JPH0444384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel arc tube. Specifically, the mechanical fracture surface is formed by a tightly packed state of fine crystal grains that are distinguished from each other by clear contours, and the clear contours of the fine crystal grains on the fracture surface has a polygonal shape, and the fine crystals have an average particle size of 0.3D to 0.3D when the average particle diameter at the fracture surface defined by the clear outline is defined as D (μm).
A hollow tube made of an aluminum nitride sintered body in which at least 70% of the crystal grains have a particle size in the range of 1.8D, and the hollow tube has a light emitting source in its hollow part. It is an arc tube that is sealed and has electrode terminals at both ends. Conventional arc tubes, such as high pressure sodium lamps, are widely used. These known arc tube materials are generally made of translucent alumina because they are required to have excellent translucency. Translucent alumina is an excellent material for arc tubes in that it has excellent translucency, but because of its low coefficient of thermal expansion, it does not reach high temperatures when the power is turned off, such as in the case of high-pressure sodium lamps.
It has a defect in its thermal shock properties, such as being rapidly cooled from around 1000℃ to room temperature. Therefore, there has been a desire to develop a material that is resistant to heat shock and has excellent translucency. As a result of diligent efforts to develop translucent ceramics, the present inventors have discovered that a sintered body obtained by sintering a new specific aluminum nitride powder has excellent translucency and has already proposed. As a result of further research, we discovered that an arc tube using the above-mentioned novel aluminum nitride powder not only has excellent light transmittance, but also exhibits excellent thermal shock properties, and we have completed the present invention and hereby propose it. It came to this. That is, in the present invention, the mechanical fracture surface is formed by a tightly packed state of fine crystal grains that are distinguished from each other by clear contours, and the mechanical fracture surface of the fine crystal grains on the fracture surface is The clear outline has a polygonal shape, and the fine crystals have a particle size in the range of 0.3D to 1.8D when the average particle size at the fracture surface defined by the clear outline is defined as D (μm). A hollow tube made of an aluminum nitride sintered body in which at least 70% of the crystal grains have a It is an arc tube with electrode terminals provided at both ends. The material of the hollow tube constituting the arc tube of the present invention has the following characteristics. Figure 1 of the accompanying drawings shows an aluminum nitride sintered body obtained by sintering the same aluminum nitride powder as in Example 1, which is the material for the hollow tube made of the aluminum nitride sintered body obtained in Example 1, which will be described later. This is a microscopic photograph of a fractured surface obtained by mechanically rupturing. As is clear from FIG. 1, the mechanical fracture surface is formed by a close packing of fine grains separated from each other by clear contours. The clear outline of the fracture surface of the fine crystal grains has a polygonal shape. In addition, the fine crystals have an average particle diameter of D at the fracture surface defined by the clear outline.
(μm), preferably 0.3D to 1.8D
At least 70% of the grains should have a grain size in the range 0.5D to 1.5D. In this way, an aluminum nitride sintered body with a very uniform particle size distribution (for example, in Figure 1, the average particle size (D) is 5.3 μm, and the particles with a particle size of 0.3D to 1.8D, that is, 1.6 μm to 9.5 μm) (accounting for 98%) is very unique compared to the previously proposed aluminum nitride sintered bodies. In addition, the aluminum nitride sintered body has a high purity.
It is preferable to use one having a content of cationic impurities of 99.5% or more, preferably 99.9% or more, and 0.3% by weight or less, preferably 0.1% by weight or less. The above-mentioned cationic impurities in aluminum nitride are metal components such as silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc, titanium, etc. that are mixed into the aluminum nitride powder before sintering. The content of the cationic impurity is calculated based on the content calculated assuming that the compound of the cationic component is a metal. The novel aluminum nitride sintered body has a very high density, generally having a density of 2.9 g/cm ² or more, preferably 3.0 g/cm ² , and more preferably 3.2 g/cm 2 .
