Have you seen the colorful zirconia ceramic in different applications?

The colorful world is indispensable to the color. The single black and white zirconia ceramics obviously can't satisfy people's sensory needs, so how to make them "colorful" has become a focus of the ceramic industry. It can be said that "colorful" makes zirconia more valuable.

Beautiful colored zirconia jewelry

If you want to prepare colored zirconia, the key is how to evenly distribute the colored hue (including transition metal or rare earth metal oxides or other compounds such as CoO, Cr2O3, Fe2O3, etc.) in the ceramic matrix. However, for nano-powders, due to its small particle size, large surface area, high surface energy, capillary force between particles, electrostatic attraction, van der Waals force, it is easy to agglomerate between them, thus reducing the physical chemistry of ceramics. performance. Therefore, in order to prepare zirconia ceramics with good performance and various colors, it is necessary to find a suitable dispersion method. The following are commonly used:

Solid phase mixing

The preparation of colored zirconia powder by mixed ball milling technology is currently the most commonly used method. The oxide particles such as coloring agent and mineralizer are mixed with the stabilized zirconia nano powder according to a certain chemical ratio, and the solid particles are mixed. In this process, it is refined, and microcracks, lattice distortion, and surface energy increase, which are beneficial to low temperature chemical reaction, occur, and have the advantages of simple process, low cost, convenient operation, and easy industrialization.

Solid phase mixing process flow chart

However, the biggest disadvantage of the solid phase mixing method is that it cannot overcome the agglomeration of the nanoparticles, the mixing of the colored phase and the matrix nanoparticles is uneven, and the ball milling time is long, and the ball milling medium or the atmosphere may cause serious pollution to the powder. In addition, the solid-phase reaction rate is affected by the diffusion of the particles, and since the mass transfer distance between the color-reactive reactants is large, it is difficult to sufficiently carry out the color reaction of the colorant in the zirconia matrix, thereby causing coloration stability. It is difficult to control and there is a phenomenon of chromatic aberration.

Moreover, the method has long heat preservation time, high energy consumption, expensive waste of colorant waste, and agglomeration and sedimentation of dispersed particles during drying after ball milling, so electrolyte dispersant is usually used on the basis of solid phase mixing method. Or ultrasonic dispersion technology pre-forms the agglomeration and sedimentation of the powder particles to improve the dispersibility of the powder particles.

Chemical coprecipitation

The chemical coprecipitation method uses a mixture of a zirconium salt, a stabilizer salt and a colored ion salt solution, and then reacts with a base or a carbonate to form a hydroxide or a carbonate precipitate, and then thermally decomposes to obtain a zirconia composite. The process of the powder is shown in the figure below.

Process flow chart of chemical coprecipitation

The chemical coprecipitation process is complicated, but the obtained powder has high purity and excellent performance. However, the disadvantage of this method is that the color zirconia coprecipitated ions are complicated, which leads to complicated reaction in the later sintering process, and the zirconia stabilizer may have an unpredictable reaction with the colored ions, thereby being consumed in a large amount. On the one hand, it affects the properties of the final colored zirconia article, and on the other hand, it also affects the color rendering optical properties of the colored ions.

At the same time, the chemical precipitation method must pay attention to a problem, that is, the formation of hard agglomeration, in order to avoid this phenomenon, can be improved by the following measures: reduce the introduction of impurity ions; use organic solvents such as alcohol, acetone to wash the precipitated product To inhibit the agglomeration of the powder; in the drying stage of the powder, the method of drying and freeze-drying of the super-zero boundary is generally used.

Liquid phase infiltration

The liquid phase infiltration method can achieve high uniformity doping and impart new properties to the surface under the premise of maintaining the original properties of the material. The process flow is shown in the following figure:

Process flow chart of liquid phase infiltration method

First, the injection-molded body is subjected to water extraction and degreasing to obtain a green body having a connected pore structure, which is then impregnated in a solution containing the colored phase ions. The colored phase ions permeate into the interior of the body from the surface of the body via the pores; the depth of the impregnation is controlled by the length of the impregnation time, and finally various colored zirconia ceramics having excellent properties are obtained.

The impregnation matrix required for the liquid phase infiltration method must contain a pore structure with internal interconnecting surface openings, so as to ensure that the colored phase ions in the solution can slowly penetrate into the inside from the surface and be evenly distributed inside the matrix. Compared with the traditional preparation process, the liquid phase infiltration method is simpler in process, and the prepared color zirconia ceramic has obvious advantages in color uniformity and physical properties. In addition, the liquid phase infiltration method can make full use of injection molding to obtain various shapes of complex zirconia blanks, thereby producing various complex shapes of colored zirconia ceramics.

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