New Discovery on How to Stabilize Zirconia Ceramic Materials

Zirconia ceramics have undergone tremendous development in recent years. It is a new type of industrial ceramic material, mainly divided into three types: magnesium stabilized zirconia ceramics, cerium stabilized zirconia, and yttrium stabilized zirconia; These three materials have various excellent properties such as high temperature resistance and wear resistance. So how to make zirconia materials more stable? Let's take a look together next!

1、 What is the instability of zirconia?

Zirconia also has the characteristics of martensite transformation, which is an important basis for zirconia to be used to improve the toughness of ceramic materials and thermal shock stability of refractories. Monoclinal zirconia cannot be directly used for manufacturing products, as it will undergo phase structure transformation when temperature changes:

This is a reversible phase transition process. At room temperature, ZrO2 can only be a monoclinic phase. When calcined with zirconium salts to 650 ℃, a stable tetragonal phase appears. As the temperature continues to rise, the tetragonal phase gradually transforms into a monoclinic phase. When the temperature continues to rise to 830 ℃, ZrO2 begins to transform into a tetragonal phase again. At 1200 ℃, it completely transforms into a tetragonal phase, and when the temperature rises to 2300 ℃, it transforms into a cubic phase; As the temperature decreases, it gradually transforms into a tetragonal phase, and at room temperature, it becomes a stable monoclinic phase. The transformation of monoclinic zirconia at 830~1200 ℃ is relatively complex, resulting in hysteresis phenomenon. It is precisely this hysteresis phenomenon that provides an important performance for the application of zirconia in ceramics and refractory materials. During the transformation process, corresponding volume changes will occur. When the temperature increases, the transformation from monoclinic phase to tetragonal phase will cause a volume contraction of 5%, while when the temperature decreases, the transformation from tetragonal phase to monoclinic phase will cause a volume expansion of 8%. The three phase structures present have different thermal expansion.

Some oxides are added to ZrO2 as stabilizers to form solid solution and complex with ZrO2, change the internal structure of the crystal, form metastable tetragonal phase and cubic phase, and transform it from single monoclinic phase to bicrystal tetragonal phase and cubic phase. This solid solution can maintain the original tetragonal phase and cubic phase at room temperature, and even at high temperature, phase transformation will not occur. When stabilizing the crystal form of zirconia, commonly used stabilizing additives include CaO, MgO, Y2O3, CeO2, and other rare earth oxides. By controlling the amount of stabilizer added, fully or partially stable zirconia can be obtained. The following processes are often adopted to improve the impact of unstable zirconia ceramic tubes.

2、 The stabilization treatment process of zirconia?

Electrofusion method

There are two methods for producing stable zirconia by electrofusion: primary electrofusion and secondary electrofusion. The one-time electric melting method is to mix zircon, carbon powder, and stabilizer in a certain ratio in a mixing machine, and the mixture is subjected to electric arc furnace melting and desilication treatment, quenching, and then crushing and heat treatment to produce stable zirconia. Stable zirconia impurities prepared by this method

High content, low density. The process route is shown in the figure.

The secondary electric melting method is to mix zircon and carbon powder in proportion, then undergo electric arc furnace melting and desilication treatment, quenching, and then crushing to produce monoclinic zirconia. Add a certain stabilizer to the monoclinic zirconia in proportion according to the needs, mix it evenly, and perform a second electric melting. After the electric melting is completed, it is quenched, and then crushed and heat treated to produce stable zirconia. The stable zirconia prepared by this method has low impurity content and high density. The process route is shown in the figure.

Solid-phase method, also known as sintering method, usually involves wet crushing zirconia raw materials and stabilizers in a certain ratio in a rubber lined and zirconium ball ball mill until the particle size is less than 2 μ m. Then, it is separated, dried, and powdered to form agglomerates, and subjected to high-temperature solid-state reaction at 1700 ℃. The high-temperature sintered agglomerates are crushed to the required particle size to obtain stable zirconia. The stable ZrO2 prepared by this method has a wide particle size distribution and is easy to mix with impure impurities. The process route is shown in the figure.

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