RU2466217C1 - Electrolytic method of obtaining ultrafine powder of gadolinium hexaboride - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: Anhydrous gadolinium trichloride is used as gadolinium source, potassium fluoroborate is used as boron source, and equimolar mixture of potassium and sodium chlorides is used as base electrolyte. Electrolysis is carried out in potentiostatic mode at temperature of 700±10°C, current densities of - 0.1 to - 1.0 A/cm² and electrolysis potential of - 2.6 to -2.8 V relative to glass-carbon quasi-stationary comparison electrode.

EFFECT: obtaining pure ultrafine powder of gadolinium hexaboride; increase in synthesis rate of target product from molten electrolyte and reduction of costs.

2 cl, 3 ex

Description

The invention relates to electrolytic methods for producing pure gadolinium hexaboride.

The closest is a method for producing gadolinium hexaboride using electrolysis of molten media [G. Samsonov Refractory compounds of rare earth metals. M .: Publishing house "Metallurgy", 1964, p. 53-55]. Electrolysis is carried out in graphite crucibles, which simultaneously serve as an anode; the cathode is made of graphite or molybdenum. The composition of the bath for electrolysis includes oxides of rare earth metals and boric anhydride with the addition of alkali and alkaline earth metal fluorides to reduce the temperature and viscosity of the bath. The electrolysis temperature of the mixtures is 950-1000 ° C, the voltage on the bath 3-15 V, the current density of 0.3-3.0 A / cm ² . The composition of the bath to obtain gadolinium hexaboride: Cd ₂ O ₃ + 2B ₂ O ₃ + MgO + MgF.

As noted [G. Samsonov Refractory compounds of rare earth metals. M .: Publishing house "Metallurgy", 1964, p. 53-55], obtaining an individual boride phase is almost impossible or very difficult. The disadvantages are the high synthesis temperature and the difficulty of separating the target product from the molten electrolyte due to the low solubility of borates and fluorides, contamination by-products, such as borates.

The objective of the invention is to obtain a pure ultrafine powder of gadolinium hexaboride, increasing the rate of synthesis of the target product from the molten electrolyte and reducing energy consumption.

The essence of the invention lies in the fact that there is a joint electrowinning of gadolinium and boron from a chloride melt at the cathode and their subsequent interaction at the atomic level with the formation of ultrafine powders of gadolinium hexaboride. The process is carried out in a three-electrode quartz cell, where a tungsten rod is used as a cathode; reference electrode - glassy carbon plate; the anode and at the same time the container is a glassy carbon crucible (alundum crucible was also used as a container for melt and a glassy carbon plate as an anode).

The ultrafine gadolinium hexaboride powder is synthesized by potentiostatic electrolysis from an equimolar KCl-NaCl melt containing gadolinium trichloride and potassium fluoroborate. Potentiostatic electrolysis of the equimolar melt KCl-NaCl-GdCl ₃ -KBF _{4 is} carried out on a tungsten electrode in the range from -2.6 to -2.8 V relative to the glassy carbon quasistationary reference electrode. The synthesis is carried out in an atmosphere of purified and dried argon. The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride.

Anhydrous gadolinium trichloride is used as a gadolinium source, potassium fluoroborate is used as a boron source, and an equimolar mixture of potassium and sodium chlorides is used as a background electrolyte in the following ratio of components, wt.%:

gadolinium chloride 5.0-6.5

potassium fluoroborate 7.5-10.5

the rest is an equimolar mixture of potassium and sodium chlorides.

The electrolysis is carried out in potentiostatic mode at a temperature of 700 ± 10 ° C, optimal for this solvent. It is possible to carry out synthesis at a higher temperature, however, an increase in temperature leads to evaporation of the melt, an increase in the vapor pressure above the melt, and a loss of potassium fluoroborate due to its thermal instability.

The components of the electrolytic bath were selected based on thermodynamic analysis and kinetic measurements of the combined electrowinning of gadolinium and boron from chloride melts. Of the oxygen-free gadolinium and boron compounds, gadolinium chloride and potassium fluoroborate are fairly low melting and well soluble in the equimolar KCl-NaCl melt. This background electrolyte is selected from the following considerations: the decomposition voltage of the molten KCl-NaCl mixture is greater than the decomposition voltage for the GdCl ₃ and KBF ₄ melts; moreover, alkali metal chlorides are highly soluble in water.

The phase composition was identified by X-ray phase analysis on a DRON-6 diffractometer, the results observed the presence of only the GdB ₆ phase.

Example 1. In a glass-carbon crucible with a volume of 40 cm ^{3 was} placed a salt mixture weighing 38.37 g, containing 2.1 g of GdCl ₃ (5.5 wt.%); 3.01 g of KBF ₄ (7.8 wt.%); 18.63 g of KCl (48.6 wt.%); 14.63 g of NaCl (38.1 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts (700 ± 10 ° С). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.6 ÷ -2.8 V relative to the glassy carbon reference electrode (current density - 0.80 A / cm ² ), the duration of the electrolysis is 110-120 minutes The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The specific surface of GdB ₆ powders is 5 ÷ 10 m ² / g.

Example 2. In a glass-carbon crucible with a volume of 40 cm ^{3 was} placed a salt mixture weighing 38.1 g, containing 2.3 g of GdCl ₃ (6.0 wt.%); 3.3 g KBF ₄ (8.7 wt.%); 18.2 g of KCl (47.8 wt.%); 14.3 g of NaCl (37.5 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts (700 ± 10 ° С). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.7 ÷ -2.9 V relative to the glassy carbon reference electrode (current density - 0.85 A / cm ² ), the duration of the electrolysis is 110-120 minutes The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The specific surface of GdB ₆ powders is 5 ÷ 10 m ² / g.

Example 3. In an alundum crucible with a volume of 60 cm ^{3, a} salt mixture weighing 51.13 g containing 2.8 g of GdCl ₃ (5.5 wt.%) Was placed; 4.0 g KBF ₄ (7.8 wt.%); 24.83 g of KCl (48.6 wt.%); 19.5 g of NaCl (38.1 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts (700 ± 10 ° С). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.7 ÷ -2.9 V relative to the glassy carbon reference electrode (current density -0.9 A / cm ² ), the duration of the electrolysis is 110-120 minutes The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The specific surface of GdB ₆ powders is 5 ÷ 10 m ² / g.

The technical result is to obtain a pure ultrafine powder of gadolinium hexaboride, increasing the synthesis rate of the target product from the molten electrolyte and reducing energy consumption.

Claims (2)

1. The electrolytic method for producing ultrafine powder of gadolinium hexaboride, including the synthesis of gadolinium hexaboride from molten media, characterized in that the synthesis is carried out from a chloride melt in an atmosphere of purified and dried argon, anhydrous gadolinium chloride, a source of boron fluoride, boron fluoride are used as a gadolinium source electrolyte - equimolar mixture of potassium chloride and sodium chloride in the following ratio of components, wt.%:
gadolinium chloride 5.0-6.5 potassium fluoroborate 7.5-10.5 equimolar mixture of potassium and sodium chlorides rest 2. The method according to claim 1, characterized in that the synthesis is carried out at a temperature of 700 ± 10 ° C, current densities from -0.1 to -1.0 A / cm ² and electrolysis potentials from -2.6 to -2, 8 V with respect to the glassy carbon quasistationary reference electrode.