RU2580138C1 - Method for producing stabilized zirconia dioxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the synthesis of inorganic compounds, namely technology of stabilized zirconia, and may be used for the manufacture of structural ceramics, solid state fuel cell, oxygen sensors, catalysts, as well as medical, electronics and jewelry industries. Method comprises the synthesis of zirconium hydroxide by mixing zirconium oxychloride with an aqueous solution of ammonia concentration 6.0-9.5 mol / l when the ratio of the volume of solid and liquid phases of 1:(3-5) with subsequent operations decanting the solution, filtering and drying the precipitate, mixing the obtained zirconium hydroxide with a solution of rare earth acetate, in a given product to obtain the desired molar ratio of zirconium oxide and rare earth oxide, drying and heat treatment.

EFFECT: invention provides a simplification and an intensification of the process of getting stabilized zirconia to the absence of impurities and improved electro-physical characteristics.

1 cl, 1 tbl, 18 ex

Description

The invention relates to the synthesis of inorganic compounds, and in particular to a method for producing stabilized zirconia, and can be used for the manufacture of structural ceramics, solid-state fuel cells, oxygen sensors, catalysts, as well as in medical, electronic, jewelry, etc. industry.

According to an analytical review conducted by methods for producing stabilized zirconia, the two main methods are solid-phase (ceramic) and co-precipitation.

A known method for producing stabilized zirconia by co-precipitation of hydroxides using zirconium oxychloride and rare earth nitrates (REE) as starting materials (Gorelov V.P., Palguev S.F. Conductivity maxima and phase boundaries of fluorite type in ZrO ₂ -oxid systems REE // Doklady AN SSSR. 1979. T. 248. No. 6. S. 1356-1359). A variant of this method is a method for producing stabilized zirconia using zirconium oxychloride and a rare earth concentrate (REE) in the form of carbonates with a high cerium content (Patent RU 2463276 C2 [State educational institution of higher education “Perm State Technical University”] 10.10.2012) . It consists in the co-precipitation of hydroxides from an aqueous solution of zirconium oxychloride and REE concentrate dissolved in concentrated nitric acid; 25% aqueous ammonia is used as a precipitant. It turns out a gel-like product, which is washed from impurities, dried and subjected to heat treatment.

In both cases, the disadvantage is the difficulty of washing the gel-like precipitate from impurities, a large amount of wastewater. Due to the difference in pH of the precipitated hydroxides, precipitates are obtained with an uneven distribution of components, which affects the phase and particle size distribution of the resulting material. In addition, in the second method, an organic reagent (ethyl alcohol) is used to dry the product, and an additional operation involving the use of ultrasound is also required.

A known method of producing stabilized zirconia by wet grinding of zirconia and yttrium oxide, taken in the required proportions, in a ball mill, followed by drying and heat treatment at 1350-1500 ° C. These operations were repeated 2 or more times (Patent US 4542110 A [Hitachi Chemical Company, Ltd] 09/17/1985).

The disadvantage of this method is the large number of operations, high temperatures, the difficulty of obtaining single-phase samples, the introduction of additional reagents (silicon oxide - ≤0.5 wt.% Or alumina from 0.2 to 1.0 wt.%) To reduce the sintering temperature.

The closest to the proposed invention in technical essence and the achieved result is a method of producing oxide powders, including the deposition of zirconium hydroxide during the processing of zirconium oxychloride with 25% ammonia solution, the treatment of zirconium hydroxide with a solution of yttrium chloride or yttrium chloride in a given molar ratio ZrO ₂ : Y ₂ O ₃ for 23-24 hours, evaporation to dryness of the powder with further thermal treatment in the temperature range 600-1200 ° C (Author's certificate SU 1114617 a [Sopova TN, Fedosov AI Belya Ina RG, Kulagin VV], 23.09.1984).

The disadvantage of this method is that the use of a toxic concentrated solution of ammonia in the production of zirconium hydroxide determines the rapid course of the reaction reaction with the possible release and loss of zirconium oxychloride itself at the initial stage of the process. There are no data on the content of zirconium dioxide in the resulting hydroxide and on the content of impurities in the products - hydroxide and stabilized zirconium oxide. The introduction of yttrium in the form of chloride or nitrate leads to the presence of impurities of chlorine and nitrogen that are difficult to remove from the finished product, which reduce the electrophysical properties of the resulting material.

