Phosphoric acid is less corrosive than sulfuric and hydrochloric acids. This article discusses the corrosion rates of metal alloys in phosphoric acid, including aluminum, carbon steel and cast irons, stainless steels, nickel-rich G-type alloys, copper and copper alloys, nickel alloys, lead, titanium alloys, and zirconium alloys. Nonmetallic materials may be chemically attacked in some corrosive environments, which can result in swelling, hardening, or softening phenomena; extraction of ingredients; chemical conversion of the nonmetallic constituents; cross-linking oxidation; and/or substitution reactions. The article also describes the corrosion resistance of nonmetallic materials such as rubber and elastomeric materials, plastics, carbon and graphite, and ceramic materials.

This article reviews the corrosion behavior in various environments for seven important nickel alloy families: commercially pure nickel, Ni-Cu, Ni-Mo, Ni-Cr, Ni-Cr-Mo, Ni-Cr-Fe, and Ni-Fe-Cr. It examines the behavior of nickel alloys in corrosive media found in industrial settings. The corrosive media include: hydrochloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid, nitric acid, organic acids, salts, seawater, and alkalis. The modes of high-temperature corrosion include oxidation, carburization, metal dusting, sulfidation, nitridation, corrosion by halogens, and corrosion by molten salts. Applications where the corrosion properties of nickel alloys are important factors in materials selection include the petroleum, chemical, and electrical power industries. Most nickel alloys are much more resistant than the stainless steels to reducing acids, such as hydrochloric, and some are extremely resistant to the chloride-induced phenomena of pitting, crevice attack, and stress-corrosion cracking (to which the stainless steels are susceptible). Nickel alloys are also among the few metallic materials able to cope with hot hydrofluoric acid. The conditions where nickel alloys suffer environmentally assisted cracking are highly specific and therefore avoidable by proper design of the industrial components.

This article describes the eight chemical cleaning methods, namely, circulation, fill and soak, cascade, foam, vapor-phase organic, steam-injected, on-line chemical, and mechanical cleaning. It presents information on deposit types, solvents used to remove them, and construction material incompatibilities in a table. The article summarizes the uses of chemical cleaning solutions, including hydrochloric acid, phosphoric acid, and sulfamic acid, as well as the additives used to neutralize their impact on corrosion. It discusses the chemical cleaning procedures, including selection of cleaning method and solvent, documentation of cleaning, and corrosion monitoring in chemical cleaning.

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 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 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.

Mixtures of acids or acids and salts are of great importance to the chemical process industry (CPI) for use in digestion of solids, as a promoter in reactions, as a scale remover, and as a complexant. This article emphasizes the assessment of the performance of Ni-Fe-Cr-Mo alloys in mixed acids and salts in an objective manner. It tabulates the nominal compositions of pertinent Ni-Fe-Cr-Mo corrosion-resistant alloys. The article describes the acid and acid-plus-salt mixtures classified into the following general categories: nonoxidizing acid mixtures (H 2 SO 4 +H 3 PO 4 ), nonoxidizing acids with halides (H 2 SO 4 +HCl), oxidizing acid mixtures without halides (H 2 SO 4 +HNO 3 ), and oxidizing acid mixtures with halides (HNO 3 +HF). It also illustrates the effect of alloying elements on the corrosion rate in the nonoxidizing mixtures and oxidizing acid mixtures.

Chemical brightening (bright dipping) and electrolytic brightening (electropolishing) are essentially selective-dissolution processes, in which the high points of a rough surface of aluminum are attacked more rapidly than the depressions, and the peaks and valleys are smoothed to produce a bright and beautiful finish. This article discusses the metallurgical factors, optical factors, and applications of the chemical and electrolytic brightening. It compares the chemical brightening and electrolytic brightening, and presents the advantages of the chemical and electrolytic brightening processes in terms of performance and economy. The article describes the phosphoric-nitric acid baths and phosphoric-sulfuric acid baths used for chemical brightening. Solution compositions and operating conditions for three commercial electropolishing processes, as well as for suitable post-treatments, are presented in a table.