A Common Regularity of Stoichiometry-Induced Morphology Evolution of Transition Metal Carbides, Nitrides, and Diborides during Self-Propagating High-Temperature Synthesis

Abstract

The morphologies of the transition metal carbide (TMC) (ZrC x , NbC x , and TaC x ), transition metal nitride (TMN) (TiN x ), and transition metal diboride (TMD) (NbB 2x and TaB 2x ) particles formed during the selfpropagating high-temperature synthesis (SHS) were investigated. The results indicate that the ceramics with wide stoichiometric ranges all show a stoichiometry-induced morphology evolution, i.e., octahedron → truncated-octahedron → spherelike → sphere, for TMCs and TMNs, and hexagonal prism → polyhedron → spherelike, for TMDs. For TMCs and TMNs, the increase in the stoichiometry leads to the increase in the growth rate in the ⟨111⟩ crystalline direction. Hence, their morphologies show an evolution process of gradual exposure of the {100} surfaces and shrinkage of the {111} surfaces. When the exposed {100} surfaces are roughed because of the extremely high combustion temperatures during the SHS and thus turn round, the growth shapes of the TMC and TMN crystals change to spherelike. On the other hand, when the TMCs and TMNs are stoichiometric or near stoichiometric, the critical transition temperature for thermodynamic roughening of the {100} surfaces could be very high. Then, the rounded {100} will restore to the flat surfaces, and the cubic and truncatedcubic TMCs and TMNs particles are formed. For TMDs, the morphology evolution could be caused by the decrease in the stability of the {0001} and {101̅ 0} surfaces at high stoichiometries. With the increase in the stoichiometry, these two surfaces are less-exposed gradually while the {11̅ 01} surfaces are exposed and expand. The growth shapes of TMDs change from regular hexagonal prism to polyhedron. With the rounding (roughening) transition of the {11̅ 01} surfaces at high temperatures, the TMDs particles become spherical.

Recent advances in carbon nanostructures prepared from carbon dioxide for high-performance supercapacitors

“…It is still urgently desired to develop a straightforward and environmentfriendly technique for industrial manufacturing of high-quality carbon materials directly form CO 2 . Since the pioneering work of Merzhanov et al [136] in 1960s, a self-sustaining reaction called self-propagating high-temperature synthesis (SHS) has received much attention from both academia and industry as a novel protocol to manufacture useful ceramics [137,138], intermetallics [139], refractory materials [138], and thermoelectric materials [140,141]. The foremost feature of SHS technique is an essentially exothermic reaction ignited by a small amount of energy input to one part of the system, then the released heat is sufficient to generate a combustion wave that spontaneously propagates in a self-sustaining manner throughout the remaining parts of the reaction system.…”

The Synthesis, Structure, Morphology Characterizations and Evolution Mechanisms of Nanosized Titanium Carbides and Their Further Applications

“…Jin et al found a temperature-related growth behavior in the Al-Ti-C reaction system during the self-propagating high-temperature synthesis process, and they demonstrated that the TiC x particles transformed from octahedrons and truncated octahedrons to spheres upon increasing the temperature [13]. Their later studies illustrated that the intrinsic morphology evolution of TiC crystal was caused by the induction of stoichiometric ratio [30,85,86]. The corresponding evolutions are shown in Figure 10d.…”

“…It isinexpensive and has good stability, while its average size is relatively large. In previous studies, graphite particles of approximately 5 μm, 15 μm, 38 μm or even 48 μm were reported as used to fabricate TiC [30,75,80,86]. Becasuse graphite has a large size, it always becomes a residual phase in the reactant and has not been completely reacted with Ti, except for via some special measures [81].…”

“…( b ) SEM images of TiC particles synthesized via SHS: ( b1 ) a high magnification and ( b2 ) an edge-sharing of octahedral TiC, with permission from Reference [14], copyright (2009) Elsevier; ( c ) Schematic illustration of TiC x growth morphologies. With permission from Reference [86], copyright (2012) American Chemical Society; ( d ) FESEM (Field emission scanning electron microscope) images of TiC x particles, with permission from Reference [13], copyright (2012) American Chemical Society.…”

Morphological evolution of TiC particles with different stoichiometries by hydrofluoric acid etching treatment

“…3,11,12 In literature, it has been reported that the different morphologies of TiC such as octahedron, cubic, hexagonal, and spherical can be achieved, based on the temperature of SHS. [13][14][15] However, as far as we know, no basic study regarding the reasons for these observations was reported, until the valuable studies of Jin et al 13,16,17 In their works, the morphological evolution of the TiC particles as a function of the reaction temperature was reported. With decreasing the reaction temperature during SHS, the shape of TiC particles changed from a spherical shape to an octahedron one.…”