Browsing by Author "Watari, K"

Now showing 1 - 2 of 2
  • Item
    Effect of surface roughness on grain growth and sintering of alumina
    (BULLETIN OF MATERIALS SCIENCE, 2011) Nampi, PP; Kume, S; Hotta, Y; Watari, K
    The production of ceramic bodies with less surface roughness is industrially important when one considers the aspect of final machining processes. Hence an attempt have been made to study the variation in surface roughness parameters (R(a), R(y), R(z)) of alumina having three different kinds of roughness features at different sintering temperatures. Variation in surface roughness properties are also correlated with grain size. R(z) shows significant difference between fine and intermediate surfaces, hence predicts small difference in their microstructural features. As a general trend, average grain size increases with increase in sintering temperature, but wide distribution of grains with enhanced non-uniform grain growth is observed when the surface is coarse. Hence, creation of fine surface in the green body is necessary for homogeneously distributed grains with controlled uniform grain growth. The final roughness and grain size of the sintered alumina depend on the initial surface roughness of the green body.
  • Item
    The effect of polyvinyl alcohol as a binder and stearic acid as an internal lubricant in the formation, and subsequent sintering of spray-dried alumina
    (CERAMICS INTERNATIONAL, 2011) Nampi, PP; Kume, S; Hotta, Y; Watari, K; Itoh, M; Toda, H; Matsutani, A
    The production of ceramic components using fewer processing steps on a shorter timescale is very important when considering the industrial and economic aspects of the manufacture of these materials in bulk. Spray-dried granules are expected to give compacts with fewer defects due to their low shear strength compared to conventional powders. Several extent studies show results for product of high relative densities (similar to 50% at 10 MPa), however, this study arrives at a process for making ceramic components with comparable density (48-49%) at 10 MPa), using less processing time and fewer processing steps which becomes extremely important when one considers the industrial aspects such as bulk production and manufacturing cost. In the present investigation, 35 vol% alumina slurries with 0.5% weight dispersant (ammonium polyacrylate) have been synthesized with different contents of binder (PVA) and lubricant (stearic acid). It is found that variations in the amounts of these additives plays a significant role in the formation of spray-dried granules, as well as the subsequent consolidation and densification of the compacts made using the granule particles. There is support for adopting the concept of a 'compact process'. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.