Real-time in situ observations of reaction and transport phenomena during silicate glass corrosion by fluid-cell Raman spectroscopy

Molecular insight into the initial hydration of tricalcium aluminate

Portland cement (PC) is ubiquitously used in construction for centuries, yet the elucidation of its early-age hydration remains a challenge. Understanding the initial hydration progress of tricalcium aluminate (C3A) at molecular scale is thus crucial for tackling this challenge as it exhibits a proclivity for early-stage hydration and plays a pivotal role in structural build-up of cement colloids. Herein, we implement a series of ab-initio calculations to probe the intricate molecular interactions of C3A during its initial hydration process. The C3A surface exhibits remarkable chemical activity in promoting water dissociation, which in turn facilitates the gradual desorption of Ca ions through a metal-proton exchange reaction. The dissolution pathways and free energies of these Ca ions follow the ligand-exchange mechanism with multiple sequential reactions to form the ultimate products where Ca ions adopt fivefold or sixfold coordination. Finally, these Ca complexes reprecipitate on the remaining Al-rich layer through the interface-coupled dissolution-reprecipitation mechanism, demonstrating dynamically stable inner-sphere adsorption states. The above results are helpful in unmasking the early-age hydration of PC and advancing the rational design of cement-based materials through the bottom-up approach.

Silica Polymerization Driving Opposite Effects of pH on Aqueous Carbonation Using Crystalline and Amorphous Calcium Silicates

The aqueous carbonation of calcium silicate (CS), a representative alkaline-earth silicate, has been widely explored in studies of carbon dioxide (CO2) mineralization. In this context, we conducted a specific comparison of the carbonation behaviors between the crystalline calcium silicate (CCS) and amorphous calcium silicate (ACS) across a pH range from 9.0 to 12.0. Interestingly, we observed opposite pH dependencies in the carbonation efficiencies (i.e., CaO conversion into CaCO3 in 1 M Na2CO3/NaHCO3 solution under ambient conditions) of CCS and ACS─the carbonation efficiency of CCS decreased with increasing the solution basicity, while that of ACS showed an inverse trend. In-depth insights were gained through in situ Raman characterizations, indicating that these differing trends appeared to originate from the polymerization/depolymerization behaviors of silicates released from minerals. More specifically, higher pH conditions seemed to favor the carbonation of minerals containing polymerized silica networks. These findings may contribute to a better understanding of the fundamental factors influencing the carbonation behaviors of alkaline earth silicates through interfacial coupled dissolution and precipitation processes. Moreover, they offer valuable insights for selecting optimal carbonation conditions for alkaline-earth silicate minerals.

Visualization-enhanced under-oil open microfluidic system for in situ characterization of multi-phase chemical reactions

Under-oil open microfluidic system, utilizing liquid-liquid boundaries for confinements, offers inherent advantages including clogging-free flow channels, flexible access to samples, and adjustable gas permeation, making it well-suited for studying multi-phase chemical reactions that are challenging for closed microfluidics. However, reports on the novel system have primarily focused on device fabrication and functionality demonstrations within biology, leaving their application in broader chemical analysis underexplored. Here, we present a visualization-enhanced under-oil open microfluidic system for in situ characterization of multi-phase chemical reactions with Raman spectroscopy. The enhanced system utilizes a semi-transparent silicon (Si) nanolayer over the substrate to enhance visualization in both inverted and upright microscope setups while reducing Raman noise from the substrate. We validated the system's chemical stability and capability to monitor gas evolution and gas-liquid reactions in situ. The enhanced under-oil open microfluidic system, integrating Raman spectroscopy, offers a robust open-microfluidic platform for label-free molecular sensing and real-time chemical/biochemical process monitoring in multi-phase systems.

