Vertical Scanning Interferometry Research Articles

Discontinuous Dissolution Mechanism of Olivine Deduced from a Topography Observation Method.

Olivine dissolution plays an important role in environmental science and technology, from controlling global element circulation to carbon capture for climate change mitigation. Most studies have been focused on investigating its dissolution rates by monitoring chemical effluent changes under various conditions. However, only by observation of surface reactivity can we unravel the actual mechanism (s) of dissolution. Here, we studied the dissolution of an olivine (010) plane in a flow-through reaction cell with an acidic solution, a surface-controlled regime, and far-from-equilibrium conditions. Direct mineral surface topography measurements using vertical scanning interferometry and atomic force microscopy allowed for quantitative analyses of the spatial and temporal changes in the dissolution rate. The (010) plane dissolved discontinuously in time for different surface sites, resulting in a heterogeneously distributed rate map. Pits with different depths showed opposite dissolution rate distributions from the dislocation center to further out from the etch pit. Based on the step-wave model, we propose a mechanism of dissolution that is governed by the competition between Gibbs free energy of the dissolution process, ΔG, and the critical free energy of the opening of etch pits, i.e., ΔGcrit. The migration of step waves, the distribution of surface defects, the strain field of etch pits, and other dynamic elements, resulting in the instantaneous change of ΔGcrit on the surface, are important factors leading to the discontinuous dissolution of crystal materials. This discontinuous dissolution provides new insight into the guidance of crystalline mineral applications and the prediction of material properties regarding mineral dissolution variation.

Linking calcite surface roughness resulting from dissolution to the saturation state of the bulk solution

It has long been supposed that mineral dissolution results in surface microtopography features that may be related to the weathering conditions. Detection of etch pits on weathered mineral surfaces is indicative of far-from-equilibrium conditions (Ω➔0), whereas their absence points towards close-to-equilibrium conditions (Ω➔1). However, surface microtopography characterizations limited solely to qualitative comparisons may conceal the potential of reconstructing intermediate saturation conditions. To investigate this prospect, we performed flow-through dissolution experiments at room temperature and atmospheric pCO2, on mechanically-polished {104} calcite surfaces reacting at different saturation states with respect to calcite (0 ≤ Ω ≤0.8), under alkaline conditions (pH = 7.9). Time-resolved topography data of the dissolved calcite surface were acquired ex situ using vertical scanning interferometry (VSI). Quantitative comparisons of the ensuing surface topography data relied on surface roughness characterizations, based on a combination of unidimensional descriptors (Ra) and spatial statistics metrics (power spectral density, or PSD, and semi-variogram). Time-resolved surface roughness analyses suggested a temporal stabilization of the calcite surfaces undergoing dissolution for all targeted saturation states, and that the steady-state surface roughness evaluations corresponding to different Ω values are statistically distinguishable, with larger roughness values corresponding to lower Ω values, according to a seemingly bijective relationship. We then investigated the atomic-scale mechanisms that might partially explain the empirical Ω-roughness relationship derived experimentally at the VSI-scale through kMC and Ising dissolution modeling of a Kossel crystal. We found that the Ising model successfully reproduced the Ω-roughness behavior observed experimentally, and we discussed the features that interpretative stochastic models need to satisfy to agree with the experimental findings. Overall, the present study suggests that, under the investigated conditions, the steady-state calcite surface roughness resulting from dissolution can be used as a proxy to back-estimate the saturation state of the fluid under which the reaction occurred for samples reacted under unknown conditions.

Passive vibration suppression method based on frequency domain analysis in white light vertical scanning interferometer

Vibration in manufacturing environment can significantly affects the accuracy of surface measurements, especially for the white light vertical scanning interferometry (VSI), which requires mechanical scanning for full-field measurements. This paper proposes a passive vibration suppression technique that integrates a second common-path interferometer and uses frequency domain analysis to measure vibration and reconstruct surface topography. The method is feasible for suppressing vibrations with different frequencies and amplitudes, as verified by simulation and signal recovery analysis. An in-house developed interferometer with a common optical path is used to demonstrate the measurement performance experimentally. The mathematical formula relating the vibration amplitude, the vibration frequency, the frame rate of the camera and the scanning interval is presented. The experimental results show that the precision of plane measurement decreases with increasing vibration amplitude and frequency. Moreover, the step sample signals under a maximum vibration condition of 400 nm/5 Hz are recovered, with a standard deviation of 26.07 nm for the step height measurement. As the scanning interval increases, the system can suppress higher-amplitude vibrations.

