Crevice corrosion behavior of high-alloy stainless steelsin a SWRO pilot plant

This paper presents the results of a study which has been carried out to investigate the crevice corrosion behavior of high-alloy stainless steel in a SWRO pilot plant. The study evaluated the corrosion performance of some austenitic and duplex steels in a crevice-forming environment created in a RO plant, especially in high-pressure feed and brine lines. The study of the effect of chemical dosing on crevice corrosion in the RO plant and electrochemical testing of crevice corrosion in the laboratory were the main objectives of this test program. High-alloy stainless steels, namely AL 6XN® and 254 SMO (superaustenitic), 2205, 2507 and DP3W (Duplex) were used in the test program. The tests were carried out in natural seawater and RO concentrate (conductivity: 75,000 to 80,000 μS/cm) at ambient temperature by operating the test plant at normal SWRO operating feed pressure of 54 bar. FeCl₃ was added as coagulant to maintain a silt density index of ∼3, and H₂SO₄ was added to feed in order to maintain the feed pH of ∼ 6.5. Chlorination and subsequent dechlorination agents were not added to the feed. For crevice corrosion tests in RO unit, the exposure periods were 6 and 12 months, respectively. The results of the tests showed that alloy DP3W has the best pitting resistance in crevice forming environment of seawater. In RO concentrate, alloys 2507 and 254 SMO showed lowest “maximum pit depth”. The results of potentiodynamic cyclic polarization (PCP) indicate that all the alloys have high pitting potential and small hysteresis loop. The results of critical crevice solution pH (CCSpH) indicated excellent resistance of alloys 254 SMO and DP3W against crevice corrosion attack and 2205 had least resistance in most aggressive sodium chloride solution.     

Effect of ionic content,solid content,degree of neutralization,and chain extension on aqueous polyurethane dispersions prepared by prepolymer method

There are many variables in the preparation of aqueous polyurethane (PU) dispersions. Carboxylic acid content, solid content, degree of pre/postneutralization of the carboxylic acids, and chain extension all impact dispersion particle size, viscosity, pH, molecular weights, and glass transition temperature. This study evaluated the impact of these variables on a given PU dispersion formulation prepared from isophorone diisocyanate, an aliphatic polyester polyol, dimethylol propionic acid, and hexamethylene diamine with triethyl amine as the neutralizing base and N‐methyl pyrrolidone as the cosolvent. Changes in carboxylic acid content, degree of preneutralization, and chain extension were found to have the expected impacts on dispersions properties. Increased ionic content in the dispersion step led to lower particle size and higher viscosity, increased chain extension with its concurrent increase in molecular improved subsequent film properties. Surprising results were obtained by varying the amount of postneutralization and from increased solids content at the time of dispersion. Unexpectedly, both of these variations led to much higher dispersion viscosities and particle size in solution. To have these changes take place, it is theorized that there is a major change in solution morphology caused by these modifications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2514–2520, 2005     

Processing of Composite Thin Film Solid Oxide Fuel Cell Structures

A solid oxide fuel cell (SOFC) structure is proposed in which a composite thin film cathode substrate supports a dense thin film electrolyte with a thickness of less than 1 μm. The cathode substrate has a graded porosity achieved through the partial sintering of a spin-coated CeO₂ colloidal suspension. The resulting surface has a pore size and surface roughness which allowed a fully dense ZrO₂:16%Y (YSZ) electrolyte to be spin-coated directly from a polymeric precursor without capillary forces removing the precursor from the surface of the porous substrate. Using this process, fuel cell structures were constructed with temperatures not exceeding 800°C. The porous CeO₂ interlayer should allow for decreased ohmic losses, as well as decreased reactions between the YSZ and the cathode substrate. In addition, the nanocrystalline grain sizes should allow for increased catalytic activity on the cathode. Calculated ohmic losses indicated the resistance of the CeO₂ interlayer limited the power of the structure, which was minimized by impregnating the porous layer with a mixed-conducting perovskite. The final structure shows significantly reduced ohmic losses as calculated at 400°C.     