Unveiling Corrosion Pathways of Sn Nanocrystals through High-Resolution Liquid Cell Electron Microscopy

Unveiling materials' corrosion pathways is significant for understanding the corrosion mechanisms and designing corrosion-resistant materials. Here, we investigate the corrosion behavior of Sn@Ni3Sn4 and Sn nanocrystals in an aqueous solution in real time by using high-resolution liquid cell transmission electron microscopy. Our direct observation reveals an unprecedented level of detail on the corrosion of Sn metal with/without a coating of Ni3Sn4 at the nanometric and atomic levels. The Sn@Ni3Sn4 nanocrystals exhibit "pitting corrosion", which is initiated at the defect sites in the Ni3Sn4 protective layer. The early stage isotropic etching transforms into facet-dependent etching, resulting in a cavity terminated with low-index facets. The Sn nanocrystals under fast etching kinetics show uniform corrosion, and smooth surfaces are obtained. Sn nanocrystals show "creeping-like" etching behavior and rough surfaces. This study provides critical insights into the impacts of coating, defects, and ion diffusion on corrosion kinetics and the resulting morphologies.

Probing corrosion using a simple and versatile in situ multimodal corrosion measurement system

In this work, we have developed a unique in situ multimodal corrosion system that is capable of acquiring electrochemical data, sample imaging/visualization and hydrogen collection, simultaneously. Each of these modalities yield valuable information pertaining to the ongoing corrosion process. Combining them can yield holistic information on the role of microstructure, processing history, presence of coatings, etc., on the sequence of steps occurring during the corrosion process, and how they correlate with the acquired electrochemical data. Four materials systems, namely AA6061-T6 aluminum alloy, AZ91 magnesium alloy, galvanized DP590 steel, and pure Zn, were investigated under open circuit potential and under potentiodynamic polarization. The multimodal corrosion system was utilized to observe processes such as surface passivation and dissolution, pit and filiform corrosion initiation and propagation, and was correlated with location and magnitude of hydrogen evolution. This approach is shown to yield a truly multimodal understanding of the ongoing corrosion processes.

Enhancing Aqueous Carbonation of Calcium Silicate through Acid and Base Pretreatments with Implications for Efficient Carbon Mineralization

Carbon dioxide (CO2) mineralization based on aqueous carbonation of alkaline earth silicate minerals is a promising route toward large-scale carbon removal. Traditional aqueous carbonation methods largely adopt acidification-based approaches, e.g., using concentrated/pressurized CO2 or acidic media, to accelerate mineral dissolution and carbonation. In this study, we designed and tested three distinctive routes to evaluate the effect of pretreatments under different pH conditions on aqueous carbonation, using amorphous calcium silicate (CS) as an example system. Pretreating CS with high concentrations (100 mM) of HCl (Route I) or NaOH (Route II and III) enhanced their carbonation degrees. However, NaOH pretreatment overall yielded higher carbonation degrees than the HCl pretreatment, with the highest carbonation degree achieved through Route III, where an extra step is taken after the NaOH pretreatment to remove the solution containing dissolved silica prior to carbonation. The HCl and NaOH pretreatments formed different intermediate silica products on the CS surface. Silica precipitated from the HCl pretreatment had a minimal effect on the carbonation degree. The high Ca/Si ratio intermediate phases formed from the NaOH, on the other hand, can be readily carbonated. In contrast to commonly utilized acidification-based approaches, basification offers a more promising route to accelerate aqueous carbonation as it can mitigate the need for costly pH swing and high-concentration/pressurized CO2. The key to aqueous carbonation under basic conditions, as suggested by this study, is the control of aqueous silica species that have a suppressing effect on carbonation. Overall, this study highlights the critical needs for investigations of aqueous mineral carbonation in a broader pH region.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Demonstrating low Raman background in UV-written SiO2 waveguides

