The synthesis and microstructure of morph-genetic TiC/C ceramics
Introduction
Recently, it was reported in the literature [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] that natural materials with special structure like wood, jute, bamboo, rice husks and coconut shells were utilized as a bio-template to produce porous materials. In comparison with artificial synthetic templates, natural materials exhibit a hierarchically built anatomy, developed and optimized in a long-term evolution process, and are considered cheap, abundant, renewable and environmentally conscious. The porous materials, which are obtained by infiltrating with various organic or inorganic solutions and then sintering at high temperatures, maintain the original cellular and open porous morphology of biological structures. This hierarchical characteristic offers porous ceramics a promising industrial application, such as catalysis, filter, selective separations and absorbents. This structural–functional designs or processing approaches with creative and biological conception may offer significant improvement in performance over more traditional designs and fabrication methods.
The fabrication of porous silicon carbide ceramics with wood templates was reported earlier. Ota et al. [9] produced SiC ceramic with a wood-like microstructure by vacuum-infiltration charcoal with tetraethyl orthosilicate (TEOS). After TEOS hydrolysis, SiO2 gel was reacted with charcoal at 1400 °C in Ar to form α-SiC in the cellular wall. Greil et al. [11], [12], [13], [14], [15] reported the study of converting the carbon template into porous SiC ceramic by a rapid liquid Si infiltration-reaction process at 1600 °C. These approaches improved the mechanical properties such as compression and bending strength. However, most of the residual pores were filled with excessive Si and led to the sharp decrease of porosity in the final products [16]. And moreover, in the silicified wood tissues, the silicate minerals were deposited in the inner space of the cellular wall and produced small pieces of negative cast or a replica of the cell aggregates [17], [18].
In the present study, we have developed a method to fabricate the morph-genetic TiC/C ceramics with wood templates by infiltrating with tetrabutyl titanate followed by sintering at high temperatures. In this process, the ordered structure of wood is replicated well, and only a few pores were still filled with the remaining reactant in the morph-genetic TiC/C ceramics. The changes of pore-size distribution of the original wood template, the carbon preform and the morph-genetic TiC/C ceramic are also studied.
Section snippets
TiC/C ceramic synthesis
The pine was selected mainly as a raw material. After drying at 80 °C for 24 h, the wood specimens were first changed to carbon preform at 650 °C for 2 h. The morph-genetic TiC/C ceramics were subsequently produced by impregnating the carbon preform with tetrabutyl titanate (content: >98%, density: 0.999–1.003 g/ml). It was then sintered in vacuum furnace at various temperatures. The processing scheme is summarized in Fig. 1.
Characterization
The phases of morph-genetic ceramics were identified by X-ray
XRD analysis
The typical X-ray diffraction patterns of the morph-genetic materials after the various treatments of tetrabutyl titanate infiltration, hydrolysis, drying and by firing at various temperatures are shown respectively in Fig. 2.
It demonstrates that the tetrabutyl titanate was firstly decomposed to anatase-type titania with a small amount of rutile-type titania at 800 °C. The reactions are shown in Eqs. , . And then anatase-type titania was converted into rutile-type titania with temperature
Conclusions
Wood is a natural material with novel and ordered hierarchical structure. Based on its unique intrinsic structure, the morph-genetic TiC/C ceramics was obtained through infiltration with tetrabutyl titanate, and by sintering at high temperatures. It exhibited a good replica of integral cellular structure of original wood template. The crystalline TiC obtained by the reaction between TiO2 and carbon preform was distributed on the surface layer of the cell wall. The original uniform pore
Acknowledgements
The authors wish to express thanks to the financial support of the National Natural Science Foundation of China (NSFC) (No. 50271041), “863” Program (No. 2002AA334030), Research Fund for the Doctoral Program of Higher Education, Research Fund of Science and Technology Commission of Shanghai Municipality and Excellent Young Teacher Program of MOE, P.R. China.
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2020, Materials Today BioCitation Excerpt :It has to be finally mentioned that the results reported in the present study indicate that outstanding mechanical properties could be obtained for materials different from BA but obtained with a process similar to that used for BA, which can therefore be used as a guide for the fabrication of a new generation of inorganic materials with significant improvement in structural performance. This perspective is encouraged by previous results obtained with the chemical transformation of natural woods into various oxide (for instance, Al2O3, ZrO2, TiO2, and MnO) [33–37], and non-oxide (for instance, SiC, TiC, and ZrC) [38–42] ceramics, which are particularly relevant for structural applications. Nanotwinned HA lamellae are a unique nanostructure characterizing BA [28] and form a complex multiscale porosity, where large pores (approximately 300 μm in diameter) are surrounded by medium-sized pores (up to 50 μm in diameter) and coexist with a distributed fine porosity (1 μm of diameter) (see the scanning electron microscopy image in Fig. 2).