The Effect of Sc2O3 on the Physicochemical Properties of Low-Melting Cryolite Melts КF–AlF3 and КF–NaF–AlF3

Zaikov

2019

The main kinetic features of the aluminum and scandium electrowinning during the electrolysis of the KF-AlF 3 -Al 2 O 3 -Sc 2 O 3 melts were studied by means of voltammetry, stationary polarization, as well as electrolysis. Aluminum electrowinning from the KF-AlF 3 -Al 2 O 3 melt on tungsten cathode occurs in the potential range from −0.1 to −1.3 V relative to the potential of the aluminum electrode. Replacing Al 2 O 3 by Sc 2 O 3 in KF-AlF 3 melts leads to a co-electrowinning of aluminum and scandium with the same kinetic parameters. Based on the electrochemical measurements, the parameters of stable galvanostatic electrolysis of the melts under study were selected and electrolysis tests were carried out to obtain Al-Sc master alloys. The cathode current efficiencies during co-electrowinning of aluminum and scandium on tungsten were evaluated, and the microstructure of the obtained Al-Sc master alloys was studied. A novel approach for the synthesis of the Al-Sc master alloys proposed that includes the electrolysis of the KF-AlF 3 -based melts with the addition of Al 2 O 3 and Sc 2 O 3 , electrowinning of aluminum and scandium on a solid cathode, and dissolution of formed cathode deposit in liquid aluminum.

Section: Methodsmentioning

confidence: 99%

Electrowinning of Aluminum and Scandium from KF-AlF₃-Sc₂O₃ Melts for the Synthesis of Al-Sc Master Alloys

Nikolaev

Zaikov

2019

“…-measuring directly in the electrolytic cell a property or parameter of the investigated system, reliably and reasonably correlating with the concentration of alumina dissolved in the melt; -analysis of melt samples taken from the electrolytic cell by physicochemical methods. -The following methods are used for studying the solubility and kinetics of alumina dissolution in cryolite: -potentiometry (according to the emf of the concentration element) [6][7][8][9] ; -the method of a rotating disk electrode 10,11 ; -linear and square-wave voltammetry (according to the peak of the anode current) [12][13][14][15] ; -chronopotentiometry (in transition time) [16][17][18] ; -thermal analysis (by liquidus temperature) [19][20][21][22] ; -impedance spectroscopy (by resistance or electrical conductivity of the melt) [23][24][25] ; -stationary polarization (by anode overvoltage) 26,27 ; -optical method (by changing the structure of the melt) 28 ;…”

mentioning

confidence: 99%

Electrochemical Sensor for Monitoring the Alumina Dissolution and Concentration in a Cryolite-Alumina Melt

Nikolaev

Pavlenko

et al. 2020

The alumina dissolution in a cryolite-alumina melt was studied by voltammetry using a new design of the electrochemical sensor. It consisted of a working carbon electrode, shielded with a pyrolytic boron nitride tube, and the counter electrode, forming an alloy with aluminum, with a developed surface. The difference of such electrochemical measuring devices from the known designs is the use of a copper counter electrode (cathode), which forms an alloy with the deposited aluminum. It allows excluding the measurement error associated with the depolarizing effect of the dissolved aluminum. The alumina dissolution process in the NaF-AlF 3 -(5 wt%)CaF 2 -Al 2 O 3 melt with a molar ratio of [NaF]/[AlF 3 ] = 2.1 mol mol −1 at 995 °C and the alumina concentration from 0.7 to 4.5 wt% was investigated. According to the linear calculation, the integral alumina dissolution rates varies from 0.02 to 0.35 mol s −1 depending on the initial alumina concentration in the melt. The differential rates of the alumina dissolution for the initial moments of time (0.1-5 s) were also estimated from the obtained empirical dependencies. Its maximum values for equal additions of alumina in the concentration range from 1.2 to 2.8 wt% were from 24 to 37 mol s −1 .

“…8 in the form of fluoride-oxide quasi-binary phase diagrams. 65,66 At the same concentration of NaF the solubility of Sc 2 O 3 is higher in melts with CR = 1.5. In this case, the liquidus temperature of the melt at the Sc 2 O 3 content of 2 mol% is higher by 25-50 degrees.…”

Section: Interaction Of Oxides With Kf-naf-alf 3 Meltsmentioning

confidence: 99%

“…According to the results of XRD analysis during the Sc 2 O 3 dissolution in KF-NaF-AlF 3 melts KScF 4, NaScF 4 и ScAlO 3 72 compounds are formed, while on the basis of the data 66 the assumption that products of Sc 2 O 3 dissolution in NaF-AlF 3 melts are AlF 6…”

Section: Interaction Of Oxides With Kf-naf-alf 3 Meltsmentioning

confidence: 99%

See 1 more Smart Citation

Review—Synthesis of Aluminum Master Alloys in Oxide-Fluoride Melts: A Review

Pershin

Филатов

et al. 2020

Self Cite

A review of the existing methods for producing aluminum master alloys with silicon, zirconium, scandium and boron are given. Basic parameters, advantages and disadvantages of the existing methods are analyzed, indicating the need to develop new more energy-efficient technologies. The prospects of obtaining aluminum master alloys in the electrolysis of melts based on the KF-NaF-AlF 3 -Al 2 O 3 -MeO (MeO = SiO 2, ZrO 2 , Sc 2 O 3 , and B 2 O 3 ) system are considered. For this purpose, the results of physical and chemical measurements in these melts are presented, including data on the solubility of Al 2 O 3 , SiO 2, ZrO 2 , Sc 2 O 3 , and B 2 O 3 oxides in KF-NaF-AlF 3 melts, data on the effect of oxide additives on the liquidus temperature of studied melts, as well as data on the kinetics of electrowinning of aluminum and alloying element from KF-AlF 3 -Al 2 O 3 -MeO melts. Based on the measurements, the parameters were selected and electrolysis tests were carried out for obtaining aluminum master alloys with silicon, zirconium, scandium, and boron from its oxides. The composition and structure of the obtained master alloys were studied.