A method for gelcasting high-strength alumina ceramics with low shrinkage
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unzo Shimai Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China; and Tokyo University of Agriculture and Technology, Tokyo 183-8538, Japan
Xiang Peng Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China; and University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
Manjiang Dong Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China
Hidehiro Kamiya Tokyo University of Agriculture and Technology, Tokyo 183-8538, Japan
Shiwei Wanga) Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China (Received 27 September 2013; accepted 25 November 2013)
A new kind of nontoxic, water-soluble copolymer consisting of isobutylene and maleic anhydride was used to gelcast alumina ceramics at room temperature in air. The polymer acts as both a dispersant and a gelling agent. The influence of the polymer on zeta potential, rheological and gelling behavior of the alumina slurry was studied. Copolymers with a lower molecular weight had greater dispersing ability. Copolymers with a larger molecular weight had greater gelling ability. Alumina slurries with solids loading up to 58 vol% were prepared by adding copolymer (0.3 wt%, relative to the powder) with both short and long molecular chains. Increasing solids loading from 50 to 58 vol% decreased the linear shrinkage from 4.63% to 1.50% after drying, and from 14.51% to 13.18% after sintering, respectively. A solids loading of 56 vol% was associated with the highest flexural strength, as high as 534 MPa. I. INTRODUCTION
The preparation of large-sized and complicated structural ceramics is an important issue in the semiconductor industry. Large-sized alumina grinding disks, plates, and frames of stepper machines are necessary for this application. A conventional forming technique used to prepare large-sized ceramics is cold isostatic pressing, which is a rather mature and acceptable method in the actual industrial production.1,2 However, the required equipment and molds involved tend to be complex and costly.3 Slip casting is also used to make large-sized ceramic parts with complex shapes. Limitations of this process are the low strength of the green body and possible contamination from the mold.4–6 Gelcasting, a near-net shaping method, has exhibited advantages in low cost for the production of ceramics with large-sized or complicated shapes and in high strength of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.381 J. Mater. Res., Vol. 29, No. 2, Jan 28, 2014
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the green bodies over the other techniques.7–10 It is noted that the main problems of gelcasting are the timeconsuming drying process and the crack appearance during the drying and/or sintering process. Large-sized ceramic parts have greater internal stress caused by shrinkage that lead to cracki
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