Hydrochloric acid

Summary

Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride with the chemical formula HCl(aq). It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical. History In the early tenth century, the Persian physician and alchemist Abu Bakr al-Razi (865–925, Latin: Rhazes) conducted experiments with sal ammoniac (ammonium chloride) and vitriol (hydrated sulfates of various metals), which he distilled together, thus producing the gas hydrogen chloride. In doing so, al-Razi may have stumbled upon a primitive method for producing hydrochloric acid, as perhaps manifested in the following recipe from his ("The Book of Secrets"): Take equal parts of sweet salt, Bitter salt, salt, sal

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Scattering HCl Molecules from Au(111) and Ag(111) Surfaces

Jan Daniel Geweke

In this thesis, I present an experimental molecular beam surface scattering study of dynamical processes involved when HCl molecules are scattered from Au(111) and Ag(111) surfaces. I investigated vibrational excitation, translational inelasticity and dissociative adsorption in combination with associative desorption. The experiments were conducted in an ultra-high vacuum (UHV) molecular beam/surface scattering apparatus equipped with a pulsed nanosecond infrared (IR) laser source for vibrational state manipulation and pulsed nanosecond ultraviolet (UV) lasers for quantum-state-resolved detection of molecules via resonance enhanced multi-photon ionization (REMPI) before and after the collisions. For HCl/Au(111), I found surface temperature dependent vibrational excitation probabilities (VEPs) from vibrational state v = 0 -> 1 to be in the range of 10^-5 - 10^-3 for incidence energies of Ei = 0.67 - 0.99 eV, which is low compared to other molecule-surface systems. On the other hand, VEPs for the v = 1 -> 2 transition were substantially higher at 10^-3 - 10^-2 for comparable incidence energies. In both cases, excitation probabilities could be divided into electronically adiabatic and nonadiabatic contributions where the latter exponentially depended on the surface temperature Ts. This combination of adiabatic and nonadiabatic vibrational excitation has so far been uniquely observed for HCl scattered from Au(111) and Ag(111) surfaces. Extracting Ei and Ts independent interaction coefficients, I found the nonadiabatic excitation to be stronger than the adiabatic one by a factor of 67 for the v = 0 -> 1 and 24 for the v = 1 -> 2 channel. In comparison, on Ag(111) only the excitation from the vibrational ground state could be observed. With VEPs in the range of 10^-4 - 10^-3 being slightly higher than on gold, this difference was interpreted as enhanced nonadiabatic interactions on silver. Relatively low barriers to dissociation on both metal surfaces (e. g., compared to NO/Au(111)) might have led to the higher v = 1 -> 2 VEPs on Au(111). Further, the absence of higher excitation channels (v = 2 -> 3 on gold, v = 1 -> 2 on silver) might also be explained by the enhanced dissociation of HCl molecules incident in excited vibrational states. Dissociation probabilities of HCl on metal surfaces were measured by AUGER electron spectroscopy after controlled molecular beam dosage monitored by a quadrupole mass spectrometer. Even though the dissociation probabilities on Ag(111) were predicted to be higher than on Au(111), I could not determine them within the current technical limitations. Additionally, the actual dissociation probabilities I determined on Au(111) employing AES remained below 0.06 - 0.17, which is lower than those predicted by a series of computational studies by a factor of 2 - 6. On the other hand, translational energy losses calculated in the latest AIMDEF study match the experimental results for v = 1 -> 1 and v = 1 -> 2 quite accurately. In sum, the results of this thesis, which all indicate that HCl exhibits both electronically adiabatic and nonadiabatic interactions with metal surfaces during scatter- ing events, can serve as benchmark data to test and improve theoretical descriptions of gas-surface interactions, especially in those cases were nonadiabaticity plays an important role.

