Site News  |   Monitor Keywords  |   Monitor Archive  |   Organizer  |   Account Info  |

Oxide-dispersion strengthened platinum material

Oxide-dispersion strengthened platinum material description/claims

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.

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.

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.

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.

[Patent Document 1:] Japanese Patent Application Laid-Open No. 2002-12926

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.

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° 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.

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.

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.

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.

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.

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.

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.

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.

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.

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° 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.

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° 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° C. or higher; and quantifying the amount of oxygen in the latter oxygen peak.

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.

From such a viewpoint, a platinum material according to the present invention preferably has an average diameter of dispersed particles of 0.2 μm or smaller, and an average value of distances between the particles of 0.01 to 2.7 μm. The reason why the average particle diameter of the dispersed particle is set to be 0.2 μm or smaller is that the platinum material needs to disperse particles as fine as 0.2 μm 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.

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.

• Provisional Patent
• Utility Patent

• What Is a Patent?
• What Is a Trademark or Servicemark?
• What Is a Copyright?
• Patent Laws