Citric Acid as an Alternative to Sulfuric Acid for the Hard-Anodizing of AA6061

Hard-anodized is a widely used method in the aeronautical sector to improve aluminum alloys abrasion and corrosion resistance. Aim of this work was to characterize the mechanical properties and resistance hard-anodized aluminum 6061 in citric acid solution as a replacement sulfuric acid solution were investigated. Aluminum alloy 6061 was used as the base material to produce the hard anodizing; this process was carried out in a citric and sulfuric acid solution, applying current densities 3 and 4.5 A/cm2 and subsequently exposed to 3.5 wt. % NaCl solution. Microstructure and mechanical properties of the anodizing material were characterized by scanning electron microscopy (SEM) and Vickers microhardness (HV). Corrosion behavior of the hard-anodized material it was carried out with electrochemical techniques as cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) respectively. Results obtained indicated that all samples anodized in citric acid solution showed negative hysteresis and lower corrosion current density (1 × 10−10 A/cm2), indicating generalized corrosion on the material surface. EIS results show that anodizing in citric acid solution and a current density of 4.5 A/dm2 provides better corrosion protection than a sulfuric acid solution.

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Corrosion Behavior of AA 1100 Anodized in Gallic-Sulfuric Acid Solution

Coatings ◽

10.3390/coatings11040405 ◽

2021 ◽

Vol 11 (4) ◽

pp. 405

Author(s):

Marlon L. Mopon ◽

Jayson S. Garcia ◽

Dexter M. Manguerra ◽

Cyril John C. Narisma

Keyword(s):

Corrosion Resistance ◽

Sulfuric Acid ◽

Acid Solution ◽

Gallic Acid ◽

Acid Concentration ◽

Sulfuric Acid Solution ◽

Current Density ◽

Electrochemical Impedance ◽

Anodized Aluminum ◽

The Common

Sulfuric acid anodization is one of the common methods used to improve corrosion resistance of aluminum alloys. Organic acids can be added to the sulfuric acid electrolyte in order to improve the properties of the anodized aluminum produced. In this study, the use of gallic acid as an additive to the sulfuric acid anodization of AA1100 was explored. The effect of varying anodization current density and gallic acid concentration on the properties of anodized aluminum samples was observed using electrochemical impedance spectroscopy, linear polarization, and scanning electron microscopy. It was observed that the corrosion resistance of samples anodized in gallic-sulfuric acid solution at 10 mA·cm−2 is lower than samples anodized in sulfuric acid. It was also observed that higher anodization current density can lead to lower corrosion resistances for aluminum samples anodized in gallic-sulfuric acid solution. However, samples anodized at 5 mA·cm−2 and at a gallic acid concentration of 5 g·L−1 showed better corrosion performance than the samples anodized in sulfuric acid only. This suggests that the use of low amounts of gallic acid as an additive for sulfuric acid anodization can lead to better corrosion resistances for anodized aluminum.

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Highly gas permselective polyetherketone hollow fibre membranes using aqueous sulfuric acid solution as coagulant

e-Polymers ◽

10.1515/epoly.2007.7.1.884 ◽

2007 ◽

Vol 7 (1) ◽

Author(s):

Jiping Yang ◽

Philip J Brown

Keyword(s):

Mechanical Properties ◽

Sulfuric Acid ◽

Acid Solution ◽

Gas Separation ◽

Sulfuric Acid Solution ◽

Hollow Fibre ◽

Injection Rate ◽

Fluid Injection ◽

Aqueous Sulfuric Acid ◽

Membrane Morphology

AbstractHollow fibre membranes with more sponge-like morphology and improved gas permeation performance were spun from 20% polyetherketone (PEK) /sulfuric acid (H2SO4) dope solution with aqueous sulfuric acid solution as coagulant using dry-jet wet spinning process. The membrane morphology, mechanical properties and gas separation performance (hydrogen, methane and carbon dioxide) of as-spun PEK hollow fibres have been measured using SEM, Instron and gas test rig. Better cross section structures and mechanical properties in as-spun PEK hollow fibres were observed when aqueous sulfuric acid solution replaced water as coagulant (internal and external). The hydrogen/methane selectivity of up to 40 and hydrogen permeation rate of 3.65 GPU obtained in PEK hollow fibre membranes using 30% sulfuric acid solution as internal and external coagulant simultaneously at the bore fluid injection rate of 30 ml/h are higher than those reported in literatures. Furthermore the effects of bore fluid injection rate and various coagulants on the membrane morphology, mechanical properties and gas separation properties were investigated, as well.

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