AgNO<Subscript>3</Subscript> spray tests: advantages,weaknesses, and various applications to quantify chloride ingress into concrete. Part 1: Non-steady-state diffusion tests and exposure to natural conditions

Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO₃ spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch procedure (spraying of 0.1-N AgNO₃ solution + K₂CrO₄) as well as the procedure based on the use of a sole AgNO₃ solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi procedure (spraying of 0.1-N AgNO₃ + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone) and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The possible sources of discrepancy on the results have been analysed.     

Statistical studies of branched ester latex and paint properties

Vinyl versatate, butyl acrylate and 2-ethylhexyl acrylate were compared as comonomer, for colloid-stabilized vinyl acetate latex polymers to assess their impact on latex coating properties. Vinyl versatate afforded advantages in scrub resistance, gloss, hydrophobicity and higher glass transition temperatures. Butyl acrylate developed better wet adhesion efficiency, gel content and hiding efficiency. 2-Ethylhexyl acrylate offered performance comparable to butyl acrylate in hiding efficiency, lowering copolymer glass transition temperatures, and gloss development. Combinations of these monomers, in many instances, afforded a better balance of performance properties than individual monomers alone. In the subject study, a simplex-centroid design was utilized to statistically map polymer compositions for determining the effect of comonomer composition on latex and paint film properties. In addition to developing contour maps of polymer and paint properties as a function of composition, a technique for studying structure-property relationships is presented.     

Vinyl acetate monomer—a pilot plant study

The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.     

The effect of Cu-rich sub-layer on the increased corrosion resistance of Cu-xZn alloys in chloride containing borate buffer

The electrochemical behaviour of Cu-xZn alloys, as well as their constituent metals, in a borate buffer containing chloride ions in the molar range from 0.01 to 1 M are studied. Characteristics of these materials under anodic polarization are compared and the composition and morphology of the corrosion products formed in the course of polarization experiment are analysed by SEM and EDS. X-ray photoelectron spectroscopy and electrochemical impedance measurements are used for characterization of the surface layers formed on Cu, Zn and Cu-40Zn alloy during 2-h immersion at E_oc in a borate buffer containing two different concentrations of chloride ions. New aspects of the behaviour of brass under E_oc condition are revealed. The improved corrosion resistance of brass in chloride media, if compared to zinc metal, is attributed to a Cu-rich layer formed by the selective dissolution of zinc. Based on the results, a structural model describing the improved corrosion resistance of Cu-40Zn alloy with respect to Zn metal is proposed.     

Cathodic processes in the leaching and electrochemistry of covellite in mixed sulfate–chloride media

The cathodic processes that occur on a covellite (CuS) surface in mixed sulfate–chloride solutions in the absence and presence of copper(II) ions have been studied using potentiostatic transients and cyclic voltammetry at rotating disk electrodes in the potential range 0.3–0.7 V (versus SHE). This range is relevant to the oxidative leaching of this copper mineral in sulfate and chloride lixiviants. Variations in the concentrations of sulfate and chloride ions had a small effect on the cathodic reduction of covellite in the potential range of 0.5–0.3 V, although the presence of chloride ion resulted in a significant increase in the anodic current on the reverse sweep. On the other hand, addition of copper(II) ions resulted in enhanced cathodic currents and subsequent anodic currents in both sulfate and chloride solutions due to reduction of covellite to an undefined reduced copper sulfide species. Reduction of copper(II) to copper(I) ions becomes the preferred cathodic reaction as the concentration of chloride ions increases, becoming mass transport controlled at a rotating disc electrode at potentials below about 0.4 V. Potentiostatic measurements at potentials negative to the mixed potential in acidic chloride solutions have shown that reduction of copper(II) ions is reversible and have been used to estimate the rate of oxidative dissolution of the mineral which value agrees reasonably well with previously reported leaching rates under similar conditions. Reduction of dissolved oxygen has been found to be very much slower that that of copper(II) ions under ambient conditions.     

