Zirconium atomic properties

Finally, in Chap. F, a description of the most refined theoretical methods, as employed in actinides, is given, and its results for actinide solids are discussed. In the first part of the chapter, the author starts discussing actinides by presenting... the zirconium atom a striking beginning, purposely introduced in order to show the transition metal properties of 5 f wave functions. 

E. Zirccmium hydride. The moderating properties of zirconium hydride for slow neutrons are sufficiently unique to warrant a separate discussion. Unhke all the other moderators that we have discussed, the hydrogen atom motions in zirconium hydride have a high degree of symmetry. The crystal structure is such that each hydrogen atom sits at the center of a regular tetrahedron of zirconium atoms. The dominant atomic motion for the... 

The amount of water added can also affect the final properties of the zirconia aerogels [28]. In theory, four molecules of water should be required to completely hydrolyze each Zr(OR)4 molecule. However, complete hydrolysis is not necessary to form polymeric gels. In fact, 2-4 water molecules per zirconium atom are used to form hydrous oxides. For example, Ko et al. [27] reported that hydrolysis molar ratio (H2O/Z1 = 2) appears to yield the highest surface areas after low-temperature SCD followed by calcination at 500°C. However, with the higher water ratios, larger concentrations of acid were required to prevent precipitation. 

O. Kubaschewski, ed.. Zirconium Physico-Chemical Properties of its Compound and Alloys, International Atomic Energy Agency, Vieima, 1976, p. 8. 

The effect of the lanthanide contraction on the metal and ionic radii of hafnium has already been mentioned. That these radii are virtually identical for zirconium and hafnium has the result that the ratio of their densities, like that of their atomic weights, is very close to Zr Hf = 1 2.0. Indeed, the densities, the transition temperatures and the neutron-absorbing abilities are the only common properties of these two elements which differ... 

Generally, for the chemical engineer not particularly associated with atomic energy, unalloyed zirconium containing hafnium is an appropriate choice for those occasions which require the special corrosion resistant properties exhibited by the metal. 

Zirconium carbide is a highly refractory compound with excellent properties but, unlike titanium carbide, it has found only limited industrial importance except as coating for atomic-fuel particles (thoria and urania) for nuclear-fission power plants.l " ] This lack of applications may be due to its high price and difficulty in obtaining it free of impurities. 

On the basis of his quantum theory of atomic structure, Niels Bohr believed that, since Urbain s celtium had been obtained from the rare earths, it could not be element 72, for the latter must be quadrivalent rather than trivalent and must belong to the zirconium family. He showed that the chemical properties of an atom are determined by the number and arrangement of the electrons within it and especially by the number... 

Georg von Hevesy. Hungarian chemist who, with Dr. Dirk Coster of the University of Groningen, discovered the element hafnium in zirconium ores and made a thorough study of its properties. Author of many papers on chemical analysis by X-rays, radioactivity, the rare earths, and electrolytic conduction. In 1943 he was awarded the Nobel Prize in Chemistry and in 1959 he received the Atoms for Peace Award. 

Synthesis, reactions, and physical properties of stable mononuclear platinum and zirconium complexes of cyclohexyne reported prior to the late 1980s have been comprehensively covered in earlier reviews.2-8 More recently, reaction of the zirconocene complex of cyclohexyne with trimethyla-luminum and trimethylgallium has been reported to give 247 and 248, respectively [Eq. (36)].57-58 These products are novel because four atoms (carbons Cl and C3, the transition metal, and the main group metal) are covalently bonded to an sp2 hybridized carbon (C2) in a planar tetracoordi-nate fashion. Synthesis of this type of complex, which Erker describes as anti-van t Hoff/LeBel, does not require the strained cycloalkyne ring zirconocene complexes of acyclic alkynes react similarly.57-58... 

Zirconium and hafnium possess nearly identical chemistry. No other pair of congeners has chemical properties so similar to each other. This is mostly a result of the metals possessing nearly identical atomic and ionic radii (1.45 and 1.44 A for Zr and Hf, and 0.86 and 0.85 A for Zi + and Hf +) as a resnlt of the lanthanide contraction. They are relatively electropositive, but less so than the group 3 metals. The metals themselves... 

Zwitterionic structures with a borate anion covalently attached to a cyclopentadienyl donor can be obtained by a number of synthetic approaches. In the known compounds, the means by which the borate is tethered to the ring has a significant impact on the properties of the zwitterions. In particular, the length of the tether connecting the ring with the borate is crucial for the stability and intramolecular ion-ion contacts. For example tris cyclopentadienyl zirconium betaine complex in which boron atom is directly bonded to Cp can be generated from boron substituted cyclopentadienyl anion (equation 21). ... 

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