Kinetics and Mechanisms of the Anodic Dissolution of Metallic Glasses

Abstract

The dissolution rates of active homogeneous metallic glasses are greater than those of homogeneous crystals of the same composition. If thermodynamically unstable homogeneous crystals are first formed, their later disintegration into a heterogeneous alloy usually results in an increase of the dissolution rate which may exceed the dissolution rate of the glass. Several examples of this behavior are discussed. A general theory for the dissolution rate of active alloys was developed and tested experimentally with metallic glasses offering the advantage that the composition can be changed in wide limits without changing the structure. In ideal cases th e rate constants for the dissolution of the components are independent of their concentration in the alloy. Usually the total dissolution rates were faster than in the ideal case. The behavior is explained in terms •fthe atomistic structure and of the composition of the alloy surface: Theeffect of some components on the passivity of metallic glasses is considered.Metallic glasses were used to establish the influences of structure and of composition on electrochemical reactivity (1-4). The influence of structure follows from a comparison of the active dissolution rates of the glasses to those of the crystals of the same homogeneous composition. The effect of substitution on the dissolution rates can be studied with glasses better than with crystalline alloys because changes of the composition at constant structure are possible in wider limits. Mechanisms of the dissolution of crystalline alloys were reviewed by Kaiser (5), and the electrochemical properties of metallic glasses by Archer et al. (6).Experiments were performed with binary and ternary boron glasses containing Fe, Co, Ni, V, Cr, Pt, or Pd, etc., and with zirconium or titanium glasses containing Fe, Co, Ni, or Cu. The electrolytes usually were deaerated acid sulfate or perchlorate solutions at 298 K. Other electrolytes were used to study the influence of the electrolyte composition on the dissolution rates. Details of the experimental procedure are described elsewhere (1, 2, 4, 7).

Pit growth in a Ni–Nb metallic glass compared with its crystalline counterpart

“…From the present analysis on pit growth, it indicates that amorphous structure can produce a higher active dissolution rate in pits. This agrees well with a previous work [21] on kinetics of the anodic dissolution of metallic glasses, from which the authors conclude that metallic glasses would undergo a faster active dissolution comparing with their crystallized states. In most of the metallic glasses with easilypassivating elements, spontaneous passivation obscures the structural effect on anodic dissolution [27], while such an effect can be revealed by a careful study on the growth of active pits.…”

“…It is found that the initiation of nanoscale pits on amorphous Ni 50 Nb 50 samples is significantly inhibited compared with the crystallized samples [12]. Considering that metastable alloys are susceptible to rapid dissolving and the active metastable pits would be dissolved faster in the amorphous alloys than the crystallized ones [21], it is highly needed to clarify the nanoscale pit growth behavior and its correlation to the corrosion properties. In this work, a detailed study on metastable pit growth behavior of the amorphous and crystallized Ni 50 Nb 50 alloys in 1 mol/L HCl solution is made and some notable effects of amorphous structure on the early growth of pits are characterized.…”

Corrosion Resistance and Electrocatalytic Properties of Metallic Glasses

“…Some Fe-based metallic glasses with high electrocatalytic efficiency are reported, such as a low overpotential η 300 = 318 mV for amorphous Fe 71 [133]. It is evident that the Tafel slope as well as overpotential decrease with increase of Mo content at the same conditions [132].…”

Characterisation of three-dimensional porosity in an Fe-based amorphous coating and its correlation with corrosion behaviour

“…First, for the present Fe-based amorphous alloy, the metastable nature of the amorphous structure may accelerate the passive dissolution rates and lead to passive current density rising with potential. Heusler and Huerta [54] have investigated the anodic dissolution of metallic glasses and demonstrated that homogeneous alloys dissolve faster in the amorphous state than in the crystalline state. Second, the high dose of molybdenum (7.4 at.%) could increase the passive current density.…”