Effects of crystallographic orientation on calcite dissolution under alkaline conditions

This study investigates the dissolution of calcite’s (104) and (100) surfaces under alkaline conditions (pH 8.8–13.1) using vertical scanning interferometry under flow-through conditions. The dissolution rate of (100) surfaces decreases with increasing pH. For example, the dissolution rate at pH 8.8 is more than 20 times higher than that at pH 13.1. In contrast, the dissolution rate of (104) surfaces is far less sensitive to pH. We explain these observations as being on account of the preferential adsorption of [OH−] on (100) surfaces, inhibiting their dissolution. Particularly, this is because Ca-surface sites on (100) surfaces are less coordinated and have a stronger tendency for [OH−] adsorption. As a result, (100) surfaces dissolve nearly twice as fast as (104) surfaces at pH 8.8, whereas (104) surfaces dissolved ∼4.5 times faster than (100) surfaces at pH 13.1; indicating an inversion in dissolution behavior. The dissolution rate of (104) surfaces at pH 13.1 is 60 % of the rate at pH 10–12 because of the formation of slow dissolving microfacets of other orientations. The rhombohedral dissolution etch-pits formed on (104) surfaces, at lower pH’s, disappeared upon exposure to solutions with pH > 12 and were replaced by protrusions. The addition of up to 4 m (molality) NaCl enhances the dissolution of (104) surfaces at pH 8.8–13.1 and (100) surfaces at pH 8.8–11.0, and inhibited the dissolution of (100) surfaces at pH = 12.0–13.1. In addition, the competing adsorption between OH− and CO32− species mitigates the inhibition effects of CO32− on both surfaces at pH 13.1 compared to pH 11, and the dissolution of (100) surfaces is far less affected by CO32− than (104) surfaces. These results provide new insights into the rates and mechanisms of how crystallographic orientations affect calcite’s dissolution at alkaline pH conditions.

Predicting Dissolution Kinetics of Tricalcium Silicate Using Deep Learning and Analytical Models

The dissolution kinetics of Portland cement is a critical factor in controlling the hydration reaction and improving the performance of concrete. Tricalcium silicate (C3S), the primary phase in Portland cement, is known to have complex dissolution mechanisms that involve multiple reactions and changes to particle surfaces. As a result, current analytical models are unable to accurately predict the dissolution kinetics of C3S in various solvents when it is undersaturated with respect to the solvent. This paper employs the deep forest (DF) model to predict the dissolution rate of C3S in the undersaturated solvent. The DF model takes into account several variables, including the measurement method (i.e., reactor connected to inductive coupled plasma spectrometer and flow chamber with vertical scanning interferometry), temperature, and physicochemical properties of solvents. Next, the DF model evaluates the influence of each variable on the dissolution rate of C3S, and this information is used to develop a closed-form analytical model that can predict the dissolution rate of C3S. The coefficients and constant of the analytical model are optimized in two scenarios: generic and alkaline solvents. The results show that both the DF and analytical models are able to produce reliable predictions of the dissolution rate of C3S when it is undersaturated and far from equilibrium.

Temporal and spatial evolution of enzymatic degradation of amorphous PET plastics

Biocatalytic degradation is an emerging strategy aiming for energy-efficient recycling of poly(ethylene terephthalate) (PET), the most commonly used thermoplastic polyester. Besides material composition and physico-chemical parameters, the degradation kinetics is co-determined by the evolving nanotopography. In this study, the 3-dimensional development of the surface characteristics of an amorphous PET film, reacted with a highly effective hydrolase enzyme for up to 24 h, was explored by vertical scanning interferometry and confocal microscopy. The spatio-temporal analysis unveiled that the degradation process is not uniform with respect to reaction time and spatial reactivity distribution. An early phase of an unspecific roughness evolution is followed by an advanced phase characterized by a circular degradation pattern, consisting of shallow pits that are steadily renewed over time. The data suggest a hindrance of degradation during the initial roughening process, demonstrating the potential role of targeted surface modification in the large-scale treatment of plastic waste.

