Method for producing a powdered precursor material, powdered precursor material and use thereof

Abstract

A method is provided for producing a pulverulent precursor material of the general formula M1.sub.xM2.sub.y(Si,Al).sub.12(O,N).sub.16 or M1.sub.2-zM2.sub.zSi.sub.8Al.sub.4N.sub.16 having the method steps A) producing a pulverulent mixture of starting materials, B) calcining the mixture under a protective gas atmosphere and subsequent grinding, wherein in method step A) at least one nitride with a specific surface area of greater than 2 m.sup.2/g is selected as starting material. A pulverulent precursor material and the use thereof are additionally provided.

Claims

1. A method for producing a pulverulent precursor material of the general formula M1.sub.2-zM2.sub.zSi.sub.8Al.sub.4N.sub.16, wherein M1 comprises at least one of Li, Mg, Ca, Y and the group of lanthanoids without Ce and La, M2 comprises at least one of Ce, Pr, Eu, Tb, Yb and Er and wherein 0z2 applies, comprising the method steps A) producing a pulverulent mixture of starting materials, B) calcining the mixture under a reducing atmosphere in a tube furnace or chamber furnace and subsequent grinding, wherein in method step A) at least one silicon nitride with a specific surface area of more than 2 m.sup.2/g to 11 m.sup.2/g is selected as starting material, wherein the calcining in method step B) is carried out at a temperature selected from the range of 1300 C. to 1600 C., and wherein the pulverulent precursor material is produced with an average grain size d50 which is less than 2.3 m.

2. The method according to claim 1, wherein method step B) is carried out at least once.

3. The method according to claim 1, wherein the calcining in method step B) includes a holding time selected from the range of 1 minute to 24 hours.

4. The method according to claim 1, wherein Si.sub.3N.sub.4 is selected as the silicon nitride in method step A).

5. The method according to claim 1, wherein in method step A) at least one fluxing agent is added to the mixture of starting materials.

6. The method according to claim 5, wherein the fluxing agent is selected from a group comprising boric acid, borates, chlorides, fluorides and mixtures thereof.

7. The method according to claim 5, wherein the fluxing agent is added in a concentration selected from the range of 0.001 mol to 0.2 mol.

8. The method according to claim 1, wherein in a method step C) following method step B) the pulverulent precursor material is washed in base and/or acid.

9. A method for producing a pulverulent precursor material of the general formula M1.sub.xM2.sub.y(Si,Al).sub.12(O,N).sub.16, wherein M1 comprises at least one of Mg, Ca, Y and the group of lanthanoids without Ce and La, M2 comprises at least one of Ce, Pr, Eu, Tb, Yb and Er and wherein 0.3x+y1.5 and 0y0.7 apply, comprising the method steps: A) producing a pulverulent mixture of starting materials, B) calcining the mixture under a reducing atmosphere in a tube furnace or chamber furnace and subsequent grinding, wherein in method step A) at least one silicon nitride with a specific surface area of more than 2 m.sup.2/g to 11 m.sup.2/g is selected as starting material, wherein the calcining in method step B) is carried out at a temperature selected from the range of 1300 C. to 1600 C., and wherein the pulverulent precursor material has an average grain size d50 which is less than 2.3 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example of an electron micrograph of a precursor material produced using a conventional method.

(2) FIGS. 2a and 2b show examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

(3) FIGS. 3a and 3b show further examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

(4) FIGS. 4a and 4b show further examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

(5) FIGS. 5a and 5b show further examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

(6) FIGS. 6a and 6b show further examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

(7) FIGS. 7a and 7b show further examples of electron micrographs of pulverulent precursor materials produced using a method according to the invention.

DETAILED DESCRIPTION

(8) A comparative example for producing a coarse-grained powder and a number of exemplary embodiments for producing finely divided pulverulent precursor materials are indicated below.

Comparative Example: Production of (Ca,Eu)2Si8Al4N16

(9) 48 g Ca.sub.3N.sub.2, 82 g AlN, 187 g Si.sub.3N.sub.4 (specific surface area roughly 1 m.sup.2/g) and 4 g Eu.sub.2O.sub.3 are weighed out and homogenised under a protective gas atmosphere. Then the lightly compacted starting material mixture is calcined for several hours under a reducing atmosphere in the tube or chamber furnace at temperatures of between 1500 C. and 1800 C. Then further calcining operations may proceed, likewise under a reducing atmosphere, between 1500 C. and 1800 C. Between the calcining operations, the calcined cake is ground, optionally screened and introduced with light compaction into a crucible. After final grinding and screening of the calcined cake, a coarse-grained, spherical luminescent material of the general formula (Ca,Eu).sub.2Si.sub.8Al.sub.4N.sub.16 is produced. The coarse-grained, spherical luminescent material shown in FIG. 1 has an average grain size d.sub.50 of 4.7 m after work-up subsequent to the first calcining operation.

