In-flight Synthesis of Nanosized ZrC Particles from Various Precursors in RF Thermal Plasma

Abstract

Synthesis of zirconium carbide (ZrC) powder was investigated applying a non-conventional atmospheric radiofrequency (RF) thermal plasma process. In one case, zirconium dioxide (ZrO2) was reacted with solid carbon or with methane with varying molar ratio. In the other, zirconium-propoxide (NZP), containing both constituents, was thermally decomposed in the Ar plasma.
 Temperature-dependent thermodynamic analysis was performed in the 500-5500 K temperature range to estimate the formation of possible equilibrium products for each reaction stoichiometry. Broad temperature range exists for the stability of solid ZrC for each explored reaction system. In accordance with this prediction, X-ray diffraction studies detected the ZrC as the major phase in all the prepared powders. The yield of particular runs ranged from 39 % to 98 %. Practically, full conversion was typical for the case of NZP precursor, however only partial conversion could be detected in ZrO2 reactions.
 The average particle size of the powders falls between 10 nm and 100 nm depending on the type of the reaction systems (either calculated from the specific surface area or derived from broadening the XRD reflections). The transmission electron micrographs indicated mostly globular shape of the nanosize particles. Quantitative analysis of the surface of the powders by X-ray photoelectron spectroscopy revealed the presence of oxygen and carbon. Evaluating the spectra of the powders prepared from NZP, and taking in the account its spherical shape, a ZrC core covered by a very thin (≈1.0 nm) ZrO2 layer may be accounted for the measured oxygen and a thicker carbonaceous layer.

Plasma-assisted preparation of nano-(ZrC, ZrO2)@carbon composites from Zr-loaded sulfonated styrene–divinylbenzene copolymers

“…The direct RF plasma treatment of 2-and 8-DVB-Zr samples was not successful due to their high water content and the short residence time of the injected grains in the plasma, which ultimately led to incomplete carbonization. However, RF thermal plasma treatment offers suitable conditions for the dehydrated intermediates for an in-flight reaction between ZrO 2 and carbon [22,55]. For those tests, the 8-DVB-ZrO 2 -1000-2 sample was selected and plasma processing was performed under an inert (He) and reducing atmosphere (H 2 ), respectively.…”

“…Zirconium acetate or zirconium oxychloride can also be reacted with sucrose [19,20]. Sacks et al used zirconium n-propoxide/n-propanol (as a zirconia source) and phenolic resin or glycerol as a carbon source, [21], and Martiz et al used a plasma-assisted synthesis route from analogous starting materials [22]. Scales et al synthesized porous, mechanically stable bead-like ZrC@C composites via carbothermal reduction of polyacrylonitrile-ZrCl 4 composites [3] and quaternary ammonium salt group containing styrene-divinylbenzene copolymers loaded with anionic zirconium complexes [4].…”

Nano-ZrO2@C, Nano-(ZrC, ZrO2)@C and Nano-ZrC@C Composites Prepared by Plasma-Assisted Carbonization of Zr-Loaded Iminodiacetate-Functionalized Styrene-Divinylbenzene Copolymers

“…A recently developed method of synthesizing (nano-ZrC,nano-ZrO 2 )@C composites is the high-temperature or plasma-assisted carbonization of Zr-loaded functionalized polymers. This can be achieved with polyacrylonitrile-ZrCl 4 composites [3] and quaternary ammonium salt or styrene-divinylbenzene copolymers containing a sulfonate group and loaded with anionic [4] and cationic zirconium species [5], respectively, as precursors. The homogeneous distribution of the functional groups allows for zirconium to be bound at an atomic level, enhancing the distribution of ZrC in the carbon matrix after carbonization.…”

“…The chemical nature of functional groups (sulfonate or iminodiacetate) and DVB content in the STY-DVB copolymer have a significant influence on the chemical nature of metal compounds embedded in the carbon matrix during the carbonization of metalloaded, functionalized, styrene-divinylbenzene (STY-DVB) copolymers, [6][7][8]. In fact, ZrC could be prepared by the carbonization of the quaternary ammonium group-containing and anionic Zr-loaded STY-DVB resins at 1350 • C [3], whereas only ZrO 2 @C composites were formed from the sulfonated resins [5]. Due to the moderate reactivity of ZrO 2 in these composites, their subsequent RF plasma treatment in either a He or H 2 atmosphere [5] only resulted in a partial conversion of ZrO 2 into ZrC.…”

“…In fact, ZrC could be prepared by the carbonization of the quaternary ammonium group-containing and anionic Zr-loaded STY-DVB resins at 1350 • C [3], whereas only ZrO 2 @C composites were formed from the sulfonated resins [5]. Due to the moderate reactivity of ZrO 2 in these composites, their subsequent RF plasma treatment in either a He or H 2 atmosphere [5] only resulted in a partial conversion of ZrO 2 into ZrC.…”