Unimolecular and hydrolysis channels for the detachment of water from microsolvated alkaline earth dication (Mg2+, Ca2+, Sr2+, Ba2+) clusters

We examine theoretically the three channels that are associated with the detachment of a single water molecule from the aqueous clusters of the alkaline earth dications, [M(H₂O) _n ]²⁺, M = Mg, Ca, Sr, Ba, n ≤ 6. These are the unimolecular water loss (M²⁺(H₂O) _n?1 + H₂O) and the two hydrolysis channels resulting the loss of hydronium ([MOH(H₂O) _n?2]⁺ + H₃O⁺) and Zundel ([MOH(H₂O) _n?3]⁺ + H₃O⁺(H₂O)) cations. Minimum energy paths (MEPs) corresponding to those three channels were constructed at the Møller–Plesset second order perturbation (MP2) level of theory with basis sets of double- and triple-ζ quality. We furthermore investigated the water and hydronium loss channels from the mono-hydroxide water clusters with up to four water molecules, [MOH(H₂O) _n ]⁺, 1 ≤ n ≤ 4. Our results indicate the preference of the hydronium loss and possibly the Zundel-cation loss channels for the smallest size clusters, whereas the unimolecular water loss channel is preferred for the larger ones as well as the mono-hydroxide clusters. Although the charge separation (hydronium and Zundel-cation loss) channels produce more stable products when compared to the ones for the unimolecular water loss, they also require the surmounting of high-energy barriers, a fact that makes the experimental observation of fragments related to these hydrolysis channels difficult.     

Collision-induced dissociation studies of protonated alcohol and alcohol—water clusters by atmospheric pressure ionization tandem mass spectrometry. 1?Methanol

Cluster size distribution and collision-induced dissociation (CID) studies of protonated methanol and protonated methanol—water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH₃OH)_n · H₂O · H⁺ clusters, where n ? 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen-bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n ? 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.     

Radical loss in a chain reaction of CO and NO in the presence of water: Implications for the radical amplifier and atmospheric chemistry

Atmospheric pressure rate coefficients for the loss of HO₂, CH₃O₂, and C₂H₅O₂ radicals to the wall of a ¼″ Teflon tube have been measured. In dry air, they are 2.8 ± 0.2 s⁻¹ for HO₂ and 0.8 ± 0.1 s⁻¹ for both CH₃O₂ and C₂H₅O₂ radicals. The rate coefficient for HO₂ loss increases markedly with the relative humidity of the air; however, the organic radicals show no such dependence. These data are used in a kinetic model of the radical amplifier chemistry to investigate the reported sensitivity to water concentration. The increased wall loss accounts for only some of the observed water dependence, suggesting there is an unreported water contribution to the gas phase chemistry. Including the reaction of the HO₂/water adduct with NO to yield HNO₃ or HOONO into the mechanism is shown to provide a better simulation of the observed water dependence of the radical detector. This reaction would also be important in atmospheric chemistry as it provides an additional loss mechanism for both radicals and NO_x. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 145–152, 1999     

Thermogravimetric analysis of the copper silicate mineral dioptase Cu6[Si6O18]·6H2O

There have been a few studies on the thermal decomposition of dioptase Cu₆[Si₆O₁₈]·6H₂O. The results of these analyses are somewhat conflicting and the conclusions vary among these thermo-analytical studies. The objective of this research is to report the thermal analysis of dioptase from different origins and to show the mechanism of decomposition. Thermal decomposition occurs over a very wide temperature range from around 400 to 730 °C with the loss of water. Two additional mass loss steps are observed at around 793 and 835 °C with loss of oxygen. The infrared spectra of dioptase in the hydroxyl stretching region enables the hydrogen bond distances of water molecules in the dioptase structure to be calculated. The large variation in the hydrogen bond distances offers an explanation as to why the decomposition of dioptase with loss of water occurs over such a wide temperature range.     

