RU2328448C1 - Method for producing metal fluorides - Google Patents

Abstract

FIELD: nanotechnology.

SUBSTANCE: invention relates to the method for producing the metal fluorides and comprises in the interaction of the gaseous hydrogen fluoride with the powder-like micron-sized compounds of the alkaline, alkali-earth and rare-earth metals, with producing the metal fluoride nanopowders. The hydrofluorination is performed at 150-200°C within 1-2 hours. As the compounds, the hydrides, nitrates and oxides of the said metals are used.

EFFECT: enables producing of subtle metal fluoride powders at lower temperature as compared to methods currently in use, and with less hydrogen fluoride consumption.

5 cl, 5 dwg, 2 tbl

Description

The invention relates to nanotechnology for the development of optically transparent nanoceramics based on simple and complex fluorides with low (10 ^-2 -10 ^-3 cm ^-1 ) optical losses to create active and passive photonics based on it.

For the production of nanoceramics, it is necessary to have nanopowders of metal fluorides activated by rare-earth elements. Elements of optical ceramics should have a higher radiation resistance compared to single crystals of the corresponding compounds, a transmission spectrum from 0.2 to 6 μm, and optical losses not worse than 10 ^-2 cm ^-1 at the generation wavelength.

It is also well known that the technology for producing optical ceramics is less labor-consuming and economically more profitable compared to growing single-crystal materials for optical purposes.

At present, powdered inorganic fluorides are obtained by various methods, which can conditionally be divided into two main groups. The first combines methods based on the precipitation of fluorides from soluble salts of the corresponding metals with hydrofluoric acid (aqueous methods), followed by thermal decomposition of the hydrated fluorides obtained to an anhydrous state. The second group includes methods based on fluorination (HF, F ₂ and other fluorinating agents) at elevated temperatures of various compounds (oxides, hydroxides, carbonates, oxalates, etc.) of the corresponding metals. All methods have their own advantages and disadvantages.

The methods belonging to the second group have significant advantages over the water series:

- the resulting fluorides are anhydrous;

- excludes the operation of sedimentation, washing, decantation, filtration of fluorides, their drying and calcination;

- easier to organize continuous fully automated processes;

- there is no need to process mother liquors;

- occupy smaller production areas.

Only the use of anhydrous processes allows the production of fluorides with a minimum oxygen content in them. The starting material is the oxides of the corresponding metals, which are obtained by thermal decomposition of carbonates, hydroxides, oxalates, etc.

When obtaining anhydrous RE fluorides by the dry method, fairly high temperatures of 600-700 ° C are used and the treatment time for the oxides with hydrogen fluoride is 8-10 hours. HF consumption reaches 200-250% of stoichiometry (Spedding F., Daan A. Obtaining yttrium and some heavy rare earth metals. // Rare-earth metals. - M.: Publishing House of Foreign Literature., 1957. p. 325-328.) At the same time, corrosion problems and difficulties in choosing structural materials for equipment are noted.

Temperature conditions and process time can be significantly reduced due to the preparation of feedstock (Mashirev V.P. et al. Development of pyrometallurgical methods and equipment for the production of anhydrous metal fluorides. // Report at the 9th International Congress on Chemical Processes and Equipment. HISA-87. Prague, 1987, p. 46). It is well known that the reactivity or activity of solid-phase reagents is more dependent on the state of the crystal lattice, due, in particular, to the method of preparation or processing of the reagents.

One of the most common methods for preparing active powder preparations is the thermal decomposition of the starting materials.

Known methods for producing REE fluorides and alkaline earth elements by exposure to gaseous hydrogen fluoride on the oxides obtained by thermal decomposition of the starting substances (patent No. 2104934, MKI C01F 3/00, patent No. 2107029, MKI C01F 17/00). The disadvantage of these methods is the inability to obtain fine powders.

The closest is essentially a method for producing fluorides of rare-earth metals and yttrium (patent No. 2038310, C01F 17/10), which consists in the fact that oxides, oxalates, carbonates and hydroxides were subjected to hydrofluorination at a temperature of 380-550 ° C.

The disadvantage of this method is the inability to obtain fine powders.

The technical result of the proposed invention is to obtain nanopowders of fluorides of alkali, alkaline earth and rare earth elements.

The technical result is achieved by the fact that nanopowders of fluorides of alkali, alkaline earth and rare earth elements are obtained by the action of hydrogen fluoride on the powders of their micron-sized compounds. As compounds used oxide, hydride and nitrate of the above elements.

Hydrofluorination was carried out at a temperature of 150-250 ° C for 1-2 hours. The consumption of hydrogen fluoride is in the range of 120-150% to stoichiometry.

