Previous reviews on the thermochemistry of zirconium

There have been a number of previous reviews of various aspects of the thermochemical properties of zirconium and its compounds. The chemical behaviour of zirconium was reviewed by Blumenthal [58BLU]. The review of [58BLU] contains an extensive history of the element and its compounds. It references much of the older literature, including those on the thermochemistry of zirconium and its compounds. The data given for thermochemical parameters in [58BLU], however, were not critically reviewed and therefore do not agree with the present review. Nevertheless, the review of [58BLU] is of particular value due to the detailed historical information it contains. 

Clearfield [64CLE] reviewed the structural aspects of zirconium chemistry. One of the important findings of this review was the substantial amount of evidence that was presented for the absence of the zirconyl (ZrO ) ionic structure in aqueous solution and in solids. Even in monoclinic zirconium oxide, Zr-O-Zr bonds are present rather than the Zr=0 double bond. Many compounds in both aqueous solution and the solid state contain hydroxo-zirconium bridges (see Section V.2.2). Clearfield presented evidence of the moiety [Zr4(0H)g(H20)i6] occurring in both aqueous solution and the solid state and argued that measurements by Zielen and Connick [56Z1E/CON] to determine the stability of polymeric zirconium hydrolysis species confirmed the existence of this species in aqueous solution. 

Alcock et al. [76ALC/JAC] reviewed the thermochemical properties of zirconium metal and a range of zirconium compounds and presented a considerable amount of data with assigned uncertainties. However, a number of important parameters were not determined and studies that post-date [76ALC/JAC] indicate that alternative interpretations of the data may be more realistic. 

Fernandez Guiliermet [87FER], [95FER] performed extensive reviews of the thermochemistry of the forms of zirconium metal and zirconium carbide, respectively. These studies critically evaluated the available data and then utilised all of the accepted data to determine values of each of the thermochemical parameters. Although both of these studies were extremely thorough, no uncertainties were presented for any of the thermochemical parameters determined. As such, these reviews can be used as a good guide to the relevant thermoehemical data but, such data is reevaluated in the present review such that uncertainty limits can be presented. 

A recent review on the aqueous complexes of zirconium has been published by Nagra/Paul Scherrer Institute (PSI) as part of an update to their thermochemical database [2002HUM/BER]. For the hydrolysis species, these authors included in the Nagra/PSI update the stability constants proposed by [76BAE/MES] for ZrOH, Zr(OH)4 and Zr(OH)j. As indicated above, the stability constant derived for Zr(OH)4 may be questionable due to the fact it was obtained from solutions that may contain a 

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