The evolution of structural changes in ettringite during thermal decomposition

The thermal decomposition of ettringite, Ca₆[Al(OH)₆]₂(SO₄)₃·∼26H₂O, was studied with pulsed neutron time-of-flight diffraction combined with Rietveld structure refinement. Like prior investigations, transition from a crystalline to amorphous state occurred following the loss of ∼20 water molecules. In contrast to earlier investigations, which relied upon indirect measurements of water and hydroxyl occupancies, the present study inferred the occupancies directly from Rietveld crystal structure refinement of the diffraction data. The decomposition pathway was shown to be more complex than previously envisioned, involving the simultaneous loss of hydroxyl and water molecules. Nuclear magnetic resonance (NMR) spectroscopy studies of the rigid lattice lineshapes of fully and partially hydrated ettringite were performed and confirmed our decomposition model.     

The mechanism for elimination of acetic acid from 1-acetoxy- and 2-acetoxytetralin

By employing deuterium substitution and metastable ion defocusing methods, it has been determined that 1-acetoxytetralin undergoes a highly regiospecific (>98%) 1,4-elimenation of acetic acid. The mechanism closely parallels that for loss of water from 1-tetralol in terms of specificity. However, unlike the water loss, which shows a significant kinetic isotope effect (K_H/K_D = 2.0) and a large release of translational energy (270 meV), the expulsion of acetic acid occurs without an isotope effect and with release of only 10 meV of kinetic energy. Competitive with acetic acid loss is the elimination of ketene which has been shown to occur by a 4-centered transition state. The 2-acetoxytetralin exhibits the more traditional 1,2-elimination of acetic acid which contrasts with a 1,3-elemination of water for the corresponding alcohol.     

Performance losses at H2/O2 alkaline membrane fuel cell

H₂/O₂ alkaline membrane fuel cell (AMFC) is evaluated by polarization curves and conductivity measurements to determine the performance limiting factors. The analysis of IR corrected polarization curves shows that at medium to high current region significant potential loss in AMFC is caused by low ionic conductivity of membrane and catalyst layer, and limitations from mass transport of water. In low to medium current region the severe performance loss is caused by low water concentration at catalyst surface due to insufficient water concentration in the fully humidified oxidant at ≤ 60 °C.     

The effect of water on the anodic dissolution of aluminum in non-aqueous electrolytes

The influence of water concentration on the electrochemical behavior of Al anodes in Al/active-non-aqueous electrolytes is investigated. Normally passive, Al exhibits facile electrochemical oxidation in both AlCl₃/γ-butyrolactone (AlCl₃/BLA) and (C₂H₅)₄NCl acetonitrile (TEAC/ACN) electrolytes. However, in these two electrolytes, the influence of water on Al oxidation shows opposite effects. Incremental increase from 0 to 1.5 M H₂O (0 to 3% water by volume) hinders Al oxidation in 1 M AlCl₃/BLA, increasing polarization loss from 100 to 400 mV cm² mA⁻¹. Yet in 0.3 M TEAC/ACN, Al is passive in the absence of water, exhibiting currents only in the μA cm⁻² domain, equivalent to oxidative polarization losses of over 1000 mV cm² mA⁻¹. This polarization loss is alleviated by water addition, and decreases from 20 to 7 mV cm² mA⁻¹ as water is increased from 0.3 to 1.5 M. FT-IR spectroscopy, linear voltammetry, galvanostatic reduction, surface microscopy and electrolytic conductivity measurements were conducted to probe competing water activation or water passivation effects on organic-phase Al electrochemistry.     

Translational energy release and stereochemistry of steroids. VIII-The mechanism of the elimination of water from metastable ions in epimeric 3-hydroxy steroids of the 5α-series

The mechanism of water elimination from metastable molecular, [M ? CH₃˙]⁺ and [M ? ring D]⁺˙ ions of epimeric 3-hydroxy steroids of the 5α-series has been elucidated. Deuterium labelling, the measurement of the translational energy released during the loss of water, and collision-induced decomposition mass-analysed kinetic energy spectrometry were the techniques used. It was found that the mechanisms of water loss from metastable M⁺˙ and [M ? ring D]⁺˙ ions is different from that from [M ? CH₃˙]⁺ ions.     

