Benjamin Valdez

Atmospheric corrosion of electro-electronics metals in urban desert simulated indoor environment

Abstract The corrosion of pure Ag, Cu, Ni, and Sn specimens exposed for 1 to 24 months in a simulated indoor environment, consisting of a rain sheltered atmospheric corrosion test chamber placed in an urban desert environment (Baja California) has been measured. The corrosion rates of the metals were determined by mass loss measurement and the environment was thus classified in the low to medium indoor corrosivity category (IC2–IC3) according to ISO. Silver and copper weight losses were found to be very similar, while the nickel and tin weight losses were several times lower. The silver surface was tarnished in a non-uniform manner, presenting Ag2S and AgCl corrosion products, while the copper specimens corrode uniformly, being covered with Cu2O corrosion product. Owing to the presence of chloride contamination, the nickel and tin oxide corrosion films show fracture and pitting corrosion, developed over the first few months of exposure.

Corrosion and scaling at Cerro Prieto geothermal field

Purpose – The aim of this work is to study the corrosion and scaling factors, mechanisms and processes affecting the materials, equipment and installations of the Cerro Prieto geothermal field (GTF).Design/methodology/approach – The physicochemical characteristics of the geothermal well and fluids were analysed, recorded and related to the corrosion and scaling phenomena.Findings – The high temperature and salinity of the steam‐brine mixture and the presence of hydrogen sulphide and carbon dioxide impart a severe level of corrosivity.Originality/value – Corrosion and scaling control assure an efficient production regime, provide for the durability of the GTF engineering materials and equipment and contribute to environmental quality.

Anticorrosion behavior of conversion coatings obtained from unbuffered cerium salts solutions on AA6061-T6

Abstract The anticorrosive properties of cerium based conversion coatings deposited on AA6061-T6 alloy by immersion in unbuffered cerium chloride and cerium nitrate solutions in the presence of hydrogen peroxide were investigated and characterized by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 0.5 mol/L NaCl aqueous solution. The microstructure and chemical composition of the protective films were examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was found that the best corrosion protection was afforded by the samples treated during 600 s in cerium chloride solution at pH values ∼5.5-4, showing higher amounts of cerium and polarization resistance values greater than 10 Ω m2. Moreover, an ennoblement of the corrosion potential and decreasing of the cathodic and anodic currents were obtained compared with the cerium nitrate solutions application. This behavior was attributed to the influence of the deposition parameters such as type of the salt anion, i.e., chelating effect and chaotropic characteristics, pH fluctuations in the conversion solution and deposition time.

The Immobilized Lipases in Biodiesel Production

Recently, biodiesel production by lipase catalyzed transesterification has been suggested as a promising alternative to the conventional chemical catalysis, in spite of the high conversion and reaction rates of the latter (Akoh et al., 2007; Bajaj et al., 2010; Bisen et al., 2010; Demirbas, 2009; Fjerbaek et al., 2009; Fukuda et al., 2001, 2009; Ghaly et al., 2010; Helwani et al., 2009; Jegannathan & Abang, 2008; Man Xi Ao et al., 2009; Marchetti et al., 2007; Ranganathan et al., 2008; Robles-Medina et al., 2009; Semwal et al., 2011). The enzymatic process enables eliminating the drawbacks of the alkalior acid-catalyzed transesterification, namely: product contamination, wastewater release, free fatty acids and water interferences, and difficult glycerol recovery. Nevertheless, the commercialization of

Lipase Production Through Solid-State Fermentation using Agro-Industrial Residues as Substrates and Newly Isolated Fungal Strains

ABSTRACT Extracellular lipase production by Penicillium chrysogenum, Trichoderma harzianum and Aspergillus flavus was carried out through solid state fermentation using agro-industrial residues as substrates. For all three strains, the growth temperature was 29±1 °C, and 65% w (g/gds) moisture content. The effect of three factors on lipase production rate was investigated: initial pH (6.0 and 7.0), time of fermentation (72 h, 96 h and 120 h), and type of mixed substrate (wheat bran-olive oil, and wheat bran-castor oil cake). The process was optimized applying a mixed level factorial design. Fermentation time and pH were found to have positive effects on lipase production and secretion rates. However, the time effect was larger than initial pH. Type of substrate demonstrated minor effective importance than the other two factors, and Aspergillus flavus showed the larger lipase production among the three strains. Results indicated that the three fungal strains were able to grow and produce lipase in both culture mediums. The maximum lipase activity achieved was 121.35 U/gds by Aspergillus flavus, which was five and nine times the lipase produced by Trichoderma harzianum and P. chrysogenum respectively, at the same conditions. An initial neutral pH and 96 h of fermentation time were the optimum conditions for lipase production by Aspergillus flavus.