Raman spectroscopy can give a chemical 'fingerprint' from both inorganic and organic samples, and has become a viable method of measuring the chemical composition of single biological particles. In parallel, integration of waveguides and microfluidics allows for the creation of miniaturized optical sensors in lab-on-a-chip devices. The prospect of combining integrated optics and Raman spectroscopy for Raman-on-chip offers new opportunities for optical sensing. A major limitation for this is the Raman background of the waveguide. This background is very low for optical fibers but remains a challenge for planar waveguides. In this work, we demonstrate that UV-written SiO2 waveguides, designed to mimic the performance of optical fibers, offer a significantly lower background than competing waveguide materials such as Si3N4. The Raman scattering in the waveguides is measured in absolute units and compared to that of optical fibers and Si3N4 waveguides. A limited study of the sensitivity of the Raman scattering to changes in pump wavelength and in waveguide design is also conducted. It is revealed that UV-written SiO2 waveguides offer a Raman background lower than -107.4 dB relative to a 785 nm pump and -106.5 dB relative to a 660 nm pump. Furthermore, the UV-written SiO2 waveguide demonstrates a 15 dB lower Raman background than a Si3N4 waveguide and is only 8.7 - 10.3 dB higher than optical fibers. Comparison with a polystyrene bead (in free space, diameter 7 µm) reveal an achievable peak SNR of 10.4 dB, showing the potential of UV-SiO2 as a platform for a Raman-on-chip device capable of measuring single particles.

Tracking Molecular Diffusion across Biomaterials' Interfaces Using Stimulated Raman Scattering

The determination of molecular diffusion across biomaterial interfaces, including those involving hydrogels and tissues remains important, underpinning the understanding of a broad range of processes including, for example, drug delivery. Current techniques using Raman spectroscopy have previously been established as a method to quantify diffusion coefficients, although when using spontaneous Raman spectroscopy, the signal can be weak and dominated by interferences such as background fluorescence (including biological autofluoresence). To overcome these issues, we demonstrate the use of the stimulated Raman scattering technique to obtain measurements in soft tissue samples that have good signal-to-noise ratios and are largely free from fluorescence interference. As a model illustration of a small metabolite/drug molecule being transported through tissue, we use deuterated (d⁷-) glucose and monitor the Raman C-D band in a spectroscopic region free from other Raman bands. The results show that although mass transport follows a diffusion process characterized by Fick's laws within hydrogel matrices, more complex mechanisms appear within tissues.

Influence of Environmental Parameters and Fiber Orientation on Dissolution Kinetics of Glass Fibers in Polymer Composites

Glass fibers slowly dissolve and age when exposed to water molecules. This phenomenon also occurs when glass fibers are inside fiber-reinforced composites protected by the matrix. This environmental aging results in the deterioration of the mechanical properties of the composite. In structural applications, GFRPs are continuously exposed to water environments for decades (typically, the design lifetime is around 25 years or even more). During their lifetime, these materials are affected by various temperatures, pH (acidity) levels, mechanical loads, and the synergy of these factors. The rate of the degradation process depends on the nature of the glass, sizing, fiber orientation, and environmental factors such as acidity, temperature, and mechanical stress. In this work, the degradation of typical industrial-grade R-glass fibers inside an epoxy fiber-reinforced composite was studied experimentally and computationally. A Dissolving Cylinder Zero-Order Kinetic (DCZOK) model was applied and could describe the long-term dissolution of glass composites, considering the influence of fiber orientation (hoop vs. transverse), pH (1.7, 4.0, 5.7, 7.0, and 10.0), and temperature (20, 40, 60, and 80 °C). The limitations of the DCZOK model and the effects of sizing protection, the accumulation of degradation products inside the composite, and water availability were investigated. Dissolution was experimentally measured using ICP-MS. As in the case of the fibers, for GFRPs, the temperature showed an Arrhenius-type influence on the kinetics, increasing the rate of dissolution exponentially with increasing temperature. Similar to fibers, GFRPs showed a hyperbolic dependence on pH. The model was able to capture all of these effects, and the limitations were addressed. The significance of the study is the contribution to a better understanding of mass loss and dissolution modeling in GFRPs, which is linked to the deterioration of the mechanical properties of GFRPs. This link should be further investigated experimentally and computationally.

