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Column 技術屋の解説

Column 技術屋の解説

2017.10.31

[No.17/17] Mistake-prone basic knowledge on the anticorrosive paper No. 2

Don’t you have a concern that you had better pay attention on the volatile corrosion inhibitor employed in VCI Paper, and therefore it eventually becomes just paper? Alternatively, don’t you have an expectation that there is a sufficient effect even in a place away from, because the volatile corrosion inhibitor is employed in VCI Paper? 

What do you think of when you have heard “Volatile”? For example, do you think of Alcohol to be used prior to injection for disinfection or Fragrance to be put the toilet?

Both, it will run out if you do not tightly sealed by the cap.  The reason is that highly volatile substance is used in both of these. Well, what about the water? Indeed, the water placed in a cup without the lid, the volume is reduced by evaporation and will get lost. However, it would not be fast enough to disappear between viewing. Well, how about the hot water after adding heat?  I think you can feel this time the volume is reduced between viewing. 

Now, let me explain what happens in the case of VCI Paper. Please refer to Figure 2. 

This figure shows the relationship between the vapor pressure of various substances such as the volatile corrosion inhibitor and the temperature. It is shown by taking the temperature on the horizontal axis and the vapor pressure on the vertical axis on a logarithmic scale. One scale becomes 10 times because of logarithmic scale. You can see any substance has become a curve of upward-sloping. This is due to the vapor pressure increases as the temperature is high. 

The curve drawn to the top shows the water. Previously, I referred water and hot water as an example. The vapor pressure is larger an order of magnitude, 10 times, when 20℃ water is heated up to 60℃ hot water. This fact shows that it is easy to vaporize when the vapor pressure is large.   

DICHAN, a representative of volatile corrosion inhibitor, is under 4~5 degree than the water. In other words, it indicates the vapor pressure of DICHAN is in the magnitude of one of 10,000~100,000th of the water.  The vapor pressure of DICHAN is smaller than the mercury, which is famous because this metal is vaporized but now is lost to be seen. This vapor pressure is 3 digits smaller than Camphor which is put in the closet as insect repellent. Can you see that it is not so much immediately disappearing even though that DICHAN is vaporizing? 

Although the vapor pressure of the substances used in VCI Paper is not known to all, the vapor pressure would be greater than DICHAN in the extent about one order of magnitude, even though likely to be vaporized. 

If you had the image that “volatile corrosion inhibitor” would easily vaporize more and more when you hear it. It may be influenced and dragged by the word “volatile”.
I do hope you make rational judgment by having the correct knowledge, rather than sensuous.

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