When metal is exposed to an oxidizing gas at elevated temperature, corrosion can occur by direct reaction with the gas, without the need for the presence of a liquid electrolyte. This type of corrosion is referred to as high-temperature gaseous corrosion. This article describes the various forms of high-temperature gaseous corrosion, namely, high-temperature oxidation, sulfidation, carburization, corrosion by hydrogen, and hot corrosion.

This article describes the classification of fuel cells depending on the operating temperature and type of electrolytes used. This classification includes alkaline fuel cells, phosphoric acid fuel cells, polymer electrolyte membrane fuel cells (PEMFCs), molten carbonate fuel cells (MCFCs), and solid oxide fuel cells (SOFCs). The article explains the corrosion processes in fuel cells due to solid-gas interactions, solid-liquid interactions, and solid-solid interactions. It discusses the long-term performance stability and long-term degradation processes of PEMFCs, MCFCs, and SOFCs. The article reviews the development of chemically and structurally compatible component materials in PEMFCs, MCFCs, and SOFCs.

This article provides a summary of the concepts discussed in the articles under the Section “Fundamentals of Corrosion” in ASM Handbook, Volume 13A: Corrosion: Fundamentals, Testing, and Protection. In this section, the thermodynamic aspects of corrosion are descried first followed by a group of articles discussing the fundamentals of aqueous corrosion kinetics. The fundamentals of gaseous corrosion are addressed next. The fundamental electrochemical reactions of corrosion and their uses are finally described.

Iron powders are the most widely used powder metallurgy (P/M) material for structural parts. This article reviews low to medium density iron and low-alloy steel parts produced by the pressing and sintering technology. It explains different powder production methods, including Hoeganaes process, Pyron process, atomization of liquid metal, thermal decomposition and the electrodeposition process for carbonyl and electrolytic iron powders. It describes the types of compaction and sintering, explaining their effects of processing with designations. Further, the article deals with the mechanical and physical properties of ferrous P/M materials, which may depend on certain factors, namely microstructure, porosity, density, infiltration, re-pressing, chemical composition, and heat treatment.

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.

Electrode potential is a key parameter in the thermodynamic and kinetic processes that drive aqueous corrosion. This article discusses the complexities associated with measuring electrode potential and explains where and how to use reference electrodes to improve measurement accuracy. It describes a three-electrode approach that compensates for measurement error stemming from nonequilibrium conditions. It also examines electrode materials and behaviors and offers insights on selection and operating conditions.

This article describes the ideal performance of various low-temperature and high-temperature fuel cells that depends on the electrochemical reactions that occur between different fuels and oxygen. Low-temperature fuel cells, such as polymer electrolyte, alkaline, and phosphoric acid, and high-temperature fuel cells, such as molten carbonate and solid oxide, are discussed. The article contains tables that provide information on the evolution of cell-component technology for these fuel cells. It concludes with information on the advantages and limitations of the fuel cells.

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.

This article provides a discussion on the fundamentals of corrosion thermodynamics. The discussion focuses on electrochemical reactions, molten salt corrosion thermodynamics, and geochemical modeling.

This article introduces various analytical techniques commonly used in the characterization of organic solids and liquids and discusses the challenges in performing the analysis, with examples. Some general advice in approaching a material analysis is also provided.

This article describes the fundamentals of various techniques used for the production of copper and copper alloy powders. These include atomization (water, air, and gas), oxide reduction, and electrolysis. The article discusses the effects of electrolyte composition and operating conditions on the characteristics of copper and copper alloy powders.

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.

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 is a comprehensive collection of terms related to corrosion fundamentals, testing, and protection.

Electrochemical discharge grinding (ECDG) is a combination of electrochemical grinding (ECG) and electrical discharge grinding (EDG), with some modification of each. This article commences with a schematic illustration of a setup for ECDG using a solid bonded graphite wheel. It describes the process characteristics of ECDG in terms of current density, wheel speed, wear ratio, accuracy and finish, wheel maintenance, and profile grinding. The article concludes with a comparison of ECDG with EDG and ECG.

A tin deposit provides sacrificial protection to copper, nickel, and many other nonferrous metals and alloys. Tin also provides good protection to steel. Tin can be deposited from either alkaline or acid electrolytes. This article explains the compositions and operating conditions of these electrolytes.

This article provides a discussion on the process descriptions, processing conditions, and processing variables of the most common chemical methods for metal powder production. These methods include oxide reduction, precipitation from solution, and thermal decomposition. Methods such as precipitation from salt solution and gas, chemical embrittlement, hydride decomposition, and thermite reactions are also discussed. The article also discusses the methods used to produce powders electrolytically and the types of metal powders produced. The physical and chemical characteristics of these powders are also reviewed.