Comprehensive utilization of complex rubidium ore resources:Mineral dissociation and selective leaching of rubidium and potassium

Currently,the process of extracting rubidium from ores has attracted a great deal of attention due to the increasing application of rubidium in high-technology field.A novel process for the comprehensive utilization of rubidium ore resources is proposed in this paper.The process consists mainly of mineral dissociation,selective leaching,and desilication.The results showed that the stable silicon–oxygen tetrahedral structure of the rubidium ore was completely disrupted by thermal activation and the mineral was completely dissociated,which was conducive to subsequent selective leaching.Under the optimal conditions,extractions of 98.67% Rb and 96.23%K were obtained by leaching the rubidium ore.Moreover,the addition of a certain amount of activated Al(OH)_(3) during leaching can effectively inhibit the leaching of silicon.In the meantime,the leach residue was sodalite,which was successfully synthesized to zeolite A by hydrothermal conversion.The proposed process provided a feasible strategy for the green extraction of rubidium and the sustainable utilization of various resources.

An Experimental Observation of the Thermal Effects and NO Emissions during Dissociation and Oxidation of Ammonia in the Presence of a Bundle of Thermocouples in a Vertical Flow Reactor

Ammonia (NH3) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH3 concentrations (5%, 10%, and 15%) and reactor temperatures between 700 K and 1000 K. The thermal effects during both NH3 dissociation (endothermic) and oxidation (exothermic) were observed using a bundle of thermocouples positioned along the central axis of the quartz reactor, while the corresponding NH3 conversions and nitrogen oxides emissions were determined by analysing the gas composition of the reactor exit stream. A stronger endothermic effect, as indicated by a greater temperature drop during NH3 dissociation, was observed as the NH3 feed concentration and reactor temperature increased. During NH3 oxidation, a predominantly greater exothermic effect with increasing NH3 feed concentration and reactor temperature was also evident;however, it was apparent that NH3 dissociation occurred near the reactor inlet, preceding the downstream NH3 and H2 oxidation. For both NH3 dissociation and oxidation, NH3 conversion increased with increasing temperature and decreasing initial NH3 concentration. Significant levels of NOX emissions were observed during NH3 oxidation, which increased with increasing temperature. From the experimental results, it is speculated that the stainless-steel in the thermocouple bundle may have catalysed NH3 dissociation and thus changed the reaction chemistry during NH3 oxidation.

Investigation on small molecule-aptamer dissociation equilibria based on antisense displacement probe

Food safety is a major issue to public health and have attracted global attention.Fast,sensitive,and reliable detection methods for food hazardous substances is highly desirable.Aptamers which can bind to the target molecules with high affinity and specificity represent an attractive tool for the recognition of food hazardous substances,which play an important role in the development and application of new food safety detection technology.But current assays for characterizing small molecule-aptamer binding are limited by either the mass sensitivity or the size differentiation ability.Herein,we proposed a comprehensive method for assessing the dissociation equilibria of small molecule-aptamer,which is immobilized-free under ambient conditions.The design employs the Le Chatelier’s principle and could be used to effectively measure small molecule-aptamer interactions.ATP binding aptamer and anti-aflatoxin B1 aptamer were used as the model system to determine their affinity,in which their dissociation equilibria measurements are in excellent close to their previous work.Due to the simplicity and sensitivity of this new method,we believe that it could be recommended as an effective tool for characterizing small molecule-aptamer interactions and promote the further application of small molecular aptamer in food safety.

Activated dissociation of H_(2) on the Cu(001)surface:The role of quantum tunneling

The activation and dissociation of hydrogen molecules(H_(2))on the Cu(001)surface are studied theoretically.Using first-principles calculations,the activation barrier for the dissociation of H_(2) on Cu(001)is determined to be~0.59 eV in height.It is found that the electron transfer from the copper substrate to H_(2) plays a key role in the activation and breaking of the H–H bond,and the formation of the Cu–H bonds.Two stationary states are identified at around the critical height of bond breaking,corresponding to the molecular and the dissociative states,respectively.Using the transfer matrix method,we also investigate the role of quantum tunneling in the dissociation process along the minimum energy pathway(MEP),which is found to be significant at or below room temperature.At a given temperature,the tunneling contributions due to the translational and the vibrational motions of H_(2) are quantified for the dissociation process.Within a wide range of temperature,the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are observed.The deduced energetic parameters associated with the thermal equilibrium and non-equilibrium(molecular beam)conditions are comparable to experimental data.In the low-temperature region,the crossover from classical to quantum regime is identified.

