RU2507314C1 - Electrolytic method of producing ultrafine gadolinium hexaboride powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: powder is synthesised by electrolysis from a molten medium which includes gadolinium chloride and calcium fluoroborate in a background electrolyte at temperature of 550±10°C in an atmosphere of purified and dried argon. The background electrolyte used is a eutectic mixture of potassium, sodium and caesium chlorides, with the following ratio of components, wt %: gadolinium chloride 3.0-7.0, potassium fluoroborate - 6.0-10.0, eutectic mixture of potassium, sodium and caesium chlorides - the balance.

EFFECT: invention enables to obtain pure ultrafine gadolinium hexaboride powder, increases the rate of synthesis of the end product from a molten electrolyte and reduces power consumption.

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Description

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

The closest is the method of producing gadolinium hexaboride by electrolysis of molten media [Kushkhov Kh.B., Uzdenova A.S., Mukozheva R.A., Vindizheva M.K., Salekh M.M.A. Electrolytic method for producing ultrafine gadolinium hexaboride powder. Application No. 2011120024/07 (029576) Decision on the grant of a patent dated 02.21.2012]. Electrolysis is carried out in a glassy carbon crucible, which simultaneously serves as the anode or alundum crucible; the cathode is made of tungsten. The electrolysis bath contains gadolinium chloride and potassium fluoroborate; an equimolar mixture of sodium and potassium chlorides served as the background electrolyte. The temperature of the electrolysis of the mixtures is 690-710 ° C, the voltage on the bath is from -2.6 to -2.8 V, the current density is 0.1-1.0 A / cm ² . The composition of the bath to obtain gadolinium hexaboride: GdCl ₃ + KBF ₄ + NaCl + KCl.

The disadvantages of this method are the high temperature synthesis.

The objective of the invention 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.

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-CsCl melt containing gadolinium trichloride and potassium fluoroborate. Potentiostatic electrolysis of the equimolar melt KCl-NaCl-CsCl-GdCl ₃ -KBF _{4 is} carried out on a tungsten electrode in the range from -2.4 to -2.6 V relative to a 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 a eutectic mixture of potassium, sodium and cesium chlorides is used as a background electrolyte in the following ratio of components, wt.%:

gadolinium chloride 3.0 ÷ 7.0;

potassium fluoroborate 6.0 ÷ 10.0;

the rest is a eutectic mixture of potassium, sodium and cesium chlorides.

The electrolysis is carried out in potentiostatic mode at a temperature of 550 ± 10 ° C, optimal for this solvent. It is possible to carry out synthesis at a higher temperature, however, an increase in temperature leads to the evaporation of the melt, an increase in the vapor pressure above the melt, and the 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-CsCl melt. This background electrolyte is selected from the following considerations: the decomposition voltage of the molten KCl-NaCl-CsCl 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 diffraction analysis on a DRON-6 diffractometer, the results noted the presence of only the GdB6 phase.

Example 1. In a glass-carbon crucible with a volume of 40 cm ^{3 was} placed a salt mixture weighing 37.61 g, containing 2.53 g of GdCl3 (6.7 wt.%); 3.63 g of KBF ₄ (9.66 wt.%); 20.67 g of CsCl (54.97 wt.%), 5.48 g of KCl (14.57 wt.%); 5.3 g of NaCl (14.1 wt.%). The crucible with the salt mixture is placed in a quartz cell, and in a dry argon atmosphere is maintained until the system melts (550 ° C). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.4 ÷ 2.5 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 particle size of the obtained gadolinium hexaboride powder is 50-70 nm.

Example 2. In a glass-carbon crucible with a volume of 40 cm ^{3 was} placed a salt mixture weighing 35.8 g, containing 2.2 g of GdCl ₃ (6.1 wt.%); 2.15 g KBF ₄ (6.05 wt.%); 20.67 g of CsCl (57.75 wt.%), 5.48 g of KCl (15.3 wt.%); 5.3 g of NaCl (14.8 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts (550 ° C). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.5 ÷ -2.6 V relative to the glassy carbon reference electrode (current density -0.12 A / cm ² ), the duration of the electrolysis 110 ÷ 120 minutes The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The particle size of the obtained powder of gadolinium hexaboride 90-110 nm.

Example 3. In a glass-carbon crucible with a volume of 40 cm ^{3 was} placed a salt mixture weighing 33.87 g, containing 1.9 g of GdCl ₃ (5.6 wt.%); 2.73 g of KBF ₄ (8.05 wt.%); 19.94 g of CsCl (58.9 wt.%), 4.74 g of KCl (14.0 wt.%); 4.56 g of NaCl (13.45 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts (550 ° C). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. A current of -0.6 A (current density -0.5 A / cm) is supplied from the source. Potential -3.5 V, electrolysis duration 80 ÷ 90 min. The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The particle size of the obtained gadolinium hexaboride powder is 70-90 nm.

Example 4. In an alundum crucible with a volume of 60 cm ^{3, a} salt mixture weighing 58.43 g containing 2.0 g of GdCl ₃ (3.4 wt.%) Was placed; 3.83 g of KBF ₄ (6.6 wt.%); 36.3 g of CsCl (62.1 wt.%), 8.3 g of KCl (14.2 wt.%); 8.0 g of NaCl (13.7 wt.%). The crucible with the salt mixture is placed in a quartz cell and in an atmosphere of dry argon, kept to the melting temperature of the system (550 ° C). Upon reaching operating temperature, a tungsten cathode is lowered into the melt. The electrolysis is carried out at a potential of -2.4 ÷ -2.5 V relative to the glassy carbon reference electrode (current density -0.4 A / cm ² ), the duration of the electrolysis is 110-5-120 minutes The cathode-salt pear is washed from gadolinium fluoride in potassium fluoride. The particle size of the obtained powder of gadolinium hexaboride 80-110 nm.

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

Claims (2)

1. The method of electrolytic production of ultrafine powder of gadolinium hexaboride, including the synthesis of gadolinium hexaboride from a molten medium, including gadolinium chloride and potassium fluoroborate, in a background electrolyte, characterized in that the synthesis is carried out from the molten medium at a temperature of 550 ± 10 ° C in an atmosphere of purified and dried argon, and as a background electrolyte, a eutectic mixture of potassium, sodium and cesium chlorides is used in the following ratio of components, wt.%:
gadolinium chloride 3.0 ÷ 7.0 potassium fluoroborate 6.0 ÷ 10.0 eutectic mixture potassium chloride sodium and cesium rest 2. The method according to claim 1, characterized in that the synthesis is carried out at current densities from -0.1 to -1.0 A / cm ² and electrolysis potentials from -2.4 to -2.6 V relative to the glassy carbon quasistationary reference electrode .