Papers by Keyword: ZrB₂

Abstract: Regarding materials development, our studies have been mainly focused on ZrB₂-SiC and HfB₂-SiC compositions with TaSi₂ or Y₂O₃ additions using hot pressing and spark plasma sintering. These additives have been used to decrease the sintering temperature and to improve the oxidation resistance. Interesting mechanical properties at room and high temperature have been measured. Moreover, excellent oxidation behaviors have been observed up to 2000-2200°C with Y₂O₃. Last developments are centered on the manufacturing of ultrahigh temperature ceramic matrix composites (UHTCMC) using slurry infiltration and pyrolysis for example. First results are encouraging.

Abstract: Different molar ratio of HfB₂ and ZrB₂ had been mixed, and 30 vol.% SiC was selected as sintering additives. The mixing powders were sintered by hot pressing at 1900 °C for 1 h under a pressure of 20 MPa in Ar atmosphere. X-ray diffraction, scanning microscopy and Archimedes’s method were used to characterize the phase, microstructure and density of the sintered composites. Meanwhile, the hardness, the fracture toughness and flexural strength of the obtained composites were considered too. It can be found that the (Zr,Hf)B₂ solid solutions were formed by HfB₂ and ZrB₂ during the sintering. The flexural strength of (Zr,Hf)B₂-SiC composites increased with the amount of HfB₂ increasing, which reached (332±40) MPa for the composites content of 70% HfB₂. Which fracture toughness was (2.22±0.25) MPa·m^1/2. The highest Vickers’ harness of was (24.8±3.4) GPa for the composites content of 50% HfB₂.

Abstract: Zirconium diboride (ZrB₂) ceramics with high melting point, high hardness, good electrical and thermal conductivity, good neutron control and other characteristics, can be widely used in high-temperature structural ceramics, composite materials, electrode materials. In order to improve ZrB₂ difficult densification and high-temperature oxidation, the properties of coated Al (OH)₃-Y(OH)₃/ZrB₂ composite powders prepared by co-precipitation method were investigated in this paper, The conclusions are shown that the effect of coated composite powders is getting worse with the accelerated titration rates. the coating effect will be worse with the increasing reaction time. When the concentration of mixed solution is lower, the coated effect is better. When the synthesis condition is that the titration rate of 10ml/min, and the reaction time was 1h, mixed solution ion concentration of Y³⁺=0.119mol/L and Al³⁺=0.231mol/L, the coated effect of composite powders is better.

Abstract: Zirconium diboride (ZrB₂) is a material of particular interest because of the excellent and unique property combination of high melting point and high electrical and thermal conductivity. In this work, the effect of TiB₂ addition on pressureless sintering and hot pressing sintering of ZrB₂ was investigated. Four compositions were prepared with 0, 5, 10 and 20 wt% of TiB₂. First, ZrB₂ and TiB₂ powders were milled by planetary mill with SiC spheres at for 4 h and then they were wet mixed. Compacted samples were pressureless sintered at 2150 oC/1h and hot pressed at 1850 °C/30min with 20 MPa, both in Ar atmosphere. The added TiB₂ completely dissolved into the structure and formed a solid solution with ZrB₂. Addition of TiB₂ in ZrB₂ ceramic improved densification and hardness for both sintering process, but hot pressed samples exhibited better results.

Abstract: Dense ZrB2-SiC composites were fabricated by high pressure and high temperature sintering(HPHT) at 1500 oC for 3 min under a pressure of 5 GPa. The vickers’ hardness of ZrB2-SiC composite is 25 GPa. The flexural strength of the ZrB2-SiC composite is 300 MPa with the amount of SiC increased to 30wt.%, which increased after the composites oxidized at high temperature. The generated glass phase like SiO2 sealed pores and cracks on the surface of the ZrB2-SiC composite to increase the mechanical properties of the ZrB2-SiC composite. After oxdized at 1500oC for 45 mins, the dense oxidized film formed on the surface of ZrB2-SiC composites to improve the resistance oxi dation of ZrB2 ceramics.

