Electrolytic method for obtaining ultradisperse powder of lanthanum hexaboride

FIELD: metallurgy.

SUBSTANCE: method for obtaining pure lanthanum hexaboride is implemented by combined electrodeposition of lanthanum and boron from chloride molten metal on the cathode and their further interaction at atomic level. The process is performed in three-electrode quartz cell, where a tungsten bar serves as a cathode; a glassy carbon bar sealed in pyrex glass serves as a comparison electrode; a glassy carbon melting pot serves as anode and at the same time as a container. Synthesis of ultradisperse powder of lanthanum hexaboride is performed by means of controlled potential electrolysis from equimole KCl-NaCl melt containing lanthanum trichloride and potassium fluoroborate in the environment of cleaned and dried argon at potentials of -2.0 to -2.6 V relative to glassy carbon comparison electrode at the temperature of 700±10°C.

EFFECT: obtaining pure target product owing to good solubility of background electrolyte in water; reduction of electric power costs.

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The invention relates to an electrolytic process for the production of pure hexaboride lanthanum.

The closest is the way to get hexaboride lanthanum by electrolysis of molten environments [Samsonov, G.V. Refractory compounds of rare earth metals, M, Izd-vo "metallurgy", 1964, p.53-55]. The electrolysis is carried out in a graphite crucible, employees simultaneously anode; a cathode made of graphite or molybdenum. The composition of the bath to electrolysis include oxides of rare earth metals and boric anhydride with the addition of fluorides of alkali and alkaline earth metals to reduce the temperature and viscosity of the bath. The temperature of the electrolysis of mixtures is 1000°C, the voltage on the tub 3,2 B, the current density of 20 A/cm². The composition of the bath to obtain hexaboride lanthanum:.

As noted [Samsonov, G.V. Refractory compounds of rare earth metals, M, Izd-vo "metallurgy", 1964, p.53-55], the receipt of individual boride phase is almost impossible or very difficult.

The disadvantages of the method are the complexity of the separation of the target product from the molten electrolyte due to the low solubility of borates and fluorides, high temperature synthesis and pollution by-products, in particular the borates.

The objective of the invention is to obtain pure ultrafine powder is and hexaboride lanthanum, the increase rate of the synthesis of the target product from the molten electrolyte, saving energy by lowering the synthesis temperature.

The invention consists in the fact that exercising a joint electromedicine lanthanum and boron from chloride melt at the cathode and their subsequent interaction at the atomic level with the formation of ultrafine powders of hexaboride lanthanum. The process is carried out in three-electrode quartz cell where the cathode is a tungsten rod; the reference electrode is a glassy carbon rod, sealed in Pyrex; the anode and at the same time the container is a glassy carbon crucible. Synthesis of ultrafine powder hexaboride lanthanum performed by potentiostatic electrolysis of equimolar melt KCl-NaCl containing trichloride lanthanum and perborate potassium in the atmosphere of cleaned and dried argon at potetial from-2.0 to -2,6 B relative to a glassy carbon reference electrode and a temperature of 700±10°C. of the Obtained cathode and electrolyte pear washed from fluoride, lanthanum fluoride of potassium.

As a source of lanthanum use waterless trichloride lanthanum, boron source - perborate potassium, background electrolyte - equinology mixture of the chlorides of potassium and sodium in the following ratio, wt.%:

the lanthanum chloride 2,5÷5,0;

perborate ka the Oia 8,0÷11,0;

else: equimolar mixture of the chlorides of potassium and sodium.

The choice of the components of the electrolytic bath was made on the basis of thermodynamic analysis and kinetic measurements of joint electromedicine lanthanum and boron from chloride melts. Of the compounds of lanthanum and boron containing no oxygen, lanthanum chloride and perborate potassium are fairly low melting and soluble in the background electrolyte, which is selected from the following considerations: voltage decomposition of the molten mixture of KCl-NaCl than oneís melts LaCl₃and KBF₄; good solubility in water.

Phase composition identified by the method of x-ray phase analysis on the diffractometer DRON-6, he showed the presence of only phase LaB₆. The particle size of the powder was determined using a scanning probe microscope Solver PRO R.

Example 1.

In a glassy carbon crucible volume of 40 ml was placed a mixture of salt mass 33,01 g containing 1.0 g LaCl₃(3 wt.%); 2,01 g KBF₄(8 wt.%); 16,8 g KCl (51 wt.%); 13,2 g NaCl (40 wt%). The crucible with the salt mixture is placed in a quartz cell, and in an atmosphere of dry argon to withstand temperature melting system. Upon reaching the operating temperature of 700°C in the melt is lowered tungsten cathode, the electrolysis is carried out at a potential -2,0 B relative to a glassy carbon reference electrode (density is the eye of 0.6 A/cm ²), the duration of the process of electrolysis is 150 minutes Cathode and electrolyte pear, consisting of hexaboride lanthanum, washed from fluoride, lanthanum fluoride potassium. The particle size of the obtained powder hexaboride lanthanum 150-180 nm.

Example 2.

In a glassy carbon crucible volume of 40 ml was placed a mixture of salt by weight of 34.2 g, containing 1.0 g LaCl₃(2.9 wt.%); 3.2 g KBF₄(to 9.4 wt.%); 16,8 g KCl (49 wt.%); 13,2 g NaCl (38,6 wt.%). The crucible with the salt mixture is placed in a quartz cell, and in an atmosphere of dry argon to withstand temperature melting system. Upon reaching the operating temperature of 700°C in the melt is lowered tungsten cathode., the electrolysis is carried out at a potential -2,6 B relative to a glassy carbon reference electrode (current density of 0.5 A/cm²), the duration of the process of electrolysis is 120 minutes Cathode and electrolyte pear, consisting of hexaboride lanthanum, washed from fluoride, lanthanum fluoride potassium. The particle size of the obtained powder hexaboride lanthanum 150 nm.

Example 3.

In a glassy carbon crucible 40 ml was placed a mixture of salt by weight of 34.8 g, containing 1.2 g LaCl₃(3.4 wt.%); 3.6 g KBF₄(to 10.3 wt.%); 16,8 g KCl ($48.3 wt.%); 13,2 g NaCl (38 wt.%). The crucible with the salt mixture is placed in a quartz cell, and in an atmosphere of dry argon to withstand temperature melting system. Upon reaching the working pace is atory 700°C in the melt is lowered tungsten cathode, the electrolysis is carried out at a potential -2,6 B relative of a glassy carbon electrode, the current density of 0.7 A/cm²), the duration of the process of electrolysis is 150 minutes Cathode and electrolyte pear, consisting of hexaboride lanthanum, washed from fluoride, lanthanum fluoride potassium. The particle size of the obtained powder hexaboride lanthanum 170 nm.

The technical result is: obtain the pure desired product due to the good solubility of the background electrolyte in the water, reducing the cost of electricity.

1. Electrolytic method of obtaining ultrafine powder hexaboride lanthanum, including the synthesis of hexaboride lanthanum from molten environments, characterized in that the synthesis is carried out from the chloride melt in the atmosphere cleared and drained argon, as a source of lanthanum use anhydrous lanthanum chloride, a source of boron - perborate potassium, background electrolyte - equinology mixture of potassium chloride and sodium chloride in the following ratio, wt.%:

2. The method according to claim 1, characterized in that the synthesis is carried out at a temperature of 700°C, current density from 0.1 to 1.0 A/cm²and the potential electrolysis relatively glassy carbon reference electrode from-2.0 to -2,6 Century