U.S. patent application number 10/583827 was filed with the patent office on 2009-02-19 for oxide-dispersion strengthened platinum material.
Invention is credited to Hideo Segawa, Toru Shoji, Seiji Takeishi, Seiichiro Tanaka.
Application Number | 20090047170 10/583827 |
Document ID | / |
Family ID | 36148290 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090047170 |
Kind Code |
A1 |
Shoji; Toru ; et
al. |
February 19, 2009 |
Oxide-Dispersion Strengthened Platinum Material
Abstract
The present invention provides an oxide-dispersion-strengthened
platinum material in which dispersed particles made from a metallic
oxide of an additive metal are dispersed in a matrix made from
platinum or a platinum alloy, characterized in that the
concentration of oxygen in the material except oxygen bound to the
additive metal is 100 ppm or lower. The platinum material according
to the present invention has preferably an average diameter of the
dispersed particles of 0.2 .mu.m or smaller, and an average
interparticle distance of 0.01 to 2.7 .mu.m. The platinum material
also preferably has the concentration of the dispersed particles in
an amount of 0.01 to 0.5 wt %, and an oxidation rate of the
additive metal of 50 to 100%.
Inventors: |
Shoji; Toru; (Kanagawa,
JP) ; Tanaka; Seiichiro; (Tokyo, JP) ;
Takeishi; Seiji; (Kanagawa, JP) ; Segawa; Hideo;
(Kanagawa, JP) |
Correspondence
Address: |
ROBERTS & ROBERTS, LLP;ATTORNEYS AT LAW
P.O. BOX 484
PRINCETON
NJ
08542-0484
US
|
Family ID: |
36148290 |
Appl. No.: |
10/583827 |
Filed: |
October 6, 2005 |
PCT Filed: |
October 6, 2005 |
PCT NO: |
PCT/JP05/18519 |
371 Date: |
June 19, 2006 |
Current U.S.
Class: |
420/466 |
Current CPC
Class: |
B22F 1/0088 20130101;
B22F 2998/10 20130101; B22F 2999/00 20130101; B22F 2999/00
20130101; B22F 2201/05 20130101; B22F 3/18 20130101; B22F 3/10
20130101; B22F 9/082 20130101; B22F 3/17 20130101; B22F 3/18
20130101; B22F 3/02 20130101; B22F 9/04 20130101; B22F 2201/11
20130101; B22F 1/0088 20130101; B22F 3/24 20130101; B22F 9/04
20130101; B22F 9/082 20130101; C22C 5/04 20130101; C22C 32/0021
20130101; B22F 2998/10 20130101; C22C 1/1084 20130101; B22F 2999/00
20130101 |
Class at
Publication: |
420/466 |
International
Class: |
C22C 5/04 20060101
C22C005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2004 |
JP |
2004-295598 |
Claims
1. An oxide-dispersion-strengthened platinum material which
comprises dispersed particles made from a metallic oxide of an
additive metal are dispersed in a matrix made from platinum or a
platinum alloy, wherein a concentration of oxygen in the material
except oxygen bound to the additive metal is 100 ppm or lower.
2. The oxide-dispersion-strengthened platinum material according to
claim 1, wherein an average diameter of the dispersed particles is
0.2 .mu.m or smaller, an average value of distances between the
particles is 0.01 to 2.7 .mu.m, and the concentration of the
dispersed particles in the matrix is 0.01 to 0.5 wt %.
3. The oxide-dispersion-strengthened platinum material according to
claim 1, wherein the oxidation rate of the additive metal is 50 to
100%.
4. The oxide-dispersion-strengthened platinum material according to
claim 1, wherein the additive metal is any of zirconium, calcium,
yttrium and samarium.
5. The oxide-dispersion-strengthened platinum material according to
claim 1, wherein the matrix is any of a platinum-rhodium alloy, a
platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
6. The oxide-dispersion-strengthened platinum material according to
claim 2, wherein the oxidation rate of the additive metal is 50 to
100%.
7. The oxide-dispersion-strengthened platinum material according to
claim 2, wherein the additive metal is any of zirconium, calcium,
yttrium and samarium.
8. The oxide-dispersion-strengthened platinum material according to
claim 3, wherein the additive metal is any of zirconium, calcium,
yttrium and samarium.
9. The oxide-dispersion-strengthened platinum material according to
claim 6, wherein the additive metal is any of zirconium, calcium,
yttrium and samarium.
10. The oxide-dispersion-strengthened platinum material according
to claim 2, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
11. The oxide-dispersion-strengthened platinum material according
to claim 3, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
12. The oxide-dispersion-strengthened platinum material according
to claim 4, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
13. The oxide-dispersion-strengthened platinum material according
to claim 6, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
14. The oxide-dispersion-strengthened platinum material according
to claim 7, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
15. The oxide-dispersion-strengthened platinum material according
to claim 8, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
16. The oxide-dispersion-strengthened platinum material according
to claim 9, wherein the matrix is any of a platinum-rhodium alloy,
a platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
17. The oxide-dispersion-strengthened platinum material according
to claim 1 wherein an average diameter of the dispersed particles
is 0.2 .mu.m or smaller, an average value of distances between the
particles is 0.01 to 2.7 .mu.m, the concentration of the dispersed
particles in the matrix is 0.01 to 0.5 wt %; wherein the oxidation
rate of the additive metal is 50 to 100%; wherein the additive
metal is any of zirconium, calcium, yttrium and samarium; and
wherein the matrix is any of a platinum-rhodium alloy, a
platinum-gold alloy, a platinum-rhodium-gold alloy and a
platinum-iridium alloy.
Description
TECHNICAL FIELD
[0001] The present invention relates to an
oxide-dispersion-strengthened platinum material in which oxides are
dispersed in platinum or a platinum alloy, and particularly which
can keep strength at high temperature for a long period, and has
adequate weldability.
BACKGROUND ART
[0002] An oxide-dispersed platinum material in which metal oxides
such as zirconium oxide (zirconia) are finely dispersed in platinum
or platinum alloy has superior high-temperature strength
characteristics, particularly, creep strength, and accordingly has
been used for a structural material in a glass production apparatus
which is used in an environment.
[0003] As a method for producing the oxide-dispersed platinum
material, a powder metallurgy process has been generally employed.
In the method, a platinum material is produced by preparing an
alloy powder of platinum and zirconium, subjecting the alloy powder
to oxidation treatment to internally oxidize zirconium in the alloy
powder into zirconium oxide, thereby preparing a platinum powder in
which zirconium oxides are finely dispersed, sintering it, and
working it.
[0004] In addition, the present applicant has variously improved an
oxide-dispersed platinum material in order to further increase
high-temperature strength, and for instance, has disclosed the
oxide-dispersed platinum material that makes the grain size of
crystals and the aspect ratio of crystals in platinum or a platinum
alloy optimized, which is a matrix, in addition to making dispersed
particles finely dispersed. The platinum material is produced by
the steps of: employing a mixture solution of a platinum suspended
solution and a zirconium nitrate solution as a raw material;
subjecting it to predetermined treatment to produce a platinum
powder carrying zirconium hydroxide therein; compacting the
platinum powder; and then heating it and working it to make
dispersed particles comprising zirconium oxide, and at the same
time to adjust grain sizes of crystals of a matrix.
[0005] [Patent Document 1:] Japanese Patent Application Laid-Open
No. 2002-12926
[0006] As described above, an oxide-dispersed platinum material
improves the high-temperature strength (creep strength) of the
platinum material, and has a remarkable effect in this respect.
However, the present inventors have been elucidated that these
oxide-dispersed platinum materials have some points to be improved,
though they are extremely excellent in terms of strength.
[0007] At first, stability when used in a high-temperature
environment for a long period is pointed out as an improvement of
an oxide-dispersed platinum material. In a glass-making apparatus
using the platinum material, the atmospheric temperature
occasionally reaches 1,500.degree. C. or higher. The present
inventors recognize that the oxide-dispersed platinum material may
cause a void (cavity) or a blister (swelling) in the material, when
exposed to such a high temperature for a long period. The problem
of the blister tends to occur more often particularly in a material
of a thin sheet. The void existing in the material can be a factor
of decreasing the strength of the whole material.
[0008] In addition, an oxide-dispersed platinum material needs
improvement in weldability as well. A glass-melting tank and the
like are manufactured with the use of a welding technique, and the
oxide-dispersed platinum material has a comparatively high
possibility of causing a weld defect such as a blow hole in a
junction after having been welded. The weld defect leads to a
rupture of an apparatus if having been overlooked, and leaves a
problem of yield even if having been discovered by inspection
beforehand.
[0009] For this reason, an object of the present invention is to
provide an oxide-dispersed platinum material which can be stably
used at high temperatures and is superior in weldability as
well.
DISCLOSURE OF THE INVENTION
[0010] The present inventors researched factors affecting the above
described problems, and as a result, focused attention on the
behavior of oxygen in a material, as the factor of producing a
blister at a high temperature and a blow hole in welding.
[0011] Oxygen is an element which constitutes a dispersed particle
and the constituent element indispensable for an oxide-dispersed
alloy. However, an amount of oxygen in an oxide-dispersed platinum
material generally exceeds the amount necessary to compose the
dispersed particle, so that oxygen which is not bound to an
additive metal exists in the material in an atomic form or a
molecular form. The reason is considered to be because the material
essentially needs to pass a step of treatment in high-temperature
air in a production process, and in the step, excessive oxygen can
be possibly introduced into the material.
[0012] Then, oxygen in an atomic form or a molecular form, which is
not bound to an additive metal, diffuses and aggregates in a
material into gaseous oxygen in a high-temperature environment and
forms a void and a blister. In addition, the oxygen in the atomic
form and the molecular form expands its volume when a material is
melt during welding, and becomes a blow hole which is likely to
remain in the material.
[0013] The present inventors researched a proper range of oxygen
concentration in an oxide-dispersed platinum material on the basis
of the above described discussion, and conceived the present
invention.
[0014] Specifically, the present invention provides an
oxide-dispersion-strengthened platinum material in which dispersed
particles made from a metallic oxide of an additive metal are
dispersed in a matrix made from platinum or a platinum alloy,
characterized in that the concentration of oxygen in the material
except oxygen bound to the additive metal is 100 ppm or lower.
[0015] The reason why the concentration of oxygen which does not
constitute a dispersed particle (hereafter referred to as the
concentration of excessive oxygen occasionally) is set to be 100
ppm or lower in the present invention is that when oxygen of more
than 100 ppm exists in a matrix, it is remarkably converted into
gaseous oxygen at a high temperature or while a material melts, and
tends to produce a blister or a blow hole. The oxygen concentration
is more preferably 50 ppm or lower, and the closer is the oxygen
concentration to 0 ppm, the better is the performance. For
information, the concentration of excessive oxygen in an
oxide-dispersed platinum material conventionally on the market is
150 ppm or higher.
[0016] Here, as for a method of calculating the concentration of
excessive oxygen, it can be calculated by determining a difference
between the oxygen concentration in the whole platinum material and
a product of the oxygen concentration theoretically determined by
the concentration of an additive metal multiplied by the oxidation
rate of the additive metal described below. The concentration of
oxygen in the whole platinum material can be measured by heating
the platinum material to a temperature of about 3,000.degree. C. in
a carbon crucible by passing an electric current through the
platinum material to melt it, and analyzing the quantity of carbon
dioxide gas generated therefrom by oxygen concentration analysis
for quantitative analysis or by device analysis such as GD-MS.
[0017] The concentration of excessive oxygen can be also calculated
by subtracting the concentration of oxygen bound to an additive
metal from the concentration of oxygen in the whole platinum
material. Here, the concentration of oxygen bound to the additive
metal can be calculated by the steps of: slowly heating the
platinum material to about 3,000.degree. C., when analyzing the
concentration of oxygen in the above described whole platinum
material; detecting an amount of generated oxygen at each
temperature on the way; distinguishing a peak detected in the
vicinity of the melting point of platinum from the peak of oxygen
derived from an oxide of an additive metal, which is detected at
2,500.degree. C. or higher; and quantifying the amount of oxygen in
the latter oxygen peak.
[0018] In the meantime, it is the most effective means in the
present invention to regulate the concentration of oxygen in a
platinum material, however according to the present inventors, in
addition to this, it is also effective means to specify a condition
of dispersed particles. A strengthening mechanism in a
particle-dispersed alloy is not affected by an amount (volume
fraction) of the dispersed particles, but affected by the fineness
of the dispersed particles even though the amount of them are very
small. As described in the above described Patent Document 1,
particularly, the strength of a particle-dispersed platinum
material increases with the increase of an aspect ratio of a
crystal grain, and the aspect ratio is affected by an average value
of distances among the dispersed particles. Specifically, in order
to secure weldability while making the strengthening mechanism
sufficiently developed in the particle-dispersed alloy, it is
preferable to make fine dispersed particles uniformly dispersed
into a highly dispersed condition.
[0019] From such a viewpoint, a platinum material according to the
present invention preferably has an average diameter of dispersed
particles of 0.2 .mu.m or smaller, and an average value of
distances between the particles of 0.01 to 2.7 .mu.m. The reason
why the average particle diameter of the dispersed particle is set
to be 0.2 .mu.m or smaller is that the platinum material needs to
disperse particles as fine as 0.2 .mu.m or smaller for sufficiently
strengthening itself, while considering the particle diameter of
the manufacturable dispersed particles. Furthermore, the reason why
a range of the average value of distances among the particles is
set is to improve an aspect ratio of the crystal grains in a
platinum matrix and secure an effect of improving strength.
[0020] On the other hand, the platinum material preferably contains
dispersed particles in an amount (concentration) of 0.01 to 0.5 wt
%. The amount of the dispersed particles does not affect the
weldability of an alloy, but has the minimum value for developing
an effect of improving strength due to dispersed particles; and
affects workability (deep drawability and ductility) of the alloy.
The reason why the concentration of the dispersed particles is set
to be 0.01 to 0.5 wt % in the present invention is that the minimum
required concentration for making dispersed particles show the
effect of increasing strength is 0.01 wt %; and that an amount of
more than 0.5 wt % is unfavorable from the perspective of
preventing aggravation of the workability. Here, when the alloy is
used in the application which does not require much deep
drawability and ductility such as in the case of working to make a
bushing base plate or the like, the concentration of the dispersed
particles is preferably in the above described range, and may be
0.3 wt % and 0.4 wt % as long as it is in the range. On the other
hand, when the alloy is used in the application which requires the
deep drawability and the ductility such as in the case of working a
large-sized platinum apparatus, the concentration of the dispersed
particles is preferably 0.01 to 0.14 wt % so as to further enhance
the workability, and thus an upper limit value is preferably
further reduced.
[0021] In addition, when a dispersed state and the amount of
dispersed particles is in the above described range, all the
additive metals in a platinum material do not always need to be in
a state of oxide. For instance, as described above, there is a
method for producing the particle-dispersed platinum material by
oxidizing a platinum alloy powder to oxidize the additive metal and
form the dispersed particle, and in this case, not all the additive
metals need to be converted into the oxide in the oxidizing
treatment, but a necessary amount of the dispersed particles has
only to be finely dispersed.
[0022] Then, an oxidation rate of an additive metal is preferably
50 to 100%. The oxidation rate indicates a ratio of an atomic
number (mole number) of the additive metal which has been converted
into an oxide, with respect to the atomic number (mole number) of
the additive metal in a platinum material. The reason why the
oxidation rate is set to be 50 to 100% is that when the
strengthened platinum material is used at high temperature, oxygen
in the atmosphere diffuses into the platinum material, which
promotes so-called internal oxidation. The diffusion of oxygen in
this case occurs preferentially in a crystal grain boundary, and
the additive metal diffuses and precipitates in the crystal grain
boundary into which oxygen preferentially diffuses. The reason why
the lower limit of the oxidation rate is necessary to be set at 50%
is that when a large amount of the additive metal precipitates in
the crystal grain boundary in the above step, the material is
embrittled. The oxidation rate can be calculated in the formula of
(amount of additive metal having formed oxide)/(amount of additive
metal).times.100. The amount of the additive metal having formed
the oxide can be determined by dissolving a platinum material in
aqua regia or a solution of hydrochloric acid and chlorine,
separating a residue by filtrating the solution, weighing the
residue, and measuring the amount of the additive metal oxide.
[0023] In an oxide-dispersed platinum material according to the
present invention, a preferred additive metal includes calcium,
yttrium and samarium in addition to zirconium. The oxides of these
metals stably exist in the platinum material, and can develop an
effect of improving the strength when dispersed in the material as
a particle.
[0024] In addition, the matrix may be a platinum alloy in addition
to (pure) platinum. A preferred platinum alloy includes a
platinum-rhodium alloy, a platinum-gold alloy, a
platinum-rhodium-gold alloy and a platinum-iridium alloy.
[0025] In the next place, a method for producing a platinum
material according to the present invention will be described. The
oxide-dispersed platinum material according to the present
invention basically has a feature of limiting the concentration of
oxygen contained in the material, so that a conventional production
method can be adapted for producing it as long as it can reduce
oxygen concentration. Specifically, for instance, the method of
internally oxidizing a platinum alloy powder, and compacting and
solidifying it makes excessive oxygen not to enter into the
material by adjusting an internal oxidation condition. In addition,
as the method according to Patent Document 1, the method of
compacting and solidifying a platinum powder carrying the hydroxide
of an additive metal therein and heat-treating it to form a
dispersed particle also makes excessive oxygen not to enter into
the material, by controlling the heat treatment condition.
[0026] However, even though the method of adjusting these
conditions of internal oxidation treatment and heat treatment is
employed, there may be cases where it is difficult to definitely
set the conditions. In addition, the internal oxidation treatment
and the heat treatment need to be carried out at high temperatures,
then are feared growing the oxide because of being carried out in a
high-temperature atmosphere, and accordingly hardly make formed
dispersed particles into an ideally dispersed state.
[0027] For this reason, the present inventors concluded that a
comparatively low temperature process is preferable for producing
an oxide-dispersed platinum material according to the present
invention, and found a specific method of stirring a platinum alloy
powder or an alloyed wire material (hereafter may be abbreviated
merely as powder occasionally) in water accommodated in a
high-energy dispersion mill such as an attritor, and oxidizing an
additive metal in the alloy with the water (oxygen of constituting
water).
[0028] In this process, a powder which has been stirred in a
high-energy dispersion mill is repeatedly pulverized, compressed
and agglutinated through receiving a high-energy impact. In the
process, the powder exposes a new surface when being pulverized,
and the new surface is active and in a state to be easily oxidized.
Accordingly, when water is arranged as an atmosphere around the
alloy of being stirred, the exposed new surface of an alloy is
oxidized by the water; and the oxidation reaction in the
high-energy dispersion mill can proceed even not at high
temperatures. Accordingly, the method hardly causes a problem of
grain growth because it can oxidize the alloy even at ordinary
temperatures, and can disperse oxide particles into an ideal
state.
[0029] The production method begins by producing an alloy powder or
an alloyed wire material consisting of platinum and an additive
metal. A preferred method for producing the alloy powder includes
an atomization method (gas atomization or water atomization) using
a molten alloy with a predetermined composition as a raw material.
This is because the atomization method can easily adjust a melting
atmosphere and provide a preferable powder while preventing the
oxidation of the additive metal. The alloy powder to be produced
here preferably has a particle diameter of 300 .mu.m or smaller.
This is because when the alloy powder with a particle diameter of
larger than 300 .mu.m is employed, it takes a long period to
subsequently treat the alloy powder in a high-energy dispersion
mill. When an alloyed wire material is employed, it is manufactured
by subjecting a melt and cast alloy block to wire drawing, drawing
or the like. At this time, it may be appropriately cut so as to be
introduced into a device.
[0030] After an alloy powder has been produced, the alloy powder is
introduced into a high-energy ball mill together with water, and is
stirred to oxidize an additive metal in the alloy powder. The
high-energy ball mill is a device having a vessel filled with steel
balls or ceramic balls of pulverizing media and having a stirring
blade further arranged therein, and includes, for instance, a Dynor
mill and an Ultra Visco mill in addition to an attritor, as a well
known device.
[0031] It is necessary to select a component material of a
high-energy ball mill while considering contamination originating
from the component material of a device during high-energy
stirring. In the present invention, a preferred material is
ceramic, and particularly zirconia. This is because the component
material hardly contaminates the powder, and gives the least
influence to material properties even when having contaminated the
powder. In addition, a pulverizing medium preferably has a diameter
of 1 to 10 mm. This is because, when the pulverizing medium has a
smaller diameter than 1 mm, the device needs to rotate a stirring
blade at high speed in order to compensate for decrease in a
pulverizing power, and has difficulty in separating the powder and
the pulverizing medium after having finished oxidation treatment.
In addition, that is because, when the pulverizing medium has a
larger diameter than 10 mm, a torque necessary for rotation
excessively increases, which further easily damages a vessel and a
stirring blade. It is preferable to set an amount of the filled
pulverizing medium at 50% of a vessel capacity as a measure, but
the amount hardly causes a detrimental effect unless excessively
exceeding the value.
[0032] Water to be introduced into a high-energy ball mill together
with an alloy is preferably of high purity, and is particularly
preferably ultrapure water. This is because when impurities are
contained in water being used in oxidation treatment, the
impurities adhere to a powder, consequently are included in an
oxide-dispersed alloy to be produced, cause gas generation while
the alloy containing the impurities is used at a high temperature,
and are feared causing strength degradation. In addition, it is
preferable to charge water in such a level as to immerse the powder
thereunder. This is because a new active surface formed by
high-energy stirring in an attritor can be reliably contacted with
water. An atmospheric gas in a vessel may be air, but is preferably
oxygen. This is because a material is prevented from containing
nitrogen in the air.
[0033] In addition, in this method, an additive metal is oxidized
by stirring in a high-energy ball mill, but it is also acceptable
to subsequently further oxidize the alloy powder by heating it in
an oxidative atmosphere, as long as the final concentration of
excessive oxygen is controlled to 100 ppm or less. The heating step
is carried out so as to additionally oxidize the additive metal
through the subsequent heat treatment and increase an amount of the
oxide, when not all of the additive metals in the alloy powder were
oxidized (when an oxidation rate was less than 100%) in the
oxidation treatment in the high-energy ball mill. However, even
when the additive metal is partially oxidized in the high-energy
ball mill, the oxidation treatment by heating is not always
necessary, because the alloy can reliably acquire strength as long
as the required amount of dispersed particles is achieved. In
addition, when the additional oxidation treatment is employed, it
is preferable to set an oxygen pressure at a high pressure of about
7 to 9 atmospheres and heat the alloy powder in a range of a
temperature of 700 to 900.degree. C., because the dispersed
particle may be coarsened by the additional oxidation
treatment.
[0034] In addition, when the powder has been treated in a
high-energy ball mill for a long period, the powder shows a
phenomenon that oxygen dissolves into platinum, but then, the
excessive oxygen can be discharged by heat-treating the powder in
an atmosphere with a reduced pressure and in a range of a
temperature of 700 to 900.degree. C.
[0035] An alloy powder which has been oxidized in the high-energy
ball mill as was described above can be formed into a block alloy
through compact solidification treatment. The compact
solidification treatment is preferably carried out by such a method
of sintering the alloy powder while pressurizing it, as in a hot
press. It is preferable to set conditions in the hot press at a
temperature of 700 to 1,300.degree. C., and a press pressure of 10
MPa or higher. It is also preferable to set an atmosphere of the
hot press to a vacuum atmosphere in order to prevent the oxidation
of the alloy. In addition, it is preferable to preliminarily and
tentatively sinter the alloy powder before compact solidification
treatment.
[0036] An alloy after having been compacted and solidified can
acquire an improved denseness by a forging process. The alloy also
can be subjected to plastic working such as rolling, extruding and
drawing to be formed into a predetermined shape, and heat treatment
may be performed prior to these plastic workings. In a rolling
step, a reduction ratio for a material is important in order to
increase an aspect ratio of a structure, and thus can change the
existence density of dispersed particles of an oxide in a rolling
direction and a sheet thickness direction. Specifically, when the
alloy is rolled, a distance between the dispersed particles of the
oxide decreases in the sheet thickness direction of the material,
whereas the distance increases in the rolling direction. In
addition, when the material is subjected to heat treatment after
having been rolled, it easily forms recrystallized grains having
the shape which extends in the rolling direction through growth and
has a high aspect ratio. The reduction ratio is preferably 70% or
higher, and the higher is the reduction ratio, the higher aspect
ratio acquires the obtained structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is an SEM image of a platinum-zirconia alloy powder
produced by an atomization method in the first embodiment;
[0038] FIG. 2 is an SEM image of an alloy powder after having been
treated in an attritor in the first embodiment;
[0039] FIG. 3 is an SEM image of a wire rod after having been
treated for two hours in an attritor in the third embodiment;
[0040] FIG. 4 is an SEM image of a wire rod after having been
treated for 30 hours in an attritor in the third embodiment;
and
[0041] FIG. 5 is a photograph showing a condition of blow holes in
a comparative example after having been welded.
BEST MODE FOR CARRYING OUT THE INVENTION
[0042] In the next place, a preferred embodiment according to the
present invention is described. In the present embodiment, an
oxide-dispersed platinum material was produced in which particles
of zirconium oxide (zirconia) were dispersed in platinum.
[0043] First Embodiment: a platinum-zirconium alloy powder was
produced by preparing a platinum--0.05 wt % zirconium alloy through
vacuum melting, and gas-atomizing the molten metal of the alloy in
argon atmosphere. As for conditions of atomization, an atomization
temperature was controlled to 2,000.degree. C., and a gas pressure
to 40 kPa. Thus obtained alloy powder had a particle diameter of 40
.mu.m. FIG. 1 shows an SEM image of the alloy powder. As is clear
from FIG. 1, the alloy powder produced here was an approximately
spherical powder.
[0044] Subsequently, 1,500 g of an alloy powder was introduced into
an attritor (with dimension: inside diameter of 200
mm.phi..times.height of 185 mm, with material of zirconia, and
consisting of vessel made from zirconia and zirconia-coated
stainless stirring blade). In the above step, 7 kg of zirconia
balls with a diameter of 5 mm and 1.0 L of ultrapure water were
simultaneously introduced. Then, the attritor stirred the alloy
powder at 340 rpm for 11 hours with a mixing impeller to oxidize
the alloy powder. FIG. 2 shows a shape of the alloy powder after
having been treated in the attritor. After a spherical alloy powder
was treated in the attritor, it showed an indefinite shape by
having been changed through the repetition of deformation and
adhesion.
[0045] After having been oxidized, an alloy powder was taken out,
was charged into a die, and was tentatively sintered by being
heated in an atmosphere of 1.5.times.10.sup.-2 Pa at 1,200.degree.
C. for one hour. The sintered alloy had a dimension of 40
mm.times.40 mm.times.135 mm, a density of 7.42 g/cm.sup.3 and a
denseness of 34.6%.
[0046] Then, tentatively-sintered alloy was compacted and
solidified with a hot press. In the above step, a press temperature
was set at 1,200.degree. C. and a press pressure at 20 MPa. In
addition, an atmosphere was controlled to be the vacuum atmosphere
of 1.5.times.10.sup.-2 Pa, and a pressing period of time to be one
hour. As a result of this, an obtained alloy compact had a
dimension of 40.34 mm.times.40.45 mm.times.60.53 mm, a density of
16.23 g/cm.sup.3 and a denseness of 75.6%.
[0047] Then, a compact was hot-forged at a temperature of
1,300.degree. C. in order to further have improved denseness. The
forged alloy had a dimension of 65 mm.times.65 mm.times.18 mm, and
acquired a denseness of about 100%. Finally, three sorts of sheet
materials made from an oxide-dispersed platinum-zirconium alloy was
obtained by the steps of: cold-rolling the alloy into a sheet
thickness of 4 mm; heat-treating it (at 1,250.degree. C..times.30
min) to anneal it; and further cold-rolling it to the sheet
thicknesses of 1.0 mm, 0.8 mm and 0.3 mm.
[0048] An amount of all oxygen in an oxide-dispersed
platinum-zirconium alloy produced in the embodiment was firstly
quantified with an oxygen analyzer. In addition, the amount of
zirconia (amount of additive metal oxide) was quantified by melting
a platinum material in aqua regia, separating a residue by
filtration, and weighing the residue. As a result of having
calculated the concentration of excessive oxygen and an oxidation
rate of a platinum material according to the present embodiment
from the above measured values, the concentration of excessive
oxygen was 0 ppm, and the oxidation rate was 50%. In addition, a
particle diameter and a dispersion state of dispersed particles in
the produced alloy were confirmed by immersing the produced alloy
in aqua regia (at 80.degree. C.) to dissolve platinum, and
observing the dispersed particles. As a result, the particle
diameter of the zirconia particles in the platinum alloy according
to the present embodiment was estimated to be 0.02 .mu.m. In
addition, as a result of having calculated an average value of
distances between particles based on a regular tetrahedron model
(which supposes that dispersed particles are placed on the vertices
of a regular tetrahedron), it was estimated to be 0.19 .mu.m.
[0049] Second Embodiment: a platinum material was prepared by the
steps of: preparing a platinum alloy powder through attritor
treatment as in the case of the first embodiment; further oxidizing
the platinum alloy powder in an oxidizing pot; and compacting and
solidifying the powder in the same conditions as in the first
embodiment. In the above step, the oxidation treatment condition
was set at an oxygen pressure of 9 atmospheres, a temperature of
800.degree. C. and a heating period of time of 10 hours.
[0050] As a result of having calculated an oxidation rate and the
concentration of excessive oxygen in an oxide-dispersed
platinum-zirconium alloy produced according to the present
embodiment as in the case of the first embodiment, the
concentration of excessive oxygen was 95 ppm, and the oxidation
rate was 100%. In addition, as a result of having confirmed a
particle diameter and a dispersion state of dispersed particles in
the produced alloy as in the case of the first embodiment, the
diameter of the zirconia particle was estimated to be 0.02 .mu.m,
and an average value of distances between the particles to be 0.34
.mu.m.