Abstract: ZrB₂ has some excellent high-temperature performance. However, due to it is easily oxidized in the high-temperature air to impact high-temperature strength, which restricts its applied range. To decrease the oxidization and sintering temperature, and improve the strength of ZrB₂ at high temperature, in this paper, the prepared composite powders is analyzed with XRD, SEM, EDS and TEM, which proves ZrB₂@A1₂O₃-Y₂O₃ core-shell composite powders are successfully synthesized by co-precipitation method, the synthesis mechanism of ZrB₂@A1₂O₃-Y₂O₃ core-shell composite powders is received through the results discussion.

Abstract: This work investigates the removal of B in Si by the addition of Zr in the electromagnetic solidification refinement of silicon-aluminum melts. As Zr has a strong affinity for B and can form the thermodynamically stable compound of ZrB₂, the B content of lower-grade Si is expected to be effectively removed by adding a small amount of Zr to the Si-55 at% Al melt. The results show that Zr is strongly responsible for the decrease in B content of refined Si. The removal fraction of B significantly increased from 60.2% to 97.3% by adding a small amount of Zr (0 to 3500 ppmw). In addition, the removal fraction of Zr from Si was found to be as high as 98.6%; however, its residual content in the refined Si was significantly larger than its solid solubility in Si, possibly due to the non-equilibrium solidification occurring during the refining process.

Abstract: With honeycomb lattice of sp² hybridized carbon atoms, graphene has demonstrated excellent electrical and mechanical properties. One of its promising applications is to fabricate graphene-ceramic composite to improve the mechanical properties. In order to quantify the strength between graphene-ZrB₂ interactions, molecular dynamic method was utilized to simulate typical interface of graphene/ZrB₂ ceramic structure. Berendsen method was used to control the temperature and pressure during the whole simulation process. Universal potential function was employed to simulate the force filed between graphene and ZrB₂ structure. The binding structures of graphene/ZrB₂ (0001) interface were analyzed in detail and the bonding energy of the interface was calculated. The influence of numbers of graphene layer and sandwich structures on the bonding energy of interface is discussed. The study helped to understand the influence of graphene on mechanical properties of ZrB₂ ceramic.

Abstract: Zirconium diboride (ZrB₂) is a material of particular interest because of the excellent and unique property combination of high melting point, high electrical and thermal conductivity. In this work, the effect of addition of beta-silicon carbide (β-SiC) on hot pressing sintering of ZrB₂ was investigated. Four compositions were studied with 0, 10, 20 e 30 vol% of SiC. ZrB₂ powder and mixtures were prepared by planetary milling with SiC spheres during 4 h. Samples were sintered at 1850 °C/1h with a pressure of 20 MPa in argon atmosphere. β-SiC has undergone phase transformation to α-SiC during sintering. The addition of SiC increased densification with increasing of SiC content. The total densification of sample was 96.8 % of theoretical density for sample with 30 vol% of SiC and Vickers hardness was 19.9 ± 0.3 GPa.

Abstract: Zirconium diboride (ZrB₂) is a covalent compound that leads the category of ultra high temperature ceramics materials owing to its unique properties. In this work, the effect of addition of beta-silicon carbide (β-SiC) in pressureless sintering of ZrB₂ was investigated. Four compositions were prepared with 0, 10, 20 e 30 vol% of SiC. ZrB₂ powder and mixtures were prepared in by planetary milling with SiC spheres at 4 h. Two sintering temperatures were used, one at 2050 oC/1h and other at 2150 °C/1h. The addition of SiC has promoted an increasing in densification with the increasing of SiC content. The total densification of sample sintered at 2050 oC was 90% of theoretical density for sample with 30 vol% of SiC, while the maximum densification for temperature of 2150 oC was 91,0 %TD.