JP2014210686A - Manufacturing method of translucent ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of new translucent ceramic having high permeability and low scattering.SOLUTION: In a manufacturing method of translucent ceramic, a temporarily baked body of a compact produced from alumina (AlO) as a main raw material is put in a nearly sealed vessel at least partly made of an oxide and baked in a vacuum atmosphere. The vessel is made of, for example, alumina or porous alumina.

Description

  The present invention relates to a method for producing a translucent ceramic. More specifically, for example, the present invention relates to a method of manufacturing a translucent ceramic discharge vessel used for a ceramic metal halide lamp.

  In ceramic metal halide lamps, a ceramic discharge vessel is used. In manufacturing ceramic discharge vessels, a manufacturing method called a mud casting method (a mud casting method) is generally employed. In the sludge casting method, a gypsum mold is filled with a slurry containing alumina and held for a predetermined time. The water content of the slurry is absorbed by the gypsum, and the solid content of the slurry deposits on the inner surface of the mold. Next, when waste mud (removal of slurry) is performed, the alumina that has been deposited on the inner surface of the mold remains. This is dried, released, and the obtained molded body is temporarily fired. A ceramic discharge vessel is obtained by subjecting this formed body to main firing.

  In order to efficiently radiate light emitted from the discharge vessel to the outside of the lamp, the ceramic discharge vessel is required to have good translucency and transparency. The translucency is mainly affected by the presence or absence of blackening of the ceramic. The translucency is quantified as “transmittance”, and the higher the value, the better. Transparency is mainly influenced by the presence of pores inside the ceramic. Transparency is quantified as “scattering rate”, with lower numbers being better.

  Regarding the method for manufacturing such a ceramic discharge vessel, there are the following prior art documents.

JP 2004-315313 “Alumina arc tube manufacturing method and alumina arc tube manufactured by the manufacturing method” (publication date: 11/11/2004) JP-A 63-242964 “Alumina Ceramics and Manufacturing Method Thereof” (Release Date: 10/07/1988) Japanese Patent Laid-Open No. 7-237983 “Translucent Ceramics” (Publication Date: 9/12/1995), Patent No. 3407284

In order to realize the high transmittance and low scattering rate of the translucent ceramic, various firing methods have been proposed.
For example, Patent Document 1 describes that a molded body is sintered in a hydrogen atmosphere or a vacuum atmosphere (summary).

  Patent Document 2 discloses a method for producing alumina ceramics suitable as an ultraviolet transmitting material such as an EPROM package. Unlike the arc tube of a high-pressure metal discharge lamp, this translucent alumina ceramic has enhanced mechanical strength, particularly bending strength. Therefore, the purity and crystal grain size of alumina ceramics are specified. Furthermore, a method for producing alumina ceramics is disclosed in which a predetermined sintering aid and a molding aid are added to a predetermined aluminum oxide powder obtained by pyrolyzing aluminum ammonium sulfate, and firing is performed in a non-oxidizing atmosphere. Yes.

Document 3 discloses an invention that provides translucent ceramics having excellent corrosion resistance. After the molded body on which the slurry film is formed is temporarily fired, a hot isostatic pressing process (HIP process) is performed under predetermined conditions to obtain an arc tube. Thus, it is disclosed that translucent ceramics having corrosion resistance such as Sc ₂ O _{3 which} does not contain bubbles at all and hardly decreases in linear transmittance is formed.

  An object of this invention is to provide the manufacturing method of the novel translucent ceramics which has a high transmittance | permeability and a low scattering rate.

The method for producing a translucent ceramic according to the present invention includes forming a molded body mainly made of alumina (Al ₂ O ₃ ), calcining the molded body to obtain a calcined body, and then calcining the calcined body. Is stored in a substantially sealed state in a storage container containing an oxide at least partially, and is heated and fired in a vacuum atmosphere.

Furthermore, in the manufacturing method of the said translucent ceramics, the said storage container may consist of alumina.
Furthermore, in the above method for producing a translucent ceramic, the storage container may be porous alumina.
Furthermore, in the above method for producing a translucent ceramic, the storage container may be configured by combining a plurality of alumina plate-like bodies.
Furthermore, in the above method for producing a translucent ceramic, the storage container may be configured as a rectangular container by fixing a plurality of alumina plate-like bodies with metal wires.
Furthermore, in the above method for producing a translucent ceramic, the storage container may be maintained in a substantially sealed state by covering with a lid on which a plurality of slits are formed.

  Furthermore, a discharge vessel for a discharge lamp according to the present invention is a vessel manufactured according to the above-described method for manufacturing a translucent ceramic.

