Method of obtaining stabilised water sol of nanocrystalline cerium dioxide, doped with gadolinium. RU patent 2503620.

FIELD: chemistry.

SUBSTANCE: invention relates to technologies of nanomaterials production for obtaining of oxide fuel elements, thin coatings, films, which have high ionic conductivity. Method includes preparation of water solution of cerium and gadolinium salts, in which total concentration of rare earth elements constitutes 0.005÷0.02 mole per litre of water, and molar ratio of Ce:Gd constitutes from 19:1 to 4:1, addition of anion-exchange resin in OH-form to obtained solution until pH 9.0÷10.0 is reached, separation of formed colloidal solution from anion-exchange resin by filtering, hydrothermal processing at 120÷210°C for 1.5÷4 h and cooling to room temperature. Obtained unstable sol of nanocrystalline cerium dioxide, doped with gadolinium, is additionally stabilised with salt of polybasic acid (citric or polyacrylic) with molar ratio of rare earth elements in acid, equal 1:1÷4, and following slow drop-by-drop addition of ammonia water solution until pH 7÷8 is obtained.

EFFECT: invention makes it possible to obtain aggregative-stable water sols with average diameter approximately 4 nm, which have high morphological homogeneity, preserving their properties for long time.

5 cl, 4 dwg, 4 ex

The invention relates to the technology of nanomaterials, namely the method of obtaining a stable aqueous colloidal solution of nanocrystalline cerium dioxide doped with gadolinium. Sols dioxide cerium-doped gadolinium, can be used to obtain a thin coating film having a high ion conductivity, the production of oxide fuel cells [.Patsalas, S.Logothetidis, .Metaxa // Optical performance of transparent nanocrystalline ceria films // Appl. Phys. Lett. 2002, V.81, P.466; K. Mohan Kant, V. Esposito, N. Pryds Strain induced ionic conductivity enhancement in epitaxial http://Ceo.9Gdo.1O2₂thin films // Appl. Phys. Lett. 2012, 100, P.033105; patent CN 101560679].

To obtain solid solutions on the basis of cerium dioxide is usually used method of co-precipitation with subsequent precipitation annealing at high temperatures [L.D. Jadhava, M.G. Chourashiy, A.R., Jamale, A.U. Chavan, S.P. Patil. Synthesis and characterization of nano-crystalline Ce_1-xGd_xO_2-x/2(x=0-0 .30) solid solutions // Journal of Alloys and Compounds 2010. V.506, P.739-744]. Thus obtained materials consist of strongly aggregated particles of relatively large size (up to 100 nm and more). To obtain solid solutions on the basis of cerium dioxide nanoparticles smaller proposed a method based on hydrothermal processing soosazhdennykh hydrated oxide of cerium and other rare earth elements at 260°C for 10 h [S. Dikmen, P. Shuk, M. Greenblatt, .Gomez. Hydrothermal synthesis and properties of Ce 1-xGd_xO_2-δsolid solutions // Solid State Sciences. 2002. V.4, P.585-590].

The disadvantage of these methods is that they do not provide aggregately-resistant aqueous sols of solid solutions on the basis of rare earth elements.

A method of obtaining powder of solid solutions on the basis of cerium dioxide doped with neodymium and europium [Polezhaeva O.S, Ivanov V.K., Dolgopolov E.A., rams AU, Shcherbakov A.B., Tretyakov UD Synthesis of nanocrystalline solid solutions Ce_1-xR_xO_2-δ(R=Nd, Eu) by the method of homogeneous hydrolysis Dokl. Acad. Sciences. 2010. T. No. 2. S-198], by the method of homogeneous hydrolysis of solutions of nitrates of cerium(III) and neodymium (europium) in the presence of hexamethylenetetramine at relatively low temperatures (90°C), allowing to obtain nanoparticles of solid solutions based on CERIC oxide of less than 10 nm.

The disadvantage is that this method also does not allow aggregately-stable sols of solid solutions on the basis of cerium dioxide.

