D.A. Rozhentsev, N.K. Tkachev.
ABSTRACT
Nano-porous metals obtained by dealloying in the percolation mode have the structure of a network of ligaments with pore sizes that can vary from several nanometers to several microns. Nano-porous iron and some ferroalloys containing manganese could be extremely promising materials as bio-degradable implants for regenerating bone tissue after fractures and other injuries. Molten salts, as electrolytes, are capable of accelerating percolation dealloying due to elevated temperatures, as well as higher current densities can be applicable in this case. Electrochemical dealloying of ferromanganese of various compositions (30, 50, 70 Mn at %) in molten mixtures of alkali metal chlorides has been carried out. A complex combination of temperature and electrochemical processes in the percolation mode, which leads not only to the formation of bi-continuous structures, but also to structures of the dendritic type. The evolution of the structure of the synthesized nano- and ultraporous iron depending on temperature from a dendrite-like and streamline-oriented morphology at 300℃ to a typical bi-continuous nanoporous structure with a pore size of about 100 nm at 400℃ was observed. Activation of the effects of coagulation and coarsening of ligaments and a loss of orientation along the field line were noted. However, under these conditions, a bi-continuous structure (100 nm) sufficiently uniform in size is formed. Further increasing the temperature results in another porous material with a 3D pore hierarchy at (500℃), which is distinguished by the distribution of pores of different sizes from 100 nm to 1 μm. An observation was made about the formation of a porous structure of an enlarged, micron scale at 600℃ with «ginger-root-like» ligaments. Dividing the process of dealloying at 500℃ and simple annealing at 600℃ into two independent steps leads to a similar result, but the structure has less coherence of the metal particles.
KEYWORDS: selective anodic dissolution, dealloying, ferroalloy, chloride melt, annealing, nanoporous iron
DOI: 10.31857/S0235010622050061