CN1539747A - Chemical coprecipitation method for synthesizing powder material of terrae rare salt of normal niobic acid - Google Patents

Abstract

A process for preparing RE niobate powder by chemical codeposition synthesis includes proportionally mixing K2CO3 with Nb2O5 powder, cofusing at 950 deg.C for 1-2 hr, dissolving in water to obtain K3NbO4 solution, codeposition reaction between K3NbO4 solution and R2(Co3) while adding HCl solution to control the reaction progress, dripping ammonia water to make pH=9-11, ageing, filtering, washing, low-temp baking and high-temp 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 diluentSoil salt RNbO₄The chemical coprecipitation method of the powder material, wherein R can be respectively replaced by rare earth elements of La to lutetium Lu including yttrium Y, and the synthesized positive niobate rare earth salt powder material can be used as functional powder and can also 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 phasereaction 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 its own characteristics that the raw materials are directly reacted in a solid state, and therefore, the reaction must be carried out 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, so that the chemical coprecipitation method and other methods are often adopted in the occasions with high requirements on the purity and the particle size of the powder. The chemical coprecipitation method is the reaction of atoms and molecules in a solution systemThe processes of nucleation, growth, collection and treatment can obtain powder with high purity, fine and uniform particles. Currently, the chemical coprecipitation method is adopted to synthesize RNbO₄Can be prepared by chlorinating the rare earth RCl₃Solution and niobium chloride NbCl₅Hydrolysis of the solution to produce RNbO₄Alternatively, the citrate method may be employed. 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 the synthesis of high purity, ultra-fine, uniform RNbO₄The invention provides a chemical coprecipitation method, which is a powder material and reduces the preparation cost. Since Nb₂O₅Is amphoteric oxide (mainly acidic), and is difficult to dissolve in water, alkaline solution and dilute mineral acid, and its technical scheme is characterized by that firstly, the water-soluble niobate is prepared, then the niobate and rare earth compound are undergone the process of coprecipitation reaction to synthesize RNbO₄。

The technical scheme of the invention is as follows: the coprecipitation reaction adopts a liquid-solid approach, namely, the reactant participating in the coprecipitation reaction is K₃NbO₄Solution and rare earth carbonate R₂(CO₃)₃Solid particles.

The method is based on the use of niobium pentoxide Nb₂O₅As a key raw material, according to Nb₂O₅And K₂CO₃The 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 ℃, and dissolving the eutectic in water to obtain the potassium niobate (K)₃NbO₄) A solution;

mixing K according to the molar ratio of 1: 1₃NbO₄Solution and rare earth carbonate R₂(CO₃)₃Chemical coprecipitation reaction is carried out to synthesize RNbO₄By addition of a compoundwith R in the reaction₂(CO₃)₃Controlling the reaction process by using an equimolar HCl solution, and then controlling the pH value of a reaction system to 9-11 by adding ammonia water;

RNbO synthesized by chemical coprecipitation reaction₄The amorphous product is aged, filtered, washed, dried at low temperature and crystallized at high temperature to prepare the polycrystal RNbO₄And (5) ultrafine 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-solid route₄Powder process flow chart

FIG. 2 shows that LaNbO is prepared by chemical coprecipitation method through liquid-solid route₄Particle size distribution of powder

In the figure: 1. liquid-solid route, d₅₀0.97 μm; 2. liquid-liquid route, d₅₀＝0.97μm

Detailed Description

Lanthanum niobate LanbO₄For example, the process flow of the liquid-solid route powder synthesis is shown in fig. 1:

firstly, preparing K by adopting an alkaline solvent melting method₃NbO₄. Mixing K in a molar ratio of 3: 1₂CO₃And Nb₂O₅Uniformly mixing the powder, carrying out a eutectic reaction for 1-2 hours at a temperature of above 950 ℃, and dissolving the eutectic in water to obtain K₃NbO₄A solution asThe reactants of the reaction are co-precipitated. The eutectic reaction is as follows:

the main reaction mechanism of the liquid-solid route is the heterogeneous reaction. Reaction (1) is present at the beginning of the reaction, although the conversion of this reaction is low. After HCl is added into the system, La in the reaction system is caused to exist due to the dissolving action (2) of HCl₂(CO₃)₃Can act as a reservoir to release trivalent lanthanum ions (La)³⁺) Participating in the coprecipitation reaction (3), and simultaneously, K is also present in the system₃NbO₄Hydrolysis reaction (4). Then, the pH value of the system is kept between 9 and 11 due to the addition of ammonia water, so that the hydrolysis reaction (4) is inhibited, and the amorphous LanbO is obtained₄The precipitated product.

