CN1958882A - Method for synthesizing sheet single crystal grains of sodium niobate through molten salt growth method - Google Patents

Abstract

This invention relates to a molten salt method for synthesizing lamellar NaNbO3 single crystal particles. The method comprises: utilizing Bi2O3, Na2CO3 and Nb2O5 as the raw materials and NaCl or Na2CO3 as the medium, preparing lamellar Bi2.5Na3.5Nb5O18 single crystal particles by molten salt method, and preparing lamellar NaNbO3 single crystal particles with perovskite structure. The obtained lamellar NaNbO3 single crystal particles have lengths of 0.5-30 mum, and length to thickness ratio of 1-25.

Description

The method of method for synthesizing sheet single crystal grains of sodium niobate through molten salt growth

Technical field

The present invention relates to a kind of method of method for synthesizing sheet single crystal grains of sodium niobate through molten salt growth, belong to the ceramic crystalline grain preparing technical field.

Background technology

Piezoelectric ceramics has mechanical resonant characteristic and energy transformation ability, and its application spreads all over the different corners of many high-tech areas such as electronics, medical treatment, space flight and human daily life.The extensive now piezoceramic material that uses is based on the lead base piezoelectric ceramics, bring serious harm in production, use, waste treatment process the mankind and ecotope, each major industrial country just competitively researches and develops the friendly high-performance Pb-free piezoelectric ceramics of novel environmental.

Ferro-electricity single crystal has excellent piezoelectric property, but adopts the crystal grain random arrangement of the pottery of traditional solid sintering technology preparation, and piezoelectric property can not be given full play of.Utilize the crystalline anisotropy to carry out the texture engineering, the pottery that the preparation crystal grain orienting is arranged is arranged of preferred orient the ceramic crystalline grain of script random orientation, and its performance presents tangible anisotropy, and the excellent properties on the material specific direction is shown.Template grain growth technology (TGG) is to utilize the anisotropic single crystal particle of pattern to make crystal seed, in moulding process, make the crystal seed orientation, crystal seed consumption in the sintering process, the growth of close grain preferred orientation, form textured microstructure, significantly improve the piezoelectric ceramics performance.

The base metal niobate based leadless piezoelectric ceramic excellent performance is perovskite structure, does not also have suitable anisotropic particles as the template in the template grain growth technology at present.If but adopted suitable anisotropic particles as presoma, would utilize reaction template grain growing technology (RTGG) also can prepare the pottery that crystal grain orienting is arranged.

Adopting reaction template grain growing technology to prepare the arrange key of pottery of crystal grain orienting is the synthetic anisotropic crystal grain of pattern.Molten-salt growth method is a kind of powder synthetic method commonly used, because the mass transfer velocity in the fused salt far above the mass transfer velocity in the solid phase, so adopt molten-salt growth method can reduce temperature of reaction and shortening reaction times, can also be controlled the size and the pattern of crystal grain simultaneously effectively.The perovskite structure reaction template is pseudo-isotropic, has the isotropic growth characteristic, and the ceramic powder of the perovskite structure of traditional liquid phase method preparation is generally cubic, can not be as the template in the reaction template grain growing.Studies show that, two step synthesis methods can prepare the template crystal grain with the anisotropic perovskite structure of pattern, promptly at first in liquid phase environment, react the synthetic anisotropic precursor compound of pattern that has, by the synthetic compound that obtains needed perovskite structure of chemical reaction, keeping the shape characteristic of precursor compound simultaneously again then.

With the synthetic sheet NaNbO that obtains of this method ₃Single crystal particle is original powder, adopts the template grain growth technology, can make (Na, K) NbO that crystal grain orienting is arranged ₃Based leadless piezoelectric ceramics improves ceramic piezoelectric property.

Summary of the invention

The object of the present invention is to provide a kind of method for preparing the flaky sodium niobate single crystal particle with molten-salt growth method.

The method of a kind of method for synthesizing sheet single crystal grains of sodium niobate through molten salt growth of the present invention is characterized in that: with analytically pure Na ₂CO ₃, Nb ₂O ₅, Bi ₂O ₃Be raw material, with NaCl or Na ₂SO ₄Be medium, by two-step reaction method synthesizing flaky NaNbO ₃Single crystal particle; The first step reaction prepares the bismuth laminated Bi of sheet with molten-salt growth method _2.5Na _3.5Nb ₅O ₁₈Single crystal particle; The reaction of second step is with the bismuth laminated Bi of above-mentioned sheet _2.5Na _3.5Nb ₅O ₁₈Single crystal particle is a raw material, adopts topochemical reaction to prepare sheet perovskite structure NaNbO ₃Single crystal particle; Its specific embodiment and step are as follows:

(a) with analytically pure Bi ₂O ₃, Na ₂CO ₃, Nb ₂O ₅Be starting raw material, press Bi _2.5Na _3.5Nb ₅O ₁₈Stoichiometric ratio batching, add dehydrated alcohol, carry out ball milling;

