WO2008062092A1

WO2008062092A1 - Nanostructured oxide ceramic/n-w material, method for preparing and uses thereof

Info

Publication number: WO2008062092A1
Application number: PCT/ES2007/070192
Authority: WO
Inventors: José Serafín MOYA CORRAL; Carlos Pecharroman Garcia; Sonia Lopez Esteban; Teresa Rodriguez Suarez; Luis Antonio Diaz Rodriguez; Ramón TORRECILLAS SAN MILLAN
Original assignee: Consejo Superior De Investigaciones Cientificas
Priority date: 2006-11-21
Filing date: 2007-11-20
Publication date: 2008-05-29
Also published as: ES2300208B1; ES2300208A1

Abstract

The subject matter of the present invention is an nanostructured ceramic oxide/n-w composite material of nanometric size, 1 to 20 nm, with a tungsten content between 0.05 vol.% and 30 vol.%. Also described is the method for preparing the ceramic oxide/n-W material of the invention. This novel material can be useful in the manufacture of electronic components, catalysers, structural technical ceramics and pigments, dyes and coatings on metal substrates.

Description

CERAMIC OXIDE NANOESTRUCTURED MATERIAL / N-W, OBTAINING PROCEDURE AND ITS APPLICATIONS

SECTOR OF THE TECHNIQUE

New materials such as electronic components, catalysts, structural technical ceramics, pigments and dyes, coatings on metal substrates, etc.

STATE OF THE TECHNIQUE

Tungsten (W) is a metal with exceptional intrinsic properties: high melting point (3422 ° C), high hardness (3.43 GPa), the thermal expansion coefficient lowest of all metals (4.5-1CT ⁶ K ^"1) and one of the lowest vapor pressures within them:

Alumina (8.5 10 ^"6 K ^{" 1} ) and spinel (7.3 10 ^"6 K ^{" 1} ) are chemically stable oxides, resistant to corrosion and have thermal expansion coefficients very similar to tungsten (5.4-10 ^"6 K ^{" 1} ) which minimizes possible problems arising from the formation of residual stresses at the interface.

On the other hand, it is well known that metallic materials, in the nanometric range, have less ductility than the same micrometer particle size materials [Siegel RW, Nanostruct Mater; 3

(1993) 1-18]. In the particular case of W, which has a high value of G (shear modulus), the expected Vickers hardness - taking into account the linear relationship between G and H _v - can be increased in tungsten nanoparticles to values of the order of 30 GPa. This, together with the high values of H _v that alumina or spinel matrices possess, it can result in ceramic / nanometal composite materials of much greater hardness than the corresponding microparticulate compounds [C. Pecharromán, F. Esteban-Betegón, JF Bartolomé, G. Richter, and JS Moya, Nanoletters, 4 [4];

(2004) 747-51].

In the field of catalysis, multiple metal and metal oxide systems supported on ceramic oxides have been studied for various applications since there are many catalytically active metals (V, Nb, Ta, Re,

Rh, Rb, Co, Fe, Mn, Pt, Mo, etc.) with sizes between some nanometers and approximately 0.5 microns

[Wong Michael S; Wachs Israel E; Knowles William V. Patent WO2005 / 002714 of 01/13/2005; J. -W. Yoon, T. Sasaki, N. Koshizaki, Thin Solid Films 483 (2005) 276-282; T. Sanders, M. Kirchhoff, U. Specht, G. Veser, AIChE Annual Meeting, Conference Proceedings (2005) 10004; X. -H. Yun, M. -X. Chen, J. -W. Shi, W. -F. Shangguan, Shanghai Jiatong Daxue Xuebao / Journal of Shanghai Jiatong University, 39 [11]

(2005) 1886-1890; L. Bultel, P. Vernoux, F. Gaillard, C. Roux, E. Siebert, Solid State Ionics, 176 (7-8) (2005) 793-801; Y. Guo, G. Lu, X. Mo, Y. Wang, Chemistry Letters 33

[12] (2004) 1628-1629; G. Li, W. Li, M. Zhang, K. Tao, Catalysis Today 93-95 (2004) 595-601; H. -R. Chen, J. -L. Shi, L. Li, M. -L. Ruan, D. -S. Yan, Journal Of Chemical Engineering of Japan 36 [10] (2003) 1212-1215; XL Pan, N. Stroh, H. Brunner, GX Xiong, SS Sheng, Separation and Purification Technology, 32 [1-3] (2003) 265-270]. Such is the variety of systems, today, such catalysts are in processes as diverse as chemical, environmental protection (such as catalytic converters for cars), in the reduction of NO _x in energy plants, in oil refineries, drug synthesis, petrochemical processes, etc.