Field Measurement of NO2 and RNO2 by Two-Channel Thermal Dissociation Cavity Ring Down Spectrometer

A two-channel thermal dissociation cavity ring down spectroscopy （CRDS） instrument has been built for in situ, real-time measurement of NO2 and total RNO2 （peroxy nitrates and alkyl nitrates） in ambient air, with a NO2 detection limit of 0.10 ppbv at 1 s. A 6-day long measurement was conducted at urban site of Hefei by using the CRDS instrument with a time resolution of 3 s. A commercial molybdenum converted chemiluminescence （Mo-CL） instrument was also used for comparison. The average RNO2 concentration in the 6 days was measured to be 1.94 ppbv. The Mo-CL instrument overestimated the NO2 concentration by a bias of ＋1.69 ppbv in average, for the reason that it cannot distinguish RNO2 from NO2. The relative bias could be over 100% during the afternoon hours when NO2 was low but RNO2 was high.

Low-Energy Electron Attachment to Serine Conformers： Shape Resonances and Dissociation Dynamics

Shape resonances of electron-molecule system formed in the low-energy electron attachment to four low-lying conformers of serine （serine 1, serine 2, serine 3, and serine 4） in gas phase are investigated using the quantum scattering method with the non-empirical model potentials in single-center expansion. In the attachment energy range of 0-10 eV, three shape resonances for serine 1, serine 2, and serine 4 and four shape resonances for serine 3 are predicted. The one-dimensional potential energy curves of the temporary negative ions of electron-serine are calculated to explore the correlations between the shape resonance and the bond cleavage. The bond-cleavage selectivity of the different resonant states for a certain conformer is demonstrated, and the recent experimental results about the dissociative electron attachment to serine are interpreted on the basis of present calculations.

Theoretical Study of the C-CI Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds

Quantum chemical calculations were used to estimate the bond dissociation energies （BDEs） for 13 substituted chlorobenzene compounds. These compounds were studied by the hybrid density functional theory （B3LYP, B3PW91, B3P86） methods together with 6-31G^＊＊ and 6-311G^＊＊ basis sets. The results show that B3P86/6-311G^＊＊ method is the best method to compute the reliable BDEs for substituted chlorobenzene compounds which contain the C-C1 bond. It is found that the C-C1 BDE depends strongly on the computational method and the basis sets used. Substituent effect on the C-C1 BDE of substituted chlorobenzene compounds is further discussed. It is noted that the effects of substitution on the C-C1 BDE of substituted chlorobenzene compounds are very insignificant. The energy gaps between the HOMO and LUMO of studied compounds estimate the relative thermal stability ordering are also investigated and from this data we of substituted chlorobenzene compounds.

Neutral Dissociation of Superexcited Nitric Oxide Induced by Intense Laser Fields

Superexcited states of NO molecule and their neutral dissociation processes have been studied both experimentally and theoretically. Neutral excited N^＊ and O^＊ atoms are detected by fluorescence spectroscopy for the NO molecule upon interaction with 800 nm intense laser radiation of duration 60 fs and intensity 0.2 PW/cm^2. Intense laser pulse causes neutral dissociation of superexcited NO molecule by way of multiphoton excitation, which is equivalent to single photon excitation in the extreme-ultraviolet region by synchrotron radiation. Potential energy curves （PECs） are also built using the calculated superexcited state of NO^＋. In light of the PECs, direct dissociation and pre-dissociation mechanisms are proposed respectively for the neutral dissociation leading to excited fragments N^＊ and O^＊.

