Ceramic heater

Details Ceramic heater Ceramic heater

2000-03-27

2001-07-24

Hoang, Tu Ba (Department: 3742)

Electric heating

Heating devices

With heating unit structure

C219S542000, C219S548000

Reexamination Certificate

active

06265700

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a ceramic heater comprising a resistance heating element embedded in ceramics.
BACKGROUND OF THE INVENTION
The ceramic heater comprising a resistance heating element of high-melting metal as embedded between a core and an insulation sheet covering the core is in widespread use as a heating means for the automotive oxygen sensor, glow system, etc. or as a heat source for devices for gassification of petroleum oil, such as a heater for use in semiconductor heating or an oil fan heater.
FIG.
3
(
a
) is a perspective view showing a ceramic heater of this type schematically and (b) is a sectional view taken along the line A—A of (a).
This ceramic heater comprises a cylindrical core
10
, an insulation sheet
12
wrapped around said core
10
with an adhesive layer
11
interposed, and a resistance heating element
13
embedded between said core and insulation sheet, with terminal portions of said resistance heating element
13
being connected to external terminals
14
disposed externally of said insulation sheet
12
and lead wires
16
being connected to said external terminals
14
, respectively.
As illustrated in FIG.
3
(
b
), each terminal portion of said resistance heating element
13
is connected to the corresponding external terminal
14
via a plated-through hole
15
provided under the external terminal
14
in the insulation sheet
12
. In this arrangement, as an electric current is applied between said external terminals
14
through said lead wires
16
, the resistance heating element
13
generates heat and thereby functions as a heater.
When this heater is operated under a high temperature setting as in the above application, the resistance heating element must be caused to generate a high-temperature heat and, therefore, it is common practice to use a high-melting metal such as tungsten (W) as the material of the resistance heating element. However, there is the problem that, when used at a high temperature, a metal of this kind reacts with the surrounding ceramics to form the silicide and oxide and affect the resistance value of the heating element. Generally a ceramic heater is operated at a constant voltage and, therefore, as the resistance value of the resistance heating element is altered in this manner, the heater temperature is also affected. Such a change in heater temperature should be avoided as far as possible. Moreover, as the oxidation progresses further, the heater is degraded to suffer a problem in durability.
Therefore, it is common practice to supplement a high-melting metal with rhenium (Re) and use the alloy for the high resistance heating element to thereby control the change in resistance. Thus, Re is added to the high-melting metal such as W to reduce its reactivity with the surrounding ceramics at a high temperature and thereby control the change in resistance.
However, Re is a very expensive element and, for this reason, is a factor in the high production cost of a ceramic heater.
Moreover, in order to avoid degradation of the resistance heating element (conductor), the connecting terminals and resistance heating element proper to be formed inside of the insulation sheet are conventionally composed of an Re-containing conductor (resistance heating material) but this practice leads to a further increase in the production cost of a ceramic heater.
SUMMARY OF THE INVENTION
In view of the above state of the art, the inventors of the present invention scrutinized the mechanism of reaction between the metal constituting the resistance heating element and ceramics in a ceramic heater and found that while the high-melting metal such as W in the high-temperature part of the resistance heating element which reaches 300° C. or higher reacts with the surrounding ceramics to form the silicide and oxide, this reaction does not substantially take place in the low-temperature part of the heating element and that, therefore, by using an Re-containing high-melting metal selectively for only the high-temperature part of the heating element which reaches 300° C. or higher, the change in resistance of the resistance heating element and the heater degradation due to aging can both be sufficiently precluded and, in addition, the ceramic heater can be fabricated at a low cost as compared with the prior art. The present invention has accordingly been developed.
The present invention, therefore, is directed to a ceramic heater comprising a core, an insulation sheet covering said core, and a resistance heating element of high-melting metal as embedded between said core and insulation sheet,
a high-temperature part of said resistance heating element, the operating temperature of which reaches 300° C. or higher, comprises a high-melting metal supplemented with Re or Mo.


REFERENCES:
patent: 4035613 (1977-07-01), Sagawa et al.
patent: 4540479 (1985-09-01), Sakurai et al.
patent: 4733056 (1988-03-01), Kojima et al.
patent: 5451748 (1995-09-01), Matsuzaki et al.
patent: 5948306 (1999-09-01), Konishi et al.
patent: 6049065 (2000-04-01), Konishi
patent: 6084220 (2000-07-01), Suematsu et al.

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