Electrochemical synthesis of refractory borides from molten salts

Kaptay, George; Kuznetsov, S. A.

doi:10.1016/s1288-3255(00)87686-8

Cited by 64 publications

(40 citation statements)

References 29 publications

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“…Therefore, an important role in electrolysis is played by the initial stages of crystal nucleation. The results of related investigations for electrodeposited Mo and W were presented earlier [5][6][7]. The initial stages of Mo and W carbide nucleation have not been studied so far.…”

Section: Introductionmentioning

confidence: 99%

Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

2007

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The electrochemical nucleation of Mo 2 C and W 2 C crystals for tungstate-molybdate-carbonate melts of specific compositions on Ag, Au, Cu, Pt, and Ni substrates was studied by the electrodeposition method. The influence of electrocrystallization conditions (temperature, deposition time, initial current pulse, and current density) was investigated. Experimental measurements indicate that crystallization overvoltage is associated with threedimensional nucleation. Carbide deposition onto the substrates prepared from the same solid materials was not associated with crystallization overvoltage. The maximum value of the initial overvoltage, g max , which includes crystallization and electrolysis overvoltages, is proportional to the electrode surface area. Under these conditions, surface diffusion limits the electrode process rate. An increase in carbide deposition rate leads to an increase in the number of crystallization centers. This reduces the duration of surface diffusion. A rise in the melt temperature complicates the crystallization process by alloy-formation phenomena. Overvoltage maximum height for metals, which do not form alloys, is proportional to the reciprocal of their formation time. Melt temperature increase promotes interdiffusion of refractory metal, carbon, and substrate, and also intensifies their chemical interaction. Structural mismatch is observed during molybdenum and tungsten carbide electrodeposition onto different singlecrystal substrates.

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Section: Introductionmentioning

confidence: 99%

Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

2007

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“…Sodium chloride, potassium chloride, sodium fluoride and potassium tetrafluoroborate (all reagent grade, Sigma-Aldrich) were used for the measurements. Prior to experiments, the salt mixture (NaF -9.678 g, KBF 4 -9.678 g, NaCl -42.591 g and KCl -54.210 g) was weighed in a glassy carbon crucible (HTW Hochtemperatur-Werkstoffe GmbH) which was placed in the bottom of the electrolytic cell and thoroughly dried in vacuum at a temperature of 120°C for 99 h. After that the temperature was raised to 300°C and held for 1 h. To enhance the moisture removal, periodic flushing with purified dry argon gas was applied. After that the salts were melted in argon.…”

Section: Methodsmentioning

confidence: 99%

“…The principal advantage of the electrolytic process for simple shape substrates (rods, plates, sheets) is that very high rates of the boride layer growth can be achieved [1]. The electrochemical boriding of metals in molten salts using the cathode discharge of complex fluorides such as KBF 4 from a fluoride bath is known to be an interesting method of obtaining very hard layers on the surface [2]. Molten salts generally can be considered as a very promising medium for chemical and electrochemical synthesis of different compounds.…”

Section: Introductionmentioning

confidence: 99%

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Increasing the Surface Hardness of Cast Iron by Electrodeposition of Borides in Molten Salts

Al-Azzawi¹,

Sytchev²,

Baumli³

2017

Archives of Metallurgy and Materials

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In this paper the electrodeposition of boron on the surface of cast iron as a coating is applied to increase the hardness and protect the substrate against abrasive wear. The boron containing coating was synthesized by electrodeposition process from a NaCl-KCl (1:1 mol)-10 w%NaF-10w% KBF 4 molten salt. The effect of electrolysis parameters (temperature and time) on the hardness is presented; the current density varied in the range -37 --4.5 mA/cm 2 , allowing perfect coverage of and respect for dimensions. The electrochemical process was carried out at different temperatures (750°C-900°C) and for different periods of time (5-10 hours). Depending on the current density and duration of electrolysis, the deposits consist of FeB or Fe 2 B. Microhardness measurements across the boride layer indicated very high hardness values (between 1600 and 2100 HV0.05).The structure of the boride layer is linked to its boron content and thermal history: as-deposited coatings present very small grain sizes and can be considered as nearly amorphous.

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“…If the substrate is a metal or a metal alloy the boronizing process results in refractory metal borides on the surface [2]. The boronizing process can be carried out thermally [3,4] or by the electrolysis of molten boron salts [5,6]. Both these processes take place at elevated temperatures [7].…”

Section: Introductionmentioning

confidence: 99%

Mechanism of boron tribromide electroreduction

et al. 2009

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This study was carried out to investigate the electrochemical behavior of boron tribromide in dimethlyformamide. The reduction of the compound was found to follow a CE mechanism. The kinetic parameters and the diffusion coefficient were calculated by the use of ultramicrodisc electrodes and chronoamperometry. The number of electrons transferred was found to be 2 by rotating disc and ultramicro disc electrodes and 3 by coulometry. These results are in good accordance with those obtained from molten boron salts. This study is important in regard to electrochemical boronizing at low temperatures.

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Electrochemical synthesis of refractory borides from molten salts

Cited by 64 publications

References 29 publications

Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

Increasing the Surface Hardness of Cast Iron by Electrodeposition of Borides in Molten Salts

Mechanism of boron tribromide electroreduction

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