  Furthermore, the high-pressure discharge lamp according to the present invention is a high-pressure discharge lamp using the discharge vessel.

  ADVANTAGE OF THE INVENTION According to this invention, the novel manufacturing method of translucent ceramics which has a high transmittance | permeability and a low scattering rate can be provided.

FIG. 1A is a diagram illustrating an example of a ceramic metal halide lamp. FIG. 1B is a diagram illustrating an arc tube of a ceramic metal halide lamp. FIG. 2 is a diagram for explaining a process of a method for manufacturing a discharge vessel for an arc tube. FIG. 3 is a graph showing the transmittance and scattering rate corresponding to the type of storage container that stores the sample during the main firing. FIG. 4 is a diagram illustrating the shape, material, durability, and production efficiency of a storage container that stores a sample during main firing. FIG. 5 is a diagram illustrating the shape of a lid used for the storage container.

Hereinafter, embodiments of a method for producing a translucent ceramic according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[Ceramic metal halide lamp and its discharge vessel]
FIG. 1A is a diagram illustrating an example of a ceramic metal halide lamp. The ceramic metal halide lamp 100 has a hermetically sealed bulb-shaped translucent outer tube 111, and the inside of the translucent outer tube 111 is maintained at a high vacuum of 10 Pa or less, and has a base 12 at the end. Is provided.

  A light emitting tube 130 is sealed at substantially the center inside the translucent outer tube 111. A translucent sleeve 108 is provided around the arc tube 130. The arc tube 130 and the translucent sleeve 108 are arranged at predetermined positions by an outer metal frame 109. A starter 110 is provided above the arc tube 130. A getter 113 is attached to the upper end of the frame 109.

  The frame 109 is positioned by connecting the lower end to the mount support plate 114 and connecting the upper end to an introduction line (not shown) of the stem 115. The frame 109 is an electrical connection member as well as a position fixing member, and supplies power from the base 112 to the arc tube 130 through an introduction line of the stem 115.

The structure of the arc tube 130 will be described with reference to FIG. 1B. The discharge vessel 135 forming the arc tube 130 is made of high-purity alumina (Al ₂ O ₃ ) as a raw material, and a central light-emitting portion 135C and narrow tube portions 135A and 135B at both ends thereof are integrally molded. Current introducing bodies 120a and 120b are mounted on the thin tube portions 135A and 135B, respectively. Each of the current introduction bodies 120a and 120b includes a tungsten electrode 123, a current supply body 122, and a lead wire 121. The tungsten electrode 123 is disposed in the light emitting unit 135C. Each of the current supply bodies 122 includes a halogen-resistant intermediate material 122a and a conductive cermet rod 122b.

  The lead wire 121 is connected to the tip of the conductive cermet rod 122b. The connecting portion between the lead wire 121 and the conductive cermet rod 122b is surrounded by the reinforcing material 131. The lead wire 121 extends from the ends of the narrow tube portions 135A and 135B.

  Inside the discharge vessel 135, a luminescent material, mercury, and an inert gas are sealed. The inert gas is, for example, a rare gas. In this embodiment, argon is used. When the ceramic metal halide lamp is energized, the luminescent material is heated by the discharge generated in the discharge vessel 135, and a part thereof is evaporated and excited by the discharge to emit light. The remaining part of the luminescent material is pooled in the liquid phase in the coldest part at the bottom of the discharge vessel 135. A part of the liquid phase luminescent material evaporates, circulates inside the discharge vessel 135 by convection, and returns to the coldest part at the bottom. Such a cycle is repeated while the lamp is on.

[Method of manufacturing discharge vessel]
(Drainage casting method)
FIG. 2 is a diagram for explaining the steps of the method for manufacturing the discharge vessel 135 that forms the arc tube 130. The manufacturing method of the discharge vessel 135 can be roughly divided to generate slurry (step S10), waste mud casting (step S20), pre-firing and surface treatment (step S30), and main firing (step S40). To finish.

Each step will be briefly described.
In the slurry generation step of step S10, the raw materials are weighed. As raw materials, high-purity alumina powder (particle diameter 0.1 to 2.0 μm) and auxiliary agents (magnesium oxide and the like) are used. These auxiliaries, particularly magnesium oxide, have a function of suppressing crystal grain coarsening in the ceramic. A raw material in which alumina powder, auxiliary agent and water are mixed is put in a container and mixed for 10 hours in a ball mill to produce a slurry. To this, a binder is added and further mixed. Thereafter, the slurry is passed through a nylon sieve (screen) to remove alumina having a particle size of a certain size or more. For example, a sieve having an opening of 32 μm is used. Finally, bubbles in the slurry are removed by a defoaming device.

