Study Of Nano-alumina Composite Powder And Its Sintered Body Performance

Al₂O₃ ceramics is one of structure ceramics widely used. The primary disadvantages of brittleness and ceramics difficulty restrict its wider application. So it is a tide of ceramic development to prepare ceramic matrix composites. In this paper, TiO₂/MnO₂/Y₂O₃ composite additives are selected to decrease the sintering temperature. In the same time, a novel coating processing is employed to introduce the second phase into Al₂O₃ ceramic matrix. Then, hot-press processing is used to sinter the Al₂O₃/Fe composite ceramic.Two sizes Al₂O₃ composite powders coated additives were prepared by liquid-coating method. The influence of temperature and preparation methods on properties of material was studied. TiO₂/MnO₂/Y₂O₃ composite additives and Al₂O₃ powder can form a solid solution with relative density 99%, hardness about 14GPa and fracture toughness 4.79MPa after sintering at 1550℃for nano-Al₂O₃ composite powders. The sizes of powders have an affect on firing property of Al₂O₃ ceramics. Nanometer powders have high surface activity, and it is easy to sinter. Micrometer powders have low surface activity, it is difficult to sinter and the sample has bad mechanical properties. The sample added TiO₂/MnO₂/Y₂O₃ composite additives were sintered at 1600℃for 2h. Its relative density reached 93.8% and its hardness increased 32%. Composite powders of nanometer Al₂O₃ with additives washed by absolute ethyl alcohol can prevent conglobation perfectly and make additives have a good dispersity in powders. The sample washed by absolute ethyl alcohol was sintered at 1550℃. Its relative density and its hardness increased 6.2% and 12% respectively in comparison with those of the sample without being washed.Composite powders of Al₂O₃ coated by nano-Fe particles were prepared with nanometerα-Al₂O₃ and Fe(NO₃)₃·9H₂O by heterogeneous precipitation method. The composite powders were analyzed by DSC-TG,XRD,SEM. We found that in order to obtain Fe coating Al₂O₃ nano-composite powders the condition of the preparation is sintered at 500℃for 30min and reduced at 700℃for 1h in H₂. Fe particles coating Al₂O₃ are in the shape of sphericity with diameter about 30nm and the dispersion of the powders is uniform. Al₂O₃/Fe composite ceramics were obtained by hot-pressing(30MPa). With the increasing of Fe content in composite ceramics, the hardness of the material decreased. The ceramic material with 10mol% Fe content was sintered in 1400℃by hot-pressing. Its fracture toughness is 5.62MPa, which increases by 57% in comparison with that of single-phase Al₂O₃ ceramics(K_1c=3.57MPa).