Example 1. Anhydrous LiF samples were obtained from lithium hydride. Lithium hydride is a colorless crystal with a cubic face-centered lattice (a = 0.4083 nm). When grinding, the powder becomes white. The hydride powder of the particle size distribution presented below was subjected to interaction with HF (Table 1). The hydrofluorination temperature was 150 ° C.

Table 1 radius, microns <2 2-4 4-6 6-8 8-10 10-20 > 20 wt.% 26 17 2 2 3 25 25

The reaction time of the samples of lithium hydride powder with hydrogen fluoride was 45 minutes at a flow rate of HF up to 125% of stoichiometry. The degree of fluorination was 99.9%. X-ray phase analysis showed only the LiF phase with a cubic lattice (a = 0.403 nm). The average particle size radius was about 20 nm.

Example 2. Powders Y (NO ₃ ) ₃ × H ₂ O were converted by interaction with gaseous hydrogen fluoride in YF ₃ at temperatures of 200 ° C and with an excess of HF 25% to stoichiometry. The interaction time is 60 minutes The degree of fluorination of YF ₃ powders was in the range of 99.91-99.98%. X-ray phase analysis showed that the samples contain one phase of yttrium trifluoride with a rhombic lattice of the FeC type (a = 0.637 nm, b = 0.686 nm, c = 0.439, z = 4, Pnma space group; X-ray density 5.069 g / cm ³ ). YF ₃ samples had a specific surface area in the range of 22-65 m ² / g and an average particle size diameter in the range of 30-70 nm.

Example 3. Nd (NO ₃ ) ₃ powders were also converted by interaction with gaseous hydrogen fluoride to NdF ₃ at a temperature of 250 ° C and with an excess of HF, 50% to stoichiometry. The interaction time is 120 minutes The degree of fluorination of NdF ₃ powders was in the range of 99.83-99.93%. The specific surface area was in the range of 8-35 m ² / g. The average particle diameter was 40-100 nm. Samples have a trigonal lattice (a = 0.702 nm, c = 720 nm).

Example 4. As a starting material for obtaining CeF ₃ powder, cerium oxide samples obtained by thermal decomposition of oxygen-containing cerium compounds were used. Hydrofluorination of the samples was carried out at a temperature of 150 ° C with an excess of hydrogen fluoride 15-25% to stoichiometry. The degree of fluorination of the samples is presented in table.2.

Table 2 Sample No. Ref. substance Hydrofluorination Temperature Process time, min Degree of fluorination one Cerium oxide obtained from nitrate 150 120 min 95.2 250 97.0 2 Cerium oxide obtained from carbonate 150 120 min 94.5 250 98.5 3 Cerium oxide obtained from hydroxide 150 120 min 95.3 250 98.8

X-ray phase analysis of fully profluorinated samples showed the presence of only a hexagonal structure (a = 0.711 nm, s = 0.727 nm) with an estimated density of 6.13 g / cm ³ . The specific surface area of the samples is in the range 13-47 m ² / g.

Example 5. CaF ₂ nanopowders were synthesized by the interaction of gaseous HF with CaO obtained from Ca (OH) _{3 by} thermal decomposition at temperatures up to 450 ° C, at a flow rate of 140% to stoichiometry. The fluorination temperature was 250 ° C. The degree of fluorination was in the range of 99.91-100%. The interaction time was 90 min. X-ray phase analysis indicated that the samples represent one phase with a cubic lattice (a = 0.546 nm) with a density of 3.18 g / cm ³ . The samples had a specific surface area in the range of 12-46 m ² / g. The particle diameter was about 50 nm.

The above examples showed that nanopowders of anhydrous fluorides can be synthesized from the oxides, hydrides, and nitrates of these elements at a hydrofluorination temperature of 150-250 ° C. The average diameter diameter of the powders ranges up to 100 nm. Powders have a well-developed specific surface area. The consumption of HF for the synthesis of fluorides was in the range of 125-150% to stoichiometry.

Claims (5)

1. The method of producing metal fluorides by the action of gaseous hydrogen fluoride on their compounds when heated, characterized in that the interaction of gaseous hydrogen fluoride with powders of compounds of alkaline, alkaline earth and rare earth metals of micron sizes produce nanopowders of metal fluorides. 2. The method according to claim 1, characterized in that the hydrofluorination is carried out at a temperature of 150-250 ° C for 1-2 hours 3. The method according to claim 1, characterized in that as the compounds used are hydrides of alkaline, alkaline earth and rare earth elements. 4. The method according to claim 1, characterized in that as the compounds used nitrates of alkaline, alkaline earth and rare earth elements 5. The method according to claim 1, characterized in that the compounds used are oxides of alkaline, alkaline earth and rare earth elements.