In this research, synergetic and separate influence of nano-carbon black (C.Bn) and SiC on the microstructure and flexural strength of ZrB2 were investigated. So, ZrB2 and ZrB2- 30vol%-based composites containing 10 and 15 vol% C.Bn as well as ZrB2- 15 vol% SiC were fabricated via spark plasma sintering at 1850 °C for soaking time of 8 min under the applied pressure of 35 MPa. Relative density was measured by Archimedes method. Microstructural evaluation was carried out by applying the field emission electron microscopy (FESEM), and flexural strength was measured by three-point bending test. It was found the relative density improves in the presence of C.Bn and SiC especially in synergetic state so that the full densification was gained in Z30Si10C.Bn and Z30Si15C.Bn composites through their reactions with impurities at 1850 °C. In the monolithic ZrB2 system, the C.Bn addition improves the flexural strength slightly to 300 MPa and 315 MPa from 290 MPa. However, co-doped 10 vol% C.Bn with 30 vol% SiC resulted to achieve maximum flexural strength of 486 MPa in comparison with individually applying each of them (395 MPa for Z30Si and 300 MPa for Z10 C.Bn).

In this work, the ablation behavior of monolith ZrB2-30 vol%SiC (Z30S) composites were studied under various oxy-acetylene flame angles. Typical oxidized microstructures (SiO2/SiC-depleted/ZrB2-SiC) were observed when the flame to Z30S was arranged vertically. However, formation of the outmost glassy SiO2 layer was hindered when the Z30S was tilted. The SiC-depleted region was fully exposed to air with reduced thickness when highly tilted. Traces of the ablated and island type SiO2 were observed at intermediate flame angles, which clearly verified the effect of flame angle on the ablation of the SiO2 layer. Furthermore, the observed maximum surface temperature of the Z30S gradually increased up to 2,200 °C proving that surface amorphous silica was continuously removed while monoclinic ZrO2 phase began to be exposed. A proposed ablation mechanism with respect to flame angles is discussed. This observation is expected to contribute to the design of complex-shaped UHTC applications for hypersonic vehicles and re-entry projectiles.

Few studies have been performed on ZrB2- graphite platelet composite made by spark plasma sintering (SPS) technique. In this research, the influence of adding graphite platelets (Gp) with and without SiC on the fracture toughness of ZrB2 ceramic was studied. The ZrB2- 10Gp, ZrB2- 15Gp, ZrB2- 30SiC-10Gp, and ZrB2- 30SiC-15Gp specimens were sintered by the SPS method at the temperature of 1850 °C for 8 min. The fracture toughness and work of fracture (WOF) were evaluated using the Single-Edge Notched Beam (SENB) technique. It was found that the fracture toughness and WOF were improved by the alone and combined addition of Gp and SiC to the monolithic ZrB2. The maximum fracture toughness of 4.8 ± 0.1 MPa m1/ 2 was obtained for the ZrB2- 15Gp specimen. It seems that adding Gp alone was more effective in enhancing the fracture toughness of ZrB2 than the combined addition of Gp and SiC. While the addition of Gp and SiC simultaneously modified the densification behavior to reach full-densified samples.

ZrB2 ceramic and ZrB2 ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO2 amorphous outer scale layer and SiC-deplete ZrO2 scale layer, which decrease the oxidation rate. WC addition forms WO3 during the oxidation process to result in a ZrO2/WO3 liquid sintering layer, which is known to improve the antioxidation effect. The addition of SiC and WC to ZrB2 reduces the oxygen effective diffusivity by one-fifth of that of ZrB2. The addition of both SiC and WC shows the formation of a SiO2 outer dense glass layer and ZrO2/WO3 layer so that the anti-oxidation effect is improved three times as much as that of ZrB2. Therefore, SiC- and WC-added ZrB2 has a lower two-order oxygen effective diffusivity than ZrB2; it improves the anti-oxidation performance 3 times as much as that of ZrB2.

Zirconium boride is an artificial or which is rarely found in the nature. ZrB2 is popular in the hard material industry because it has a high melting point, excellent mechanical properties and chemical stability. There are two known methods to synthesize ZrB2. The first involves direct reaction between Zr and B, and the second is by reduction of the metal halogen. However, these two methods are known to be unsuitable for mass production. SHS(Self-propagating High-temperature Synthesis) is an efficient and economic method for synthesizing hard materials because it uses exothermic reactions. In this study, ZrB2 was successfully synthesized by subjecting ZrO2, Mg and B2O3 to SHS. Because of the high combustion temperature and rapid combustion, in conjunction with the stoichiometric ratio of ZrO2, Mg and B2O3; single phase ZrB2 was not synthesized. In order to solve the temperature problem, Mg and NaCl additives were investigated as diluents. From the experiments it was found that both diluents effectively stabilized the reaction and combustion regime. The final product, made under optimum conditions, was single-phase ZrB2 of 0.1-0.9μm particle size.

