RU2503754C1 - Method of producing yttrium aluminium garnet alloyed with rare earth elements - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method consists in precipitation at introduction of starting compounds of aluminium, yttrium and alloying agents in arrester to extract precipitated product and to calcine obtained powder at 1100°C. Note here that precipitation is performed in the presence of fluorine-bearing additive taken in amount corresponding to 1-5% content of fluorine atoms relative to amount of arrester. Arrester represents ammonium bicarbonate. Mixed aqueous solution of aluminium, yttrium and alloying element nitrates are added to said bicarbonate in amount corresponding to molar ratio of ammonium bicarbonate to total amount of metal cations equal to 3.6:1. Thereafter, obtained mix is mixed at the rate of 300-500 rpm to flush precipitated product, to dry is at 100-150°C and to calcine it.

EFFECT: higher efficiency and quality.

5 cl, 1 tbl, 2 ex

Description

The present invention relates to new compounds belonging to the group of complex oxides with a garnet structure containing rare and rare earth elements that can be used for the manufacture of LED lighting sources.

Yttrium aluminum garnet (rus: AIG or YAG; English: YAG) is a complex oxide of yttrium and aluminum with the chemical formula Y ₃ Al ₅ O ₁₂ and the structure of garnet.

For practical applications in the field of optoelectronics, as a rule, doped derivatives of aluminum yttrium garnet are used, in particular garnet doped with rare-earth elements of the general formula Y _3-x PZ _x Al ₅ O ₁₂ , where PZ-Ce, Eu, x = 0.03 (CN 101985397, C01F 17/00, 2011, US 2003/0111644, 2003; US 6409938, 2002; US 2006/0100088, 2006).

Various methods have been developed for producing yttrium aluminum garnet in the form of single crystals: a method for growing crystals [Refractory compounds. - Novosibirsk: Nauka, 1979, p. 579], the method of horizontal directional crystallization (CN 1552956, C30B 15/00, 2004); and in the form of powders: conventional solid-state method (JP 27966321, C09K 11/08, 1998), hydrothermal method (solvothermal method) [Puttbach R.C. et al., J. Pharm Chem. Solids, 1967 No. 1, 569-571; RU 2137867, C01F 17/00, 2000], the flame-synthesis method or the CBC method (self-propagating high-temperature synthesis) [WO 2011102566, C09K 35/10, 2011], cryochemical method (CN 101497790, C30B 29 / 28, 2009), coprecipitation method (CN 1562880, С04В 35/50, 2005; CN 101973569, C01F 17/00, 2011; CN 101870491, C01F 17/02, 2010;

Ji Guang Coprecipitation synthesis, European Ceramic Soc, 2000, 20, p.2395-2405), sol-gel method (Yanovskaya MI Formation of ultrafine oxide systems. Physicochemical ultrafine systems. - M. : Science, 1987, pp. 189-191].

Of great interest for the present invention are known analogues related to the coprecipitation method, since this method does not require expensive equipment, can be successfully scaled for industrial production tasks, and provides fine products with high productivity and relatively low energy consumption.

Coprecipitation is carried out from solutions containing the corresponding soluble salts (e.g. nitrates, chlorides). As precipitants in the known methods for producing yttrium aluminum garnet (AIG), for example, ammonium bicarbonate and ammonia water are used (CN 1562880, С04В 35/50, 2005; CN 101973569, C01F 17/00, 2011; CN 101870491, C01F 17/02, 2010) or ammonium bicarbonate and urea ([Ji Guang Coprecipitation synthesis, European Ceramic Soc, 2000, 20, p.2395-2405]).

According to the work cited above, the process of producing yttrium aluminum garnet is carried out under the action of ultrasound (US) and at room temperature. In this case, a precipitant is introduced into the solution of yttrium and aluminum nitrates (with a ratio of 3: 5), which is used as ammonium bicarbonate or urea, and then the precipitated product is washed, dried with an infrared lamp, and annealed in air at 700-1000 ° C for 2 hours FROM. If ammonium bicarbonate is used as a precipitant, the cubic YAG phase in the form of a monodisperse powder is obtained at 900 ° C, and in the case of urea, the pure YAG phase is obtained at 1300 ° C. However, these studies relate to the production of only yttrium aluminum garnet and are not considered for the production of doped aluminum yttrium garnet.

Additionally, studies to obtain doped aluminum yttrium garnet show that the products obtained by this synthesis scheme do not have the desired degree of dispersion.

