Zirconia Ceramic Powder Requirements
(1) The particle size is submicron or finer;
(2) It has an equispherical shape;
(3) No reunion;
(4) High purity and uniform chemical composition;
(5) The distribution of particle sizes is narrow.
Among them, purity and particle size are the determinants of the properties of the powder.
Zirconia Ceramic Preparation methods
Liquid Phase Reaction Precipitation Method
Precursor particles are extracted from the solution using the liquid phase reaction precipitation method. Due to its advantages of low cost and simple industrialization, the method, which is straightforward, safe, and low-consumption, has become a research hotspot. The powder produced using this conventional method, however, has a wide particle size distribution and an irregular shape.
Homogeneous Precipitation Method
Using a specific chemical reaction, the crystal-forming ions in the solution are slowly and uniformly released using the uniform precipitation method.
The precipitating agent that is now added does not immediately react with the precipitating component; instead, it slowly produces precipitating agent throughout the entire solution through chemical reaction, effectively lowering the reactant's concentration gradient and controlling the nanoparticles' particle size distribution.
This approach has an easy large-scale production process, low cost, and straightforward chemical reaction. However, the uniform precipitation method's entire precipitation reaction takes place in an aqueous solution, making it challenging to control the growth and agglomeration of the particles as well as their shape. The performance of powder dispersion is impacted by how easily the preparation process can agglomerate.
Emulsion Method
The metal salt can be dissolved using the emulsion method in the water nucleus with surfactant surrounded by the oil phase. A chemical reaction then takes place in the water nucleus, producing particles that are spherical, small, and uniform in size, which is what is needed to prepare ceramic raw materials.
A microemulsion containing the ion to be precipitated must be combined with another microemulsion, general solution, solid, or even gas that contains a precipitating agent in order to use this method. The water nuclei of the microemulsion will inevitably be in different microscopic environments as a result of the concentration gradient that is created during the mixing process. This will cause varying degrees of changes in the size of the water nuclei, the water nuclei themselves, and the stability of the product particles. The precipitation reaction process is asynchronous in different regions, which widens the size distribution of the synthesized nanoparticles. Simultaneously, the water phase content that exists as a reaction product in the microemulsion is frequently relatively low, and the price of the organic solvent used is relatively high, resulting in excessively high production costs for nano-powder.
Hydrothermal Synthesis Method
With the hydrothermal synthesis method, the entire process is carried out in a reactor, resulting in a product with high purity, little agglomeration, good powder dispersion, and extremely small particles that can reach the nanometer level. The equipment is complex and costly, the environment is harsh, the energy consumption is high, and it is challenging to realize industrial production, all of which are drawbacks.
Electrochemical Method
With good dispersibility, nano zirconia crystal nuclei can be prepared electrochemically. Tetragonal nano zirconia crystals can be produced after heat treatment. The powder has an average primary particle size of 7.6 nm. It has not, however, been put into factory production and is only available in the laboratory currently.
New Technique of Impingement Flow Tube Reaction
In contrast to the conventional method, this method employs impinging flow feed and a high-efficiency micro-mixing tubular reactor; the latter's distinctive design prevents back-mixing, strengthens the process's micro-mixing, and achieves uniform nucleation. The process is simple to control, which enhances its controllability. It is possible to produce nano-zirconia powder with a very narrow particle size distribution using this process, which produces ultra-fine zirconia powder with an average particle size of about 14 nm, which is fluffy after drying and calcining without any hard agglomeration. The technique is straightforward to use and is suitable for large-scale industrial production.
High-Temperature Spray Pyrolysis Method
In order to produce ZrO2 powders with uniform particles, high activity, and a particularly narrow particle size distribution, this method combines the spray drying and decomposition synthesis processes. This streamlines the process and reduces the aggregation of powders during the synthesis process.
Freeze-Drying Method
To create a well-dispersed powder, the appropriate salt solution must first be atomized, quickly frozen to create the powder, quickly desolved, and then converted into highly active ZrO2 at a low temperature. ZrO2 powder produced using this method is superior to powder produced using any other method, but it also has obvious drawbacks, including expensive and complicated equipment and a challenging and complicated solution preparation process.
Explosion Method
The explosion method is a recent innovation in technology. Its ability to quickly produce nanocrystals and create zirconia powder with incredibly small particle sizes are the advantages. Its excessively large temperature gradient, however, requires a lot of energy.
Solid Phase Suspension Grinding Method
The raw materials are ground and stirred, and then crushed into nanoparticles primarily using the rotation and vibration of the ball mill. The solid phase reactants are suspended in the liquid phase and are encapsulated in microemulsion micelles during the milling process. With this approach, the flaw of an incorrect stoichiometric ratio in a liquid phase reaction is overcome, and the issue of poor reaction uniformity in a straightforward solid phase reaction is resolved.
Sol-Gel Method
In terms of raw materials, the precipitant method and the hydrolysis method are comparable to the sol-gel method. The sol-gel method can be used to create spherical nano-ceramic particles with a particle size that can reach submicron levels or even smaller. The particles have an equiaxed spherical shape, and there are no aggregates. The purity is high, the chemical composition is consistent, and the size distribution is narrow. It is clear that the sol-gel method is currently the most effective and valuable way to make powder. However, as a result of the high cost of the raw materials, it is not feasible for use in mass production.