The surface topography of compacted agglomerates; a means to optimize compaction conditions

Abstract

The measurement and quantification of the surface topography of single-ended die-pressed cylindrical compacts, prepared using agglomerated alumina powders at various values of compaction pressure and cylinder aspect ratio, are described and a means to study the deformation and breakdown of the agglomerates at the die walls is evaluated. A specially constructed non-contacting laser scanning profilometer, with associated hardware and software, is described and has been used to obtain the surface topographical profiles of the green alumina compacts. Selected data are reported and interpreted using conventional roughness parameters, autocorrelation functions, and bearing area curves. These computed parameters are used to elucidate the deformation characteristics of the agglomerates within the compacts. The deformation of the alumina agglomerates, at the planar (upper and lower) surfaces of the compacts, commences at very low compaction pressures and the inter-agglomerates surface pores are eventually annihilated at relatively high compaction pressures. The optimum normal pressure for the elimination of these inter-agglomerate surface pores, in the present alumina system, was determined as 74 MPa. The results obtained from the curved surface profiles of the compacts, as a function of the distance from the compression sourc,, show that the wall normal pressure distribution, along the height of the compact, decreases exponentially as a function of the height of the compact (from top to bottom).