Studies on cross-linked polyurethane acrylate-based electrolyte consisting of reactive vinyl/divinyl diluents

A series of cross-linked polyurethane acrylate (PUA) electrolytes have been prepared by using 4,4′-methylene bis(phenyl isocyanate), polyethylene glycol, hydroxyethyl methacrylate and different reactive vinyl/divinyl diluents, such as methyl methacrylate (MMA), ethyl acrylate and acrylonitrile, tripropylene glycol diacrylate (TPGDA). The electrolytes were prepared by UV radiation induced cross-linking of the PUA-diluent mixture followed by swelling in a liquid electrolyte (LP-30). Depending upon the composition of the components, these electrolytes exhibited a wide range of mechanical and electrical properties. The system containing MMA as reactive diluent showed highest conductivity, but poor mechanical properties and stability in the liquid electrolyte. The TPGDA cross-linked system possesses a good combination of ionic conductivity and stability in liquid electrolytes. These systems showed good compatibility with Li-electrodes and sufficient electrochemical stability to allow safe operation in rechargeable Li-batteries.     

VAc／MMA半连续乳液共聚合的研究：Ⅱ分子量及其分布

以过硫酸铵为引发剂，十二烷基硫酸钠为乳化剂，于７０℃下进行了ＶＡｃ／ＭＭＡ乳液共聚合试验。试验确定了不同组成ＶＡｃ／ＭＭＡ共聚物的Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程参数Ｋ和α值。对ＧＰＣ测试数据处理给出了加料速率，乳化剂量，单体比例及种子与非种子法对分子是及其分布的影响。     

γ 射线引发 VAc 乳液聚合以制备白乳胶的动力学及工艺条件研究

研究了ＶＡｃ的辐射乳液聚合动力学，并对其聚合工艺条件作了初步探索。得出ＶＡｃ乳液在进行辐射聚合时，成核期结束较早（转化率在１０％以下），有相当长的恒速期存在。乳胶粒子直径在０．５～３μｍ之间，比一般的乳液聚合乳胶粒子要大。同时从动力学数据还可以看出几种成核机理（胶束成核，水相成核和液滴成核）同时存在，由此对试验条件提出了相应的要求。     

Stability of protective oxide films in waste incineration environment—solubility measurement of oxides in molten chlorides

Solubility measurements of several oxides in molten NaCl-KCl and NaCl-KCl-Na₂SO₄-K₂SO₄ were conducted in three different levels of basicity. The dissolution behavior of the oxides showed almost the same tendency as that shown by the dissolution behavior of the oxides in molten Na₂SO₄ in literature. In a waste incineration environment, a protective Cr₂O₃ film easily dissolves in molten chlorides as CrO₄²⁻ because pO²⁻ of the molten chlorides tends to have a small value due to the effect of water vapor contained in the combustion gas. From the result of the solubility measurement, the addition of molybdenum and/or silicon was expected to improve the corrosion resistance of alloys. Laboratory corrosion tests confirmed this expectation. However, the scale analysis suggested that the effect of molybdenum could not be explained completely by only the mechanism derived from the result of the solubility measurement.     

Synergistic inhibition between o-phenanthroline and chloride ion for steel corrosion in sulphuric acid

The corrosion inhibition of cold rolled steel in 0.5 M sulphuric acid in the presence of o-phenanthroline and sodium chloride (NaCl) has been investigated by using weight loss and electrochemical techniques. The experimental data suggest that the inhibition efficiency increases with increasing NaCl concentration in the presence of 0.0002 M o-phenanthroline, but decreases with increasing temperature. A synergistic effect is observed when o-phenanthroline and chloride ions are used together to prevent cold rolled steel corrosion in 0.5 M sulphuric acid. The polarization curves showed that the complex of o-phenanthroline and NaCl acts as a mixed type inhibitor. The experimental results suggested that the presence of chloride ions in the solution stabilized the adsorption of o-phenanthroline molecules on the metal surface and improved the inhibition efficiency of o-phenanthroline. The adsorption of the complex accords with the Langmuir adsorption isotherm. Some thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy have been calculated by employing thermodynamic equations. Kinetic parameters such as apparent activation energy and pre-exponential factor have been calculated and discussed.