There is a way to obtain sols of nanocrystalline cerium dioxide, stabilized citric and polyacrylic acids [Ivanov VK, Polezhaeva O.S, Sapori A.S., rams AU, Shcherbakov A.B., Usatenko A.V. Synthesis and study of thermal stability of the sols of nanocrystalline cerium dioxide, stabil the inpatient lemon and polyacrylic acids, Zh. norgan. chemistry. 2010. T. No. 3. S-373]. This method includes obtaining nanoparticles of cerium dioxide using different initial salt of cerium nitrate (III) or sulfate cerium (IV). As a stabilizer of colloidal solution using citric acid and polyacrylic acid (PAC). Sols of cerium dioxide, stable low molecular weight (average molecular weight of 8000 g/mol) poly (acrylic acid), was prepared as follows. To 50 ml of 0.1 M sulfate solution of cerium (IV) in 0.1 N sulfuric acid was added 10 ml of 2%aqueous solution of PAK. Under continuous stirring, the system was added dropwise 3 M aqueous ammonia to pH>11. The resulting solution was heated to 40÷45 min, were injected 2 ml of 50% hydrogen peroxide, and continued boiling for a further 3÷4 h After heat treatment, the solution was cooled and acidified with 0.01 N sulfuric acid to pH 4.5. The precipitation was separated by decantation, washed with water and dissolved in 50 ml of an aqueous solution of ammonia (pH 8).

The disadvantage of the method described in the above work, is the fact that this method is unsuitable for further doping the nanoparticles of cerium dioxide lanthanides, in particular gadolinium.

The known method [Wang S., Chen, S., Navrotsky, A., Martin M., Kim Z.A. Modified polyol-mediated synthesis and consolidation of Gd-doped ceria nanoparticles // Solid State Ionics. 2010. V.181. P.372-378] obtain colloidal solutions of cerium dioxide doped g is dolinie with a particle size of 2÷3 nm. Way to obtain is based on the solvolysis of nitrates of rare-earth elements in propylene glycol at 140°C for 1 h with the addition of a small amount of aqueous sodium hydroxide solution.

The disadvantage of this method is the formation of non-aqueous (propylene glycol) sols dioxide cerium-doped gadolinium, the use of such sols to obtain coatings and films is impractical, because the removal of solvent and film formation occurs at sufficiently high temperatures (>140°C), and this, in turn, leads to aggregation of the particles, i.e. low morphological homogeneity.

A method of obtaining colloidal aqueous solutions based on oxide of cerium-doped gadolinium [Gasymov G.A., Ivanov O., rams AU, Shcherbakov A.B., Ivanov V.K., Tretyakov UD Synthesis of colloidal solutions of nanocrystalline cerium dioxide doped gadolinium // Nanosystems: physics, chemistry, mathematics. 2011. Vol.2. No. 3. P.113-120]. Way to obtain is as follows: anion-exchange resin, pre-translated in OH-form, was gradually added to a mixed aqueous solution of cerium nitrate (III) and gadolinium, where the total concentration of rare earth elements was 0.01 M, to achieve pH=10.0. The molar content of gadolinium in the original solutions ranged from 0 to 20%. SFOR is isovaline sols was separated from the resin by filtration, immediately transferred into the autoclave and subjected to hydrothermal-microwave-treated at 190°C for 1 h after the experiments, the autoclaves were removed from the furnace and cooled to room temperature in air. This method is considered as a prototype.

The disadvantage of the prototype is that it allows to obtain aqueous sols dioxide, cerium dioxide and cerium-doped gadolinium, preserving aggregate stability for only a very short time, not more than 1 day during which the observed aggregation of particles to micron size and deposition of sediment. Sols of nanocrystalline cerium dioxide doped gadolinium deposited in the sediment cannot be used to obtain homogeneous coatings, respectively heterogeneity coatings will lead to a decrease in their functional characteristics, including conductivity.

The invention is aimed at finding ways of getting aggregately-stable aqueous colloidal solution of nanocrystalline cerium dioxide doped with gadolinium, with a typical average particle diameter of about 4 nm, with a hydrodynamic diameter of 25±5 nm, with high morphological homogeneity, which retains its properties for a long time.

