JPS6124463B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating the inner wall of an iron container, particularly a high-pressure gas container for storing a reactive standard gas. In recent years, related laws and regulations have been strengthened to prevent pollution, and reactive standard gases such as nitrogen oxide, carbon monoxide, and sulfur dioxide gas, which are used for calibrating analyzers, have come to be produced in large quantities. In particular, there is a high demand for low-concentration nitrogen oxide standard gases for measuring automobile exhaust gas. These standard gases must be stable so that their composition values do not change over a long period of time, but when low concentration standard gases are stored for a long period of time, their composition values may change over time. The main causes of this compositional change are that the component gases are adsorbed by rust existing in the container, dissolved in or reacted with moisture remaining in the container, adsorbed and desorbed to the inner wall of the container and reacting with the inner wall of the container, etc. It is thought that. Therefore, in order to eliminate these causes and to store low-concentration standard gas stably for a long period of time, conventional measures have been taken such as applying various treatments to the inner walls of the high-pressure gas containers. That is, a large quantity of containers with Teflon coating, gold plating, and pickling of the inner walls of the containers are manufactured and quality products are selected. In the Teflon coating method, a fluororesin is applied to the inner surface of the container, and in the gold plating method, the entire inner wall of the container is plated with gold to prevent contact between the iron on the inner wall and the component gases, thereby maintaining the stability of the composition. Acid washing is a method of cleaning the inner surface of a container by removing rust using acid. However, containers for low-concentration reactive standard gases are particularly difficult to process, making it difficult to obtain homogeneous products, and even if they are obtained, they are expensive. That is, the Teflon coating method has problems with the adhesion between the iron wall and the resin and is expensive. Gold-plated containers have an excellent effect on the stability of low-concentration standard gases, and are recognized as containers for official standard gases (reference standard gases) by the Chemical Inspection Association, but they are very expensive. It cannot be used for general commercially available standard gases. Further, there are drawbacks such as variations in the results of the plating process. Although the acid treatment method is inexpensive, the treatment results vary widely and it is generally difficult to obtain high quality products. In order to overcome these disadvantages of the conventional methods, the present invention was achieved by investigating the cause of the change in composition over time of the above-mentioned low concentration reactive standard gas and by conducting numerous experiments. In other words, for pickling and heating and vacuum treatment, we examined the treatment conditions of conventional methods and determined the optimal range through experiments. Furthermore, by filling in oxidizing gas, which had not been done in the past, we created a stable coating on the inner wall surface of the container. It is designed to form an oxide film, and after the container to be treated is subjected to the following treatments: pickling process, steam or steam hot water washing process, drying process, heating vacuum evacuation process,
This is a method for treating the inner wall of an iron container, characterized by performing a step of sealing an oxidizing gas in the container and leaving it to form an oxide film. This treatment method makes it possible to minimize adsorption and desorption of component gases on the inner wall surface of the container and prevent reactions within the container, thereby reducing the composition of the low-concentration reactive standard gas. This makes it possible to maintain stability for a long period of time. The method of the present invention will be explained in detail below using examples. Remove the valve of a commonly used manganese steel high-pressure gas container, inject approximately 6N of hydrochloric acid through its installation port, and leave the container with hydrochloric acid near the opening for approximately 12 hours. In this case, the concentration of hydrochloric acid may be 5 to 7N, and the standing time is not limited to 12 hours, but may be longer depending on the state of rust in the container, the concentration of hydrochloric acid, etc. When the treatment with hydrochloric acid is completed, the hydrochloric acid is discharged from the container to be treated, and the inside of the container is washed with a steam cleaner for at least 1 minute. After the hydrochloric acid and peeled rust remaining in the container are completely washed away with the steam or a mixture of steam and hot water ejected from the steam cleaner, dry nitrogen gas is blown into the container for at least 1 minute to dry the inside of the container. . After this, attach the container valve and perform heating and evacuation. That is, a container fitted with a container valve is placed in a heating furnace, connected to a vacuum pump, and heated while being evacuated. In this case, maintain the container temperature at 140°C or higher and evacuate it for more than 3 hours until the final vacuum level reaches 2.
Check that it is below ×10 ^-2 Torr. When this degree of vacuum has not been reached, heating and evacuation are further continued. Through this process, the gas and moisture adsorbed on the inner wall of the container are completely desorbed and discharged to the outside of the container, making the inside of the container completely clean. Next, an oxidizing gas such as oxygen or an oxygen-containing gas is sealed in the container whose interior has been completely cleaned, and an oxidized film is formed on the inner wall of the container by leaving it for a certain period of time. The sealed gas may be any oxygen-containing gas such as oxygen, an oxygen-containing gas mixed with an arbitrary amount of oxygen in an inert gas such as nitrogen, dry air, ozone, an ozone-containing gas, or an oxidizing gas such as nitrogen dioxide. As long as the oxygen content is about 100 ppm or more, treatment can be performed at various concentrations. The same applies to ozone-containing gas. The enclosure period must be one day or more. Through the above treatment, the inside of the container was completely cleaned, and the gas that had been adsorbed on the upper inner wall surface was removed.
Moisture is desorbed and a stable oxide film is formed on the inner wall surface, so when a reactive low concentration standard gas such as nitrogen oxide is stored in this container, its composition will not change and it will be extremely stable. It can be kept. The following is an example in which a container treated by the above method was filled with various low-concentration reactive standard gases, and changes in the composition of the gases over time were investigated. That is, a high-pressure gas container made of manganese steel with an internal volume of 10 is subjected to the above treatment and the sealed gas is evacuated, then it is filled with 150 kg/cm ² G of a standard gas containing nitrogen oxide mixed with nitrogen, and then this standard gas is periodically pumped. It was extracted and measured using a nitrogen oxide analyzer. When the changes in composition over time were investigated over a period of about one year, the changes were within the analytical error as shown in Table 1. Table 2 shows the results of a similar experiment using a standard gas containing nitrogen and carbon monoxide. According to these tables, it is clear that the low-concentration reactive standard gas filled in the container undergoing treatment according to the method of the present invention maintains an extremely stable composition over a long period of time.

