1. Preparation method of millimeter-level zirconia ceramic balls Preparation method of millimeter-level ceramic balls At present, the methods for preparing millimeter-level ceramic balls mainly include mold pressing method, "planetary" rolling method, direct pyrolysis method, etc.
(1) mold pressing method mold pressing method is a widely used molding method, the process advantage is high production efficiency, easy to automate; The firing shrinkage of the product is small and not easy to deform. The disadvantage is that the size of the ceramic ball is large and the spherical shape is not good. The mold pressing method is mostly used to prepare simple porcelain parts in the shape of rods and columns or discs, and has high requirements for the quality of the mold. If small ceramic balls are prepared, the efficiency is low.
(2) "Planetary" rolling method The "planetary" rolling method is to put the zirconia ceramic powder into the rolling cylinder, add a small amount of deionized water dropwise, and the particles roll on the cylinder wall with the rotation of the rolling cylinder, and finally form a small ball. The advantages of this preparation method are that it is simple and easy to implement, and the investment is less; The disadvantage is that the ball size distribution is larger.
(3) Direct pyrolysis method Direct pyrolysis method is suitable for the preparation of zirconia ceramic pellets from metal carbonates. It not only makes full use of raw materials, but also is environmentally friendly; The method is simple and suitable for industrial mass production. The key step in the process is calcination, a thermal decomposition reaction that produces a large amount of gas that must be warmed up slowly.
(4) Reversed-phase suspension polymerization Suspension polymerization refers to the method of polymerization reaction by mechanical stirring and dispersant to disperse the monomer in the form of droplets in the suspension medium. The system is generally composed of four parts: monomer, oil-soluble initiator, water and dispersant. Reversed-phase suspension polymerization is the polymerization of water-soluble monomers in an organic solvent by dispersing them into fine droplets. The advantages of reversed-phase suspension polymerization method are: low viscosity of the system, easy removal of polymerization heat, and convenient operation; The pellets are relatively stable and of uniform quality. The disadvantages are: the size distribution of the balls is wide, and further grading is required; It is suitable for the preparation of small-sized balls.
(5) External gelling method The main feature of the external gelling method is that the pellets dripping out of the slurry are pre-cured by NH3 and then cured in NH4OH at room temperature. At present, the preparation process of Y2O3, stabilized ZrO2 and ceramic balls: yttrium-containing zirconium salt solution mixed with PVA is dropped by a shaking device, and the free-falling balls are pre-cured by NH3 and then solidified in NH4OH. The final sintering yields Y2O3-ZrO2, ceramic balls. Germany Brace company used this method to prepare ZrO2, HfO2, A12O3 and other ceramic balls, and put them into industrial production. This method is also used in the preparation of nuclear reactor pellets such as UO2, ThO2-UO3 and other spheres. The advantages are: the size of the ball can be adjusted by the vibrating nozzle, and the size distribution is narrow; Raw materials are cheap. The disadvantage is: the liquid pellet should be solidified by NH3 and NH4OH in the gel column, and the gel time is long and cumbersome, and it is difficult to control.
(6) Internal gelling method The internal gelling method is characterized by the fact that the sixth-time methyltetramine is premixed into the cold raw material liquid, and ammonia and formaldehyde are released at the same time in various parts of the liquid pellet through heating; Formaldehyde and urea are condensed to form polymers, metal ions are converted into hydroxides, and sols become gels. The advantages are: the diameter of the ball is adjustable, and the size distribution is narrow; The gel rate is fast and the quality is uniform; Low equipment requirements. The disadvantages are: more impurity ions and moisture, and greater volume shrinkage.
2. The preparation method of micron-level zirconia ceramic balls There are many studies on micron-level ceramic balls at home and abroad in France. ZrO2 microspheres have been prepared and used as high-performance liquid chromatography stationary phases, mainly by oil emulsification and polymerization-induced colloidal agglomeration (PICA).
