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Powder Processing for the Fabrication of Si 3 N 4 Ceramics: I, Influence of Spray‐Dried Granule Strength on Pore Size Distribution in Green Compacts
Author(s) -
Kamiya Hidehiro,
Isomura Kenji,
Jimbo Genji,
Junichiro Tsubaki
Publication year - 1995
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1995.tb08359.x
Subject(s) - agglomerate , granule (geology) , materials science , intergranular corrosion , composite material , ceramic , fabrication , hot isostatic pressing , flexural strength , pressing , relative density , green body , sintering , mineralogy , microstructure , chemistry , medicine , alternative medicine , pathology
The effect of spray‐dried granule strength on the micro‐structure of green compacts obtained by isostatic pressing was quantitatively analyzed. The fracture strength of single granules of Si 3 N 4 powder made with ultrafine A1 2 O 3 and Y 2 O 3 powders was measured directly by diametral compression. It was found that fracture strength increased notably with the increasing relative density of the granule and the decreasing size of agglomerates in suspension before spray‐drying. Even when green bodies were prepared at an isostatic pressure of 200 MPa, intergranular pores, which negatively affected densification of the sintered bodies, occurred between unfractured granules. The volume and size of these pores in the green compacts increased with the increasing fracture strength of the granules. In the case of closely packed granules, an isostatic pressure of 800 MPa was required to completely collapse the intergranular pores. A simple equation was derived to calculate the isostatic pressure necessary for complete collapse of intergranular pores in the green compacts, and it was determined that granule strength must be kept as low as possible to obtain uniform green compacts.