Zirconium oxide ceramics have a lot of pores on the surface, but some are very smooth with almost no pores. So what is the reason?
Zirconium oxide ceramics can be used not only as functional materials, but also as carriers, additives or active components of industrial catalysts. They play an important role in the reaction of CO2 adding H2 to synthesize methanol. There have been many reports on the influence of pore size distribution on sintering and microstructure development. Changes in pore size distribution of the same powder blank are often caused by the agglomeration of primary particles. Studies have shown that not only density but also densification rate is greatly affected by pore size distribution.
Research on microstructure found that the more large pores in the blank, the lower the sintering density. In the extreme case, when the pore size distribution is bimodal, large pores between agglomerates, or so-called secondary pores, can hardly be excluded. Experiments have found that although the grain growth is affected by the phase structure, the properties of the powder and green body (green body density, pore size distribution) do not affect the grain growth in the green body during heating and heat preservation.
The properties of Mingrui ceramic blanks such as density do not affect grain growth, but affect the size ratio of pores to particles. The properties of the blank do not affect the grain growth, but affect the pore growth, so they also affect the densification behavior. The relationship between grain size and density in the initial stage of densification is as mentioned above. 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 but no grain growth in the early 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.
From this we can draw the following conclusions:
①The grain growth in the blank 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 pores and grains to grow simultaneously, while the latter causes pores to shrink and the R value of pores to decrease. Stomatal growth is affected by Influence of the properties of the molded body;
③ The initial sintering stage of ultrafine powder is almost negligible. Grain growth and densification occur simultaneously. From the beginning to the end of sintering, the grain size and density are linearly related. , this linear relationship can be explained based on the fact that grain growth and densification occur in the same diffusion mass transfer mechanism, and the dependence of grain growth and density on time during the isothermal process;
④The linear relationship between grain size and density is affected by the properties of the molded body, because grain growth is driven by the chemical potential of the size difference between particles, while densification is driven by the chemical potential of the size difference between particles. The sintering compressive stress of pores drives;
⑤Higher dihedral angle, molding density, narrow particle and pore size distribution are conducive to moving the grain size-density relationship trajectory toward high density and small grain size. .
