WO2008141793A1

WO2008141793A1 - Method for the production of doped yttrium aluminum garnet nanoparticles

Info

Publication number: WO2008141793A1
Application number: PCT/EP2008/004012
Authority: WO
Inventors: Norbert Roesch
Original assignee: Clariant Finance (Bvi) Limited
Priority date: 2007-05-24
Filing date: 2008-05-20
Publication date: 2008-11-27
Also published as: DE102007024338A1

Abstract

The invention relates to a method for the production of doped yttrium aluminum garnet nanoparticles. According to said method, an aqueous solution comprising aluminum chlorohydrate, a yttrium salt and a doping metal salt is dried. The resulting salt mixture is calcinated and disagglomerated.

Description

description

PROCESS FOR PRODUCING DOTED YTTRIUM ALUMINUM GRANATE NANOPARTICLES

The present invention relates to the preparation of doped and fluorescent YAG nanoparticles (yttrium aluminum garnet).

YAG is an interesting ceramic material characterized by high hardness and thermal conductivity. The crystalline matrix can be used to pick up dopants that emit fluorescent light when excited. As dopants cerium, terbium, europium, cobalt or samarium are described. By combining cerium-doped YAG with a blue fluorescent pigment, it is possible to construct white light-emitting diodes (US 2005/0 136 782; DE 103 16 769).

According to the prior art doped YAG material from the respective oxides (KR 2001 0049014) or carbonates is made with admixed dopants by milled dry the starting materials with each other and sintered at 1500 ⁰ C. Disadvantage of this method is the long sintering time (days) and the low fluorescence yield due to the insufficient mixing.

It is also described to be based on the corresponding metal salts such as nitrates, from which the hydroxides are precipitated with ammonia. The precipitates are then after separation and drying (32 h at 110 ^C C) at temperatures between 800 - 1000 ⁰ C in 2 h in the corresponding YAG powder transferred (J.Su et al., / Materials Research Bulletin 40 (2005) 1279-1285).

The sol-gel method is also based on the metal salts and citric acid. Also in this process, the resulting dried gel (40 ⁰ C for 24 h) must be calcined at 800 - 1000 ⁰ C for 16 h. In the methods described so far, the powder is due to the high calcination temperatures and long residence times in strongly agglomerated form and consisting of large primary particles.

One way to get nano-materials is the aerosol process. The desired molecules are obtained from chemical reactions of a Precursorgases or by rapid cooling of a supersaturated gas. The formation of the particles occurs either through collision or the constant equilibrium evaporation and condensation of molecular clusters. The newly formed particles grow by further collision with product molecules (condensation) and / or particles (coagulation). However, if the coagulation rate is greater than that of the new growth or growth, agglomerates of spherical primary particles are formed.

Flame reactors are based on this principle

Manufacturing variant dar. Nanoparticles are formed here by the decomposition of Precursormolekülen in the flame at 1500 - 2500 ⁰ C. As examples, the oxidations of TiCl ₄ ; SiCu and Si ₂ θ (CH ₃ ) ₆ in methane / θ ₂ flames leading to TiO ₂ and SiO ₂ particles. Flame reactors are now used industrially for the synthesis of submicroparticles such as carbon black, pigment TiO ₂₎ silica and alumina. Although the resulting powders contain small primary particles due to the low residence time, due to the high temperatures in the flame, very hard agglomerates form.

Hydrothermal syntheses are also described for the preparation of nanoparticles. A nanostructured YAG powder can be obtained at 500 ^° C., a pressure of 100 Mpa, within 20 hours (T. Takamori, LD David, Am. Ceram. Soc., Bull., 65 (9), 1986). Disadvantage of this method are again the long reaction time and the high expenditure on equipment.

In another known method (US 2006/0 145 124) is based on an anionic solution containing oxalic acid or citric acid or ammonium carbonate or mixtures of these substances. A cationic O

Solution of the corresponding metal salts or oxides is then contacted with the anionic solution and the precipitate formed is isolated and dried for 12 to 36 hours. The calcination is then carried out at 800 - 1500 ⁰ C for 0.5 - 12 h. Also in this long reaction and drying times must be taken into account.

