Search Results for anodic oxide film

Anodizing is one of the most common surface treatments of aluminum and is performed for corrosion protection. This article describes the structure and growth characteristics of the types of anodic oxide films such as a barrier-type oxide film and a porous-type anodic oxide film. It discusses each step involved in the anodizing process of an aluminum or aluminum alloy specimen. The anodizing process includes pretreatments (degreasing, etching, and polishing), anodizing, coloring, and sealing. The article provides an observation of the morphology of the anodic oxide films by transmission electron microscopy and the scanning electron microscopy for testing properties of anodic oxide films.

This article provides a background of the complex relationship between titanium and its alloys with aqueous environments, which is dictated by the presence of a passivating oxide film. It describes the corrosion vulnerability of titanium and titanium oxides by the classification of oxide failure mechanisms. The mechanisms are spatially localized oxide film breakdown by the ingress of aggressive anions; spatially local or homogenous chemical dissolution of the oxide in a strong reducing-acid environment; and mechanical disruptions or depassivation such as scratching, abrading, or fretting. Titanium alloys can be classified into three primary groups such as titanium alloys with hexagonal close-packed crystallographic structure; beta titanium alloys with body-centered cubic crystallographic structures; and alpha + beta titanium alloys including near-alpha and near-beta titanium alloys. The article also illustrates the effects of alloying on active anodic corrosion of titanium and repassivation behavior of titanium and titanium-base alloys.

This article reviews the types of passivity and presents tactics that employ passivity to control corrosion. Thermodynamics provides a guide to the conditions under which passivation becomes possible. A valuable guide to thermodynamics is the potential-pH diagram and the Pourbaix diagram. The article presents a potential-pH diagram for the iron-water system and an illustration of an idealized anodic polarization curve for a metal surface, which serves as a basis for describing the kinetics of passivation. It discusses five properties of passive films: thickness, composition, structure, electronic properties, and mechanical properties. The article outlines three possible processes that can form passive films: direct film formation, dissolution precipitation, and anodic oxidation of metal ions in solution. It describes the breakdown of the passive film using various models and highlighting the effect of alloy composition and structure.

Zirconium and hafnium surfaces require cleaning and finishing for reasons such as preparation for joining, heat treatment, plating, forming, and producing final surface finishes. This article provides information on various surface treatment processes, surface soil removal, blast cleaning, chemical descaling, pickling or etching, anodizing, autoclaving, polishing, buffing, vapor phase nitriding, and electroplating. Applications of these surface treatment processes are also reviewed.

This article discusses the properties of aluminum surface and the applications of aluminum alloys. It explains the effects of trace elements on aluminum alloys. The article considers microstructural development of aluminum in terms of the surface and explains how it will impact corrosion resistance and surface treatment. It describes the thermodynamics of equilibrium oxidation processes and non-equilibrium corrosion processes. The article provides a discussion on aluminum oxidation under atmospheric and dynamic conditions. It presents the potential/pH (Pourbaix) diagram for aluminum under atmospheric and dynamic conditions. The article also explains the polarization effects during the formation of stable aluminum oxide under dynamic conditions. It concludes with information on the designation system for aluminum finishes.

Anodizing produces a uniform, continuous, highly ordered network of individual cells comprising a layer whose thickness and cell dimensions, and ultimately engineering properties, depend on the electrochemical parameters of the anodizing process. This article discusses the nucleation and growth of anodic aluminum oxide and the important characteristics of the finished porous anodic aluminum oxide. In industry, anodic oxides and the anodizing processes have been categorized into types that exhibit specific properties to suit specific applications. The article reviews the two most basic types of oxides, namely, barrier-layer anodic oxides and porous anodic oxides. It concludes with a description of postanodizing processes, such as dyeing and sealing.

This article provides a general introduction to the kinetics of aqueous corrosion with an emphasis on electrochemical principles. It describes the thermodynamic basis for corrosion by determining the equilibrium potentials of electrochemical reactions from the Nernst equation. A corrosion process can be controlled by the electronic conductivity of passive films when the cathodic reaction occurs on the surface of the film and by activation control of corrosion. Passivation becomes thermodynamically possible when the corrosion potential exceeds the potential corresponding to the equilibrium between a metal and one of its oxides/hydroxides. The article schematically illustrates a current-potential or polarization curve for an anodic process.

