The Behavior of KBF 4 in Potassium-Cryolite-Based Melts

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 .

mentioning

confidence: 99%

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

Nikolaev

Pavlenko

Suzdaltsev

et al. 2020

“…The decomposition temperature is much lower than that of LiBF 4 (above 300 °C) 21 and KBF 4 (530 °C). 22 The Mg(CF 3 BF 3 ) 2 , Mg(C 2 F 5 BF 3 ) 2 and Mg(CF 3 OC 2 F 4 BF 3 ) 2 showed a higher stability and their residual weight is greater than that of Mg(BF 4 ) 2 . However, this result conflicts with the weight ratio of MgF 2 in these salts.…”

Section: Resultsmentioning

confidence: 87%

Preparation of Magnesium Salts Composed of Perfluoro Anions and These Electrochemical Behaviors in Molten Salts

Kubota

Matsumoto

2020

Magnesium secondary batteries are expected to be one of the popular post-lithium ion batteries due to their high capacity and the bountiful resources of this element. Reversible plating by the reduction of Mg 2+ and stripping by the oxidation of Mg metal are critical problems for this battery. In this study, we attempted to investigate the dependence of the Mg plating/stripping behavior on the anion species. Various Mg salts containing perfluoro anions were synthesized and their thermal stabilities were measured by thermogravimetry. For the Mg salts possessing a high thermal stability, Mg molten salt electrolytes were developed with potassium or cesium salts having common anions and their plating/stripping behaviors were investigated.

“…A significant pressure of BF 3 vapors above the KF-AlF 3 melt was noted in the work. 83 In this case, it could seem that the solubility of B 2 O 3 is higher than the solubility of Al 2 O 3 in KF-AlF 3 melts (Fig. 14), although part of the boron leaves the melt as BF 3 .…”

Section: [ ]mentioning

confidence: 88%

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

Suzdaltsev

Pershin

Филатов

et al. 2020

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.