Effect of NO2 - in the Corrosion Behavior of Cerium Based Conversion Coatings on AA6061-T6

addition to the cerium chloride and hydrogen peroxide solution improved the corrosion resistance and coating morphology. Electrochemical measurements were performed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 0.01 M NaCl aqueous solution and the coating morphology was analyzed by Atomic Force Microscopy (AFM).

In vitro Actinomyces israelii biofilm development on IUD copper surfaces.

BACKGROUND Female pelvic actinomycosis may involve fallopian tubes, ovaries, uterus and bladder. This condition is often associated with the use of intrauterine contraceptive devices (IUDs), vaginal pessaries and/or tampons. The predominant causative agent of human actinomycosis is Actinomyces israelii, which has been found on copper IUDs retrieved from patients. STUDY DESIGN In this work, a biofilm of A. israelii was developed in vitro on copper surfaces immersed in a simulated uterine fluid under anaerobic conditions. The biofilm was characterized using scanning electron microscopy (SEM), energy dispersive X-ray and atomic force microscopy. RESULTS The capacity of A. israelii to develop a biofilm over copper surfaces in synthetic media was demonstrated. SEM micrographies illustrate the exopolysaccharides production and bacterial distribution. CONCLUSION A. israelii was able to attach and grow in synthetic intrauterine media and to present on the copper surface is likely due to the production of biofilm.

Leptospirillum ferrooxidans based Fe2+ sensor.

A novel electrochemical biosensor integrating the strictly autotrophic bacterial strain Leptospirillum ferrooxidans as a recognition element and a Clark type oxygen probe as a transducer was designed, metrologically and analytically characterized and applied for the specific Fe(2+) determination. The bacterial Fe(2+) oxidation involves O(2) consumption, thus the quantification was performed registering the decrease of the oxygen reduction current. The limit of detection was found to be 2.4 micromol L(-1) and the sensitivity of the determinations-3.94 nAL micromol(-1). The response time of the biosensor is 18s for Fe(2+) concentrations of 10(-5) to 10(-4) mol L(-1). The biosensor was applied as well for the indirect determination of Fe(2+) oxidizing species such as Cr(2)O(7)(2-), reaching a sensitivity of 2.47 nAL micromol(-1). The transducer characteristics were evaluated and optimized to obtain short response time and high sensitivity. The analytical performances of the biosensor subject of the present work were found to be similar to that of the At. ferrooxidans based one developed by the authors earlier, avoiding however the sulfur compounds interference, because of the substrate specificity of the applied bacterial strain.

Organophosphorus Pesticides Determination by Electrochemical Biosensors

According to the definition given by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA, 2008), a pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest (insects, mice and other animals, unwanted plants, fungi, microorganisms such as bacteria and viruses, and prions). Considering their chemical structure, the pesticides are organophosphorus, carbamates, organochlorines, and pyrethroid ones (U. S. EPA, 2009). Currently, more than 30 % of the registered pesticides in the world market (Hill, 2003) and about 45 % of those registered with U. S. Environmental Protection Agency (EPA) (Roger & Dagnac., 2006) are organophosphorus (OP). The organophosphorus pesticides, because of their high toxicity, fast biodegradation, low bioaccumulation, and broad target spectrum are extensively used in the agricultural and veterinary practices for protection of field and fruit crops, and for parasites control in domestic animals. However, their intensive and indiscriminate application, as well as their high acute toxicity generated risks to man and his environment. The resulting public concern created a demand for the development of reliable, sensitive, simple and low-costing methods for their fast “ in field” detection. In this work are reviewed the principles of the emerging electrochemical biosensors based methods for organophosphorus pesticides determination during the last decades, as methods of choice for “in situ” and “on line” application. Two main analytical techniques are considered, involving respectively the direct enzyme transformation of the pesticide and its enzyme activity inhibition effect, both followed by the conversion of the signal produced by the interaction between the bioreceptor and the analyte, into electrical one. The advantages and the drawbacks of each of them are discussed. The recent trends in the development of electrochemical biosensors for OP pesticides quantification, including nanomaterials transducer modification and genetic engineering of the biological recognition element are revised. Special attention is paid to the electrochemical biosensors based methods application for OP pesticides residues detection in food and in the environment.

Application of Vapour Phase Corrosion Inhibitors for Silver Corrosion Control in the Electronics Industry

The indoor corrosion of silver components used in the manufacture of electronic devices represents a hard challenge for the electronic industry in Mexico. In this work, a case of silver corrosion occurring in a TV manufacturing plant was documented, analysed and diagnosed. The main pollutant present in the indoor environment of the factory was hydrogen sulphide, which causes rapid silver tarnishing due to the formation of silver sulphide corrosion products. Silver corrosion rates were evaluated by gravimetric assays and surface SEM and EDX analyses were performed to characterize the corrosion film. In order to control the corrosion process VAPPRO vapour phase corrosion inhibitors were used.