RU2466090C1 - Electrolytic method of producing ultrafine cerium hexaboride powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrolytic methods of producing pure cerium hexaboride. The cerium source used is 1-4 wt % anhydrous cerium chloride, the boron source is 1-3 wt % potassium fluoroborate and the background electrolyte is a eutectic mixture of potassium, sodium and cerium chlorides, which makes up the balance amount. Synthesis of ultrafine cerium hexaboride powder takes place via electrolysis from a eutectic melt of KCl-NaCl-CsCl, which contains cerium chloride and potassium fluoroborate.

EFFECT: invention enables to obtain a pure end product owing to good solubility of the eutectic background electrolyte in water and reducing power consumption by reducing synthesis temperature.

2 cl

Description

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

The closest is a method of producing cerium hexaboride by electrolysis of molten media [G. Samsonov Refractory compounds of rare earth metals, Publishing House "Metallurgy". M. 1964, pp. 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 is 8.5 ÷ 12 V, the current density is 2.5 ÷ 2.6 A / cm ² . The composition of the bath to obtain cerium hexaboride:

CeO ₂ + 2B ₂ O ₃ + CeF ₂

or 1 / 3СеО ₂ + В ₂ О ₃ + CaF ₂

or 1 / 10CeO ₂ + 2B ₂ O ₃ + MgO + MgF ₂

As noted [G. Samsonov Refractory compounds of rare earth metals, Publishing House "Metallurgy". M. 1964, pp. 53-55], obtaining an individual boride phase is practically impossible or very difficult. The disadvantages of the method 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, in particular borates.

The objective of the invention is to obtain a pure ultrafine powder of cerium hexaboride, increasing the synthesis rate of the target product from the molten electrolyte and saving electricity by reducing the synthesis temperature.

The essence of the invention lies in the fact that they carry out the joint electrowinning of cerium and boron from a halide melt at the cathode and their subsequent interaction at the atomic level with the formation of ultrafine powders of cerium hexaboride. The process is carried out in a three-electrode quartz cell in an atmosphere of purified and dried argon, where silver and glass-carbon rods serve as the cathode; reference electrode - glassy carbon plate; anode and at the same time a container - a glassy carbon crucible. The ultrafine cerium hexaboride powder is synthesized by means of potentiostatic electrolysis from a KCl-NaCl-CsCl eutectic melt containing cerium chloride and potassium fluoroborate at potentials from -2.0 to -3.0 V relative to a glassy carbon reference electrode and a temperature of 550 ° ± 10 ° C and at current densities from 0.1 to 1.0 A / cm ² . The optimal duration of the electrolysis process is 50 ÷ 60 minutes The resulting cathode-salt group is washed from cerium fluoride with potassium fluoride.

Anhydrous cerium chloride is used as a source of cerium, potassium fluoroborate, a source of boron, and a background eutectic mixture of potassium, sodium, and cesium chlorides are used in the following ratio, wt.%:

cerium chloride 1.0 ÷ 4.0;

potassium fluoroborate 1.0 ÷ 3.0;

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

The components of the electrolytic bath were selected based on thermodynamic analysis and kinetic measurements of the combined electrowinning of cerium and boron from halide melts. Cerium chloride and potassium fluoroborate are quite low melting and well soluble in the eutectic melt KCl-NaCl-CsCl. The background electrolyte (eutectic melt KCl-NaCl-CsCl) was selected from the following considerations: the decomposition voltage of the molten KCl-NaCl-CsCl mixture is greater than that for CeCl ₃ and KBF ₄ melts, and it has good solubility in water.

The phase composition was identified by X-ray diffraction analysis on a DRON-6 diffractometer, which showed the presence of only a CeB ₆ phase. The particle size of the powder was determined using a Solver PRO P47 scanning probe microscope.

Example 1

A salt mixture weighing 31.96 g containing 1.3 g CeCl ₃ (4.07 wt.%) Was placed in a 40 ml glass-carbon crucible; 0.66 g KBF ₄ (2.06 wt.%); 4.869 g KCl (15.23 wt.%); 4.68 g of NaCl (14.6 wt.%); 20.45 g of CsCl (63.98 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts. Upon reaching a working temperature of 550 ° C, the glassy carbon cathode is lowered into the melt, electrolysis is carried out at a potential of -2.7 V relative to the glassy carbon reference electrode (current density 0.5A / cm ² ). The cathode-salt group consisting of cerium hexaboride is washed from cerium fluoride with potassium fluoride. The particle size of the obtained cerium hexaboride powder is 130-140 nm.

Example 2

A salt mixture weighing 30.92 g containing 0.37 g of CeCl ₃ (1.2 wt.%) Was placed in a 40 ml glass-carbon crucible; 0.55 g KBF ₄ (1.8 wt.%); 4.869 g KCl (16 wt.%); 4.68 g of NaCl (15 wt.%); 20.45 g of CsCl (66 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts. Upon reaching a working temperature of 550 ° C, a silver cathode is lowered into the melt, electrolysis is carried out at a potential of -2.45 V relative to the glassy carbon reference electrode (current density 0.8 A / cm ² ). The cathode-salt group consisting of cerium hexaboride is washed from cerium fluoride with potassium fluoride. The particle size of the obtained cerium hexaboride powder is 130 nm.

Example 3

A salt mixture weighing 31.22 g, containing 0.39 g CeCl ₃ (1.3 wt.%) Was placed in a 40 ml glass-carbon crucible; 0.83 g of KBF ₄ (2.7 wt.%); 4.869 g of KCl (15.5 wt.%); 4.68 g of NaCl (15 wt.%); 20.45 g of CsCl (65.5 wt.%). The crucible with the salt mixture is placed in a quartz cell and kept in a dry argon atmosphere until the system melts. Upon reaching a working temperature of 550 ° C, the glassy carbon cathode is lowered into the melt, electrolysis is carried out at a potential of -2.5 V relative to the glassy carbon reference electrode (current density 0.7 A / cm ² ). The cathode-salt group consisting of cerium hexaboride is washed from cerium fluoride with potassium fluoride. The particle size of the obtained cerium hexaboride powder is 140 nm.

The technical result is: obtaining a pure target product due to the good solubility of the eutectic background electrolyte in water and reducing energy costs by lowering the synthesis temperature.

Claims (2)

1. An electrolytic method for producing ultrafine cerium hexaboride powders, including the synthesis of cerium hexaboride from molten media, characterized in that the synthesis is carried out from a halide melt in an atmosphere of purified and dried argon, wherein anhydrous cerium chloride is used as a source of cerium, and potassium fluoroborate is a source of boron, background electrolyte is a eutectic mixture of potassium, sodium and cesium chlorides in the following ratio of components, wt.%:
cerium chloride 1,0 ÷ 4,0 potassium fluoroborate 1,0 ÷ 3,0 eutectic mixture of potassium chlorides, sodium and cesium rest 2. The method according to claim 1, characterized in that the synthesis is carried out at a temperature of 550 ° C, current densities from 0.1 to 1.0 A / cm ² and electrolysis potentials relative to the glassy carbon reference electrode from -2.0 to -3, 0 V.