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Preparation of near net size porous alumina‐calcium aluminate ceramics by gelcasting‐pore‐forming agent processs
Author(s) -
Hao BianLei,
Lang Ying,
Bian DaQian,
Wang ChangAn
Publication year - 2020
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/jace.17075
Subject(s) - materials science , porosity , shrinkage , sintering , ceramic , composite material , green body , compressive strength , microstructure , aluminate , foaming agent , chemical engineering , cement , engineering
In the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina‐calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore‐forming agent process by adjusting the amount of CaCO 3 and polymethyl methacrylate (PMMA) microspheres added. Al 2 O 3 and CaCO 3 were used as raw materials, PMMA microspheres were used as pore‐forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO 3 and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina‐calcium aluminate ceramics were investigated. The results show that as the CaCO 3 addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina‐calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO 3 during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al 2 O 3 . The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.