The technical result of the invention is to simplify and intensify the process of obtaining stabilized zirconium oxide.

The technical result of the task is achieved by the synthesis of zirconium hydroxide in a heterophasic way by mixing zirconium oxychloride with an aqueous solution of ammonia with a concentration of 6.0-9.5 mol / l with a ratio of the volumes of solid and liquid phases (T: W) = 1: (3-5), followed by decantation of the mother liquor, separation of the solid phase by filtration and drying in air. This provides a dense, well-filtered sediment of zirconium hydroxide with a high content of zirconium dioxide - 66-74 mass. % and low in chloride ions (less than 0.05 wt.%). The resulting hydroxide is treated with an aqueous solution of REE acetate in the molar ratio of zirconium oxide and rare earth oxide specified to obtain the desired product and stirred for 15-20 hours. The suspension is evaporated on a hot plate until dry. The powder mixture is subjected to heat treatment in the temperature range 500-900 ° C.

The table shows the results of the studies. Examples 1-4 carried out in the conditions of the prototype method.

Example 5. Zirconium oxychloride ZrOCl ₂ · 8H ₂ O in an amount of 36 g is added in small portions with stirring in a pre-cooled ammonia solution with a concentration of 7.6 mol / l, taken in an amount of 60 ml. The reaction mixture was left without stirring for 2 hours. The clarified mother liquor is drained by decantation, the precipitate is poured with a fresh portion of distilled water in a volume of 200-300 ml and left to settle. To avoid the difficulties associated with the sedimentation of fine particles of the precipitate, further washing of the precipitate is carried out by decantation, controlling the pH of the mother liquor and the content of chloride ion (using AgNO ₃ ). The decantation is completed when the pH of the solution reaches 7-7.5 and a negative reaction to the chloride ion. The zirconium hydroxide precipitate is transferred to a filter and dried to a friable state in air.

19.7 g of zirconium hydroxide are obtained in the form of amorphous (XRD data), free-flowing white powder. The content of zirconium dioxide is 66.7 mass. %, chloride ion less than 0.02 mass. % The pycnometric density of the hydroxide powder is 2.4 g / cm ³ , the dispersion of the powder is 2.2 μm.

Take 3.5 g of powdered amorphous zirconium hydroxide, 12.3 ml of an aqueous solution of yttrium acetate with a concentration of 0.154 mol / l (the ratio of the components corresponds to the composition of Y ₂ O ₃ · 20ZrO ₂ ). Mixing and shaking of zirconium hydroxide with yttrium acetate solution is carried out in closed containers at room temperature for 15-20 hours. The suspension is evaporated on a hot plate until dry. Heat treatment of the resulting mixture is carried out at 670 ° C for 10 hours. According to x-ray phase analysis (XRD), the resulting powder is a solid solution of cubic modification. The dispersion of the powder is 1.5 microns.

To obtain a solid electrolyte and determine electrophysical values, the charge powder is pressed at a pressure of 4.5-5.0 t / cm ² , the resulting tablet is sintered at a temperature of 1200 ° C. The conductivity of the material was 2.6 · 10 ^-3 Ohm ^-1 · cm ^-1 .

Examples No. 6-18 are carried out analogously to example No. 5, the modes are shown in the table. The density of the obtained powders is in the range of 6.05-6.15 g / cm ³ .

According to the data in the table, our proposed method, in contrast to that described in the prototype, provides stable zirconium oxide with no impurities and improved electrophysical characteristics.

Claims (1)

A method of obtaining stabilized zirconium oxide, including the synthesis of zirconium hydroxide by mixing zirconium oxychloride with aqueous ammonia followed by decantation of the solution, filtering and drying the precipitate, mixing the obtained zirconium hydroxide with a rare-earth salt solution in a molar ratio of zirconium oxide to the desired product to obtain the desired product rare earth oxide, drying and heat treatment, characterized in that the processing of zirconium oxychloride is carried out with solution a ammonia with a concentration of 6.0-9.5 mol / l with a ratio of the volumes of solid and liquid phases (T: G) 1: (3-5), and a solution of rare-earth element acetate is used as a solution of the salt of the rare-earth element.