Ceramic heater

Details Ceramic heater Ceramic heater

2000-03-27

2001-05-22

Hoang, Tu Ba (Department: 3742)

Electric heating

Heating devices

With heating unit structure

C219S270000, C219S546000, C219S548000

Reexamination Certificate

active

06236027

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cylindrical ceramic heater comprising a resistance heating element embedded in ceramics.
BACKGROUND OF THE INVENTION
The compact cylindrical ceramic heater comprising a resistance heating element of high-melting metal as embedded between a core and an insulation layer 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.
6
(
a
) is a perspective view showing a typical ceramic heater of this type schematically and FIG.
6
(
b
) is a sectional view taken along the line A—A of Fig. (a).
This ceramic heater comprises a cylindrical core
31
, an insulation layer
32
wrapping around said core
31
with an adhesive layer
37
interposed, and a resistance heating element
33
embedded between said core and insulation layer, with terminal portions of said resistance heating element
33
being connected to external terminals
34
disposed externally of said insulation layer
32
and lead wires
36
being connected to said external terminals
34
, respectively.
As shown in FIG.
6
(
b
), each terminal portion of said resistance heating element
33
and the corresponding external terminal
34
are interconnected via a plated-through hole
35
provided in the insulation layer
32
beneath the external terminal
34
. In this arrangement, as an electric current is applied between the external terminals
34
through the lead wires
36
, the resistance heating element
33
generates heat and thereby functions as a heater.
The insulation layer
32
of said ceramic heater generally comprises Al
2
O
3
supplemented with, as sintering aids, SiO
2
, MgO, CaO, etc. and, for such insulation layer, compaction to the theoretical density is difficult at the usual sintering temperature. Moreover, depending on characteristics of the starting material Al
2
O
3
powder, the particle size distribution of said sintering aids, and impurities, the ultimate density is sometimes more or less lower than a set density value.
In addition, as heating is continued for a long time, the alumina ceramics forming the insulation layer
32
is degraded by grain boundary migration etc. to develop voids in some cases.
In such cases, the resistance heating element
33
embedded in the alumina ceramics is oxidized to suffer a progressive increase in resistance and the resistance heating element
33
as such undergoes expansion at times. Moreover, as the oxidation of the resistance heating element
33
progresses, its heating temperature is altered and, in addition, the element
33
becomes easily destroyed and, in extreme cases, develop a disconnection trouble.
Moreover, because the resistance heating element usually comprises a high-melting metal and the metal and the ceramics are widely different in the coefficient of thermal expansion, the repeated heating load on the ceramic heater induces cracks across the interface between the resistance heating element and the ceramics owing to the thermal stress, resulting in local destruction of the ceramic heater and a disconnection in the resistance heating element.
SUMMARY OF THE INVENTION
In the above state of the art, the present invention has for its object to provide a durable ceramic heater which is not only protected against the oxidation of its resistance heating element on prolonged operation of the heater and the consequent change in the resistance heating element but also against heater degradation due to aging and is free from the risks for cracking and other troubles due to the difference in thermal expansion coefficient between the resistance heating element and the insulation layer or the core.
The present invention is concerned, in a first aspect, with a ceramic heater comprising a core, an insulation layer and a resistance heating element of high-melting metal as embedded between said core and insulation layer,
wherein the operating temperature is not less than 300° C. and said insulation layer comprises a sintered compact composed of 88 to 95 weight % of Al
2
O
3
supplemented with, as sintering aids, 3 to 10 weight % of SiO
2
, 0.4 to 1.0 weight % of MgO and 1.0 to 2.5 weight % of CaO and having a density of not less than 3.60 and a thickness of 100 to 300 &mgr;m.
The present invention is further concerned, in a second aspect, with a ceramic heater comprising a core, an insulation layer and a resistance heating element of high-melting metal as embedded between said core and insulation layer,
said insulation layer comprising a sintered compact composed of 88 to 95 weight % of Al
2
O
3
supplemented with, as sintering aids, 3 to 10 weight % of SiO
2
, 0.4 to 1.0 weight % of MgO and 1.0 to 2.5 weight % of CaO and having a density ratio of not less than 96% and an average thermal expansion coefficient of 6×10
−6
to 8×10
−6
° C.
−1
at room temperature to 1000° C.,
said resistance heating element comprising a metal composite composed of 92 to 99 weight % of a high-melting metal component and the remainder of a ceramic component and having an average thickness of not less than 15 &mgr;m in the area where the operating temperature reaches 300° C. or higher and an average thermal expansion coefficient of 3.6×10
−6
to 7.0×10
−6
° C.
−1
at room temperature to 1000° C., and
the ratio of the difference in the average thermal expansion coefficient at room temperature to 1000° C. between said insulation layer and said resistance heating element to the average thermal expansion coefficient of the insulation layer being not greater than 40%.


REFERENCES:
patent: 5451748 (1995-09-01), Matsuzaki et al.
patent: 5948306 (1999-09-01), Konishi et al.
patent: 6049065 (2000-04-01), Konishi

Affiliated with

Also associated with

Rating

Ceramic heater does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ceramic heater, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ceramic heater will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2468986