OVERVIEW

In the case of ductile-ductile systems ( e.g. Al-Mg), it is difficult to use the MA technique because of the excessive cold welding. In such cases, MA results in lumping of the alloyed material, which in turn suppresses the process of alloying. Organic surfactants called 'process control agents' (PCAs) are used to achieve the critical balance between cold welding and fracturing, and enhance the process efficiency [1]. The PCAs help in preventing fresh surface contact by giving a surface coating on powders. During the MA process, the PCA is embedded and finely distributed among the layers of flaky powder. The PCAs also help in alleviating the tendency of ductile powder particles towards powder-to-ball/vial welding. A common problem encountered with MA the contamination with elements contained in the mill vial and/or balls. The level of contamination depends on the type of ball mill used, the powder being milled and the milling conditions. The use of a surfactant can also reduce such contamination by at least a factor of 10 [2]. Thus, use of a PCA may be of great practical significance when contamination with surfactant itself does not pose a problem.

Benjamin & Bomford used a number of organic compounds including acids, alcohols and ketones [3], for this purpose. Table 4.1 lists the commonly used PCAs during MA.