On the other hand, there are abundant bibliographic references in the literature related to the processing of ceramic materials containing metal nanoparticles, such as Al ₂ O ₃ / Ni, Al ₂ 0 ₃ / Mo,

Al ₂ O ₃ / Cr, Al ₂ O ₃ / Cu, etc. Most of these composite materials have been obtained from powder mixtures

(rust and metal) that are homogenized by the classic wet routes [M. Nawa, T. Sekino, K. Niihara, Journal of Materials Science, 29 [12] (1994) 3185-3192], or from oxide mixtures with metal precursors (eg nitrates [T. Sekino, S. Etoh, Y. -H. Choa, K. Niihara, Materials Research Society Symposium- Proceedings, 501 (1998) 289-294 and ST Oh, JS Lee, K. Niihara, Scripta Mater. 44 (2001) 2117-2120] or acetylacetonate [ Y. Ji, JA Yeomans, Journal of the European Ceramic Society 22 (2002) 1927-1936] Other groups have obtained nanostructured alumina / metal powders using physical techniques such as laser abrasion [J. Naser, H. Ferkel, NanoStructured Materials, 12 (1999) 451-451], or by the sol-gel technique [P. Bhattacharya, K. Chattopadhyay, NanoStructured Materials, 12 (1999) 1077-1080].

In the case of alumina / nW powders, the work of Sekino et al [T. Sekino, K. Niihara, NanoStructured Materials, 6 (1995) 663-666 and T. Sekino, K. Niihara, NanoStructured Materials, 6 (1995) 663-666]. The authors obtain dense compounds of said material from homogeneous mixtures of alumina powders and tungsten oxide. The processing followed by these authors consists in completely dissolving the WO3 powder in an ammoniacal solution, to which the alumina powder and water are subsequently added. distilled The mixture is homogenized ball mill, a subsequent vacuum drying and calcined at 500 ⁰ C in air for 3 hours or Ar is made. The resulting powder is re-ground in ethanol for 24 hours and subsequently, reduced under an H ₂ atmosphere. The authors do not mention the sizes or morphology of the alumina powder / nW obtained.

On the other hand, Yan et. to [H. Yan, B. S. Xu, Journal of

Inorganic Materials 18 (5) 2003 1127-1130] report in the literature the preparation of nanostructured alumina powder / W by heterogeneous precipitation. In this specific case, it is a powder metallurgical processing.

The authors start from Al (NO3) 3 ^• 9H2O and (NH4) 2CO3 as raw materials, subsequently add nanometric dust from

W and homogenize it by a simple mechanical mixture. Explain that the nanostructured powder obtained by calcining the dried gel to vacuum of Al (OH) 3 / W at 1000 ⁰ C for 1 h.

In the case of nanostructured powders of MgAl ₂ O ₄ / W no references have been found in the literature.

DESCRIPTION OF THE INVENTION Brief Description

An object of the present invention is a composite nanostructured material, hereinafter ceramic oxide / n-W material of the invention, constituted by a nanostructured ceramic oxide / nW material with a nanometric metal particle size between 1 and 100 nm, preferably between 1 and 20 nm, which are strongly adhered to the oxidic substrate. This nanostructured ceramic oxide / nW material of the invention can have a tungsten content between 0.05% and 30% by volume, for example, 1%.

