High-Energy Milling

Abstract

Nanoparticles can be produced by mechanical attrition. Such nanoparticles are formed in a mill in which energy is used to transform course-grained materials into nanostructured powders. The particles themselves can have a size distribution of less than 100 nm, called a nanoparticle, or, as is common in materials milled using mechanical attrition, the product is highly crystalline, and the crystallite size after milling is between 1 and 10 nm in diameter, called nanocrystalline materials [1].The milling of materials has been a component of ceramic processing and powder metallurgy industries for many years. The main objectives of milling include mixing material or phases; particle size reduction; shape changing; solidstate alloying and modifying such properties of materials as density, flowability, or work hardening. Mechanical attrition began to be used in the late-1960s as a way to mix and decrease the size of metal powders in a process called Mechanical Alloying (MA). In the mid-1990s, several researchers were researching mechanical milling to synthesize a variety of stable and meta-stable phases of all classes of materials, from metals to ceramics and polymers.Different terms are used in the literature to denote the processing of powder particles in high-energy ball mills. Mechanical Alloying describes the process where mixtures of powders, usually of different metals or alloys/compounds, are milled together. Milling of uniform composition powders, such as pure metals, is called Mechanical Milling (MM). Another variation of milling is Cryomilling, where the milling operation is carried out at cryogenic temperatures, usually with liquid nitrogen. Mechanically Activated Annealing (M2A) is a process that combines mechanical alloying with isothermal annealing. For example, MA of molybdenum and silicon powders for 1-2 h in a planetary ball mill followed by a 2-24 h annealing at 800 °C produced the MoSi 2 phase [2].