Zirconium chemical properties

Hafnium [7440-58-6] Hf, is in Group 4 (IVB) of the Periodic Table as are the lighter elements zirconium and titanium. Hafnium is a heavy gray-white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior. This close similarity in chemical properties is related to the configuration of the valence electrons, and for zirconium and... 

Zirconium i dride. Zirconium hydride [7704-99-6] ZrH2, is a britde, metaUic-gray soHd that is stable in air and water, and has a density of 5.6 g/cm. The chemical properties of ZrH2 closely resemble those of titanium hydride. Thermal decomposition in vacuum (1 mPa (7.5 x 10 //mHg)) begins at 300°C and is nearly complete at 500—700°C. It is prepared in the same manner as T1H2. 

Zirconium and hafnium have very similar chemical properties, exhibit the same valences, and have similar ionic radii, ie, 0.074 mm for, 0.075 mm for (see Hafniumand hafnium compounds). Because of these similarities, their separation was difficult (37—40). Today, the separation of zirconium and hafnium by multistage counter-current Hquid—Hquid extraction is routine (41) (see Extraction, liquid—liquid). 

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

Chemical Designations - Synonyms Zirconium nitrate Chemical Formula Zr(N03) 5H20. Observable Cbaracteristics - Physical State (as normally shipped) Solid Color White Odor. Nine. Physical and Chemical Properties - Physical State at 15 XI and 1 atm. Solid Molecular Weight 429.3 Boiling Point at 1 atm. Not pertinent (decomposes) Freezing Point Not pertinent Critical Temperature Not pertinent Critical Pressure Not pertinent ecific Gravity > 1 at 20 °C (solid) Vapor (Gas) Density Not pertinent Ratio of Specific Heats cf Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat of Combustion Not pertinent Heat of Decomposition Not pertinent. 

The chemical properties of hafnium are very much similar to those of zirconium. In aqueous solutions, the metal exists in tetravalent state. The elec-... 

TABLE 1 Physico-Chemical Properties of Various Crystalline Zirconium Phosphonates... 

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... 

Due to its 5t/-6.v- electron configuration, hafnium forms tctravalent compounds readily, although the Ilf1 ion docs not exist as such In aqueous solution except at very low pH values, Ihe common cation being HfO lor Hf OH)i ) and many of the tctravalent compounds are partly covalent. There are also less stable Hf(lll) compounds, There is close similarity in chemical properties to those of zirconium due to the similar outer electron configuration (4identical ionic radii (ZrJ is 0.80 A) the relatively low value for Hf being due lo the Lanthanide contraction. 

The similarity in size causes a very close similarity in chemical properties hafnium and zirconium compounds occur together in nature and are very difficult to distinguish from each other, and other pairs of elements following zirconium and hafnium resemble each other more closely than is usual for two successive members of a family. 

Solvent extraction has proved to be the most effective method for the separation of zirconium and hafnium, which invariably occur in nature in close association, owing to their almost identical chemical properties. These metals have found considerable use in the nuclear-power industry on account of their unusually high (hafnium) and low (zirconium) neutron-capture cross-sections. It is evident that the mutual separation of the two metals must be of a high degree to make them suitable for such applications. Two different solvent-extraction processes are known to be used on a commercial scale in one process, zirconium is selectively extracted from nitrate media into TBP in the second process, hafnium is selectively extracted from thiocyanate solutions into methyl isobutyl ketone (MIBK). 

In this chapter we will review the synthesis, structural aspects, and basic chemical properties of formally divalent and trivalent titanium and zirconium metallocene complexes. We have restricted our coverage to the low-valent bis(rj-cyclopentadienyl) and related metallocenes metal halide complexes and organometallic mixed metal systems will not be discussed here. We have not attempted to present an exhaustive coverage of the field. Rather, our aim has been to describe critically and to evaluate the often confusing chemistry that has been reported for the reactive low-valent titanium and zirconium metallocenes. More general reviews (7) and a book (2) on the organometallic chemistry of titanium, zirconium, and hafnium have been published. 

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... 

Another effect of lanthanide contraction is that the third row of the d-block elements have only marginally larger atomic radii than the second transition series. For example, zirconium and hafnium, niobium and tantalum, or tungsten and molybdenum have similar ionic radii and chemical properties (Zr + 80 pm, Hf + 81 pm Nb + 70 pm, Ta + 73 pm Mo + 62 pm, W + 65 pm). These elements are also found in the same natural minerals and are difficult to separate. 

Hafnium (Hf, at. mass 178.49) is much the same as zirconium in chemical properties. It usually accompanies zirconium to the extent of 1.5-2%. The methods for separation and determination of zirconium outlined below, also apply for hafnium. 

Zirconium and hafnium have very similar chemical properties, invariably occur together in nature, and are difficult to separate. Yet their absorption cross sections for thermal neutrons are very different ... 

Source International Atomic Energy Agency, Zirconium Physico-Chemical Properties of Its Compounds and Alloys, Atomic Energy Rev., Special Issue No. 6, 1976. 

Chapters S, 6, and 7 take up uranium, thorium, and zirconium in that order. Each chapter discusses the physical and chemical properties of the element and its compounds, its natural occurrence, and the processes used to extract the element from its ores, purify it, and convert it to the forms most useful in nuclear technology. 

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