Magnesium aluminum spinel(MgAl2O, MgO·Al2Oor MA)has superior high temperature mechanical properties, excellent peeling resistance and corrosion resistance. It is the most typical high temperature ceramic in the Al2O-MgO system. The preferential growth of calcium hexaaluminate (CaAl12O19, CaO·6AlO or CA6) crystal grains along the basal plane makes it grow into platelet or needle morphology, which can greatlly enhance the toughness of the material. Calcium dialuminate(CaAlO or CaO·2Al203, CA2)has a low coefficient of thermal expansion. When CAz is compounded with other materials with high melting point and high coefficient of expansion, it can well resist damage caused by thermal shock. Therefore, MA-CA composites have received extensive attention as a new type of high temperature ceramic material in the high- temperature industry because of its comprehensive properties of CA6 and MA.
In this paper, MA ceramic, MA-CA2-CA ceramic composites and MA-CA ceramic composites were prepared by high temperature solid-phase sintering, and the influence of mineralizers on the properties of these ceramic materials were studied. The strengthening mechanism of mineralizers on the performance of ceramics were discussed, and the following research results were obtained:
(1)The results showed that the bulk density and flexural strength of MA ceramic materials increased gradually with the increase of sintering temperature. After sintering at 1600 for 2hthe sintering performance of MA ceramic was poor, with a bulk density of 3. 17g/cm3 and a flexural strength value of133. 31MPa. With the increase of the mineralizer Fez03, the bulk density of MA ceramic materials increased gradually, and the flexural strength first increased and then decreased. When the addition amount was 3wt. %, the flexural strength reached the maximum 209. 3MPa.
(2)The performance and phase composition of MA-CA6 ceramic are related to the particle size of CaCO and a-AlO raw materials, the purity of a- Al2O3, the temperature of synthesis and the holding time. Using small particle size CaCO and high purity a-AlzO3 as raw materials, after sintering at 1600℃ and holding for 2h, the synthesized MA-CA6 ceramic has great flexural strength. The particle size of CaCO3 plays an important role in the formation of CA phase and the growth and development of crystal grains in MA-CA6 ceramic materials. At high temperature, the impurity Si in a-Alz0 will form a transient liquid phase, which makes the morphology of CA6 grains evolve from platelet to equiaxed.
(3)The effect of mineralizers ZnO and Mg(BO2)z on the properties of MA-CA composites and the strengthening mechanism were investigated. It is found that(Mg-Zn)AI2O4 solid solution and boron-containing liquid phase formed by the mineralizers ZnO and Mg(BO2)z make the grain size of MA smaller and the content of MA increased. These dense phases are coated with microcrystalline MA particles to form regional dispersed dense bodies, which leads to the transformation of CA6 grains into equiaxed grains, thus promoting the densification of MA-CA ceramic materials and improving its flexural strength.
(4)By using analytically pure Al2Oinstead of a-AlzO, MA-CA2-CA ceramic composites were synthesized from analytically pure raw materials. The effects of mineralizers SnO₂ and HBO on the physical and mechanical properties, microstructure and phase composition of the composites were studied.
The results show that solid solution and boron-containing transient liquid phase appear in the ceramic material after adding mineralizers SnO2 and H2BO ; respectively, it makes the CA2 phase change to CA phase and accelerates the formation of MA and CA6, thus improving the sintering activity of the ceramic material. The dense phase formed by the excess Ca makes the bond between MA and CA6 grains tight, which improves the mechanical properties of ceramic materials
Post time: Aug-29-2023