, where the graphite surface mainly forms blisters. In fact, the graphite surface is covered by a thin layer of modified (oxidized) material that can be observed when an electrochemical potential is swept in the anodic current regime. We characterize this particular surface evolution by means of a combined electrochemical, atomic force microscopy and Raman spectroscopy investigation

Sei mesi "diversi"

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Midterm Results of Intravascular Lithotripsy for Severely Calcified Common Femoral Artery Occlusive Disease: A Single-Center Experience

Purpose: Common femoral artery (CFA)-occlusive disease has traditionally been treated with open surgery, yet nowadays the frailty of patients has induced to find new techniques of revascularisation by endovascular means. So far, intravascular lithotripsy (IVL) has shown promising results in several lower limbs arterial districts. The purpose of this article is to report our experience with IVL for severely calcified peripheral arterial disease (PAD) of the CFA. Methods: From November 2018 and October 2020, 10 consecutive patients (12 limbs) treated with IVL were prospectively enrolled in a dedicated database. Inclusion criteria were CFA localization of PAD, with a severe degree of calcification, a lesion length >= 10 mm, and a degree of stenosis >= 70% (severe). The only admitted adjunctive treatment was drug-coated balloon (DCB) angioplasty. Primary outcomes were technical and procedural success, clinical success, and target lesion revascularisation (TLR). Secondary outcomes were target extremity revascularisation (TER) and major adverse events (MAEs). Results: All patients underwent IVL with associated DCB angioplasty. The median percentage of achieved stenosis reduction was 55.5% (interquartile range [IQR] 50-60.75), with a technical and procedural success of 100%. Over the study period, TLR only occurred in one limb (8.3%), with a mean upgrade in Rutherford class of 2.7 +/- 0.77. No target vessel and access site complications were reported, as well as no distal embolization. One death and one major amputation occurred over the follow-up period, both in the same patient. Conclusions: Based on our experience, IVL for selected cases of severely calcified CFA disease, associated with DCB angioplasty, may be considered a safe and effective technique. Of course, a long-term follow-up and a larger series of patients are needed to validate our results

Un caso di neurofibromatosi ad esordio molto precoce.

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