Narrow Results

We show that it is possible to construct a model in (3 + 1) dimensions where only composite scalars take place in physical processes as incoming and outgoing particles, whereas constituent spinors only act as intermediary particles. Hence while the spinor–spinor scattering goes to zero, the scattering of composites give nontrivial results.

We show that we can construct a model in 3+1 dimensions where it is necessary that composite vector particles take place in physical processes as incoming and outgoing particles. Cross-section of the processes in which only the constituent spinors take place goes to zero. While the spinor–spinor scattering goes to zero, the scattering of composites gives nontrivial results.

With the fast development of new materials investigation, attention is paid to. The performance of superfine powders, which must be modified on the surface to acquire some points. Coating technology of particles is one especial method of surface modification. In this paper, coating methods of particles are classified into solid state, liquid state, and gaseous state, main methods and mechanisms during current time are reviewed, respectively, and some research examples are listed. The choice of diversified coating technologies is decided synthetically based on powder materials, performance of the modified substance, and application of coated powders. In the future, the researches of the core-shell modification mechanism, coated particles with an ordered arrangement coating layer, a new surface active agent, the facilities of suiting surface modification, and the evaluation methodology of the surface coating effect are very exigent and necessary for the preparation and application of superfine powders.

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 A1(OH)₃–Y(OH)₃ is coated on the ZrB₂ surface to prepare A1(OH)₃–Y(OH)₃/ZrB₂ composite particles. In this paper, the effect of coating content on the properties of A1(OH)₃–Y(OH)₃/ZrB₂ composite particles is investigated. It is analyzed that the particle size and particle size distribution of A1(OH)₃–Y(OH)₃/ZrB₂ composite particles is increased with the coating content. The dispersion of ZrB₂ particles is largely increased with the coating content of 0%–20%; the dispersion of ZrB₂ particles is similar when the coating content is from 20% to 30%. The oxidation resistance ratio of the ZrB₂ particles with 30% coating content is the best than that of other conditions—it is about three times more than that of the original ZrB₂ particles.

Although ZrB₂ 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 ZrB₂, Al₂O₃ and Y₂O₃ particles are coated on the ZrB₂ surface to prepare ZrB₂–Al₂O₃–Y₂O₃ composite particles. The oxidation resistance mechanism of ZrB₂–Al₂O₃–Y₂O₃ composite particles is investigated by DTA-TG, TEM, and XRD. The surface of ZrB₂ particle is coated with compact Al₂O₃ and Y₂O₃ particles, which establishes the foundation to attain good oxidation resistance. ZrB₂ particle is mainly oxidized to increase the weight, from 600°C to 800°C. B₂O₃, obtained through the oxidization reaction, might coat on the surface of ZrB₂ particle to retard the oxidization reaction, which further increases the oxidation resistance. The oxidation resistance of coated ZrB₂ particle is far better than that of original ZrB₂ particle.

Silicon nitride (Si₃N₄) has attracted substantial interest because of its extreme chemical and physical properties, but the sintering densification of Si₃N₄ 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 Si₃N₄ at high temperature, the surface of Si₃N₄ is coated with Al(OH)₃ and Y(OH)₃ to synthesis Si₃N₄@Al(OH)₃–Y(OH)₃ core-shell composite particles. Through TEM, XRD, and BET analysis, when pH is about 9, Si₃N₄@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 Si₃N₄ with Al(OH)₃ and Y(OH)₃ particles are very good. Synthesis of Si₃N₄@Al(OH)₃–Y(OH)₃ core-shell composite powder will lay the foundation for preparing high-performance YAG/Si₃N₄ multiphase ceramic materials.

ZrB₂ are widely applied because of some excellent performances; however, ZrB₂ 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 ZrB₂ particles surfaces, ZrB₂ particles must be adequately dispersed in the ZrB₂ suspension during the coating process. The dispersion of ZrB₂ particles and the influence of dispersion on coating effect of ZrB₂@Al(OH)₃–Y(OH)₃ core-shell composite particles were investigated. The dispersion of ZrB₂ suspension adding the polyelectrolyte dispersant is better than that of ZrB₂ suspension adding the nonionic dispersant; the dispersant content is 2 vol% of ZrB₂ suspension to reach the best dispersion. The best dispersion is obtained by the ultrasonic dispersion for 10 min. ZrB₂ particles are coated using the dispersant and the ultrasonic dispersion in the ZrB₂ suspension to obtain the better coating effect. The dispersion of ZrB₂ particles is increased with increasing the coating content.