Sonoluminescence of aqueous solutions of sulfuric acid and sulfur dioxide

Sonoluminescence (SL) of aqueous solutions of sulfuric acid and sulfur dioxide enhances with an increase in their concentration and reaches a maximum at 16 and 0.05 mol L^–1, respectively. The further increase in the concentration of these substances decreases the SL intensity. The SL spectra of the solutions have a broad maximum at 450 nm. Excited SO₂ molecules formed in sulfuric acid due to sonolysis are luminescence emitters. The proposed mechanism of bright SL in these systems is based on the energy transfer from the electron-excited sonolysis products to the SO₂ molecules in cavitation bubbles.     

Tribological behaviors of a novel trilayer nanofilm: the influence of outer chain length and interlayer thickness

Polydopamine (coded as PDA) is reported to be very adhesive and reactive due to the attached functional groups, such as amine and hydroxyl groups. In this work, taking advantage of the condensation between Si–OH of the hydroxylated alkyltrichlorosilane (ATS) and C–OH on PDA surface, ATS molecules with different chain carbon number of 10, 14 and 18 were grafted onto the 3‐aminopropyl triethoxysilane (APTES)‐PDA dual‐layer film, which was composed of PDA outerlayer and APTES underlayer, on Si substrate. Thus, hydrophobic trilayer films coded as APTES‐PDA‐ATS were prepared successfully. In order to reveal the dependence of the tribological behaviors upon the microstructures of the film, tribological experiments were conducted on an atomic force microscope and a ball‐on‐plate tribometer. Experimental results showed that the (micro‐) friction reducing (characterized by a parameter of relative friction coefficient or friction coefficient, RFC or FC) and macro‐wear resisting (characterized by anti‐wear life) behaviors were related with the chain length of outerlayer and the PDA thickness. Specifically, on one hand, as the chain length increases, RFC/FC decreased and macro anti‐wear life lengthened; on the other hand, as PDA gets thicker, RFC increased and the anti‐wear life enhanced. Copyright © 2013 John Wiley & Sons, Ltd.     

Solubility and thermodynamics of solution of argon in aqueous solutions of sodium octanoate and sodium dodecylsulfate

The ostwald absorption coefficient of argon was measured in aqueous solutions of two surfactants; sodium n-octanoate and in sodium dodecylsulfate, at several concentrations and at a few temperatures between 10–25°C. The free energies, entropies and enthalpies of solution were computed. A tentative interpretation of the results is given, based on a competition between the solubilization and the salting-out effects of the surfactants.     

A multi-technique study of compact and hydrous Au oxide growth in 0.1 M sulfuric acid solutions

The growth and reduction of compact (α-) and overlying hydrous (β-) oxide films on polycrystalline Au electrodes in aqueous 0.1 M H₂SO₄ solutions have been investigated using potentiostatic, cyclic voltammetry, ellipsometric and quartz crystal microbalance (QCMB) techniques. All α-oxide films, formed with time at constant potentials up to 2.6 V, or by multicycling of the potential, are non-hydrated in nature, even when covered by a thick β-oxide film. The α-oxide film composition is suggested to be AuO below 1.5 V, and a mixture of AuO+Au₂O₃ at potentials above this, becoming predominantly Au₂O₃ at very high potentials. Up to three monolayers of Au₂O₃ can be formed. When formed at constant potential, the β-oxide film becomes increasingly hydrated as it thickens with time of growth, with a mass to charge ratio and refractive index consistent with Au₂O₃·H₂O and later with Au₂O₃·2H₂O. In contrast, the β-oxide film formed by multicycling has a higher mass overall, and becomes less hydrated as it thickens with time, with a mass and refractive index consistent with Au₂O₃·10H₂O at short times, ranging to Au₂O₃·2H₂O as the film thickens.     