The technical result is achieved in that a method of obtaining abilityone water Zola nanocrystalline cerium dioxide, doped gadolinium high aggregative stability, namely, that prepare a water solution of salts of cerium and gadolinium, in which the total concentration of rare earth elements is 0.005÷0.02 moles per liter of water, and the molar ratio of Ce:Gd is from 19:1 to 4:1, to the obtained solution of salts of cerium and gadolinium type anion exchange resin in OH-form, to achieve pH 9.0÷10.0 formed colloidal solution is separated from the anion exchange resin by filtration and subjected to hydrothermal treatment at 120÷210°C for 1.5÷4 h after then cooled to room temperature, characterized in that the volatile Sol dioxide nanocrystalline cerium-doped gadolinium, additionally stabilize the salt of the polybasic acid, by adding a polybasic acid with a molar ratio of rare earth elements to acid is 1:1÷4, and followed by slow dropwise addition of aqueous ammonia solution to achieve pH 7÷8.

It is advisable that as a polybasic acid is used lemon or polyacrylic acid.

It is also advisable that, as a salt of cerium use water-soluble cerium salt with a solubility of not less than 6·10^-3mol of cerium in 1 l of water, and as the salt of the gadolinium use of water-soluble salts of g is doline with a solubility of not less than 6·10 ^-3mol of gadolinium in 1 l of water.

It is possible that as the anion exchange resin used resin grade Amberlite IRA 410 CL, which is pre-transferred to the OH-form by interaction with alkali.

It is important that the hydrothermal treatment is carried out using microwave heating.

The essence of the invention lies in the fact that to obtain aggregately-stable aqueous colloidal solution of nanocrystalline cerium dioxide doped with gadolinium, conduct additional stabilization, and not at the stage of dissolution of salts of cerium and gadolinium, and after the formation of the solid solution of cerium dioxide doped with gadolinium, where the water-soluble stabilizer use lemon or polyacrylic acid.

The specified technical task and the specified technical result is achieved by using as the stabilizer of polybasic, well adsorbiruya on the surface of the CERIC oxide particles doped with gadolinium, lemon or polyacrylic acid. Moreover, the stabilizer provides obtaining aggregated particles and stabilization Zola due to the steric barrier to aggregation of particles and precipitation.

The essence of the invention is illustrated by the following accompanying illustrations:

Figure 1. Microphotograph the I (left) and diagram of distribution of particle size (right) for a sample of the aqueous Sol of cerium dioxide, doped gadolinium, with a molar ratio of cerium gadolinium is 19:1, stabilized citric acid.

Figure 2. Micrograph (left) and diagram of distribution of particle size (right) for sample water Zola dioxide cerium-doped gadolinium, with a molar ratio of cerium gadolinium equal to 9:1, stabilized citric acid.

Figure 3. Micrograph (left) and diagram of distribution of particle size (right) for sample water Zola dioxide cerium-doped gadolinium, with a molar ratio of cerium gadolinium equal to 16:3, stabilized citric acid.

Figure 4. Micrograph (left) and diagram of distribution of particle size (right) for sample water Zola dioxide cerium-doped gadolinium, with a molar ratio of cerium gadolinium equal to 4:1, stabilized citric acid.

The present invention is implemented as follows.

In the vessel of appropriate volume to prepare an aqueous solution of salts of cerium and gadolinium. Pre-anion-exchange resin Amberlite IRA 410 CL translated in the OH-form by repetition of the procedure of soaking and incubation in 10% aqueous sodium hydroxide solution, after the transfer of anion exchange resin in OH-form is washed with distilled water. With vigorous stirring, the pH of the water rest the RA nitrates of cerium and gadolinium quickly increase with anion-exchange resin to pH 9÷10, and the solution is quickly filtered from the anion-exchange resin. If the pH of an aqueous solution of nitrates of cerium and gadolinium to increase slowly, or it will be more than 10÷11, it will lead to aggregation of the nanoparticles and the Deposit of sediment. If the pH is less than 8÷9, will be the formation of hydroxocobalamine cerium and gadolinium. After filtration of the formed Sol is subjected to hydrothermal treatment at a temperature of 120÷210°C for 1.5÷4 hours. Shorter duration of this stage leads to the formation of solid solution containing the number of gadolinium, less given that it is not economically feasible. The increase in the duration of this stage is not economically feasible. Then in the resulting colloidal solution of nanocrystalline cerium dioxide doped with gadolinium, add stabilizer, citric acid, with a molar ratio of cerium with gadolinium and stabilizer 1:1÷4. When this Sol dioxide cerium-doped gadolinium, turbid, then the pH of the Sol was adjusted with an aqueous solution of ammonia to a value of 7÷8, after which the Sol becomes transparent. The obtained Sol store in a cool place until use.

