RU2545304C2 - Method of obtaining barium fluoride powder, activated with cerium fluoride for scintillation ceramics - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in production of scintillation ceramics with increased light output. Method of obtaining barium fluoride powder, activated with cerium fluoride, includes interaction of ammonium fluoride solution with solution, containing barium nitrate and cerium nitrate. For interaction used is solution, containing barium and cerium ions with their molar ratio from 99.999:0.001 to 99.990:0.010, respectively. After that, sediment is separated, washed, dried and subjected to thermal processing at temperature 550-600°C. Washed residue is re-processed with highly pure hydrofluoric acid.

EFFECT: invention makes it possible to obtain finely disperse water-free powder of barium fluoride, activated with cerium fluoride, with homogeneous chemical and phase composition and low content of activator, hydrogen and carbon admixtures.

3 cl, 9 dwg, 2 tbl, 5 ex

Description

The invention relates to the field of synthesis of inorganic materials, in particular to the production of fluorides of rare-earth and alkaline earth metals, which can be used as feedstock for hot pressing of optically transparent scintillation ceramics. The invention can be used for the production of efficient high-speed scintillation detectors designed to detect gamma and x-ray quanta.

Ceramics BaF ₂ : Ce ^{3+ is} characterized by an increased light output of radioluminescence compared to single crystals (Batigov S.Kh., Bolyasnikova L.S., Garibin A.E., Demidenko V.A., Doroshenko M.E., Dukelsky K.V. ., Luginina A.A., Mironov I.A., Osiko V.V., Fedorov P.P. Scintillation ceramics BaF ₂ : Ce ³⁺ . // Reports of the Russian Academy of Sciences. 2008. V.422. No. 2. C. .323-325 Native P. A., Gain S. D., Mironov I. A., Garibin E. A., Demidenko A. A., Seliverstov D. M., Gusev Yu. I., Fedorov P. P., Kuznetsov SV Spectral-kinetic characteristics of crystals and nanoceramics based on BaF ₂ and BaF ₂ : Ce. Solid state physics. 2010, 52 (9), 1780-17 84, patent RU 2462733, G01T 1/202, 2011).

The quality of the initial charge has a significant effect on the optical transmission and light output of scintillation ceramics. It is known that the most important requirements for the initial charge for hot pressing are a uniform chemical and phase composition, ultrafine powder, high purity. In addition to the requirement for the content of limited microimpurities of metals, there are requirements for the absence of oxygen and carbon-containing impurities. In the manufacture of ceramics by hot pressing, carbon-containing impurities undergo thermal decomposition with the release of free carbon, which extremely negatively affects the transparency and emissivity of the resulting ceramics. The content of limited impurities of cations in excess of 1 ppm (0.0001 wt.%) And residual oxygen of more than 100 ppm (0.01 wt.%) Impairs the scintillation and optical properties of the material (patent JP 2007045870, C09K 11/00, 2005). Since the possibility of contamination with oxygen impurities is determined by the specificity of fluorides - their tendency to pyrohydrolysis, interaction with water vapor at elevated temperatures (Rakov E.G., Teslenko V.V. Pyrohydrolysis of inorganic fluorides. // M .: Energoatomizdat. 1987. 152 p.) , the mixture should not contain traces of moisture.

A known method of producing fluorides of rare earth and alkaline earth metals, including mixing fluorides of alkaline and chlorides of alkaline earth or rare earth elements, melting the mixture at a temperature of 700-800 ° C in a refractory reactor, cooling the melt and treating it with distilled water during boiling (AC SU No. 802178, C01B 9 / 08, 1981). This method provides a reduction in the content of oxygen impurities by more than an order of magnitude compared with reagents, but is intended only for the synthesis of individual fluorides.

When barium carbonate is calcined with ammonium fluoride or bifluoride, fluoride is obtained in crystalline form, however, due to high temperatures, sintering of the product particles is observed (AC SU No. 998352, C01F 11/22, 1983). This method allows to obtain high-quality fluorides suitable for growing single crystals, but by the granulometric composition such a product is not suitable for hot pressing.

A known method of producing barium fluoride, including the interaction of barium carbonate powder with a solution of ammonium fluoride at 80-100 ° C for 1-2 hours, followed by filtering and drying the precipitate of barium fluoride (Patent CN No. 101376519, C01F 11/22, 2007). However, when using a water-insoluble carbonate, the reaction does not completely occur, and the product is contaminated with impurities of carbonate and oxide.

To obtain barium fluoride with a low content of oxygen impurities (not more than 0.0001%), the filtered precipitate obtained by reacting a suspension of barium carbonate with concentrated hydrofluoric acid, after drying and calcining, was subjected to melting at 1340-144 ° C in the atmosphere of decomposition products of polytetrafluoroethylene ( AC SU No. 1778071, C01F 11/22, 1992). Since the product is a large single-crystal blocks, it cannot be used for hot pressing ceramics.