Another object of the invention is the process for obtaining the ceramic oxide / nW material of the invention, hereinafter method of obtaining the invention, which comprises the following steps: a) the oxidic powder is suspended in absolute ethanol, with a solids concentration generally less than 85%, with the whole assembly being stirred by stirring. any magnetic or mechanical device that favors dispersion, b) in parallel, a solution of tungsten chloride in absolute ethanol (purity> 99%) is prepared with the concentration required to obtain the nanostructured powder with the desired metal concentration, heating the solution below 70 ⁰ C, c) once all the tungsten chloride has been transformed into tungsten ethoxide W, (colorless solution) in step b), it is added in a controlled manner to the oxidic powder suspension of a) which is kept under continuous agitation to favor the homogeneous mixing of both liquids, d) the remaining solvent is removed by evaporation at a temperature, generally , less than 70 ⁰ C and always under continuous agitation, being able to heat it in an oven at 60 ⁰ C for 24 hours until obtaining a dry powder, e) subsequently, the dry powder of d), is screened by a standard mesh, preferably below of 63 microns, and it is calcined at temperatures between 500 ⁰ C and 700 ⁰ C, preferably at 600 ⁰ C, for a period of time sufficient to remove the organic components and favor the crystallization of tungsten oxide on the surface of the particles oxidic, preferably, for one hour, and f) reduce the tungsten oxide to metallic tungsten by a heat treatment between 750 ⁰ C and 1100 ⁰ C, preferably at 900 ⁰ C, in a hydrogen reducing atmosphere of the nanostructured powder of e) between a hour and half and two and a half hours, preferably two hours, which produces the crystallization of the metal nanoparticles on the surface of the oxidic particles.

Finally, another object of the present invention is the use of the ceramic oxide / n-W material of the invention in the preparation, by way of illustration and without limiting the scope of the invention, of products belonging to the following group: electronic components, catalysts , structural technical ceramics, pigments and dyes and coatings on metal substrates.

Detailed description

The invention faces the problem of providing new nanostructured materials for products such as electronic components, catalysts, structural technical ceramics, pigments and dyes, coatings on metal substrates.

The invention is based on the fact that the inventors have observed that it is possible to obtain a nanostructured alumina powder / W and spinel / W of high purity, with a metal particle size of less than 100 nm, even less than 20 nm, and that they are strongly adhered to the oxidic substrate, by means of a chemical procedure that favors the substitution reaction between the metal alkoxide and the OH groups that cover the surface of the oxidic particles (alumina or spinel) where M-OH schematically represents the surface of the oxidic particles with presence of OH groups (alumina or spinel). In this way, a coating of the oxidic particles with the corresponding organo-metallic molecules [W (OCH ₂ -CH ₃ ) _x ] is achieved (see Figures 1 to 3). On the other hand, the cost of this procedure is low due to the non-use of chloride during the synthesis process In summary, the process for obtaining the ceramic oxide / nW material of the invention is based on two types of chemical reactions, namely: i) The one that occurs in a first stage between tungsten chloride and the solvent medium (absolute ethanol ), and ii) The reaction that occurs between the latter solution and the surface of the oxidic particles (alumina or spinel). Therefore, an object of the present invention is a composite nanostructured material, hereinafter ceramic oxide / n-W material of the invention, constituted by a nanostructured ceramic oxide / nW material with a nanometric metal particle size between 1 and 100 nm, preferably between 1 and 20 nm, which are strongly adhered to the oxidic substrate. This nanostructured ceramic oxide / nW material of the invention can have a tungsten content between 0.05% and 30% by volume, for example, 1%.

A particular object of the invention is the ceramic oxide / nW material of the invention where the oxide, by way of illustration and without limiting the scope of the invention, belongs to the following group: a) alumina, in any of its crystallographic forms, namely, α, β, δ, γ, K, p, η, θ and χ, with a grain size between 20 and 1000 nm [K. Wefers and C. Misra, Alcoa Laboratories, Oxides and Hydroxides of Aluminum (1987)], b) alumina with any oxide that can enter a solid solution in its network - such as, for example, TÍO2, Fe2Ü3, Y2O3, etc.- and, in particular, chromite (Cr ₂ C> 3) whose solid solution with alumina is continuous in the range between 0% and 100% by weight, and c) aluminum-magnesium spinel (MgAl ₂ O ₄ ) in any of its varieties (stoichiometric, rich in alumina or rich in magnesia), with a molar ratio that can range between 66 and 91%, for example 78%, and a grain size between 20 and 1000 nm [EM Levin, Phase Equilibrium diagrams for Ceramics, The American Ceramic Society Inc ., Figs 259 and 260, (1964)]. The particle size of these ceramic oxides can be nanometric (<200 nm) or micrometric (<10 μm) (Example 1).