Below are examples of implementations of the claimed invention. The examples illustrate but do not limit the proposed method.

Example 1

For the cooking the colloidal solutions of cerium dioxide, doped gadolinium, at the rate of 0.01 mole of rare earth elements per liter of solvent, 0.412 g of cerium nitrate (III) and 0.023 g of gadolinium nitrate (molar ratio of cerium: gadolinium is 19:1) was dissolved in 100 ml of distilled water, the resulting solution was added anion exchange resin Amberlite IRA 410 CL, pre-translated in OH-form, to achieve pH=10.0. Formed sols was separated from the resin by filtration, immediately transferred to PTFE autoclaves volume of 100 ml (degree of completion - 50%) and subjected to hydrothermal-microwave-treated at 210°C for 1.5 hours At the end of the experiments, the autoclaves were removed from the furnace and cooled to room temperature in air. To the resulting aqueous colloidal solution of solid solution of oxides of rare earth elements were added citric acid, the concentration of which in the ash amounted to 0.01 moles per liter of solvent.

Parameter crystal cell for sample Ce_{of 0.95}Gd_0,05O_2-δas defined in the refinement of the crystal structure of solid solutions according to the method of Rietveld, was 0.54144(5) nm. According to the results of the EMP (see Figure 1), the average particle diameter of the cerium dioxide doped gadolinium was 4.47±0.52 nm. According to dynamic light scattering, the average hydrodynamic diameter of the particles of cerium dioxide, dopirovannom what about gadolinium and stabilized with citric acid was 25 nm. In addition, the hydrodynamic diameter within 6 months varies by no more than 5 nm, indicating that aggregate stability obtained Zola.

Example 2

For the preparation of colloidal solutions of cerium dioxide doped with gadolinium, at the rate of 0.01 mole of rare earth elements per liter of solvent, 0.391 g of cerium nitrate, 0.045 g of gadolinium nitrate (molar ratio of cerium: gadolinium equal to 9:1) was dissolved in 100 ml of distilled water, the resulting solution was added anion exchange resin Amberlite IRA 410 CL, pre-translated in OH-form, to achieve pH=10.0. Formed sols was separated from the resin by filtration, immediately transferred to PTFE autoclaves volume of 100 ml (degree of completion - 50%) and subjected to hydrothermal-microwave-treated at 190°C for 1.5 hours At the end of the experiments, the autoclaves were removed from the furnace and cooled to room temperature in air. To the resulting aqueous colloidal solution of solid solution of oxides of rare earth elements were added citric acid, the concentration of which in the ash amounted to 0.01 moles per liter of solvent.

According to x-ray phase analysis parameter crystal cell for sample Ce_0,90Gd_0.10C_2-δas defined in the refinement of the crystal structure of solid solutions according to the method of RIT is Elda, was 0.54174(4) nm. According to the results of the EMP (see Figure 2), average particle diameter of the cerium dioxide doped gadolinium was 3.0±0.84 nm. According to dynamic light scattering, the average hydrodynamic diameter of the particles of cerium dioxide doped with gadolinium and stabilized with citric acid was 15 nm. In addition, the hydrodynamic diameter within 6 months varies by not more than 5 nm, indicating that aggregate stability obtained Zola.

Example 3

For the preparation of colloidal solutions of cerium dioxide doped with gadolinium, at the rate of 0.01 mole of rare earth elements per liter of solvent, 0.369 g of cerium nitrate and 0.068 g of gadolinium nitrate (molar ratio of cerium: gadolinium is 16:3) was dissolved in 100 ml of distilled water, the resulting solution was added anion exchange resin Amberlite IRA 410 CL, pre-translated in OH-form, to achieve pH=10.0. Formed sols was separated from the resin by filtration, immediately transferred to PTFE autoclaves volume of 100 ml (degree of completion - 50%) and subjected to hydrothermal-microwave-treated at 190°C for 2 hours At the end of the experiments, the autoclaves were removed from the furnace and cooled to room temperature in air. To the resulting aqueous colloidal solution of solid solution of oxides redcot the land elements added citric acid, the concentration of which in the ash amounted to 0.01 moles per liter of solvent.