To remove carbon and oxygen impurities, fluorides of rare earth and alkaline earth metals were treated at a temperature of 200-350 ° C in an inert gas atmosphere containing 5-50% fluorine (Application US No. 2004402696, C01B 9/08, 2004). However, the high corrosivity of gaseous fluorine creates significant difficulties in creating equipment and requires the use of expensive structural materials.

Known methods for producing fluorides of rare earth and alkaline earth metals by the action of gaseous hydrogen fluoride on their compounds when heated to a temperature of 150-250 ° C for 1-2 hours (Patent RU No. 2323248, C01F 17/00, 2006) or gaseous SF ₆ at a temperature of 750 -800 ° C (Application WO No. 9746488, C09K 11/08, 1996). The use of anhydrous processes allows to obtain fluorides with a minimum oxygen content in them, but are intended only for the synthesis of individual fluorides.

Known methods for producing coprecipitation from aqueous solutions of powders of fluorides of alkaline earth metals, namely calcium and strontium, activated by rare-earth ions with a concentration of from 0.5 to 25 mol.%. (Patents: EP No. 1728763, C01F 17/00, 2006; EP No. 1942172, C09K 11/85, 2006; US No.2010012898, C09K 11/61, 2006). However, upon the production of barium fluoride activated by rare-earth ions, practically pure barium fluoride is synthesized in a mixture with the Ba ₄ R ₃ F ₁₇ phase by coprecipitation from nitrate solutions with hydrofluoric acid (Kuznetsov S.V., Fedorov P.P., Voronov V. V., Samarina KS, Osiko VV Synthesis of Ba ₄ R ₃ F ₁₇ powders (R - rare-earth elements) from aqueous solutions. // J. Inorganic Chemistry. 2010. V.55. No. 4. C .536-545). The anomalous behavior of barium nitrate is explained by the formation instead of barium fluoride, which has a cubic crystal structure such as fluorite and has a high isomorphic capacity with respect to rare-earth ions, barium hydrofluoride BaF ₂ · HF, the monoclinic structure of which does not present such crystallochemical capabilities. It was shown that barium fluoride precipitates from nitrate solutions using another fluorinating compound, ammonium fluoride (Luginina A.A., Fedorov P.P., Kuznetsov S.V., Mayakova M.N., Voronov V.V., Baranchikov A .E. // Features of the synthesis of barium hydrofluoride and fluoride from nitrate solutions. Nanosystems: physics, chemistry, mathematics. 2012. V.3. No. 5. 125-137).

Closest to the proposed technical solution is a method for the synthesis of a single-phase nanopowder of barium fluoride doped with a rare-earth metal, comprising mixing a fluorinating compound with a solution containing a barium salt and a salt of a rare-earth element with a molar ratio of 0.74: 0.26 to 0.30 : 0.70, respectively, to obtain a precipitate, washing and drying it. However, as can be seen from the description of the prototype method, the resulting product is characterized by a high content of rare earth metal from 0.26 to 0.70 moles, and the known method does not allow to obtain single-phase barium fluoride activated by rare earth metal fluoride with a content of rare earth metal less than 0.26 moles. A very important disadvantage of this method is also the heat treatment of the product by heating to 400 ° C in air, without a protective inert or fluorinating atmosphere, which does not ensure complete dehydration and prevention of pyrohydrolysis of the product, in addition, the low heat treatment temperature does not remove carbon impurities, the listed disadvantages in further adversely affect the purity of the final product (Patent RU No. 2411185 C1).

The present invention is to develop a method for producing a finely divided homogeneous anhydrous powder of barium fluoride activated by cerium fluoride with a low content of activator.

To solve this problem, a new method is proposed for producing barium fluoride powder activated by cerium fluoride for scintillation ceramics, including the interaction of a fluorinating compound with a solution containing barium and cerium nitrates at a molar ratio of 99.999: 0.001 to 99.990: 0.010, respectively, followed by separation sediment, washing and re-treatment with high purity hydrofluoric acid, followed by filtration, drying and heat treatment of the product.

Preferably, in the reaction, a solution of ammonium fluoride in a stoichiometric amount corresponding to the production of barium and cerium fluorides is used as the fluorinating compound.

Preferably, the re-treatment of the washed precipitate is carried out with 45-47% hydrogen fluoride, taken with a 10% stoichiometric excess.

Preferably, the heat treatment of the dried precipitate is carried out at a temperature of 550-600 ° C in an atmosphere of gaseous hydrogen fluoride released during its decomposition for 2-3 hours.

