Search Results for anode materials

Cathodic protection (CP) is an electrochemical means of corrosion control widely used in the marine environment. This article discusses two types of CP systems: impressed current systems and sacrificial anode (passive) systems. It describes the anode materials used in these systems and the CP criteria. The article examines the design considerations and procedures involved in the CP of marine pipelines, offshore structures, and ship hulls. An illustration of sacrificial anode calculation is also provided.

Most decorative chromium coatings have been applied using hexavalent and trivalent plating processes that are based on chromic anhydride. This article provides a discussion on chromium electrodeposits and their use as microdiscontinuous coating for corrosion protection. It focuses on the operating conditions of various chromium plating parameters: bath composition, temperature, voltage, anode materials, and current density. These parameters need to be considered for obtaining high quality decorative chromium coatings. An overview of plating problems encountered in chromium plating and their corrections is also provided.

This article discusses the process considerations and deposit properties of nickel plating. It describes the Watts solution and the anode materials used. The article focuses on the nickel plating processes used for decorative, engineering, and electroforming purposes. It provides information on the quality control of nickel plating. It concludes with a review of the environmental, health, and safety considerations associated with nickel plating.

Cathodic protection is an electrochemical means of corrosion control in which the oxidation reaction in a galvanic cell is concentrated at the anode, which suppresses corrosion of the cathode in the same cell. This article provides a detailed discussion on the fundamentals and types of cathodic protection as well as their power sources and design considerations. The criteria for the cathodic protection and types of materials used in sacrificial anodes and impressed-current anodes are also discussed. The article provides examples selected for familiarizing the design engineer with the steps for selecting a specific corrosion control method.

Galvanic corrosion, although listed as one of the forms of corrosion, is considered as a type of corrosion mechanism that is evaluated by modifying the tests used for conventional forms of corrosion. This article focuses on component testing, computer and physical scale modeling, and laboratory testing methods of evaluating galvanic corrosion. The laboratory tests fall into two categories, namely, electrochemical tests and specimen exposures.

This article examines constructive corrosion that occurs in power-generating devices, specifically batteries. It discusses the kinetic aspects of constructive corrosion in batteries and provides examples to illustrate how the kinetics of a corrosion process varies among different battery systems. The article illustrates the constructive roles played by corrosion at anodes in batteries through the use of a zinc anode in a mercury battery and a lithium metal anode in a rechargeable lithium battery. It also outlines the destructive role played by corrosion by illustrating shelf reactions in zinc-carbon batteries and lead grid corrosion in lead-acid batteries.

The gas-tungsten arc welding (GTAW) process is performed using a welding arc between a nonconsumable tungsten-base electrode and the workpieces to be joined. The arc discharge requires a flow of electrons from the cathode through the arc column to the anode. This article discusses two cases of electron discharge at the cathode: thermionic emission and nonthermionic emission, also called cold cathode, or field emission. It schematically illustrates relative heat transfer contributions to workpiece in the GTAW process. The article provides information on the effects of cathode tip shape and shielding gas composition in the GTAW process.

Selective plating, also known as brush plating, differs from traditional tank or bath plating in that the workpiece is not immersed in a plating solution (electrolyte). Instead, the electrolyte is brought to the part and applied by a handheld anode or stylus, which incorporates an absorbent wrapping for applying the solution to the workpiece (cathode). This article focuses on the selective plating systems that include a power pack, plating tools, anode covers, specially formulated plating solutions, and any auxiliary equipment required for the particular application. It provides a detailed account of the applications of selective plating, with examples. The article describes the advantages, limitations, key process elements, and health and safety considerations of selective plating. It also includes the most important industrial, government, and military specifications.

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.

This article describes the characteristics of continuous cathodic arc sources and filtering process for removing macroparticles from a cathodic arc. It provides information on the types of arc sources and the properties of deposited materials. The advantages, limitations, and applications of arc deposition are also discussed.

Steel storage tanks are the primary means for storing large volumes of liquids and gaseous products. The stored fluid could be water, but it could also be volatile, corrosive, and flammable fluid requiring special precautions for storage as well. Corrosion is generally worst where the tank is in contact with the soil. This article describes the soil characteristics and addresses cathodic protection (CP) criteria for submerged metallic piping systems. It provides information on the data required for designing a CP system, alone or in conjunction with a protective coating system. These data are collected from predesign site assessments, tank electrical characteristics, and soil-resistivity measurements. The article addresses NACE Standard RP0169, which gives requirements and desired characteristics for coating in conjunction with CP. It also explains the methods of protecting aboveground storage tanks and underground storage tanks.

This article provides the basic physics of the two most widely used arc welding processes: gas tungsten arc welding and gas metal arc welding. It describes the various control parameters of these processes such as arc length control, voltage control, heat input control, and metal-transfer control.

Electrochemical machining (ECM) is the controlled removal of metal by anodic dissolution in an electrolytic cell in which the workpiece is the anode and the tool is the cathode. This article begins with a description of the ECM system and then discusses the primary variables that affect current density and the material removal rate in the ECM process. It reviews the various characteristics of electrolytes and considers tool material and design. It also provides an overview of the properties of the workpiece and defines the surface finish and accuracy of an electrochemically machined sample. The variety of work done by electrochemical machining is also exemplified in the article.

Batteries and fuel cells are popular forms of portable electrical energy sources. This article discusses the operation and corrosion problems inherent in batteries and fuel cells. Batteries are classified into two groups: primary or nonrechargeable batteries and secondary or rechargeable batteries. Fuel cells are classified into five types: phosphoric acid fuel cell (PAFC), solid polymer electrolyte fuel cell, alkaline electrolyte fuel cell, molten carbonate fuel cell (MCFC), and solid oxide fuel cell. The article presents reactions that occur during charging and discharging of lead-acid batteries, PAFCs, and MCFCs.

This article describes the Bayer process for the purification of alumina. The process includes four major stages: digestion, clarification, precipitation, and calcination. The article discusses the aluminum electrolytic process in terms of aluminum electrolysis cell design, magnetohydrodynamic forces, and cathode lining. It reviews the electrochemical reactions and thermodynamics for aluminum electrolysis standard Gibbs. The article also describes the cell operations and cell stability, as well as the key indicators of cell performance. It schematically illustrates the typical costs producing aluminum in an aluminum smelter. The article also discusses various environmental issues, such as fluoride recovery; perfluorocarbons, polycyclic aromatic hydrocarbons, and sulfur emissions; spent pot lining; and development of inert anodes and CO2 emissions.

Corrosion of marine- and land-based infrastructure is of major concern and its control forms an important objective. Thermal spray coatings (TSCs) are widely used for corrosion protection. This article focuses on two types of TSCs: cathodic or noble coatings and anodic or sacrificial coatings. It describes the factors affecting the performance of sacrificial TSCs in atmospheric and immersion environments. The article provides information on the applications of sacrificial TSCs, non-sacrificial coatings, and sealants/top coats, and exemplifies the use of sacrificial TSCs on structures for corrosion protection.

Corrosion of metallic materials is governed by electrochemical kinetics, so that the general concepts developed for studying electrochemical reaction mechanisms may be applied to corrosion. This article presents the fundamental aspects of electrode kinetics. The processes of charge transfer taking place at the electrode interface within the double layer and of mass transport at the vicinity of the electrode surface are discussed. The article describes the corrosion processes, which involve anodic and cathodic reactions at specific electrode sites. Some experimental methods for devising a reliable reaction model are detailed. The article explains some reaction mechanisms for cathodic and anodic processes to illustrate the great variety of reaction mechanisms occurring at the electrode interface.