Modelling of Environmental Ageing of Polymers and Polymer Composites-Modular and Multiscale Methods

Service lifetimes of polymers and polymer composites are impacted by environmental ageing. The validation of new composites and their environmental durability involves costly testing programs, thus calling for more affordable and safe alternatives, and modelling is seen as such an alternative. The state-of-the-art models are systematized in this work. The review offers a comprehensive overview of the modular and multiscale modelling approaches. These approaches provide means to predict the environmental ageing and degradation of polymers and polymer composites. Furthermore, the systematization of methods and models presented herein leads to a deeper and reliable understanding of the physical and chemical principles of environmental ageing. As a result, it provides better confidence in the modelling methods for predicting the environmental durability of polymeric materials and fibre-reinforced composites.

Online discovery of the molecular mechanism for directionally detoxification of Fuzi using real-time extractive electrospray ionization mass spectrometry

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum carmichaelii Debeaux, a famous traditional medicinal herb for collapse, rheumatic fever, and painful joints, always raises global concerns about its fatal toxicity from toxic alkaloids when improperly processed. Therefore, it is urgent to clarify the internal molecular mechanism of processing detoxification on Aconitum and develop simple and reliable approaches for clinical application, which is also of great significance to the rational medicinal use of Aconitum.

AIM OF THE STUDY

The study aimed at developing a complete molecular mechanism exploration strategy in complex medicinal herb decocting system, clarifying the internal molecular mechanism of processing detoxification on Aconitum, and exploring valid approaches for detoxification.

MATERIALS AND METHODS

Aconiti Lateralis Radix Praeparata (Fuzi) was selected as the model for exploring the complex Aconitum detoxification mechanism using an advanced online real-time platform based on extractive electrospray ionization mass spectrometry. The methods realized the sensitive capture of dynamic trace intermediates, accurate qualitative and quantitative analysis, and real-time and long-term monitoring of multi-components with satisfactory accuracy and resistance to complex matrices.

RESULTS

Components in the complex Aconitum decocting system were real-timely characterized and fat meat was discovered and verified to directionally detoxify Aconitum while reserving the therapy effect. More importantly, the dynamic detoxification mechanism in the chemically complex Aconitum decoction was molecularly profiled. A novel reaction pathway based on nucleophilic substitution reaction mechanism was proposed. As confirmed by the theoretic calculations at DFT B3LYP/6-31G (d) levels, fatty acids (e.g., palmitic acid) acted as a green, cheap, and high-performance catalyst and promote the decomposition of toxic diester alkaloids to non-toxic and active benzoyl-monoester alkaloids through the discovered mechanism.

CONCLUSION

The study exposed a novel detoxification molecular mechanism of Aconitum and provided an effective method for the safe use of Aconitum, which could effectively guide the development of traditional processing technology and compatibility regulation of the toxic herb and had great value to the modernization and standardization development of traditional medicine.

Recent Advances in Corrosion Science Applicable To Disposal of High-Level Nuclear Waste

High-level radioactive waste is accumulating at temporary storage locations around the world and will eventually be placed in deep geological repositories. The waste forms and containers will be constructed from glass, crystalline ceramic, and metallic materials, which will eventually come into contact with water, considering that the period of performance required to allow sufficient decay of dangerous radionuclides is on the order of 10⁵-10⁶ years. Corrosion of the containers and waste forms in the aqueous repository environment is therefore a concern. This Review describes the recent advances of the field of materials corrosion that are relevant to fundamental materials science issues associated with the long-term performance assessment and the design of materials with improved performance, where performance is defined as resistance to aqueous corrosion. Glass, crystalline ceramics, and metals are discussed separately, and the near-field interactions of these different material classes are also briefly addressed. Finally, recommendations for future directions of study are provided.