A particular embodiment of the invention is the ceramic oxide / nW material of the invention in which the material is α-Al ₂ O ₃ / nW.

Another particular embodiment of the invention is the ceramic oxide / n-W material of the invention in which the material is spinel / nW.

Another object of the invention is the process for obtaining the ceramic oxide / nW material of the invention, hereinafter method of obtaining the invention, which comprises the following steps: a) the oxidic powder is suspended in absolute ethanol, with a solids concentration generally less than 85%, by stirring the whole assembly by any magnetic or mechanical device that favors dispersion, b) in parallel, a solution of tungsten chloride in absolute ethanol (purity> 99%) is prepared with required for the nanostructured powder with the desired concentration of metal concentration, heating the solution below 70 ⁰ C, c) once all the tungsten chloride has been transformed into tungsten ethoxide W, (colorless solution) in step b), it is added in a controlled manner to the oxidic powder suspension of a) which is kept under continuous stirring to promote homogeneous mixture of two liquids, d) the remaining solvent is removed by evaporation at a temperature generally below 70 ⁰ C and always under continuous stirring and can heat it in an oven at 60 ⁰ C for 24 hours to obtain a dry powder e) subsequently, the dry d) powder, sieved using a standard mesh, preferably below 63 microns, and calcined at temperatures between 500 ⁰ C and 700 ⁰ C, preferably at 600 ⁰ C for a period of sufficient time to remove the organic components and favor the crystallization of the tungsten oxide on the surface of the oxidic particles, preferably, for one hour, and f) reduce the tungsten oxide to tungsten me by means of a heat treatment between 750 ⁰ C and 1100 ⁰ C, preferably at 900 ⁰ C, in a hydrogen-reducing atmosphere of the nanostructured powder of e) between one hour and a half and two and a half hours, preferably two hours, whereby It produces the crystallization of the metal nanoparticles on the surface of the oxidic particles.

Another particular object of the invention is the process of the invention where the oxidic powder of a) can be selected, by way of illustration and without limiting the scope of the invention, from the following group: a) alumina, in any of its crystallographic forms, namely, α, β, δ, γ, K, p, η, θ and χ, with a grain size between 20 and 1000 nm, b) alumina with any oxide that may enter a solid solution in its network - such as, for example, TIO2, Fe ₂ O ₃ , Y ₂ O ₃ - and, in particular, chromite (Cr ₂ O ₃ ) whose solid solution with alumina is continuous in the range between 0% and 100% by weight, and c) aluminum-magnesium spinel (MgAl ₂ O ₄ ) in any of its varieties (stoichiometric, rich in alumina or rich in magnesia), with a molar ratio that can range between 66 and 91%, for example, 78%, and a grain size between 20 and 1000 nm.

Another particular object of the invention is the process of the invention where the concentration of the tungsten chloride metal phase of b) can vary depending on the tungsten concentration that is desired in the ceramic material of the invention, for example , between 0.05 and 30% by volume of W, for example, in particular 1% (Example 1).

Another particular embodiment of the invention is the process for obtaining the invention where alumina (Ot-Al ₂ O ₃ ) is used as an oxidic powder (Example 1).

Another particular embodiment of the invention is the process for obtaining the invention where spinel is used as an oxidic powder (Example 1). Finally, another object of the present invention is the use of the ceramic oxide / n-W material of the invention in the preparation, by way of illustration and without limiting the scope of the invention, of products belonging to the following group: electronic components, catalysts , structural technical ceramics, pigments and dyes and coatings on metal substrates.

As a catalyst, the ceramic oxide / n-W material of the invention can be used in a wide variety of processes as diverse as in the chemical industry, environmental protection (such as automobile catalytic converters), in the reduction of NO _x in power plants, in oil refineries, in drug synthesis, in petrochemical processes , etc.

