Morphological evolution of TiC from octahedron to cube induced by elemental nickel
Morphological evolution of TiC from octahedron to cube induced by elemental nickel
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镍元素诱导TiC从八面体到立方体的形貌演化
DOI：
10.1039/c1ce06205k
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发表时间：
2012-01-01
期刊：
影响因子：
3.1
通讯作者：
Liu, Xiangfa
中科院分区：
文献类型：
--
作者：
Nie, Jinfeng;Wu, Yuying;Liu, Xiangfa
合成了从八面体到立方体的各种形貌的TiC颗粒，并利用场发射扫描电子显微镜（FESEM）在三维空间进行了研究。讨论了TiC晶粒的形貌演化及其生长机制。在Al-Ti-C合金中，TiC颗粒倾向于形成由8个{111}面包围的八面体形貌（平衡形状），其总表面自由能最小;而在Al-Ni-Ti-C合金中，在Ni的影响下，TiC颗粒倾向于形成由6个{100}面包围的立方体形貌。由于Ni-3d和C-2 p轨道之间的强相互作用，熔体中的Ni原子选择性地吸附在TiC晶体生长的{100}面上，而不是极性的{111}面上，从而降低了{100}面的比表面能。根据Wuff定理，{100}的增长率相应降低，而{111}的相对增长率加快。因此，沿沿着方向较高的生长速率将导致{111}面逐渐收缩，而六个{100}面由于生长速率较低而保留形成TiC立方体。此外，在含Fe和Co的熔体中也可以发现类似于TiC晶体的形态演变。结果表明，在第八族元素Fe、Co、Ni的作用下，TiC晶体的生长遵循相同的生长模式。
TiC particles with various morphologies from octahedron to cube were synthesized and investigated by Field emission scanning electron microscopy (FESEM) in three-dimensional space. The morphological evolution of TiC grain and its growth mechanism were also discussed. TiC particles prefer an octahedral morphology (equilibrium shape) enclosed by eight {111} facets with minimized total surface free energy in Al–Ti–C alloy, while they tend to form a cube enclosed by six {100} facets under the influence of Ni in Al–Ni–Ti–C alloy. Due to the strong interaction between Ni–3d and C–2p orbitals, Ni atoms in the melt selectively absorb on {100} faces of the growing TiC crystal rather than on the polar {111} faces and reduce the specific surface energy of {100}. According to Wuff's theorem, the growth rate of {100} is lowered correspondingly, while the relative growth rate of {111} is accelerated. Thus, the higher growth rate along direction will lead to the shrinkage of {111} faces gradually, while six {100} faces are reserved to form a TiC cube because of their lower growth rates. Furthermore, a similar morphology evolution to TiC crystals can also be found in Fe- and Co-containing melts. It is revealed that the crystal growth of TiC follows the same model under the effect of group VIII elements (Fe, Co and Ni).