Correlated Study of Material Interaction Between Capillary Printed Eutectic Gallium Alloys and Gold Electrodes.

Liquid metals (LMs) play a growing role in flexible electronics and connected applications. Here, LMs come into direct contact with metal electrodes thus allowing for corrosion and additional alloying, potentially compromising device stability. Nevertheless, comprehensive studies on the interfacial interaction of the materials are still sparse. Therefore, a correlated material interaction study of capillary-printed Galinstan (eutetic alloy of Ga/In/Sn) with gold surfaces and electrodes is conducted. Comprehensive application of optical microscopy, vertical scanning interferometry, scanning electron microscopy/spectroscopy, x-ray photon spectroscopy, and atomic force microscopy allow for an in depth characterization of the spreading process of LM lines on gold films, revealing the differential spread of the different LM components and the formation of intermetallic nanostructures on the surface of the surrounding gold film. A model for the growth process based on the penetration of LM along the gold film grain boundaries is proposed based on the obtained time-dependent characterization. The distribution of gold, Galinstan, and intermetallic phases in a gold wire dipped into LM is observed using X-ray nano tomography as a complementary view on the internal nanostructure. Finally, resistance measurements on LM lines connecting gold electrodes over time allow to estimate the influence on the material interaction on electronic applications.

In Vitro Analysis of Shear Stress: CAD Milled vs Printed Denture Base Resins with Bonded Denture Tooth.

As the fabrication of computer-aided design (CAD) milled and 3D printed denture base resins with bonded denture teeth increase in popularity, there is a need for research comparing the shear bond stress of milled and printed denture base resins with bonded denture teeth to that of a conventional heat processed denture base. Denture base resin specimens (n = 9) were fabricated according to manufacturers' instructions using a novel test design. Two milled (Ivobase CAD PMMA, Ivoclar Vivadent and Polident PMMA, Polident Dental) and two 3D printed (Denture Base LP Resin, Formlabs and Lucitone Digital Print, Dentsply Sirona) materials were used. Conventional heat processed polymethylmethacrylate was used as the control (Lucitone 199, Dentsply Sirona). Denture teeth (VITA Vitapan XL T44, #8, VITA Zahnfabrik) were bonded to their respective bases using denture tooth bonding agent (Ivobase CAD bonding system, Ivoclar). Specimens were aged in water for 600 hours at 37°C and loaded until failure in a Universal testing machine. Shear bond stress was calculated. All specimens were evaluated for mode of failure and select specimens under scanning electron microscope and vertical scanning interferometry. Data were analyzed with one-way ANOVA followed by Tukey test (IBM SPSS) and fracture analysis performed. Shear stress was highest for the heat processed control (mean = 180 N ±26.76) and Polident test groups (mean = 180 N ± 34.90). Milled specimens were not significantly different from the control (p = 0.076 for IvoBase CAD and 1.00 for Polident), while the printed groups were significantly different from the control (p = 0.012 for Formlabs Denture Base Resin and p = 0.00 for Carbon Lucitone Digital Print). Milled denture base resins performed similarly to heat processed denture base resin and better than 3D printed denture bases. For complete denture wearers, all resin materials used in this study may be clinically acceptable, as the sheer stress for all groups was higher than the reported maximum biting force of complete denture patients. However, for implant retained prostheses, the incorporation of additional retentive features should be considered when bonding denture teeth to printed bases. More research is needed to evaluate methods to increase the bond strength of denture teeth to printed denture base resins.

