Microstructure and growth mechanism of ZrO2 nanorod network via oxyacetylene torch ablation
Graphical abstract
Introduction
Great research interest has been devoted to one-dimensional (1D) nanostructural materials such as carbon nanotubes [1], nanowires [2] and nanorods [3] owing to their small dimensions and unique physical characteristics. ZrO2 nanorods have attracted much attention in the fields of superplastic structural ceramics and transformation toughening, electrochemical devices, catalysis and sensors [4] due to their crystalline perfection, large surface area and small dimensions. However, only few studies on the synthesis of ZrO2 nanorods have been reported, except for using annealing the precursor powders originating from the inverse microemulsion system [5] and eggshell membranes as templates while using inexpensive inorganic salts as precursors [6]. The vapor–liquid–solid (VLS) process is a fundamental mechanism for the growth of ZrO2 nanorods similar to other kinds of 1D nanomaterials [7].
Recently, Li et al. [8] reported a useful method of synthesizing silica nanowires via ablation of SiC-containing coating using an oxyacetylene torch. The average diameter of the obtained nanowires was only 150 nm with a length of more than 100 µm. This method could be extended for manufacturing other 1D nanoscale oxide materials by ablation of the corresponding original carbide coatings. To expand the preparation methods of ZrO2 nanorods, here, ZrO2 nanorods are fabricated by ablation of a ZrC nanostructural coating [9] using an oxyacetylene torch. The growth model and mechanism of ZrO2 nanorods are proposed and discussed.
Section snippets
Experimental
The ZrC nanostructure coating was prepared on carbon/carbon (C/C) composites (∅30 mm×10 mm, 1.72 g/cm3, 2D) by chemical vapor deposition (CVD). The experimental procedures were described in our previous papers [10]. The ablation test was carried out in a flowing oxyacetylene torch environment according to the GJB323A-96 Ablation Standard of China with 4200 kW/m2 heat flux [10]. Table 1 shows the ablation parameters of the oxyacetylene torch.
Phase composition and morphology of the coatings before
Results and discussion
The XRD result (Fig. 1a) indicates that the ablation products are mainly composed of monoclinic ZrO2. The ablation morphology of the cross-section in the center region (Fig. 1b) shows some micropores filled by molten ZrO2 in the dense coating after ablation, which results from the release of CO and CO2 produced by the oxidation of ZrC during ablation. Additionally, it should be noted that the ZrO2 layer composed of network nanorods is found firstly on the ablated coating surface (labeled by the
Conclusions
ZrC network nanorods were synthesized without a metal catalyst via ablation of ZrC nanostructure coating using an oxyacetylene torch in this work. The developed VLS and OAG model is proposed to illustrate the growth mechanism of the nanorods. Owing to the formation of ZrO2 nanoparticles, acting as the catalyst and growth site, the appropriate temperature and the supplement of ZrO2 vapor in different regions, the ZrO2 network nanorods can be synthesized with different lengths from the center to
Acknowledgments
This work has been supported by the National Natural Science Foundation of China under Grant nos. 51272213 and 51221001.
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