The aim of the present invention is to produce fluorescent YAG nanoparticles using a cost-effective method.

The invention relates to a method for producing doped

Yttrium aluminum garnet nanoparticles, which consists in drying an aqueous solution containing aluminum chlorohydrate, an yttrium salt and a doping metal salt, calcining the resulting salt mixture and deagglomerating.

The starting point for the process according to the invention is an aqueous solution of aluminum chlorohydrate which has the formula Al ₂ (OH) _x Cl y, where x is a number from 2.5 to 5.5 and y is a number from 3.5 to 0.5 and the sum of x and y is always 6. In this aqueous solution, an yttrium salt and a doping metal salt are then dissolved. As the yttrium salt, the commercially available salts are suitable, such as, for example, the chloride, nitrate or acetate. Suitable doping salts are the salts of rare earths and salts of transition metals, for example cerium, dysprosium, gadolinium, europium, terbium, praseodymium, neodymium or cobalt salts. These salts can also be used in the form of their chlorides, nitrates or acetates.

The amounts of aluminum chlorohydrate, yttrium salt and doping metal salt with the cation M are chosen so that the molar ratio of the sum of the cations of Y and M to Al is about 0.6: 1, corresponding to the sum formal Y3AI5O12. The amount of doping metal salt having the cation M is generally selected so that the amount of cation M is 0.01 to 6, preferably 0.01 to 2 wt .-%, based on the total amount of cation M and yttrium. After all starting materials have been dissolved in water, the solution is dried to obtain homogeneous salt mixtures. The drying can be carried out in a freeze dryer, on a roller dryer, in a vacuum dryer or in a spray dryer. This drying takes place without special formation of gel phases, as required in the sol-gel process.

Subsequently, the resulting powder mixture containing all the salts in homogeneous distribution is calcined, preferably in a rotary kiln or chamber furnace, to convert the metal salts into the granate-type compound oxide. The calcination is carried out at about 800 - 1500 ⁰ C, preferably at 900-1000 ⁰ C. The residence time is less than 30 min, preferably 10 min.

Another possibility is to inject the salt solution directly into a calcination apparatus without separate predrying. In this case, the drying and calcining takes place within a process step.

In both cases, a doped YAG powder consisting of agglomerates of nanoparticles is obtained. From these agglomerates, the nanoparticles must be released. This is preferably done by grinding or by treatment with ultrasound. According to the invention, this deagglomeration is carried out in the presence of a solvent and preferably in the presence of a coating agent, preferably a silane or siloxane, which saturates the resulting active and reactive surfaces during the milling process by a chemical reaction or physical addition, thus preventing reagglomeration. The nano-mixed oxide remains as a small particle. It is also possible to add the coating agent after deagglomeration.

To obtain nanoparticles, the agglomerates are preferably comminuted by wet grinding in a solvent, for example in an attritor mill, bead mill or stirred mill. This gives doped YAG nanoparticles which have a crystallite size of less than 1 μm, preferably less than 0.2 μm, more preferably between 0.001 and 0.1 μm. Thus, for example, after a six-hour grinding, a suspension of Nanoparticles with a d90 value of approximately 50 nm. Another possibility of deagglomeration is sonication.

For the inventive modification of the surface of these nanoparticles with coating agents such. As silanes or siloxanes there are two possibilities.

According to the first preferred variant, deagglomeration can be carried out in the presence of the coating agent, for example by adding the coating agent to the mill during milling. A second possibility consists of first destroying the agglomerates of the nanoparticles and then treating the nanoparticles, preferably in the form of a suspension in a solvent, with the coating agent.

Suitable working medium for deagglomeration are both water and customary solvents, preferably those which are also used in the paint industry, such as, for example, C 1 -C 4 -alcohols, in particular methanol, ethanol or isopropanol, acetone, tetrahydrofuran, butyl acetate. When deagglomerating in water, an inorganic or organic acid such as HCl, HNO ₃ , formic acid or acetic acid should be added to stabilize the resulting nanoparticles in the aqueous suspension. The amount of acid may be 0.1 to 5 wt .-%, based on the garnet. From this aqueous suspension of the acid-modified nanoparticles is then preferably the grain fraction having a particle diameter of less than 20 nm separated by centrifugation. Subsequently, at elevated temperature, for example at about 100 ^° C., the coating agent, preferably a silane or siloxane, is added. The nanoparticles thus treated precipitate, are separated and dried to a powder, for example by freeze-drying.

