KR100227064B1 - Process for passivating metal surfaces to enhance the stability of gaseous hydride mixtures at low concentration in contact therewith - Google Patents

Abstract

According to the present invention there is provided a method of passivating a metal surface in contact with it to enhance the stability of a gas mixture containing one or more low concentration gaseous hydrides. This method consists of the following steps:

a) purifying the gas in contact with the metal surface using an inert gas to remove the purified gas,

b) passivating this metal surface with a passivating agent consisting of an effective amount of a gaseous hydride of silicon, germanium, tin or lead for a time sufficient to passivate it,

c) The gaseous passivation agent is purified using an inert gas.

Description

Passivation of metal surfaces in contact with them to enhance the stability of low concentration gaseous hydrides

1 shows a schematic diagram of a flow system according to the invention.

Figure 2 graphically shows the relationship between trapping time and loss of 1 ppm AsH ₃ / Ar in 316L stainless steel tubing.

The present invention relates to a method of passivating a metal surface in contact with it to enhance the stability of a low concentration gaseous hydride mixture.

In the electronics industry and environmentally, there is a great need for stable gas mixtures containing low concentration gaseous hydrides in the ppb to ppm range. A common practical process in this industry is to provide such mixtures to compressed gas cylinders, in which the mixtures are often stored for long periods of time. However, due to the reaction of the gas mixture containing this amount of gaseous hydride with the metal surface of the vessel containing the mixture, it is very difficult to stabilize it.

One approach to addressing this instability problem and to keep the gas mixture constant is to minimize the contact time between the low concentration hydride and the metal container by storing the high concentration mixture in the cylinder and then diluting immediately before use. Unfortunately, however, long-term storage of the gas mixture in the metal cylinder is desirable even if not necessary.

Another approach to keeping the concentration of the gas mixture of low hydride constant is saturation passivation. In this technique, the filling and introduction of much higher concentrations of the same gaseous hydride into the vessel is repeated several times before filling the desired low concentration hydride mixture. This process is repeated several times based on the previous experimental studies. This technique, however, is very disadvantageous because its use is limited because higher concentrations of the same hydride must be used to condition the vessel and toxic gases such as arsine must be handled in large quantities in the process.

Therefore, there is still a need for a passivation method that is suitable for stabilizing gaseous hydride mixtures, without the drawbacks of the conventional approach described above.

Accordingly, one object of the present invention is to provide a method of passivating a metal surface in contact with it in order to increase the stability of a gas mixture containing low concentration gaseous hydride.

Another object of the present invention is to provide a passivation method of a metal surface, which is advantageous for treating all metal surfaces used for manufacturing, for example, gas storage cylinders, conduits, vessels, pipes, tank truck storage devices or railway tank storage vehicles. will be.

In particular, one object of the present invention is to provide a method for passivating a metal surface, which is particularly advantageous for treating metallic compressed gas storage cylinders.

The above and other objects will become more apparent from the following description, which is a method of passivating a metal surface in contact with it to enhance the stability of a gas mixture containing low concentration gaseous hydride, which consists of the following steps: Is achieved by:

a) purifying the gas in contact with the metal surface using an inert gas to remove the purified gas,

b) exposing the metal surface to an amount of gas phase passivating agent in an effective amount of a gaseous hydride of silicon, germanium, tin or lead,

c) Purifying the passivation agent using an inert gas.

According to the present invention, there is provided a method of passivating a metal surface in contact with it to enhance the stability of a gas mixture containing low concentrations of gaseous hydrides such as arsine, phosphine, or styrene.

Currently, passivation is used to increase corrosion protection of metal particles and steel surfaces in very special applications. For example, WO 89/12887 describes a silane passivation process for metal particles, which enhances the corrosion resistance to metal oxidation, and GB2,107, 360 for promoting corrosion resistance in carbon dioxide rich environments at high temperatures and pressures. A silane passivation process for steels is disclosed.