Dissociation Pathway Analysis of Thymine under Low Energy VUV Photon Excitation

Photon-induced dissociation pathways of thymine are investigated with vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. The photoionization mass spectra of thymine at different photon energy are measured and presented. By selecting suitable photon energy, exclusively molecular ion m/z=126 is obtained. At photon energy of 12.0 eV, the major ionic fragments at m/z=98, 97, 84, 83, 70, and 55 are obtained, which are assigned to C4H6N2O＋, C4H5N2O＋, C3H4N2O＋ （or C4H6NO＋）, C4H5NO＋, C2NO2＋, and C3H5N＋, respectively. With help of theoretical calculations, the detailed dissociation pathways of thymine at low energy are well established.

Assessment of Contemporary Theoretical Methods for Bond Dissociation Enthalpies

The density functional theory （DFT） is the most popular method for evaluating bond dis- sociation enthalpies （BDEs） of most molecules. Thus, we are committed to looking for alternative methods that can balance the computational cost and higher precision to the best for large systems. The performance of DFT, double-hybrid DFT, and high-level com- posite methods are examined. The tested sets contain monocyclic and polycyclic aromatic molecules, branched hydrocarbons, small inorganic molecules, etc. The results show that the mPW2PLYP and G4MP2 methods achieve reasonable agreement with the benchmark val- ues for most tested molecules, and the mean absolute deviations are 2.43 and 1.96 kcal/mol after excluding the BDEs of branched hydrocarbons. We recommend the G4MP2 is the most appropriate method for small systems （atoms number≤20）; the double-hybrid DFT methods are advised for large aromatic molecules in medium size （20≤atoms number≤50）, and the double-hybrid DFT methods with empirical dispersion correction are recommended for long-chain and branched hydrocarbons in the same size scope; the DFT methods are ad- vised to apply for large systems （atoms number〉50）, and the M06-2X and B3P86 methods are also favorable. Moreover, the differences of optimized geometry of different methods are discussed and the effects of basis sets for various methods are investigated.

Photodissociation Dynamics of 2-1odotoluene Investigated by Femtosecond Time-Resolved Mass Spectrometry

The photodissociation dynamics of 2-iodotoluene following excitation at 266 nm have been investigated employing femtosecond time-resolved mass spectrometry. The photofragments are detected by multiphoton ionization using an intense laser field centered at 800 nm. A dissociation time of 3804-50 fs was measured from the rising time of the co-fragments of toluene radical （C7H7） and iodine atom （I）, which is attributed to the averaged time needed for the C-I bond breaking for the simultaneously excited nσ and ππ＊ states by 266 nm pump light. In addition, a probe light centered at 298.23 nm corresponding to resonance wavelength of ground-state iodine atom is used to selectively ionize ground-state iodine atoms generated from the dissociation of initially populated hσ＊ and ππ＊ states. And a rise time of 4004-50 fs is extracted from the fitting of time-dependent I＋ transient, which is in agreement with the dissociation time obtained by multiphoton ionization with 800 nm, suggesting that the main dissociative products are ground-state iodine atoms.

Simulating the Effect of Hydrate Dissociation on Wellhead Stability During Oil and Gas Development in Deepwater

It is well known that methane hydrate has been identified as an alternative resource due to its massive reserves and clean property. However, hydrate dissociation during oil and gas development(OGD) process in deep water can affect the stability of subsea equipment and formation. Currently, there is a serious lack of studies over quantitative assessment on the effects of hydrate dissociation on wellhead stability. In order to solve this problem, ABAQUS finite element software was used to develop a model and to evaluate the behavior of wellhead caused by hydrate dissociation. The factors that affect the wellhead stability include dissociation range, depth of hydrate formation and mechanical properties of dissociated hydrate region. Based on these, series of simulations were carried out to determine the wellhead displacement. The results revealed that, continuous dissociation of hydrate in homogeneous and isotropic formations can causes the non-linear increment in vertical displacement of wellhead. The displacement of wellhead showed good agreement with the settlement of overlying formations under the same conditions. In addition, the shallower and thicker hydrate formation can aggravate the influence of hydrate dissociation on the wellhead stability. Further, it was observed that with the declining elastic modulus and Poisson's ratio, the wellhead displacement increases. Hence, these findings not only confirm the effect of hydrate dissociation on the wellhead stability, but also lend support to the actions, such as cooling the drilling fluid, which can reduce the hydrate dissociation range and further make deepwater operations safer and more efficient.