It is known to use the coprecipitation method to obtain powders of aluminum yttrium garnet doped with HfO ₂ , Sc ₂ O ₃ and ZrO ₂ or with rare earth oxides (REE), for example Nd, Yb, Cr, Eu, Er, Sm, Ce, for the manufacture of highly transparent ceramics ( CN 101985397, C04B 35/05, 2011). According to the cited patent, a mixture is obtained by spraying in an aqueous solution of ammonia extremely concentrated solutions of yttrium and aluminum chlorides, and the above additives are introduced either during precipitation or during grinding of the resulting hydroxides. The powders obtained in this way are then ground in acetone in a planetary mill for three minutes and calcined at 800-1400 ° C. In the description of the method under consideration, attention is drawn to the fact that grinding the powders after calcination makes it possible to obtain YAG powders with an aggregate size of 0.5-1 μm.

The purpose of the new invention is to develop a method for producing a group of derivatives of yttrium aluminum garnet doped with rare and rare-earth elements in the form of high-purity, single-phase powders with submicron particle size and high brightness.

The proposed method for producing yttrium aluminum garnet doped with rare earth elements is carried out by the precipitation method by introducing ammonium hydrogen carbonate, used as a precipitant, a mixed aqueous solution of aluminum nitrate, yttrium and alloying elements in an amount corresponding to the molar ratio of ammonium hydrogen carbonate to the total amount of metal cations equal to 3.6: 1, and the deposition is carried out with stirring and in the presence of a fluorine-containing additive introduced into the target precipitator in an amount of 1-5 mol.% fluorine atoms of the amount of precipitant, after which the reaction mixture is stirred at a speed of 300-500 rpm, the precipitated product is isolated, washed with water, dried at 100-150 ° C and calcined at a temperature of 1100 ° C.

Precipitation is preferably carried out with a 2 molar aqueous solution of ammonium bicarbonate.

As the initial solution of a joint aqueous solution of nitric salts of aluminum, yttrium and alloying elements, a solution with a total concentration of metal ions of 1 mol / L is preferably used.

A mixed solution of cations is preferably added at a rate of 60 ml / min. An aqueous solution of ammonium fluoride is used as a fluorine-containing additive during precipitation.

The proposed method relates to the production of previously known compounds, derivatives of an aluminum yttrium fan doped with rare-earth elements, of the general formula

Y _3-x PZ _x Al ₅ O ₁₂ , where x = 0.03 (CN 101985397, C01F 17/00, 2011, US 2003/0111644, 2003; US 6409938, 2002; US 2006/0100088, 2006).

The method is considered on the example of obtaining derivatives of cerium and europium, but can be used in a similar way to obtain derivatives of other rare earth elements.

The proposed method for producing doped rare-earth elements of aluminum yttrium garnet differs from its prototype in a number of essential ways (CN 101985397, С04В 35/05, 20011). First of all, in the proposed method, aluminum, yttrium and rare-earth nitrates (REE) are used as starting products, and ammonium bicarbonate is used as a precipitant. In the analogue, the chlorides of these metals are used as the starting salts, and ammonium hydroxide is used as the precipitant. The choice of metal nitrates as the initial salts is explained by the fact that they are completely removed from the product during calcination and do not participate in the formation of extraneous phases. Thus, the use of nitrates avoids contamination of the final product by extraneous phases.

For the synthesis, a so-called reverse deposition scheme is used, in which a solution containing metal cations is added to a precipitator solution. At the same time, for the incoming solution of metal salts, the conditions of excess precipitant are ensured, which contributes to the formation of a precipitate by the predominant nucleation mechanism, rather than particle growth. Such a sedimentation mechanism is necessary to obtain a finely divided product.

The use of a fluorine-containing additive leads to the formation of samples with a high degree of perfection of the crystal structure at lower temperatures, which leads to a higher luminescence brightness of the synthesized samples compared to samples obtained without the use of a fluorine-containing additive.

The output and quality of the resulting product are exerted by experimentally selected process modes: the weight ratio of components, temperature and speed modes.

So, the molar ratio of ammonium bicarbonate to the total number of metal cations is chosen equal to 3.6: 1. This amount of precipitant ensures complete precipitation of the product and creates a sufficient process window to ensure process reliability. With a smaller amount of precipitant, incomplete precipitation can occur (due to decomposition of ammonium bicarbonate in the solution, for example, when it is accidentally heated), which leads to a decrease in the yield of the product.

According to the proposed method, a solution of metal nitrates is added to the precipitant from a dropping funnel, preferably at a rate of 60 ml / min. Such an infusion rate is optimal for the reaction volumes used in the examples described below; it provides the necessary local excess of precipitant at the point of contact of the solution of metal nitrates with the precipitant solution, thus contributing to the nucleation process and the subsequent production of a finely divided product.

