Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Zirconium

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Zirconium, symbol Zr, metallic element with an atomic number of 40. Zirconium is one of the transition elements of the periodic table. The element was discovered in 1789 by the German chemist Martin Heinrich Klaproth and isolated 1824 by the Swedish chemist Baron Jöns Jacob Berzelius.

PROPERTIES AND OCCURRENCE

In its pure state zirconium exists in two forms: the crystalline form, a soft, white, ductile metal; and the amorphous form, a bluish-black powder. Both forms are insoluble in water, slightly soluble in alcohol, and completely soluble in hydrofluoric acid. The metal burns in air at 500° C (932° F).

Zirconium ranks 18th in abundance among the elements in the crust of the earth. Zirconium melts at about 1852° C (about 3362° F), boils at about 4377° C (about 7911° F), the atomic weight the element is 91.22.

Zirconium is never found free in nature; it occurs chiefly as a silicate in the mineral zircon and as an oxide in the mineral baddeleyite, which is found in commercial quantities in Brazil. Zirconium ores also contain the element hafnium, a metal with properties similar to those of zirconium.

USES

Zirconium is used in the manufacture of steel, porcelain, certain nonferrous alloys, and refractories. It is also used in vacuum tubes to remove traces of gases because it combines readily with oxygen, hydrogen, and nitrogen at high temperatures. Zirconium is used in heat exchangers, pump housings, valves, and other equipment subject to corrosion by acids. Special alloys of the metal called zircaloy-2 and zircaloy-4, which contain 1.5 percent tin, are used in nuclear reactors as a cladding material for uranium-fuel elements and as a structural material. Zirconium is especially suitable in water-moderated reactors because of its low neutron-absorption cross section, excellent corrosion resistance at moderately elevated temperatures, strength, ductility, and ease of fabrication.