Upscaling calcite dissolution rates in a tight reservoir sandstone

Calcite is a highly abundant mineral in the Earth’s crust and occurs as a cement phase in numerous siliciclastic sediments, where it often represents the most reactive component when a fluid percolates through the rock. Hence, the objective of this study is to derive calcite dissolution rates on different scales in a reservoir sandstone using mineral surface experiments combined with vertical scanning interferometry (VSI) and two types of core plug experiments. The 3D geometry of the calcite cement phase inside the rock cores was characterized by X-ray micro-computed tomography (µXCT) and was used to attempt dissolution rate upscaling from the mineral surface to the core scale. Initially (without upscaling), our comparison of the far-from-equilibrium dissolution rates at the mineral surface (µm-mm-scale, low fluid residence time) and the surface normalized dissolution rates obtained from the core experiments (cm-scale, high fluid residence time) revealed differences of 0.5–2 orders of magnitude. The µXCT geometric surface area connected to the open pore space left( {GSA_{{Cc,{text{open}}}} } right) considers the fluid accessibility of the heterogeneously distributed calcite cement that can largely vary between individual samples, but greatly affects the effective dissolution rates. Using this parameter to upscale the rates from the µm- to the cm-scale, the deviation of the upscaled total dissolution rates from the measured total dissolution rates was less than one order of magnitude for all investigated rock cores. Thus, GSA_{{Cc,{text{open}}}} showed to be reasonably suitable for upscaling the mineral surface rates to the core scale.

A sensitive impedimetric immunosensor for the detection of Interleukin-8 in nasal epithelial lining fluid of asthma patients

We report the development of a label-free, affinity-based impedimetric biosensor for the quantitative detection of interleukin-8 (IL-8) present in the nasal epithelial lining fluid (NELF). Early diagnosis of IL-8 in NELF samples enables prognosis of inflammatory respiratory disorders including asthma, chronic obstructive pulmonary disease, and adult respiratory distress syndrome. The study involves the fabrication of an electrochemical biosensor by immobilising polyclonal anti-IL-8 antibody on the anti-fouling zwitterionic hydrogel; polycarboxybetaine methacrylate (pCBMA). The immunosensor was characterised using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), vertical scanning interferometry (VSI) and scanning electron microscopy (SEM). Faradaic EIS measurements were conducted to explore the performance of the immunosensor via changes in charge transfer resistance. The sensor exhibited a good analytical performance in the detection and quantification of IL-8 in complex biological media. The biosensor showed a wide range of IL-8 detection, ranging from 55 fM to 55 nM with a 10 fM limit of detection (LOD). The biosensor showed a high selectivity to IL-8 and 90% reproducibility using untreated NELF samples, with 15-min time to result. These results provide a promising potential for multiplexing the cytokine platform for the profiling, diagnosis and clinical signaturing of associated respiratory disorders.

Low Carbon Footprint Recycling of Post-Consumer PET Plastic with a Metagenomic Polyester Hydrolase.

Earth is flooded with plastics and the need for sustainable recycling strategies for polymers has become increasingly urgent. Enzyme‐based hydrolysis of post‐consumer plastic is an emerging strategy for closed‐loop recycling of polyethylene terephthalate (PET). The polyester hydrolase PHL7, isolated from a compost metagenome, completely hydrolyzes amorphous PET films, releasing 91 mg of terephthalic acid per hour and mg of enzyme. Vertical scanning interferometry shows degradation rates of the PET film of 6.8 μm h−1. Structural analysis indicates the importance of leucine at position 210 for the extraordinarily high PET‐hydrolyzing activity of PHL7. Within 24 h, 0.6 mgenzyme gPET −1 completely degrades post‐consumer thermoform PET packaging in an aqueous buffer at 70 °C without any energy‐intensive pretreatments. Terephthalic acid recovered from the enzymatic hydrolysate is then used to synthesize virgin PET, demonstrating the potential of polyester hydrolases as catalysts in sustainable PET recycling processes with a low carbon footprint.

