ZrO2 (CAO) and ZrO2 (1 / 2O3) are the two most commonly used ceramic materials for zirconia based solid electrolyte. Because zirconia is difficult to sinter, an appropriate amount of stabilizer needs to be added. In the stabilized ZrO2, the metal ions of the stabilizer are not equivalently replaced with Zr4 +, resulting in oxygen vacancies. For example, taking Ca2 + as an example, when Ca2 + replaces Zr4 +, there are two less positive charges. Therefore, an O2 ion in the normal position must be lost around Ca2 + in order to maintain the electrical neutrality of the lattice, thus creating an oxygen vacancy. Similarly, if you replace Zr4 + with Y3 +, there is one less positive charge, and there is an oxygen vacancy around the two yttrium ions. Therefore, there are a large number of oxygen vacancies in the stabilized ZrO2 lattice, making ZrO2 Ceramics conductive ceramics.
The conductivity of ZrO2 Ceramics with different stabilizers is different.
2. Manufacturing process of zirconia conductive ceramics
The key to the manufacture of zirconia (ZrO2) conductive ceramics is the purity of raw materials and the preparation of powder. Generally, the purity of ZrO2 should reach 99.5% 5%, belonging to ultra-fine powder (< 0.05 μ m）; Y2O3 or Al2O3 shall be used as stabilizer, and its purity shall be reagent grade.
During powder preparation, due to the high hardness of stable ZrO2, steel ball mill is generally used for ball milling. After ball milling for about 80h, it is less than 1 seventy-six μ The fine powder of M is about 60%. If fineness < 1 μ m. The milling time shall be extended by 100 ~ 200H. After ball milling, the powder shall be treated with hydrochloric acid for 48h, washed with water to neutral after pickling, and dried for standby.
If it is formed by grouting, the grouting material can be prepared into neutral material in plastic or porcelain ball milling bottle (barrel). For example, the ratio of reclaiming: Ball: water: gum Arabic is 1:1.5:0.16:0.15, and the mixture is ground for 8 ~ 10h to make it have good suspension and fluidity.
Dry press molding shall be used. Appropriate binder (carboxymethyl cellulose, etc.) shall be added to the bad material, and isostatic pressing molding is the best.
The formed green body is fired at 1800 ~ 1840 ℃ in a kiln with neutral or oxidizing atmosphere.
3. Properties and applications of zirconia conductive ceramics
ZrO2 with stabilizer has conductivity at high temperature. Using the conductivity of ZrO2 at high temperature, zirconia conductive ceramics can be used as high temperature electrode and heating material.
ZrO2 has the characteristics of transmitting oxygen ions under certain conditions, so it can be made into solid oxygen concentration battery and oxygen sensor for the determination of oxygen concentration.
Oxygen concentration cell can detect oxygen concentration, manufacture fuel cell, produce oxygen, decompose water to produce hydrogen, etc.
The oxygen analyzer for steelmaking can accurately determine the oxygen content in molten steel. The main body of the oxygen meter is ZrO2 Solid electrolyte.
Zirconia oxygen sensor can be used to measure the oxygen content in automobile exhaust gas, so as to control the air-fuel ratio, save fuel and reduce the pollution of exhaust gas to the surrounding environment.
In addition, the thermal conductivity and conductivity of zirconia conductive ceramics can also be used as high-temperature heating materials (the maximum heating temperature in the air can reach 2100 ~ 2200 ℃) and high-temperature electrode materials (such as electrodes in MHD power generation devices). At the same time, the composite can be made by using the respective advantages of zirconia and lanthanum chromate.