Microcone Anodic Oxide Films on Sintered Niobium Powders

Abstract

Information on the anodizing of sintered powders (SP) of niobium is limited by the study of the growth of barrier-type fi lms. The formation of a nanostructured anodic oxide fi lm (AOF) on the surface of powder particles should lead to a noticeable increase in the specifi c surface of the sample and an increase in the chemical activity of the m aterial. In view of the above, the study of the anodic nanostructuring of sintered niobium powders is of high importance and offers opportunities for creating new functional nanomaterials. This paper was aimed at the study of the anodizing process of sintered Nb powders in a fl uorine-containing aqueous electrolyte 1М Н2SO4 + 1% HF. The objects of the study were samples of sintered Nb powder with a specifi c area of Sspec = 800 cm2/g. Anodizing was conducted in a 1М Н2SO4 + 1% HF electrolyte with various values of current density ja. Surface morphology before and after anodising was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). X-ray diffractometry was used to study the phase composition. Kinetics of the growth of anodic oxide fi lms (АОF) on the surface of sintered Nb powders SP in galvanostatic mode was studied. The optimal conditions were defi ned for obtaining Ua(t) voltage-time transients, characteristic of the formation of self-organised porous anodic oxide fi lms (AOF). It was established that anodizing at current density values ja = 0.10–0.20 mA/cm2 leads to the formation of a Nb2O5 oxide fi lm on the surface of sintered powders SP with a regular-porous layer adjacent to metal and a crystalline microcone layer over it. The microcones (up to 0.6 μm high, up to 2 μm in effective base diameter) consist of branched fi brils with a diameter of ~18–30 nm, connected on top. It was established for the fi rst time that anodizing of sintered niobium powders in a fl uorine-containing aqueous electrolyte leads to the formation of an oxide fi lm with an upper crystalline microcone layer on the surface of powder microparticles. The suggested method for surface processing can be used for the development of biocompatible powder implants.

Keywords

• sintered niobium powders
• anodic oxide fi lms
• microcones
• crystalline
• nanostructured. funding: the study was supported by the flagship university development program of the fsfei he petrozavodsk state university for 2017–2021.