Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution.

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm2. After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm2 was the best, with corrosion current densities of 2 × 10-8 and 2 × 10-9 A/cm2. Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.

Effect of Cathodic Protection on Reinforced Concrete with Fly Ash Using Electrochemical Noise.

Corrosion of steel reinforcement is the major factor that limits the durability and serviceability performance of reinforced concrete structures. Impressed current cathodic protection (ICCP) is a widely used method to protect steel reinforcements against corrosion. This research aimed to study the effect of cathodic protection on reinforced concrete with fly ash using electrochemical noise (EN). Two types of reinforced concrete mixtures were manufactured; 100% Ordinary Portland Cement (OCP) and replacing 15% of cement using fly ash (OCPFA). The specimens were under-designed protected conditions (-1000 ≤ E ≤ -850 mV vs. Ag/AgCl) and cathodic overprotection (E < -1000 mV vs. Ag/AgCl) by impressed current, and specimens concrete were immersed in a 3.5 wt.% sodium chloride (NaCl) Solution. The analysis of electrochemical noise-time series showed that the mixtures microstructure influenced the corrosion process. Transients of uniform corrosion were observed in the specimens elaborated with (OPC), unlike those elaborated with (OPCFA). This phenomenon marked the difference in the concrete matrix's hydration products, preventing Cl- ions flow and showing passive current and potential transients in most specimens.

Corrosion Behavior of Steel-Reinforced Green Concrete Containing Recycled Coarse Aggregate Additions in Sulfate Media.

Novel green concrete (GC) admixtures containing 50% and 100% recycled coarse aggregate (RCA) were manufactured according to the ACI 211.1 standard. The GC samples were reinforced with AISI 1080 carbon steel and AISI 304 stainless steel. Concrete samples were exposed to 3.5 wt.% Na2SO4 and control (DI-water) solutions. Electrochemical testing was assessed by corrosion potential (Ecorr) according to the ASTM C-876-15 standard and a linear polarization resistance (LPR) technique following ASTM G59-14. The compressive strength of the fully substituted GC decreased 51.5% compared to the control sample. Improved corrosion behavior was found for the specimens reinforced with AISI 304 SS; the corrosion current density (icorr) values of the fully substituted GC were found to be 0.01894 µA/cm2 after Day 364, a value associated with negligible corrosion. The 50% RCA specimen shows good corrosion behavior as well as a reduction in environmental impact. Although having lower mechanical properties, a less dense concrete matrix and high permeability, RCA green concrete presents an improved corrosion behavior thus being a promising approach to the higher pollutant conventional aggregates.

Effect of photocatalytic Fe2O3 nanoparticles on urban runoff pollutant removal by permeable concrete.

Permeable pavements are an efficient urban runoff (UR) management solution that also improve water quality. In this work, a photocatalytic layer of Fe2O3 nanoparticles (NP) was incorporated into permeable concrete to evaluate its impact on the removal of several microbiological (Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, and Enterococcus faecalis) and physicochemical (N-NH4+, N-NO3-, phenol, PO43-, Fe, Mn, and Pb) pollutants. First, permeable concrete samples were created with sufficient compressive strength and hydraulic conductivity for light traffic. The test samples were then coated with a mixture containing either 3% or 5% Fe2O3 NP by cement weight. Control samples were prepared without NP. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy analyses showed that the nanoparticles remained unaltered on the concrete's surface. Synthetic URs simulating the microbiological or physicochemical composition of real UR were applied to the samples to evaluate their pollutant removal efficiencies. The depollution performances of the test (with 3% and 5% Fe2O3 NP) and control samples were statistically compared. The test samples (3% NP, 5% NP, and the controls) significantly modified (p < 0.05) most of the measured variables (i.e., the concentrations of E. coli, A. hydrophila, PO43-, Fe, Mn, and Pb) in the synthetic URs. Unexpectedly, the test samples (with 3% or 5% Fe2O3 NP) did not significantly remove (p > 0.05) some pollutants prone to oxidation, such as phenol or ammonium. However, the 5% NP sample significantly enhanced Mn removal. In general, the decontamination performances of the concrete samples with Fe2O3 NP were not influenced by the nanoparticles; thus, they did not appear to add value to the generated permeable concrete. Nevertheless, our results indicate the considerable benefits of implementing permeable concrete to improve the quality of UR.

Función el cuerpo lúteo formado a partir de la ovulación de un folículo dominante persistente, en vaquillas holstein tratadas con un dispositivo intravaginal de liberación de progesterona (CIDR-B), en ausencia de un cuerpo lúteo / Function of the corpus luteum developed from the ovulation of a persistent dominant follicle in Holstein heifers treated with a controlled internal drug release-bovine device (CIDR-B) in absence of a corpus luteum

Se evaluó la función del cuerpo lúteo (CL) formado a partir de la ovulación de un folículo dominante persistente, en vaquillas Holstein tratadas con un dispositivo intravaginal de liberación de progesterona (CIDR-B), en ausencia de un CL. Veinticuatro vaquillas recibieron 25 mg de prostaglandina F2Ó (PGF2Ó) im. Once días después a las vaquillas del grupo 1 (n=12) se les insertó un CIDR.B (CIDR-B con CL), a las vaquillas del grupo 2 (N=2) se les insertó sin estradiol y permaneció 12 días. Se evaluó el desarrollo folicular mediante ultrasonografía. En 2 vaquillas (16.6 por ciento) del grupo 1 y en 8 del grupo 2 (66.6 por ciento; P< 0.05) el folículo dominante observado el día de la inserción del CIDR-B persistió y ovuló después del tratamiento; en los animales restantes ovuló un folículo diferente. Se obtuvieron muestras sanguíneas para la determinación de progesterona diariamente, a partir del día del estro (día 1) hasta el día 16 del ciclo de 7 vaquillas del grupo 1, en las cuales ovuló el folículo diferente, y de 7 vaquillas del grupo 2, en las que ovuló un folículo dominante persistente. Las concentraciones de progesterona fueron similares en las vaquillas de ambos grupos (P > 0.05). En el presente trabajo no se encontró evidencia de que el cuerpo lúteo que se desarrolla a partir de la ovulación de un folículo dominante persistente en vaquillas tratadas con un CIDR-B en ausencia de un cuerpo lúteo, tenga afectada su función