Preparation methods of millimeter ceramic balls At present, the methods for preparing millimeter ceramic balls mainly include die pressing method, "planetary" rolling method, and direct pyrolysis method.
1) Mold pressing method
The mold pressing method is a widely used molding method. The advantages of this process are high production efficiency and easy automation; the product has a small firing shrinkage rate and is not easy to deform. The disadvantage is that the prepared ceramic balls are large in size and the spherical shape is not good.
The mold pressing method is mostly used to prepare simple ceramic parts in the shape of rods and cylinders or discs, and requires high mold quality. If small-sized ceramic balls are prepared, the efficiency is low.
2) "Planetary" rolling method
The "planetary" rolling method is to put the granulated zirconia ceramic powder into a rolling cylinder, add a small amount of deionized water, and the particles roll on the cylinder wall with the rotation of the rolling cylinder, and finally form small balls.
The advantages of the preparation method are simple and easy to implement, with less investment; the disadvantage is that the size distribution of the small balls is larger.
3) Direct pyrolysis method
The direct pyrolysis method is suitable for preparing zirconia ceramic pellets using metal carbonates as raw materials. It can not only make full use of raw materials, but also is environmentally friendly; the method is simple and suitable for large-scale industrial production.
The key step of the process is calcination. The thermal decomposition reaction produces a large amount of gas, and the temperature must be slowly raised.
4) Inverse suspension polymerization method
Suspension polymerization refers to a method in which the monomers are dispersed in the suspension medium in the form of droplets by mechanical stirring and dispersing agents to carry out the polymerization reaction. The system generally consists of four parts: monomer, oil-soluble initiator, water, and dispersant. Inverse suspension polymerization is polymerization in which water-soluble monomers are dispersed into fine droplets in an organic solvent.
The advantages of the inverse suspension polymerization method are: low viscosity of the system, easy removal of polymerization heat, convenient operation; relatively stable pellets and uniform quality. Disadvantages are: the small ball size distribution is wide, and further classification is required; it is suitable for the preparation of small-size balls.
5) External gelation method
The main feature of the external gelling method is that the balls dropped from the slurry are pre-cured with NH3 at room temperature and then cured in NH4OH.
At present, Y2O3, stabilized ZrO2, the preparation process of ceramic balls: the yttrium-containing zirconium salt solution is mixed with PVA and then dropped by a shaking device. The free-falling balls are pre-cured with NH3, and then dropped into NH4OH to solidify.
Finally sintered to obtain Y2O3-ZrO2, ceramic balls. The German Brace company used this method to prepare ceramic balls such as ZrO2, HfO2, A12O3, and put them into industrial production. Nuclear reactor pellets such as UO2, ThO2-UO3, etc. are also often prepared by this method.
The advantages are: the size of the ball can be adjusted through the vibrating nozzle, the size distribution is narrow, and the raw materials are cheap. The disadvantage is that the liquid pellets need to be solidified by NH3 and NH4OH in the gel column. The gel time is long and cumbersome, and it is difficult to control.
6) Internal gelation method
The characteristic of the internal gelation method is that hexamethylenetetramine is pre-mixed in the cold raw material liquid, and it decomposes and releases ammonia and formaldehyde at various parts of the liquid pellets at the same time by heating; formaldehyde and urea condense to form polymers, and metal ions are converted into hydrogen Oxide, the sol becomes a gel.
The advantages are: the diameter of the small ball is adjustable, the size distribution is narrow; the gel rate is fast, and the quality is uniform; the equipment requirements are low. The disadvantage is that there are more impurity ions and water, and the volume shrinkage rate is larger.