Numerical Study on Dissociation of Gas Hydrate and Its Sensitivity to Physical Parameters

The natural gas hydrate resource is tremendous. How to utilize the gas from hydrates safely is researchers＇ concern. In this paper, a one-dimensional model is developed to simulate the hydrate dissociation by depressurization in hydratebearing porous medinm. This model can De used to explain the effects of the flow of multiphase fluids, the endothermie process of hydrate dissociation, the variation of permeability, the convection and conduction on the hydrate dissociation. Numerical results show that the hydrate dissociation can be divided into three stages： a rapid dissociation stage mainly governed by hydrate dissociation kinetics after an initially slow dissociation stage governed mainly by flow, and finally a slow dissociation stage. Moreover, a numerical approach of sensitivity analysis of physical parameters is proposed, with which the quantitative effect of all the parameters on hydrate dissociation can be evaluated conveniently.

Dissociation characteristics of methane hydrate using depressurization combined with thermal stimulation

Methane hydrate is considered as a potential energy source in the future due to its abundant reserves and high energy density.To investigate the influence of initial hydrate saturation,production pressure,and the temperature of thermal stimulation on gas production rate and cumulative gas production percentage,we conducted the methane hydrate dissociation experiments using depressurization,thermal stimulation and a combination of two methods in this study.It is found that when the gas production pressures are the same,the higher the hydrate initial saturation,the greater change in hydrate reservoir temperature.Therefore,it is easier to appear the phenomenon of icing and hydrate reformation when the hydrate saturation is higher.For example,the reservoir temperature dropped to below zero in depressurization process when the hydrate saturation was about 37%.However,the same phenomenon didn’t appear as the saturation was about 12%.This may be due to more free gas in the reservoir with hydrate saturated of 37%.We also find that the temperature variation of reservoir can be reduced effectively by combination of depressurization and thermal stimulation method.And the average gas production rate is highest with combined method in the experiments.When the pressure of gas production is 2 MPa,compared with depressurization,the average of gas production can increase 54%when the combined method is used.The efficiency of gas production is very low when thermal stimulation was used alone.When the temperature of thermal stimulation is 11℃,the average rate of gas production in the experiment of thermal stimulation is less than 1/3 of that in the experiment of the combined method.

Mechanical properties of gas hydrate-bearing sediments during hydrate dissociation

The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.

DISLOCATION DISSOCIATIONS AND FAULTENERGIES IN Ni_3Al ALLOYS DOPED WITH PALLADIUM

Dislocation structures in polycrystalline Ni 3Al alloy doped with palladium deformed at room temperature have been investigated by transmission electron microscopy. The structure consists mainly of dislocations dissociated into a /2〈011〉 super partials bounding an anti phase boundary (APB). Dislocations dissociated into a /3〈112〉 super Shockley partials bounding a superlattice intrinsic stacking fault (SISF) are also common debris. The majority of the SISFs are truncated loops, i.e. the partials bounding the SISF are of similar Burgers vector. These faulted loops are generated from APB coupled dislocations, according to a mechanism for formation of SISFs proposed by Suzuki et al , and recently modified by Chiba et al . The APB energies for {111} and {010} slip planes are measured to be 144±20 mJ/m 2 and 102±11 mJ/m 2 respectively, and the SISF energy has been estimated to be 12 mJ/m 2 in this alloy. It is concluded that the dislocation structure in Ni 74.5 Pd 2Al 23.5 alloy deformed at room temperature is similar to that in binary Ni 3Al, and the difference in fault energies between these two alloys is small. Thus, it seems unlikely that the enhancement of ductility of Ni 74.5 Pd 2Al 23.5 results from only such a small decrease of the ordering energy of the alloy. SISF bounding dislocations also have no apparent influence on the ductilization of Ni 74.5 Pd 2Al 23.5 alloy.