  In the waste mud casting molding step S20, for example, the slurry is supplied to a gypsum mold and the gypsum mold molding chamber is filled with the slurry. In this state, hold for a predetermined time. The water content of the slurry is absorbed by the gypsum, and the solid content of the slurry deposits on the inner surface of the gypsum mold. Casting may be performed under atmospheric pressure, but may be performed in a vacuum atmosphere or a pressurized atmosphere. Next, drain mud. A compact is formed by the solid content of the slurry that has been applied to the inner surface of the gypsum mold. The molded body formed in this gypsum mold is dried as it is. After drying, the molded body is removed from the mold release, that is, the gypsum mold.

  In the preliminary firing and surface treatment step of step S30, the molded body is temporarily fired. For example, the temperature is raised to 950 ° C. over 10 hours and held at that temperature for 30 minutes. Thereafter, a small projecting parting line is formed on the surface of the molded body along the gypsum-type joint, and is polished and removed using water-resistant abrasive paper. Next, acid treatment is performed. Undesirable components such as calcium resulting from gypsum remain in the molded body. If these components remain, they become cloudy after the main firing and the transmittance decreases. Therefore, unnecessary components such as calcium are removed by acid treatment. Acid treatment also reduces magnesium oxide added as an aid. Therefore, the calcined body is immersed in a magnesium nitrate aqueous solution. Next, magnesium hydroxide is fixed by immersing the calcined body in aqueous ammonia. Then, in order to make magnesium hydroxide magnesia, the calcined body is secondarily calcined at 500 ° C.

(Main firing process)
The main baking process in step S40 will be described in detail.
The present inventors made a plurality of samples with different conditions when the alumina molded body was subjected to main firing, and measured transmittance and scattering rate. The sample is the discharge vessel 135 described in connection with FIG. 1B. FIG. 3 is a diagram showing the results. On the horizontal axis, sample types (a), (b),..., (E) are shown. Directly below the type of sample, the material of the container of the sample, the state of the container during the main firing, the sintering conditions, the measurement results of the transmittance and the scattering rate, and the appearance are shown. The measurement results of the transmittance (◯) and the scattering rate (*) of the sample are shown directly above the sample type. It should be noted that the transmittance (ie, translucency) is better when the numerical value is higher, and the transparency (ie, opacity) is better when the numerical value is lower.

  A brief description of each sample type will be given. In samples (a) to (d), the material of the container for storing the sample during the main firing is a molybdenum container, and the container is in an open state. In the sample (e), the material of the storage container is an alumina container, and the container is in a substantially sealed state. Regarding the sintering conditions, sample (a) is a hydrogen atmosphere and sample (c) is a vacuum atmosphere. The sample (b) is reheated in an air atmosphere after the hydrogen atmosphere baking treatment of the sample (a). The sample (d) is further reheated in an air atmosphere after the vacuum atmosphere baking treatment of the sample (c).

Hereinafter, it demonstrates in detail for every sample.
Regarding sample (a), the container for storing the pre-fired alumina molded body was a molybdenum container, and during the main firing, the storage container was in an open state without a lid, and the sintering conditions were performed in a hydrogen atmosphere. As a result, the appearance of the sample was changed to black (blackened). The sample has a relatively low transmittance of 75% and a scattering rate of 20%. Since the reduction action of hydrogen is strong and the storage container is in an open state, the sample seems to have been strongly reduced.

  The sample (b) is a sample that is further subjected to reheating treatment in the air after the “hydrogen atmosphere” that is the sintering condition of the sample (a). As a result, the blackening of the appearance of the sample was removed. The transmittance of the sample was a very high value of 99%. It seems that the oxidation action worked by reheating in the atmosphere. Note that the scattering rate has deteriorated from 20% to 25%.

  The sample (c) is a sample in which the “hydrogen atmosphere” that is the sintering condition of the sample (a) is changed to a vacuum atmosphere. The scattering rate of the sample decreased to 8%. When fired in a vacuum atmosphere, pores in the sample are removed, and the scattering rate seems to decrease. However, the appearance of the sample turned black (blackened), and the transmittance decreased to 76%. It seems that a strong reducing action was applied to the sample in the firing in the vacuum atmosphere.

  The sample (d) is a sample that has been further reheated in the atmosphere after the “vacuum atmosphere” that is the sintering condition of the sample (c). In sample (b), the transmittance changed to a very high numerical value by “hydrogen atmosphere → reheating treatment in air”. Although the same change was expected, the transmittance did not change in the “vacuum atmosphere → reheating treatment in air” of the sample (d). Due to the strong reducing action in the firing in a vacuum atmosphere, the inside of the sample was blackened, and it seems that blackening could not be removed even by reheating treatment in the atmosphere.