Determination of total heterogeneity and fractal dimensions of high-temperature superconductors

Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa₂Ca₂Cu₃O₈₊, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal stability of the ‘cave’ mineral ardealite Ca<Subscript>2</Subscript>(HPO<Subscript>4</Subscript>)(SO<Subscript>4</Subscript>)·4H<Subscript>2</Subscript>O

Thermogravimetry combined with evolved gas mass spectrometry has been used to characterise the mineral ardealite and to ascertain the thermal stability of this ‘cave’ mineral. The mineral ardealite Ca₂(HPO₄)(SO₄)·4H₂O is formed through the reaction of calcite with bat guano. The mineral shows disorder, and the composition varies depending on the origin of the mineral. Thermal analysis shows that the mineral starts to decompose over the temperature range of 100–150 °C with some loss of water. The critical temperature for water loss is around 215 °C, and above this temperature, the mineral structure is altered. It is concluded that the mineral starts to decompose at 125 °C, with all waters of hydration being lost after 226 °C. Some loss of sulphate occurs over a broad temperature range centred upon 565 °C. The final decomposition temperature is 823 °C with loss of the sulphate and phosphate anions.     

Thermal requirements to obtain calcined and frits of ulexite

Ulexite has a substantial amount of hydration water, which allows using calcination methods to increase the B₂O₃ content from 42.97 to 66.69%, due to the loss of 35.54% of its weight, corresponding to its hydration water.In this study, determinations of changes in the heat content at each temperature were made using an isoperibol calorimeter. The mean specific heat was calculated from these values. The reaction enthalpy was also determined by DTA methods.The sample used in the experiments contains 39.04% B₂O₃. The temperature was between 80 and 1000 °C. Curves of weight loss and enthalpy changes are presented and analysed.The results have industrial application in order to determine the thermal requirements for calcining ulexite at different temperatures, as well as its complete dehydration.     

Study on kinetics of the pyrolysis process of aluminum sulfate

Abstract

Using high aluminum gangue as a raw material, aluminum sulfate 18 hydrate was made by the sulfuric acid leaching method under certain conditions. The product was characterized using X-ray diffraction (XRD) analysis of the phases, x-ray-fluorescence (XRF) analysis of the aluminum and sulfur content and thermogravimetric analysis of the crystallized water [Al₂(SO₄)₃·18H₂O]. Change characteristics of the crystal form and morphology during pyrolysis of octadecahydrate aluminum sulfate were studied by thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC), differential thermogravimetry (DTG), XRD and scanning electron microscope (SEM). The theoretical basis for the preparation of metallurgical alumina from octadecahydrate aluminum sulfate was provided. According to the characteristics of the crystal structure change, the pyrolysis process of octadecahydrate aluminum sulfate can be separated into three stages. The first stage (dehydration stage 87–250?°C) had a weight loss rate of 40.5% and a loss of 15 water molecules; the weight loss rate of the second stage (dehydration stage 280–414?°C) was 8.1% with three water molecules lost; the weight loss rate of the third stage (decomposition stage 770–900?°C) was 36.1%, where three SO₃ molecules were lost. The pyrolysis products were mainly Al₂O₃. The activation energies of the three reaction stages were calculated using the Coats-Redfern method as 90.02?kJ/mol, 205.74?kJ/mol and 284.40?kJ/mol, respectively.     

Dielectric and conductivity relaxations in poly(hema) and of water in its hydrogel

The dielectric permittivity ε′ and loss ε″ of anhydrous poly(2-hydroxyethyl methacrylate) and its 38.6 w/w% hydrogel have been measured in the frequency range from 12 Hz to 200 kHz and the temperature range from 77 to 273 K. The former has a sub-T_g relaxation with a half-width of 4.5 decades for the loss spectra, whose strength increases with temperature, and an activation energy of 62.5 kJ/mol. The dielectric relaxation time of the α process of supercooled water in the hydrogel is 53 s at its calorimetric T_g of 135 K. The half-width of the relaxation spectrum is 2.85 decades and, in the narrow temperature range, its apparent activation energy is 60.8 kJ/mol. Heating of the hydrogel causes crystallization of water which begins at about 207 K and becomes readily detectable as a second dielectric loss peak at about 230 K. For each temperature between 207 and 267 K, supercooled water in the hydrogel coexists with its crystallized form, with the amount of the crystallized solid increasing with increasing temperature. These results are discussed in terms of “bound” and “free” states of water in the hydrogel.     