Dissolution Kinetics of International Simple Glass and Formation of Secondary Phases at Very High Surface Area to Solution Ratio in Young Cement Water

Static dissolution experiments were carried out with the reference International Simple Glass under hyperalkaline pH at 70 °C and very high SA/V ratio. Three aspects of glass dissolution behavior were investigated, (1) the rate drop regime and the residual rate (stage II), (2) the formation of secondary phases including thermodynamic aspects, and (3) the microstructure of the interface of altered glass and secondary phases. A very low residual rate of 6 × 10⁻⁶ g/m²d was determined based on boron release, which was several orders of magnitude lower than the initial rate established between the start of the experiments and the first sampling on day 59. The presence of a porous layer with a thickness varying between 80 nm and 250 nm and a pore size between 10 nm and 50 nm was observed. CSH phases with a low Ca/Si ratio of 0.3–0.4 and zeolites were also visible at the surface of the altered glass grains, but no glass alteration resumption occurred, probably due to an important pH decrease already at day 59. Thermodynamic calculations assuming congruent glass dissolution and precipitation of the dissolved aqueous species confirmed the precipitation of CSH phases and zeolites.

Progress and Perspective for In Situ Studies of CO2 Reduction

CO₂ conversion to chemical fuels through photoreduction, electroreduction, or thermoreduction is considered as one of the most effective methods to solve environmental pollution and energy shortage problems. However, recent studies show that the involved catalysts may undergo continuous reconstruction under realistic working conditions, which unfortunately causes controversial results concerning the active sites and reaction mechanism of CO₂ reduction. Thus, it is necessary, while challenging, to monitor in real time the dynamic evolution of the catalysts and reaction intermediates by in situ techniques under experimental conditions. In this Perspective, we start with the working principle and detection modes of various in situ characterization techniques. Subsequently, we systematically summarize the recent developments of in situ studies on probing the catalyst evolution during the CO₂ reduction process. We further focus on the progress of in situ studies in monitoring the reaction intermediates and catalytic products, in which we also highlight how the theoretical calculations are combined to reveal the reaction mechanism in detail. Finally, based on the achievements in the representative studies, we present some prospects and suggestions for in situ studies of CO₂ reduction in the future.

Following in Situ the Degradation of Mesoporous Silica in Biorelevant Conditions: At Last, a Good Comprehension of the Structure Influence

Mesoporous silica nanoparticles (MSNs) have seen a fast development as drug delivery carriers thanks to their tunable porosity and high loading capacity. The employ of MSNs in biomedical applications requires a good understanding of their degradation behavior both to control drug release and to assess possible toxicity issues on human health. In this work, we study mesoporous silica degradation in biologically relevant conditions through in situ ellipsometry on model mesoporous nanoparticle or continuous thin films, in buffer solution and in media containing proteins. In order to shed light on the structure/dissolution relationship, we performed dissolution experiments far from soluble silicate species saturation. Via a complete decorrelation of dissolution and diffusion contributions, we proved unambiguously that surface area of silica vectors is the main parameter influencing dissolution kinetics, while thermal treatment and open mesoporous network architecture have a minor impact. As a logical consequence of our dissolution model, we proved that the dissolution lag-time can be promoted by selective blocking of the mesopores that limits the access to the mesoporous internal surface. This study was broadened by studying the impact of the organosilanes in the silica structure, of the presence of residual structuring agents, and of the chemical composition of the dissolution medium. The presence of albumin at blood concentration was found affecting drastically the dissolution kinetics of the mesoporous structure, acting as a diffusion barrier. Globally, we could identify the main factors affecting mesoporous silica materials degradation and proved that we can tune their structure and composition for adjusting dissolution kinetics in order to achieve efficient drug delivery.