It has a property of g/cm ² . Among the aluminum nitride sintered bodies, the aluminum nitride purity is 99.5% or more, preferably 99.9% or more, and the content of cationic impurities is 0.3% by weight or less, preferably 0.1% by weight or less. Particularly, among the metals as impurity components, iron, chromium An aluminum nitride sintered body having a total metal content of nickel, cobalt, copper, zinc or titanium of 0.1% by weight or less has particularly excellent transparency. In this sense, the aluminum nitride sintered body having the above properties is particularly suitable as a material for the hollow tube of the present invention. According to X-ray diffraction, the novel aluminum nitride sintered body has six distinct diffraction lines originating from hexagonal aluminum nitride crystals between diffraction angles (2θ) of 30° and 70°, that is, 33.3°± 0.5°, 36.2°±0.5°, 38.1°±
0.5°, 49.8°±0.5°, 59.6°±0.5 and 66.3°±0.5
The diffraction lines are shown with a diffraction angle of °. When these diffraction lines are converted into interplanar spacings (d, A) using Bragg's equation, they are 2.69±0.04A, 2.48±0.03A, and 2.36±, respectively.
0.03A, 1.83±0.02A, 1.55±0.01A and 1.41±
Equivalent to 0.01A. Conventional aluminum nitride sintered bodies require a large amount of sintering aids (for example,
CoO, _{Y2O3 ,} etc.) and the high oxygen content of the raw aluminum nitride itself, in addition to the diffraction lines originating from the hexagonal crystal of aluminum nitride, e.g.
CaO・6Al ₂ O ₃ , CaO・2Al ₂ O ₃ or Y ₃ Al ₅ O ₁₂
It has been reported that diffraction lines derived from crystals such as According to the aluminum nitride sintered body, even when such a sintering aid is used for sintering, the aluminum nitride sintered body is of high purity and does not substantially exhibit the above-mentioned crystal diffraction lines derived from the sintering aid. It is a high-density aluminum nitride sintered body. The method for manufacturing the hollow body made of the aluminum nitride sintered body is not particularly limited and any method may be used, but the properties and sinterability of the aluminum nitride powder usually depend on the aluminum nitride powder used for sintering. Ru.
Typical aluminum nitride powders that provide the above-mentioned properties and typical methods for producing the same are as follows. First, the aluminum nitride powder has an average particle size of 2 μm or less, and the proportion of particles with a particle size of 3 μm or less is 70% by weight of the total aluminum nitride powder.
The aluminum nitride powder has the above properties, and has an oxygen content of 3.0% by weight or less, preferably 1.5% by weight or less, and an aluminum nitride purity of 95% or more, preferably 97% or more. Such aluminum nitride powder can be obtained, for example, as follows. That is, (1) Fine aluminum particles with an average particle size of 2 μm or less and fine carbon powder with an ash content of 0.2% by weight and an average particle size of 1 μm or less are tightly mixed in a liquid dispersion medium such as water, alcohol, or hydrocarbon. mix,
At that time, the weight ratio of the fine aluminum powder to the fine carbon powder is 1:0.36 to 1:1; (2) The intimate mixture obtained is suitably dried and heated at 1400 to 1700°C under an atmosphere of nitrogen or ammonia. (3) The resulting fine powder is then heated in an oxygen-containing atmosphere at a temperature of 600 to 900°C to remove unreacted carbon so that the aluminum nitride content is at least 95% by weight. and the content of bound oxygen is maximum
3.0% by weight, preferably 1.5% by weight, and the content of metal compounds as impurities is a maximum of 0.3% by weight as metal, and the average particle size is 2 μm or less,
It can be produced by producing aluminum nitride powder in which particles having a particle size of 3 μm or less account for 70% by weight or more. In order to impart transparency to the aluminum nitride powder obtained above, as described for the aluminum nitride sintered body,
