Classes of metals Classes of metals Class A metals are metals that form hard acids. Hard acids are acids with relatively ionic bonds. These metals, such as iron, aluminium, titanium, sodium, calcium and the lanthanides, would rather bond with fluorine than iodine. They form stable products with hard bases, which are bases with ionic bonds. They target molecules such as phospholipids, nucleic acids and ATP. Class B metals are metals that form soft acids. Soft acids are acids with relatively covalent bonds. These metals, such as lead, gold, palladium, platinum, mercury and rhodium, would rather bond with iodine than fluorine. They form stable
Refractory metals 1900 K. An environment must not interact with the material in question. Liquid alkali metals as the heat transfer fluids are used as well as the ultra-high vacuum. The high-temperature creep strain of alloys must be limited for them to be used. The creep strain should not exceed 1–2%. An additional complication in studying creep behavior of the refractory metals is interactions with environment, which can significantly influence the creep behavior. Refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy