THE EFFECT OF QUANTITATIVE PHASE COMPOSITION AND DIFFERENT TYPES OF COMPONENTS ON THE ELECTROCHEMICAL CHARACTERISTICS OF THE ZrNiMnCrV ALLOY

Abstract

X-ray diffraction revealed that the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy powder exposed to air demonstrated different stability of the quantitative phase composition of its surface depending on the sample weight. When a powder sample with a lower weight (5 g) was exposed to air for two days, its quantitative phase composition was quite stable and varied within 1%, while a powder sample with a greater weight (40 g) had polymorphic C15 and C14 phase (the amount of the C15 phase became 4% higher and the amount of the C14 phase became 4% lower). The sample that was more stable in exposure to air for 2 days demonstrated higher cyclic stability in the hydrogeneration–dehydrogenation process. The stability of the quantitative phase composition of the lighter sample exposed to air was assumed to be present in the hydrogenation–dehydrogenation process and to induce greater cyclic stability, while changes in the quantitative phase composition affected the cyclic stability. The activation of electrodes compacted from freshly made ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy powders depended on the type of nickel and manganese used for melting and occurred at different rates. In the case of electrolytic nickel and electrolytic manganese in alloy melting (40 g samples), the maximum discharge capacity was reached six cycles faster than in the case of cathodic nickel and ferromanganese. Contrastingly to the activation rate, the cyclic stability of electrodes made of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy powders using different types of nickel and manganese primarily depended on the weight of samples. The cyclic stability curves for the electrodes pressed from freshly ground powders from 5 g alloy samples (cathodic nickel and ferromanganese in one sample and cathodic nickel and electrolytic manganese in another sample) matched. The cyclic stability curves for the electrodes made of 40 g samples (cathodic nickel and ferromanganese in one sample and electrolytic nickel and electrolytic manganese in another sample) matched as well. The best cyclic stability was demonstrated by the electrodes made of the powder samples with a lower weight. This was possible due not only to the sample size but also to the use of cathodic nickel in alloy melting. The loss of discharge capacity for 80 cycles was 8%, while that for the electrodes made of the powders ground from the samples of greater weight reached 50%.