From the evaluation results of these samples (a) to (d), the following was found.
(1) From the results of samples (a) and (c), the vacuum atmosphere has stronger pore removing power and the scattering rate is lower than that in the hydrogen atmosphere. Originally, the calcined body (the calcined molded body) has pores throughout. Before the pores are removed, if the alumina crystals stick together, they become closed pores and turn white. In order to increase the transparency (that is, to decrease the scattering rate), it is necessary to adhere alumina crystal grains while removing pores during the main firing step. It is considered that this pore removing power is stronger in the vacuum atmosphere than in the hydrogen atmosphere.
(2) The blackening of the sample in a hydrogen atmosphere could be removed by subsequent reheating in the atmosphere, and the transmittance could be increased. However, the blackening of the sample in a vacuum atmosphere could not be removed even after the subsequent reheating in the atmosphere, and the transmittance could not be increased.

  Based on these findings, the present inventors first studied a method of adopting a vacuum atmosphere in which a low scattering rate can be expected and further suppressing a decrease in transmittance. That is, a method for reducing the blackening of the sample by suppressing the reducing action during firing in a vacuum atmosphere and maintaining a high transmittance was examined.

  As a result of the study, an alumina storage container was adopted as the storage container at the time of sample baking, and the container storing the sample was made to be in a substantially sealed state. The intent was that oxygen was supplied from the storage container during firing, the oxygen partial pressure in the storage container was increased, and the reduction effect was expected to be reduced by the vacuum atmosphere surrounding the sample. This aimed to reduce the blackening of the sample.

  Therefore, for the sample (e), first, the sintering was performed under a vacuum atmosphere, and further, an alumina storage container was employed, and the container was substantially sealed during firing. This “substantially sealed state” means a state in which the opening of a box as a storage container is covered with a lid, and is not in a state like an airtight seal.

As a result, the appearance of the sample was kept black without being blackened. The sample had a very high transmittance of 99% and a scattering rate of 7%, which was very low.
At the present time, the inventors believe that oxygen is supplied from an alumina storage container during firing, and the periphery of the sample is maintained in an oxygen atmosphere by making the storage container substantially sealed.

  In addition, it confirmed also by experiment, when the container made from an alumina was made into the open state which opened the lid | cover, without making a substantially sealed state. The sample was blackened and the transmittance was about 75 to 76%. Therefore, in order to reduce the reducing action on the sample, it is important to make the storage container substantially sealed and to have a sufficient oxygen atmosphere around the sample.

  Regarding the use of alumina storage containers, the following has been confirmed. Since the supply of oxygen from alumina was expected, there was a concern that there might be a limit in the number of uses (lifetime). However, at present, it has been confirmed that the effect does not change even when the number of times of use (the number of times of main firing) is 20 times or more. That is, there is no change in the transmittance and the scattering rate obtained by measuring the sample.

  In addition, at the start of use of the alumina container, it is confirmed that a stable result can be obtained thereafter by performing an empty baking process (processing at the same temperature and time as the main baking) for the first time.

  Compared to hydrogen treatment and HIP treatment, firing in a vacuum atmosphere is easy to process because there is no need for gas supply or pressurization, and it is possible to safely perform firing with inexpensive equipment. have.

[Consideration of container]
Next, the present inventors performed a detailed examination of an alumina container. In the production of ordinary ceramics, the temperature is raised relatively slowly, and when firing is completed, the temperature is lowered relatively slowly. With such a temperature change, the container is not damaged.

  However, due to demands for improving production efficiency in factories, rapid temperature rise and rapid temperature drop after firing are required in the manufacture of discharge vessels. For example, when the temperature was increased from room temperature to 1,750 ° C. in 2 hours and then decreased from 1,750 ° C. to room temperature in 2 hours, many alumina storage containers were damaged.

  Therefore, an alumina storage container that can withstand such rapid temperature increase / decrease was investigated. This will be described with reference to FIG.

  No. It has been found that the integral rectangular container made of dense alumina No. 1 tends to cause deformation and breakage because the stress concentrates on the corners and the strain exceeds the mechanical strength of the container. Therefore, durability is inferior. However, since a relatively large number of discharge containers (samples) can be stored, the production efficiency is high.