Stirring of the reaction mass is carried out at a speed of 300-500 rpm, which is sufficient to average the reaction mass over the reaction volume during the deposition process and allows you to maintain the necessary local excess of precipitant at the point of contact of the metal nitrate solution with the precipitator solution. In the case of underestimation of the mixing speed below the claimed, there is a risk of creating an excess of metal cations with respect to the precipitant, which can lead to undesirable enlargement of the size of the formed precipitate particles.

According to the proposed method, the resulting product after isolation and washing with water is dried at 100-150 ° C. A lower drying temperature leads to a slower drying of the precipitate and a necessary increase in drying time. A higher drying temperature leads to the risk of formation of hard agglomerates of particles, which is undesirable.

Calcination is carried out at a temperature of 1100 ° C, since at this temperature a garnet phase is formed in the calcined samples, and the use of a fluorine-containing additive makes it possible to ensure high luminescence brightness in these samples.

The concentrations of an aqueous solution of nitrate precipitated metals of 1 mol / L (rather than concentrated solutions of salts, as in the analogue of CN 101985397 considered above) and an aqueous solution of ammonium bicarbonate of 2 mol / L were experimentally tested as the most suitable for obtaining a fine precipitate with a high yield. The use of solutions with a lower concentration is impractical for technological reasons. The use of a solution of metal nitrates with a higher concentration does not provide significant technological advantages, but creates the risk of unwanted enlargement of sediment particles and uneven reaction mass.

According to the proposed method, the deposition is carried out using a fluorine-containing additive to the precipitant. Table 1 shows the experimental data confirming the positive effect of the fluorine-containing additive on the brightness of the resulting phosphors. In the case of the introduction of a fluorine-containing additive in an amount of 1 mol% of fluorine atoms of the amount of precipitant, the intensity of the main emission band increases from 1 to 4.2 rel. units for Y _2.97 Eu _0.03 Al ₅ O ₁₂ and from 2.2 to 4.8 rel. units for Y _2.97 Ce _0.03 Al ₅ O ₁₂ , which is shown in table 1.

Table 1 Comparison of the characteristics of various samples of yttrium aluminum garnets obtained by coprecipitation Sample Name Chemical formula of oxide Precipitation Optimizer Particle size The wavelength of the main emission band Baseband Intensity AIG: Xie Y _2.97 Ce _0.03 Al ₅ O ₁₂ No <1 μm 530 nm 2.2 rel units AIH: Ce + F Y _2.97 Ce _0.03 Al ₅ O ₁₂ Fluorine 1% <1 μm 530 nm 4.8 rel units AIG: Eu Y _2.97 Eu _0.03 Al ₅ O ₁₂ No <1 μm 590 nm 1 rel units AIG: Eu + F Y _2.97 Eu _0.03 Al ₅ O ₁₂ Fluorine 1% <1 μm 590 nm 4.2 rel units

The following is a general outline of the synthesis of yttrium aluminum garnet doped with rare earth elements.

Stage 1. Preparation of a mixed aqueous solution of nitric acid salts (nitrates) Al ³⁺ , Y ³⁺ , RE ³⁺

To obtain the compounds of the above composition, first prepare a joint aqueous solution of nitric salts (nitrates) Al ³⁺ , Y ³⁺ , PZ ^{3+ of the} required composition, preferably with a total concentration of metal ions of 1 mol / L.

Stage 2. Preparation of a precipitant solution (ammonium bicarbonate)

The amount of precipitant (ammonium bicarbonate, NH ₄ HCO ₃ ) is calculated based on ratios in the range of 3.6 mol of precipitant per 1 mol of metal cations in solution. Use an aqueous solution of NH ₄ HCO ₃ preferably with a concentration of 2 mol / liter.

Ammonium fluoride solution is added to the precipitator solution in an amount of 0.1-5% fluorine atoms relative to the amount of precipitant.

Stage 3. Precipitation of compounds of yttrium, aluminum and alloying elements and filtering the precipitate

A mixed solution of cations is poured into a dropping funnel and at a rate optimally equal to 60 ml / min, it is poured into a solution of ammonium bicarbonate. Stirring of the reaction medium is carried out at a speed of 300-500 rpm

The precipitate was separated by filtration and washed with water.

Stage 4. Drying the precipitate

The filtered precipitate is loaded onto a heat-resistant tray and placed in an oven. Drying is carried out at a temperature of 100-150 ° C. Preferably for 8-12 hours.

Stage 5. Calcination of sediment

The dried precipitate is placed in quartz or corundum crucibles and placed in an electric furnace. Calcination is carried out at a temperature of 1100 ° C, preferably within 1-5 hours after the furnace goes into operation.

