Niobium and tantalum separation by gas-phase fluorination

Pienaar, A.D.; Wagener, J. B.; Crouse, Philip

doi:10.1016/j.minpro.2012.08.002

Cited by 9 publications

(10 citation statements)

References 9 publications

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“…From the DFT calculations for gas-bulk (R1 and R2) as well as gas–surface reactions –R5, it is proposed that niobium most likely forms the volatile NbOF 3 species. The existence of gaseous NbOF 3 has been previously reported, and its volatility has been studied. − The reaction NbOF 3(s) → NbOF 3(g) is favorable (Δ G < 0) above 140 °C . Moreover, thermogravimetric analysis of NbOF 3 showed mass loss above 80 °C …”

Section: Resultsmentioning

confidence: 93%

“…CCl 4 is used to carry out the halide-exchange reactions with the fluorinated aluminum oxide surface in order to form volatile AlF X Cl Y species. Moreover, CCl 4 is relatively more stable than the trimethyl aluminum (TMA) used in the ALE literature, ,, which decomposes below 400 °C. − Despite NbF 5 being solid, it has sufficient vapor pressure (about 0.1 Torr at 45 °C) and forms volatile species upon fluorinating the Al 2 O 3 surface (at least at 460 °C) and thus leads to almost no surface contaminations. Moreover, it is relatively safer to handle and store and is compatible with the semiconductor vacuum processing equipment.…”

Section: Introductionmentioning

confidence: 99%

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Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

et al. 2021

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Thermal atomic layer etching (ALEt) of amorphous Al2O3 was performed by alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4). The ALEt of Al2O3 is observed at temperatures from 380 to 460 °C. The etched thickness and the etch rate were determined using spectroscopic ellipsometry and verified by X-ray reflectivity. The maximum etch rate of about 1.4 Å/cycle and a linear increase of the removed film thickness with the number of etch cycles were obtained at a temperature of 460 °C. With the help of density functional theory calculations, an etch mechanism is proposed where NbF5 converts part of the Al2O3 surface into an AlF3 or aluminum oxyfluoride layer, which upon reacting with CCl4 is converted into volatile halide-containing byproducts, thus etching away the converted portion of the material. Consistent with this, a significant surface fluorine content of about 55 at. % was revealed when the elemental depth profile analysis of a thick NbF5-treated Al2O3 layer was performed by X-ray photoelectron spectroscopy. The surface morphology of the reference, pre-, and postetch Al2O3 surfaces was analyzed using atomic force microscopy and bright-field transmission electron microscopy. Moreover, it is found that this process chemistry is able to etch Al2O3 selectively over silicon dioxide (SiO2) and silicon nitride (Si3N4).

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Section: Resultsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

et al. 2021

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“…The decomposition of C 2 F 4 in the air was associated with the formation of CO 2 , CO, and COF 2 . The SiF 4 and TaF 5 phases are known to be the most stable fluorides of Si and Ta [80,81]. The melting and evaporation of TaF 5 occurred at 95 and 229 • C, respectively.…”

Section: Sintering Of Tasic-nw Composition: Thermodynamic Analysismentioning

confidence: 99%

Effect of In Situ Grown SiC Nanowires on the Pressureless Sintering of Heterophase Ceramics TaSi2-TaC-SiC

