Alkali-Resistant Materials

Alkali-Resistant Materials


materials capable of resisting the action of alkalies. The behavior of a material in alkalies depends on the material’s chemical composition, structure, and particle size, on the concentration and temperature of the alkali, and on the duration of the action of the alkali. Alkali-resistant materials are subdivided into metallic and nonmetallic (inorganic and organic) materials.

Metallic materials. Strong alkaline solutions do not affect metals of the copper subgroup (copper, silver, and gold) and the iron subgroup (iron, cobalt, and nickel) and cadmium, magnesium, the rare-earth metals, thallium, thorium, and the platinum metals. Molybdenum, tungsten, vanadium, and tantalum are stable in alkaline solutions at room temperature. Most metals react with molten alkalies. Zirconium and hafnium are quite resistant to alkaline solutions and melts. Copper-base, nickel-base, and zirconium-base alloys are also stable in aqueous alkaline solutions.

Nonmetallic inorganic materials. Many inorganic materials whose composition includes the basic oxides (portland cement, dolomite, and magnesite) are alkali resistant. Many oxides, including Cr2O3, ZrO2, HfO2, ThO2, CeO2, Al2O3, and CdO, are stable in aqueous alkaline media at room temperature and upon heating; they react with molten alkalies. Aluminum oxide and zirconium oxide are the most stable to the action of molten sodium hydroxide at 540°C.

Quartz glasses and multicomponent silicate glasses, which contain ZrO2, are the most resistant glasses to alkaline solutions. Many pigments, such as cadmium yellow, cinnabar, ocher, and iron minium (Berlin brown), are resistant to alkaline solutions.

Hot concentrated alkaline solutions do not affect graphite and crystalline boron. The carbides of boron, chromium, titanium, zirconium, and tungsten are highly resistant to dilute and concentrated alkaline solutions, as are metalloceramic alloys based on chromium carbide with nickel. Also resistant to alkaline solutions are the nitrides of chromium, niobium, zirconium, silicon, and boron, nickel boride, iron boride, the hexaborides of the rare-earth metals, and the suicides, sulfides, and fluorides of some elements.

Organic materials. Many polymer materials have high resistance to alkaline solutions and are used to produce anticorrosion coatings and dyes. Polyisobutylene, polypropylene, polyethylene, and fluoroplastics are stable in hot and cold alkaline solutions. Vinyl asbestos, Pentaplast, polyamides, polyvinyl chloride, and polystyrene exhibit satisfactory resistance in hot alkaline solutions and high resistance in cold solutions.


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