JPH0114183B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in a sealing composition for airtightly sealing end caps, electrodes, etc. to the ends of translucent polycrystalline alumina tubes used as arc tubes of metal halide lamps. The following are commonly known sealing compositions for airtightly sealing end caps, electrodes, etc. to the ends of polycrystalline alumina tubes. The main components are aluminum oxide (Al ₂ O ₃ ) and alkaline earth metal oxides (e.g. calcium oxide) [Special Publication No. 47-49290]. This poses no particular problem when used in the arc tubes of high-pressure sodium lamps, but because of its high chemical reactivity with halogens, it cannot be used at all in the arc tubes of metal halide lamps. Those containing aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), beryllium oxide (BeO) and silicon oxide (SiO ₂ ) [Special Publication No. 32301 of 1972];
Alternatively, lanthanum oxide (La ₂ O ₃ ), boron oxide (B ₂ O ₃ ), phosphorus oxide (P ₂ O ₅ ), aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO)
[Unexamined Japanese Patent Publication No. 55-37496]. In these materials, halogen-resistant boron oxide (B ₂ O ₃ ) is selected as an oxide for lowering the melting point of the sealing composition and vitrifying it. However, sealing compositions containing boron oxide tend to form bubbles, making it difficult to achieve reliable airtight sealing. Aluminum oxide (Al ₂ O ₃ ) and a rare earth metal oxide with a thermal expansion coefficient close to that of aluminum oxide (USP 3588573), or dysprosium oxide (Dy ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ). Contains silicon oxide (SiO ₂ ) [Special Publication No. 56-44025]. The former has a high melting point, which poses a manufacturing problem, and the latter has a problem in that a stable airtight seal cannot be formed because the sealing composition has a smaller coefficient of thermal expansion than polycrystalline alumina. The present invention has been made in view of the above points, and has excellent properties such as halogen resistance, heat resistance, melting temperature, airtightness, and spalling resistance (no generation of bubbles, cracks, etc.). The present invention aims to provide a sealing composition with excellent performance. Hereinafter, the sealing composition according to the present invention will be explained in detail. In the present invention, the main component of the sealing composition is a material that has high halogen resistance and a higher coefficient of thermal expansion than the polycrystalline alumina that constitutes the arc tube, especially lanthanum oxide (La ₂ O ₃ ) or cerium oxide (CeO ₂ ).
Select. The reason why we chose lanthanum oxide and cerium oxide, even though their coefficient of thermal expansion is larger than that of polycrystalline alumina, is that these rare earth oxides have a high melting point (for example, lanthanum oxide has a high melting point of 2300℃), so we ended up using melting point depressants such as beryllium oxide. This is because it is unavoidable that the coefficient of thermal expansion will decrease if this is added. FIG. 1 shows changes in the coefficient of linear thermal expansion of various rare earth oxides with respect to temperature changes, in comparison with that of polycrystalline alumina constituting the arc tube. As the main component, lanthanum oxide is more stable and easier to handle than cerium oxide, but there is not much difference in other respects. Next, in the present invention, beryllium oxide and silicon oxide are selected as melting point depressants to be added to the main component. When beryllium oxide is mixed with lanthanum oxide or cerium oxide, it has a great effect of lowering their melting points. Silicon oxide does not have a great effect on lowering the melting point, but it has the effect of forming a glass phase, contributing to increased airtightness. Although it is desirable to add both beryllium oxide and silicon oxide, it is also possible to add only one of them. FIGS. 2 and 3 respectively show equilibrium diagrams when beryllium oxide is mixed with lanthanum oxide and when silicon oxide is mixed with lanthanum oxide. Furthermore, in the present invention, in order to increase the adhesive strength of the sealing composition to polycrystalline alumina, it is necessary to add a rare earth oxide that is highly reactive with alumina and has halogen resistance. this is,
This is because lanthanum oxide and cerium oxide hardly react with the polycrystalline alumina of the base. Rare earth oxides used for this purpose include many rare earth oxides other than lanthanum oxide and cerium oxide, such as scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), and praseodymium oxide (Pr ₂ O _{3 )} . ), neodymium oxide (Nd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ),
Europium oxide (Eu ₂ O ₃ ), Gadolinium oxide (Gd ₂ O ₃ ), Terbium oxide (Tb ₂ O ₃ ), Dysprosium oxide (Dy ₂ O ₃ ), Holmium oxide (Ho ₂ O ₃ ), Erbium oxide (Er ₂ O ₃ ), thulium oxide (Tm ₂ O ₃ ), iteribium oxide (Yb ₂ O ₃ )
and lutetium oxide (Lu ₂ O ₃ ) are suitable. The effect of yttrium oxide is particularly large. Note that when using yttrium oxide, aluminum oxide (Al ₂ O ₃ ) is added to the sealing composition in order to quickly react with polycrystalline alumina and shorten the sealing time.
It is better to add Based on the above idea, experiments were conducted by making sealing compositions having various composition ratios as shown in Table 1.