According to x-ray phase analysis parameter crystal cell for sample Ce_{of 0.85}Gd_{of 0.15}O_2-δas defined in the refinement of the crystal structure of solid solutions according to the method of Rietveld, was 0.54198(6) nm. According to the results of the EMP (see figure 3), the average particle diameter of the cerium dioxide doped gadolinium was 3.310.42 nm. According to dynamic light scattering, the average hydrodynamic diameter of the particles of cerium dioxide doped with gadolinium and stabilized with citric acid was 11 nm. In addition, the hydrodynamic diameter within 6 months varies by not more than 5 nm, indicating that aggregate stability obtained Zola.

Example 4

For the preparation of colloidal solutions dioxide cerium-doped gadolinium based 0.01 mole of rare earth elements per liter of solvent, 0.347 g of cerium nitrate (III) and 0.090 g of gadolinium nitrate was dissolved in 100 ml of distilled water (the molar ratio of cerium: gadolinium equal to 4: 1), to the resulting solution was added anion exchange resin Amberlite IRA 410 CL, pre-translated in OH-form, to achieve pH=10.0. Formed sols was separated from the resin by filtration, immediately transferred in polytetrafluorethylene the e autoclaves volume of 100 ml (degree of filling - 50%) and subjected to hydrothermal-microwave-treated at 120°C for 4 h after the experiments, the autoclaves were removed from the furnace and cooled to room temperature in air. To the resulting aqueous colloidal solution of solid solution of oxides of rare earth elements were added citric acid, the concentration of which in the ash amounted to 0.01 moles per liter of solvent.

According to x-ray phase analysis parameter crystal cell for sample Ce_0,80Gd_0,20O_2-δas defined in the refinement of the crystal structure of solid solutions according to the method of Rietveld, was 0.54205(7) nm. According to the results obtained TEM average particle diameter was 3.3±0.64 nm (see Figure 4). According to dynamic light scattering, the average hydrodynamic diameter of the particles of cerium dioxide doped with gadolinium and stabilized with citric acid was 21 nm. In addition, the hydrodynamic diameter within 6 months varies by not more than 5 nm, indicating that aggregate stability obtained Zola.

Materials and methods

For the synthesis of colloidal solutions of oxides of rare earth elements use the following source reagents: gadolinium, the uranyl nitrate (Gd(NO₃)₃·6H₂O, reagent grade., Aldrich), cerium nitrate, the uranyl (Ce(NO₃)₃·6H₂O, reagent grade., Aldrich), lemon KIS the PTA (C ₆H₈O₇, o'clock, Hemmed), Amberlite IRA 410 CL resin (Aldrich), sodium hydroxide (NaOH, reagent grade., Aldrich). The synthesis is carried out as follows: anion exchange resin Amberlite IRA 410 CL, pre-translated in OH-form, is gradually added to a mixed aqueous solution of cerium nitrate(III) and gadolinium nitrate to achieve pH=9.0÷10.0 with the total concentration of 0.0025% to 0.1 mol per liter of solvent, and the molar ratio of Ce:Gd is 19:1 to 4:1. Formed sols is separated from the resin by filtration, immediately transferred into a PTFE autoclaves volume of 100 ml and subjected to hydrothermal treatment at 120÷210°C for 1.5÷4 h after the experiments autoclaves remove from the oven and cooled to room temperature in air. To the resulting aqueous colloidal solution of solid solutions of rare earth elements add citric acid concentration, which in the ash amounted to 0.01÷0.1 moles per liter of solvent. After adding citric acid, add aqueous ammonia to pH=7÷8.

