MgO-C refractory samples were prepared using fused magnesia, flake graphite, Al-Mg alloy and Si powders as raw materials, Ni(NO3)(2)center dot 6H(2)O as catalyst and phenolic resin as binder. After mixing and pressing, the specimens were coked in reducing atmosphere at 1200 degrees C and 1400 degrees C for 3 h. The characteristics of phase composition, microstructure, thermal shock resistance and mechanical strength of the samples with different catalyst contents were studied. The results show that after 1200 degrees C heating treatment, the Al-Mg alloy has been oxidized and turned into MgAl2O4. After 1400 degrees C heating treatment, there appear AIN and SiC ceramic phases while metallic Si disappears. At the same time, the amount of MgAl2O4 formation increases. When the contents of Ni(NO3)(2)center dot 6H(2)O are more than 0.4%, the thermal shock resistance and fracture toughness of specimens are improved significantly, which should be contributed to the formation of SiC, AIN and MgAl2O4 whiskers.

以热固性酚醛树脂和金属铝粉为原料、纳米镍为催化剂,采用机械搅拌法制备了金属铝和纳米镍共掺杂酚醛树脂,研究了金属铝和纳米镍共掺杂对树脂炭结构及其抗氧化性能的影响.结果表明:在埋炭气氛下,树脂材料内部CO分压较高而无氮化物存在,体系属于Al-C-O系统;随着温度的升高,氧分压增大,Al2O3(s)相的稳定区间增大.900℃炭化后体系中生成纳米碳管和Al3C4晶须,1 000℃处理后有A13C4晶须和A12O3颗粒同时存在.当温度升高到1 200℃时,Al3C4相消失,Al2O3晶须生成量增加.随着热处理温度升高,纳米碳管的直径从60 nm增大到100 nm.添加金属铝粉和纳米镍后,掺杂改性树脂炭化后炭产物的氧化峰值为664.6℃,相比单一掺杂,氧化峰值温度提高了约122℃,增幅达到22％.

研究了炭化温度对掺杂改性树脂炭结构及其抗氧化性能的影响.借助于X射线衍射仪、红外光谱仪、扫描电子显微镜和差示扫描量热仪对掺杂改性树脂炭化后的炭结构及其抗氧化性能进行了表征.结果表明:在埋炭条件下,炭化温度对掺杂改性树脂炭化后的炭结构有显著影响:随炭化温度升高,掺杂改性树脂炭化后的炭结构逐渐向石墨化碳结构方向演化;当炭化温度为600℃时,掺杂物表面开始有大量碳晶须生成,晶须的直径约为50～100 nm,长度约为几百纳米,随炭化温度升高,碳晶须长径比提高,但碳晶须的产量逐渐下降;当炭化温度为1 000℃时,掺杂物表面生成大量的碳微球,碳微球的直径约为100～500 nm.与树脂炭相比,掺杂改性树脂炭化后碳产物的氧化峰值温度提高了约80℃.

Upon application of nano-sized metallic Ni particles as catalyst, the in-situ synthesis mechanism of spinel whiskers in MgO-C refractories was studied. Their phase composition and morphology were determined by means of X-ray diffraction and scanning electron microscopy supported by energy dispersive spectroscopy. The results show that when the catalyst of nano-sized Ni was added in MgO-C refractories, the granular MgAl2O4 (MA) spinels transformed into the shape of whiskers at 1200 degrees C. The presence of Ni catalyst can accelerate the generation of Mg vapor, which can react with Al vapor to form MA spinel whiskers. Through dissolution and precipitation, MA spinel crystals nucleate directly and grow into whiskers from the catalytic droplets of nano-sized metallic Ni particles. The growth of spinel whiskers follows a typical vapor-liquid-solid (V-L-S) growth mechanism.

In order to tackle the shortcomings of high brittleness,hard graphitization,and poor oxidation resistance resulted from carbonization of phenolic resin of Mg O- C refractories, effects of 2 mass% spherical Ni, and2 mass% spherical Ni plus 7. 5 mass% Al composite powder on microstructure of the secondary carbon in Mg O- C refractories matrix were investigated. The results show that a large number of carbon whiskers form after the carbonization of phenolic resin with Ni powder;in the Mg O- C refractories matrix with only Ni powder,the carbon microspheres form at all treatment temperatures and change slightly with the temperature rising;the carbon whiskers begin to generate in the specimens with composite powder at 1 000 ℃,the diameter of the carbon whiskers is about 0. 4- 0. 5 μm,and the length is about 3- 4 μm,and the formed carbon whiskers increase gradually with the temperature rising.

Structure evolution and oxidation resistance of pyrolytic carbon derived from Fe doped phenol resin in a coke bed from 600 to 1100 degrees C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and thermogravimetry-differential scanning calorimetric analysis (TG-DSC). The results show that the doping of Fe powders in the phenol resin significantly reduces the graphitizing temperature. The graphitization degree of the phenol resin increases with temperature increment in a range of 600-1100 degrees C. The SEM and TEM analysis show that massive onion-like carbon nanoparticles with about 150 nm in diameter are generated on the surface of dopants at the temperatures below 800 degrees C. With the raising of carbonization temperature, onion-like carbon nanoparticles were evolved to bamboo-shaped carbon nanotubes, which were furtherly transformed into bamboo-shaped carbon chains at 1000 degrees C and bamboo-shaped carbon nanotubes at 1100 degrees C, the corresponding diameter and length of formed bamboo-shaped carbon nanotubes are about 150 nm and several tens of micrometers. The oxidation resistance of the pyrolytic carbon derived from Fe doped phenol resin after carbonization at 1000 degrees C is greatly improved in comparison with the carbon without Fe doped. The oxidation peak temperature of the former reaches 574.09 degrees C, much higher than 506.53 degrees C for the latter.

With fused magnesia ,flake graphite and coal tar pitch as main raw materials ,metallic Al and Si powders as additives ,and phenolic resin as binder ,MgO-C refractory specimens were prepared and then heat-treated at 1000 ℃ ,1200 ℃ ,1400 ℃ × 3h respectively under nitrogen atmosphere to study the characteristics of the specimens in phase composition , microstructure and mechanical strength .The results show that after 1000 ℃ heating treatment ,the metallic Al has reacted with C (CO) or N2 ,resulting in the formation of strip-like AlN and octahedral MgAl2 O4 .It is also found that the metallic Si has not taken part in any reaction at this stage .After 1200 ℃ heating treatment , the reaction between Si and C or CO leads to the formation of platelike SiC which is then interlocked into magnesia matrix ,raising the specimen’s modulus of rupture and residual strength after thermal shock test .After 1400 ℃ heating treatment ,besides strip-like AlN and octahedral MgAl2 O4 ,a large amount of SiC whiskers and needlelike β-Si3 N4 are formed within the skeleton structure ,giving the specimen excellent hot modulus of rupture and thermal shock resistance .