In accordance with the present invention, any metal surface can be treated to enhance the stability of the gas mixture containing the gaseous hydride in contact therewith. The metal surface can be, for example, a metal tubing, a metal valve, or a metal cylinder for compressed gas storage. However, any type of metal surface can be so treated.

For example, the present invention allows passivation of any type of metal, particularly metals useful for making all types of storage tools, including gas storage cylinders, conduits, vessels, pipes, and rail tank storage vehicles and tank truck trailer equipment. For example, metals such as iron, steel and aluminum can be passivated in accordance with the present invention.

The present invention can be advantageously used to treat various steels and alloys thereof, such as, for example, ferritic steel, austenitic steel, stainless steel and other iron alloys, and is particularly advantageous for the treatment of stainless steel. However, other types of metals can also be treated this way.

Generally, the present invention enhances the stability of gas mixtures containing low concentrations of gaseous hydrides by passivating the metal surface using relatively less toxic gaseous hydrides.

In the context, relatively less toxic gaseous hydrides include silicon hydride, germanium hydride, tin hydride and lead hydride. No toxic gaseous hydrides such as arsine or phosphine are used.

Especially useful are silicon hydrides having the general formula Si _n H _{2n + 2} , such as SiH ₄ , Si ₂ H ₆ , and Si ₆ H ₁₄ . However, it may also be used other hydride, such as _{Ge 2 H 6, Ge 9 H} 20, SnH 4, SnH 6 or PbH _4.

In the above general formula, n is generally 1 to about 10. However, since silicon hydride is also known to chain, n may be a larger value. See Advanced Inorganic Chemistry, Cotton and Wilkinson, 3rd edition.

In the present text, low concentration gaseous hydride generally means a gaseous hydride having a concentration of about 10 ppm to about 10 ppm. More preferably, the concentration is from about 50 ppm to about 5 ppm. As such, most preferred is a concentration of about 100 ppm to about 1 ppm.

In order to passivate the metal surface in contact with it in order to enhance the stability of the gas mixture containing low concentration gaseous hydride according to the present invention, first, an inert gas is used to It is necessary to purify to remove the purified gas. As the inert purge gas, it is generally chemically non-reactive and may be any gas. For example, so-called rare gases such as krypton, xenon, helium, neon and argon can be used. However, other gases such as hydrogen and nitrogen are also available. In general, the inert purge gas is allowed to pass over the metal surface for a period of time in an amount sufficient to actually remove all of the purged gas. Typically, purge gas is passed over a metal surface for a few seconds to about 30 minutes at 1 to about 3 atmospheres, or through a volume defined by a continuous metal surface, such as a compressed gas storage cylinder. However, higher pressures can also be used if desired.

According to the present invention, nitrogen has been found to be advantageous as an inert purge gas, but other inert gases are also available.

After purifying the gas that is in contact with the metal surface, the metal surface is exposed to an amount of passivation agent containing an effective amount of one or more gaseous hydrides of silicon, germanium, tin or lead, for a time sufficient to passivate the metal surface.

In general, the higher the concentration of passivation agents, such as silane, the shorter the required exposure time. However, the concentration of the passivation agent may be as low as 1 ppm, or as high as 100%. For example, when using very low concentrations of silane, the exposure time usually exceeds 80 hours. In general, exposure times of about 100 hours are used in the case of thin passivation agents. However, for example, when a relatively pure passivation agent is used, an exposure time of less than 60 minutes is generally required, and more preferably less than 30 minutes.

Pure passivation agent as described above means that the passivation agent used is a pure gaseous hydride of at least one of silicon, germanium, tin or lead.

Passivation agents are available in any concentration, but generally need to be used in a concentration range of about 0.01% to 20% by volume. However, it is preferred to use at concentrations ranging from about 0.01% to 5% by volume. Generally, larger volumes of passivation agents can be used for large metal surfaces, such as large containers.

According to the present invention, it is possible to substitute or remove all the gas purified by the inert gas.

