In the industry: somezirconia ceramics have porosity, see when you zoom in There will be many tiny pores on the surface, while otherszirconia ceramics are very smooth and have almost no pores. So what is the reason? In fact, this has a lot to do with the sintering of zirconia ceramics.
Zirconium oxide ceramic It can be used not only as functional materials, but also as carriers, additives or active components of industrial catalysts. Zirconia ceramics play an important role in the synthesis of methanol from carbon dioxide and H2. There have been many reports on the influence of pore size distribution on sintering and microstructure development. Changes in the pore size distribution of the same powder biscuits are often caused by the agglomeration of primary particles. Studies have shown that the pore size distribution has a great influence not only on the density of zirconia ceramics but also on the densification rate.
Research on microscopic nodules found that the larger the pores in zirconia ceramics, the lower the sintering density. In extreme cases, when there is a bimodal distribution of pore sizes, it is difficult to exclude macropores or so-called secondary pores between aggregates. The study found that although the grain growth is affected by the phase structure, the properties of the powder and biscuits (biscuit density, pore size distribution) do not affect the growth of grains in the biscuits during the heating and heat preservation processes.
Although the density and other properties of the ceramic body do not affect grain growth, they will affect the ratio of pore diameter to grain size. The properties of the biscuit do not affect the growth of grains, but they affect the growth of pores and therefore the densification behavior.The relationship between grain size and density in the initial stage of densification is as mentioned above, and there is a linear relationship between grain size and density in the middle stage of sintering. According to the definition of the sintering stage, there is only densification without grain growth in the initial stage of sintering.
This phenomenon may exist in green bodies with larger initial particle sizes, but for green bodies composed of ultrafine powders, such as the ultrafine zirconia used in this study, Even in the initial stages of sintering, grain growth and densification occur almost simultaneously. This result means that for solid-phase sintering of ultrafine powders, the initial stage of sintering can be approximately considered to be non-existent or at least negligible.
Zirconium oxide ceramicThe following conclusions can be drawn:
(1) The grain growth in zirconia ceramics is not affected by the properties of the molded body;
(2) The growth of pores is controlled by both grain growth and densification. The former causes stomatal growth to be synchronized with grain growth, while the latter causes stomatal shrinkage and a decrease in stomatal R value. The growth of pores is affected by the properties of the phantom.
(3) The initial stage of ultrafine powder sintering is almost negligible. Grain growth and densification occur simultaneously. There is a linear relationship between grain size and density from the beginning of sintering to the end of the intermediate stage. This linear relationship can be explained based on the fact that grain growth and densification occur on the same diffusion and mass transfer mechanisms and the time dependence of grain growth and density in an isothermal process.
(4) The linear relationship between grain size and density is affected by the properties of the molded body, since grain growth is driven by the chemical potential of size differences between grains, while densification is driven by the chemical potential acting on the pores. Sintering compressive stress drive;
(5) Higher dihedral angle, molding density, narrow particle and pore size distribution are conducive to the movement of the grain density relationship trajectory toward high density and small grains.