This article addresses the general effects of the composition, mechanical treatment, surface treatment, and processing on the corrosion resistance of aluminum and aluminum alloys. There are five major alloying elements: copper, manganese, silicon, magnesium, and zinc, which significantly influence the properties of aluminum alloys. There are organic coatings or paints that provide a barrier between a corrosive environment and aluminum surface. Inorganic coatings, including claddings, and enhanced oxides, such as anodized films, Boehmite films, and conversion coatings also help in corrosion prevention. The article assists in the information on selection of fabrication operations, as they play an important role in corrosion resistance.

Tantalum is one of the most versatile corrosion-resistant metals known. The outstanding corrosion resistance and inertness of tantalum are attributed to a very thin, impervious, protective oxide film that forms on exposure of the metal to slightly anodic or oxidizing conditions. This article provides a discussion on the mechanism of corrosion resistance and on the behavior of tantalum in different corrosive environments, namely, acids; salts; organic compounds; reagents, foods, and pharmaceuticals; body fluids and tissues; and gases. It contains several tables that summarize the effects of acids, salts, and miscellaneous corrosive reagents on tantalum and applications for tantalum equipment in chemical, pharmaceutical, and other industries. Finally, the article presents a discussion on hydrogen embrittlement, the galvanic effects, and cathodic protection of tantalum and describes the corrosion resistance of different types of tantalum-base alloys.

This article reviews cleaning and finishing operations that have proven to be effective on titanium, its alloys, and semi-fabricated titanium products. It explains how to remove scale, tarnish films, grease, and other soils and how to achieve required finishes and/or improve wear and oxidation resistance through the use of polishing, buffing, and wire brushing operations. The article also covers a wide range of surface modification and coating processes, including ion implantation, diffusion, chemical and physical vapor deposition, plating, anodizing, and chemical conversion coatings as well as sprayed and sol-gel coatings and laser and electron-beam treatments.

Titanium alloys are often used in highly corrosive environments because they are better suited than most other materials. The excellent corrosion resistance is the result of naturally occurring surface oxide films that are stable, uniform, and adherent. This article offers explanations and insights on the most common forms of corrosion observed with titanium alloys, including general corrosion, crevice corrosion, anodic pitting, hydrogen damage, stress-corrosion cracking, galvanic corrosion, corrosion fatigue, and erosion-corrosion. It also provides practical strategies for expanding the useful application range for titanium and includes a comprehensive overview of available corrosion data.

Aluminum components are often plated with other metals to mitigate the effects of corrosion and wear, improve application performance, and extend service life. This article discusses some of the more common aluminum plating processes, including electroplating, immersion plating, and electroless plating, and describes various plating materials and the types of applications in which they are used. It provides critical processing details such as temperatures, ratios, ranges, times, and rates. The article explains how to prepare aluminum components for electroplating, discussing surface roughening, anodizing, and immersion procedures along with expected results.

This article discusses the factors affecting corrosion behavior. It describes galvanic corrosion and its protection methods. The article also provides information on coatings and inhibitors, which are used in corrosion protection.

Electropolishing is an electrochemical process that involves anodic dissolution of a metal specimen (anode electrode) in an electrolytic cell. This article reviews the two-electrode and three-electrode systems for electropolishing. It presents the equations of anodic reactions and the selection criteria of electrolyte for electropolishing. The article also describes the mechanism of electropolishing and the effect of electropolishing on properties of metals.

The sealing of the anodized aluminum is a critical process in achieving the durability and extended functionality of anodizing. This article discusses the different methods for sealing the anodic coatings produced by using sulfuric acid, namely, hot deionized water, hot nickel acetate, midtemperature, cold, and dichromate sealing. It reviews the factors that affect seal quality: immersion time, chemistry concentration, temperature, pH, water quality, coating thickness, and contaminants/dye bleeding. The article describes the various tests that are used for determining the quality of the seal, namely, salt spray, modified dye stain, acid dissolution, impedance, copper accelerated acetic acid salt spray, high-alkaline resistance, SO 2 fog, and clorox tests.

Adhesive bonding is a proven technology in the manufacture of automotive assemblies, helping carmakers achieve weight reduction goals without compromising body stiffness, crash performance, and noise-vibration-handling characteristics. This article discusses the advantages and limitations of adhesive-bonded aluminum joints and the procedures used to produce them. It addresses surface preparation, the addition of interfacial coatings and primers, and the application of thermoplastic and thermosetting resins. The article examines the nature and role of the various layers that constitute the joint and explains how each contributes to performance. It also discusses adhesive selection factors, joint design, and testing procedures.