X-Ray diffraction investigations of concentrated aqueous solutions of calcium halides

Concentrated aqueous solutions of calcium chloride and calcium bromide have been investigated by X-ray diffraction. In the diffraction patterns of aqueous chloride solutions of different concentrations, a maximum of intensity is observed in the region 0.6–1.1 Å⁻¹, while in the investigated aqueous bromide solution no maximum is observed in that region. This pre-peak suggests the existence of positional correlations in solution beyond direct contact. The interpretation is similar to the one proposed by the authors in previous investigations, and is supported by the calculations based on ad hoc molecular models. The influence of the anion is discussed.     

EPR studies on aqueous sucrose solutions using (Cu(H2O)6)2+ spin probe

EPR investigations using Cu²⁺ ion as a probe have been performed on supersaturated sucrose solution with percent concentration c = 66 as a function of temperature T, and at room temperature as a function of c. The motionally averaged spectrum of [Cu(H₂O)₆]²⁺ was used to monitor the changes in intermolecular interactions that occur as a function of [c, T]. A drastic increase in the line width, symptomatic of increase in the rotational correlation time of [Cu(H₂O)₆]²⁺, is observed between 293 and 288 K. The motionally averaged spectrum disappears below 281 K. The motionally averaged spectrum is also absent in the room temperature spectra of the solution with c= 85. Even in the [c, T] range where [Cu(H₂O)₆]² is found to be nearly static, these molecules appear to have an orientational fluctuation manifesting in the m ₁ dependence of the line width of the parallel component.     

Intermediate range order in concentrated aqueous solutions of copper nitrate. X-ray diffraction and Raman investigations

Concentrated aqueous solutions of copper nitrate of different concentrations (0.66 mol dm⁻³ up to 4.84 mol dm⁻³) have been investigated by X-ray diffraction at room temperature. In these solutions a maximum of intensity (prepeak) is observed at low values of Q (approx. 0.6 to 1 Å⁻¹) suggesting the existence of an intermediate range order in their structure, in agreement with previous investigations on different electrolytes. In order to get information on the solvation shell of the copper cation, Raman spectroscopy experiments have been performed for the more concentrated solution. Polarization observations, isotopic substitution of the solvent and the comparison with a Raman spectrum of a concentrated aqueous solution of aluminum nitrate were performed in order to improve the interpretation of the obtained results with these convergent observations.     

Caffeine as non-toxic corrosion inhibitor for copper in aqueous solutions of potassium nitrate

Different electrochemical methods were employed in order to confirm the ability of caffeine (1,3,7-trimethylxanthine) to inhibit the corrosion processes of copper in aqueous potassium nitrate solutions in the absence and in the presence of chloride. Some experiments were repeated in potassium perchlorate in order to compare the influence of the medium. The interaction between the organic compound and the electrode surface occurs independently of the electrode potential. However, maximum interaction was observed at 0.0 V (Ag/AgCl) in aerated solutions, and at −0.25 V (Ag/AgCl) in deaerated solutions.The presence of the organic compound adsorbed on the electrode surface was confirmed by comparing the voltammograms of copper electrode in the absence and presence of 1.5 mmol L⁻¹ of dissolved caffeine. The same results were observed by comparing polarization curves in the absence and in the presence of caffeine.Anodic currents decrease noticeably in the presence of the organic compound. Chronoamperometric experiments were conclusive to prove the inhibitor capability of caffeine to decrease the corrosion dissolution processes of copper under anodic polarization.     

用光电双脉冲LIBS技术快速测量水中痕量汞元素

用木片吸收水溶液,将水溶液样品转变为固体样品,从而解决用激光诱导击穿光谱(LIBS)技术直接分析水样品所带来的诸多问题,并首次采用光电双脉冲LIBs技术来增强激光等离子体中汞的原子辐射.实验绘制了用单脉冲LIBS技术和光电舣脉冲LIBS技术所得到的汞的校正曲线并得出这两种技术中汞的最低检出限分别为2.4和0.3 mg·...     

Effects of salt on solute association behavior in nanoconfined aqueous solutions

Using molecular dynamics simulations, we have studied the effects of salt on the association behavior of solute molecules in nanoconfined aqueous solutions. Three types of solute association states – dispersion, reversible and aggregation states – are still observed in nanoconfined aqueous solutions in the presence of salt. With the increase of ion concentration, the tendency toward the formation of larger clusters is enhanced and the solute critical aggregation number decreases. We even found the transformation of solute association state from the dispersion to the reversible state or from the reversible to the aggregation state within an intermediate range of solute number. This phenomenon is similar to the salting out process and is attributed to the decrease of free water molecules induced by the ion polarization.     