Exemplary Embodiment 1: Production of (Ca,Eu)2Si8Al4N16

(10) 39 g Ca.sub.3N.sub.2, 66 g AlN, 150 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) and 4 g Eu.sub.2O.sub.3 are weighed out and homogenised under a protective gas atmosphere. Then the lightly compacted starting material mixture is calcined for several hours under a reducing atmosphere in the tube or chamber furnace at temperatures of between 1300 C. and 1600 C. Then further calcining operations may proceed, likewise under a reducing atmosphere, between 1300 C. and 1600 C. Between the calcining operations, the calcined cake is ground, optionally screened and introduced with light compaction into a crucible. After final grinding and screening of the calcined cake, a finely divided, spherical precursor material is produced, which may for example be used for a ceramic diffusion barrier layer or a ceramic wavelength conversion layer. The precursor material is shown in FIGS. 2a and 2b after work-up of the second calcine. The average grain size d.sub.50 amounts to 2.2 m.

Exemplary Embodiment 2: Production of (Ca,Eu)SiAl3ON15

(11) 98 g CaCO.sub.3, 123 g AlN, 421 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) and 4 g Eu.sub.2O.sub.3 are weighed out. Further production proceeds as described in exemplary embodiment 1. The resultant, finely divided and spherical precursor material, which may for example be used for a ceramic diffusion barrier layer or a ceramic wavelength conversion layer, is shown in FIGS. 3a and 3b after work-up of the first calcine. The average grain size d.sub.50 amounts to 1.7 m.

Exemplary Embodiment 3: Production of CaSiAl3ON15

(12) 100 g CaCO.sub.3, 122 g AlN and 421 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) are weighed out. Further production proceeds according to the explanations in exemplary embodiment 1. The resultant precursor material, which may be used for example in a ceramic diffusion barrier layer, is fine-grained and spherical.

Exemplary Embodiment 4: Production of Ca2Si8Al4N16

(13) 50 g Ca.sub.3N.sub.2, 82 g AlN and 187 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) are weighed out under a protective gas atmosphere. Production proceeds as described in exemplary embodiment 1. The result is a finely divided and spherical precursor material, which may be used in a ceramic diffusion barrier layer. After work-up of the first calcine, the average grain size d.sub.50 amounts to 1.6 m.

Exemplary Embodiment 5: Production of (Ca,Eu)2Si8Al4N16

(14) 39 g Ca.sub.3N.sub.2, 66 g AlN, 150 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g), 2 g CaF.sub.2 and 4 g Eu.sub.2O.sub.3 are weighed out under a protective gas atmosphere. The added concentration of the fluxing agent CaF.sub.2 is crucial for the length or size of the resultant rods and may be between 0.01 mol and 0.2 mol, in particular between 0.01 mol and 0.1 mol. The above-stated weighed-out quantity constitutes an example of a CaF.sub.2 concentration of 0.03 mol relative to Ca.sub.3N.sub.2. Production of the precursor material proceeds according to exemplary embodiment 1. The result is a fine-grained, rod-shaped or acicular material, which may be used for example in a ceramic diffusion barrier layer or in a ceramic wavelength conversion layer (illustration of the material in FIGS. 4a and 4b). After work-up of the second calcine, the average grain size d.sub.50 amounts to 0.8 m. The phase purity of the precursor material was confirmed with XRD measurements.

(15) Tests with different holding times during calcining and different maximum temperatures, which are selected from the range 1300 C. to 1600 C., for example 1400 C., 1450 C., 1550 C., have shown that both parameters have only slight influence on particle size. In terms of the efficiency (QE) of the precursor material, maximum temperature has a greater influence than holding time. As maximum temperature increases, QE increases irrespective of holding time with identical particle size. These trends are illustrated in Table 1 on the basis of the samples produced in exemplary embodiments 1 and 5.