【table】

[Table] As described above, the present invention is the result of numerous experiments in which the causes of changes in the composition of low-concentration reactive standard gases over time have been investigated, and treatment methods for eliminating them have been obtained.
Steam cleaning completely removes rust inside the container.
After completely removing moisture and adsorbed gas from the inner wall of the container by nitrogen drying and heating vacuum treatment,
It is designed to form a stable oxide film that is suitable for enclosing oxidizing gas. By performing these treatments, it becomes possible to minimize adsorption and desorption of component gases to the inner wall surface of the container and prevent reactions within the container. It became possible to keep the composition stable for a long period of time. Moreover, since the method of the present invention can use conventionally used equipment for acid treatment, heating vacuum treatment, etc., there is no need to add new equipment to carry out the method of the present invention, and the process of filling the oxidizing gas is relatively easy. It is inexpensive and easy to implement. This is an extremely advantageous feature compared to the Teflon coating method and the gold plating method, which each require processing equipment and the coating itself is expensive. Further, according to the method of the present invention, homogeneous containers with uniform treatment results can be easily obtained in large quantities, and the method has desirable conditions as a method for treating high-pressure gas containers for general commercially available standard gases.

Claims (1)

[Scope of Claims] 1 After a container to be treated is subjected to each of the following treatments: pickling process, steam or steam hot water washing process, drying process, and heating vacuum evacuation process, an oxidizing gas is sealed in the container and left to stand. 1. A method for treating the inner wall of an iron container, comprising a step of forming an oxide film. 2. The method for treating the inner wall of an iron container according to claim 1, wherein the pickling step involves injecting 5 to 7N hydrochloric acid into the container to be treated and leaving the container to stand. 3. The method for treating the inner wall of an iron container according to claim 2, wherein the pickling step involves injecting 6N hydrochloric acid into the container to be treated and leaving it for about 12 hours. 4 After the steam or steam hot water cleaning process discharges the acid salt injected in the previous process, the inside of the container to be treated is washed with steam or a steam hot water mixture.
The method for treating the inner wall of an iron container according to claim 1, wherein the cleaning is performed for at least a minute. 5. The method for treating the inner wall of an iron container according to claim 1, wherein the drying step includes blowing dry nitrogen gas into the container to be treated for one minute or more. 6 The above heating vacuum evacuation process
A method for treating the inner wall of an iron container according to claim 1, characterized in that evacuation is carried out for 3 hours or more while maintaining the temperature at or above .degree. 7 In the step of sealing an oxidizing gas in the container to be treated and leaving it, the oxidizing gas to be sealed is oxygen,
2. The method for treating the inner wall of an iron container according to claim 1, wherein the method uses an oxygen-containing gas, dry air, ozone, an ozone-containing gas, or nitrogen dioxide, and is left to stand for one day or more. 8. The method for treating the inner wall of an iron container according to claim 7, wherein the concentration of oxygen or ozone in the oxygen-containing gas or ozone-containing gas sealed in the container to be treated is 100 ppm or more.