DESCRIPTION OF THE FIGURES

Figure 1.- Scheme of the chemical reaction between tungsten chloride and absolute ethanol from step b) of the process of the invention (Formula 1). Figure 2.- Image of transmission electron microscopy

(MET) of the nanostructured powders α-Al2θ3 / nW. The size of the metal particles is between 5 and 20 nm. Tungsten nanoparticles are monodisperse and firmly adhered to the oxidic particles.

Figure 3.- MET micrograph corresponding to spinel powder / nW. In this case, the size of the metal particles is between 3 and 20 nm.

EXAMPLES OF REALIZATION

Example 1. Obtaining nanostructured powders of Al ₂ O ₃ / nW and spinel / nW as particular embodiments of the ceramic oxide / n-W material of the invention. The starting raw materials are:

- oxidic powder: Taimei alumina (Ot-Al ₂ O ₃ , TM-DAR, Taimei Chemicals, Japan, average particle size 147 nm, purity> 99%) and aluminum magnesium spinel (AR-78, Alcoa Industrial Chemicals , Germany) average particle size of 700 nm, purity> 99%, with 78% by weight of Al ₂ O ₃ . Both alumina powder or spinel of high purity, with a grain size in the range 0.1-1 μm, - Tungsten Chloride (WCl ₆ ) [Aldrich, Tungsten (V)

Chloride, 99.9%], and - Absolute ethanol used as solvent medium (Panreac 99.5% pure).

For this, the following procedure, identical for both oxides (alumina and spinel), has been followed, with the particularities of each case as follows. 50 g of alumina (01-AI2O3) and 20 g of spinel were used which were suspended in 70 g and 60 g of absolute ethanol, respectively, in continuous magnetic stirring [step a)]. The solids concentration remained below 85%. In parallel, 5,348 g of tungsten chloride (WCl ₆ ) were used for alumina and

2.402 g WCl ₆ for the spinel in solution with the amount of absolute ethanol required (350 ml for alumina and 240 ml for spinel) to transform the yellow color of the tungsten chloride powder solution into colorless, the solution being heated by below 70 ⁰ C

[stage b)]. In these two particular embodiments the conditions were defined to establish a concentration of the tungsten metal phase of 1% in the final ceramic material of the invention. At the time of contact between tungsten chloride and absolute ethanol from step b) of the process of the invention, the following chemical reaction occurs (Formula 1; see Figure 1):

5 (CH -CH OH) + WCl W (CH -CH O) + 5 HCl _(g) í

3 2; 3 2 5

As noted in Formula (1) there is a release of hydrochloric acid (gas) that will not cease until the solution, initially yellow, becomes colorless, at which time a solution of W ethoxide in absolute ethanol is achieved.

Then, this solution is added dropwise onto the alumina and spinel suspension, respectively, gradually turning the whitish solution into blue [step c)]. This solution was stirred and heated (<70 ° C) to bring it to a viscous state to finally enter the assembly in an oven at 60 ⁰ C for 24 hours [step d)]. The dried product thus obtained, was sieved using standard mesh below 63 microns and the powder was heat treated at 600 ⁰ C for 1 hour [step e)]. Again, the treated powder was screened below 63 microns and reduced in a tubular oven under an atmosphere of H ₂ at 900 ⁰ C for 2 hours [step f)] •

In this way, nanostructured α-Al ₂ O ₃ / nW powders have been obtained in which the size of the metal particles is between 5 and 20 nm (Figure 2), the tungsten nanoparticles being monodispersed and firmly adhered to the particles oxidic as can be seen from the MET study of the oxide / metal interface. Similarly, it has been observed that in the spinel powder / nW obtained, the size of the metal particles is between 3 and 20 nm (Figure 3). Finally, indicate that the nanostructured powders of Al ₂ O ₃ ZnW and spinel / nW obtained have a tungsten content of 1% by volume, which has been determined by subsequent chemical analysis and coincides with the amount of W programmed in the experiment.

Claims

1.- Nanostructured composite material characterized in that it is constituted by a ceramic oxide / nW material with a nanometric metal particle size between 1 and 100 nm, preferably between 1 and 20 nm, adhered to the oxidic substrate and with a tungsten content between 0.05% and 30% by volume.