A sensitive impedimetric immunosensor for the detection of Interleukin-8 in nasal epithelial lining fluid of asthma patients

We report the development of a label-free, affinity-based impedimetric biosensor for the quantitative detection of interleukin-8 (IL-8) present in the nasal epithelial lining fluid (NELF). Early diagnosis of IL-8 in NELF samples enables prognosis of inflammatory respiratory disorders including asthma, chronic obstructive pulmonary disease, and adult respiratory distress syndrome. The study involves the fabrication of an electrochemical biosensor by immobilising polyclonal anti-IL-8 antibody on the anti-fouling zwitterionic hydrogel; polycarboxybetaine methacrylate (pCBMA). The immunosensor was characterised using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), vertical scanning interferometry (VSI) and scanning electron microscopy (SEM). Faradaic EIS measurements were conducted to explore the performance of the immunosensor via changes in charge transfer resistance. The sensor exhibited a good analytical performance in the detection and quantification of IL-8 in complex biological media. The biosensor showed a wide range of IL-8 detection, ranging from 55 fM to 55 nM with a 10 fM limit of detection (LOD). The biosensor showed a high selectivity to IL-8 and 90% reproducibility using untreated NELF samples, with 15-min time to result. These results provide a promising potential for multiplexing the cytokine platform for the profiling, diagnosis and clinical signaturing of associated respiratory disorders.

Simultaneous film thickness and refractive index measurement using a constrained fitting method in a white light spectral interferometer.

Film is widely used in optoelectronic and semiconductor industries. The accurate measurement of the film thickness and refractive index, as well as the surface topography of the top and bottom surfaces are necessary to ensure its processing quality. Multiple measurement methods were developed; however, they are limited by the requirements of a known dispersion model and initial values of thickness and refractive index. Further, their systems are rarely compatible with surface topography measurement methods. We propose a constrained nonlinear fitting method to simultaneously measure the thickness and refractive index of film in a simple white-light spectral interferometer. The nonlinear phase extracted by the spectral phase-shifting is fitted with the theoretical nonlinear phase obtained by multiple reflection model. The constraints of nonlinear fitting are obtained by the interferometric signal of vertical scanning, reconstructed by the integration of the white-light spectral signal to avoid local minima. The proposed method does not require a priori knowledge of the dispersion model and initial values of thickness and refractive index, and its system is compatible with the vertical scanning interferometry (VSI) method to reconstruct the surface topography of the top and bottom surfaces of film. Three SiO2 films with different thicknesses are measured, and the results show that the measured refractive index is within the theoretical value range of wavelength bandwidth and the measured thicknesses are closely aligned with the values provided by the commercial instrument. The measurement repeatability of refractive index reaches 10-3. Measurements on a polymer film demonstrate that this method is feasible for measuring the film without a priori information.

Heterogeneous Sorption of Radionuclides Predicted by Crystal Surface Nanoroughness.

Reactive transport modeling (RTM) is an essential tool for the prediction of contaminants' behavior in the bio- and geosphere. However, RTM of sorption reactions is constrained by the reactive surface site assessment. The reactive site density variability of the crystal surface nanotopography provides an "energetic landscape", responsible for heterogeneous sorption efficiency, not covered in current RTM approaches. Here, we study the spatially heterogeneous sorption behavior of Eu(III), as an analogue to trivalent actinides, on a polycrystalline nanotopographic calcite surface and quantify the sorption efficiency as a function of surface nanoroughness. Based on experimental data from micro-focus time-resolved laser-induced luminescence spectroscopy (μTRLFS), vertical scanning interferometry, and electron back-scattering diffraction (EBSD), we parameterize a surface complexation model (SCM) using surface nanotopography data. The validation of the quantitatively predicted spatial sorption heterogeneity suggests that retention reactions can be considerably influenced by nanotopographic surface features. Our study presents a way to implement heterogeneous surface reactivity into a SCM for enhanced prediction of radionuclide retention.