(16) TABLE-US-00001 TABLE 1 Holding QE d.sub.50 EE CaF.sub.2 T.sub.max time [%] [m] 1 T1 H3 40 1.1 1 T2 H3 46 1.3 1 T3 H1 57 1.4 1 T3 H2 58 1.6 1 T3 H3 60 1.6 5 T1 H3 33 0.6 5 T2 H3 45 0.6 5 T3 H1 67 0.5 5 T3 H2 72 0.6 5 T3 H3 72 0.6 EE: Exemplary embodiment T.sub.max: maximum temperature T1 < T2 < T3 H1 < H2 < H3

Exemplary Embodiment 6: Production of Ca2Si8Al4N16

(17) 50 g Ca.sub.3N.sub.2, 82 g AlN, 187 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) and 2 g CaF.sub.2 are weighed out under a protective gas atmosphere. In this example, the CaF.sub.2 concentration amounts to 0.03 mol relative to Ca.sub.3N.sub.2. Production of the precursor material corresponds to that stated in exemplary embodiment 1. The result is a fine-grained, rod-shaped precursor material, which may for example be used in a ceramic diffusion barrier layer. The average grain size amounts to approximately 0.7 m both after work-up of the first and after work-up of the second calcine.

Exemplary Embodiment 7: Production of (Ca,Eu)2Si8Al4N16

(18) 39 g Ca.sub.3N.sub.2, 66 g AlN, 150 g Si.sub.3N.sub.4 (specific surface area roughly 3 m.sup.2/g), 2 g CaF.sub.2 and 4 g Eu.sub.2O.sub.3 are weighed out under a protective gas atmosphere. The concentration of the fluxing agent CaF.sub.2 amounts in this example to 0.03 mol relative to Ca.sub.3N.sub.2. Production of the precursor material proceeds as stated in exemplary embodiment 1. Work-up of the second calcine results in a fine-grained, rod-shaped or acicular precursor material as shown in FIGS. 5a and 5b with an average grain size of 1.1 m.

(19) Depending on the selection of the starting materials, QE and grain size and the phase purity of the precursor material may be influenced. In contrast to AlN, the particle shape may be varied by purposeful selection of the silicon nitride.

(20) Washing of the finished pulverulent precursor material in acids or bases leads to further improvement in QE. QE may be increased by 7 to 8%, which corresponds to around 5 to 6 percentage points.

Exemplary Embodiment 8: Production of (Ca,Eu)2Si8Al4N16

(21) 39 g Ca.sub.3N.sub.2, 66 g AlN, 150 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) and 4 g Eu.sub.2O.sub.3 are weighed out together with CaCl.sub.2 under a protective gas atmosphere. The concentration of fluxing agent CaCl.sub.2 amounts to 0.01 mol or 0.1 mol relative to Ca.sub.3N.sub.2. Production of the precursor material proceeds according to exemplary embodiment 1. The resultant finely divided and rod-shaped precursor material, which may be used for example in a ceramic diffusion barrier layer or a ceramic wavelength conversion layer, is shown in FIG. 6. FIG. 6A shows (Ca,Eu).sub.2Si.sub.8Al.sub.4N.sub.16 with 0.01 mol CaCl.sub.2 and FIG. 6b shows the material with 0.1 mol CaCl.sub.2.

Exemplary Embodiment 9: Production of (Ca,Eu)2Si8Al4N16

(22) 39 g Ca.sub.3N.sub.2, 66 g AlN, 150 g Si.sub.3N.sub.4 (specific surface area roughly 11 m.sup.2/g) and 4 g Eu.sub.2O.sub.3 are weighed out together with AlF.sub.3 with a concentration of 0.01 mol or 0.05 mol relative to Ca.sub.3N.sub.2 under a protective gas atmosphere. Production proceeds according to exemplary embodiment 1. The result is a fine-grained, rod-shaped precursor, which is shown in FIG. 7 and may be used for example in a ceramic wavelength conversion layer or a ceramic diffusion barrier layer. FIG. 7a shows (Ca,Eu).sub.2Si.sub.8Al.sub.4N.sub.16 with 0.01 mol AlF.sub.3 and FIG. 7b shows the material with 0.05 mol AlF.sub.3.

(23) NH.sub.4Cl is a possible further fluxing agent. The addition of NH.sub.4Cl results in a finely divided precursor material, the particle size of which reduces as the concentration of fluxing agent, selected from the range of 0.01 to 0.2 mol, increases. Furthermore as the NH.sub.4Cl concentration increases, rods are formed from initially spherical particles.