The content of cationic impurities is 0.3% by weight or less, preferably 0.1% by weight or less. Particularly, the impurity components used include iron, chromium, nickel, cobalt, copper, zinc, or titanium, whose total metal content is 0.1% by weight or less. It is particularly suitable to do so. It is often preferable to mix the aluminum nitride powder with a sintering aid, a binder, etc., if necessary, and then subject it to shaping and sintering. The method for manufacturing the hollow tube made of the aluminum nitride sintered body is not particularly limited, and any method may be employed. Typical methods for manufacturing hollow tubes that are generally suitably employed include the following methods. That is, a metal core, for example, an iron core, is fixed by surrounding the outside with an elastic material so that a certain gap is left around the periphery. This gap is filled with the aluminum nitride powder, mixed with a sintering aid consisting of a metal compound of group a or group a of the periodic table, if necessary. Thereafter, a pressure of, for example, 300 to 3000 kg/cm ² is applied from the outside to form the material by a so-called rubber press method. By removing the elastic material, i.e., rubber, and the metal core from this molding, the original shape of the hollow tube is obtained. The hollow tube is then sintered in the presence of an inert gas, such as nitrogen gas, at a high temperature, for example, 1,600 to 2,100° C., to obtain a hollow tube with high density, high strength, and high translucency. It was completely unexpected that hollow tubes could be manufactured using pressureless sintering when considering conventional aluminum nitride powder, and it was even more unexpected that transparent hollow tubes could be manufactured from aluminum nitride material. I couldn't even do it. It is considered that these effects are largely due to the characteristics of the aluminum nitride powder. The luminescent tube of the present invention is obtained by housing a light emitting source inside the hollow tube, sealing it, and providing electrode terminals at both ends of the hollow tube. The light emitting source is not particularly limited, and it is preferable to use one that emits light by conducting electricity to an electrode terminal. Further, the method of incorporating the light emitting source into the hollow tube and sealing it is not particularly limited, and may be carried out in the same manner as in the case of a light emitting tube using a hollow tube made of known translucent alumina. Generally, the light emitting source and an inert gas such as neon gas or Canon gas are contained therein, and both ends of the hollow tube have conductive lead parts, and a cap made of aluminum nitride sintered body is sealed with glass. This can be done by doing the following: FIG. 2 of the accompanying drawings is an explanatory view showing an example of use of the arc tube of the present invention in a sodium lamp. Fig. 2 shows that Na-Hg amalgam and Canon gas are put into the interior 2 of a hollow tube 1 made of an aluminum nitride sintered body, and both ends 3 and 3' of the hollow tube are provided with lead portions 5. Caps 4 and 4' made of sintered aluminum are fused with low thermal expansion glass (not shown). A conductive wire from a power source is connected to this lead portion, and electrical conductivity is established between the lead portions at both ends of the hollow tube. This conduction causes sodium to emit light within the hollow tube, creating a sodium lamp. When using the arc tube of the present invention, since the aluminum nitride sintered body has excellent thermal conductivity, it is less affected by temperature differences and will not be crushed by thermal shock. Furthermore, as will be clear from the examples described later, the arc tube exhibits excellent light transmittance and is therefore suitably used as an arc tube. EXAMPLES In order to explain the present invention more specifically, the present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Example 1 The purity is 99.99% (impurity analysis values are shown in Table 1), the average particle diameter is 0.52 μm, and the proportion of particles of 3 μm or less is
100 parts by weight of 95 vol% alumina and 50 parts by weight of carbon black having an ash content of 0.08 wt% and an average particle diameter of 0.45 μm were uniformly mixed in a ball mill using a nylon pot and a nylon-coated ball using ethanol as a dispersion medium. After drying the resulting mixture, it was placed in a flat plate made of high-purity graphite and heated at a temperature of 1600° C. for 6 hours while continuously supplying nitrogen gas at 3/min in an electric furnace. The resulting reaction mixture was heated in air at a temperature of 750° C. for 4 hours to oxidize and remove unreacted carbon. The white powder obtained is
