scholarly journals Relative Contributions of Mg Hydration and Molecular Structural Restraints to the Barrier of Dolomite Crystallization: A Comparison of Aqueous and Non-Aqueous Crystallization in (BaMg)CO3 and (CaMg)CO3 Systems

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1214
Author(s):  
Shi Zhou ◽  
Yuebo Wang ◽  
Henry Teng
Keyword(s):  
Aqueous Solutions ◽  
Solvation Shell ◽  
State Theory ◽  
Aqueous Environment ◽  
Atmospheric Conditions ◽  
Conventional View ◽  
Hydration Effect ◽  
Shell Chemistry ◽  
Energy Penalty ◽  
Activated Complex

Carbonate mineralization is reasonably well-understood in the Ca–CO2–H2O system but continuously poses difficulties to grasp when Mg is present. One of the outstanding questions is the lack of success in dolomite MgCa(CO3)2 crystallization at atmospheric conditions. The conventional view holds that hydration retards the reactivity of Mg2+ and is supported by solvation shell chemistry. This theory however is at odds with the easy formation of norsethite MgBa(CO3)2, a structural analogue of dolomite, leading to the premise that crystal or molecular structural constrains may also be at play. The present study represents our attempts to evaluate the separate contributions of the two barriers. Crystallization in the Mg–Ba–CO2 system was examined in a non-aqueous environment and in H2O to isolate the effect of hydration by determining the minimal relative abundance of Mg required for norsethite formation. The results, showing an increase from 1:5 to 6:4 in the solution Mg/Ba ratio, represented a ~88% reduction in Mg2+ reactivity, presumably due to the hydration effect. Further analyses in the context of transition state theory indicated that the decreased Mg2+ reactivity in aqueous solutions was equivalent to an approximately 5 kJ/mol energy penalty for the formation of the activated complex. Assuming the inability of dolomite to crystallizes in aqueous solutions originates from the ~40 kJ/mol higher (relative to norsethite) Gibbs energy of formation for the activated complex, a hydration effect was estimated to account for ~12% of the energy barrier. The analyses present here may be simplistic but nevertheless consistent with the available thermodynamic data that show the activated complex of dolomite crystallization reaction is entropically favored in comparison with that of norsethite formation but is significantly less stable due to the weak chemical bonding state.

Bimolecular Reactions, Transition-State Theory

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Transition State ◽  
Saddle Point ◽  
Transition State Theory ◽  
Classical Mechanics ◽  
Small Degree ◽  
State Theory ◽  
Reaction Coordinate ◽  
Partition Functions ◽  
Bimolecular Reactions ◽  
Activated Complex

This chapter discusses an approximate approach—transition-state theory—to the calculation of rate constants for bimolecular reactions. A reaction coordinate is identified from a normal-mode coordinate analysis of the activated complex, that is, the supermolecule on the saddle-point of the potential energy surface. Motion along this coordinate is treated by classical mechanics and recrossings of the saddle point from the product to the reactant side are neglected, leading to the result of conventional transition-state theory expressed in terms of relevant partition functions. Various alternative derivations are presented. Corrections that incorporate quantum mechanical tunnelling along the reaction coordinate are described. Tunnelling through an Eckart barrier is discussed and the approximate Wigner tunnelling correction factor is derived in the limit of a small degree of tunnelling. It concludes with applications of transition-state theory to, for example, the F + H2 reaction, and comparisons with results based on quasi-classical mechanics as well as exact quantum mechanics.

THEORETICAL STUDIES OF ANHARMONIC EFFECT IN THE RICE–RAMSPERGER–KASSEL–MARCUS THEORY

2008 ◽  
Vol 22 (31) ◽  
pp. 3043-3052 ◽  
Author(s):  
L. YAO ◽  
Y. L. LIU ◽  
S. H. LIN
Keyword(s):  
Theoretical Approach ◽  
Transition State Theory ◽  
State Theory ◽  
Model Systems ◽  
Partition Functions ◽  
Morse Oscillator ◽  
Anharmonic Effect ◽  
Oscillator Potential ◽  
Inverse Laplace Transformation ◽  
Activated Complex

The purpose of this paper is to propose a theoretical approach, which can evaluate anharmonic effects on the rate constants within the transition state theory. In treating unimolecular reactions under collision-free conditions by using the RRKM theory, we make use of the inverse Laplace transformation of the partition functions to obtain both the total number of states for the activated complex and density of states for the reactant with the Morse oscillator potential. To demonstrate the applications of our theoretical approach, we choose some model systems and a real reaction as examples.

