Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-01-26
2003-01-14
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S450000, C156S089120, C156S089140, C156S089190, C156S089210
Reexamination Certificate
active
06506481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to members required to have bonding strength, airtightness, and other properties as in the case of bonding a metal to a ceramic. More particularly, the invention relates to a process for producing a ceramic member for bonding and to a ceramic member for bonding, bonded objects, a vacuum switch, and a vacuum vessel.
2. Background Art
The molybdenum-manganese method (Mo—Mn method; Telefunken method) has conventionally been known as a method for metallizing a surface of a ceramic base.
In this Mo—Mn method, a metallizing ink prepared by adding bonding aids, which help bonding with ceramics, such as a manganese powder, titanium powder, and glass ingredient (SiO
2
) to a powder of high-melting metals such as tungsten and molybdenum and mixing the powder mixture with an organic binder to make the mixture paste (hereinafter sometimes referred to as “metallizing ink”) is applied to a ceramic base and the ink layer is baked (baking method).
The technique of the related art described above necessitates a baking temperature as high as from 1,300 to 1,500° C. for metallization and, hence, has had a problem that the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. is high.
Another problem is that the ceramic itself deforms in the high-temperature baking, resulting in a product which does not satisfy dimensional accuracy.
Although a measure in overcoming the problem described above may be to bake a metallizing ink having a conventional composition at a temperature lower than 1,300° C., this low-temperature baking poses a problem that a sufficient bonding strength cannot be obtained. An improvement in this respect has been desired.
Furthermore, in the case where the metallic layer formed by metallization by the Mo—Mn method is to be bonded to another metallic member or the like by brazing, it is necessary to improve the wettability thereof by a brazing material so as to obtain satisfactory bonding. Although it is hence inevitable to conductor post-treatments such as nickel plating and subsequent sintering, there has been a problem that these post-treatments make the protection process complicated.
SUMMARY OF THE INVENTION
The invention has been achieved in order to eliminate the problems described above.
an object of the invention is to provide a process by which a ceramic member for bonding having a metallization-deposited metallic film with sufficient bonding strength can be obtained even through low-temperature sintering.
Another object of the invention is to provide a ceramic member for bonding, bonded objects, a vacuum switch, and a vacuum vessel.
In the method of the related art of metallization, metals are bonded to a ceramic mainly by two actions, i.e., the sintering of high-melting metal particles and the diffusion and infiltration of a glass ingredient into spaces among the particles.
When this method of the related art of metallization is conducted at a sufficiently high sintering temperature, not only the sintering of the high-melting metals proceeds to give a metallic layer having improved strength, but also a vitreous ingredient (e.g., SiO
2
) contained in the ceramic or ink infiltrates into spaces among the high-melting metal particles to mechanically improve the bonding strength based on an anchoring effect. However, in order for the reactions which bring about these effects to proceed sufficiently, a temperature of 1,300° C. or higher has been necessary.
In contrast, sintering in the invention can be conducted at a lower temperature because nickel reacts with high-melting metals to accelerate the sintering. In the case where the ink contains SiO
2
, the metallic layer which is being formed by metallization is sufficiently filled with a vitreous ingredient due to the SiO
2
, so that baking can be conducted at a temperature as low as, e.g., from 1,080 to 1,250° C. (preferably from 1,100 to 1,250° C., more preferably from 1,100 to 1,200° C.).
The invention has been completed based on that finding. The invention will be explained below.
(1) Those objects are accomplished with the invention of item 1, which is
a process for producing a ceramic member for bonding which comprises mixing a mixture comprising high-melting metal particles of tungsten and/or molybdenum and particles of nickel with an organic binder to produce a paste metallizing ink, applying the metallizing ink to a ceramic base which is a sintered ceramic, and baking the resultant ink layer to form a metallic layer.
In this invention, since the metallizing ink contains nickel, the nickel reacts with high-melting metals to accelerate sintering in the layer which is being formed by metallization, as stated above. Because of this, the metal particles can be sufficiently sintered even at a temperature as low as, e.g., from 1,080 to 1,250° C.
As a result, the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. can be reduced as compared with conventional ones. Moreover, the baking conducted at a low temperature produces a marked effect that the ceramic itself is less apt to deform and high dimensional accuracy is obtained. A further advantage is that since the metal particles can be sufficiently sintered even at such a low temperature, high bonding strength can be secured.
While the organic binder for use in the present invention is not limiting, an organic binder where solid binder (e.g., ethyl cellulose) is dissolved in a solvent (e.g., turpentine oil, butyl glycol) may be used. The organic binder may be used in an amount of about 10 to 35% by weight based on 100% by weight of the total amount of the organic binder and the particle mixture. The solid binder may be used in an amount of about 2 to 4.5% by weight based on 100% by weight of the total amount of the solid binder and the particle mixture.
(2) The invention of item 2 is
the process for producing a ceramic member for bonding, wherein the mixture comprises from 70 to 97% by weight the high-melting metal particles of tungsten and/or molybdenum and from 1 to 10% by weight the particles of nickel.
Since the metallizing ink for use in this invention contains nickel in an amount of from 1 to 10% by weight, the nickel reacts with high-melting metals to accelerate sintering in the layer which is being formed by metallization, as stated above. Because of this, the metal particles can be sufficiently sintered even at a temperature as low as, e.g., from 1,080 to 1,250° C. As a result, the same effects as of item 1 are produced.
(3) The invention of item 3 is
the processing for producing a ceramic member for bonding of item 1 or 2, wherein the metallizing ink further contains at least one member selected from the group consisting of from 5 to 10% by weight particles of manganese, from 0.5 to 2% by weight particles of titanium and/or TiH
2
, and from 2 to 15% by weight particles of SiO
2
.
In this metallizing ink, the manganese ingredient, serving as a bonding aid, is oxidized by the moisture contained in the sintering atmosphere to thereby improve the wetting ability and flowability of a glass ingredient.
The titanium ingredient, which also serves as a bonding aid, is exceedingly active and hence contributes to chemical bonding to the ceramic base.
Furthermore, SiO
2
, which is vitreous, infiltrates into spaces among high-melting metal particles to thereby mechanically improve bonding strength based on an anchoring effect. In particular, when sintering is conducted at a low temperature, SiO
2
is less apt to be fed from the ceramic member for bonding. Even through such low-temperatures sintering, however, high bonding strength can be obtained by using a metallizing ink to which SiO
2
has been added.
(4) The invention of item 4 is
a ceramic member for bonding which comprises a ceramic base which is a sintered ceramic and a metallic layer formed on the ceramic base by metallization, the metallic layer comprising tungsten and/or molybdenum as high-melting metal(s) and particles of nickel.
As explained
Makino Yusuke
Takashima Tsuneaki
Lam Cathy
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
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