Chemical vapor deposition of C on SiO2 and subsequent carbothermal reduction for the synthesis of nanocrystalline SiC particles/whiskers

https://doi.org/10.1016/j.ijrmhm.2011.03.005Get rights and content

Abstract

This study investigates chemical vapor deposition of C from CH4 on particulate SiO2 and subsequent carbothermal conversion of the resultant composite particles to SiC powders. Mass measurements, HR-TEM, SEM and XRD were used to characterize the products at various stages of the processes. It was found that oxide particles gained mass rapidly at 1300 K under CH4 atmosphere owing to enhanced C uptake. Pyrolytic carbon layers 5–8 nm thick were deposited on SiO2 particles. The coated powders with high C loadings (40–42.6 wt.% C) were converted to SiC under Ar flow in a temperature range of 1700–1800 K. Almost pure SiC powders containing a mixture of particles and whiskers of ~ 100 nm were synthesized at 1750 K for 45 min and at 1800 K for 30 min using the starting powder with 40 wt.% C. Whisker diameter increased with the C content of the coated powder. It was proposed that SiC whisker was grown by a vapor–solid mechanism. Equilibrium thermodynamic analysis by the method of minimization of Gibbs’ free energy predicted the reaction pathways to SiC and to the product species in the Si–O–C–Ar system. This study demonstrated that either C shell-SiO2 core powders or SiC powders could be synthesized rapidly in the same reactor.

Graphical abstract

Pyrolytic C shells 5–8 nm thick were grown on particulate SiO2 by chemical vapor deposition technique using CH4 at 1300 K. Mixtures of SiC particles and whiskers of ~ 100 nm were synthesized from the coated powders at 1750 and 1800 K. Either C shell-SiO2 core composite or SiC powders could be obtained rapidly in the same reactor.

  1. Download : Download full-size image

Research highlights

►Carbon layer 5–8 nm thick was formed on SiO2 particles at 1300 K under CH4 flow. ►Pyrolytic C shell/SiO2 core nanocomposite powder with high C loading was attained. ►SiC particles/whiskers of ~ 100 nm were produced from C shell-SiO2 core powder. ►Both material could be synthesized in the same reactor using CH4 as a carbon source. ►Gibbs free energy minimization method is useful to better understand processes.

Introduction

Because silicon carbide (SiC) has a high melting point, good oxidation resistance, high thermal stability and high hardness, it has been exploited in many areas including abrasives, varistors, armor, catalyst supports. SiC particles or whiskers are incorporated into metallic and ceramic matrices as a reinforcement component to produce advanced composites.

SiC powder is commercially produced by Acheson process which involves carbothermal reduction of SiO2 by C at 1873–2373 K [1]. It, however, requires high temperatures and long reaction times because of sluggish reaction rates between separate precursors leading to coarse powders. Subsequent prolonged milling reduces powder particle size, but it introduces impurities into SiC. Since demands for nanosized ceramic powders have increased due to improved properties (such as better densification, higher hardness and lower wear rate) in the products produced from them [2], numerous processes have been developed for the synthesis of the materials. The approaches [3], [4], [5], [6], [7], [8], [9], [10] for SiC essentially focus on the use of precursors which provide close contact between the reactants to enhance SiC formation reactions at low temperatures. Saito et al. [3] synthesized SiC whiskers with a mean diameter of 500 nm by vapor phase reactions between SiO and CO without catalyst, while Kennedy and North [4] obtained SiC particles by reaction of gaseous SiO with particulate carbon. Koc and Cattamanchi [5] used C3H6 (propylene) and silica to produce fine SiC particles of 100–300 nm. They reported that silica particles were coated with carbon by thermal cracking of the hydrocarbon at elevated pressure and at 873 K. It was also stated that thirty cycles, each lasting ~ 20 min, were necessary to achieve the amount of carbon required for subsequent carbothermal conversion of SiO2 to SiC, which was carried out in a separate vessel. Multicycle C coating process and the use of a different reactor for the carbothermal reduction seem to limit mass production of the powder. Recently, fine SiC powders have been synthesized by other techniques such as thermal plasma [6], direct reaction between silicon and carbon [7], combustion synthesis [8], high-energy ball-milling [9] and mechanically activated carbothermic reduction [10]. These approaches, however, involve complex, time consuming processes or high cost precursors.

Carbon shell–silicon oxide core composite powders have received considerable attention for tribological applications [11]. Recently, Vital et al. [12] produced C–SiO2 nanocomposite particles with carbon loading of maximum 14 wt. % by flame synthesis and studied their carbothermal conversion to SiC. Extra carbon was, however, needed to complete the carbothermal reduction at 1773 K within 2 h. Hence, it is worthy of studying carbon coating processes using different techniques and precursors for possible alternative routes to carbon encapsulated SiO2 particle synthesis.