  Therefore, no. The cylindrical container of No. 2 was used, the side surface was cylindrical, and the bottom portion was eliminated, thereby distributing stress. Furthermore, by using porous alumina instead of dense alumina, deformation was reduced and thermal shock resistance was improved. That is, durability was improved. However, in this shape of the storage container, the number of discharge containers stored decreases, so that the production efficiency is slightly inferior.

  No. 1 to avoid the stress concentration of the one-piece square container. The study for avoiding the decrease in production efficiency of No. 2 was conducted. As a result, no. In the plate combination type rectangular container shown in Fig. 3, stress concentration is avoided by stopping the large-sized integral container and combining a plurality of small-sized porous alumina plate-shaped bodies to constitute the storage container. ing. Furthermore, the production efficiency is increased by using a rectangular container.

  This plate-combined rectangular container is composed of a plurality of porous alumina plate-like bodies combined with a molybdenum band (for example, φ0.5 mm) with a thermal expansion coefficient close to the periphery. It is fixed to do. This plate combination type rectangular container provides high durability and high production efficiency.

  It has been found that the molybdenum band is in a shabby state when used in multiple firing steps. It seems to be an oxidation effect by oxygen supplied from the alumina container. This phenomenon is one of the grounds for the assumption that oxygen is supplied from the alumina container during firing.

  Furthermore, a lid that makes the storage container substantially sealed will be described. No. 4 in FIG. The lid used for the No. 3 plate combination type rectangular container was originally a single plate of size 12 cm × 12 cm. As shown to Fig.5 (a), when it was set as the cover 200 of 1 sheet, it turned out that it is easy to crack at the time of this baking. Therefore, the durability is slightly inferior. As shown in FIG. 5 (b), it was found that when this was divided into four to form a divided lid 201 of size 6 cm × 6 cm, it was difficult to break. However, it is not easy to handle four divided lids for one lid at all times. Therefore, as shown in FIG. 5C, an appropriate groove (slit) 202a was formed on the lid 202 of a single plate. This also proved difficult to crack in the firing process.

[Alternative examples and others]
As mentioned above, although demonstrated centering on the manufacturing method of the discharge vessel made from ceramics, these are illustrations and do not restrict | limit the scope of the present invention.

First, the subject of the present invention is not limited to a ceramic discharge vessel. The present invention can be applied to a method for producing a translucent ceramic material that uses alumina (Al ₂ O ₃ ) as a main raw material and realizes good translucency and transparency.

  The container for storing the sample (translucent ceramic material) at the time of firing is not limited to an alumina storage container. The storage container only needs to include at least part of a member (that is, an oxide) having an ability to supply oxygen during firing.

  Other additions, deletions, changes, improvements, and the like that can be easily made by those skilled in the art with respect to the present embodiment are within the scope of the present invention. The technical scope of the present invention is defined by the appended claims.

  100: Ceramic metal halide lamp, 108: Translucent sleeve, 109: Frame, 110: Starter, 111: Translucent outer tube, 112: Base, 113: Getter, 114: Mount support plate, 115: Stem, 120a, 120b: current introduction body, 121: lead wire, 122: current supply body, 122a: halogen-resistant intermediate material, 122b: conductive cermet rod, 123: tungsten electrode, 130: arc tube, 131: reinforcing material, 135: discharge Container, 135A, 135B: Narrow tube part, 135C: Light emitting part, 200, 202: 1 Lid lid, 201: Divided lid, 202a: Groove,

Claims (8)

Forming a molded body mainly made of alumina (Al ₂ O ₃ ),
After calcining the molded body to obtain a calcined body, the calcined body is stored in a substantially sealed state in a storage container containing at least a portion of the oxide, and is heated and fired in a vacuum atmosphere. The manufacturing method of translucent ceramics. In the manufacturing method of the translucent ceramics of Claim 1,
The manufacturing method, wherein the storage container is made of alumina. In the manufacturing method of the translucent ceramics of Claim 1 or 2,
The manufacturing method, wherein the storage container is porous alumina. In the manufacturing method of the translucent ceramics as described in any one of Claims 1-3,
The said storage container is a manufacturing method comprised by combining the several plate-like body made from an alumina. In the manufacturing method of the translucent ceramics of Claim 4,
The said storage container is a manufacturing method comprised by fixing the several alumina plate-shaped object with the metal wire to the square container. In the manufacturing method of the translucent ceramics as described in any one of Claims 1-5,
The said storage container is the manufacturing method which is maintaining the substantially sealed state by covering with the cover in which the several slit is formed.   The discharge vessel for discharge lamps manufactured according to the manufacturing method of the translucent ceramics as described in any one of Claims 1-6.   A high-pressure discharge lamp using the discharge vessel according to claim 7.