CN1539739A - Chemical coprecipitation method for synthesizing, powder material of terrae rare salt of normal niobic acid - Google Patents

Abstract

A process for synthesizing the powdered RE niobate by chemical codeposition method includes proportionally mixing K2CO3 and Nb2O5 powder, cofusion reaction at 950 deg.C for 1-2 hr. dissolving the cofused substance in water to obtain K3NbO4 solution, dissolving R3(CO3)3 in HCL solution, adding it to said K3NbO4 solution to obtain white floc deposit, dripping ammonia water until pH=9-11, ageing the deposit, filter, washing, low-temp baking and high-temp calcining for crystallizing.

Description

Chemical coprecipitation synthesis method of n-niobic acid rare earth salt powder material

Technical Field

The invention relates to a method for synthesizing a normal niobic acid rare earth salt RNbO₄Chemical coprecipitation method for powder material, wherein R can be lanthanum L respectivelyThe rare earth elements from a to lutetium Lu are replaced by yttrium Y, and the synthesized n-niobate rare earth salt powder material can be used as functional powder and also can be used as a raw material of a ceramic material.

Background

N-columbate rare earth salt RNbO₄Is a series of rare earth compounds with similar structures and phase change characteristics, and when R in the rare earth compounds is respectively La to Lu and is replaced by Y, the structures of the rare earth compounds do not change greatly: the phase change is monoclinic phase at room temperature, the point group is 2/m, and the phase change is generated at 500-850 ℃ to form a tetragonal phase with the point group being 4/m. RNbO₄It is a material with wide application prospect, and has unique application in the aspects of shape memory effect, toughened ceramic, luminescence and the like due to the specific ferroelastic domain structure and domain switching behavior. However, the key to the ability to prepare such materials in large quantities is the high purity, ultra-fine RNbO₄And (3) preparing powder. In relation to RNbO₄The preparation method of the powder comprises two methods of solid phase reaction and chemical coprecipitation, wherein the former method can be found in Li Jian et al, reported in Materials Letters, volume 21, 1994, and S.Maschio et al, reported in Journal of European Ceramic Society, volume 18, 1998; the latter can be found in S.Maschio et al, Journal of Materials Science, Vol.30, 1995 and Li Jian et al, Vol.26 Materials Letters, Vol.1996. In general, the solid phase synthesis method synthesizes RNbO₄The equipment and the process are simple, and the rare earth oxide R with equal molar ratio can be obtained₂O₃And niobium pentoxide Nb₂O₅Is prepared by reaction at high temperature, is easy to realize and is commonly used RNbO₄A powder synthesis method. However, the solid-phase synthesis method has the characteristics that the raw materials directly react in a solid state, the reaction must be realized at a certain high temperature, the energy consumption is high, and the inevitable defects of large powder particle size, wide particle size distribution, uneven components and the like generally exist. The chemical coprecipitation method is a reaction, nucleation, growth, collection and treatment process at the atomic and molecular level in a solution system, and can obtain powder with high purity, fine particles and uniformity. Currently, the chemical coprecipitation method is adopted to synthesize RNbO₄By chlorinating the rare earth RCl₃Solution and niobium chloride NbCl₅Hydrolysis of the solution to produce RNbO₄Alternatively, citrate methods may be used, however, these chemical coprecipitation methods produce RNbO₄Has the disadvantage that the raw materials all need to use NbCl which is expensive₅At present, the preparation of RNbO by other raw materials is not seen₄Chemical coprecipitation method (1).

Disclosure of Invention

For synthesizing and preparing the superfine and uniform RNbO with low cost and high purity₄The invention provides a chemical coprecipitation synthesis method of a powder material of a rare earth salt of n-niobic acid. Since Nb₂O₅Is amphoteric oxide (mainly acidic) and is difficult to dissolve in water, alkaline solution and dilute mineral acid, and the technical scheme adopted for the preparation is to prepare the water-soluble niobiumAcid salt and then have coprecipitation reaction with rare earth compound to synthesize RNbO₄。

The technical scheme of the invention is as follows: the coprecipitation reaction adopts a liquid-liquid approach, namely, the reactant participating in the coprecipitation reaction is K₃NbO₄Solutions and RCl₃And (3) solution.