et al. 2020

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To ascertain the influence of SiC nanowires on sintering kinetics of heterophase ceramics, two composite powders (TaSi2-TaC-SiC and TaSi2-TaC-SiC-SiCnanowire) are fabricated by mechanically activated combustion synthesis of Ta-Si-C and Ta-Si-C-(C2F4) reactive mixtures. Remarkable compressibility is achieved for the TaSi2-TaC-SiC-SiCnanowire composition (green density up to 84% as compared with 45.2% achieved for TaSi2-SiC-TaC) which is attributed to the lubricating effect of residual adsorbed fluorinated carbon (most likely C4F8). The outcomes of pressureless sintering of TaSi2-TaC-SiC and TaSi2-TaC-SiC-SiCnanowire compositions are vastly different; the former experiences no significant densification or grain growth and does not attain structural integrity, whereas the latter achieves relative density up to 93% and hardness up to 11 GPa. The SiC nanowires are not retained in consolidated ceramics, but instead, act as a sintering aid and promote densification and grain growth. Sintering mechanisms of TaSi2-TaC-SiC and TaSi2-TaC-SiC-SiCnanowire powders are analyzed using thermodynamic and ab initio grand potential calculations, as well as the analysis of grain size versus relative density relations. In the case of solid-state sintering, the densification and grain growth in heterophase non-oxide ceramics are governed by the same mechanisms as previously investigated single-phase oxides. The presence of SiC nanowires enhances grain-boundary related diffusion processes due to the high specific surface and aspect ratio of the nanowires. At 1500 °C, where the formation of the transient Si-based liquid phase is thermodynamically viable, only the SiC nanowire-containing composition demonstrated the intense grain coarsening and densification associated with liquid-assisted sintering. This effect can be attributed both to the presence of SiC nanowires and purification of residual oxide impurities due to C2F4-activated combustion synthesis employed for the in situ formation of SiC nanowires.

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“…According to the work of Brocchi and Moura (2008) the leaching of a tin slag with HCl increased the niobium and tantalum pentoxide content only from 3.3% and 4.1% to 7.2% and 8.4%, respectively. Dry halogenation methods are often used for the recovery or separation of the halogenated compounds of refractory metals (including tantalum and niobium) from their bearing materials (Allain, 1993;Gaballah, Allain and Djona, 1997;Kanari, Gaballah and Allain, 1999, 2000, 2001Brocchi and Moura, 2008;Adipuri et al 2011;Pienaar, Wagener and Crouse, 2012). This paper summarizes the results of a greener approach for the selective dissolution of the slag amorphous matrix resulting in a (Ta,Nb) 2 O 5 concentrate grade that is comparable to commercial grade mineral concentrates.…”

Section: Introductionmentioning

confidence: 99%

Development of a process for the concentration of the strategic tantalum and niobium oxides from tin slags

Allain

Kanari

Diot

et al. 2019

Minerals Engineering

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The extraction of tin through smelting of cassiterite (SnO 2) has generated considerable amounts of slag in the main production areas of SouthEast Asia, Africa, and South America. Tantalum and niobium naturally occur in cassiterite deposits and are concentrated in the slag during the smelting process. Tin slags have often been disposed as industrial waste despite contents of tantalum and niobium ranging from 2 to 25 %. Conventional hydrometallurgical processes for the concentration of tantalum and niobium oxides utilizing high concentration of strong acids such as HF or H 2 SO 4 are environmentally and economically challenging. This paper describes an original and greener approach for the selective dissolution of the slag amorphous matrix, and the concentration of tantalum and niobium oxides in a solid residue. Starting from a slag containing about 15 % (Ta,Nb) 2 O 5 , sequential alkaline and acid leaching stages resulted in the production of a 63 % (Ta + Nb) oxides concentrate, which is comparable to commercial grade of mineral concentrates.

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Niobium and tantalum separation by gas-phase fluorination

Cited by 9 publications

References 9 publications

Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Effect of In Situ Grown SiC Nanowires on the Pressureless Sintering of Heterophase Ceramics TaSi2-TaC-SiC

Development of a process for the concentration of the strategic tantalum and niobium oxides from tin slags

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Niobium and tantalum separation by gas-phase fluorination

Cited by 9 publications

References 9 publications

Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Effect of In Situ Grown SiC Nanowires on the Pressureless Sintering of Heterophase Ceramics TaSi2-TaC-SiC

Development of a process for the concentration of the strategic tantalum and niobium oxides from tin slags

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Product

Resources

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Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism