U.S. patent application number 10/318307 was filed with the patent office on 2003-09-25 for joined bodies, assemblies for high pressure discharge lamps and high pressure discharge lamps.
This patent application is currently assigned to NGK INSULATORS, LTD.. Invention is credited to Niimi, Norikazu.
Application Number | 20030178939 10/318307 |
Document ID | / |
Family ID | 19189276 |
Filed Date | 2003-09-25 |
United States Patent
Application |
20030178939 |
Kind Code |
A1 |
Niimi, Norikazu |
September 25, 2003 |
Joined bodies, assemblies for high pressure discharge lamps and
high pressure discharge lamps
Abstract
The invention provides a joined body of a first member 7 made of
a metal and a second member 4 made of a ceramic or a cermet. The
joined body comprises a joining portion 6 interposed between the
first member 7 and the second member 4 for joining the member 7 and
the member 4. The joining portion 6 comprises main phase 14
contacting the first member 7 and an intermediate ceramic layer 13
existing between the second member and the main phase 14 as well as
contacting the second member 4. The main phase 14 is composed of a
porous bone structure, with open pores and made of a sintered
product of metal powder, and ceramic phase impregnated into the
open pores in the porous bone structure. Herewith, the joined
structure has resistance to fatigue and fracture, even when the
structure is subjected to repeated thermal cycles between a high
temperature, for example 1000.degree. C. or higher, and room
temperature.
Inventors: |
Niimi, Norikazu;
(Kasugai-city, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NGK INSULATORS, LTD.
2-56, Suda-cho Mizuhlo-ku
Nagoya-city
JP
467-8530
|
Family ID: |
19189276 |
Appl. No.: |
10/318307 |
Filed: |
December 13, 2002 |
Current U.S.
Class: |
313/623 |
Current CPC
Class: |
C04B 37/026 20130101;
B22F 2999/00 20130101; C04B 2237/348 20130101; C04B 2237/34
20130101; C04B 2237/76 20130101; B22F 2999/00 20130101; C04B
2237/62 20130101; C04B 2237/122 20130101; C04B 35/117 20130101;
C04B 2237/12 20130101; C04B 2237/066 20130101; C04B 35/44 20130101;
C04B 2237/404 20130101; H01J 61/366 20130101; C04B 2237/064
20130101; B22F 7/064 20130101; C04B 2237/72 20130101; C04B 2237/84
20130101; C04B 2237/403 20130101; C04B 35/581 20130101; C04B
2237/61 20130101; C04B 2237/343 20130101; C04B 2237/765 20130101;
C04B 2237/597 20130101; B22F 3/26 20130101; B22F 7/064
20130101 |
Class at
Publication: |
313/623 |
International
Class: |
H01J 017/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2001 |
JP |
2001-398054 |
Claims
1. A joined body of a first member made of a metal and a second
member made of a ceramic or a cermet, wherein said joined body
comprises a joining portion interposed between said first member
and said second member for joining said first and second members,
said joining portion comprising main phase contacting said first
member and an intermediate ceramic composition layer contacting
said second member and existing between said second member and said
main phase, and said main phase comprising a porous bone structure
with open pores and made of a sintered product of powder of a
metal, and said main phase further comprising ceramic composition
layer impregnated into said open pores in said porous bone
structure each of said intermediate ceramic composition layer and
said impregnated ceramic composition layer has a crystallinity of
more than 50%.
2. The joined body of claim 1, wherein said intermediate ceramic
composition layer and said impregnated ceramic composition layer
contain a main component of said ceramic or said cermet
constituting said second member.
3. The joined body of claims 1 or 2, wherein said metal
constituting said porous bone structure contains a main component
of said metal constituting said first member.
4. The joined body of any one of claims 1 to 3, wherein said
intermediate ceramic composition layer and said impregnated ceramic
composition layer are made of ceramic materials comprising the same
ingredient system.
5. The joined body of any one of claims 1 to 4, wherein said porous
bone structure has a porosity of open pores of not lower than 30%
and not higher than 80%.
6. The joined body of any one of claims 1 to 5, wherein each of
said intermediate ceramic layer and said impregnated ceramic phase
has a crystallinity of not lower than 60%.
7. The joined body of claim 6, wherein each of said intermediate
ceramic layer and said impregnated ceramic phase has a
crystallinity of not lower than 70%.
8. The joined body of claim 7, wherein each of said intermediate
ceramic layer and said impregnated ceramic phase has a
crystallinity of not lower than 80%.
9. The joined body of any one of claims 1 to 8, wherein each of a
ceramic constituting said intermediate ceramic composition layer
and a ceramic constituting said impregnated ceramic composition
layer comprises one or more oxide selected from the group
consisting of Al.sub.2O.sub.3, Sc.sub.2O.sub.3, Y.sub.2O.sub.3,
La.sub.2O.sub.3, Gd.sub.2O.sub.3, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3,
Tm.sub.2O.sub.3, SiO.sub.2, MoO.sub.2 and MoO.sub.3.
10. The joined body of claim 9, wherein each of a ceramic
constituting said intermediate ceramic composition layer and a
ceramic constituting said impregnated ceramic composition layer
comprises three or more oxides selected from the group consisting
of Al.sub.2O.sub.3, Sc.sub.2O.sub.3, Y.sub.2O.sub.3,
La.sub.2O.sub.3, Gd.sub.2O.sub.3, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3,
Tm.sub.2O.sub.3, SiO.sub.2, MoO.sub.2 and MoO.sub.3.
11. The joined body of claim 10, wherein each ceramic has a content
of SiO.sub.2 of not higher than 15 weight percent.
12. The joined body of claim 11, wherein each ceramic has a content
of SiO.sub.2 of not lower than 5 ppm.
13. The joined body of any one of claims 1 to 12, wherein said
first member comprises one or more metal selected from the group
consisting of molybdenum, tungsten, rhenium, niobium, tantalum and
the alloys thereof.
14. The joined body of any one of claims 1 to 13, wherein said
second member comprises a ceramic selected from the group
consisting of alumina, magnesia, yttria, lanthania and zirconia, or
a cermet containing said ceramic.
15. The joined body of any one of claims 1 to 15, wherein each of a
material constituting said intermediate ceramic composition layer
and a ceramic constituting said impregnated ceramic composition
layer has a melting point not more than a temperature subtracted
200.degree. C. from a melting point of a ceramic or a cermet
constituting said second member.
16. A high pressure discharge lamp comprising: a ceramic discharge
tube with an inner space formed therein and end portions, said
inner space being filled with an ionizable light-emitting material
and a starter gas and an opening being formed within said end
portion; an electrode system provided within said inner space; a
sealing member comprising a ceramic or a cermet with a through hole
formed therein, at least a part of said sealing member being fixed
within said opening of said ceramic discharge tube; and a metal
member; wherein said lamp comprises a joined body interposed
between said metal member and said sealing member, and said joined
body is a joined body of any one of claims 1 to 15, said metal
member is said first member, and said sealing member is said second
member.
17. A high pressure discharge lamp comprising: a ceramic discharge
tube with an inner space formed therein and end portions, said
inner space being filled with an ionizable light-emitting material
and a starter gas and an opening being formed within said end
portion; an electrode system provided within said inner space; and
a metal member; wherein said lamp comprises a joined body
interposed between said metal member and said discharge tube, and
said joined body is a joined body of any one of claims 1 to 15,
said metal member is said first member, and said discharge lamp is
said second member.
18. The lamp of claims 16 or 17, wherein a heat resisting
temperature of said discharge tube is not less than 1000.degree.
C.
19. The lamp of claims 16 or 17, wherein said intermediate ceramic
layer and said impregnated ceramic phase contain a main component
of said ceramic constituting said discharge tube.
20. The lamp of claims 16 to 19, wherein said metal member has
tubular shape, and a clearance between said metal member and an
electrode to be inserted into said metal member is between 30 to
150 .mu.m at a diameter direction.
Description
[0001] This is a continuation-in-part of application Ser. No.
09/631,419 filed in Feb. 27, 2001 which is a continuation-in-part
of application Ser. No. 09/631,419 filed in Aug. 3, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a joined body, particularly
relates to a high pressure discharge lamp using a ceramic discharge
tube.
[0004] 2. Description of the Related Art
[0005] A high pressure discharge lamp has a ceramic discharge tube
with two end portions, in which sealing members (usually referred
to as a ceramic plug) are inserted, respectively, to seal the
respective end portions. A through hole is formed in each sealing
member and a metal member, to which a predetermined electrode
system is attached, is inserted within the through hole. An
ionizable light-emitting material is introduced and sealed within
the inner space of the discharge tube. Known high pressure
discharge lamps include a high pressure sodium vapor and metal
halide lamps, the latter exhibiting more superior color
coordination. The lamp may be used in high temperature condition by
forming the discharge tube by a ceramic material.
[0006] In such discharge lamp, it is necessary to air-tightly seal
between the end portion of the ceramic discharge tube and a member
for supporting an electrode system. The ceramic discharge tube has
a main body with a shape of a tube with two narrow ends, or a
barrel, or a straight tube. The ceramic discharge tube is made of,
for example, alumina sintered body.
[0007] Specification of Japanese patent application No.
178,415/1999 (EPO EP0982278, A1) discloses the following structure.
The joining portion between the end portion of a ceramic discharge
tube and a member for supporting an electrode system comprises main
phase contacting the discharge tube, and an intermediate ceramic
layer contacting the supporting member and existing between the
supporting member and the main phase. The main phase is composed of
a porous bone structure, with open pores and made of a sintered
product of metal powder, and ceramic phase impregnated into the
open pores in said porous bone structure. Herewith, such joined
structure has improved air-tightness and resistance to corrosion,
and repeated thermal cycles does not result in the fracture of the
joined structure.
SUMMARY OF THE INVENTION
[0008] The inventor further examined the above sealing structure
and, therefore, achieved to provide a joined structure having
resistance to fatigue and fracture, even when the structure is
subjected to repeated thermal cycles between a high temperature,
for example 1000.degree. C. or higher, and room temperature.
[0009] That is, it is an object of the invention to provide a
joined structure having resistance to fatigue and fracture, even
when the structure is subjected to repeated thermal cycles between
a high temperature, for example 1000.degree. C. or higher, and room
temperature.
[0010] It is another object of the invention to apply such joined
structure to a high pressure discharge lamp, for improving the
resistance to a corrosive gas, such as a metal halide, and the
air-tightness and for avoiding the fracture of the joined structure
due to repeated cycles of turning-ons and turning-offs.
[0011] The present invention provides a joined body of a first
member made of a metal and a second member made of a ceramic or a
cermet. The joined body comprises a joining portion interposed
between the first member and the second member for joining the
first and second members, wherein the joining portion comprises
main phase contacting the first member and an intermediate ceramic
composition layer contacting the second member and existing between
the second member and the main phase. The main phase is composed of
a porous bone structure, made of a sintered product of metal powder
and with open pores, and ceramic composition layer impregnated into
the open pores in the porous bone structure. Each of the
intermediate ceramic composition layer and said impregnated ceramic
composition layer has a crystallinity of more than 50%.
[0012] The present invention further provides a ceramic discharge
lamp comprising:
[0013] a ceramic discharge tube with an inner space formed therein
and end portions, the inner space being filled with an ionizable
light-emitting material and a starter gas and an opening being
formed within the end portion;
[0014] an electrode system provided within the inner space;
[0015] a sealing member with a through hole formed therein, a part
of the sealing member being fixed within the opening of the ceramic
discharge tube; and
[0016] a metal member; wherein the metal member and the sealing
member constitute the above air-tight joined body. The metal member
is the first member and the sealing member is the second
member.
[0017] The present invention further provides a ceramic discharge
lamp comprising:
[0018] a ceramic discharge tube with an inner space formed therein
and end portions, the inner space being filled with an ionizable
light-emitting material and a starter gas and an opening being
formed within the end portion;
[0019] an electrode system provided within the inner space; and
[0020] a metal member; wherein the metal member and the ceramic
discharge tube constitute the above air-tight joined body. The
metal member is the first member and the ceramic discharge tube is
the second member.
[0021] The present invention provides a joined structure of a first
member made of a metal, such as molybdenum, and a second member
made of a ceramic or a cermet, in which the members may be joined
with a high strength, the joined structure has improved
air-tightness and resistance to corrosion, and repeated thermal
cycles do not result in the fracture of the joined structure. The
invention provides a method for manufacturing the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross sectional view schematically showing the
state wherein a porous bone structure 2 is provided between a
sealing member 4 and a metal member 7.
[0023] FIG. 2 is a cross sectional view schematically showing a
joined body.
[0024] FIG. 3 is a cross sectional view schematically showing the
state wherein a porous bone structure 2 is provided between a
sealing member 4 and a metal member 7.
[0025] FIG. 4 is a photograph, taken by a scanning type electron
microscope, showing the joint interface between a metal member and
a sealing member.
[0026] FIG. 5 is a photograph showing an enlarged view of a part of
FIG. 4.
[0027] FIG. 6 is a diagram illustrating the photograph of FIG.
4.
[0028] FIG. 7 is a diagram illustrating the photograph of FIG.
5.
[0029] FIG. 8 is a diagram showing the relation among the heat
resisting temperature, the thermal stress, and the corrosion
resistance of the high pressure discharge lamp.
[0030] FIG. 9 is a diagram showing the relation between the
crystallinity and the failure rate of a ceramic discharge tube
during the thermal cycle test under the temperature of 950.degree.
C.
[0031] FIG. 10 is a diagram showing the relation between the
crystallinity and the failure rate of a ceramic discharge tube
during the thermal cycle test under the temperature of 1050.degree.
C.
[0032] FIG. 11 is a diagram showing the relation between the weight
% of SiO.sub.2 and the crystallinity of a ceramics.
[0033] FIG. 12 is a diagram schematically showing a layered
structure of the joining portion of the joined body of FIG. 1 and
the thermal coefficients of the layers.
[0034] FIG. 13 is a cross sectional view showing the state wherein
a clogging member 19 is inserted within the metal member 7 of the
high pressure discharge lamp of FIG. 1.
[0035] FIG. 14 is a cross sectional view showing a high pressure
discharge lamp after the metal member 7 of FIG. 12 and a sealing
member 19 is joined to form a sealing portion 21.
[0036] FIG. 15 is a diagram schematically showing an example of a
high pressure discharge lamp.
[0037] FIG. 16 is a cross sectional view schematically showing an
embodiment of an end portion of a high pressure discharge lamp
according to the invention, wherein a metal member 7 is joined to
the inner wall surface of a sealing member 4 substantially along
the full length of the wall.
[0038] FIG. 17 is a cross sectional view schematically showing an
embodiment of an end portion of a high pressure discharge lamp
according to the invention, wherein a metal member 7 is joined to
an end portion 1a of a discharge tube 1 and a metal element 7 and a
metal axis of an electrode system 27 is electrically connected by a
metallized layer 32, covering the surface of the end portion
1a.
[0039] FIG. 18 is an enlarged view showing the region near a hollow
31 shown in FIG. 17.
[0040] FIG. 19 is a cross sectional view schematically showing an
end portion of a high pressure discharge lamp according to another
embodiment of the invention, wherein a metal member 7 is joined to
an inner wall surface of the end portion 1a of a discharge tube 1
substantially along the full length of the surface.
[0041] FIG. 20 is a cross sectional view schematically showing an
end portion of a high pressure discharge lamp according to another
embodiment of the invention, wherein a through hole 46 of a sealing
member 39 is sealed by a joining portion 6D of the invention.
[0042] FIG. 21 is a cross sectional view schematically showing an
end portion of a high pressure discharge lamp according to another
embodiment of the invention, wherein an opening 40 of an end
portion 1a of a discharge tube 1 is sealed by a joining portion 6E
of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIGS. 1 to 7 are cross sectional views showing an end
portion of a high pressure discharge lamp of the invention.
[0044] An inner wall surface 1b of an end portion 1a of a ceramic
high pressure discharge tube 1 is formed so as to extend
straightforwardly in the direction of the central axis of the tube.
A part of a sealing member 4 is inserted within an opening 40 of
the end portion 1a. 4c is an outer surface and 46 is a through hole
of the sealing member 4.
[0045] A depression or hollow 9 is formed on the inner wall surface
4a of the sealing member 4. A metal member 7 is held in the hollow
9. In the embodiment, the metal member 7 has a shape of a tube and
an opening is formed in its end portion 7d, the opening being
sealed after introducing a starter gas and an ionizable
light-emitting substance. 7b is an inner surface and 7c is an outer
surface of the metal member 7. An inner space of the metal member 7
is commuted with an inner space of the ceramic discharge tube 1
(described below). A protrusion 42 is provided in the sealing
member 4 and faces an end portion 7a of the metal member 7.
[0046] As shown in FIG. 1, the inventors provided a porous bone
structure 2, made of a sintered product of metal powder and with
open pores, between the metal member 7 and sealing member 4. A
ceramic material ring was then positioned on the bone structure 2.
The melting point of the bone structure 2 is adjusted so as to
exceed that of the ceramic material.
[0047] When the ceramic material was melted, as schematically shown
in FIG. 2, the inventor found that the melted material was
impregnated into the open pores to form main phase 14, comprising
the porous bone structure and ceramic composition layer impregnated
into the open pores. The inventor further found that the thus
melted material is flown into the interface of the sealing member 4
and the main phase 14 so that the bone structure is slightly
floated from the surface of the sealing member 4 to form the
intermediate ceramic composition layer 13. The main phase 14 and
intermediate ceramic composition layer 13 together form a joining
portion 6 joining the metal member 7 and sealing member 4. 41 is a
joint interface of the sealing member 4. The joining portion 6
extends to the region near the protrusion 42. A joining ceramic
composition layer 48 is formed between the protrusion 42 and the
end portion 7a of the metal member 7.
[0048] As shown in FIG. 3, it is also possible to apply a paste
ceramic composition 20' at the peripheral of the metal member 7,
the bone structure 2 and the sealing member 4 instead of
positioning the ceramic material ring 20 on the bone structure
2.
[0049] Such structure will be explained referring to scanning type
microscopic photographs of FIGS. 4 and 5, and line diagrams of
FIGS. 6 and 7. FIG. 4 is a photograph showing the region near the
interface between the metal member 7 and the sealing member 4, and
FIG. 6 is a diagram illustrating the photograph of FIG. 4. FIG. 5
is an enlarged view showing the photograph of FIG. 4, and FIG. 7 is
a diagram illustrating the photograph of FIG. 5.
[0050] The intermediate ceramic composition layer 13 and main phase
14 is formed on the surface of the sealing member 4. The main phase
14 is composed of the bone structure 15 and the ceramic composition
layer 10 impregnated into open pores of the bone structure 15. The
intermediate ceramic composition layer 13 is composed of the same
composition as the impregnated ceramic composition layer 10. The
main phase 14 of the joining portion 6 is formed on the surface of
the metal member 7. In the photograph of the FIG. 4, the whitish
region in the main phase 14 is metallic molybdenum, and gray or
black region in the main phase 14 is the impregnated ceramic
composition layer. The difference of the brightness in the
impregnated ceramic phase shows that the ratio of the components in
the ceramic, such as alumina, has been changed microscopically.
[0051] In the joined body having the above structure, tensile
stresses on the ceramic is dispersed by means of metal particles
(porous bone structure) and compression stress on the bone
structure is dispersed by means of the ceramic impregnated into its
open pores. That is, the different kinds of materials may cooperate
with each other to cope with both of the tensile and compression
stresses on the joining portion. Further, it is relatively hard to
generate cracks in the ceramic materials. In addition, when cracks
develop within the ceramic composition layer, such cracks may be
interrupted by the porous bone structure made of a metal, thereby
preventing the fracture of the joining portion. Further, such main
phase comprising the porous bone structure and impregnated ceramic
composition layer adheres to the metal member and the intermediate
ceramic composition layer strongly adhere to the sealing
member.
[0052] Further, ceramic components susceptible to corrosion is
mainly impregnated into the open pores of the bone structure.
[0053] According to the present invention, it is found that there
are the thermal stress factor and the corrosion factor in the
failure mechanism of the high pressure discharge lamp. It is also
found that there are the temperature region in which the thermal
stress factor is dominant and the temperature region in which the
corrosion factor is dominant. FIG. 8 is a diagram showing the
relation among the heat resisting temperature, the thermal stress,
and the corrosion resistance of the high pressure discharge lamp.
As shown in FIG. 8, the thermal stress factor is dominant at the
heat resisting temperature lower than 980.degree. C., preferably
equal to or lower than 950.degree. C., and the corrosion factor is
dominant at the heat resisting temperature higher than 980.degree.
C., preferably equal to or lower than 1050.degree. C. According to
the inventor's investigation, it is advantageous for the high
pressure discharge lamp to have not less than 50% of the
crystallinity in view of the corrosion.
[0054] The above mentioned phenomenon can be explained as follows.
It is thought that the thermal stress is proportional to the
difference between the real temperature and the melting point (the
softening temperature) of the object. Therefore, as shown by curve
a in FIG. 8, the contribution to the thermal stress decreases as
the heat resisting temperature increases. A substantial thermal
stress does not occur at the temperature equal to or higher than
melting point.
[0055] On the other hand, as shown by curve b in FIG. 8, the
corrosion (the chemical reaction) decreases as the heat resisting
temperature decreases. This is because the activity of an ionizable
light-emitting material filled into the discharge tube decreases as
the temperature of the discharge tube and thus attacks to the inner
wall of the discharge tube and so on decreases. Therefore, at a
relatively high temperature, the chemical stabilization of the high
pressure discharge lamp increases as the rate of the crystallinity
increases.
[0056] When the thermal cycle test of the ceramic discharge tube is
performed at the 950.degree. C. of the temperature in which the
thermal stress is dominant in the failure mechanism of the high
pressure discharge lamp, the stress relaxation mechanism fully acts
and the corrosion is relatively low on condition that the
intermediate ceramic composition layer and the impregnated ceramic
composition layer of the high pressure discharge lamp has a
crystallinity of not more than 50%. This is because the thermal
stress is dominant in the failure mechanism of the high pressure
discharge lamp when the crystallinity is not more than 50%. As a
result, the failure of the high pressure discharge lamp does not
occur. On the other hand, it is not advantageous for the high
pressure discharge lamp to have not less than 50% of the
crystallinity because the stress relaxation mechanism does not
fully act. (refer to FIG. 9) In the thermal cycle test, 1000 times
of the thermal cycles was performed. In this case, the temperature
of the high pressure discharge lamp was firstly maintained at the
room temperature for 15 minutes, subsequently was increased to
1050.degree. C. and maintained at 1050.degree. C. for 5 minutes,
and finally was decreased to the room temperature every thermal
cycle.
[0057] When the thermal cycle test of the ceramic discharge tube is
performed at the 1050.degree. C. of the temperature in which the
corrosion is dominant in the failure mechanism of the high pressure
discharge lamp, the corrosion resistance fully acts and the thermal
stress is relatively low on condition that the intermediate ceramic
composition layer and the impregnated ceramic composition layer of
the high pressure discharge lamp has a crystallinity of more than
50%. As a result, the failure of the high pressure discharge lamp
does not occur. On the other hand, it is not advantageous for the
high pressure discharge lamp to have not more than 50% of the
crystallinity because the corrosion resistance does not fully act.
(refer to FIG. 10)
[0058] The following table shows the result in which cubes were
arranged into a quarts tube and exposed to DyI.sub.3 and ScI.sub.3
for 4000 hours at the temperature of 950.degree. C. Each of the
cubes has 5 mm of sides and is composed of ceramic compositions of
46%, 54% and 75 a % of the crystallinity.
1 TABLE 1 rare earth metal halide (wt %) crystallinity (%) 0 5 10
15 20 40 46 .circleincircle. .largecircle. .DELTA. .DELTA. .DELTA.
54 .circleincircle. .circleincircle. .largecircle. .largecircle. 75
.circleincircle. .circleincircle. .circleincircle. : less than 5%
of the corrosion region .circleincircle.: 5 to 20% of the corrosion
region .largecircle.: 20 to 30% of the corrosion region .DELTA.: 30
to 40% of the corrosion region
[0059] As already stated, when the heat resisting temperature is
higher than 980.degree. C., or the crystallinity is more than 50%,
the contribution to the corrosion resistance is higher than that to
the relaxation of the thermal stress. On the other hand, when the
heat resisting temperature is lower than 980.degree. C., or the
crystallinity is less than 50%, the contribution to the relaxation
of the thermal stress is higher than that to the corrosion
resistance. However, If the ionizable light-emitting material
contains a main component of a rare earth metal halide, it is
prefer to have more than 50% of the crystallinity regardless of the
heat resisting temperature because the contribution to the
corrosion is relatively high at the temperature lower than
980.degree. C. due to the high corrosion thereof. The "main
component" herein means a component of an ionizable light-emitting
material occupying not less than 15 weight percent of the ionizable
light-emitting material except for a starting medium.
[0060] According to the present invention, the heat resisting
temperature is 1050.degree. C. if the crystallinity is 55%. As a
result, the present invention can be applied to not only a lamp for
general lighting but also a head lamp for vehicle which requires
the relatively high heat resisting temperature not less than
1000.degree. C. and a severe heat resisting cycle.
[0061] The joined body in the present invention is particularly
suitable to a high discharge lamp. In this case, such high pressure
discharge lamp may be extremely stable to repeated cycles of
turning-on and turning-off and a corrosive gas contained within the
inner space of a ceramic discharge tube.
[0062] In the invention, preferably, an intermediate ceramic
composition layer and impregnated ceramic composition layer have
the substantially same kind of composition. This means that both
belong to the same ingredient system as a whole, thereby improving
the strength of the joining portion. The intermediate ceramic
composition layer and the impregnated ceramic composition layer
further preferably have substantially same composition. This means
that the intermediate ceramic composition layer and the impregnated
ceramic composition layer are derived from the same material.
[0063] The degree of crystallization of the intermediate ceramic
composition layer and the impregnated ceramic composition layer is
not limited, but may preferably be 80% or more. In such a case, the
maximum degree is not limited, and may be 100%.
[0064] In order to examine the relation between the rate of the
crystallinity and that of the corrosion, cubes were arranged into a
quarts tube and exposed to DyI.sub.3 and ScI.sub.3 for at the
temperature of 1000.degree. C., each of the cubes having 5 mm of
sides and being composed of ceramic compositions of 60%, 70% and
80% of the crystallinity. The result shows as follows.
2 TABLE 2 time crystallinity (%) 1000 2000 3000 4500 6000 60
.circleincircle. .largecircle. .DELTA. .DELTA. 70 .circleincircle.
.largecircle. .largecircle. .DELTA. 80 .circleincircle.
.circleincircle. .circleincircle. .circleincircle. : less than 5%
of the corrosion region .circleincircle.: 5 to 20% of the corrosion
region .largecircle.: 20 to 30% of the corrosion region .DELTA.: 30
to 40% of the corrosion region
[0065] As shown in table 2, the corrosion increases as the rate of
the crystallinity increases. In other words, the corrosion at 70%
of the crystallinity is higher than that at 60% of the
crystallinity, and the corrosion at 80% of the crystallinity is
higher than that at 70% of the crystallinity. Especially, when the
crystallinity is 80%, the corrosion can be not more than 20% even
if the time to expose the cube reaches 6000 hours.
[0066] Each of ceramic constituting the intermediate ceramic
composition layer and ceramic constituting the impregnated ceramic
composition layer may preferably comprise one or more oxide
selected from the group consisting of Al.sub.2O.sub.3,
SC.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Gd.sub.2O.sub.3,
Dy.sub.2O.sub.3, H.sub.2O.sub.3, Tm.sub.2O.sub.3, SiO.sub.2,
MoO.sub.2 and MoO.sub.3. The mixture of not less than two of the
oxides may be particularly preferable.
Dy.sub.2O.sub.3--Al.sub.2O.sub.3, Sc.sub.2O.sub.3--Al.sub.2O.sub.3
two eutectic component is more preferable because it has
substantially high melting point of the order of 1800.degree.
C.
[0067] To prevent corrosion caused by the corrosive gas contained
within the high pressure discharge lamp over a long term, the
composition of SiO.sub.2 in each ceramic, which is a relatively
corrosive ingredient, may preferably be 15 weight percent or less,
and more preferably 5 weight percent or less. As a result, it is
possible to control the crystallinity of the ceramics well. FIG. 11
is a diagram showing the relation between the weight % of SiO.sub.2
and the crystallinity of a ceramics. It shows the relation when it
takes 15 minutes to decrease 500.degree. C. from the treatment
temperature. As shown in FIG. 11, the crystallinity is not less
than 50% when a content of SiO.sub.2 of ceramics is less than 15
weight percent.
[0068] SiO.sub.2 also act as a kind of binder to retain a shape of
the ceramic material when this joined body is produced. Therefore,
on the view of improving the shape retaining character, SiO.sub.2
may preferably be contained 5 ppm or more, and more preferably 20
ppm or more.
[0069] Each ceramic may preferably contain particularly
Al.sub.2O.sub.3. On the view point of wettability, each ceramic may
preferably contain a main component of the ceramic or cermet
constituting the second member. The "main component" herein means a
ceramic component constituting 70 weight percent or more of the
ceramic or a ceramic component constituting 60 weight percent or
more of the cermet.
[0070] The followings are the preferred composition ranges.
3 (1) Al.sub.2O.sub.3 10 to 80 weight percent Si.sub.2O.sub.2 10
weight percent or less (preferably 5 ppm or more) Y.sub.2O.sub.3 0
to 40 weight percent Dy.sub.2O.sub.3 0 to 50 weight percent
B.sub.2O.sub.3 0 to 10 weight percent MoO.sub.3 0 to 10 weight
percent (2) A.sub.2O.sub.3 10 to 80 weight percent SiO.sub.2 0 to
10 weight percent Y.sub.2O.sub.3 10 to 25 weight percent
Dy.sub.2O.sub.3 10 to 50 weight percent
[0071] The metal member may be made of one or more metal selected
from the group consisting of molybdenum, tungsten, rhenium,
niobium, tantalum and alloys thereof.
[0072] Among them, niobium and tantalum have thermal expansion
coefficients matching with that of a ceramic, especially alumina
ceramic, constituting a ceramic discharge tube. However, it is
known that niobium and tantalum are susceptible to corrosion to a
metal halide. Therefore, it is desirable to form a metal member by
a metal selected from the group consisting of molybdenum, tungsten,
rhenium and alloys thereof, for improving the life of the metal
member. However, such metals, with high resistance to a metal
halide, generally have a low thermal expansion coefficient. For
example, alumina ceramic has a thermal expansion coefficient of
8.times.10.sup.-6K.sup.-1, molybdenum has that of
6.times.10.sup.-6K.sup.-1, and tungsten and rhenium have those of
not more than 6.times.10.sup.-6K.sup.-1. In such a case, as
described above, the inventive joined structure effectively reduces
the stress due to the difference of the thermal expansion
coefficients of the metal member and the ceramic discharge tube or
the sealing member.
[0073] Molybdenum is suitably used for the invented structure in
such advantages that it has high resistance to a metal vapor,
particularly to a metal halide gas, and that it has high
wettability to a ceramic.
[0074] When using molybdenum as a material of a metal member, at
least one of La.sub.2O.sub.3 and CeO.sub.2 may preferably be added
to molybdenum in a ratio of 0.1 to 2.0 weight percent as a
total.
[0075] A porous bone structure is made of a sintered product of
metal powder. The metal powder may preferably be made of a metal
selected from the group consisting of molybdenum, tungsten,
rhenium, niobium, tantalum and the alloys thereof. For further
improving the resistance of the structure to a halogen, a metal
selected from the group consisting of molybdenum, tungsten, rhenium
and the alloys thereof is particularly preferable.
[0076] The main components of the metals constituting the metal
member and constituting the porous bone structure may preferably be
the same and more preferably molybdenum. Such (main component)
means that the component constitutes not lower than 60 weight
percent of the metal.
[0077] The porous bone structure may preferably has a porosity, of
open pores, of not lower than 15%, and more preferably not lower
than 40%, thus improving the strength of the joining portion. The
porosity may preferably be not higher than 80%, and more preferably
be not higher than 70%, thus effectively impregnating the ceramic
into the open pores of the bone structure and dispersing the stress
applied on the structure to improve the resistance thereof to
repeated thermal cycles.
[0078] The second member or sealing member is made of a ceramic or
cermet. The ceramic may preferably be a ceramic alone, selected
from the group consisting of alumina, magnesia, yttria, lanthania
and zirconia, or the mixed compound thereof.
[0079] More particularly, the sealing member may be made of the
same or the different kinds of material as that of the ceramic
discharge tube. When the electric conductor is made of niobium or
tantalum, the ceramic discharge tube and sealing member may
preferably be made of the same kind of material, because in this
case the thermal expansion coefficient of the electric conductor is
approaching those of the ceramic discharge lamp and sealing member.
Such (same kind of material) means that their base components of
the ceramic materials are the same and the added component or
components may be the same or different with each other.
[0080] When the metal member is made of molybdenum, tungsten,
rhenium or the alloys thereof, the difference of the thermal
expansion coefficients of the ceramic discharge tube and metal
member are relatively increased. Therefore, it is preferable to
adjust the thermal expansion coefficient of the sealing member
between those of the electric conductor and the end portion of the
ceramic discharge tube. For that reason, the sealing member may be
formed of a cermet.
[0081] A cermet is a composite material of a ceramic and a metal.
Such ceramic may preferably be a ceramic alone, selected from the
group consisting of alumina, magnesia, yttria, lanthania and
zirconia, or the mixed compound thereof, and more preferably be the
same kind of ceramic as that of the ceramic discharge tube, thereby
making it possible to co-fire the ceramic discharge tube and
sealing member simultaneously. On this point of view, the ceramic
components of the ceramic discharge tube and the cermet may more
preferably be alumina ceramic.
[0082] The metal component of the cermet may preferably be a metal,
having a high temperature melting point and resistance to a metal
halide, such as tungsten, molybdenum, rhenium or the like, or the
alloys thereof, thus giving the sealing member improved resistance
to the metal halide. The cermet may preferably has not lower than
55 weight percent, and more preferably not lower than 60 weight
percent, of a ceramic component (the balance is a metal
component.).
[0083] Preferably, each of a material constituting the intermediate
ceramic composition layer and a ceramic constituting the
impregnated ceramic composition layer has a melting point not more
than a temperature subtracted 200.degree. C. from a melting point
of a ceramic or a cermet constituting the second member. Thereby,
grain boundary crack seldom occurs in the second member. In this
case, the melting point of each materials is not less than
1500.degree. C.
[0084] The above described joining method may be applied to both
ends of a ceramic tube. However, in one end, it is necessary to
apply a tubular-shaped metal member for introducing an ionizable
light-emitting substance through the inner space of the metal
member. In the other end, metal members with various shapes such as
a rod, a tube or the like may be applied.
[0085] The shape of a ceramic discharge tube is not particularly
limited, and includes a tube, a cylinder, a barrel or the like.
When the metal member is a tubular shaped member supporting an
electrode system, through which an ionizable light-emitting
substance is introduced into the inner space of the discharge tube,
the electrode-system-supporting member is sealed by laser welding
or TIG welding. When using laser welding, for example, Nd/YAG laser
is used. In this case, a clearance between the metal member and an
electrode to be inserted into the metal member is between 30 to 150
.mu.m at a diameter direction because, if the clearance is too
wide, there is a tendency to accumulate the light-emitting material
in the clearance so that the unevenness of the property increases,
on one hand, and if the clearance is too small, the electrode
system substantially contacts the electrode-system-supporting
member and the thermal stress of the joining portion thereof
increases so that there is a tendency to break the joining portion,
on the other hand.
[0086] In the case of a metal halide high pressure discharge lamp,
an inert gas, such as argon, a metal halide and optionally mercury
is introduced into the inner space of the ceramic discharge
tube.
[0087] FIGS. 1, 2, 3, 12, 13 and 14 show the embodiments of the end
portions of the lamp to which the invention is applied.
[0088] A joining portion 6 of the invention is interposed between a
sealing member 4 and a metal member 7 to join them with each other
and to secure air-tightness.
[0089] As shown in FIG. 12, an axis 27 of an electrode system 18 is
attached to a clogging member 19 (preferably made of a metal), the
electrode system 18 is inserted into the inner space of a ceramic
discharge tube and the clogging member 19 is inserted into the
inner space of the metal member 7. As shown in FIG. 13, it is
possible to expose a metal end 7a to an inner space of the metal
member 7 of the ceramic discharge tube and provide a stopper 48'.
As shown in FIG. 14, an end portion 19a of the clogging member 19
is joined, by means of the above welding or the like, to the metal
member 7 to form a sealing portion 21, thereby sealing an ionizable
light-emitting substance and a starter gas in the inner space of
the ceramic discharge tube from the outer atmosphere and providing
an electric power to the electrode system 18 through the clogging
member 19. A protrusion 42 functions to position the metal member 7
and to make flow path of the corrosive gas longer.
[0090] FIG. 15 is a diagram schematically showing an embodiment of
a high pressure discharge lamp. A high pressure discharge lamp
system 23 has an outer tube 30 generally made of a hard glass, in
which a high pressure discharge lamp 1 is contained. The outer tube
30 has both ends sealed with ceramic caps 22. Each clogging member
19 is inserted into and joined with each metal member 7. An outer
lead wire 25 is connected with each outer end 19a of each clogging
member 19.
[0091] In the embodiment shown in FIG. 16, the sealing member 4 has
no protrusion on its inner wall surface. And, the metal member 7
and the inner wall surface of the sealing member 4 is joined
substantially along the full length of the through hole 46 of the
sealing member 4. 6A is a joining portion, 13A is an intermediate
glass layer and 14A is main phase.
[0092] In the embodiment shown in FIG. 17, the inner wall surface
1b of the end portion 1a of the ceramic discharge tube 1 extends
straightforwardly in the direction of the main axis of the ceramic
discharge tube. A hollow 31 is formed in the end portion 1d of the
inner wall surface 1b of the end portion 1a. An end portion 7a of a
metal member 7 is supported in the hollow 31. A joining portion 6B
is interposed between the discharge tube 1 and the metal member 7
and join them with each other in the hollow 31 to secure the
air-tightness. 32 is a metallized layer.
[0093] FIG. 18 is an enlarged view of the region near the hollow 31
shown in FIG. 17. The joining portion 6B comprises main phase 14B
contacting the metal member 7 and an intermediate ceramic
composition layer 13B contacting the discharge tube 1. The
metallized layer 32 covers the inner wall surface 1b of the end
portion 1a of the discharge tube 1, further covers the surface of
the hollow 31, contacts the edge of the end portion 7a of the metal
member 7 and extends to the edge of the joining portion 6B.
[0094] The embodiment of FIG. 19 have no protrusion on the inner
wall surface 1b of the end portion 1a of the discharge tube 1 and
the inner wall surface 1b extends substantially straightforwardly.
The inner wall surface 1b of the end portion 1a and the metal
member 7 are joined with each other substantially along the full
length of an opening 40 of the end portion 1a. 6C is a joining
portion, 13C is an intermediate ceramic composition layer and 14C
is main phase.
[0095] In each embodiment described above, the inventive joining
portion is provided between the outer surface of the metal member
and the inner wall surface of the end portion of the ceramic
discharge tube or the sealing member. In the other words, the above
inventive joining portions do not seal the opening in the end
portion of the ceramic discharge tube or through hole of the
sealing member. However, the inventive joining portion has high
resistance to corrosion and therefore may seal the opening of the
ceramic discharge tube by itself, by contacting the intermediate
ceramic composition layer with the inner wall surface, facing the
opening, and by sealing it with the intermediate ceramic
composition layer and the main phase with preserved air-tightness.
Alternatively, the intermediate ceramic composition layer may be
contacted with the inner wall surface, facing the through hole of
the sealing member, to seal the through hole by this intermediate
ceramic composition layer and the main phase with preserved
air-tightness. In these cases, the metal member is joined to the
main phase without passing through the joining portion. FIGS. 20
and 21 relate to such embodiments.
[0096] In the embodiment of FIG. 20, a first sealing member 37 is
inserted within an inner surface 38b near an end face 38c of the
ceramic discharge tube 38 of a high pressure discharge lamp. An
outer surface 38a of the discharge tube 38 extends
straightforwardly in its longitudinal direction. The thickness of
the discharge tube 38 is substantially uniform. A second
cylindrical sealing member 39 is inserted within the interior of
the first sealing member 37. The sealing members 37 and 39 are made
of a ceramic or cermet, same as the sealing members described
above. The inventive joining portion 6D is formed within the second
sealing member 39.
[0097] When forming the joining portion 6D, a porous bone structure
is inserted within the sealing member 39. Preferably, a metal
member 35 and a metal axis 27, made of molybdenum, is joined to the
bone structure in advance. When the outer diameter of the porous
bone structure and the inner diameter of the inner wall surface 39a
of the sealing member 39 is strictly adjusted to the same value, it
might be impossible to insert the bone structure due to the
dimension clearance. Preferably, a clearance of 0.05 to 0.10 mm is
provided. When inserting the porous bone structure and melting a
ceramic material on the bone structure, the ceramic is impregnated
into the porous bone structure to form main phase 14D and an
intermediate ceramic composition layer 13D is formed in the
clearance of the bone structure and sealing member 39.
[0098] Consequently, the through hole 46 of the sealing member 39
is substantially sealed by the main phase 14D and the intermediate
ceramic composition layer 13D is formed within the clearance
between the main phase 14D and the inner wall surface 39a of the
sealing member 39. The axis 27 is joined onto the surface, facing
the inner space 17, of the main phase 14D and a metal member 35 is
joined to the outer surface of the main phase 14D. A ceramic
composition layer 45 is further formed within the clearance between
the metal member 35 and sealing member 39.
[0099] In the embodiment shown in FIG. 21, as shown in FIG. 20, the
inventive joining portion 6E is formed within an opening 40 of the
end portion 1a of the discharge tube 1.
[0100] When forming the joining portion 6E, a porous bone structure
is inserted into the inner opening 40 of the end portion 1a of the
discharge tube 1. A metal member 35 and a metal axis 27 are joined
to the bone structure in advance. A clearance, preferably of 0.05
to 0.10 mm, is provided between the outer surface of the bone
structure and the inner surface 1b of the discharge tube 1. When
inserting the porous bone structure and melting the ceramic
material on the bone structure, the melted ceramic is impregnated
into the porous bone structure to form main phase 14E and an
intermediate glass layer 13E is formed in the clearance between the
main phase 14E and the discharge tube 1.
[0101] The relation among the clearance between the outer surface
of the bone structure and the inner surface of the discharge tube,
the insertion of the electrode system (easiness to insert), and the
fullness of ceramic composition into the bone structure shows as
follows.
4 TABLE 3 evaluation item insertion fullness of ceramic clearance
(mm) (easiness to insert) composition in porous bone 0.03 .DELTA.
.circleincircle. 0.05 .largecircle. .circleincircle. 0.08
.circleincircle. .circleincircle. 0.10 .circleincircle.
.largecircle. 0.12 .circleincircle. .DELTA. .circleincircle.:
excellent .largecircle.: good .DELTA.: average
[0102] If the clearance is 0.03 mm, the outer surface of the bone
structure makes contacts with the inner surface of the discharge
tube and thus the bone structure may be damaged when the electrode
system inclines to the insertion direction of thereof. On the other
hand, if the clearance is 0.12 mm, the ceramics composition is not
filled into the bone structure and thus the ceramics composition
may flow downward.
