JPS5837944B2 - Electrode materials for discharge lamps - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode material for a discharge lamp such as a xenon short arc lamp. A tungsten material is used.

Conventionally, a drawback of xenon short arc lamps has been that as the lighting time elapses, arc fluctuations increase, making them inconvenient as precision point light sources.

This phenomenon is commonly called arc instability.

This is thought to be caused by the coarsening of the tungsten crystal at the cathode tip, resulting in insufficient thorium supply and instability.

In order to prevent this arc instability, it is considered important to prevent the minute tungsten crystal structure from recrystallizing at high temperatures.

Based on this idea, we investigated tungsten powder, its processing conditions, forging conditions, and thorium oxide content, and found that when high-purity tungsten powder is made into a triated tungsten rod using the normal method, the thorium oxide content and after forging It was found that the crystal structure of the tungsten rod is strongly related to the arc instability phenomenon.

From this, the relationship between the thorium oxide content, crystal structure, and arc stability was determined as follows.

The thorium oxide content is expressed in terms of weight, and the crystal structure is expressed as the ratio L/W of the average particle diameter L in the axial direction of the tungsten rod and the average particle diameter W perpendicular thereto, measured from a crystal structure photograph.

As examples of these, Table 1 shows the relationship between time and arc stability of xenon short arc lamps using triated tungsten materials containing 2 weight thorium oxide and 4 weight thorium oxide.

Table 2 also shows the L/W of triated tungsten materials.
The relationship between the arc stability and the arc stability of a xenon short arc lamp after 700 hours of operation is shown.

Arc stability S is calculated by projecting an arc and placing a thin slit in the center of the arc projection image, and calculating the fluctuation of the light intensity passing through the slit as S (%) = [ (Imax - Imm) / Ima
x ]X 100 (%).

Here, Imax is the maximum light intensity, and the space between ■ is the minimum light intensity.

The arc stability standard is 7 or less after 700 hours of lighting.Thorium oxide content is 2 weight φ and triated tungsten material with L/W of 5 or more is the conventional product, and thorium oxide content is 3 to 5 weight φ. The triated tungsten material according to the present invention has an L/W of 3 or less, and if the thorium oxide content is 3 weight φ or less, the arc stability will not be sufficient, and if it exceeds 5 weight As shown, the inner surface of the discharge lamp bulb becomes black due to sputtering of the electrode material.

There are eight levels of blackness from 0 to 7, with 0 being transparent and 7 being black.

The standard is that the degree of blackening in 1000 hours is 4.0 or less.

That is, a thoriated tungsten material with a thorium oxide content of 3 to 5% by weight and a crystal structure of L/W≦3 is used for the electrodes of discharge lamps such as xenon short arc lamps to improve arc stability. It is.

Claims (1)

[Claims] 1. Triatec for a discharge lamp, characterized in that the ratio of the average particle diameter in the axial direction of the crystal structure to the average particle diameter in the direction perpendicular to this is 3 or less, and the thorium oxide content is 3 to 5 by weight. Dotungsten electrode material.