Theoretical study on the chemical formation mechanism of a β-myrcene ozonolysis reaction under atmospheric conditions

2012 ◽  
Vol 90 (8) ◽  
pp. 708-715 ◽  
Author(s):  
Yuyang Zhao ◽  
Jing Bai ◽  
Chenxi Zhang ◽  
Chen Gong ◽  
Xiaomin Sun
Keyword(s):  
Rate Constants ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Single Point ◽  
State Theory ◽  
Tunneling Effect ◽  
Atmospheric Conditions ◽  
Functional Theory ◽  
Real Atmosphere ◽  
Energy Surfaces

Density functional theory (DFT) was used to study the β-myrcene ozonolysis reaction. The reactants, intermediates, transition states, and products were optimized at the MPWB1K/6–31G(d,p) level. The single-point energies were performed at the MPWB1K/6–311+G(3df,2p) level. The profiles of the potential energy surfaces were constructed and the rate constants of the reaction steps were analyzed. The possible reaction mechanisms for the ozonolysis intermediates in real atmosphere are also discussed. Based on quantum chemistry information, the rate constants were calculated using Rice–Ramsperger–Kassel–Marcus (RRKM) theory and the canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). Arrhenius equations of rate constants over the temperature range of 200–800 K are provided, and the lifetimes of the reaction species in the troposphere were estimated according to rate constants.

scholarly journals Aqueous-phase behavior of glyoxal and methylglyoxal observed with carbon and oxygen K-edge X-ray absorption spectroscopy

2021 ◽  
Vol 21 (4) ◽  
pp. 2881-2894
Author(s):  
Georgia Michailoudi ◽  
Jack J. Lin ◽  
Hayato Yuzawa ◽  
Masanari Nagasaka ◽  
Marko Huttula ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Absorption Spectroscopy ◽  
Atmospheric Chemistry ◽  
Aldol Condensation ◽  
Cloud Formation ◽  
Aqueous Environment ◽  
Aerosol Formation ◽  
X Ray ◽  
Dilute Aqueous Solutions ◽  
X Ray Absorption

Abstract. Glyoxal (CHOCHO) and methylglyoxal (CH3C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by the addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na2SO4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, supported by quantum chemical calculations we identified not only C–H, C=O and C–OH bonds, but also fingerprints of C–OH(CH2) and C=C bonds. The relatively low intensity of C=O transitions implies that the monohydrated form of methylglyoxal is not favored in the solutions. Instead, the spectral intensity is stronger in regions where products of aldol condensation and enol tautomers of the monohydrates contribute. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that XAS in the near-edge region is not very sensitive to these intermolecular organic–inorganic interactions at the studied concentrations. The identified structures of glyoxal and methylglyoxal in an aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution to secondary organic aerosol formation.

Static Solvent Effects, Transition-State Theory

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Transition State ◽  
Rate Constant ◽  
Solvent Effects ◽  
Transition State Theory ◽  
Equilibrium Structure ◽  
State Theory ◽  
Potential Of Mean Force ◽  
Distribution Functions ◽  
Average Force ◽  
Activated Complex

This chapter discusses static solvent effects on the rate constant for chemical reactions in solution. It starts with a brief discussion of the thermodynamic formulation of transition-state theory. The static equilibrium structure of the solvent will modify the potential energy surface for the chemical reaction. This effect is analyzed within the framework of transition-state theory. The rate constant is expressed in terms of the potential of mean force at the activated complex. Various definitions of this potential and their relations to n-particle- and pair-distribution functions are considered. The potential of mean force may, for example, be defined such that the gradient of the potential gives the average force on an atom in the activated complex, Boltzmann averaged over all configurations of the solvent. It concludes with a discussion of a relation between the rate constants in the gas phase and in solution.

scholarly journals Synthesis of a Layered Organic-Inorganic Nanohybrid of 4-Chlorophenoxyacetate-zinc-Layered Hydroxide with Sustained Release Properties

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Mohd Zobir Hussein ◽  
Nor Farhana binti Nazarudin ◽  
Siti Halimah Sarijo ◽  
Mohd Ambar Yarmo
Keyword(s):  
Active Agent ◽  
Grain Structure ◽  
Aqueous Environment ◽  
Direct Reaction ◽  
Atmospheric Conditions ◽  
Variable Size ◽  
Release Formulation ◽  
Pure Phase ◽  
Pseudo Second Order ◽  
Zinc Layered Hydroxide

A zinc-layered hydroxide-4-chlorophenoxy acetate (4CPA) organic-inorganic nanohybrid was prepared using a simple direct reaction of 4CPA anions with ZnO under an aqueous environment to be used as a controlled release formulation of the herbicide, 4CPA. The concentration of the active agent, 4CPA, was found to be a controlling factor for the formation of a pure phase well-ordered nanolayered hybrid in which it could be synthesised at 0.2 M 4CPA. ZnO shows a well-defined grain structure of variable size in the nanometre range. However, the formation of the 4CPA-ZLH nanohybrid resulted in a flake-like fibrous structure. On heating at 500°C for 5 h under atmospheric conditions, the nanohybrid transformed back to a well-defined grain structure, as previously observed with the starting material, ZnO. The release of 4CPA was found to occur in a controlled manner and was generally governed by pseudo-second-order kinetics.

scholarly journals Aqueous phase behavior of glyoxal and methylglyoxal observed with carbon and oxygen K-edge X-ray absorption spectroscopy

2020 ◽  
Author(s):  
Georgia Michailoudi ◽  
Jack J. Lin ◽  
Hayato Yuzawa ◽  
Masanari Nagasaka ◽  
Marko Huttula ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Absorption Spectroscopy ◽  
Atmospheric Chemistry ◽  
Aldol Condensation ◽  
Cloud Formation ◽  
Aqueous Environment ◽  
Aerosol Formation ◽  
X Ray ◽  
Dilute Aqueous Solutions ◽  
X Ray Absorption