Analysis of the obtained colloidal solutions produced using the methods of transmission electron microscopy (transmission electron microscope Leo IV with subsequent determination of the photos size 200-300 particles and determining the mean size of particles). X-ray phase analysis (XRD) performed on the diffractometer Rigaku D/MAX2500 (CuK _α-radiation). The size of coherent scattering regions (CSR) samples of cerium dioxide calculated using the sherrer formula. Refinement of unit cell parameters of the samples doped cerium dioxide according to the method of Rietveld performed using software JANA2000. The profile of the x-ray peaks describe pseudo-functions of Voigt in the range of 15÷90°2θ with regard to nemonokhromaticheskogo radiation (Cu_Kα1and Cu_Kα2). Lines of the background are approximated by Chebyshev polynomials 15 degrees. The particle size by dynamic light scattering (DSM) is measured on the analyzer Malvern Zetasizer Nano ZS.

Results and conclusions

According to the results of XRD all the products obtained in examples 1 to 4 are single phase and have a crystalline fluorite structure (space group Fm3m). Diffraction maxima corresponding to the oxo - or hydroxidealuminum cerium and gadolinium, the diffraction patterns are absent. With decreasing molar ratio of cerium gadolinium from 19:1 to 4:1 is observed shift of the position of diffraction peaks towards lower angles, indicating the occurrence of gadolinium ions in the crystal lattice of the cerium dioxide. The analysis of the broadening of diffraction peaks (111) and (200) shows that obtained by centrifugation of the sols powders really are nanocrystallites them. Based on the data of x-ray phase analysis was calculated from the particle size of solid solutions Ce_1-xGd_xO_2-δ. With the increasing content of gadolinium in the solid solution Ce_1-xGd_xO_2-δthe particle size is reduced from 9 to 4 nm. The overestimation of the particle size of solid solutions Ce_1-xGd_xO_2-δdetermined according to the XRD, compared with TEM data (particle size of 4.5÷3 nm), due, including, x-ray scattering on the crystal of polydisperse powders.

The study of the dependence of the lattice parameter of the samples Ce_1-xGd_xO_2-δfrom the nominal content of gadolinium, a certain refinement of the crystal structure of solid solutions on the Rietveld method, showed that the obtained dependence is linear, that is, corresponds to Vegard's rule for solid solutions. This result is a direct proof of the occurrence of gadolinium ions in the crystal lattice of the cerium dioxide. According to DSM, the size of aggregates in the nuclei of solid solutions Ce_1-xGd_xO_2-δcontaining gadolinium, is 25÷11 nm, which indicates a low degree of aggregation of the nanoparticles.

The proposed invention allows to obtain a stable aqueous Sol of nanocrystalline cerium dioxide, duperow the frame gadolinium, stable when stored for more than 6 months.

1. A method of obtaining a stable aqueous Sol of nanocrystalline cerium dioxide doped with gadolinium, which is characterized by high aggregate stability, namely, that prepare a water solution of salts of cerium and gadolinium, in which the total concentration of rare earth elements is 0,005÷0,02 mole per liter of water, and the molar ratio of Ce:Gd is from 19:1 to 4:1, to the obtained solution of salts of cerium and gadolinium type anion exchange resin in OH-form to achieve a pH of 9.0÷10,0 formed colloidal solution is separated from the anion exchange resin by filtration and subjected to hydrothermal treatment at 120÷210°C within 1.5÷4 h, then cooled to room temperature, characterized in that the volatile Sol dioxide nanocrystalline cerium-doped gadolinium, additionally stabilize the salt of the polybasic acid by adding a polybasic acid with a molar ratio of rare earth elements to acid is 1:1÷4, and followed by slow dropwise addition of aqueous ammonia solution to achieve pH 7÷8.

2. The method according to claim 1, characterized in that as the polybasic acid is used lemon or polyacrylic acid.

3. The method according to claim 1, characterized in that kachestvenii cerium use water-soluble cerium salt with a solubility of not less than 6·10 ^-3mol of cerium in 1 l of water, and as the salt of the gadolinium use water-soluble salt of gadolinium with a solubility of not less than 6·10^-3mol of gadolinium in 1 l of water.

4. The method according to claim 1, characterized in that as the anion exchange resin used resin grade Amberlite IRA 410 CL, which is pre-transferred in the form of interaction with the alkali.

5. The method according to claim 1, wherein the hydrothermal treatment is carried out using microwave heating.