Research On Zircon Toughening 95-alumina Ceramics

During the manufacturing of 95 alumina ceramics, high damage is a significant problem, for its brittleness. ZrO₂ can tough alumina ceramics by the mechanism of stress induced phase transformation, but the cost was high. Our research project aimed to solve the problem by prepared ZrO₂ toughed ceramics using the raw material of zircon, which is cheaper than ZrO₂. Through this method, not only the problem can be well solved, but also cut down the cost. So this project is of unique importance as to practical production.In this experiment, 95 alumina ceramics was toughed by adding zircon as the source of ZrO₂. For contrast, another sample of 95 alumina ceramics was prepared by add ZrO₂ directly. The samples' sintering properties, bulk density and mechanical properties were tested. And their microstructure and phase constituent were investigated. Based on the data, the relation between structure and property were discussed. In the last, the sintering process and the reaction mechanism were discussed. We draw the conclusions as followed:1. Compared the improvement of properties of 95 alumina ceramics, which wereprepared by two different sources of ZrO₂, and arrived the conclusions as followed: a). Adding ZrO₂ directly to the 95 alumina ceramics will results in sintering temperature heading up. Therefore under the same process condition, the ceramics can not be well sintered. The high density ceramics can be attained only by elevating the sintering temperature. However, from the point of saving energy that was not what manufacture expected. Also, through this method only monocline ZrO₂ was founded in the matrix of 95 ceramics, which lacks the requirement of toughness of stress induced phase transformation. So ceramics with high performance can not be obtained in this way. b). For the sample with the zircon additive, which can be well sintered under the same condition. The result shows the effect of toughenness relates to the zircon content. At the first, the fracture toughness of ceramics increased with content of zircon, then decreased with the continuous increase of the zircon additive.c).Using zircon as additive to toughing 95 alumina ceramics was reasonable and feasible.2. The composition 95 alumina ceramics was designed and optimized in our experiment. Ceramics with high mechanical performance can be attained through controlling the particle size, the content of zircon, and sintering under proper temperature. According to the experiment and investigation, we arrived the conclusions as followed:a). 95 alumina ceramics with fine grain size can be obtained by adding small content of magnesia; Y2O3 pre-sintered with zircon, then used as an additive will help reserving the t-ZrO2 at room temperature, which contribute to prove the mechanical properties of 95 alumina ceramics. The optimal content of zircon in the matrix of 95 alumina ceramics was 4.5 wt%.b). The particle size of zircon also play a significant role on the properties of the 95-alumina ceramics. When the matrix grain size was close to that of zircon particle, can reached an ideal effect, the fracture toughness up to 6.04 MPa-m1/2, which was 1.5 times as high as common 95 alumina ceramics.3. The sintering process and the reaction mechanism of toughed 95 alumina ceramics which was prepared by adding zircon as the resource of ZrCh were discussed. From the discussion, we found that:a). The decomposition temperature of zircon decreased and zircon was almost completely decomposed since the sintering additive of 95 alumina ceramics. The whole process of reaction sintering should be sintering —> reacting —> sintering.b). There exists an competition for SiC>2 among zircon, mullite and the formation of low-melting liquid with CaO. The competition results in no mullite emerged during the process of reacting.