Suitable coating agents here are preferably silanes or siloxanes or mixtures thereof. In addition, suitable coating agents are all substances which can physically bind to the surface of the mixed oxides (adsorption) or which can bond to form a chemical bond on the surface of the garnet particles. Since the surface of the garnet particles is hydrophilic and free hydroxy groups are available, suitable coating agents are alcohols, compounds having amino, hydroxyl, carbonyl, carboxyl or mercapto functions. Examples of such coating compositions are polyvinyl alcohol, mono-, di- and tricarboxylic acids, amino acids, amines, waxes, surfactants, hydroxycarboxylic acids.

Suitable silanes or siloxanes are compounds of the formulas

a) R [-Si (R ¹ R ¹¹ JOJ _n Si (R ¹ R ¹¹ JR ¹ "or cyclo - [- Si (R ¹ R ¹¹ JO-Jr Si (R ¹ R ¹¹ JO

wherein

R, R ', R ", R" ¹ - identical or different from each other, an alkyl radical having 1-18 C atoms or a phenyl radical or an alkylphenyl or a phenylalkyl radical having 6 - 18 C-atoms or a radical of the general formula - ( CmH2m-O) p C _q H2q + i, or a radical of the formula -C H2 _S _S Y or a radical of general formula -XZM,

n is an integer meaning 1 ≤ n ≤ 1000, preferably 1 <n <100, m is an integer 0 <m <12 and p is an integer 0 ≤ p <60 and q is an integer 0 <q <40 and r is an integer 2 ≤ r <10 and s is an integer 0 ≤ s <18 and

Y is a reactive group, for example α, β-ethylenically unsaturated groups, such as (meth) acryloyl, vinyl or allyl groups, amino, amido, ureido,

Hydroxyl, epoxy, isocyanato, mercapto, sulfonyl, phosphonyl, trialkoxylsilyl, alkyldialkoxysilyl, dialkylmonoalkoxysilyl, anhydride, and / or carboxyl groups, imido, imino, sulfite, sulfate, sulfonate, phosphine, phosphite, phosphate, phosphonate and

X is a .functional oligomer with t an integer 2 <t ≦ 8 and Z in turn a residue

R [-Si (R'R ") - O-] _n Si (R ¹ R ¹ OR" ¹ or cyclo - [-Si (R'R ") - O-] r Si (R'R") - O -

represents as defined above.

The t-functional oligomer X is preferably selected from:

Oligoether, oligoester, oligoamide, oligourethane, oligohamine, oligoolefin, oligovinyl halide, oligovinylidenedihalogenide, oligoimine, oligovinyl alcohol, esters, acetal or ethers of oligovinyl alcohol, cooligomers of maleic anhydride, oligomers of (meth) acrylic acid, oligomers of (meth) acrylic esters, oligomers of (meth ) Acrylic acid amides, oligomers of (meth) acrylsäureimiden, oligomers of (meth) acrylonitrile, particularly preferably oligoether, oligoester, oligourethanes.

Examples of radicals of oligoethers are compounds of the type - (C _a H _2a -O) _b - C _a H _2a - or O- (C _a H2a-O) _b -CaH ₂ aO with 2 <a <12 and 1 < b <60, z. A diethylene glycol, triethylene glycol or tetraethylene glycol residue, a dipropylene glycol, tripropylene glycol, tetrapropylene glycol residue, a dibutylene glycol, tributylene glycol or tetrabutylene glycol residue. Examples of residues of Oligoestem are compounds of the type -C _b H _2b - (C (CO) CaH _2a - (CO) OC _b H ₂ b) c- or -OC _b H ₂ b- (C (CO) C ₃ H ₂₃ - (CO) OC _b H _2b -) _c -O- where a and b are different or equal to 3 <a <12, 3 <b <12 and 1 ≤ c ≤ 30, z. B. an oligoester of hexanediol and adipic acid. b) Organosilanes of the type (RO) ₃ Si (CH 2) m R 'R = alkyl, such as methyl, ethyl, propyl m = 0.1-20 R '= methyl, phenyl,

