Time filter

Source Type

San Luis Potosí, Mexico

Miranda Vidales J.M.,Institute Metalurgia
Protection of Metals and Physical Chemistry of Surfaces | Year: 2014

One of main disadvantages of using environmentally friendly chemical mixtures for pickling, is stabilization of hydrogen peroxide (H 2O2), due to its decomposition is affected by the presence of metal ions. In previous studies, p-toluenesulfonic acid (C7H 10O4S) was used as a hydrogen peroxide stabilizer; however, benzene rings in its structure have a certain level of toxicity. In this work, ascorbic acid (C6H8O6) was tested as a stabilizer agent for H2O2 in a pickling mixture composed by sulfuric acid (H2SO4) and hydrofluoric acid (HF)-H2O2, this mixture was tested on 316L stainless steel (SS). Decomposition of H2O2 in pickling solution was evaluated for different ferric ions concentration between 0 to 40 g/L and at different temperatures from 25° to 60°C. Pickling rates at 25°C for 316L SS were 26873 mg/dm2 and 27799 mg/dm2 using ascorbic acid and p-toluenesulfonic acid, respectively. Ascorbic acid has a positive influence on stabilization processes of H2O2. © 2014 Pleiades Publishing, Ltd.

Alvarado L.,Lakehead University | Torres I.R.,Institute Metalurgia | Chen A.,Lakehead University
Separation and Purification Technology | Year: 2013

Mining and electroplating wastewaters contain many harmful ions, which are discharged into waterways and water bodies and cause significant environmental damage. Hexavalent chromium (Cr(VI)) is an ion that is commonly present in these effluents, which has been proven as toxic to humans. In the present work, continuous ion exchange and electrodeionization are proposed as a new hybrid technology for the effective treatment of Cr(VI) wastewater as well as the recovery of chromium ions. We have systemically studied a strong basic macroreticular anion exchange resin (Amberlite® IRA900) for the removal of Cr(VI). The ion exchange isotherm and kinetics of the resin were determined, showing that the IRA900 anionic ion exchange resin has a high capacity for ion exchange with hexavalent chromium (116 mg Cr(VI) per gram of resin). When the anionic resin was combined with a strong acidic macroreticular cation exchange resin (Amberlite® 200C) and employed in continuous electrodeionization, over 98.5% of Cr(VI) was continuously removed from the dilute compartment with an energy consumption of less than 0.07 kW h/m3, while Cr(VI) was recovered in the concentrate compartment. © 2012 Elsevier B.V. All rights reserved.

This study reports the pickling of 316L stainless steel using mixtures of hydrogen peroxide (H2O2), sulphuric acid (H 2SO4) and fluoride ions as hydrofluoric acid (HF), sodium fluoride (NaF) and potassium fluoride (KF). The decomposition of H 2O2 in the mixtures was assessed at different temperatures 25°C to 60°C, with ferric ion contents from 0 to 40 g/l. According to the results obtained, were established the optimal condition pickling at 20 g/l of ferric ions, 25°C and p-toluensulphonic acid as stabilizer of H 2O2. The HF pickling mixture was the only capable to remove totally the oxide layer from the 316L stainless steel after 300 s. The fluoride salts pickling mixtures only remove partially the oxide layer (20 to 40 % aprox.) after 300 s. When the pickling time was increased until 1200 s, the removal percentages were around to 80 %.

Villavelazquez-Mendoza C.I.,University of Colima | Rodriguez-Mendoza J.L.,University of Colima | Hodgkins R.P.,University of Colima | Ibarra-Galvan V.,University of Colima | And 3 more authors.
Materials Letters | Year: 2014

Sea-urchin-like rutile (su-TiO2) microstructures were successfully synthesized by thermal decomposition and oxidation of a solid precursor, K2TiF6. During the synthesis, precursor temperature (640 C), N2-flow (15 cm3/min) and inner pressure (90 mbar above the atmospheric pressure) remained constant. In order to evaluate the effect of time on the morphology of su-TiO2, five levels (0.5, 1, 1.5, 2, and 2.5 h) were considered. The thermal decomposition an oxidation of the K2TiF6 precursor was studied by thermal analyses. It was found that TiO2 was segregated from the matrix, leading to the formation of su-TiO2 during processing. At 640 C, the precursor underwent thermal decomposition and oxidation that produced three different products: K3TiOF5(s), TiO2(s), and F2(g). The su-TiO2 is synthesized only at t=2 h and t=2.5 h, presenting defined spikes at the former (100 μm×100 nm) and rougher structures at the latter (50 μm×10 μm). © 2014 Elsevier B.V.

Perez-Zarate P.,National Autonomous University of Mexico | Aragon-Pina A.,Institute Metalurgia | Soria-Guerra R.E.,National Autonomous University of Mexico | Gonzalez-Amaro A.M.,Autonomous University of San Luis Potosi | And 3 more authors.
Micron | Year: 2015

Aim: To determinate the significance of risk factors with the presence of biofilm on catheters of patients attended at tertiary hospital cares. Material and methods: A total of 126 patients were included, data collection by observing the handling of the CVC, clinical history and microbiological isolation methods of CVCs tips (Roll-plate, sonication and scanning electron microscopy) were evaluated. Results: Certain factors, such as the lack of proper hand washing, the use of primary barriers and preparing medications in the same hospital service, showed an important relationship between biofilm formation in CVCs. The sonication method presented that most of the samples had isolation of multispecies 29 samples (64%); in contrast with the roll-plate method, just one sample (3%) was isolated. Conclusions: The importance of the strict aseptic techniques of insertion and of the handlings of CVC was highlighted, the failure of both techniques was related to the biofilm formation and was evidenced using the scanning electron microscopy. Since this tool is not available in most hospitals, we present the correlation of those evidences with other standard microbiological methods and risk factors, which are necessary for the sensible detection of the different steps of the biofilm formation on CVC and their correct interpretation with clinical evidences. © 2015 Elsevier Ltd.

Discover hidden collaborations