Sodium sulfate solubilities in high temperature aqueous sodium chloride and sulfuric acid solutions—predictions of solubility,vapor pressure,acidity, and speciation

Experimental measurements of the solubility of sodium sulfate in aqueous solutions containing both sodium chloride and sulfuric acid in the temperature range 250 to 374°C are reported. These measurements have been combined with previous data on the solubility of sodium sulfate in water, in aqueous sodium chloride, and in sulfuric acid solutions to produce a comprehensive model describing the solubility of sodium sulfate in such solutions. Calculations and predictions of solubility, vapor pressure, boiling point elevation, acidity, and speciation are presented. This model is of fundamental interest in itself and also is of importance because the precipitation of sodium sulfate may be a contributing factor in enhancing crevice corrosion in metals exposed to high-temperature water containing chloride and sulfate ions as impurities.     

Ions with a strong symmetric H-bond in solutions of sodium acetate in acetic acid

The multiple attenuated total reflection IR spectra of solutions of sodium acetate in acetic acid have been recorded in the range from 9000 to 4000 cm^–1. The CH₃COO^– anion and an acid molecule form be complex (CH₃COO...H...OOCCH₃) with a strong symmetric H-bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp, 1854–1857, July, 1996.     

Ionization of carbonic acid in sodium chloride solutions at 25°C

The stoichiometric pK ₁ ^* and pK ₂ ^* for the ionization of carbonic acid has been determined from emf measurements in NaCl soluions to 6.0m at 25°C. Our results at low concentrations are in good agreement with the results of Harned and Bonner, of Dyrssen and Hansson and of Roy et al. The calculated values of pK ₁ ^* using Pitzer's equations agree with the measured values to ±0.01 pK units provided higher order terms are used. It was necessary to use a triplet interaction parameter () and higher order electrostatic terms (^E) to calculate reliable values of pK ₂ ^* (±0.03 pK units) over the entire concentration range. These results demonstrate the reliability of the Pitzer equations to estimate activity coefficients in concentrated salt solutions.     

Effects of negative bias on the structural,topological and tribological properties of amorphous carbon films prepared by magnetron sputtering

Amorphous carbon films were prepared in a magnetron sputtering system at different d.c. negative substrate biases (?50, ? 100, ? 150, ? 200 and ? 250 V). The surface roughness, hardness and tribological properties of as‐deposited films were investigated based on the films' structural evolution. Compared with the films deposited at the negative bias of ? 50 and ? 250 V, the microstructure and bond configuration of the films deposited at negative bias of ? 150 V favored a more graphite‐like structure, which had the maximum of graphiticclusters and ordering structures; meanwhile, the films deposited at bias of ? 150 V showed the minimum coefficient of friction (COF) in air, while the wear rate showed a decrease of two orders of magnitude. The tribotesting results were attributed to the increase of graphitic domains of amorphous carbon films which decreased the interfacial shear force and lowered the COF. The uniform and ordering structure induced steady and smooth friction curves. Copyright © 2010 John Wiley & Sons, Ltd.     

The determination of hydroxide and carbonate in concentrated sodium chloride solutions

A computer method for the determination of carbonate and hydroxide in concentrated (2.89 M) sodium chloride solutions is described. The method is based on multiparametric curve-fitting and can also be applied to salts of dibasic acids with unknown equilibrium constants. The systematic error is not more than 1%. The titration and calculation takes less than 20 min.     

第一原理分子动力学研究类金刚石薄膜的结合强度与摩擦性能

金刚石(110)表面具有不同方向上抛光速率的强烈不对称的特征,用第一性原理全能量平面波赝势方法模拟研究了类金刚石薄膜表面的结合强度与摩擦性能,确定了相互作用模型以及排斥力作用范围,研究了范德华排斥力在摩擦表面上的分布,研究结果表明,摩擦表层感受到的力在〈001〉和〈110〉2个方向上表现明显不同,而且〈110〉方向上摩擦力一直高于〈001〉方向上的摩擦力.     

Enthalpies of dilution of l-cystine in aqueous solutions of sodium hydroxide, potassium hydroxide and hydrochloric acid

The enthalpies of dilution of l-cystine in solutions of two strong alkalis and one strong acid have been determined by isothermal flow-mix calorimetry at the temperatures 298.15 K, 303.15 K, 308.15 K, 313.15 K and 318.15 K. Equations of apparent enthalpies of dilution have been obtained from the experimental data in terms of the improved McMillan-Mayer theory. Enthalpic interaction coefficients, h₂, h₃, and h₄, are obtained and the values of pair-wise enthalpic interaction coefficient, h₂, discussed in the light of solute-solute and solute-solvent interactions.     

