JPS59221373A - Sealing composition - Google Patents

Abstract

PURPOSE:The titled composition, containing a specific amount of lanthanum oxide and cerium oxide as main components, and further beryllium oxide, silicon oxide, yttrium oxide, etc., and having improved halogen resistance, heat resistance, melting temperature, airtightness and spalling resistance. CONSTITUTION:A composition containing 30-50wt% lanthanum oxide and cerium oxide as main components and further beryllium oxide and/or silicon oxide and one of scandium oxide, yttrium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide or terbium oxide, etc. and if necessary aluminum oxide. Preferably, the above-mentioned composition contains 3-30wt% respectively beryllium oxide, silicon oxide, yttrium oxide and aluminum oxide added thereto. USE:Suitable for sealing end caps or electrodes, etc. airtight in end parts of polycrystal alumina tubes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement 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.

■ Those whose main components are aluminum oxide (Aj!20s) and alkaline earth metal oxides (eg, calcium oxide) [Japanese Patent 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.

■ Aluminum oxide (A120g) and boron oxide (n
tos) and beryliuno oxide, (Red) and silicon oxide (
SiO2) [Special Publication No. 49-32301],
Alternatively, lanthanum oxide (La20s), boron oxide (Btu3), phosphorus oxide (Ptos), aluminum oxide (A120g), and magnesium oxide (MgO)
[Unexamined Japanese Patent Publication No. 55-37496].

These include halogen-resistant boron oxide (13z
03) was selected.

However, sealing compositions containing boron oxide tend to form bubbles, making it difficult to achieve reliable airtight sealing.

■ Aluminum oxide (A40a) and its thermal expansion-I
Those containing oxides of rare earth metals with a thermal expansion r close to K [U, S, P, 3588573], dysprosium oxide (Dy203) and aluminum oxide (A
z20s) and silicon oxide (Si0,) [Japanese Patent Publication No. 56-44025].

The former has a problem in manufacturing due to its high melting point, while the latter has a problem in that a stable airtight seal cannot be formed because the thermal expansion furnace of the sealing composition is smaller than that of 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, such as polycrystalline alumina that constitutes the arc tube, and materials that have a high thermal expansion resistance, especially lanthanum oxide (Law).
's) or cerium oxide (ceot).

The reason why we chose lanthanum oxide and cerium oxide is that these rare earth oxides have a high melting point (for example, lanthanum oxide has a high melting point of 2300°C), even though their thermal expansion coefficient P is larger than that of polycrystalline alumina. It is necessary to add a melting point depressant because the addition of this agent inevitably lowers the thermal expansion balance.

FIG. 1 shows changes in linear thermal expansion coefficient p with respect to temperature changes of various rare earth oxides 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, aluminum 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. Although silicon oxide does not have a large effect on lowering the melting point, it has the effect of forming a glass phase, contributing to increased airtightness.

Although it is difficult to add both beryllium oxide and silicon oxide, it is possible to add only one of them.

FIGS. 2 and 3 respectively show equilibrium diagrams for the case where 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 is also resistant to corrosion. 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,
For example, scandium oxide (S c!all ), yttrium oxide (Y, Os), praseodymium oxide (P rt
os), neodymium oxide (Nd, 03), samarium oxide (Sm, 03), europium oxide (E 020g
), gadolinium oxide (GdzOs), terbium oxide (TbtOs), dysprosium oxide (DYyOx)
), holmium oxide (Hox Os), erbium oxide (Er, 03), thulium oxide (T mt Os ),
Itteribium oxide (YbzOs) and lutetium oxide (Lutes) are suitable. The effect of yttrium oxide is particularly large. In addition, when iturium oxide is used, in order to quickly react with polycrystalline alumina and shorten the sealing time, aluminum oxide (
It is better to add A120s).

Experiments were conducted by making sealing compositions with various composition ratios.

Table 1 Results: La, C1s...40%, B
e 0---6%, Sin.

...17chi, y, o, ...25%, A
A! , O,...12 sealing composition (A4)
showed the best performance. That is, the sealing composition of the queen composition has a melting point of 1360°C and a coefficient of thermal expansion of 1.2
10 /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, use less beryllium oxide.1. Alternatively, it is possible to use silicon oxide. However, belu oxide I
If the amount of Jum 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, it is difficult to obtain sufficient adhesion between the base alumina and the sealing composition.

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 of each component of the sealing composition and the limits of the composition ratio, and found that the main components, lanthanum oxide and cerium oxide, are particularly effective if the weight is within the range of 30 to 50 cm. It turned out that there was no way to override it. Further, it was confirmed that there is no problem even if beryllium oxide and silicon oxide are varied within a range of 3 to 30%, and rare earth oxides such as yttrium oxide and aluminum oxide are varied within a range of 3 to 3 degrees.

As is clear from the above description, the present invention makes it 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 the drawing]

Figure 1 shows curves showing changes in linear expansion curves with respect to temperature changes for polycrystalline alumina and various rare earth oxides. Figure 2 is an equilibrium state diagram of La, 03-BeO, and Figure 3-.

Claims (1)

[Claims] (1) Contains 30 to 50% by weight of lanthanum oxide or cerium oxide as a main component, and contains both or one of benzium oxide and silicon oxide, as well as scandium oxide, yttrium oxide, praseodymium oxide, neodymium oxide, samarium oxide, and cerium oxide. europium, gadolinium oxide. Terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide. A sealing composition comprising one of ytterbium oxide and lutetium oxide, and optionally aluminum oxide. (The sealing composition according to claim 1, wherein each of beryllium 21 oxide, silicon oxide, yttrium oxide, and aluminum oxide is 3 to 30 inches by weight.