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2Stable color(Color)Beauty that lasts over time

Kyushu National Museum
(in 2004)
Oita Sports Park Stadium
(in 2001)
General titanium
(Titanium discoloration)
Upon completion Kyushu National Museum Oita Sports Park Stadium
About 20 years later About 20 years later 4 years later
After completion Kyushu National Museum Oita Sports Park Stadium

1)Mechanism of discoloration

<Explanation of discoloration>

In the early 1990s, phenomena where the color of titanium roofing tiles changed from silver to brown occurred in part of the buildings that had been constructed were reported.
Titanium is colored by means of formation of an oxide layer on its surface. The phenomenon is attributable to the fact that the oxide layer thickened due to natural forces including acid rain, resulting in color change where a silver color appeared as a brown color due to the interference color of light.
*This phenomenon has nothing to do with the corrosion resistance of titanium.

Example of discoloration [The test specimen is made of conventional titanium material.]

In 2001, at the start of the 21st century, Nippon Steel was the first in the world to successfully clarify the mechanism thereby clearing a path toward titanium's evolution in the filed of color, one of the element technologies of TranTinokite.

<Mechanism of discoloration>

As a result of the investigation of the discolored part, it was found that a small amount of carbon and fluoride was retained in the oxide layer and on the surface of the titanium substrate. And as a result of various experiments, it was found that these substances reacted with acid rain to let the oxide layer grow.
It was also found that this tendency becomes more conspicuous with the increase in temperature.

Theory of discoloration phenomenon

Theory of discoloration phenomenon

2)Effect of resistant-to-discoloration treatment

While the acidity of rainwater in Okinawa is equivalent to the average value in Japan, Okinawa is one of the most discoloration-prone regions due to its hot and humid climate.
The discoloration of the developed titanium building materials is minimal even after 4-year exposure.

Results of the exposure test in Okinawa

3)STABLE COLOR Points to note for STABLE COLOR(Less-Discoloration Technology)

  • This technology intends to slow down the speed of discoloration by retarding the rate of growth of the oxide layer in the natural environment but not to stop discoloration.
  • It is assumed that discoloration would take place particularly in hot and humid tropical areas and in such regions that are exposed to severe acid rain.
  • The titanium building materials less subject to discoloration installed and subjected to exposure tests in and after 2000 are now in good condition with little color change observed in the substrate and anodized color titanium.
  • Titanium appears to be discolored with splotch and fingerprints in the same way as other metals.
    Splotches can be removed by means of appropriate cleaning but removal becomes more difficult if it is left uncleaned.

4)Example of use

Oita Sports Park Stadium(32,000m²)

Since NIPPON STEEL clarified the mechanism of discoloration caused by the growth of oxide layer in the surface through its reaction with acid rain, and established the technology to remove impurities in the surface layer that cause discoloration, the ”titanium less subject to discoloration” was adopted for the Oita Sports Park Stadium first in the world in 2001.
As a result of the observation and investigation of the roofing made in 2016, it was confirmed that nice-looking and sound titanium surface is retained with extremely small change in color tone after the lapse of 15 years since the completion.

More information, click here
Oita Sports Park Stadium(32,000m2)

1.Expression of various beauty

3.Material variation

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