Methane hydrate formation and dissociation in synthetic seawater

The formation and dissociation of methane gas hydrate at an interface between synthetic seawater （SSW） and methane gas have been experimentally investigated in the present work. The amount of gas consumed during hydrate formation has been calculated using the real gas equation. Induction time for the formation of hydrate is found to depend on the degree of subcooling. All the experiments were conducted in quiescent system with initial cell pressure of 11.14 MPa. Salinity effects on the onset pressure and temperature of hydrate formation are also observed. The dissociation enthalpies of methane hydrate in synthetic seawater were determined by Clausius-Clapeyron equation based on the measured phase equilibrium data. The dissociation data have been analyzed by existing models and compared with the reported data.

Effect of rapidly depressurizing and rising temperature on methane hydrate dissociation

Two methods, rapidly depressurizing to 0.1 MPa at a constant temperature and rising temperature under equilibrium P, T conditions, were used to study the dissociation of pure CH4 hydrate formed below the ice point. At a constant temperature with rapidly depressurizing to 0.1 MPa, CH4 hydrate dissociated rapidly at initial dissociation and then the dissociation rate gradually decreased. However, the dissociation of CH4 hydrate at temperatures of 261 to 266 K was much faster than that at temperatures of 269 to 272 K, indicating its anomalous preservation. Under an equilibrium P, T conditions, rising temperature had extensively controlling impact on dissociation of CH4 hydrate at equilibrium pressures of 2.31, 2.16 and 1.96 MPa. In this study, we report the effect of pressure on CH4 hydrate dissociation, especially the effect of equilibrium pressure on dissociation at various melting temperatures. And we find that the ice particles size of CH4 hydrate formed may dominant the CH4 hydrate dissociation. Dissociation of CH4 hydrate formed from ice particles of smaller than 250 μm may not have an anomalous preservation below the ice point, while particles larger than 250 μm may have more extensive anomalous preservation.

Overview of the detection methods for equilibrium dissociation constant KD of drug-receptor interaction

Drug-receptor interaction plays an important role in a series of biological effects, such as cell pro- liferation, immune response, tumor metastasis, and drug delivery. Therefore, the research on drug-re- ceptor interaction is growing rapidly. The equilibrium dissociation constant （KD） is the basic parameter to evaluate the binding property of the drug-receptor. Thus, a variety of analytical methods have been established to determine the KD values, including radioligand binding assay, surface plasmon resonance method, fluorescence energy resonance transfer method, affinity chromatography, and isothermal ti- tration calorimetry. With the invention and innovation of new technology and analysis method, there is a deep exploration and comprehension about drug-receptor interaction. This review discusses the differ- ent methods of determining the KD values, and analyzes the applicability and the characteristic of each analytical method. Conclusively, the aim is to provide the guidance for researchers to utilize the most appropriate analytical tool to determine the KD values.

Methane hydrate formation and dissociation behaviors in montmorillonite

The methane hydrate formation and the methane hydrate dissociation behaviors in montmorillonite are experimentally studied. Through the analyses of the microstructure characteristic, the study obtains the porous characteristic of montmorillonite. It is indicated that methane hydrate in montmorillonite forms the structure I (si) crystal. Meanwhile, molecular dynamics simulation is carried out to study the processes of the methane hydrate formation and the methane hydrate dissociation in montmorillonite. The microstructure and microscopic properties are analyzed. The methane hydrate formation and methane hydrate dissociation mechanisms in the montmorillonite nanopore and on the montmorillonite surface are expounded. Combining the experimental and simulating analyses, the results indicate the methane hydrate formation and methane hydrate dissociation processes have little influence upon the crystal structure of porous media from either micro- or macro-analysis. It is beneficial to the fundamental researches on the exploitation and security control technologies of natural gas hydrate in deep-sea sediments.