2. Composite nanostructured material according to claim 1 characterized in that the oxide belongs to the following group: a) alumina, in any of its crystallographic forms, namely, α, β, δ, γ, K, p, η, θ and χ , with a grain size between 20 and 1000 nm, b) alumina with any oxide that can enter into solid solution in its network whose solid solution with alumina is continuous in the range between 0% and 100% by weight , and c) aluminum-magnesium spinel (MgAl ₂ O ₄ ) in any of its varieties (stoichiometric, rich in alumina or rich in magnesia), with a molar ratio that can range between 66 and 91%, for example, 78%, and a grain size between 20 and 1000 nm.

3. Material nanostructured compound according to claim 2 wherein the alumina b) belongs to the following group: TiO _2, Fe ₂ θ3, Y ₂ Ü3 and chromite (Cr ₂ O _3).

4- Nanostructured composite material according to claim 2 characterized in that the ceramic oxide / nW material is α-Al ₂ O ₃ / nW _.

5. Composite nanostructured material according to claim 2 characterized in that the ceramic oxide / nW material is spinel / nW.

6. Procedure for obtaining the nanostructured material according to claims 1 to 5, characterized in that it comprises the following steps: a) the oxidic powder is suspended in absolute ethanol, with a solids concentration generally less than 85%, putting all the set under stirring by any magnetic or mechanical device that favors dispersion, b) in parallel, a solution of tungsten chloride in absolute ethanol (purity> 99%) is prepared with the concentration required to obtain the nanostructured powder with the metal concentration desired, it warming the solution below 70 ⁰ C, c) once all chloride tungsten has become ethoxide tungsten W, (colorless solution) in step b) is added in a controlled manner to the powder slurry oxidic of a) which is kept under continuous agitation to favor the homogeneous mixing of both liquids, d) the remaining solvent is removed by evap prayer at a temperature, generally, less than 70 ⁰ C and always under continuous agitation, being able to heat it in an oven at 60 ⁰ C for 24 hours until obtaining a dry powder, e) subsequently, the dry powder of d), is screened by means of a standard mesh, preferably below

63 microns, and is calcined at temperatures between 500 ⁰ C and 700 ⁰ C, preferably at 600 ⁰ C, for a period of time sufficient to remove the organic components and favor the crystallization of tungsten oxide on the surface of the oxidic particles , preferably, for one hour, and f) reduce the tungsten oxide to metallic tungsten by a heat treatment between 750 ⁰ C and 1100 ⁰ C, preferably at 900 ⁰ C, in a reducing atmosphere of hydrogen of the nanostructured powder of e) between an hour and a half and two and a half hours, preferably two hours, whereby the crystallization of the metal nanoparticles on the surface of the oxidic particles occurs.

7. - Method according to claim 6 characterized in that the oxidic powder of a) is selected from the following group: a) alumina, in any of its crystallographic forms, namely, α, β, δ, γ, K, p, η , θ and χ, and with a grain size between 20 and 1000 nm, b) alumina with any oxide that can enter a solid solution in its network and whose solid solution with alumina is continuous in the range between 0% and 100% by weight, and c) aluminum-magnesium spinel (MgAl2θ4) in any of its varieties (stoichiometric, rich in alumina or rich in magnesia), with a molar ratio that can range between 66 and 91%, by example, 78%, and a grain size between 20 and 1000 nm.

8. Method according to claim 7 characterized in that the alumina of b) is selected from the following group: TiO ₂ , Fe ₂ O ₃ , Y ₂ O ₃ and chromite (Cr ₂ O ₃ ).

9. Method according to claim 7 characterized in that the concentration of the tungsten chloride metal phase of b) can vary depending on the concentration of tungsten in the material to be obtained, preferably, between 0.05 and 30% by volume of W , and for example, 1%.

10. Method according to claim 7 characterized in that alumina (Ot-Al ₂ O ₃ ) is used as an oxidic powder.

11. Method according to claim 7 characterized in that spinel is used as oxidic powder.

12. Use of the nanostructured material according to claims 1 to 5 in the preparation of a product belonging to the following group: electronic components, catalysts, structural technical ceramics, pigments and dyes and coatings on metal substrates.