Abstract. Glyoxal (CHOCHO) and methylglyoxal (CH3C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na2SO4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, we identified, supported by quantum chemical calculations, not only C-H, C=O and C-OH bonds, but also fingerprints of C-OH(CH2) and C=C bonds. This implies the presence of both mono- and dihydrated forms of methylglyoxal, as well as products of aldol condensation, and enol tautomers of the monohydrates. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that the organic-inorganic interactions at the studied concentrations are not strong enough to affect the spectra in this work. The identified structures of glyoxal and methylglyoxal in aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution on secondary organic aerosol formation.

Competitive adsorption of boric acid and chromate onto alumina in aqueous solutions

2013 ◽  
Vol 69 (2) ◽  
pp. 378-384 ◽  
Author(s):  
A. Demetriou ◽  
I. Pashalidis
Keyword(s):  
Aqueous Solutions ◽  
Boric Acid ◽  
Formation Constant ◽  
Competitive Adsorption ◽  
Alumina Surface ◽  
Atmospheric Conditions ◽  
Surface Complexes ◽  
Surface Data ◽  
Reaction Constant

The competitive adsorption of boric acid and chromate from aqueous solutions by alumina has been investigated by spectrophotometry at pH 8, ionic strength = 0.0, 0.1 and 1.0 M NaClO4, T = 22 ± 3 °C and under normal atmospheric conditions. The experimental data show that addition of excess boric acid in the system leads to the increase of Cr(VI) concentration in solution, indicating the replacement of adsorbed chromate by boron on the alumina surface. Data evaluation results in the determination of the competition reaction constant and the formation constant of the Cr(VI) surface complexes, which are logKCr(VI)–B(III) = −3.5 ± 0.2 and logβ*Cr = 7.6 ± 0.3, respectively.

scholarly journals Solution thermodynamics of aqueous nicotinic acid solutions in presence of tetrabutylammonium hydrogen sulphate

2013 ◽  
Vol 78 (8) ◽  
pp. 1225-1240 ◽  
Author(s):  
Abhijit Sarkar ◽  
Biswajit Sinha
Keyword(s):  
Aqueous Solutions ◽  
Nicotinic Acid ◽  
Ambient Pressure ◽  
Activation Parameters ◽  
Partial Molar Volumes ◽  
State Theory ◽  
Group Interactions ◽  
Molar Volumes ◽  
Solvent Interactions ◽  
Hydrogen Sulphate

In this study we investigated the effects of tetrabutylammonium hydrogen sulphate (Bu4NHSO4) on the solute-solute and solute-solvent interactions in the aqueous solutions of nicotinic acid in terms of apparent molar volumes (?V), standard partial molar volumes (?V0) and viscosity B-coefficients at 298.15, 308.15, and 318.15 K under ambient pressure. These interactions are further discussed in terms of ion-dipolar, hydrophobic- hydrophobic, hydrophilic-hydrophobic group interactions. The activation parameters of viscous flow for Bu4NHSO4 in the aqueous solutions of nicotinic acid were discussed in terms of transition state theory. The overall results indicated that ion-hydrophilic and hydrophilic-hydrophilic group interactions are predominant in the aqueous solutions of nicotinic acid and Bu4NHSO4 has a dehydration effect on the hydrated nicotinic acid.

Underwater Testing of a Typical Ambient-Cure Epoxy Resin for Composite Repairs of Structural Piping and Vessels

2011 ◽  
Author(s):  
Timothy S. Mally ◽  
Allison L. Johnston ◽  
Michael W. Keller ◽  
Roger H. Walker
Keyword(s):  
Carbon Fiber ◽  
Epoxy Resin ◽  
Pressure Vessels ◽  
Field Application ◽  
Aqueous Environment ◽  
Ambient Atmosphere ◽  
Atmospheric Conditions ◽  
Wall Defect ◽  
Carbon Fiber Epoxy ◽  
Composite Repairs

The rehabilitation of piping and pressure vessels is well suited to the field application of carbon fiber/epoxy composites. Ambient-cure resins are ideal for repairs performed in atmospheric conditions. However, the ability for ambient-cure resins to set in alternative environments is critical to their proliferation. The goal in the described experimentation is to determine if one type of ambient-cure resin can be shown to be equally as effective when cured in an aqueous environment as in ambient atmosphere. This paper details the testing of an ambient-cure polymer matrix composite cured underwater. Experimentation consists of testing of panels cured in laboratory settings and burst hydro testing of repaired pipe components. Test coupons are fabricated and cured for 48 hours at ambient water temperatures. After curing, the coupons are tested for indicators of performance. Hardness, total strain, and tensile strength are measured and compared to ambient cure data for the same polymer composite. Elbow joints and tee joints containing a through wall defect are wrapped underwater using the same carbon fiber and epoxy resin used for the panels. A thermoplastic stretch film is applied immediately after installation underwater. The pipes are pressurized after curing and the burst pressure and wrap hardness are measured.

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