Closure to “Discussion of ‘The Nature of the Zinc-Containing Ion in Strongly Alkaline Solutions’ [Thedford P. Dirkse (pp. 328–331)]”

Abstract

The Knoop hardness determinations set forth above (excepting Be~C) were obtained from a paper by Thibault and Nyquist. 4~ Values for Be2C were more recently obtained.The paper under discussion also quotes Knoop hardness readings obtained at both 50-and 25-gram loads on the Tukon tester. In the paper by Thibault and Nyquist 4~ it is pointed out that the Knoop numbers obtained at different loadings are not directly comparable. In order to obtain comparable data, all tests must be conducted at a common load. The cause of the variation of the measured Knoop hardness with indenting load is discussed in a paper by Tarasov and Thibault. 41 ~V[ANLEY W. MALLETT: We wish to thank Mr. Upper for drawing our attention to the fact that Knoop hardness numbers based on indentations made by a 25-or 50-gram load are not directly comparable with numbers determined from indentations mad~ at higher loads. Accordingly, we should revise our statement on the hardness of Be2C to read that it lies between those of zirconium carbide and silicon carbide.

The Anodic Dissolution and Passivation of Zinc in Concentrated Potassium Hydroxide Solutions

“…By emf measurements, Dirkse has shown that this species is the complex tetrahydroxyl anion, Zn(OH)4--, an interpretation supported by recent Raman and infrared, as well as NMR, studies (2,4,5).…”

Evaluation of the diffusion coefficient of the zincate ion using a rotating disk electrode

“…The largest discrepancies in D values occur at alkali concentrations between 1 and 5 M. The polarographic values obtained by Dirkse (7) in KOH media are about five times larger than those of Meites (24) in NaOH media, a difference much too large to be ascribable to the change from potassium to sodium hydroxide. The value of 9 x cm2/s was used by Popova et al (12) without reference to its origin and is listed in the Bard Encyclopedia (25).…”

“…With regard to the latter, corrosion is one of the principal factors that restricts the application of the zinc-zincate system as an efficient energy source over very long periods of time. In the range of 1-10 M alkali, the predominant corrosion product is the complex ion tetrahydroxyzincate (7)(8)(9).…”

The Behavior of the Amalgamated Zinc Electrode in Supersaturated Alkaline Zincate Solutions

“…[1][2][3][4][5] Many authors studied the equilibrium potential of the zinc electrode in unsaturated and nearsaturated zincate solutions. Non-Nernstian behavior was observed at high zincate concentration.…”

“…It was thought that water was a reactant in the electrode reaction and the zincate ion was hydrated to some extent. 2 It was also explained as being due to the dependence of the hydroxyl and zincate ion activities on concentration in strong potassium hydroxide solutions. 3 The junction potential between the electrolyte in the reference electrode and the electrolyte under test was also a major contributor to this non-Nernstian behavior.…”