It appears that a fast, simple and economical process for producing C–SiO2 composite powders with high carbon loading and fine SiC powders is presently needed. The current study shows that both powders can be synthesized in the same reactor within a short time by allowing CH4 flow during heating to 1300 K and by switching to Ar flow at higher temperatures. We used CH4 (natural gas) as a carbon source because it is relatively cheap and abundant. Hence, the process described here has inherent advantages including a simple flexible synthesis procedure, low cost carbon source and short reaction time, providing a sound rationale for massive productions of either C–SiO2 nanocomposite powders or nanocrystalline SiC powders. Consequently, the present work was undertaken to establish optimal conditions for the syntheses of these materials by chemical vapor deposition of C on SiO2 particles from CH4 and by carbothermal conversion of the C coated powders to SiC.

Section snippets

Experimental procedures

The experimental set-up used for the present study essentially consists of a hot-wall tubular (20 mm in diameter) alumina furnace equipped with SiC heating elements and gas flow meters. The chemicals used were SiO2 (99.5%) powder (Sigma-Aldrich), high purity argon (99.999%) and methane (99.5%). Particle size of the SiO2 powder was reported to be 10–20 nm by the producer. The alumina boat with gas entrance side cut to allow smooth gas flow was loaded with the powder. The boat was placed at the hot

Chemical vapor deposition of C on particulate SiO2

Fig. 1 displays the non-isothermal variation of the sample mass heated to the temperatures up to 1300 K under CH4 flow. Initial mass change during heating is observed to be slightly below zero, suggesting that there is oxide loss. The samples slowly gain mass with temperature increasing to 1200 K due to carbon uptake. The color of the products changed progressively from white at 800 K to black at 1200 K. The mass change increases rapidly to the level of 54% during heating to a higher temperature of

Conclusions

SiO2 particles gained mass rapidly during heating under CH4 atmosphere owing to enhanced CH4 pyrolysis at 1300 K. Pyrolytic C shell/SiO2 core nanocomposite particles with high C loadings (40–50wt.%) were synthesized in a short time (< 5 min) by chemical vapor deposition of C from CH4 on particulate SiO2. HR-TEM images of the product containing 42.6wt.% C revealed that pyrolytic carbon layer 5–8 nm thick was grown on SiO2 particles. Carbothermal reactions in the coated powders with slightly

Acknowledgements

This work was supported by the Scientific Research Projects Coordination Unit of Istanbul University through the project numbered 1453. It was partially based on a Ph. D. thesis pursued by S. Cetinkaya.

Dr. Cetinkaya received his B.Sc., M.Sc. and Ph.D. degrees in Metallurgical and Materials Engineering from Istanbul University in 2001, 2005 and 2011, respectively. He is currently a research assistant at Istanbul University. He specialized on powder metallurgy and material synthesis by vapor phase reactions.

References (19)

There are more references available in the full text version of this article.

Cited by (43)

  • Occurrence forms of major impurity elements in silicon carbide

    2022, Ceramics International
    Citation Excerpt :

    Recently, SiC production has substantially increased due to its applications in high-temperature nozzles, turbine rotors, diesel engines, optical components, atomic thermal reactor materials, and other fields [9–13]. Numerous methods, such as sol–gel methods [14–16], chemical vapour deposition [17,18], molten salt methods [19,20], laser pyrolysis [21], self-propagating high-temperature synthesis [22], combustion synthesis [23–25], thermal plasma [26,27], and microwave synthesis [28,29], have been developed to synthesise SiC powders. However, most of these techniques present various drawbacks, including the high production costs and low yield, which limit their application for large-scale production.

  • Preparation and characterization of mesoporous SiC/SiO<inf>2</inf> composite nanorods

    2020, Materials Chemistry and Physics
    Citation Excerpt :

    What's more, SiC nanowires are effective not only for applications as additive of reinforcement but for field emission and nanoelectrical devices. One-dimensional SiC nanostructures can be produced by many processes [8–12]. Commercially, they are prepared by chemical vapor deposition (CVD) through thermal decomposition of silianes and thermal reduction of silicon oxides.

View all citing articles on Scopus

Dr. Cetinkaya received his B.Sc., M.Sc. and Ph.D. degrees in Metallurgical and Materials Engineering from Istanbul University in 2001, 2005 and 2011, respectively. He is currently a research assistant at Istanbul University. He specialized on powder metallurgy and material synthesis by vapor phase reactions.

Dr. Eroglu received his B.Sc. from Istanbul Technical University in 1982. He earned his M.Sc. and Ph.D. degrees in 1986 and 1991 at Stevens Institute of Technology, NJ. He was a teaching assistant at the same institute. He worked at Marmara Research Center mainly in the field of powder metallurgy. He was with Penn State University in 1994 and with Rutgers University in 2000 as a Visiting Scientist. He now works at the Dept. Metallurgical and Materials Engineering in Istanbul University as a professor since 2006. He published papers on chemical vapor deposition, thermodynamic and XRD analyses of thin films and powder metallurgy.

View full text