Actinide metals melting point

Table 5.18. Highest melting points (°C) in the alloys of rare earth metals and actinides with compound-forming elements of the 4th and 6th rows of the Periodic Table. See the introduction for the meaning of symbols. 

Thorium is a radioactive, silvery-white metal when freshly cut. It takes a month or more for it to tarnish in air, at which point it forms a coating of black oxide. Although it is heavy, it is also a soft and malleable actinide metal. The metal has a rather low melting point, but its oxide has a very high melting point of about 3,300°C. Thorium reacts slowly with water but reacts more vigorously with hydrochloric acid (HCl). 

AH the isotopes of americium belonging to the transuranic subseries of the actinide series are radioactive and are artificially produced. Americium has similar chemical and physical characteristics and is hofflologous to europium, located just above it in the rare-earth (lanthanide) series on the periodic table. It is a bright-white malleable heavy metal that is somewhat similar to lead. Americiums melting point is 1,176°C, its boiling point is 2,607°C, and its density is 13.68g/cm. ... 

Fig. 1. Vapor pressures and some melting points of actinide metals Pa- Es. O, melting point.

Proceeding from thorium to plutonium along the actinide series, the vapor pressure of the corresponding iodides decreases and the thermal stability of the iodides increases. The melting point of U metal is below 1475 K and for Np and Pu metals it is below 975 K. The thermal stabilities of the iodides of U, Np, and Pu below the melting points of the respective metals are too great to permit the preparation of these metals by the van Arkel-De Boer process. 

Efficient refining of the more volatile actinide metals (Pu, Am, Cm, Bk, and Cf) is achieved by selective vaporization for those (Pu, Am, Cm) available in macro quantities. The metal is sublimed at the lowest possible temperature to avoid co-evaporation of the less volatile impurities and then deposited at the highest possible temperature to allow vaporization of the more volatile impurities. Deposition occurs below the melting point of the metal to avoid potential corrosion of the condenser by the liquid metal. Very good decontamination factors can be obtained for most metallic impurities. However, Ag, Ca, Be, Sn, Dy, and Ho are not separated from Am metal nor are Co, Fe, Cr, Ni, Si, Ge, Gd, Pr, Nd, Sc, Tb, and Lu from Cm and Pu metals. 

Table XI gives the room-temperature, atmospheric pressure crystal structures, densities, and atomic volumes, along with the melting points and standard enthalpies of vaporization (cohesive energies), for the actinide metals. These particular physical properties have been chosen as those of concern to the preparative chemist who wishes to prepare an actinide metal and then characterize it via X-ray powder diffraction. The numerical values have been selected from the literature by the authors.

Actinide metal Crystal structure Density (g/cm ) Atomic volume (A ) Melting point (K) Enthalpy of vaporization AH, g (kJ/mol)... 

Some properties of berkelium metal have been reported. Thus, its melting point is 986 + 25 °C and its volatility, relative to its congeners, is in the order Cm < Bk < Am < Cf. Its chemical behaviour is described as somewhat similar to Sm, and it does not correspond, as a metal, to Tb or Lu. It reacts with hydrogen at 225 °C to give BkH2, which is isomorphous with other lanthanide and actinide hydrides of the type MH2+ (x < 1). BkO may be formed as an impurity in the production of metallic Bk. 

Lanthanides are silvery metals with high melting points that are found mixed in nature and are hard to separate. Actinides are radioactive elements. 

The influence of unoccupied 5/band states on the Fermi surface of thorium metal has been evaluated from precise calculations of the Fermi surface areas and effective masses.Comparison of the results with those obtained from experiments showed agreement when the 5/electrons were treated as itinerant. The nature of the bonding, electronic configurations and degree of localization of 5/ electrons in the actinide elements have been described in terms of a phenomenal model constructed from a knowledge of the crystal structure, the metallic radii, melting points and enthalpies of sublimation of the elements. The 5/electrons in the elements between protactinium... 

Physical and Chemical Properties Natural uranium, the fourth member of the actinide series, has the atomic number 92 and an atomic mass of 238.04. It is the heaviest naturally occurring element (specific gravity 18.95), and is a silvery-white metal with a melting point of 1132 °C and a boiling point of 3818 °C. Finely divided uranium... 

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