Density, viscosity and ultrasonic velocity studies of aqueous solutions of sodium acetate at different temperatures

The densities and viscosities of aqueous solutions of sodium acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K and at atmospheric pressure. The molality range has been studied between 6.09 × 10^− 2 to 7.314 × 10^− 1 mol kg^− 1. The experimental values of density have been used to calculate apparent molar volume, partial molar volume, solute–solute interaction parameter, and Hepler's constant. The viscosity data have been analyzed with Jone–Dole equation. Furthermore, ultrasonic velocity measurements of aqueous solutions of sodium acetate have been made at 298.15 and 308.15 K and at atmospheric pressure. From experimental values of ultrasonic velocity, apparent molar isentropic compressibility and limiting apparent molar isentropic compressibility have been calculated. All the parameters calculated from density, viscosity, and ultrasonic velocity indicate that the sodium acetate is water structure maker.     

The apparition of a new reaction at lower temperature in equiatomic CuAu alloy

Recently a lot of interest has been devoted to the study of order–disorder transitions in different materials. Although the equiatomic CuAu alloy represents a classical model of this type of transformation, it still receives considerable attention because many questions about phase transitions are still raised according to its equilibrium diagram. In this context, the present paper carries a new result observed in CuAu alloy consisting of a new anomaly observed on differential scanning calorimetry (DSC) curves at low temperature and new peaks in X-ray diffraction (XRD) spectra. For that, we will try to give an explanation of the origin of this new reaction, with the help of other techniques as electrical resistivity and microhardness measurements. The kinetic behaviour of this new reaction has been also studied by anisothermal analysis during DSC tests to estimate the kinetics parameters as activation energy E _act and Avrami exponent n.     

Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions

A visualization of pressure-shift freezing of 0.7 w/w sucrose solutions was carried out at three temperatures 268, 253 and 235 K by release of pressure from 200 MPa to atmospheric value. Furthermore, pressure-shift freezing at 268 K and additionally pressure-shift thawing was carried out for a solution of 0.2 sucrose mass fraction. The solid phase observed at 268 K in the case of solution with 0.2 w/w sucrose fraction was ice I. The phase changes of 0.7 w/w sucrose solutions at 253 K and 235 K resulted in formation of spherical solids which are hypothesized to be eutectics, i.e. crystals with structure containing sucrose hydrates and water. The visual evaluation revealed differences in size and distribution of spherical crystals. The solids formed at 235 K were more numerous, more homogenously distributed and finally smaller than those observed at 253 K. It is explained by the higher supercooling of the solution in the former case, which provided higher driving force for nucleation and crystal growth.     

Raman identification of H2CO in aqueous solutions

Aqueous formaldehyde solutions of mole fraction from 0.05 to 0.20 were studied by Raman spectroscopy at temperatures up to 180 °C. The previously unreported Raman spectrum of formaldehyde under its non‐hydrated form H₂CO has been identified, in addition to the already known bands from methanediol CH₂(OH)₂ and poly(oxymethylene)glycols HO(CH₂O)_nH formed by hydration and subsequent polymerization of the formaldehyde molecules. The experimental spectrum of formaldehyde in solutions agrees perfectly with the theoretical calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Fabrication of three-dimensionally ordered macroporous Ta2O5 films through aqueous organic gel process

Ta₂O₅ thin films have been prepared in the forms of three-dimensionally ordered macroporous (3-DOM) materials through aqueous organic gel process guided by polystyrene (PS) colloidal templates. The structure of the films was strongly affected by the infiltration process. This suggests that the infiltration process which aims at introducing desired materials into the interstitial spaces between the PS templates is of critical importance. Dip-drawing method was adopted for infiltration in this article. However, excess precursor worked as a capping agent for films prepared from the precursor of high concentration. Spin-coating method can efficiently remove the excess precursor by high speed rotating, which makes it a promising process for the infiltration of Ta-citric precursor with concentration higher than 0.5 mol/L. X-ray diffraction (XRD) pattern showed that the products can crystallize at 600 °C and had a pure orthorhombic phase. The chemical composition of the product was also studied by X-ray photoelectron spectroscopy (XPS).     

The concentration effect on the ‘hydrophobic’ and ‘hydrophilic’ behaviour around DMSO in dilute aqueous DMSO solutions. A computer simulation study

We have carried out a molecular dynamics study of dimethyl sulfoxide (DMSO) in water at 298 K at two different densities by simulating two different concentrations: 0.055 and 0.19 mole fraction. We have found an enhancement in the structure of water, an effect that becomes more pronounced as the concentration of DMSO increases. At both concentrations there is a well-defined hydration structure around the oxygen atom of DMSO, which is able to establish strong hydrogen bonds with surrounding water molecules. An increase in the concentration of DMSO depletes the solution of bulk water molecules, reducing the number of hydrogen bonds that water can have in the immediate vicinity of DMSO but increasing the strength of the hydrogen bonds made between the oxygen atom of DMSO and water. There is clear evidence of ‘hydrophobic’ hydration around the methyl groups of DMSO, which is enhanced as the concentration of DMSO increases.     