EPFL2019

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Concrete is a most important geomaterial as it is used for a large part in our buildings and infrastructures. According to Planetoscope (2012) its production is about 6 billion m3 per year (190 m3 each second) which makes it the most used manufactured material in the world. The alteration of concrete, tightly associated with the durability and security of our infrastructures, depends on its primary composition but also on a wide range of environmental factors (mechanical solicitations, freezing-thawing cycles, alkali-aggregate reactions, etc.). Hence, the contribution of geological or geological-related analysis to understand concrete alteration processes is required because this material is mainly composed of aggregates made of different minerals and rocks, the type and quality of which are important due to their influence on concrete behaviour. In this study, high resolution X-ray Computed tomography (X-ray micro-CT) was used to image 3D different types of concrete cores in order to characterize their respective state of alteration. The global alteration index (GAI) developed by Christe et al. (2010) for natural cataclastic rocks was applied to the segmented X-ray CT images of these concrete cores and compared to the results of microstructural analysis on thin slices and of compression tests. Also, an internal attack of concrete by hydrochloric acid was carried out in laboratory to simulate artificial alteration through carbonate dissolution and its process was monitored along time by X-ray micro-CT imaging (4D monitoring). Our first results show that X-ray CT imagery enables, without any destruction of the specimens, to characterize concrete internal features in terms of macroporosity, highly microporous cement paste, standard cement paste or aggregates. In particular, initial entrapped porosity as well as cracks are easily detected, characterised and quantified before and after mechanical testing. Petrographic analyses on thin sections enabled to verify the physical meaning of the X-ray CT-based detected features, such as the highly microporous cement paste, the opening of the microcracks and the detachment halos around aggregates which all act as weakening parameters. Despite the limited number of samples, a coherent relation between the GAI and the compressive strength of the concrete specimens is observed as the concrete compressive strength clearly decreases when the GAI increases. In this case, it logically means that the concrete with a higher porosity is less resistant. Moreover, the 4D monitoring of the acidic attack test led to dynamically show how the carbonated structure of the concrete was progressively altered. These preliminary results demonstrate that GAI, based on XRCT imagery analysis, can be used to evaluate the degree of alteration of concrete and could thus lead to estimate its strength. In more general terms, X-ray CT analysis opens new perspectives to relate the quality of concrete with its mechanical properties. This method could probably be further applied to a wide range of problems related to the inspection and maintenance of concrete infrastructures.

2014

pH control for enhanced reductive bioremediation of chlorinated solvent source zones

David Andrew Barry, Clare Robinson

Enhanced reductive dehalogenation is an attractive treatment technology for in situ remediation of chlorinated solvent DNAPL source areas. Reductive dehalogenation is an acid-forming process with hydrochloric acid and also organic acids from fermentation of the electron donors typically building up in the source zone during remediation. This can lead to groundwater acidification thereby inhibiting the activity of dehalogenating microorganisms. Where the soils’ natural buffering capacity is likely to be exceeded, the addition of an external source of alkalinity is needed to ensure sustained dehalogenation. To assist in the design of bioremediation systems, an abiotic geochemical model was developed to provide insight into the processes influencing the groundwater acidity as dehalogenation proceeds, and to predict the amount of bicarbonate required to maintain the pH at a suitable level for dehalogenating bacteria (i.e., > 6.5). The model accounts for the amount of chlorinated solvent degraded, site water chemistry, electron donor, alternative terminal electron- accepting processes, gas release and soil mineralogy. While calcite and iron oxides were shown to be the key minerals influencing the soil’s buffering capacity, for the extensive dehalogenation likely to occur in a DNAPL source zone, significant bicarbonate addition may be necessary even in soils that are naturally well buffered. Results indicated that the bicarbonate requirement strongly depends on the electron donor used and availability of competing electron acceptors (e.g., sulfate, iron(III)). Based on understanding gained from this model, a simplified model was developed for calculating a preliminary design estimate of the bicarbonate addition required to control the pH for user- specified operating conditions.

Elsevier2009

Scattering HCl Molecules from Au(111) and Ag(111) Surfaces

Jan Daniel Geweke

EPFL2019

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2014