In the text, virtually everything of the purified gas means that the purified gas is removed to the extent of 99% by volume or more.

In general, the gas to be purified is air, or other gases or gas mixtures, such as mixtures mainly containing nitrogen and oxygen, may also be purified according to the present invention.

In general, exposure of the metal surface to the passivating agent can be performed from a very low temperature, such as about -20 ° C, to the decomposition temperature of one or more gaseous hydrides in the passivating agent. For example, the decomposition temperature of silane is 250 ° C. However, it is generally desirable to perform the exposure at a temperature of about 10 ° C to about 100 ° C. More preferred is to expose the passivation agent at about 20 ° C to about 50 ° C. However, exposure at 25 ° C. is most advantageous.

Exposure can be at high temperatures, but the gas phase reaction of one or more gaseous hydrides of passivation agents such as silanes is preferably kept to a minimum to avoid particle generation. In general, this means lowering the temperature below the decomposition temperature of the passivating agent of the gaseous hydride.

The metal surface is treated with a passivation agent and then the latter itself is purified with an inert gas such as nitrogen. However, the rare gas described above can also be used.

The present invention also provides any fourth step of exposing the metal surface to oxidizing gas to stabilize the passivation agent adsorbed on the metal surface. As the oxidizing gas, for example, a gas mixture containing nitrogen and oxygen can be used.

In general, an oxidizing gas mixture may be used which can oxidize the adsorbed passivating agent in oxidized form. For example, when oxidizing the adsorbed passivation agent, it is preferable to use a gas mixture containing about 1 to 10% by volume of oxygen in nitrogen, and metal surface film exposure time is generally used for about 30 seconds to about 3 minutes. . However, if necessary, the exposure time may be longer or shorter.

In general, the oxidation step can be carried out at the same temperature as used in the passivation step, preferably from about 10 ° C. to about 100 ° C., most preferably from 20 ° C. to about 50 ° C.

It has been found that in accordance with this aspect of the invention, the gaseous hydride adsorbed is released slowly over time to reduce the passivation treatment effect over time. Inert compounds such as SiO ₂ can be formed, for example, by oxidizing adsorbed passivation agents containing gaseous hydrides such as silanes. Therefore, the oxidation step provides a means to stabilize the passivated metal surface over long periods of use.

1 and 2 will be described in more detail below.

1 is a schematic flow diagram using valve and port valves A and B in a fluid connection, an arsine permeation device, and a massflow controller. This device can be conveniently used to test the stability of gaseous hydrides as measured by inductively coupled plasma spectrophotometers. However, other means known to those skilled in the art are also available.

2 summarizes the stability data from Samples A, B, and C as described below in the Examples. In particular, 1 ppm treatment (Sample C) failed to passivate the metal surface after 69 hours of exposure. In general, at such low concentrations, the exposure time needs to be 70 hours or more, and preferably the exposure time is 80 hours or more.

Pure silane treatment (Sample B) passivated the surface within 30 minutes of exposure. Sample A is a control sample.

In general, gas phase hydride treatment in accordance with the present invention virtually passivates all metal surfaces. In the context of the text, virtually all means that at least 90% of the metal surface in contact with the gaseous hydride is passivated. However, it is preferred that at least 99% of the metal surface in contact with the gaseous hydride is passivated. In particular, at least 99.9% of the metal surface in contact with the gas phase passivation is preferably passivated.

The present invention will be described in more detail with reference to the following Examples, but the present invention is not limited to these Examples.

EXAMPLE

1/4 ID stainless steel tubes were used to demonstrate the effect of the present invention on metal surfaces.

Three identical 1/4 ID stainless steel (A, B, and C) samples were exposed to ambient air under conditions common to gas operation and storage equipment. Under these exposure conditions, the stability of the mixture is known to be very poor. All samples were then purged with dry N ₂ gas at room temperature. Sample A was a control sample. Sample B was then treated with pure flow silane for 30 minutes at room temperature according to the conditions described below and Sample C was clarified with 1 ppm silane for 72 hours and then with dry air.