[0051] Third Embodiment: a cut wire rod was prepared by the steps
of: preparing a molten metal of a platinum alloy by vacuum-melting
the alloy as in the case of the first embodiment; casting the
molten metal to obtain an ingot; wire-drawing the ingot into a wire
rod with a diameter of 0.1 mm; and then cutting it into the length
of 3 mm. Then, the cut wire rod was treated in an attritor at 340
rpm for 30 hours. FIG. 3 shows a state of a powder after 2 hours of
attritor treatment, and FIG. 4 shows a state of the powder after 30
hours. The above treated powder was heat-treated in an atmosphere
of 800.degree. C. with a reduced pressure of 1.5.times.10.sup.-2
Pa, for 10 hours. Then, the powder was compacted and solidified
into a platinum material in the same conditions as in the first
embodiment.
[0052] As a result of having calculated an oxidation rate and the
concentration of excessive oxygen of an oxide-dispersed
platinum-zirconium alloy produced according to the present
embodiment as in the case of the first embodiment, the
concentration of excessive oxygen was 60 ppm, and the oxidation
rate was 100%. In addition, as a result of having confirmed a
particle diameter and a dispersed state of dispersed particles in
the produced alloy as in the case of the first embodiment, the
diameter of the zirconia particle was estimated to be 0.02 .mu.m,
and an average value of distances between particles to be 0.34
.mu.m.
[0053] Comparative Example: here, a platinum material was prepared
so as to contain a higher concentration of excessive oxygen than
that of the above described first to third embodiments. The
platinum material was prepared by the steps of: preparing a
platinum alloy powder through attritor treatment as in the case of
the first embodiment; further oxidizing the platinum alloy powder
in an oxidizing pot; and compacting and solidifying the powder in
the same conditions as in the first embodiment. In the above step,
the oxidation treatment condition was set at an oxygen pressure of
9 atmospheres, a temperature of 800.degree. C. and a heating period
of time of 15 hours. As a result of having calculated an oxidation
rate and the concentration of excessive oxygen of an
oxide-dispersed platinum-zirconium alloy produced in the present
comparative example as in the case of the first embodiment, the
concentration of excessive oxygen was 115 ppm, and the oxidation
rate was 100%.
[0054] A platinum material produced in each embodiment and
comparative example described above was subjected to a creep
rupture test, and further to the examinations for confirming
whether a blow hole was produced or not when the material was
welded, and whether a blister was produced or not when the material
was heated at a high temperature. The creep rupture strength was
determined by measuring a period of time before the sheet with the
thickness of 0.8 mm is ruptured after having had been placed in an
atmosphere of 1,400.degree. C. with the applied stress of 20 MPa.
In the welding test, the surface of the sheet with the thickness of
1.0 mm was swept with an automatic welding machine, and the
presence or absence of the blow hole in a melted zone was visually
observed. In addition, in a heating test, the sheet with the
thickness of 0.3 mm was heated to 1,700.degree. C. and held for 3
hours, and then it was examined by visual observation whether a
blister occurred on the surface or not. These examination results
are shown in the following table.
TABLE-US-00001 TABLE 1 Oxi- Presence Concentration dation Creep or
absence Presence of excessive rate of rupture of blow or absence
oxygen Zr time hole of blister First 0 ppm 50% 208 hr None None
Embodiment Second 95 ppm 100% 352 hr None None Embodiment Third 60
ppm 100% 251 hr None None Embodiment Comparative 115 ppm 100% 364
hr A few A few Example
[0055] It is clear from Table 1 that all the platinum materials
produced in the present embodiment exceeded 200 hours in the creep
rupture time. As for the creep rupture time, platinum shows the
creep strength of 1.7 MPa by breaking force when tested at
1,400.degree. C. for 100 hours, and is immediately broken when the
force is 20 MPa. In addition, even currently
commercially-available, conventional strengthened platinum shows
the creep rupture time of about 100 hours when tested at
1,400.degree. C. and 20 MPa. Accordingly, it is clear that the
platinum materials according to the present embodiments are
sufficiently strengthened.
[0056] In addition, the platinum materials according to the present
embodiments showed adequate appearance without forming a blow hole
after having been welded and a blister after having been heated to
a high temperature. On the other hand, the platinum material
according to the comparative example showed the blow hole and the
blister though a few. FIG. 5 shows a state of the blow hole formed
when the comparative example was welded. Such a blow hole and a
blister grow into a void while the material is used at a high
temperature for a long period, and cause the reduction of material
strength.
INDUSTRIAL APPLICABILITY
[0057] As described above, an oxide-dispersed platinum material
according to the present invention does not cause such a phenomenon
of affecting material strength as the formation of a blister, even
when having been used for a long period under a high-temperature
environment, and can be stably used. In addition, the platinum
material has adequate weldability, and can provide a wholesome weld
which does not show a weld defect such as a blow hole.
* * * * *