High-Energy Ball Milling

Mechanochemical Processing of Nanopowders

Ma?gorzata Sopicka-Lizer

• Publisher: Woodhead Publishing
• Year: 2010
• ISBN:
  9781845699444
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie minière

Mechanochemical processing is a novel and cost effective method of producing a wide range of nanopowders. It involves the use of a high energy ball mill to initiate chemical reactions and structural changes. High energy ball milling: Mechanochemical processing of nanopowders reviews the latest techniques in mechanochemistry and how they can be applied to the synthesis and processing of various high-tech materials.Part one discusses the basic science of mechanochemistry with chapters on such topics as the mechanism and kinetics of mechanochemical processes, kinetic behaviour in mechanochemically-induced structural and chemical transformations and materials design through mechanochemical processing. Part two reviews mechanochemical treatment of different materials including synthesis of complex ceramic oxides, production of intermetallic compound powders, synthesis of organic compounds, synthesis of metallic-ceramic composite powders and activation of covalent bond-based materials. Part three covers mechanochemical processes in metal powder systems and other applications with coverage of topics such as plating and surface modification using ultrasonic vibrations, activated powders as precursors for spark plasma sintering, titanium dioxide photocatalyst synthesis by mechanochemical doping and synthesis of materials for lithium-ion batteries.With its distinguished editor and international team of contributors, High energy ball milling: Mechanochemical processing of nanopowders is a standard reference for all those involved in the production of ceramic and metallic components using sintering and other powder metallurgy techniques to produce net shape components.

• Examines the latest techniques in mechanochemistry and how they can be applied to the synthesis and processing of various high-tech materials
• Discusses the basic science of mechanochemistry including kinetic behaviour, processes and mechanisms and materials design through mechanochemical processing
• Reviews mechanochemical treatment of different materials including synthesis of ceramic oxides, organic compounds and metallic-ceramic composite powders

1

Introduction to mechanochemical processing

Małgorzata Sopicka-lizer, Silesian University of Technology, Poland

Abstract:

This chapter discusses the development of mechanochemical processing in various systems throughout its short history and shows the most impressive industrial application of the technique. A brief description of the complex action that takes place during powder mechanochemical processing is also included.

Key words

crystal disordering

mechanochemical

metastable equilibrium

process feature

Mechanochemical processing (MCP) can be defined as ‘a powder processing technique involving deformation, fracturing and cold welding of the particles during repeated collisions with a ball during high-energy milling’. Using mechanical energy to grind down various materials dates back to the beginning of human history and the application of flints to make a fire can be seen as an example of a mechanochemical treatment of materials. However, throughout the centuries, mechanical milling only involved diminution of particles without changing their structure and/or properties.

The effect of chemical reactions initiated by mechanical action was found at the end of 19th century when Carey Lea first reported that the halides of gold, silver, platinum and mercury decomposed to halogen and metal during fine grinding in a mortar (Carrey Lea, 1893). His paper was published just after Ostwald introduced the term mechanochemistry in 1891. Heinicke’s much later definition (Heinicke, 1984) that ‘mechanochemistry is a branch of chemistry which is concerned with chemical and physicochemical transformation of substances in all states of aggregation produced by the effect of mechanical energy’ has been widely accepted.

Since then the main applications of mechanochemical treatment of materials were found initially within the field of extractive metallurgy, where the process was used as a pretreatment step prior to leaching and extraction in order to increase the solubility of the minerals in question. The application of this rather simple technique to manufacturing advanced materials was driven by the industrial necessity to develop an alloy combining oxide-dispersion strengthening (ODS) with γ′-precipitation hardening in a nickel-base superalloy intended for gas turbine applications. Benjamin’s work in the late 1960s showed that mechanochemical alloying (MA) must be used when ordinary dispersion of oxide particles in liquid metal is not possible (Benjamin, 1970).