Example 1

Obtaining yttrium aluminum garnet doped with cerium, corresponding to the stoichiometric formula Y _2.97 Ce _0.03 Al ₅ O ₁₂ .

First, a joint aqueous solution of nitric acid salts (nitrates) of Al ³⁺ , Y ³⁺ , Ce ³⁺ is prepared with the desired molar ratio of cations and their total content of 1 mol / L. A precipitating solution is prepared by dissolving in water an amount of ammonium hydrogen carbonate corresponding to a molar ratio with the amount of precipitated cations of 3.6: 1, and then adding to this solution an ammonium fluoride solution in an amount of 1 mol% of the amount of ammonium hydrogen carbonate.

Precipitation is carried out by pouring a nitric acid solution of cations to a precipitator solution at a rate of 60 ml / min with stirring at a speed of 300 rpm. The precipitate is filtered off and washed with distilled water by decantation 2 times. The filtered washed precipitate is dried in a heat-resistant tray in an oven at a temperature of 100 ° C for 12 hours. The dried precipitate is calcined at a temperature of 1100 ° C for 2 hours.

Get a powder with a submicron particle size and a light output exceeding the light yield of the powder obtained without the addition of fluorine.

As a comparison experiment, the synthesis of the same compound is likewise carried out under the same conditions, but without the addition of fluorine. A comparison of the characteristics of the powder obtained with the addition of fluorine and without the addition of fluorine are given in table 1.

Example 2

Obtaining yttrium-aluminum garnet doped with europium, corresponding to the stoichiometric formula Y _2.97 Eu _0.03 Al ₅ O ₁₂

First, a joint aqueous solution of nitric acid salts (nitrates) of Al ³⁺ , Y ³⁺ , Eu ³⁺ is prepared with the desired molar ratio of cations and their total content of 1 mol / L. A precipitating solution is prepared by dissolving in water an amount of ammonium hydrogen carbonate corresponding to a molar ratio with the amount of precipitated cations of 3.6: 1, and then adding to this solution an ammonium fluoride solution in an amount of 1 mol% of the amount of ammonium hydrogen carbonate.

Precipitation is carried out by pouring the nitric acid solution of the cations to the precipitator solution with stirring, while the precipitator solution is poured preferably at a speed of 60 ml / min, and the reaction mass is stirred preferably at a speed of 500 rpm. The precipitate is filtered off and washed with distilled water on the filter 2 times. The filtered washed precipitate is dried in a heat-resistant tray in an oven at a temperature of 150 ° C for 8 hours. The dried precipitate is calcined at a temperature of 1100 ° C for 2 hours.

Get a powder with a submicron particle size and a light output exceeding the light yield of the powder obtained without the addition of fluorine.

As a comparison experiment, the synthesis of the same compound is likewise carried out under the same conditions, but without the addition of fluorine. A comparison of the characteristics of the powder obtained with the addition of fluorine and without the addition of fluorine are given in table 1.

The proposed method is considered on the example of producing yttrium aluminum garnet doped with cerium and europium. Similarly, chemical compounds of the same structure, but doped with other rare-earth elements, for example, Nd, Yb, Er, Sm, can be obtained in the same way.

Claims (5)

1. The method of producing yttrium aluminum garnet doped with rare-earth elements, carried out by the method of precipitation by introducing the starting compounds of aluminum, yttrium and alloying elements into the precipitant, followed by separation of the precipitated product and calcining the obtained powdery product at 1100 ° C, characterized in that the deposition is carried out in the presence of a fluorine-containing additive taken in an amount corresponding to 1-5% content of fluorine atoms relative to the amount of precipitant, and hydrocarbon is used as the precipitant ammonium nat, into the aqueous solution of which a mixed aqueous solution of aluminum nitrate, yttrium and alloying elements is added with stirring in an amount corresponding to a molar ratio of ammonium bicarbonate to the total amount of metal cations equal to 3.6: 1, after which the resulting reaction mixture is stirred at a speed 300-500 rpm and the precipitated product isolated is washed with water, dried at 100-150 ° C and calcined. 2. The method according to claim 1, characterized in that the precipitation is carried out preferably with a 2 molar aqueous solution of ammonium bicarbonate. 3. The method according to claim 1, characterized in that the solution with a total concentration of metal ions of 1 mol / l is preferably used as the initial solution of a joint aqueous solution of nitric acid salts of aluminum, yttrium and alloying elements. 4. The method according to claim 1, characterized in that the mixed solution of cations is preferably added at a rate of 60 ml / min. 5. The method according to claim 1, characterized in that as a fluorine-containing additive during precipitation, an aqueous solution of ammonium fluoride is used, preferably in an amount of 1 mol% of the amount of ammonium bicarbonate.