Elsevier

Carbon

Volume 42, Issue 1, 2004, Pages 177-182
Carbon

The synthesis and microstructure of morph-genetic TiC/C ceramics

https://doi.org/10.1016/j.carbon.2003.10.008Get rights and content

Abstract

Wood is a natural material with a novel and ordered hierarchical structure. In the present work, it is used as a bio-template to produce morph-genetic TiC/C ceramics. This is obtained by infiltrating the carbon preform pyrolyzed from wood with tetrabutyl titanate. It was subsequently sintered at 1400 °C to produce the final ceramic structure.

By observing the microstructure under the scanning electron microscope and the transmission electron microscope, the morph-genetic TiC/C ceramics are shown retaining the complex morphology of the original template structure. The crystalline TiC was formed through the reaction of tetrabutyl titanate with carbon preform, and it was distributed mainly at the surface layer of the cellular wall. During the conversion of wood into carbon preform, the specific surface area of samples increased from 28.2 to 35.7 m2 g−1, and its porosity also increased from 64.4% to 80.3%. However, during the conversion of carbon preform into morph-genetic ceramics, the specific surface area of samples decreased from 35.7 to 33.8 m2 g−1, and its porosity also decreased from 80.3% to 76.5%. At the synthesis process, the variation of pore-size distribution is mainly in the range from 0.1 to 1 μm.

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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