Sol-Gel Synthesis and Characterization of Gels with Compositions Relevant to Hydrated Glass Alteration Layers

During the processes associated with glass corrosion, porous hydrated glass alteration layers typically form upon exposure to aqueous conditions for extended time periods. The impacts of the alteration layer on glass durability have not been agreed upon in the glass science community. In particular, the formation mechanisms of hydrated glass alteration layers are still largely unknown and require further investigation, but these layers often require months to years to develop and are often too thin to adequately characterize. Meanwhile, sol-gel-derived silicate gels are relatively easy to synthesize in bulk with custom compositions relevant to hydrated glass alteration layers. If alteration layers and synthetic silicate gels demonstrate physical and chemical properties that are sufficiently similar, synthetic silicate gels could be used as analogues for hydrated glass alteration layers in future studies. However, synthetic gels must first be prepared and evaluated before comparisons between glass alteration layers and synthetic silicate gels can be made. This work focuses entirely on the synthesis and observed physical properties of synthetic silicate gels. A future work will compare the characteristics of synthetic gels described in this work with altered waste glass formed in similar pH environments. In this study, synthetic gels were made with custom compositions at various pH values to evaluate the effect of pH on gel structure and morphology. Several other variables were examined also, such as composition, drying, and aging. Gels were produced by sequential additions of organometallic precursors in a single container. Gels were analyzed with several techniques including small-angle X-ray scattering, gas adsorption, and He pycnometry to determine the effects of the variables on physical properties. Results show that gels prepared at pH 3 consistently contained fewer primary particles with diameters larger than 7.2 nm and fewer pores with diameters larger than 30 nm compared to gels synthesized at pH 7 and 9. Composition was shown to have no discernable effect on primary particle and pore sizes at any pH.

The Effect of Heavy Ion Irradiation on the Forward Dissolution Rate of Borosilicate Glasses Studied in Situ and Real Time by Fluid-Cell Raman Spectroscopy

Borosilicate glasses are the favored material for immobilization of high-level nuclear waste (HLW) from the reprocessing of spent fuel used in nuclear power plants. To assess the long-term stability of nuclear waste glasses, it is crucial to understand how self-irradiation affects the structural state of the glass and influences its dissolution behavior. In this study, we focus on the effect of heavy ion irradiation on the forward dissolution rate of a non-radioactive ternary borosilicate glass. To create extended radiation defects, the glass was subjected to heavy ion irradiation using 197Au ions that penetrated ~50 µm deep into the glass. The structural damage was characterized by Raman spectroscopy, revealing a significant depolymerization of the silicate and borate network in the irradiated glass and a reduction of the average boron coordination number. Real time, in situ fluid-cell Raman spectroscopic corrosion experiments were performed with the irradiated glass in a silica-undersaturated, 0.5 M NaHCO3 solution at temperatures between 80 and 85 °C (initial pH = 7.1). The time- and space-resolved in situ Raman data revealed a 3.7 ± 0.5 times increased forward dissolution rate for the irradiated glass compared to the non-irradiated glass, demonstrating a significant impact of irradiation-induced structural damage on the dissolution kinetics.

In Situ Hyperspectral Raman Imaging: A New Method to Investigate Sintering Processes of Ceramic Material at High-temperature

In the last decades, Raman spectroscopy has become an important tool to identify and investigate minerals, gases, glasses, and organic material at room temperature. In combination with high-temperature and high-pressure devices, however, the in situ investigation of mineral transformation reactions and their kinetics is nowadays also possible. Here, we present a novel approach to in situ studies for the sintering process of silicate ceramics by hyperspectral Raman imaging. This imaging technique allows studying high-temperature solid-solid and/or solid-melt reactions spatially and temporally resolved, and opens up new avenues to study and visualize high-temperature sintering processes in multi-component systems. After describing in detail the methodology, the results of three application examples are presented and discussed. These experiments demonstrate the power of hyperspectral Raman imaging for in situ studies of the mechanism(s) of solid-solid or solid-melt reactions at high-temperature with a micrometer-scale resolution as well as to gain kinetic information from the temperature- and time-dependent growth and breakdown of minerals during isothermal or isochronal sintering.