Interaction of “extremely diluted solutions” with aqueous solutions of hydrochloric acid and sodium hydroxide: A calorimetric study at 298 K

The “extremely diluted solutions” (EDS) have revealed a really intriguing behaviour, characterized by multiple independent variables. Because of their behaviour, EDS can be described as far-from-equilibrium systems, capable of auto-organizing as a consequence of little perturbations.

We measured the heats of mixing of basic and acid solutions with such EDS and their electrical conductivity, comparing with the analogous heats of mixing and electrical conductivity of the untreated solvent.

In particular, calorimetric titrations have been performed with NaOH or HCl solutions at various concentrations. Plots of the excess heat as a function of the concentration of titrant reveal differences and similarities between the two. By analysing these plots we were able to formulate new hypotheses about the supramolecular organization of the solvent water, when subject to mechanical perturbations stemming from the EDS preparation protocol, that is comprised of an iterative process of successive dilutions and succussions.     

明胶水溶液分形性质的光散射研究

本文通过动态光散射技术并结合静态光散射及粘滞系数实验研究了明胶水溶液在不同温度、不同浓度下的分形性质。当Ｔ＞Ｔｇｅｌ时（Ｔｇｅｌ为胶凝临界温度），水为明胶的良好溶剂。明胶分子在水溶液中符合自避无规行走模型，分维ｄｆ＝５／３。当Ｔ＜Ｔｇｅｌ时，明胶水溶液需经历从溶液到凝胶的胶凝过程。在胶凝过程中，动态光散射弛豫谱分段具有指数衰减和随后的伸展指数两种模式，且伸展指数衰减的宽度参数β逐渐从０．８减少到胶凝点的０．６７，与此相对应，分维由５／３逐渐增加到２．０。在胶凝点，通过静态光散射及粘滞系数实验测得分维为２．０。     

Effects of polyethylenimine on morphology and property of ZnO films grown in aqueous solutions

Morphologies and properties of well-aligned ZnO films were controlled using zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine as a surfactant. Porous and dense ZnO films were fabricated with and without polyethylenimine, respectively. The addition of polyethylenimine proceeded to form porous ZnO whiskers film by preferential adsorption to nonpolar crystal faces and modifications of the surface free energy and growth rate. Dense ZnO film showed high transmittance of 80%, and low intensity of fluorescence and photo-induced current. Porous ZnO whiskers film showed low transmittance of 70%, while high intensity of fluorescence and high photo-induced current were detected because the porous ZnO nanowhisker film possessed a large interior surface area which can capture large amounts of DNA molecules labeled with dye molecules on the surface of ZnO crystals. High performance dye-sensitized sensors can be produced using ZnO whisker films prepared from an aqueous solution.     

托贝莫来石晶体的高温相变规律研究

通过差热分析(TGA/DSC)、X射线衍射分析(XRD)、傅里叶变换红外光谱分析(FTIR)等测试技术,对实验室制备的纯净托贝莫来石的高温相变规律进行系统的研究。DSC结果表明,托贝莫来石结构中有四个层间分子水,加热到300 ℃时四个层间分子水逐渐失去。当温度升高到724 ℃时,部分Si—O—H键断裂,失去羟基。XRD结果表明托贝莫来石晶体结构在724 ℃时已经破坏,衍射峰基本消失,煅烧后的样品为无定形的非晶态。当温度持续升高到861 ℃时,发生晶型重构,硅灰石晶体出现,结构转变为有序的、稳定的晶体结构。当温度到达1 000 ℃的时候,完全转变为2M型硅灰石晶体结构。托贝莫来石的高温相变经历了“托贝莫来石→脱水托贝莫来石→脱羟基托贝莫来石→硅灰石”一系列转变过程。     

基于内标CF-LIBS的混合水溶液中多金属元素的定量分析

提出一种简化内标自由定标激光诱导击穿光谱(CF-LIBS)分析方法,并应用于混合水溶液中Cr、Mn、Pb、Cd、Ca、Al、Co等金属元素绝对浓度的定量分析.实验结果表明,在最优化实验参数下产生的激光等离子体满足局部热平衡和光学薄条件,由该分析方法得到的LIBS检测精确度明显优于采用液固转换后的传统CF-LIBS方法,测定的浓度值与配置值的相对误差小于1%,说明应用该内标CF-LIBS方法能够同时精确测定液相基质中的多种微量金属元素的含量.