Statistical Description of Calcite Surface Roughness Resulting from Dissolution at Close-to-Equilibrium Conditions

Linking the evolution of the surface area (as quantified, e.g., through its spatial roughness) of minerals to their dissolution rate is a key aspect of mineral reactivity. Unraveling the nature of their main features requires relying on approaches yielding a quantitative characterization of the temporal evolution of surface topography/roughness. Here, a mechanically polished {104} calcite surface was dissolved at room temperature and at close-to-equilibrium conditions (Ω = 0.6) with an alkaline solution (pH = 8) across a temporal window of 8 days. Surface topography images were acquired daily using vertical scanning interferometry, the ensuing topography data being then embedded within a statistical analysis framework aimed at describing comprehensively the surface roughness evolution. The strongest system variations were observed after 1 day: the probability density function of surface roughness was observed to transition from being approximately Gaussian to being left-skewed and leptokurtic, exhibiting a dramatic increase in the variance and a significant change in the semi-variogram structure. After a relaxation time of approximately 2 days, the reacting surface appeared to attain a steady-state configuration, being characterized by the values of the statistical moments characterizing surface roughness that become virtually independent of time. Attempting to unravel the underlying dissolution mechanism, an original numerical model able to reproduce satisfactorily the statistical behavior observed experimentally was developed and tested. Our results suggest that under the investigated conditions, dissolution may be characterized as a spatially correlated random process, with the areas most exposed to the flowing fluid being prone to preferential dissolution. The numerical model was also used to obtain insights into the influences of the initial surface roughness and of the fluid composition on the steady-state statistical characterization of the surface roughness. Our results suggest that the influence of the initial surface roughness is limited. The present study suggests that potential empirical relations linking the surface roughness of the reacted crystals to the saturation state at which they dissolved may be developed, which would allow to back-estimate the reacting conditions only based on topography data.

Implementing Heterogeneous Crystal Surface Reactivity in Reactive Transport Simulations: The Example of Calcite Dissolution

Both surface reactivity and fluid dynamics control the dissolution kinetics of crystalline material. In this study, we performed a 3D reactive transport simulation to investigate the impact of surface topography heterogeneity superimposed to fluid transport heterogeneity on the dissolution rate of calcite. The model simulates the chemical reaction of calcite dissolution, solute transport, and crystal surface geometry evolution. Importantly, we introduce heterogeneous surface reactivity into the reactive transport simulation. We test the surface slope factor as a proxy value for the intrinsic surface reactivity of dissolving crystal surface nanotopographies. Experimental data sets collected using vertical scanning interferometry validate this approach. The novel parametrization allows for the simulation of surface-controlled heterogeneous reactivity in reactive transport simulations of mineral surface dissolution.

Effects of surface roughness and mineralogy on the sorption of Cm(III) on crystalline rock

Crystalline rock is one of the host rocks considered for a future deep geological repository for highly active radiotoxic nuclear waste. The safety assessment requires reliable information on the retention behavior of minor actinides. In this work, we applied various spatially resolved techniques to investigate the sorption of Curium onto crystalline rock (granite, gneiss) thin sections from Eibenstock, Germany and Bukov, Czech Republic. We combined Raman-microscopy, calibrated autoradiography and µTRLFS (micro-focus time-resolved fluorescence spectroscopy) with vertical scanning interferometry to study in situ the impact of mineralogy and surface roughness on Cm(III) uptake and molecular speciation on the surface. Heterogeneous sorption of Cm(III) on the surface depends primarily on the mineralogy. However, for the same mineral class sorption uptake and strength of Cm(III) increases with growing surface roughness around surface holes or grain boundaries. When competitive sorption between multiple mineral phases occurs, surface roughness becomes the major retention parameter on low sorption uptake minerals. In high surface roughness areas primarily Cm(III) inner-sphere sorption complexation and surface incorporation are prominent and in selected sites formation of stable Cm(III) ternary complexes is observed. Our molecular findings confirm that predictive radionuclide modelling should implement surface roughness as a key parameter in simulations.

