PHILIPPINE ENGINEERING JOURNAL PEJ 2005; Vol. 26 No. 2:41–56 The Relation Between Preparation, Microstructure and Mechanical Properties of Alumina Ceramics L. dela Cuesta 2∗ M. Mena 1 , G.N. Sison 1 , S. Bernardo 1 , S.J. Cho 3 , and K. Uematsu 4 1 University of the Philippines Diliman Quezon City 1101 PHILIPPINES 2 Industrial Technology Development Institute Bicutan, Taguig City PHILIPPINES 3 Korea Research Institute of Standards & Science Daejon SOUTH KOREA 4 Nagaoka University of Technology Nagaoka, Niigata JAPAN ABSTRACT The starting alumina powders were synthesized by chemical method under varied pH conditions - pH 6.5 and pH 8.5. The resulting powders were characterized by fine particle sizes, high surface area and crystalline structure. Powders at pH 8.5 were noted to have finer particle size than at pH 6.5. Due to their fine characteristic, the powders agglomerated during preparation of compacts. The alumina compacts were fabricated by (1) cold isostatic press (CIP) and sintered at 1550 ◦ C and 1650 ◦ C and (2) hot isostatic press (HIP) and also sintered at 1550 ◦ C and 1650 ◦ C. The CIP compacts showed large grains of alumina, whereas the HIP compacts were relatively fine-grained. The microstructure of both compacts exhibited abnormal grain growth more particularly in the CIP compacts. The synthesized powders were contaminated with Ca which accounted for the abnormal grain growth in both alumina compacts. The Ca present in HIP fabricated alumina compacts at pH 8.5 and sintered at 1650 ◦ C, gave high flexural strength. This was due to the formation of fine-elongated grains of regular pattern in between the fine-grains in the alumina matrix. The Ca present in the CIP fabricated alumina compacts at pH 8.5 and sintered at 1650 ◦ C gave relatively low values of flexural strength. Flexural strength of alumina compacts fabricated by HIP at pH 8.5 significantly increased with an increase in sintering temperature. For HIP alumina compacts at pH 8.5, fracture toughness increased with an increase in sintering temperature. Such increase in toughness was due to the growth of needle-like grains. 1. INTRODUCTION Nano-crystalline α-alumina powder has considerable potential for a wide range of application including high performance engineering materials, electronic ceramics, bio-materials and ∗ Correspondence to: Materials Science Division, ITDI-DOST Science Complex, Bicutan, Taguig City PHILIPPINES Received December 6, 2004 Copyright c  2005 Philippine Engineering Journal Revised January 23, 2006 Accepted February 8, 2006