-C ₄ F ₉ ; OCF ₂ -CHF-CF ₃ , -C ₆ F ₁₃ , -O-CF ₂ -CHF ₂ -NH ₂ , -N ₃ , SCN, -CH = CH ₂ , -NH-CH ₂ -CH ₂ -NH ₂ , -N- (CH ₂ -CH ₂ -NHs) ₂ -OOC (CH ₃ ) C - CH ₂

-OCH ₂ -CH (O) CH ₂ -NH-CO-NH-CO- (CH ₂ ) ₅

-NH-COO-CH ₃ , -NH-COO-CH ₂ -CH ₃ , -N H- (CH ₂ J ₃ Si (OR) ₃

SH

-NR ¹ R ¹¹ R " ¹ (R '= alkyl, phenyl; R" = alkyl, phenyl; R ¹ "= H, alkyl, phenyl, benzyl, C ₂ H ₄ NR""withR""= A, alkyl and R "" ¹ = H, alkyl).

Examples of silanes of the type defined above are, for. Hexamethyldisiloxane, octamethyltrisiloxane, other homologous and isomeric compounds of the series Si _n O _n -I (CH ₃ ) _{2n + 2} , where n is an integer 2 <n <1000, e.g. Polydimethylsiloxane ^200® fluid (20 cSt).

Hexamethyl-cyclo-trisiloxane, octamethyl-cyclo-tetrasiloxane, other homologous and isomeric compounds of the series

(Si-O) r (CH ₃ ) ₂ r, where r is an integer 3 ≤ r ≤ 12,

Dihydroxytetramethydisiloxane, dihydroxyhexamethyltrisiloxane, dihydroxyoctamethyltetrasiloxane, other homologous and isomeric compounds of the series

HO - [(Si-O) _n (CH ₃ ) ₂ n] -Si (CH ₃ ) ₂ -OH or

HO - [(Si-O) _n (CH ₃ ) _2n ] - [Si-O) _m (C ₆ H ₅ ) _2m ] -Si (CH ₃ ) ₂ -OH, where m is an integer 2 ≤ m ≤ 1000 , Preferably, the α, ω-dihydroxypolysiloxanes, z. B. polydimethylsiloxane

(OH end groups, 90-150 cSt) or polydimethylsiloxane-co-diphenylsiloxane,

(Dihydroxy end groups, 60 cST). Dihydrohexamethytrisiloxane, Dihydrooctamethyltetrasiloxan other homologous and isomeric compounds of the series H - [(Si-O) _n (CH ₃ ) ₂ n] -Si (CH ₃ ) ₂ -H, where n is an integer 2 <n ≤ 1000, are preferred the α, ω-dihydropolysiloxanes, e.g. B. polydimethylsiloxane (hydride end groups, M _n = 580).

Di (hydroxypropyl) hexamethyltrisiloxane, dihydroxypropyl) octamethyltetrasiloxane, other homologous and isomeric compounds of the series HO- (CH ₂ ) _u [(Si-O) n (CH ₃ ) ₂ (CH ₂ ) _u -OH, the α.ω are preferred -Dicarbinolpolysiloxanes with 3 ≤ u ≤ 18, 3 ≤ n ≤ 1000 or their polyether-modified successor compounds based on the ethylene oxide (EO) and propylene oxide (PO) as homopolymer or copolymer HO- (EO / PO) _v - (CH 2) u [(Si-O) _t (CH ₃ ) 2t] -Si (CH ₃ ) ₂ (CH ₂ ) u- (EO / PO) _v -OH, preferred are α, ω-di (carbinol polyether) polysiloxanes with 3 ≤ n ≦ 1000, 3 <u ≦ 18, 1 <v <50.