Influence of Processing Route on the Surface Reactivity of Cu47Ti33Zr11Ni6Sn2Si1 Metallic Glass

Recently, laser additive manufacturing (AM) techniques have emerged as a promising alternative for the synthesis of bulk metallic glasses (BMGs) with massively increased freedom in part size and geometry, thus extending their economic applicability of this material class. Nevertheless, porosity, compositional inhomogeneity, and crystallization display themselves to be the emerging challenges for this processing route. The impact of these “defects” on the surface reactivity and susceptibility to corrosion was seldom investigated but is critical for the further development of 3D-printed BMGs. This work compares the surface reactivity of cast and additively manufactured (via laser powder bed fusion—LPBF) Cu47Ti33Zr11Ni6Sn2Si1 metallic glass after 21 days of immersion in a corrosive HCl solution. The cast material presents lower oxygen content, homogeneous chemical distribution of the main elements, and the surface remains unaffected after the corrosion experimentation based on vertical scanning interferometry (VSI) investigation. On the contrary, the LPBF material presents a considerably higher reactivity seen through crack propagations on the surface. It exhibits higher oxygen content, heterogeneous chemical distribution, and presence of defects (porosity and cracks) generated during the manufacturing process.

The role of crystal heterogeneity in alkali feldspar dissolution kinetics

Intrinsic heterogeneities of crystals almost always impose challenges on the investigation of dissolution kinetics. In the case of the incomplete solid solution series of alkali feldspars, additional complexity to the wide range in chemical composition and crystallographic characteristics is introduced in the form of chemical differentiation at low cooling temperatures. In this paper, we use direct measurements of intact crystal surfaces to quantify the dissolution rate of an alkali feldspar, providing details unavailable to powder dissolution experiments alone. In particular, we show how complex intergrowth textures characteristic of feldspars may play an important role in terms of how these minerals dissolve.By means of a comprehensive experimental and analytical framework using Raman coupled vertical scanning interferometry (Rc-VSI), atomic force microscopy (AFM), light microscopy (LM), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM), detailed information on heterogeneities in surface reactivity, morphology, chemistry, structure and texture of the dissolving surface are provided. The combination of spatially resolved qualitative and quantitative data revealed significant differences both in absolute rates and rate distributions associated with the potassium- and sodium-rich compositional compounds of which the latter dissolved slower with less dispersion in rates than the former. Whereas the spatial dissolution rate variances could not be explained by compositional differences between the two distinct feldspar phases alone, surface reactivity was successfully shown to vary with unique properties of the surface texture as well. A close relationship between enhanced dissolution and defect site distribution was observed, which critically depends on intergrowth geometry and phase internal twinning patterns. These observations are of great importance to any kind of experimental study and modeling approach which aims to improve the understanding of the dissolution kinetics of chemically and crystallographically complex materials.

The contribution of hydrodynamic processes to calcite dissolution rates and rate spectra

Recent measurements on the dissolution rate of nano- and micron-scale rough calcite surfaces have shown lateral variations in dissolution rate, which can be quantified using rate spectra. This study uses numerical simulations to investigates the hydrodynamic processes during such experiments to explore whether hydrodynamic effects can explain the observed dissolution rate spectra. For this purpose, we simulated the dissolution processes of nano- and micron-scale rough calcite surfaces in COMSOL Multiphysics. We imposed surface topographies and local reaction rates measured using Vertical Scanning Interferometry (VSI), and implemented the same flow rate (i.e., 6 × 10−8 m3 s−1), solution chemistry (pH 8.8, alkalinity 4.4 meq/kg-H2O and pCO2 10−3.48 bar) and flow-cell geometry as those used in the experiment. We have compared the simulated rate spectra against the experimentally measured values at a calcite surface having the same surface topography and reactive-flow conditions.Simulations using a single dissolution rate for the rough calcite surface did not produce similarly wide dissolution rate spectra like those observed experimentally. Our results have shown that only by explicitly incorporating the rate spectra in the model the simulated and the measured rate spectra would match. Sensitivity analyses by varying chemical composition and flow velocity were performed to examine the effects of these parameters on the calculated rate spectra. This study concludes that for the reactive-flow regimes where dissolution rate spectra are observed experimentally, the chemical heterogeneity, topography of the crystal surface and the resulting heterogeneity in the free energy landscape at the surface play a major role in controlling the dissolution rate spectra. With the injection of more acidic (pH 2) solutions at higher velocities (i.e., 0.04 m s−1), we observed an increase in the hydrodynamics-induced rate variability at microscopically rough surfaces.