Fuel and related compositions
Reexamination Certificate
1999-05-14
2003-09-02
Jones, Deborah (Department: 1775)
Fuel and related compositions
C428S472200, C428S629000, C428S472100, C148S286000, C148S285000, C148S285000
Reexamination Certificate
active
06612898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming an oxidation passive layer, to a fluid-contacting part, and to a fluid feed system. In greater detail, the present invention relates to a method for forming an oxidation passive layer having a layer chiefly comprising aluminum oxides on the surface of stainless steel, a method for forming an oxidation passive layer chiefly comprising titanium oxides on a titanium base alloy surface, stainless steel or titanium base alloy having such passive layers formed thereon, and a fluid-contacting part and fluid feed system having parts in contact with a fluid (gas or liquid) employing these stainless steel and titanium materials.
2. Description of the Related Art
Chromium oxide passive layers are highly resistant to corrosion by various semiconductor manufacturing process gases. Moreover, the outgassing properties thereof are extremely superior, allowing such layers to be employed in vacuum devices, reduced-pressure devices, and gas supply pipes which require a high degree of cleanliness. These chromium oxide passive layers may also be used in supply pipes for ultrapure water and the like.
Recently, the high oxidizing power of ozone has been used in various technologies, such as cleaning of silicon substrate, ashing, and low-temperature CVD oxidation to develop highly efficient and integrated device.
However, in ozone supply piping materials, fluorine resins such as PVDF or the like, which are commonly employed in wet systems, and SUS316 and the like, which is commonly employed in gas systems, are markedly corroded by ozone. This represents a source of contamination, so that it is impossible to use such materials. Furthermore, as the ozone concentration increases, even the oxidation of the chromium oxide passive layers described above from Cr
2
O
3
to CrO
3
occurs as a result of the oxidizing power of the ozone. Therefore, it becomes impossible to maintain a high state of cleanliness in the piping and the atmosphere and the like.
In light of the above circumstances, the present invention has as an object thereof to provide a method for forming an oxidation passive layer which is highly resistant to corrosion by strongly oxidizing substances such as ozone.
Furthermore, it is an object of the present invention to provide stainless steel and titanium base alloys which are strongly resistant to corrosion by fluids containing ozone, as well as to provide fluid-contacting parts, process apparatuses, and fluid feed systems and discharge systems employing these corrosion resistent materials.
SUMMARY OF THE INVENTION
In a method for forming oxidation passive layers of the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is heat treated at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 500 ppb to 1 percent H
2
O gas, and thereby, an oxidation passive layer containing aluminum oxides is formed.
Furthermore, in another method for forming oxidation passive layers in accordance with the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is polished to a Rmax of 0.7 micrometers or less, and baked in an inert gas atmosphere, whereby moisture is removed from the surface of the stainless steel, and subjected to heat treatment at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 500 ppb to 1 percent H
2
O gas, and thereby, an oxidation passive layer containing aluminum oxides is formed.
In another method for forming oxidation passive layers in accordance with the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is subjected to heat treatment at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 1 ppm to 500 ppm of oxygen gas, and thereby, an oxidation passive layer containing aluminum oxides is formed.
In another method for forming oxidation passive layers in accordance with the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is polished to a Rmax of 0.7 micrometers or less, and then, baked in an inert gas atmosphere, whereby moisture is removed from the stainless steel surface, and then heat treatment is conducted at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 1 ppm to 500 ppm of oxygen gas, and thereby, an oxidation passive layer containing aluminum oxides if formed.
In the present invention, it is preferable that hydrogen gas be added to the mixed gas in an amount of 10 percent or less.
In another method for forming oxidation passive layers in accordance with the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is heat treated at a temperature within a range of 20° C. to 300° C. in a mixed gas atmosphere containing oxygen gas and at least 100 ppm of ozone gas, and thereby, an oxidation passive layer containing aluminum oxides is formed.
In a further method for forming oxidation passive layers in accordance with the present invention, a stainless steel surface containing Al in an amount within a range of 0.5 percent by weight to 7 percent by weight is polished to a Rmax of 0.7 micrometers or less, and baked in an inert gas atmosphere, whereby moisture is removed from the stainless steel surface, and then this is subjected to heat treatment at a temperature within a range of 20° C. to 300° C. in a mixed gas atmosphere containing oxygen gas and at least 100 ppm of ozone gas, and thereby, an oxidation passive layer containing aluminum oxides is formed.
In a further embodiment, it is characteristic that nitrogen gas is added in an amount of 10 percent or less to the mixed gas containing ozone gas as described above.
In the methods for forming oxidation passive layers in accordance with the present invention, it is preferable that the amount of Al contained in the stainless steel be within a range of 3 percent by weight to 6 percent by weight.
Additionally, in yet another embodiment, it is characteristic that the oxidation passive layer chiefly comprises a mixed oxide layer of aluminum oxides and chromium oxides.
In another method for forming oxidation passive layers in accordance with the present invention, a titanium base alloy surface is heat treated at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 500 ppb to 1 percent H
2
O gas, and thereby, an oxidation passive layer comprising titanium oxides is formed.
In a further method for forming oxidation passive layers in accordance with the present invention, a titanium base alloy surface is polished to a Rmax of 0.7 micrometers or less, and baked in an inert gas atmosphere, whereby moisture is removed from the titanium base alloy surface, and then heat treatment is conducted at a temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 500 ppb to 1 percent H
2
O, and thereby, an oxidation passive layer comprising titanium oxides is formed.
In another method for forming oxidation passive layers in accordance with the present invention, a titanium base alloy surface is heat treated at temperature within a range of 300° C. to 700° C. in a mixed gas atmosphere of an inert gas and 1 ppm to 500 ppm of oxygen gas, and thereby, an oxidation passive layer comprising titanium oxides is formed.
In a further method for forming oxidation passive layers in accordance with the present invention, a titanium base alloy surface is polished to a Rmax of 0.7 micrometers or less, and baked in an inert gas atmosphere, whereby moisture is removed from the surface of the stainless steel, and subsequently, by heat treatment at a temperature within a range of 300° C. to 700° C.
Nitta Takahisa
Ohmi Tadahiro
Jones Deborah
Knuth Randall J.
Savage Jason
Tadahiro OHMI
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