The method differs from the prototype method in the process conditions. As can be seen from the description of the method, the necessary conditions for obtaining a homogeneous anhydrous powder of barium fluoride activated with cerium fluoride are the use of ammonium fluoride solution as a fluorinating compound, re-treatment of the washed precipitate with concentrated hydrofluoric acid and heat treatment of the dried precipitate at a temperature of 550 -600 ° C for 2-3 hours.

The claimed process has been verified empirically.

The invention is illustrated by the following drawings and photographs.

Figure 1 presents the spectra - the dependence of the relative intensity of the diffraction line I / I _o from the characteristic angle 29, representing the results of x-ray phase analysis (XRD) of the powder obtained by the interaction of solutions of barium nitrate and cerium with ammonium fluoride for five specific examples of compositions, where 1, 2 , 3, 4, 5 - numbers of examples.

Figure 2 presents a snapshot of scanning electron microscopy (SEM) dried at 35 ° C of the powder obtained by the interaction of solutions of barium nitrate and cerium with ammonium fluoride in example No. 1.

Figure 3 presents the SEM image of the dried powder at 35 ° C obtained by the interaction of solutions of barium nitrate and cerium with ammonium fluoride according to example No. 2.

Figure 4 presents the spectrum - the dependence of the relative intensity of the diffraction line I / I _o from the characteristic angle 2θ - the results of XRD powder intermediate obtained by reprocessing the washed precipitate with concentrated hydrofluoric acid according to example No. 1.

a) - intermediate product example 1, b) - barium hydrofluoride, card No. 35-1378 of the JCPDS database

Figure 5 presents the IR spectra of the final products obtained according to examples No. 1, 2, 3, 4, 5.

Figure 6 presents the XRD of the final product according to examples No. 1, 2, 3, 4, 5.

Figure 7 presents an SEM image of the final product for example No. 1.

On Fig presents a SEM of the final product for example No. 2.

Figure 9 presents a snapshot showing the results of x-ray microanalysis of the final product made according to example No. 1.

Tables 1 and 2 provide summary data for various specific examples of finely divided homogeneous anhydrous barium fluoride powder activated with cerium fluoride with a low content of activator made in accordance with the claimed method.

Table 1 The content of HF in the intermediate. Sample Number Example 1 Example 2 Example 3 Example 4 Example 5 The content of HF, wt.% 10.3 10.3 10,2 10.3 10.3

table 2 Spectral emission analysis of the product. Sample Number Example 1 Example 2 Example 3 Example 4 Example 5 Content, wt.%: cerium (Ce) 0.0111 0.0011 0.0055 0.0111 0.0111 iron (Fe) 0.0001 0.0001 0.0001 0.0001 0.0001 nickel (Ni) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Manganese (Mn) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 chromium (Cr) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 cobalt (Co) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 copper (Cu) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 aluminum (Al) <0.001 <0.001 <0.001 <0.001 <0.001 silicon (Si) 0.0001 0.0001 0.0001 0.0001 0.0001

The use of ammonium fluoride provides obtaining from nitrate solutions of a fine precipitate of barium fluoride activated by cerium, a cubic fluorite structure, which is confirmed by the results of x-ray phase analysis (Figure 1) and scanning electron microscopy (Figure 2, 3). As can be seen from scanning electron microscopy images of a powder dried at 35 ° C obtained by the interaction of solutions of barium nitrate and cerium with ammonium fluoride, cubic particles with a size of 30-150 nm are formed. As a result of reprocessing the washed precipitate with concentrated hydrofluoric acid, hydrofluoride of the composition (Ba _1-x Ce _x F _{2 + x} ) · HF is formed, which is confirmed by the results of x-ray phase and chemical analysis (Figure 4, Table 1). Gaseous hydrogen fluoride released during thermal decomposition of barium hydrofluoride prevents pyrohydrolysis of the product, which ensures complete dehydration of the product and minimization of oxygen impurities. In the IR spectra of calcined powders after repeated treatment with hydrofluoric acid there are no characteristic vibrations (bands) of H ₂ O at 1640 and 3400 cm ^-1 , which confirms the absence of traces of moisture (Figure 5). Heat treatment at a temperature of 550-600 ° C also helps to remove carbon-containing impurities due to oxidation by atmospheric oxygen (combustion). The heat treatment produces a fine powder of barium fluoride activated by cerium fluoride, cubic fluorite structure, loose and stressed structure (Fig.6-8). The product yield is 95.0-97.0%.

The use of high purity reagents ensures the required purity of the product. According to the spectral emission analysis, the cerium fluoride content corresponds to the amount introduced during the synthesis (Table 2).