The stability of the hydrides in Samples A, B, and C thus prepared was tested using the apparatus shown in FIG. The tube was filled with argon gas containing 1 ppm of arsine. This gas was maintained in the tube using valve 2 shown in FIG. 1 for various periods of time. Thereafter, gas was introduced into the apparatus capable of measuring the concentration of hydride remaining in the gas. In this embodiment, the device is an inductively coupled plasma spectrophotometer. However, other searching means can also be used. The ratio of initial fill concentration to final concentration was used to measure the gas stability. Typical test results for arsine are shown in FIG.

In addition, the present invention also provides a means for storing a gas or gas mixture, which means necessarily has a passivated embedded metal surface. However, this storage means may be made entirely of metal. Preferably, the storage means is a compressed gas storage cylinder. However, this storage means may also be movable storage means such as tank tractor trailer equipment or railroad tank vehicles.

Therefore, the present invention provides a storage means having at least a passivated embedded metal surface, thereby increasing the stability of the gas mixture containing at least one low concentration gaseous hydride in contact therewith. In the context, passivated means that the inner metal surface of the storage means has undergone the passivation treatment of the present invention to prevent it from reacting with a gas or gas mixture containing a low concentration of gaseous hydride therein. According to the invention, it is advantageous that the passivation agent used is a silicon hydride of the general formula Si _n H _{2n + 2} (where n is 1-10 and more preferably n is 1).

However, it is particularly preferred that the passivated storage cylinder is passivated in accordance with the invention with its gaseous hydride passivating agent.

While the present invention has been described so far, those skilled in the art will understand that many changes and modifications can be made to the above embodiments without departing from the spirit and scope of the invention.

Claims (14)

a) purifying the gas in contact with the metal surface with an inert gas to remove the purified gas, b) exposing the metal surface to an amount of passivation agent in an effective amount of a gaseous hydride of silicon, germanium, tin or lead at 10-100 ° C. for 1 minute to 100 hours to sufficiently passivate the metal surface, c) purifying the passivation agent with an inert gas, the metal surface being in contact therewith to enhance the stability of the gas mixture containing at least one low concentration gaseous hydride of 10ppb-10ppm. How to passivate. The method of claim 1 wherein the metal surface is of steel, iron, or aluminum. The method of claim 1 wherein the metal surface is a cylinder for storing compressed gas. The method of claim 1 wherein the purified gas is air. The method of claim 1 wherein the inert gas is nitrogen, argon, krypton, xenon or neon. The method of claim 1, further comprising the step c), followed by exposing the metal surface to an amount of oxidizing gas or gas mixture sufficient to stabilize for 30 seconds to 3 minutes to allow the passivation agent adsorbed on the metal surface to be sufficiently stabilized. How is it characterized. 2. The method of claim 1, wherein said at least one low concentration gaseous hydride is selected from phosphine, arsine, and styrene. The method of claim 1, wherein the gaseous hydride passivation agent is a silicon hydride having a general formula of Si _n H _{2n + 2} , wherein n is 1 to about 10; Ge ₂ H ₆ , Ge ₉ H ₂₀ , SnH ₄ , SnH ₆ , and PbH _4- . 9. The method of claim 8, wherein the gaseous hydride passivation agent is a silicon hydride of the general formula Si _n H _{2n + 2} , wherein n is from 1 to about 10. 10. The method of claim 9, wherein the silicon hydride is SiH ₄ . A storage means having an internal metal surface passivated at 10 to 100 ° C. with a passivation agent containing an effective amount of a gaseous hydride of silicon, germanium, tin or lead. The storage means according to claim 11, which is a tank tractor trailer equipment or a railroad tank vehicle. 12. The storage means according to claim 11, which is a cylinder for storing compressed gas. A storage means according to claim 11, characterized in that it is a conduit, pipe or container.