The majority of the further work on development and production of ODS superalloys for application in the aerospace industry was done in the INCO laboratories in the USA (Ivanov and Suryanarayana, 2000). This is presently the major user of the MA process in the commercial production of nickel or iron-based high-temperature alloys which can be used at operating temperatures higher than 1300 °C in carburizing or sulphidizing environments (Benjamin, 1970). Another spectacular example of commercial application where mechanochemically alloyed powders of Mg and Fe were used as heaters of MRE (meal, ready-to-eat), comes from their intensive use during the Desert Storm Operation by the USA in 1996 (Ivanov and Suryanarayana, 2000).

On the other side of the world, in the former USSR, intensive studies on the application of mechanochemical processes in mineral and waste large-scale processing resulted in several practical applications including treatment of tungsten-containing ore which was introduced at the Chirchik Plant or production of amalgam for children’s dentistry which was introduced at the Nikolsky Plant (Boldyrev, 2002). Development of unique grinding equipment in a variety of scales broadened the range of practical applications and new types of materials are being researched all over the world. Since 2000, more than 1500 scientific papers in the field of mechanochem-istry have been published every year (Ivanov and Suryanarayana, 2000) and excellent reviews and monographs are available (Suryanarayana, 1999, 2004, 2008; Tkacova, 1989; Gutman, 1998; Arzt and Schultz, 1989; Barbadillo, 1993; Lai and Lu, 1998; Avvakumov, 1986). However, great developments in the technique itself and the accompanying milling devices have brought about new applications of MCP, broadening the range of the new materials and opening up new perspectives. There has been considerable interest in updating and summarizing existing knowledge of MCP.

Mechanochemical processes use mechanical energy to activate chemical reactions and structural changes as well as particle size reduction. Under the action of cyclic loading, after breaking crystal bonds, MCP engages powder particles into a non-equilibrium state with a relaxation time of 10^{− 7} − 10^{− 3} s (Meyer and Meier, 1968). Comparison with other far from equilibrium processes (Table 1.1; Froes et al., 1995) shows that departure from equilibrium in MCP is faster than in rapid solidification. In addition, some long-lived defects with a lifetime of 10^{− 3} − 10⁶ s can be generated because of the solid imperfections and even if relaxed, the residual disorder remains in the activated material (Meyer and Meier, 1968).

Table 1.1

Departure from equilibrium achieved in various processes (Froes et al., 1995)

Process	Maximum departure from equilibrium (kJ/Na)⁎
Solid-state quench	16
Quench from liquid (rapid solidification)	24
Condensation from vapour	160
Irradiation/ion implantation	30
Mechanical cold work	11
Mechanical alloying	30

N_a, Avogadro’s number.

^⁎Assuming relaxation owing to kinetic effects.

The mechanism of particle failure changes with the particle size and the structure of the particles undergoing grinding. A change in the accumulated energy relaxation from fracture to plastic deformation results in a dramatic increase in the strain followed by an extreme dislocation flow. Accordingly, the elastic strain energy transforms into elastic energy in the lattice defects and into structural disordering or it can be relaxed by the fracture of brittle material or crystallographic lattice rearrangement in polymorphic transformation. If more than one component is under the action of ball/powder particles collisions, then relaxation occurs by mechanical alloying, decomposition or synthesis of a new chemical compound. Thus stress, deformation and fracture initiate changes in the solids while the type and capacity of the changes involved remain a function of material’s properties (lattice bonds and crystal structure, elastic modulus, particle surface properties) and stress conditions in a milling device (the magnitude and direction of acting forces, stress rate and frequency of loading). It appears that the increase in energy of the milled powder caused by the increased volume fraction of grain boundaries and lattice disordering raises the free energy above the level of the amorphous state.

A unique feature of a mechanochemically activated mixture of powders is formation of numerous reaction couples which increase with decreasing particle size and regenerate through repeated particle fracture and welding events. What is even more important, the reaction product phase does not separate the reactants as happens in ordinary chemical reactors since continuous product phase removal takes place during ball/powder particles collisions. Lack of a diffusion barrier in the reacting couples as well as formation of various defects acting as the fast diffusion paths overcomes the problem of the diffusion as the rate-controlling process. Consequ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Chapter 1: Introduction to mechanochemical processing
• Part I: Basic science of mechanochemistry
• Part II: Mechanochemical treatment of different
• Part III: Mechanochemical processes in metal powder systems and other applications
• Index