هولميوم (Ho)

الاكتشاف والتاريخ

تاريخ الاكتشاف: 1878 · Per Teodor Cleve

Holmium (Holmia, Latin name for Stockholm) was discovered by the Swiss chemists Jacques-Louis Soret and Marc Delafontaine in 1878 who noticed the aberrant spectrographic emission spectrum of the then-unknown element (they called it "Element X"). The Swedish chemist Per Teodor Cleve also independently discovered the element while he was working on erbia earth (erbium oxide). He was the first to isolate impure oxide of the new element. Using the method developed by the Swedish chemist Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance holmia (after the Latin name for Cleve's home town, Stockholm) and the green one thulia. Holmia was later found to be the holmium oxide, and thulia was thulium oxide. The pure oxide was only isolated in 1911 and the metal in

الاستخدامات والتطبيقات

Holmium(III) oxide is the only oxide of holmium. It changes its color depending on the lighting conditions. In daylight, it has a yellowish color. Under trichromatic light, it appears orange red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions. The color change is related to the sharp emission lines of trivalent holmium ions acting as red phosphors. Holmium(III) oxide appears pink under a cold-cathode fluorescent lamp. Other chalcogenides are known for holmium. Holmium(III) sulfide has orange-yellow crystals in the monoclinic crystal system, with the space group P21/m (No. 11). Under high pressure, holmium(III) sulfide can form in the cubic and orthorhombic crystal systems. It can be obtained by the reaction of holmium(III) oxide and hydrogen sulfide at 1,598 K (1,325 °C; 2,417 °F). Holmium(III) selenide is also known. It is antiferromagnet

النظائر

Natural holmium consists of one primordial isotope, holmium-165. It is observationally stable, though theoretically should undergo alpha decay to terbium-161 with a very long half-life. The known isotopes of holmium range from 140Ho to 175Ho. The primary decay mode before the stable 165Ho, is beta plus decay to dysprosium isotopes, and the primary mode after is beta minus decay to erbium isotopes. Of the 35 synthetic radioactive isotopes among these, the most stable one is holmium-163 (163Ho), with a half-life of 4570 years. The next most stable is holmium-166 (166Ho) having a half-life of 26.812 hours, and others have half-lives under 4 hours. The metastable isomer 166m1Ho has the unusually long half-life of 1133 years. With a very low excitation energy, it does not decay to the ground state but beta-decays directly, having a particularly rich spectrum of gamma rays, making this isotope