Stepwise Change of Operating Pressure in Vacuum Fluidized Bed Drying: An Experimental Study

Vacuum‐fluidized bed drying experiments were carried out with porous as well as compact particles, employing distinct operating pressures in two periods of drying, such that the combination of the effects of decrease in the transport capacity of the exterior medium and the enhancement of the internal diffusivity results in favour of the drying process. In a variety of operating conditions, it was observed that in the case of porous particles, increasing the operating pressure during the decreasing drying rate period, after applying a vacuum pressure in the constant drying rate period results in a lower final particle humidity.     

The effect of heat sealing temperature on the properties of OPP/CPP heat seal. I. Mechanical properties

The effect of heat sealing temperature on the mechanical properties and morphology of OPP/CPP laminate films was investigated. The laminated films were placed in an impulse type heat sealing machine with both CPP sides facing each other. The temperatures investigated ranged from 100 to 250°C. T‐peel and tensile tests in combination with SEM were used to characterize the heat seals. A minimum seal initiation temperature of 120°C was identified for OPP/CPP laminate heat sealing. Peel strength increased sharply from zero at 110°C to maximum at 120°C, after which a gradual decrease was observed. Tensile strength initially increased until 120°C, after which it gradually decreased until 170°C and assumed a constant value beyond that. The initial rise has been associated to cold crystallization, while the reduction between 120°C and 170°C was due to relaxation in molecular orientation. Beyond 170°C, all the orientation in the laminate has been lost so orientation effects are nullified. Morphological studies with SEM revealed that seals were partially formed at lower temperatures, while the laminates were totally fused together at high temperatures, with intermediate temperatures showing properties that lie in between. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 753–760, 2005     

The effect of ambient moisture and temperature conditions on the mechanical properties of glass fiber/carbon fiber/nylon 6 sandwich hybrid composites consisting of skin‐core morphologies

The concept of skin‐core (SC) morphology was used to make sandwich hybrid composites in which the skin and core were composed of different fibers in the same matrix. The sandwich blends comprising glass skin with carbon core and vice versa were compared with those of the hybrid composite, while the respective carbon (CF) and glass fiber (GF) composites served as points of reference. The composites were compounded and fabricated into injection molded tensile specimens and 3‐mm thick plaques. The effect of ambient temperature and moisture was studied. The fracture mechanical characterization of the various materials was done by using notched compact tension (CT) specimens. Tensile properties were also used to characterize the composites. Morphogical studies based on scanning electron microscopy and light microscopy were used to elucidate fracture characteristics. Deterioration of properties was noticed under hot and humid conditions. Synergism in flexural properties was observed in the CF/GF/PA hybrid composite. The mechanical properties of the CF/GF/PA hybrid are closer to those of CF/PA, suggesting a cost advantage by substituting half of the carbon fibers with glass fibers. Dynamic mechanical analysis results revealed that synergism in T_g is attained by blending or sandwiching glass and carbon fibers. Morphological studies reaffirmed the skin‐core morphology of the composites. POLYM. COMPOS., 26:52–59, 2005. © 2004 Society of Plastics Engineers.     

Microstructure and Mechanical Property Correlation of Mg-Si Alloys

Silicon - The present work aims at understanding the microstructure and mechanical property correlation of hypo (Mg-0.5, 0.7, 1.15 wt% Si) and hyper (Mg-2, 4, 6, 8 and 10 wt% Si) eutectic binary...     

PVA/Gd2O3@Zno Nanocomposite Films as New Uv-Blockers: Structure and Optical Revelations

Journal of Inorganic and Organometallic Polymers and Materials - Herein we have synthesised Gadolinium oxide doped Zinc oxide (Gd2O3@ZnO) by solution combustion method and incorporated it as a...