As a result of Xray diffraction analysis, it is single phase AlN, Al ₂ O ₃
There was no diffraction peak. In addition, the average particle diameter of the powder was measured using a particle size distribution analyzer (manufactured by Horiba, Ltd. (APA-
500), it was 1.31μm, and 3μm
m or less accounted for 90% of the capacity. When observed using a scanning electron microscope, this powder was found to be uniform particles with an average size of about 0.7 μm. Also, the measured value of specific surface area is 4.0m ² /
It was hot at g. The analytical values of this powder are shown in Table 2. Table 1 Al ₂ O ₃ powder analysis values Al ₂ O ₃ content 99.99% Element Content (PPM) Mg <5 Cr <10 Si 30 Zn <5 Fe 22 Cu <5 Ca <20 Ni 15 Ti <5 Table 2 AlN Powder analysis value AlN content 97.8% Element Content Mg <5 (PPM) Cr 21 (〃) Si 125 (〃) Zn 9 (〃) Fe 20 (〃) Cu <5 (〃) Mn 5 (〃) Ni 27 (〃) Ti <5 (〃) Co <5 (〃) Al 64.8 (wt%) N 33.4 (〃) O 1.1 (〃) C 0.11 (〃) Calcium nitrate, Ca(NO ₃ ) ₂ ·4H ₂ O was added to give a concentration of 1.0% by weight in terms of CaO, and the mixture was uniformly mixed using ethanol as a dispersion medium. After mixing, the mixture was dried by gradually removing ethanol while stirring. This mixed powder was rubber pressed into a tubular shape at a pressure of 1500 kg/cm ² , processed, and then fired at a temperature of 1900° C. for 4 hours under a nitrogen atmosphere of 1 atm. Obtained density 3.25g/cm ³
The tubular sintered body is polished to have an outer diameter of 10 mm, an inner diameter of 8 mm,
A tube with a length of 100 mm was used. For this tube, 0.55~
The linear transmittance and total transmittance of light at 0.65 μm were determined to be 35% and 84%, respectively. This tube contains Na−
An arc tube was fabricated by sealing an AlN cap filled with Hg amalgam and Canon gas and having electrodes and niobium leads at both ends with low thermal expansion glass. When the electrode tip length was 11 mm, no mechanical damage was observed in repeated light emission tests using a voltage of 100 V, and no decrease in luminous efficiency was observed. Further, an electron micrograph (magnification: 1200 times) of the mechanically fractured surface of the aluminum nitride sintered body is shown in FIG. This photograph shows that the sintered body is composed of uniform polygonal particles with clear outlines. When the size of crystal grains is determined by the average value of the major axis and minor axis, the average particle diameter (D) in the photograph in Figure 1 is 5.0 μm, which is the average particle diameter (D) of particles in the range of 0.3D to 1.8D (1.5μm to 9.0μm). The number ratio is 97%. Example 2 Using the same aluminum nitride powder as in Example 1,
Table 1 shows the results of investigating the influence of the average particle diameter and its distribution on translucency in transparent tubes made by varying the sintering aid and sintering conditions. In Table 1
Nos. 3 and 4 are comparative examples. 【table】

[Brief explanation of drawings]

FIG. 1 is a micrograph showing the grain structure of the mechanically fractured surface of the aluminum nitride sintered body of Example 1, and FIG. 2 is an explanatory diagram of an embodiment of the arc tube of the present invention. In FIG. 2, each numerical value indicates the following content. 1...Hollow tube, 2...Inside of hollow tube, 3, 3'
...End of hollow tube, 4,4'...Cap, 5...
...Lead section.

Claims (1)

[Claims] 1. The mechanical fracture surface is formed by a tightly packed state of fine crystal grains that are distinguished from each other by clear contours, and the fracture surface of the fine crystal grains is The clear outline in is a polygonal shape, and the fine crystals have an average particle diameter at the fracture surface defined by the clear outline, where D (μm) is defined as
A hollow tube made of an aluminum nitride sintered body composed of at least 70% of crystal grains having a particle size in the range of 0.3D to 1.8D, the hollow tube having a hollow portion A luminous tube that is sealed with a built-in luminous source and has electrode terminals at both ends. 2. The arc tube according to claim 1, wherein the aluminum nitride sintered body contains an impurity component of 0.3% by weight or less, preferably 0.1% by weight or less as metal.