This paper reports the microstructures and thermal conductivities of -SiC composite ceramics with size and amount of SiC. We fabricated sintered bodies of -x vol.% SiC (x=10, 20, 30) with submicron and nanosized SiC densified by spark plasma sintering. Microstructure retained the initial powder size of especially SiC, except the agglomeration of nanosized SiC. For sintered bodies, thermal conductivities were examined. The observed thermal conductivity values are 40~60 W/mK, which is slightly lower than the reported values. The relation between microstructural parameter and thermal conductivity was also discussed.

This paper reports the effect of sintering processes and additives on the microstructures and mechanical properties of -SiC composite ceramics. We fabricated sintered bodies of -20 vol.% SiC with or without sintering additive, such as C or , densified by spark plasma sintering as well as hot pressing. While almost full densification was achieved regardless of sintering processes or sintering additives, significant grain growth was observed in the case of spark plasma sintering, especially with . With sintered bodies, mechanical properties, such as flexural strength and Vickers hardness, were also examined.

Zirconium diboride (ZrB2) and mixed diboride of (Zr0.7Ta0.3)B2 containing 30 vol.% silicon carbide (SiC) composites were prepared by hot-pressing at 1800˚C. XRD analysis identified the high crystalline metal diboride-SiC composites at 1800˚C. The TaB2 addition to ZrB2-SiC showed a slight peak shift to a higher angle of 2-theta of ZrB2, which confirmed the presence of a homogeneous solid solution. Elastic modulus, hardness and fracture toughness were slightly increased by addition of TaB2. A volatility diagram was calculated to understand the oxidation behavior. Oxidation behavior was investigated at 1500˚C under ambient and low oxygen partial pressure (pO2~10-8 Pa). In an ambient environment, the TaB2 addition to the ZrB2-SiC improved the oxidation resistance over entire range of evaluated temperatures by formation of a less porous oxide layer beneath the surface SiO2. Exposure of metal boride-SiC at low pO2 resulted in active oxidation of SiC due to the high vapor pressure of SiO (g), and, as a result, it produced a porous surface layer. The depth variations of the oxidized layer were measured by SEM. In the ZrB2-SiC composite, the thickness of the reaction layer linearly increased as a function of time and showed active oxidation kinetics. The TaB2 addition to the ZrB2-SiC composite showed improved oxidation resistance with slight deviation from the linearity in depth variation.

based composites are candidate materials for ultra-high temperature materials (UHTMs). has become an indispensable ingredient in UHTMs, due to its high melting temperature, relatively low density, and excellent resistance to thermal shock or oxidation. powders are usually synthesized by solid state reactions such as carbothermal, borothermal, or combined carbothermal reaction. SiC is added to this system in order to enhance the oxidation resistance of . In this study, ?based composites were successfully synthesized and densified through two different processing paths. or 25 vol.%SiC was fully synthesized from oxide starting materials with reducing agents after heat treatment at 1400. Besides, ?20 vol.%SiC was fully densified with as a sintering additive after hot pressing at 1900. The synthesis mechanism and the effect of sintering additives on densification of ?SiC composites were also discussed.

ZrO2, B2O3 및 AI을 사용하여 SHS법에 의한 붕화지르코늄을 합성을 하고 산화철과 알루미늄 분말의 첨가가 합성물의 치밀화에 미치는 영향에 대하여 검토하였다. 합성물중에 존재하는 결정상은 대부분이 ZrB2와 α-AI2O3상이었다. 산화붕소와 알루미늄의 몰비가 1.0:3.3이상일 때 합성물의 치밀화는 크게 증가하였고, ZrB2 입자도α-AI2O3용융상과 더불어 조대하였다. 산화철 1목에 대하여 알루미늄을 1-3몰을 첨가한 것과 산화철 1.5몰에 대하여 알루미늄을 3몰 첨가시 α-AI2O3를 중심으로하는 슬라그상으로부터 용융상의 분이가 가능하였고, 이들 용융상에 존재하는 결정상은 ZrB2이외에 Fe, Fe2B, Zr2Fe상이었다. 용융상의 상대밀도는 산화철 1몰에 대하여 알루미늄을 1몰 첨가시 83.2%인 반면에 그 이상의 첨가량에 대해서는 치밀화는 크게 증가하여 알루미늄을 3몰 첨가한 경우 상대밀도는 93.7%로서 최대를 나타내었다.