Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2002-10-07
2004-05-11
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S209000, C428S469000, C428S701000, C428S702000, C428S698000, C428S432000, C428S621000, C428S655000, C156S089110, C156S089120, C156S089140, C156S089190, C156S089210
Reexamination Certificate
active
06733871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a member 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, a ceramic member for bonding, a bonded object, a vacuum switch, and a vacuum vessel.
BACKGROUND OF THE INVENTION
The molybdenum-manganese method (Mo—Mn method; Telefunken method) has conventionally been known as a method for metallizing a surface of a ceramic base.
This Mo—Mn method comprises applying a metallizing ink prepared by adding a bonding aid such as Mn powder, Ti powder and glass ingredient (SiO
2
) to a powder of high-melting metal such as tungsten and molybdenum and mixing the powder mixture with an organic binder to make a paste to a ceramic base, and then baking the ink layer (baking method).
SUMMARY OF THE INVENTION
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.
Furthermore, in the case where a 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 conduct post-treatments such as nickel plating and subsequent sintering, there has been a problem that these post-treatments make the production process complicated.
Further, in recent years, a technique has been proposed which comprises applying a tungsten paste to a ceramic base to form a lower layer (sublayer), applying a nickel paste to the lower layer, baking the coated material, and then subjecting the material directly to brazing for the purpose of reducing the number of steps (see “Electronic Ceramics”, December 1991). However, this technique leaves something to be desired because it requires a baking temperature as high as not lower than 1,250° C., adding to the sintering cost and deteriorating the dimensional accuracy of the resulting ceramic product.
The invention has been worked out in order to solve the aforementioned problems. An aim of the invention is to provide a process for producing a ceramic member for bonding which enables low-temperature sintering and simplified production process and gives a high dimensional accuracy, and a ceramic member for bonding, a bonded object, a vacuum switch and a vacuum vessel produced thereby.
(1) In order to accomplish the aforementioned aim of the invention, the first essence of the invention lies in a process for producing a ceramic member for bonding, which comprises:
A first step of applying a lower layer paste prepared from a first mixture comprising nickel, tungsten and molybdenum to the surface of a ceramic base which is a sintered ceramic, and then drying the coating layer to form a lower layer;
A second step of applying an upper layer paste prepared from a second mixture of nickel or nickel oxide and at least one of copper, copper oxide, manganese and manganese oxide to the lower layer, and then drying the coating layer to form an upper layer; and
A third step of heating and baking the lower layer and the upper layer.
In the invention, a mechanism of bonding of a Mo—W—Ni layer which is a lower layer to a ceramic base is formed. For the aforementioned baking (i.e., sintering the lower layer and the upper layer by calcining), the addition of Nickel causes the acceleration of sintering of Molybdenum particles, enabling low temperature sintering. Further, since the lower layer paste comprises tungsten incorporated therein, the sintering rate of Molybdenum particles can be relaxed to accomplish fair bonding over a wide temperature range.
Moreover, in the invention, a mechanism of bonding of a Ni—(Cu, Mn) layer which is an upper layer to a Mo—W—Ni layer which is a lower layer is formed. For the aforementioned baking, the incorporation of copper or manganese in the upper layer causes the drop of melting point of nickel, making it possible to form a dense alloy layer on the lower layer. In this arrangement, fair brazing can be effected even without nickel plating and subsequent sintering. Further, since the upper layer is an alloyed layer, the excessive diffusion of nickel in the lower layer containing molybdenum can be lessened, making it possible to prevent strength drop due to oversintering of molybdenum.
In the invention, the aforementioned action allows omission of nickel plating and sintering therefor, which has heretofore been required, making it possible to drastically simplify the production process and hence drastically reduce the production cost. Further, the lower layer and the upper layer can be sintered at a temperature as low as not higher than 1,200° C., the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. can be reduced. Moreover, the low temperature sintering makes it difficult for the ceramic itself to deform and hence makes it possible to obtain a high dimensional accuracy.
The lower layer paste can be prepared by mixing a first mixture containing a nickel powder, a tungsten powder and a molybdenum powder with an organic binder. The upper layer paste can be prepared by mixing a second mixture containing a nickel powder or nickel oxide powder with at least one of a copper powder, copper oxide powder, manganese powder and manganese oxide powder or a second mixture containing a nickel-copper alloy powder or nickel-manganese alloy powder with an organic binder.
When baking at the third step is effected in a humidifying reducing atmosphere such as H
2
and H
2
/N
2
, particularly at a temperature of from 1,080° C. to 1,200° C., the resulting product has a high bonding strength and airtightness to advantage.
(2) The second essence of the invention lies in the aforementioned process for producing a ceramic member for bonding, wherein the first mixture comprises nickel, tungsten and molybdenum incorporated therein in an amount of from 1% to 10% by weight, from 20% to 69% by weight and from 30% to 69% by weight, respectively.
In the invention, since the content of nickel in the first mixture is not lower than 1% by weight, nickel reacts with molybdenum, which is a high melting metal, to accelerate sintering of the lower layer (metallic layer). In this manner, sintering can be thoroughly effected even at low temperatures. Further, since the content of nickel in the first mixture is not greater than 10% by weight, oversintering of molybdenum can be prevented, making it possible to prevent the lack of strength of bonding between the ceramic base and the metallic layer.
Moreover, since the content of tungsten in the first mixture is not lower than 20% by weight, the temperature range within which a high strength metallic layer can be formed is wide. Further, since the content of tungsten in the first mixture is not greater than 69% by weight, the incorporation of molybdenum and nickel exerts an effect of preventing undersintering at low temperatures.
Further, since the content of molybdenum in the first mixture is not lower than 30% by weight, a firm metallic layer can be formed at low temperatures. Moreover, since the content of molybdenum in the first mixture is not greater than 69% by weight, the incorporation of tungsten and nickel can exert a good effect.
Examples of materials other than the metallic ingredients of the lower layer paste include organic binder.
(3) The third essenc
Jones Deborah
Koppikar Vivek
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
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