Metal treatment – Stock – Amorphous – i.e. – glassy
Reexamination Certificate
2002-03-27
2004-06-15
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Amorphous, i.e., glassy
C420S466000
Reexamination Certificate
active
06749698
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS
The present invention relates to a precious metal-based amorphous alloy used as a material for accessories or medical devices. Specifically, the present invention relates to a precious metal-based amorphous alloy rich in precious metal components and free of nickel which may have an influence on the human body.
BACKGROUND ART
Precious metals such as platinum and palladium have been used for medical devices such as dental instruments and catheters in addition to accessories such as rings, necklaces and pendants. Each of the materials used for these applications is required to have a higher hardness because the material needs to be prevented from scoring which is caused by the friction in use. A pure precious metal, which is soft and vulnerable, is generally alloyed with a small amount of other metal elements when the precious metal is used as a material for the accessories and the medical devices. However, thus prepared precious metal alloys do not always have a fully satisfying property in terms of hardness.
A crystal structure of an amorphous alloy which is also referred to as a super-cooled metal or a glass metal is different from that of a general metal material, and this amorphous alloy is a material having a random atomic arrangement throughout the wide range. This structure provides some features that defects which would otherwise exist in its crystal structure (grain boundaries, dislocations) can not be seen, that its physical characteristics such as strength show specific tendencies, and that particularly its hardness becomes extremely high. This amorphous alloy is manufactured by super-quenching the liquid state alloy, so that the cooling rate in this case is required to be at an adequate level for inhibiting the production of crystal nuclei and their growth (a critical cooling rate) (for example, a critical cooling rate for a precious metal alloy is approximately 10
2
to 10
4
° C./sec. and critical cooling rates for other alloys are approximately 10
5
to 10
6
° C./sec.) Such a limitation on the cooling rate has so far resulted in a restriction of a size of the amorphous alloy which can be manufactured, that is, only some types of materials including foil-like, needle-like, and flake-like materials can be manufactured, so that it has been difficult to use these alloys industrially.
However, with respect to an alloy metal having a predetermined composition, it has been recently found out that its material structure can be made into an amorphous state even at a relatively low cooling rate. This results in the manufacture of a bulky (ingot-like) and thick amorphous alloy which is larger than the size of the hitherto known amorphous alloy such as a foil type material. As an alloy composition having such an ability of forming the amorphous state, various kinds of alloys have already been known. And applications of the amorphous alloys to the above described materials for accessories or medical devices, for example, are now under investigation.
As an example of studying an amorphous alloy which contains a precious metal, for example, a Pd—Ni—P based amorphous alloy (in atomic %, Pd 40%, Ni 40%, and P 20%) is described in Japanese Patent Laid-Open No. 59-35417 as one of the transition metal-semi metal based amorphous alloys. Using the precious metal alloy having this composition, it has been demonstrated that the amorphous alloy about 5 mm in thickness can be manufactured even by the metal mold casting. In addition, Japanese Patent Laid-Open No. 9-195017 describes a Pt—Pd—Cu—Si based amorphous alloy (in atomic %, Pt+Pd: 65 to 80%, Cu: 0 to 15%, and Si: 10 to 20%) and discloses that the precious metal alloy having this composition can also be made into a bulk of 100 mm in length and 1 mm in diameter.
However, these conventional amorphous alloys containing the precious metals are insufficient when considering their applications to the materials used for the accessories and the medical devices as described above. For example, the accessory is frequently desired to have an asset value as its aspect, and this asset value is commonly supposed to become greater in proportion to an amount of the precious metal contained in the accessory. Many of the conventional amorphous alloys contain less precious metals, so that in this respect it can hardly be said that these amorphous alloys are suitable for the materials used for the accessories.
In addition, many of the above described conventional precious metal -based amorphous alloys contain nickel as their components, but nickel is an element whose influence on the human body such as an metal allergy and carcinogenesis is worried. Therefore, it can be considered that these conventional amorphous alloys are not favorable to be used for substances which are in contact with the human skin continuously such as accessories and for substances which are in contact with the internal tissue of the human body of the human such as medical devices.
The present invention has developed under the background as described above, and an object of the present invention is to provide an amorphous alloy which is rich in precious metals and is completely free of nickel provided that a bulk having an amorphous structure can be formed even when the alloy is solidified at a relatively low cooling rate.
DISCLOSURE OF THE INVENTION
The inventors have intensively made an effort to develop a precious metal-based amorphous alloy by which the above described problems can be solved. Specifically, the inventors have achieved the present invention as a result of selecting platinum as the precious metal which constitutes a principal component of the alloy, platinum being the most common material for accessories, to allow platinum to be contained at a level of 50% or more of the alloy, as well as selecting Cu and P as additional elements which have the ability to form the amorphous structure, and variously changing the concentrations of theses elements to investigate the respective structures of the alloys.
A first precious metal-based amorphous alloy according to the present application is a precious metal-based amorphous alloy with a Pt—Cu—P based structure comprising 50%≦Pt≦70% by atom, 5%≦Cu≦35% by atom, and 15%≦P≦25% by atom.
A second precious metal-based amorphous alloy according to the present application is a precious metal-based amorphous alloy with a Pt—Pd—Cu—P based structure comprising 5%≦Pt≦70% by atom, 5%≦Pd≦50%, 5%≦Cu≦50% by atom, and 5%≦P≦30% by atom.
An exact mechanism of forming the amorphous structure with respect to these two kinds of precious metal alloys according to the present invention is not completely revealed, but it is supposed that copper and phosphorus both of which are additional elements have some effects of raising the crystallization temperature of the alloy and of expanding the temperature range of a super-cooled liquid (a difference between the crystallization temperature and the glass transition temperature) of the above described alloy, so that the ability of forming the amorphous structure is improved.
In addition, the precious metal-based alloy with the Pt—Cu—P based structure and the precious metal-based alloy with the Pt—Pd—Cu—P based structure according to the present invention can be made into amorphous states even when their cooling rates are relatively low by, as for the Pt—Cu—P based structure, defining a range of copper concentration as 5%≦Cu≦35% and a range of phosphorus concentration as 15%≦P≦25% provided that a concentration of platinum is 50% or more and 75% or less and by, as for the Pt—Pd—Cu—P based structure, defining a range of copper concentration as 5%≦Cu≦50% and a range of phosphorus concentration as 5%≦P≦30% provided that a concentration of platinum is 5% or more and 70% or less and a concentration of palladium is 5% or more and 50% ore less. That is, if at least one of these constituents becomes outside of the above described range, the alloy is crystallized and its amorphous structure can no
Mori Kenya
Shimizu Susumu
Shioda Shigeo
Rothwell Figg Ernst & Manbeck
Tanaka Kikinzoku Kogyo K.K.
Yee Deborah
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