Instead of α, ω-OH groups are also the corresponding difunctional compounds with epoxy, isocyanato, vinyl, AIIyI- and di (meth) acryloyl used, for. B. Polydimethylsiloxan with vinyl end groups (850 - 1150 cST) or TEGORAD 2500 from. Tego Chemie Service.

There are also the esterification of ethoxylated / propoxylated trisiloxanes and higher siloxanes with acrylic acid copolymers and / or maleic acid copolymers as a modifying compound in question, z. B. BYK Silclean 3700 of Messrs. Byk Chemie or TEGO ^® Protect 5001 from. Tego Chemie Service GmbH.

Instead of α, ω-OH groups are also the corresponding difunctional compounds with -NHR "" with R "" = H or alkyl used, for. For example, the well-known aminosilicone oils from Wacker, Dow Corning, Bayer, Rhodia, etc., which are distributed randomly on the polysiloxane chain (cyclo), are used.

Carry alkylamino groups or (cyclo) alkylimino groups on their polymer chain. c) organosilanes of the type (RO) ₃ Si (C _n H _{2n +} i) and (RO) ₃ Si (C _n H _{2n +} I), wherein R is an alkyl, such as. For example, methyl, ethyl, n-propyl, i-propyl, butyl n 1 to 20.

Organosilanes of the type R'x (RO) ySi (CnH2n + 1) and (RO) 3Si (CnH2n + 1), wherein

R is an alkyl, such as. Methyl, ethyl, n-propyl, i-propyl, butyl,

R ^{1 is} an alkyl, such as. Methyl, ethyl, n-propyl, i-propyl, butyl,

R ^{1 is} a cycloalkyl n is an integer from 1 to 20 x + y 3 x 1 or 2 y 1 or 2.

Organosilanes of the type (RO) ₃ Si (CHb) _n I-R ', wherein R is an alkyl, such as. As methyl, ethyl, propyl, m is a number between 0.1 - 20

R ^{1 is} methyl, phenyl, -C ₄ F ₉ ; OCF ₂ -CHF-CF ₃ , -C ₆ Fi ₃ , -O-CF ₂ -CHF ₂ , -NH ₂ , -N ₃ , -SCN, -CH = CH ₂ , -NH-CH ₂ -CH ₂ -NH ₂ , -N- (CH ₂ -CH ₂ -NH ₂ ) ₂ , -OOC (CH ₃ ) C = CH ₂ , -OCH ₂ -CH (O) CH ₂ , -NH-CO-N-CO- (CH ₂ ) ₅ , -NH-COO-CH ₃ , -NH-COO-CH ₂ -CH ₃ , -NH- (CH ₂ ) ₃ Si (OR) ₃ , -S _x - (CH ₂ ) ₃ ) Si (OR ) ₃ , -SH-NR ¹ R ¹¹ R " ¹ (R ¹ = alkyl,

phenyl; R "= alkyl, phenyl, R ¹¹¹ = H, alkyl, phenyl, benzyl, C ₂ H ₄ NR ¹¹¹¹ R ¹ ""withR""= A, alkyl and R ¹ ""= H, alkyl).

Preferred silanes are the silanes listed below: triethoxysilane, octadecyltimethoxysilane,

3- (trimethoxysilyl) -propylmethacrylate, 3- (trimethoxysilyl) -propylacrylate, 3- (trimethoxysilyl) -methylmethacrylate, 3- (trimethoxysilyl) -methylacrylate, 3- (trimethoxysilyl) -ethylmethacrylate, 3- (trimethoxysilyl) -ethylacrylate, 3- (Trimethoxysilyl) pentyl methacrylates, 3- (trimethoxysilyl) pentyl acrylates, 3- (trimethoxysilyl) hexyl methacrylates, 3- (trimethoxysilyl) hexyl acrylates, 3- (trimethoxysilyl) butyl methacrylates, 3- (trimethoxysilyl) butyl acrylates, 3- (trimethoxysilyl ) -heptylmethacrylate, 3- (trimethoxysilyl) -heptylacrylate, 3- (trimethoxysilyl) -octylmethacrylate, 3- (trimethoxysilyl) -octylacrylate, Methyltrimethoxysilanes, methyltriethoxysilanes, propyltrimethoxisilanes, propyltriethoxysilanes, isobutyltrimethoxysilanes, isobutyltriethoxysilanes, octyltrimethoxysilanes, octyltriethoxysilanes, hexadecyltrimethoxysilanes, phenyltrimethoxysilanes, phenyltriethoxysilanes, tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilanes,

