Elimination of Composition Segregation in 33Al-45Cu-22Fe (at.%) Powder by Two-Stage High-Energy Mechanical Alloying.

Serguei Tikhov,Amol Gokhale,Oleg Lomovsky,Svetlana Cherepanova,Sergey Petrov,Aleksei Salanov,Dina Dudina,Vladislav Sadykov,Vladimir Zaikovskii,Oleg Smorygo,Konstantin Valeev

doi:10.3390/ma15062087

Abstract

In the present work, complex powder alloys containing spinel as a minor phase were produced by mechanical alloying in a high-energy planetary ball mill from a 33Al–45Cu–22Fe (at.%) powder blend. These alloys show characteristics suitable for the synthesis of promising catalysts. The alloying was conducted in two stages: at the first stage, a Cu+Fe powder mixture was ball-milled for 90 min; at the second stage, Al was added, and the milling process was continued for another 24 min. The main products of mechanical alloying formed at each stage were studied using X-ray diffraction phase analysis, Mössbauer spectroscopy, transmission electron microscopy, and energy-dispersive spectroscopy. At the end of the first stage, crystalline iron was not found. The main product of the first stage was a metastable Cu(Fe) solid solution with a face-centered cubic structure. At the second stage, the Cu(Fe) solid solution transformed to Cu(Al), several Fe-containing amorphous phases, and a spinel phase. The products of the two-stage process were different from those of the single-stage mechanical alloying of the ternary elemental powder mixture; the formation of undesirable intermediate phases was avoided, which ensured excellent composition uniformity. A sequence of solid-state reactions occurring during mechanical alloying was proposed. Mesopores and a spinel phase were the features of the two-stage milled material (both are desirable for the target catalyst).

Highlights

Ternary Al–alloys, such as Al–Cu–Fe mixed with spinel, are among the important materials to develop ceramometal (‘cermet’) catalysts
After 90 min of milling, the peaks corresponding to iron are not visible in the XRD patterns indicating the absence of free crystalline iron in the alloy
33Al–45Cu–22Fe powders were prepared by two-stage mechanical alloying using high-energy ball milling

Summary

Introduction

Ternary Al–alloys, such as Al–Cu–Fe mixed with spinel, are among the important materials to develop ceramometal (‘cermet’) catalysts. Ceramometals are attractive in heterogeneous catalysis since their surfaces possess a higher number of catalytically active centers than oxides, and their density is about twice the density of porous oxide systems [1]. Another desirable characteristic of catalysts is their stability in reaction media, often displayed by spinels, such as CuFe2 O4 [2]. Most studies on Al–Cu–Fe alloys were aimed at the synthesis of Al63-70 Cu20-25 Fe10-12 quasicrystals of icosahedral structure [3–7] for a variety of applications: antimicrobial agents [8], decomposition of hazardous materials [9], carbon nanotube growth catalysts [10], magnetic materials [4,11], anodes in lithium batteries [12], fillers with ultralow wear [13], and catalysts in steam reforming of methanol [14,15]. Nanostructured powder alloys are becoming popular in traditional heterogeneous catalysis [16,17], e.g., in hydrogenation reactions of CO (CO2 ) [18], synthesis of carbon fibers [19], decomposition of chlorine-containing hydrocarbons [20,21], decomposition of polymers [22], and in steam and dry reforming [23]

Methods

Results

Discussion

Conclusion