The method uses niobium pentoxide Nb₂O₅As a key raw material, according to Nb₂O₅With potassium carbonate (K)₂CO₃) The binary phase diagram of (1) is obtained by melting K in a molar ratio of 3: 1 in an alkaline solvent₂CO₃And Nb₂O₅After the powders are uniformly mixed, carrying out eutectic reaction for 1-2 hours at the temperature of more than 950 ℃. Dissolving the eutectic in water to obtain potassium niobate K₃NbO₄A solution;

adding rare earth carbonate R₃(CO₃)₃Dissolving in 6M HCl solution to obtain RCl₃A solution;

RCl is added according to the molar ratio of 1: 1₃Adding K into the solution at constant speed under stirring₃NbO₄In the solution, carrying out coprecipitation reaction to obtain white flocculent precipitate, and dropwise adding ammonia water in the reaction to adjust the pH value to 9-11;

aging, filtering, washing anddrying the precipitate at low temperature to obtain an amorphous product; crystallizing and calcining at a temperature of above 800 ℃ to obtain polycrystalline RNbO₄Ultrafine powder;

starting material R₃(CO₃)₃R in the (A) can be respectively replaced by rare earth elements from La to Lu including Y, and a series of RNbO including the rare earth elements from La to Lu including Y is synthesized₄。

The invention has the beneficial effects that: the method uses Nb which is relatively cheap and easily obtained as a raw material₂O₅Substitution of unreachable NbCl₅Raw materials are synthesized into a series of RNbO by coprecipitation reaction₄The powder material has simple process, high product purity and superfine and uniform particles. The synthesized powder material can be used as functional powder and can also be used as a raw material of a ceramic material.

Drawings

FIG. 1 chemical coprecipitation method for synthesizing LaNbO by liquid-liquid route₄Powder process flow chart

FIG. 2 shows an X-ray diffraction pattern of powder prepared by a liquid-liquid method of chemical coprecipitation method under the condition of pH 9-11

Detailed Description

To prepare lanthanum niobate LanbO₄For example, the process flow for powder synthesis using the liquid-liquid route is shown in FIG. 1:

firstly, preparing K by adopting an alkaline solvent melting method₃NbO₄. Mixing K in a molar ratio of 3: 1₂CO₃And Nb₂O₅After the powder is uniformly mixed, carrying out eutectic reaction for 1-2 hours at the temperature of more than 950 ℃, and dissolving the eutectic in water to obtain K₃NbO₄A solution as a reactant of the coprecipitation reaction. The eutectic reaction is as follows:

the main reaction mechanism of the liquid-liquid route of the coprecipitation method is K with a molar ratio of 1: 1₃NbO₄Solution with LaCl₃Equivalent precipitation of the solution. At K₃NbO₄Adding LaCl into the solution₃Solution, the reaction of the formula (1) is easy to occur, and LaNbO is obtained₄Predominantly amorphous powder:

(1)

(2)

in the reaction solution, the precipitation reaction (1) and the hydrolysis reaction (2) are always a pair of reactions competing with each other. According to the equilibrium shift theory, both the addition of acid and the dilution of the solution will favor K₃NbO₄Hydrolysis of (2), addition of alkali then inhibits K₃NbO₄Hydrolysis of (3). From a kinetic point of view, the rate of the precipitation reaction (1) at the beginning of the reaction is much greater than that of the hydrolysis reaction (2), in LaCl₃Solution addition of K₃NbO₄Immediately after the solution, there is LanbO₄The precipitate forms but changes with the nature of the solution, i.e. the solution is constantly diluted by the addition of the solution and, due to the addition of LaCl₃The solution is acidic, so that the alkalinity of thesystem is gradually weakened, the hydrolysis tendency is enhanced, namely, the hydrolysis reaction (2) is promoted to a certain extent, and the solution and the precipitation reaction (1) compete with each other to compete with K₃NbO₄The reaction of (1). Adding ammonia water in the reaction process to improve the pH alkalinity of the system, leading the precipitation reaction (1) to be dominant, inhibiting the hydrolysis reaction, and leading the reaction product to be amorphous LanbO₄And (4) precipitating.

