Colored Titanium Oxide Layer Discoloration Resistance

The patent applies parameter changes by precisely controlling the phosphorus content (5.5 atomic % or less within 40 nm from surface), carbon concentration (3 to 15 atomic % within 100 nm from surface), and sulfur content (0.2 to 5 atomic % within 30 nm from surface) in the oxide layer, along with optimizing the oxide film thickness (40 to 60 nm). This multi-parameter optimization resolves the contradiction by creating a composition that simultaneously achieves both discoloration resistance and chemical stability in acid rain environments.

The patent resolves this contradiction by precisely controlling the carbon concentration parameter within the range of 3 to 15 atomic % within 100 nm from the surface. This optimized carbon content provides sufficient structural enhancement through carbide formation while preventing excessive carbon accumulation that would promote discoloration, thus achieving both strength improvement and discoloration resistance.

The patent resolves this contradiction by strictly limiting the phosphorus content to 5.5 atomic % or less within 40 nm from the surface. This controlled phosphorus level ensures adequate oxide film formation and stability while preventing phosphorus-induced degradation that would occur in high temperature and acid rain environments, thus maintaining both manufacturing quality and long-term reliability.