JPS5918537A - Thermions emission material - Google Patents

Abstract

PURPOSE:To form a free Ba in an oxide layer and achieve the high emission performance of an oxide cathode by adding the hexaboride of a specific quantity of rare earth metals to the alkaline rare earth metals containing the Ba. CONSTITUTION:Rare earth hexaborides such as LaB6, CeB6, PrB6, NdB6, YbB6, etc. are added to (B2, Sr, Ca) O, etc. The loadings of these hexaborides should be within the range of 1 to 20mol% since reduction becomes insufficient and the formation of a free Ba is reduced in 1mol% or less loadings and the quantity of the oxide of alkaline rare earth metals is too small and the absolute value of emission current is degraded in 20mol% or more loadings. As a result, the generation source of the free Ba and tervalent metal of the donor center can simply be applied in the oxide layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxide cathode used in TV cathode ray tubes and image pickup tubes, and is intended to improve its emission performance.

Oxide cathodes generally use alkaline earth metal oxides (Ba, Sr, Ca) O'e as electron-emitting substances and are coated on a Ni cathode substrate. In order to enhance electron emission ability and further improve gas poisoning resistance, it is necessary to supply free Ba into the oxide layer.

Conventionally, this problem has been dealt with by a method in which reducing impurities (<sr+Mg+si+ht, etc.) contained in the oxide coating layer '6Nt alloy substrate are reduced during operation. However, this method always has the problems of generating reaction products between the oxide layer and the base metal, causing deterioration in emissions such as peeling of the oxide layer and increased interfacial resistance.

The purpose of the present invention is to form a source of free Ba in an oxide layer, which is completely different from the conventional method that utilizes an interfacial reaction between an oxide coating layer and a Ni alloy substrate. This is because it was established.

The thermionic emission cathode of the present invention is an alkaline earth metal oxide containing at least Ba, such as BaO.

(Ba, Ca)0. (Ba, 5r)o, (Ba+Sr,
Ca) 0, etc., alkaline earth metal hexaboride MeB,
(Here, Me is La, Ce, Pr.

Nd+ Sml (at least one element selected from the group consisting of Eu, Gd, and Yb) is added to the above oxide in an amount of 1
~20 mol% is added to improve electron emission ability.

This operating principle utilizes the strong reducing power of B to O.
The purpose is to provide free Ba and rare earth metals within the oxide layer.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 The magnitude relationship of free Ba generated in the oxide layer can be determined by the amount of Ba evaporated from the oxide layer.

Figure 1 shows 18 moles (B ao, s S ro, 4 Cao
, t) Results of measuring the temperature dependence of Ba and BaO evaporation amounts after applying a mixed powder of CO3 and 1 mol LaB6 layer on an INt plate and completely decomposing the carbonate in a 10-9 TOrr pan vacuum container. shows. The dimensions of the Ni substrate are width 2 rrrm
The length was 20 mm and the thickness was 40 μm, and the above mixed powder was applied to 10 mm in the center. The sample was heated by direct current heating of a Ni short plate, and the amount of evaporation was measured using a normal mass filter. 1 in Figure 1 is 18 (Ba, Sr,
Ca) O+L a Be B from application 1- of mixed powder
a is evaporation, and 2 is BaO evaporation. 3 in the same figure does not contain the La B66 layer used as a comparison sample (
Ba, 8j, Ca) evaporation from the O coating layer. (Ba, Sr, Ca) In the case of a coating layer of 0, the amount of evaporation is BaoQt body, and the activation energy of evaporation is also 3
．． 9eV, PelcoWitch (Ph1l
ips, Res, Repts, 9 (1954
) 42). On the other hand, in the case of an oxide layer containing LaBa, Ba evaporation is 1
~2 orders of magnitude brighter, indicating that a strong chemical reaction occurred between BaO and TJ a B 6.

The following formula can be considered as a chemical reaction.

6BaO+LaB6→3B202↑+6Ba↑+La
(1) Because La has a low vapor pressure, it remains in the intoxicant layer, and because it has a trivalent valence, it acts as a donor center with a shallow donor level.

Example 2 Adding LaB6 to the (Ba, Sr, Ca)O oxide layer by H
The effectiveness of this was confirmed from the standpoint of total thermionic emission characteristics. Figure 2 shows individual (Ba, sr, Ca)0 on the Ni plate.
4 and 18 mol (Ba, Sr,
The effect of 02 partial pressure on the emission deterioration of No. 5 is shown when a mixed powder of Ca) 0 + 1 mol LaBa is spread on a cloth.

It can be seen that the oxide layer mixed with LaBa has no emission deterioration power even under a high 02 partial pressure, compared to the oxide layer without LaBa mixed therein. This is considered to be based on the generation of a high Ba concentration within the oxide layer and the generation of donor-centered TJ a.

Example 3 For (13a, S r, Ca )O, LaBa
Measurement of Ba evaporation amount described in Rare Earth Example 2 and Example 3
We measured the emission deterioration due to the introduction of the 02 gas described in . As a result, almost the same results as in the case of LaB5 were obtained. This is thought to be because the reaction between the oxide and the wood trellis occurs based on equation (1).

From the above results, the effect of adding rare earth metal trellis to alkaline earth metal oxide is clear. The optimum amount of wood trellis added was 1 mol to 20 mol%. If the amount added is less than 1 mol%, the reducing effect is insufficient, so free B
This is because the amount of alkaline earth metal oxide produced is small, and if it is 20 mol % or more, the amount of alkaline earth metal oxide is too small, resulting in a drawback that the absolute value of the emission current decreases.

As explained above, the electron emitting materials of the present invention (Ba, S
The method of mixing MeB into r, Ca)O is completely different from the conventional method of utilizing the interfacial reaction between the oxide coating layer and the Ni alloy substrate9. of trivalent metals, and is of high industrial value.

[Brief explanation of drawings]

FIG. 1 shows 18 (B
Graph showing the temperature dependence of Ba and BaO evaporation when applying a mixed powder of a+ Sr, Ca) O+ L a Ba and conductive powder of (Ba, Sr, Ca)0, 2nd
The figure shows 18 (Ba, Sr,
Mixed powder of Ca)0 and LaB5 and (Ba, Sr, C
a) It is a diagram showing the resistance to 02 gas poisoning when a single 0 powder is applied. 1, 2-48 (Ba, Sr, Ca)0+La
Ba and BaO evaporation amount from B6, 3...(Ba, Sr
, Ca) evaporation amount of BaO from 0, 4・” (Ba, S
r, 02 gas poisoning resistance of Ca)O, 5...18
(Ba, Sr, Ca)0+LaBa 02 gas poisoning resistance. Agent Patent Attorney Toshiyuki Usuda No. 1 Figure 9 Shoumu (707th) Certain 2 Figure Introduction 02 Pressure

Claims (1)

[Claims] 1. An alkaline earth metal oxide containing at least Bat, and 1 to 20 mol% based on the alkaline earth metal oxide
and a hexaboride of a rare earth metal in an amount in the range of .