(1)

(2)

(3)

(4)

Because of the continuous addition of HCl solution, the reaction in the liquid-solid way is basically uniform and continuously carried out, and the supersaturation degree is always maintained at the same level, thereby keeping the precipitation nucleation size basically consistent, ensuring the product to have small particle size and good distribution, and being beneficial to obtaining uniform and fine particles. FIG. 2 is the particle size d at the medium diameter₅₀In the same case (d)₅₀0.97 μm), liquid-solid route and direct application of LaCl₃The powder distribution curve comparison chart of the liquid-liquid path synthesis of the solution as the reactant is shown, wherein 1 represents the liquid-solid path, and 2 represents the liquid-liquid path.

Substituting different rare earth ions such as Ce, Pr to Lu including Y rare earth elements for raw material R₃(CO₃)₃R in the formula (I) can be used for synthesizing a series of compounds of niobiumRare earth salts of acids, e.g. 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 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)₃·6H₂Directly adding O powder into the aqueous solution, and stirring the K powder at a constant speed₃NbO₄Adding La into the solution₂(CO₃)₃·6H₂In the O system, the following operation sequence is carried out: (1) adding 20ml of 6M HCl solution under continuous stirring, and after stirring for a period of time, beginning to form flocculent products; (2) ammonia was added with constant stirring to pH9, with a gradual increase in white flocculent product. Ageing, filtering, washing, drying at low temperature, crystallizing and calcining at 800 ℃ to obtain LaNbO₄Polycrystalline powder. The purity of the powder material can reach 99.5 percent, d₅₀＝0.91μm。

Example two:

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)₃·6H₂Directly adding O powder into the aqueous solution, and stirring the K powder at a constant speed₃NbO₄Adding La into the solution₂(CO₃)₃·6H₂In the O system, the following operation sequence is carried out: (1) adding 20ml of 6M HCl solution under continuous stirring, and after stirring for a period of time, beginning to form flocculent products; (2) ammonia was added with constant stirring to pH10, with a gradual increase in white flocculent product. Ageing, filtering, washing, low-temp baking, crystallizing at 1000 deg.C and calciningObtaining LaNbO₄Polycrystalline powder. The purity of the powder material can reach 99.7 percent, d₅₀＝0.95μm。

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)₃·6H₂Directly adding O powder into the aqueous solution, and stirring the K powder at a constant speed₃NbO₄Adding La into the solution₂(CO₃)₃·6H₂In the O system, then according to the followingThe operation sequence is as follows: (1) adding 20ml of 6M HCl solution under continuous stirring, and after stirring for a period of time, beginning to form flocculent products; (2) ammonia was added with constant stirring to pH11, with a gradual increase in white flocculent product. Ageing, filtering, washing, drying at low temperature, crystallizing and calcining at 1200 ℃ to obtain LaNbO₄Polycrystalline powder. The purity of the powder material can reach 99.7 percent, d₅₀＝0.97μm。

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 ℃, and dissolving the eutectic in water to obtain K₃NbO₄A solution;

mixing K according to the molar ratio of 1: 1₃NbO₄Solution and rare earth carbonate R₂(CO₃)₃Chemical coprecipitation reaction is carried out to synthesize RNbO₄By addition of a compound with R in the reaction₂(CO₃)₃Controlling the reaction process by using an equimolar HCl solution, and then controlling the pH value of a reaction system to 9-11 by dropwise adding ammonia water;

RNbO synthesized by chemical coprecipitation reaction₄The amorphous product is aged, filtered, washed, dried at low temperature and crystallized at high temperature to prepare the polycrystal RNbO₄And (5) ultrafine 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。

Images