The technical effect of the implementation of this method is to obtain a fine anhydrous powder of barium fluoride activated by cerium fluoride, with a uniform chemical and phase composition, with a minimum content of oxygen and carbon impurities, which is confirmed by the above examples.

Example No. 1. An aqueous solution of barium nitrate (0.1-0.3 mol / L), prepared by dissolving a high-purity reagent in bidistilled water (part 7-5), was poured into a reactor made of polypropylene and equipped with a fluoroplastic mixer. A solution of cerium nitrate (0.1-0.3 mol / L) obtained by dissolving six-water cerium nitrate Ce (NO ₃ ) ₃ · 6H ₂ O (basic substance content of at least 99.99%) was added to the reactor. The ratio of the molar concentration of barium to cerium in the solution was 99.990: 0.010. The solutions were mixed for 20 minutes. In the resulting solution, with stirring, a 4% solution of ammonium fluoride was added dropwise (Os.h. 3-5). Upon completion of the addition of the ammonium fluoride solution, the suspension was stirred at a speed of 700 rpm for 3 hours. After settling, the mother liquor was decanted, the precipitate was washed with double-distilled water until NO ₃ ^- ions were completely removed by reaction with diphenylamine. A 46% solution of hydrofluoric acid (os. 27-5) was poured into the washed precipitate with stirring. The suspension was stirred at a speed of 700 rpm for 3 hours. The precipitate was separated on the filter from a porous fluoroplastic, then dried in a fluoroplastic cup at a temperature of 35-40 ° C for 5 hours. The HF content in the dried precipitate was 10.3 wt.% (Table 1). According to x-ray phase analysis was obtained hydrofluoride (Ba _1-x Ce _x F _{2 + x} ) · HF with lattice parameters a = 7.271, b = 4.289, c = 4.967 Å, β = 115.46 (Figure 4). The dried intermediate was calcined in a platinum crucible at a temperature of 600 ° C for 2 hours. An anhydrous powder of barium fluoride activated by cerium fluoride, a fluorite structure with a lattice parameter a = 6.1901 Å, with a cerium content of 0.0111 wt.% Was obtained (Table 2, Fig.6, 7). The method of x-ray microanalysis confirmed the homogeneity of the powder (Fig.9). The product yield was 95.7%.

Example No. 2. An example is carried out analogously to example No. 1. The ratio of the atomic concentration of barium to cerium was 99.999: 0.001. An anhydrous powder of barium fluoride activated by cerium fluoride, a fluorite structure with a lattice parameter a = 6.1961 Å, with a cerium content of 0.0011 wt.% Was obtained (Table 2, Fig.6, 8). The product yield was 96.9%.

Example No. 3. An example is carried out analogously to example No. 1. The ratio of the atomic concentration of barium to cerium was 99.995: 0.005. An anhydrous powder of barium fluoride activated by cerium fluoride, a fluorite structure with a lattice parameter a = 6.1904 Å, with a cerium content of 0.0055 wt.% Was obtained (Table 2, FIG. 6). The product yield was 96.3%.

Example No. 4. The example is carried out analogously to example No. 1, only instead of 4% used 8% solution of ammonium fluoride. An anhydrous powder of barium fluoride activated by cerium fluoride, a fluorite structure with a lattice parameter a = 6.1901 Å, with a cerium content of 0.0111 wt.% Was obtained (Table 2, FIG. 6). The product yield was 96.1%.

Example No. 5. The example was carried out analogously to example No. 1, only the intermediate was calcined at a temperature of 550 ° C for 3 hours. An anhydrous powder of barium fluoride activated by cerium fluoride, a fluorite structure with a lattice parameter a = 6.1901 Å, with a cerium content of 0.0111 wt.% Was obtained (Table 2, FIG. 6). The product yield was 95.8%.

Claims (3)

1. A method of producing a powder of barium fluoride activated by cerium fluoride for scintillation ceramics with high light output, comprising reacting a solution of ammonium fluoride with a solution containing barium nitrate and cerium nitrate, followed by separation of the precipitate, washing, drying and heat treatment, characterized in that a solution containing barium and cerium ions with a molar ratio of 99.999: 0.001 to 99.990: 0.010, respectively, is used for the interaction, and the washed precipitate is re-treated with hydrofluoric acid in sokoy purity. 2. The method according to p. 1, characterized in that the reprocessing of the washed precipitate is carried out with 45-47% hydrofluoric acid, taken with a 10% stoichiometric excess. 3. The method according to p. 1, characterized in that the heat treatment of the dried precipitate is carried out at a temperature of 550-600 ° C in an atmosphere of gaseous hydrogen fluoride released during its decomposition, preferably within 2-3 hours.

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