(24) Table 2 below shows the influence of the addition and concentration of fluxing agent on the average grain size values d.sub.50 and d.sub.90, quantum efficiency QE and morphology. For these tests, comparable temperature programmes are selected when producing samples.

(25) TABLE-US-00002 TABLE 2 Fluxing SSA of Fluxing agent d.sub.50 d.sub.90 QE EE Si.sub.3N.sub.4 agent conc. [m] [m] [%] Morphology 1 roughly 2.2 4.4 67 Spheres 11 m.sup.2/g 5 roughly CaF.sub.2 0.03 mol 0.8 2.7 81 Needles 11 m.sup.2/g 5 roughly CaF.sub.2 0.1 mol 0.7 4.0 76 Needles 11 m.sup.2/g 7 roughly CaF.sub.2 0.03 mol 1.1 3.0 77 Needles 3 m.sup.2/g 8 roughly CaCl.sub.2 0.03 mol 1.0 3.1 78 Rods 11 m.sup.2/g 8 roughly CaCl.sub.2 0.1 mol 0.9 5.7 78 Rods 11 m.sup.2/g 9 roughly AlF.sub.3 0.03 mol 0.6 2.4 77 Rods 11 m.sup.2/g 9 roughly AlF.sub.3 0.05 mol 0.7 2.2 75 Rods 11 m.sup.2/g roughly NH.sub.4Cl 0.03 mol 1.0 2.8 73 Spheres 11 m.sup.2/g roughly NH.sub.4Cl 0.1 mol 0.9 2.7 79 Rods 11 m.sup.2/g EE: Exemplary embodiment SSA: Specific surface area conc.: concentration

(26) QE and d.sub.90 may be influenced depending on the selection of AlN as starting material. Furthermore, an influence on the phase purity of the precursor material may be observed. The selection of AlN does not have any influence on morphology. The samples illustrated in Table 3 were produced without addition of a fluxing agent. The samples were produced according to the weighing-out of exemplary embodiment 1, wherein in examples 1a and 1b AlN was used in each case with different surface area values.

(27) TABLE-US-00003 TABLE 3 QE d.sub.90 EE SSA of AlN [%] [m] 1 roughly 3.3 m.sup.2/g 68 4.7 1a roughly 3 m.sup.2/g 58 8.2 1b <2 m.sup.2/g 30 14.0 EE: Exemplary embodiment SSA: Specific surface area

(28) QE, morphology and grain size may be influenced, depending on the selection of Si.sub.3N.sub.4 as starting material (see Table 4). The incorporation of oxygen into the precursor does not play any part in this respect. Without using a fluxing agent, rod-shaped or spherical precursor material was obtained, depending on the selected Si.sub.3N.sub.4. Furthermore, influence on phase purity may be observed depending on the selected Si.sub.3N.sub.4. Weighing out of samples 1c and 1d corresponds to that of exemplary embodiment 1, wherein different Si.sub.3N.sub.4 were used.

(29) TABLE-US-00004 TABLE 4 QE d.sub.90 EE SSA of Si.sub.3N.sub.4 [%] [m] Morphology 1 roughly 11 m.sup.2/g 68 4.7 Small spheres 1c roughly 3 m.sup.2/g 53 5.9 Small spheres 1d roughly 5 m.sup.2/g 58 6.5 Rods EE: Exemplary embodiment SSA: Specific surface area

(30) Washing of the finished precursor material in acids leads to an improved QE. QE may be increased by 7 to 8%, which corresponds to around 5 to 6 percentage points. The influence of washing is visible in Table 5 taking Exemplary embodiment 5 as an example.

(31) TABLE-US-00005 TABLE 5 Acid QE [%] unwashed 76.3 H.sub.3PO.sub.4 79.0 HCl 80.1 H.sub.2SO.sub.4 81.7

(32) It was thus possible to demonstrate that, through the addition of fluxing agents and through the selection of Si.sub.3N.sub.4, the morphology of the pulverulent precursor material produced may be purposefully controlled. This makes it possible to influence not only particle size but also packing density, for example during tape casting. Acid washing operations additionally increase the efficiency of the precursor material, if this is produced as a doped precursor material.

(33) The invention is not restricted by the description given with reference to the exemplary embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.