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The four most common methods of producing zirconia (ZrO2) micro powder

wallpapers Tech 2020-07-14
ZrO2 micro-powder is an essential raw material in the field of high-tech ceramics and refractory materials. There are four more sophisticated methods for industrial production of powders: plasma method, neutralization precipitation, hydrolysis precipitation and alkoxide hydrolysis.
 
1. Plasma method

In 1969, the Z-TECH company in the United States first developed a method for extracting and purifying zirconia from zircon using ultra-high temperature generated by plasma arc (Plasmaarcs) to produce high-purity monoclinic ZrO2 and obtained a patent.

When any gas is heated to 3000°C, significant ionization will occur, and by 5500°C, it has been substantially completely ionized. After ionization, due to the electron flow, it can reach a very high temperature through the resistance heat under the action of the electric field. This highly dissociated high thermal conductivity gas is called plasma. Plasma cannot be obtained by heating the gas, but generally by arc discharge. The most straightforward plasma generating device is an arc plasma torch, the principle of which is to apply a direct voltage between two specially-made electrodes, while passing a generally inert gas (nitrogen, argon, helium or their mixture) between the electrodes. Then a high-frequency current or short circuit is used to ignite a stable DC arc between the two electrodes, so that the gas that continuously passes through the arc area absorbs energy to form a high-temperature plasma flame, generating a high temperature of 80001500 ℃, and the airflow rate is very high. The fine zircon powder sent into the fire is immediately decomposed into ZrO2 and SiO2, and SiO2 is evaporated and separated from ZrO2, to achieve the purpose of preparing ZrO2 and purifying it.

The high-purity ZrO2 produced by the plasma method has unique properties. Plasma method ZrO2 is spherical particles, m-ZrO2 crystal is excellent. The practise has proved that the ZrO2 crystals formed under ultra-high temperature have high activity, and this activity is significant for manufacturing high-performance ceramic materials. The plasma process has also been continuously improved. The high-purity ZrO2 produced has a ZrO2 content of up to 99.6%, a particle size of above, and can be trimmed as needed.

2. Neutralization precipitation method

The neutralization precipitation method is a method for preparing ZrO2 by using an alkaline solution to precipitate out aqueous zirconia (also called zirconium hydroxide gel) from zirconia (ZrOCl2) salt solution. The chemical reaction formula is:

ZrOCl2+2NH4OH+(n+1)H2O→Zr(OH)4·nH2O↓+2NH4Cl

First, dissolve ZrOCl2 with water to make ZrOCl2·H2O solution, the concentration is more suitable at 0.250.4mol/L. Ammonia water (NH4OH) was added to neutralize the precipitation reaction, and the precipitate Zr(OH)4·nH2O was filtered, washed and dried at 100120°C, and finally calcined at 800°C for 1 hour to obtain ZrO2 powder. The ammonia precipitation conditions have a significant effect on the properties (particle size, dispersion, purity, density) of ZrO2 particles. When it is desired to prepare CaO, MgO or Y2O3 stable ZrO2 powder, the co-precipitation method can be used. The stabilizer is added in the form of its salt solution. Generally, 3% (mol) Y2O3 is added to obtain partially stabilized ZrO2.

3. Hydrolysis precipitation method

The hydrolysis precipitation method is to take a long time to boil the zirconium oxychloride solution so that the HCl produced by hydrolysis is continuously evaporated and removed so that the following hydrolysis reaction continues to the right to obtain the Zr(OH)4·nH2O precipitate:

ZrOCl2+(3+n)H2O→Zr(OH)4·nH2O↓+2HCl↑

The other processes are the same as the neutralization precipitation method, but the ZrOCl2 concentration should be smaller. Generally, 0.20.3mol/L is more appropriate. This method is simple but consumes a lot of energy.

4. Alcohol hydrolysis method

Alcohol hydrolysis method is an effective method to prepare high-purity, ultra-fine ZrO2 powder. First, ZrCl2 is reacted with C3H7OH and liquid ammonia under the catalysis of benzene (C6H6) to synthesize zirconium alkoxide Zr(OC3H7)4. The reaction formula is as follows:

ZrCl4+4C3H7OH+4NH3→Zr(OC3H7)4+4NH4Cl

Filter to remove NH4Cl, make Zr(OC3H7)4 crystal purified, then add water to carry out hydrolysis precipitation reaction:

Zr(OC3H7)4+2H2O→ZrO2+4C3H7OH

The precipitate is filtered out, dried at 100~110℃, crushed, and calcined at 850℃ for 0.5 hours to obtain ZrO2 powder. Compared with the above two methods, ZrO2 prepared by alkoxide hydrolysis has better powder characteristics: ZrO2 is almost all primary particles, rarely secondary particles (agglomerates) that are agglomerated; the size and shape of the particles are uniform; Chemistry High purity and single-phase structure. Therefore, ZrO2 powder prepared by alkoxide hydrolysis is more suitable for manufacturing high-performance electronic materials and structural ceramics. However, the process conditions are complicated, and the cost is high.

The final process of the last three methods is calcination. The higher the calcination temperature, the larger the particle diameter of ZrO2 powder and the smaller the specific area.

The zirconium oxides on the market mainly include high-purity ZrO2 (monoclinic ZrO2), CaO stabilized ZrO2 (Ca-PSZ), MgO stabilized ZrO2 (Mg-PSZ), Y2O3 stabilized ZrO2 (Y-PSZ) and desiliconized zirconium (Contains Al2O3). 

High-purity ZrO2 is white, when the content of ZrO2 is low, it is light yellow to yellowish-brown; stable zirconia is generally bright yellow. In the above zirconia raw materials, high-purity ZrO2 and ZrO2 in desiliconized zirconium all exist in a monoclinic phase; in fully stabilized zirconia, ZrO2 all live in a cubic period; and in partially stable ZrO2, most of ZrO2 is cubic Phase, the rest is monoclinic.

Trunnano is one of the world's largest manufacturers of zirconium dioxide. There are various sizes of zirconium dioxide products. If necessary, please contact Dr Leo, email: brad@ihpa.net.

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Tag: Trunnano   ZrO2   Zirconium dioxide