Fast synthesis of TaC under high energy conditions

Andrzej Huczko 2Olga M. Łabędź 1Jakub Nowiński 

1. Uniwersytet Warszawski, Wydział Chemii, Warszawa, Poland
2. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland

Abstract

Among the high-melting carbides, tantalum carbide is an industrially significant and attractive candidate because of its exceptional high hardness, thermal and high corrosion resistance, and catalytic properties [1]. Classical chemical procedures to synthesize TaC involve reactions of metal, metal oxide or any suitable Ta precursor with carbon sources. The long-lasting process is always performed at high temperature (from 1000 oC up to 2000 oC). It is well known, however, that TaC is a difficult material to make using conventional techniques [2]. We propose here fast one-step formation of TaC under high energetic conditions, i.e. using either (i) plasma or (ii) combustion activation of reactants. The microstucture of the products was examined using SEM and TEM, while phase composition was determined via X-ray diffraction.

Regarding the plasma synthesis of TaC, the DC arc system generating carbon vapors commonly used to produce fullerenes, carbon nanotubes and encapsulates was used [3, 4]. Two types of arc sublimated anodes were used: heterogeneous and homogeneous. To prepare the first type, graphite rods were drilled and filled with mixtures of fine graphite and Ta powders with two different ratios (5 and 55 wt % of Ta in respect to the total graphite). The homogenous anodes used for the experiments were also prepared using the same Ta/C ratio and also Ta2O5/C composition (Ta content 45 wt%). A tar pitch was added as a binding agent. The as prepared mixtures were then pressed under 2 MPa pressure to form rods of 8 mm in diameter and 30 mm in length. Next, the rods were calcinated under Ar atmosphere at 1000ᵒC for 10 hours to ensure the complete removal of all organic components of the tar pitch.

The arcing was carried out in He atmosphere, at a current value of 80-120 A in the case of heterogeneous electrodes, and 70-80 A while using the homogenous ones. The pressure in the reactor was kept at a constant value of 10 or 80 kPa. In all runs the rubbery sooth was collected from the lid and walls of the water-cooled reactor. For the experiments where Ta2O5 was used, the product had a web-like structure (formerly found in case of a high content of 1D carbon nanostructures).

In the last two decades the method known as self-propagating high-temperature synthesis (SHS), or combustion synthesis, has become an attractive method of producing advanced materials [5]. This high-temperature redox technique, when compared to traditional processing routes has the advantages of being extremely time- and energy- efficient. SHS was also successfully applied for one-step synthesizing SiC nanofibers [6]. The following Ta-containing compositions were combusted: TaSi2/PTFE, Ta/PTFE, TaCl5/C10H8, and TaCl5/C14H10. All experiments were performed in high-pressure stainless-steel reactor. A green stoichiometric mixture of the reactants was homogenized in an agate mortar. After the reactants were placed in the reactor and the desired pressure (0,1 MPa) of  Ar atmosphere was obtained in the combustion chamber, the reaction was initiated using the carbon filament. The combustion was completed usually within the fraction of a second. All compositions were successfully combusted yielding black fine powders.

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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 9, by Olga M. Łabędź
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-06-11 11:55
Revised:   2013-06-12 15:57
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