[0103] Next, the most preferred process for producing high pressure
discharge lamps according to embodiments of the invention will be
described. When using a sealing member, powdery raw material
(preferably alumina powder) of the sealing member is shaped into a
shaped body, with a shape of a ring, of the sealing member. At this
stage, it is preferred to press-mold granules, granulated with a
spray drier or the like, under a pressure of 2000 to 3000
kgf/cm.sup.2. The resulting shaped body may preferably be subjected
to dewaxing and calcination to obtain a calcined body, which is
then finish-sintered at a temperature between 1600 to 1900.degree.
C. under reducing atmosphere of a dew point of -15 to 15.degree.
C.
[0104] The dewaxing process may preferably be carried out at a
temperature of 600 to 800.degree. C. and the calcination process
may preferably be carried out at a temperature of 1200 to
1400.degree. C. under reducing atmosphere of hydrogen. The
calcination may provide a some degree of strength to the shaped
body of the sealing member and facilitate the handling of the
sealing member. A hollow may be formed, for example by
machining.
[0105] Also, metal powder is formulated, crashed, dried, and milled
with an added binder, such as ethyl cellulose, acrylic resin or the
like, to obtain paste, which is then applied onto the outer surface
of the end portion of the metal member and dried at a temperature
of 20 to 60.degree. C. The resulting calcined body is sintered
under reducing or inert atmosphere or vacuum of a dew point of 20
to 50.degree. C. at a temperature of 1200 to 1700.degree. C.
[0106] Also, a main body of a ceramic discharge tube is shaped,
dewaxed and calcined to obtain a calcined body of the ceramic
discharge tube. A pre-sintered body of the sealing member is
inserted into the end portion of the resulting calcined body, set
at a predetermined position and finish-sintered under reducing
atmosphere of a dew point of -15 to 15.degree. C. at a temperature
of 1600 to 1900.degree. C. to obtain a ceramic discharge tube.
[0107] Also, powder or frit is pre-formulated to a predetermined
ceramic composition, crashed, granulated with an added binder such
as polyvinylalcohol or the like, press-molded and dewaxed to obtain
molding material. Alternatively, powder or frit for a ceramic is
melted and solidified to obtain solid, which is then crashed,
granulated with added binder, press-molded and dewaxed. In this
case, it is preferred to add 3 to 5 weight percent of a binder to
the powder, to press-mold at a pressure of 1 to 5 ton, to dewax at
about 700.degree. C. and to calcine at a temperature of 1000 to
1200.degree. C.
[0108] Such discharge tube, sealing member, metal member, porous
bone structure and molding material are assembled as shown in FIG.
1 and heated to a temperature of 1000 to 1600.degree. C. under
non-oxidizing atmosphere.
[0109] The ceramic discharge lamp as described referring to FIGS. 1
to 7 was produced according to the above process. The ceramic
discharge tube and sealing member was made of alumina ceramic, and
a pipe made of molybdenum is used as the metal member. Molybdenum
powder with an average particle diameter of 3 .mu.m was used as the
porous bone structure, and ethyl cellulose is used as a binder. The
molybdenum powder had a tap density of 2.9 g/cc. The composition of
the impregnated ceramic phase and the intermediate ceramic layer
were dysprosium oxide 20 weight percent, lanthanum oxide 17 weight
percent, alumina 35 weight percent, yttrium oxide 20 weight percent
and silica 8 weight percent. In the resulting joined layer,
crystallinity of the ceramic constituting thereof was 80
percent.
[0110] The ceramic discharge tube was subjected to a thermal cycle
test. Particularly, in one cycle, its temperature is maintained at
a room temperature for 15 minutes, increased to 1050.degree. C.,
maintained at 1050.degree. C. for 5 minutes and decreased to a room
temperature. 1000 thermal cycles were performed. After that, helium
leak test was performed to investigate the leakage of helium. The
leak rate was lower than 10.sup.-10
atm.multidot.cc.multidot.sec.
[0111] 850.degree. C. is a temperature normally utilized and
1050.degree. C. is an overloaded temperature. The resistance to the
latter means that the discharge tube may safely preserve a starter
gas and an ionizable light-emitting substance therein for a longer
period of time, even when the gas and substance is introduced into
the discharge tube under a pressure higher than a normal value.
[0112] Besides, FIGS. 4 and 5 are photographs, taken by a scanning
type electron microscope, showing the region near the interface
between the inner surface of a metal member 7 and a sealing member
4 of this embodiment.
[0113] Also another high pressure discharge lamp was produced
according to the above process. However, the composition of the
ceramic was dysprosium oxide 47 weight percent, alumina 48 weight
percent, yttrium oxide 1 weight percent and silica 4 weight
percent. In the resulting joined layer, crystallinity of the
ceramic constituting impregnated ceramic phase and the intermediate
ceramic layer was 90 percent.
[0114] The ceramic discharge tube was subjected to a thermal cycle
test. Particularly, in one cycle, its temperature is maintained at
a room temperature for 15 minutes, increased to 1050.degree. C.,
maintained at 1050.degree. C. for 5 minutes and decreased to a room
temperature. 1000 thermal cycles were performed. After that, helium
leak test was performed to investigate the leakage of helium. The
leak rate was lower than 10.sup.-10
atm.multidot.cc.multidot.sec.
[0115] When a sealing member is not applied in a high pressure
discharge lamp, a main body of a ceramic discharge tube is shaped
to obtain a shaped body, which is then dewaxed, calcined and
finish-sintered. Also, paste of metal powder is produced as
described above, applied or printed onto the surface of a metal
member and subjected to heat treatment to form a porous bone
structure. After the discharge tube and metal member are assembled
and the above described material is set, they are heat-treated as
described above to obtain a high pressure discharge lamp.
[0116] The inventive joined body and joining method may be widely
applied to, other than a high pressure discharge lamp, all the
structural bodies, such as a switching device of vacuum, having a
conductive portion or terminal whose air-tightness at a high
temperature of about 900.degree. C. is indispensable.
[0117] The present invention has been explained referring to the
preferred embodiments, however, the present invention is not
limited to the illustrated embodiments which are given by way of
examples only, and may be carried out in various modes without
departing from the scope of the invention . Recently, it is the
worldwide requirement to use high pressure Xe gas instead of
mercury in the high pressure discharge lamp. According to the
strength at the elevated temperature achieved by the high pressure
discharge lamp of the present invention, it is possible to endure
the rising of the internal pressure occurred at the ignition of the
high pressure discharge lamp which does not contain the mercury. As
a result, the high pressure discharge lamp according to the present
invention can be applied to not only a lamp for general lighting
but also a head lamp for vehicle.
* * * * *