【table】

[Table] As a result, La ₂ O ₃ …40%, BeO…6%, SiO ₂ …
The sealing composition (No. 4) containing 17%, _Y2O3 ...25%, _{and Al2O3} ...12% showed the best _results . That is, the sealing composition having the above composition had a melting point of 1360° C., a coefficient of thermal expansion of 1.2×10 ⁻⁵ /deg, good airtightness, and extremely excellent halogen resistance. Even if the composition ratio is not the above, it is possible to obtain a sealing composition with superior properties compared to conventional compositions. For example, it is possible to reduce the amount of beryllium oxide or to not use silicon oxide. However, if the amount of beryllium oxide is reduced beyond a certain value, the melting point of the composition will increase and the sealing workability will deteriorate. Furthermore, if silicon oxide is not used, cracks tend to occur in the sealing portion, making it impossible to obtain a highly reliable seal. Furthermore, without yttrium oxide, sufficient adhesion between the base alumina and the sealing composition cannot be obtained. However, good results can be obtained by replacing this with dysprosium oxide or other rare earth oxides. When reducing the amount of aluminum oxide, it is necessary to increase the sealing time to ensure sufficient diffusion into the base alumina. In this way, we confirmed the effectiveness and limits of the composition ratio of each component of the sealing composition, and found that the main components, lanthanum oxide and cerium oxide, accounted for 30 to 50% by weight.
It has been found that the effect is not particularly impaired within the range of . Furthermore, it was confirmed that there is no particular problem even if the beryllium oxide and silicon oxide are varied within the range of 3 to 30%, and the rare earth oxides such as yttrium oxide and aluminum oxide are varied within the range of 3 to 30%, respectively. As is clear from the above description, according to the present invention, it is possible to obtain a sealing composition that is extremely suitable for sealing translucent polycrystalline alumina used as an arc tube of a metal halide lamp.

[Brief explanation of drawings]

Figure 1 is a curve diagram showing changes in linear expansion coefficient with respect to temperature changes for polycrystalline alumina and various rare earth oxides, Figure 2 is an equilibrium diagram of La ₂ O ₃ -BeO, and Figure 3 is a diagram of La ₂ O ₃ -BeO equilibrium. -Equilibrium phase diagram of SiO ₂ .

Claims (1)

[Claims] 1 Main ingredient: 30 to 50% by weight of lanthanum oxide or cerium oxide, together with beryllium oxide and/or silicon oxide, scandium oxide, yttrium oxide, praseodymium oxide, neodymium oxide, samarium oxide, A sealing composition comprising one of europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, and lutetium oxide, and optionally aluminum oxide. . 2 Beryllium oxide, silicon oxide, yttrium oxide, and aluminum oxide each weigh 3 to 30
% of the sealing composition according to claim 1.