(b) with NaCl or Na ₂SO ₄Salt carries out ball milling, join subsequently in the above-mentioned compound behind ball milling, again through ball milling, dry, sieve, put into alumina crucible then;

(c) compound in the alumina crucible is heated under 900～1200 ℃ of high temperature, make its reaction, and insulation for some time, this fused salt synthesizes Bi _2.5Na _3.5Nb ₅O ₁₈, furnace cooling subsequently;

(d) then with the above-mentioned synthetic product of washed with de-ionized water, oven dry obtains the bismuth laminated Bi of sheet _2.5Na _3.5Nb ₅O ₁₈Single crystal particle;

(e) press Na ₂CO ₃With Bi _2.5Na _3.5Nb ₅O ₁₈Mol ratio be 1: 1～2: 1 and press NaCl salt or Na ₂SO ₄Salt and (Na ₂CO ₃+ Bi _2.5Na _3.5Nb ₅O ₁₈) weight ratio of compound is 2: 1 calculational chemistry proportionings; The Na that the First Astronautic Research Institute for Measurement and Test is got ₂CO ₃And NaCl, perhaps Na ₂CO ₃And Na ₂SO ₄Compound carry out ball milling, add above-mentioned Bi then _2.5Na _3.5Nb ₅O ₁₈Single crystal particle stirs subsequently, dries, sieves;

(f) in 900～1200 ℃ of High Temperature Furnaces Heating Apparatuss, utilize topochemical reaction synthesizing flaky NaNbO ₃Single crystal particle, furnace cooling subsequently;

(g) use HNO ₃Or H ₂SO ₄The reaction product of the above-mentioned gained of pickling is used washed with de-ionized water subsequently again, to remove residual fused salt and byproduct of reaction, obtains pure sheet NaNbO after the oven dry ₃Single crystal particle.

The characteristics of the inventive method are: (1) is by regulating fused salt kind, fused salt quantity, synthetic technological condition, the pattern of may command single crystal particle and size.(2) make sheet NaNbO with molten-salt growth method ₃Single crystal particle is as the anisotropy pattern template in the reaction template grain growing technology, and the base metal niobate based leadless piezoelectric ceramic that the preparation crystal grain orienting is arranged can significantly improve ceramic piezoelectric property.

Description of drawings

Fig. 1 is synthetic sheet NaNbO of the present invention ₃The X ray diffracting spectrum of single crystal particle.

Fig. 2 is the scanning electron microscopy shape appearance figure of synthetic flaky sodium niobate single crystal particle of the present invention.

Embodiment

After now embodiments of the invention being described in.

Embodiment 1

The building-up process and the step of present embodiment are as follows:

(1) at first presses Bi _2.5Na _3.5Nb ₅O ₁₈Stoichiometric ratio batching, take by weighing analytical pure Bi ₂O ₃40.66 gram, analytical pure Na ₂CO ₃12.95 gram, analytical pure Nb ₂O ₅46.39 gram, mixed together adds dehydrated alcohol, carries out ball milling, ball milling 4 hours, and subsequent drying sieves; Add NaCl salt 200 grams that grind through ball milling then; The weight ratio of NaCl salt and above-mentioned compound is 2: 1; Carried out ball milling again 1 hour, and dried subsequently, sieve.

(2) the above-mentioned raw material that mixes is put into alumina crucible, be warming up to 900 ℃, be incubated 2 hours, be warming up to 1100 ℃ again, be incubated 4 hours, this fused salt synthesizes Bi through reaction _2.5Na _3.5Nb ₅O ₁₈, cool to room temperature subsequently with the furnace.Synthetic product with washed with de-ionized water, is removed residual NaCl salt, and oven dry obtains the bismuth laminated Bi of sheet _2.5Na _3.5Nb ₅O ₁₈Single crystal particle.

(3) according to Na ₂CO ₃With Bi _2.5Na _3.5Nb ₅O ₁₈Mol ratio be 1: 1 and press NaCl salt and (Na ₂CO ₃+ Bi _2.5Na _3.5Nb ₅O ₁₈) weight ratio of compound is 2: 1 calculational chemistry proportional quantities, promptly takes by weighing NaCl197.27 gram and Na ₂CO ₃7.15 gram, above-mentioned synthetic product Bi _2.5Na _3.5Nb ₅O ₁₈Single crystal particle material 94.48 grams; Earlier with NaCl and Na ₂CO ₃Compound mixes ball milling, adds dehydrated alcohol simultaneously, ball milling 4 hours; Add Bi then _2.5Na _3.5Nb ₅O ₁₈The single crystal particle material stirs subsequently, dries, sieves.

(4) above-mentioned compound is put into alumina crucible once more, be warming up to 950 ℃, be incubated 4 hours, utilize topochemical reaction synthesizing flaky NaNbO ₃Single crystal particle cools to room temperature subsequently with the furnace; With reaction product with washed with de-ionized water, again with HNO ₃Pickling repeats to clean repeatedly with deionized water again, and to remove residue, oven dry obtains pure sheet NaNbO subsequently ₃Single crystal particle.The length of single crystal particle is 0.5～20 μ m, and slenderness ratio is 1～20.

