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ZrB 2 belongs to a class of ceramics defined ultra-high-temperature ceramics with extremely high melting temperatures; however, ZrB 2 ceramics is easily oxidized. To make ZrB 2 ceramics possess the better oxidation resistance in the air at high temperature, in this paper, the effect of surface modification on the properties of YAG– ZrB 2 ceramics were investigated. Fracture toughness of sintered ceramics with coated raw materials is higher than that of sintered ceramics with mixed raw materials under the same phase and phase content conditions. Oxidation layer thickness of sintered ceramics with coated raw materials is thinner than that of sintered ceramics with mixed raw materials. The results indicate that the sintered coated structure ceramics with coated raw materials help to increase the mechanical property and oxidation resistance of YAG– ZrB 2 ceramics.

ZrB 2 are widely applied because of some excellent performances; however, ZrB 2 is easily oxidized in the high-temperature air. To reach better Al ( OH )3– Y ( OH )3 composite shell and higher coating ratio on the ZrB 2 particles surfaces, ZrB 2 particles must be adequately dispersed in the ZrB 2 suspension during the coating process. The dispersion of ZrB 2 particles and the influence of dispersion on coating effect of ZrB 2@ Al ( OH )3– Y ( OH )3 core-shell composite particles were investigated. The dispersion of ZrB 2 suspension adding the polyelectrolyte dispersant is better than that of ZrB 2 suspension adding the nonionic dispersant; the dispersant content is 2 vol% of ZrB 2 suspension to reach the best dispersion. The best dispersion is obtained by the ultrasonic dispersion for 10 min. ZrB 2 particles are coated using the dispersant and the ultrasonic dispersion in the ZrB 2 suspension to obtain the better coating effect. The dispersion of ZrB 2 particles is increased with increasing the coating content.

Silicon nitride ( Si 3 N 4) has attracted substantial interest because of its extreme chemical and physical properties, but the sintering densification of Si 3 N 4 is difficult, and it is easily oxidized in the high-temperature air to impact high-temperature strength, which restricts its applied range. In order to decrease the oxidization and improve the strength of Si 3 N 4 at high temperature, the surface of Si 3 N 4 is coated with Al ( OH )3 and Y ( OH )3 to synthesis Si 3 N 4@ Al ( OH )3– Y ( OH )3 core-shell composite particles. Through TEM, XRD, and BET analysis, when pH is about 9, Si 3 N 4@ Al ( OH )3– Y ( OH )3 core-shell composite particles are successfully synthesized by co-precipitation methods. Coating layer is about 200 nm, which is compaction and conformability. Dispersion of coated Si 3 N 4 with Al ( OH )3 and Y ( OH )3 particles are very good. Synthesis of Si 3 N 4@ Al ( OH )3– Y ( OH )3 core-shell composite powder will lay the foundation for preparing high-performance YAG/Si 3 N 4 multiphase ceramic materials.

Although Zirconium diboride ( ZrB 2) is a desirable combination with some good properties, it is easily oxidized in the high-temperature air to impact high-temperature properties, which dwindles the applied range. In order to decrease oxidization and improve the high-temperature properties of ZrB 2, the surface of ZrB 2 is coated with Al ( OH )3– Y ( OH )3 to synthesize Al ( OH )3– Y ( OH )3/ ZrB 2 composite particles. In this paper, the conditions of synthesizing Al ( OH )3– Y ( OH )3/ ZrB 2 composite particles by the co-precipitation method are investigated. Al ( OH )3– Y ( OH )3/ ZrB 2 composite particles are synthesized under different conditions, but the conditions of synthesizing Al ( OH )3– Y ( OH )3/ ZrB 2 composite particles with the better coating quality require pH = 9, the appropriate concentration ( Al 3+ = 0.017 mol/L , Y 3+ = 0.01 mol/L ) of composite solution, reaction time of 60 min, titration speed of 0.05 ml/s, using the dispersant in the ZrB 2 suspension and the ultrasonic dispersion, respectively.

Although ZrB 2 has some excellent performances, it is easily oxidized in the high-temperature air, which is deadly shortcoming as high-temperature materials. To increase the high-temperature performances of ZrB 2, Al 2 O 3 and Y 2 O 3 particles are coated on the ZrB 2 surface to prepare ZrB 2– Al 2 O 3– Y 2 O 3 composite particles. The oxidation resistance mechanism of ZrB 2– Al 2 O 3– Y 2 O 3 composite particles is investigated by DTA-TG, TEM, and XRD. The surface of ZrB 2 particle is coated with compact Al 2 O 3 and Y 2 O 3 particles, which establishes the foundation to attain good oxidation resistance. ZrB 2 particle is mainly oxidized to increase the weight, from 600°C to 800°C. B 2 O 3, obtained through the oxidization reaction, might coat on the surface of ZrB 2 particle to retard the oxidization reaction, which further increases the oxidation resistance. The oxidation resistance of coated ZrB 2 particle is far better than that of original ZrB 2 particle.

Zirconium diboride is widely applied to high-temperature materials, but it is easily oxidized at high temperature. To increase the oxidation resistance of zirconium diboride at high temperature, the A 1( OH )3– Y ( OH )3 is coated on the ZrB 2 surface to prepare A 1( OH )3– Y ( OH )3/ ZrB 2 composite particles. In this paper, the effect of coating content on the properties of A 1( OH )3– Y ( OH )3/ ZrB 2 composite particles is investigated. It is analyzed that the particle size and particle size distribution of A 1( OH )3– Y ( OH )3/ ZrB 2 composite particles is increased with the coating content. The dispersion of ZrB 2 particles is largely increased with the coating content of 0%–20%; the dispersion of ZrB 2 particles is similar when the coating content is from 20% to 30%. The oxidation resistance ratio of the ZrB 2 particles with 30% coating content is the best than that of other conditions—it is about three times more than that of the original ZrB 2 particles.

ZrB 2 has some excellent performances, but it is easily oxidized at high temperatures to impact the high-temperature strength, which restricts its applied range. To protect from the oxidization and improve the strength of ZrB 2 at high temperature, the surface of ZrB 2 particles is coated with the Al ( OH )3– Y ( OH )3 shell to synthesize ZrB 2@ Al ( OH )3– Y ( OH )3 core–shell composite particles. Through the thermodynamic and kinetic analyses of the heterogeneous nucleation and homogeneous nucleation, the concentration product of precursor ion ( Y 3+ or Al 3+) and OH - (Qi) must be greater than the solubility product (K sp ), respectively; the conditions of Y 3+ and Al 3+ are reached to produce Al ( OH )3– Y ( OH )3 shell on the ZrB 2 surface between the Y 3+ line and the AlO 2- line. Through TEM and XRD analyses, ZrB 2@ Al ( OH )3– Y ( OH )3 core–shell composite particles are successfully synthesized by the co-precipitation method, the shell layer quality is better at pH = 9, which established the foundation for preparing high-performance YAG / ZrB 2 and Al 2 O 3– YAG / ZrB 2 multiphase ceramic materials.