Substituting different rare earth ions such as Ce, Pr to Lu including Y rare earth elements for raw material R₃(CO₃)₃R in (1) can be respectively synthesized into a series of compounds such as CeNbO₄、PrNbO₄、LuNbO₄And YNbO₄All the powder materials of the n-columbate rare earth salt, etc. can reach the purity of more than 99.5 percent, d₅₀＜1μm。

Example one:

20.7 g of K are weighed out separately₂CO₃And 13.3 g Nb₂O₅Mixing the powder and the powder, co-melting the mixture at 950 ℃ for 2 hours, and dissolving the co-melt in water to obtain K₃NbO₄And (3) solution. 28.3 g of La were weighed₂(CO₃)₃·6H₂O powder was dissolved in 6M HCl to give LaCl₃Dissolving LaCl₃Adding K into the solution at a constant speed under stirring according to a certain proportion₃NbO₄In the solution, precipitation reaction immediately occurs to obtain white flocculent precipitate, and ammonia water is added dropwise in the reaction to adjust the pH value of 9. And aging, filtering, washing and drying the obtained precipitate at low temperature to obtain an amorphous product. Crystallizing and calcining at 800 ℃ to obtain LaNbO₄Polycrystalline powder. Purity of powder material 99.5%, d₅₀＝0.95μm。

Example two:

20.7 g of K are weighed out separately₂CO₃And 13.3 g Nb₂O₅Mixing the powder and the powder, co-melting the mixture for 1 hour at 950 ℃ and dissolving the co-melt in water to obtain the potassium niobate K3NbO₄And (3) solution. 28.3 g of La were weighed₂(CO₃)₃·6H₂O powder was dissolved in 6M HCl to give LaCl₃Dissolving LaCl₃Adding K into the solution at a constant speed under stirring according to a certain proportion₃NbO₄In the solution, precipitation reaction immediately occurs to obtain white flocculent precipitate, and ammonia water is added dropwise in the reaction to adjust the pH value of 10. And aging, filtering, washing and drying the obtained precipitate at low temperature to obtain an amorphous product. Crystallizing and calcining at 1000 ℃ to obtain LaNbO₄Polycrystalline powder. Purity of powder Material 99.7%, d₅₀＝0.97μm。

Example three:

20.7 g of K are weighed out separately₂CO₃And 13.3 g Nb₂O₅Powder, the two are mixed evenly and then are co-melted for 1 hour at 950 ℃, and the co-melted material is dissolved in water to obtain the potassium niobate K₃NbO₄And (3) solution. 28.3 g of La were weighed₂(CO₃)₃·6H₂O powder was dissolved in 6M HCl to give LaCl₃Dissolving LaCl₃Adding K into the solution at a constant speed under stirring according to a certain proportion₃NbO₄In the solution, precipitation reaction immediately occurs to obtain white flocculent precipitate, and ammonia water is added dropwise in the reaction to adjust the pH value of 11. And aging, filtering,washing and drying the obtained precipitate at low temperature to obtain an amorphous product. Crystallizing and calcining at 1200 ℃ to obtain LaNbO₄Polycrystalline powder. Purity of powder Material 99.7%, d₅₀＝0.98μm。

FIG. 2 is a powder X-ray diffraction pattern prepared by a chemical coprecipitation method liquid-liquid approach under the condition of pH 9-11. It can be seen that the amorphous powder prepared by coprecipitation method can obtain LanbO after calcination at 800-1200 deg.C₄Polycrystalline powder.

Claims (1)

1. A chemical coprecipitation process for synthesizing the powder of rare-earth salt of n-niobic acid includes such steps as preparing Nb₂O₅As one of the key raw materials, K with the molar ratio of 3: 1 is added₂CO₃And Nb₂O₅After the powder is uniformly mixed, carrying out eutectic reaction for 1-2 hours at the temperature of more than 950 ℃; dissolving the eutectic in water to obtain K₃NbO₄A solution;

by using rare earth carbonates R₃(CO₃)₃As the second key raw material, R₃(CO₃)₃Dissolving in HCl solution to obtain RCl₃A solution;

RCl is added according to the molar ratio of 1: 1₃Adding K into the solution at constant speed under stirring₃NbO₄In the solution, carrying out coprecipitation reaction to obtain white flocculent precipitate, and dropwise adding ammonia water in the reaction to adjust the pH value of 9-11;

aging, filtering, washing and drying the precipitate at low temperature to obtain an amorphous product; crystallizing and calcining at a temperature of above 800 ℃ to obtain polycrystalline RNbO₄Ultrafine powder;

starting material R₃(CO₃)₃R in the (A) can be respectively replaced by rare earth elements from La to Lu including Y, and a series of RNbO including the rare earth elements from La to Lu including Y is synthesized₄。

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