Effect of methane on magnetron sputtering graphite target deposited films and tribological properties of a-C:H:Ti/a-C:H friction pairs

In this study, we prepared a-C:H films with different nanostructures at different methane flow rates. The effect of the methane flow rate on the tribological properties of 440 steel/a-C:H friction pairs and a-C:H:Ti/a-C:H friction pairs in an atmospheric environment was studied by a reciprocating friction machine. The results show that there is no relationship between the tribological properties of 440 steel/a-C:H friction pair and methane flow rate. The tribological performance of the a-C:H:Ti/a-C:H friction pair was greatly improved. In particular, in the friction pair of a-C:H:Ti/a-C:H with a methane flow rate of 20 sccm, superlubricity is shown, and the wear rate is only 4.04 × 10⁻⁹ mm³/Nm. After tribological experiments, Raman spectroscopy, XPS, and other characterization methods were used to study the relationship between the nanostructure and tribological properties of a-C:H:Ti films and a-C:H prepared with different methane flow rates. This study is great significance to the application of a-C:H:Ti/a-C:H friction pair in mechanical parts under atmospheric environment.     

Thermal degradation behaviors of a novel nanocomposite based on polypropylene and Co-Al layered double hydroxide

The thermal degradation behaviors of a novel nanocomposite based on polypropylene and organic Co/Al layered double hydroxide (PP/CoAl-LDH) were studied via thermogravimetric analysis (TGA) in the present work. The thermal degradation activation energies of the PP/CoAl-LDH nanocomposite were determined via Friedman and Flynn-Wall-Ozawa methods, and were compared with those of neat PP. The relationship between the organic CoAl-LDH concentration and the activation energies in PP/CoAl-LDH nanocomposite also has been investigated. An internal reason and an outer reason leading to high fire retardancy of PP/CoAl-LDH nanocomposite were proposed. The presence of CoAl-LDH tended to increase significantly the decomposition activation energy of nanocomposite at full-scale temperature and had an important influence on both of internal and outer reasons.     

Electrochemical behavior of nickel and its oxides in concentrated sodium hydroxide solutions

By using the methods of cyclic voltammetry (the potential scan rates of 20 mV/s and 2–500 V/s) and preparative electrolysis at an ac frequency of 10 to 200 Hz, in 17 M sodium hydroxide, it is found that nickel oxidation proceeds with the formation of oxides of variable composition. It is shown that the dependence of nickel failure rate on the current frequency has a peak. The highest failure rate corresponds to a current frequency of 20 Hz.     

Potentiometric titration of hydroxide,aluminate and carbonate in sodium aluminate solutions

An automated potentiometric titration of hydroxide, aluminate and carbonate in sodium aluminate solutions is described. The addition of barium chloride before titration with hydrochloric acid enables the three components to be determined in one run, involving neutralization of hydroxide, protonation of aluminate and dissolution of barium carbonate. The accuracy and precision of the method are satisfactory for a rapid method used for control of aluminum oxide production.     

Electric conductivity of concentrated aqueous solutions of propionic acid, sodium propionate and their mixtures

Specific electric conductivity (EC) of concentrated aqueous solutions of propionic acid (PA), sodium propionate (SP), and water/PA/SP mixtures is measured in the temperature range of 15–90°C. Specific EC passes a maximum at the increase in the electrolyte concentration in the mixtures of water/PA, water/SP, and water/PA/SP containing a similar PA concentration. The maximum EC value of the aqueous PA solution at the given temperature is used as the generalizing term. It is shown that the values of reduced EC (ratio of EC and its maximum value at the given temperature) fall on a single curve in the whole studied range of temperatures and concentrations of the water/PA mixture. The EC activation energy is calculated for all the studied solutions. It is found that the EC activation energy of these solutions decreases at the temperature increase and grows at the increase of the concentration of electrolyte.