Tetramethoxysilane, tetraethoxysilane, tetraethoxysilane Oligomeric (DYNASIL ^® 40 Fa. Degussa), tetra-n-propoxysilane, 3-Glycidyloxypropyltrimethoxysilane, 3-Glycidyloxypropyltriethoxysilane, 3-Methacryloxylpropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilanes, 3-Mercaptopropyltrimethoxysilane,

3-aminopropyltriethoxysilanes, 3-aminopropyltrimethoxysilanes, 2-aminoethyl-3-aminopropyltrimethoxysilanes. Triaminofunctional propyltrimethoxysilanes (DYNASYLAN ^® triamino Fa. Degussa), N- (n-butyl-3-aminopropyltrimethoxysilane, 3-Aminopropylmethyldiethoxysilane.

The coating compositions, in particular the silanes or siloxanes, are preferably added in molar ratios of YAG nanoparticles to silane of from 1: 1 to 10: 1. The amount of solvent in the deagglomeration is generally 20 to 90 wt .-%, based on the total amount of YAG nanoparticles and solvent.

The deagglomeration by grinding and simultaneous modification with the coating agent is preferably carried out at temperatures of 20 to 150 ⁰ C, more preferably at 20 to 90 ⁰ C. If the deagglomeration by grinding, the suspension is then separated from the grinding beads.

After deagglomeration, the suspension can be heated to complete the reaction for up to 30 hours. Finally, the solvent is distilled off and the remaining residue is dried. It may also be advantageous to leave the modified YAG nanoparticles in the solvent and to use the dispersion for other applications. It is also possible to suspend the YAG nanoparticles in the corresponding solvents and to carry out the reaction with the coating agent after deagglomeration in a further step.

example 1

10.0 g aluminum chlorohydrate with 50% FS content, 7.98 g yttrium chloride hexahydrate and 0.39 g cerium chloride hexahydrate are mixed and the water is removed in a freeze drier. The powder thus obtained is calcined in a box furnace for 15 minutes at 950 ⁰ C.

An X-ray structure analysis showed that the garnet phase is present.

The images of the SEM image taken (scanning electron microscope) showed crystallites in the range 10 - 80 nm (estimate from SEM image), which are present as agglomerates. The residual chlorine content was only a few ppm.

In a further step, 50 g of this doped YAG powder were suspended in 150 g of water. 0.5 g of trimethoxy-octylsilane was added to the suspension and fed to a vertical stirred ball mill from Netzsch (type PE 075). The grinding beads used consisted of zirconium oxide (stabilized with yttrium) and had a size of 0.3 mm. After three hours, the suspension was separated from the milling beads and boiled under reflux for a further 4 h.

The suspension of the fluorescent YAG nanoparticles was subsequently optically characterized.

Claims

claims:

1. A process for the preparation of doped yttrium aluminum garnet nanoparticles, characterized in that drying an aqueous solution containing aluminum chlorohydrate, an yttrium salt and a doping metal salt, the resulting salt mixture is calcined and disagglomerated.

2. The method according to claim 1, characterized in that one carries out the deagglomeration in the presence of a surface-modifying compound.

3. The method according to claim 1, characterized in that one carries out the deagglomeration in the presence of a silane or siloxane.

4. The method according to claim 1, characterized in that one carries out the drying and calcining in one step.

5. The method according to claim 1, characterized in that one uses as doping metal salts salts of the elements cerium, dysprosium, gandolinium, europium, terbium, lanthanum, praseodymium, neodymium, samarium or cobalt.

6. The method according to claim 1, characterized in that the amount of cation of the doping metal salt 0.01 to 6 wt .-%, based on the total amount of cation of the doping metal salt and yttrium ion.

7. The method according to claim 1, characterized in that one carries out the deagglomeration by grinding in an organic solvent.