The sheet NaNbO of present embodiment gained ₃Single crystal particle can be referring to the XRD figure of Fig. 1 and the SEM shape appearance figure of Fig. 2.

Embodiment 2

The building-up process of present embodiment and step and the foregoing description 1 are identical.Different is: in (3) of the foregoing description 1 step, adopt Na ₂CO ₃With Bi _2.5Na _3.5Nb ₅O ₁₈Single mol ratio is 2: 1.The result shows, consistent among the pattern of gained crystal grain and size and the embodiment 1.Na ⁺Excessive in NaNbO ₃Pattern and not significantly influence of size.

Embodiment 3

The building-up process of present embodiment and step and the foregoing description 1 are identical.Different is: in (4) of the foregoing description 1 step, will change 8 hours into by 4 hours 950 ℃ of following soaking times.The result is that the XRD figure spectrum of synthetic product is accredited as single-phase NaNbO ₃, SEM microstructure photo shows that grain morphology is identical with embodiment 1.The length of single crystal particle is 3～30 μ m, and slenderness ratio increases to 5～25.

Embodiment 4

The building-up process of present embodiment and step and the foregoing description 1 are identical.Different is: in (3) of the foregoing description 1 step, change NaCl salt into Na ₂SO ₄Salt, Na ₂SO ₄Salt and (Na ₂CO ₃+ Bi _2.5Na _3.5Nb ₅O ₁₈) weight ratio of compound is 2: 1.The result is that the XRD figure spectrum of synthetic product is accredited as single-phase NaNbO ₃, SEM microstructure photo shows that grain morphology is a sheet, and is identical with embodiment 1.The length of single crystal particle is 0.5～20 μ m, and slenderness ratio is 1～20, and the grain size distribution ununiformity increases to some extent.

Claims (1)

1. the method for a method for synthesizing sheet single crystal grains of sodium niobate through molten salt growth is characterized in that: with analytically pure Na ₂CO ₃, Nb ₂O ₅, Bi ₂O ₃Be raw material, with NaCl or Na ₂SO ₄Be medium, by two-step reaction method synthesizing flaky NaNbO ₃Single crystal particle; The first step reaction prepares the bismuth laminated Bi of sheet with molten-salt growth method _2.5Na _3.5Nb ₅O ₁₈Single crystal particle; The reaction of second step is with the bismuth laminated Bi of above-mentioned sheet _2.5Na _3.5Nb ₅O ₁₈Single crystal particle is a raw material, adopts topochemical reaction to prepare sheet perovskite structure NaNbO ₃Single crystal particle; Its specific embodiment and step are as follows:

(a) with analytically pure Bi ₂O ₃, Na ₂CO ₃, Nb ₂O ₅Be starting raw material, press Bi _2.5Na _3.5Nb ₅O ₁₈Stoichiometric ratio batching, add dehydrated alcohol, carry out ball milling;

(b) with NaCl or Na ₂SO ₄Salt carries out ball milling, join subsequently in the above-mentioned compound behind ball milling, again through ball milling, dry, sieve, put into alumina crucible then;

(c) compound in the alumina crucible is heated under 900～1200 ℃ of high temperature, make its reaction, and insulation for some time, this fused salt synthesizes Bi _2.5Na _3.5Nb ₅O ₁₈, furnace cooling subsequently;

(d) then with the above-mentioned synthetic product of washed with de-ionized water, oven dry obtains the bismuth laminated Bi of sheet _2.5Na _3.5Nb ₅O ₁₈Single crystal particle;

(e) press Na ₂CO ₃And Bi _2.5Na _3.5Nb ₅O ₁₈Mol ratio be 1: 1～2: 1, and press NaCl salt or Na ₂SO ₄Salt and (Na ₂CO ₃+ Bi _2.5Na _3.5Nb ₅O ₁₈) weight ratio of compound is 2: 1 calculational chemistry proportionings; The Na that the First Astronautic Research Institute for Measurement and Test is got ₂CO ₃And NaCl, perhaps Na ₂CO ₃And Na ₂SO ₄Compound carry out ball milling, add above-mentioned Bi then _2.5Na _3.5Nb ₅O ₁₈Single crystal particle stirs subsequently, dries, sieves;

(f) in 900～1200 ℃ of High Temperature Furnaces Heating Apparatuss, utilize the topology must chemical reaction synthesizing flaky NaNbO ₃Single crystal particle, furnace cooling subsequently;

(g) use HNO ₃Or H ₂SO ₄The reaction product of the above-mentioned gained of pickling is used washed with de-ionized water subsequently again, to remove residual fused salt and byproduct of reaction, obtains pure sheet NaNbO after the oven dry ₃Single crystal particle.