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH₃, CO₂ and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH₃, CO₂, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H₂ and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.     

Aqueous process to limit hydration of thin-film inorganic oxides

Aqueous-processed aluminum oxide phosphate (AlPO) dielectric films were studied to determine how water desorbs and absorbs on heating and cooling, respectively. In-situ Fourier transform infrared spectroscopy showed a distinct, reversible mono- to bidentate phosphate structural change associated with water loss and uptake. Temperature programmed desorption measurements on a 1-μm thick AlPO film revealed water sorption was inhibited by an aqueous-processed HfO₂ capping film only 11-nm thick. The HfO₂ capping film prevents water resorption, thereby preserving the exceptional performance of AlPO as a thin-film dielectric.     

Thermal behaviour of fibrous zeolites of the natrolite group

The western region of the Deccan Volcanic Province (DVP) is constituted of tholeiitic lava flows. They host numerous cavities, varying in size and shape, largely occupied by zeolites and a variety of secondary minerals, amongst which the fibrous zeolites (natrolite group), are particularly gorgeous and attractive. Scolecite and mesolite are the only two members commonly occurring in this region. Our data on their thermal behaviour significantly differs from that reported in previous literature. Scolecite, Ca₈(Al₁₆Si₂₄O₈₀)·24H₂O shows three distinct steps instead of two and water loss is observed even beyond 550°C. It is held that the first step corresponds to the expulsion of water from the site farthest away from Ca and the next two steps in succession correspond to the two sites nearer to Ca. Mesolite, Na₁₆Ca₁₆(Al₄₈Si₇₂O₂₄₀)· 64H₂O has much more complex behaviour with four or five steps of water expulsion and a major loss around 248–270°C in a double reaction attributed here to the expulsion of water from scolecite type channels. It is further held that the natrolite type channels are emptied in further steps. Loss of water in steps even beyond 400°C is particularly noted and such reactions are well reflected in the TG and the DTG. Peak temperature dependence on sample amounts is also evident. Successive phase transformations above 700°C, up to 1000°C are reflected in the DTA curves.     

Water‐Soluble and Recyclable Cyclopalladated Ferrocenylimine for Suzuki Coupling Reaction

A series of new water‐soluble cyclopalladated ferrocenylimines were designed and prepared. They were efficient catalyst for Suzuki coupling reactions of aryl bromides and phenylboronic acid in neat water under ambient atmosphere. Among of these catalysts, the catalyst ( C₂D ) could be reused for 6 times for the Suzuki coupling reaction of 4‐bromotoluene with phenylboronic acid in EtOH/H₂O under ambient atmosphere, in which no significant loss activity of C₂D was observed.     

相变储能化合物CH3COONa·3H2O的热分解行为

通过对CH₃COONa·3H₂O进行热重(TG)及差示扫描量热法(DSC)测试,分析了其热分解行为,并从热力学的角度对其脱水过程进行了讨论。结果表明,CH₃COONa·3H₂O的脱水过程可分为两个阶段,先失液态水形成CH₃COONa溶液,再从溶液中脱出气态水,并且在加热过程中一直伴随着结晶水的蒸发逸出。用硅油覆盖的方法能很好地抑制低温时由于蒸汽压差异引起的CH₃COONa·3H₂O结晶水的不断蒸发逸出问题。     

A green MXene-based organohydrogel with tunable mechanics and freezing tolerance for wearable strain sensors

Conductive hydrogels have attracted considerable attention owing to their potential for use as electronic skin and sensors.However,the loss of the inherent elasticity or conductivity in cold environments severely limits their working conditions.Generally,organic solvents or inorganic salts can be incorporated into hydrogels as cryoprotectants.However,their toxicity and/or corrosive nature as well as the significant water loss during the solvent exchange present serious difficulties.Herein,a liqu...