What Is Titanium Anodizing?
Titanium anodizing is an electrochemical process that thickens the natural oxide layer on titanium surfaces. Unlike aluminum anodizing, titanium anodizing does not use dyes to produce color. Instead, the color is created by light interference through the precisely controlled oxide thickness — a phenomenon called structural color. By varying the anodizing voltage, manufacturers can produce a predictable spectrum of colors without any pigments or dyes.
This unique capability has made titanium anodizing popular in jewelry, medical devices, aerospace components, and decorative applications. Beyond aesthetics, anodizing also improves corrosion resistance, biocompatibility, and surface hardness of titanium components.
Types of Titanium Anodizing
Type I – Barrier Layer Anodizing (Color Anodizing)
Type I anodizing creates a thin, dense oxide barrier layer that produces interference colors. This is the most common type used for decorative and identification purposes.
- Electrolyte: Phosphoric acid (H₃PO₄) or trisodium phosphate (TSP) solution
- Voltage range: 10-120V DC (determines color)
- Oxide thickness: 20-600 nanometers (proportional to voltage)
- Color range: Bronze, purple, blue, green, yellow, pink, and more
- Current density: 1-3 mA/cm²
- Temperature: Room temperature (20-25°C)
- Time: 1-5 minutes after target voltage is reached
Type II – Integral Color Anodizing
Type II anodizing produces thicker oxide layers with bronze-to-black colors. The color is integral to the oxide structure rather than being a thin-film interference effect.
- Electrolyte: Sulfuric acid (H₂SO₄) with organic acid additions
- Voltage: Higher than Type I, typically 40-80V
- Oxide thickness: 1-5 micrometers
- Colors: Limited to bronze, brown, and black shades
- Applications: Architectural panels, military components, wear-resistant surfaces
Type III – Thick Film / Hard Anodizing
Type III anodizing produces the thickest oxide layers, primarily for wear resistance and corrosion protection rather than color.
- Electrolyte: Sulfuric acid (H₂SO₄) based, sometimes with additives
- Voltage: Up to 150V
- Oxide thickness: 5-50+ micrometers
- Colors: Opaque gray to black (no interference colors)
- Applications: Wear surfaces, aerospace bearings, biomedical implants
- Hardness: 300-500 HV (significantly harder than base titanium)
Color-Voltage Relationship
The Interference Color Spectrum
Titanium anodizing colors follow a predictable sequence based on oxide thickness, which is directly controlled by the applied voltage. The color sequence is:
| Voltage (V) | Color | Oxide Thickness (nm) |
|---|---|---|
| 10 | Bronze/Brown | ~20 |
| 15 | Purple | ~30 |
| 20 | Blue (dark) | ~40 |
| 27 | Blue (bright) | ~55 |
| 35 | Light blue/Cyan | ~70 |
| 40 | Green-blue | ~80 |
| 50 | Green-yellow | ~100 |
| 60 | Yellow | ~120 |
| 70 | Orange | ~140 |
| 80 | Red/Pink | ~160 |
| 90 | Purple (second order) | ~180 |
| 100 | Green (second order) | ~200 |
| 110 | Golden | ~220 |
| 120 | Silver/Gray | ~240 |
Color Reproducibility
Color consistency depends on precise voltage control. Key factors affecting color reproducibility:
- Voltage stability: ±0.5V maximum variation for consistent color
- Electrolyte concentration: Must be maintained within ±5%
- Temperature: ±2°C for consistent oxide growth rate
- Surface preparation: Must be uniform across the workpiece
- Time: Must allow oxide growth to stabilize at target voltage
Process Equipment and Setup
Rectifier Requirements
- DC power supply with adjustable voltage (0-120V)
- Voltage accuracy: ±0.5V
- Current capacity: 1-10A depending on workpiece size
- Ripple: Less than 5% for smooth oxide growth
Electrolyte Preparation
Common electrolyte formulations for Type I anodizing:
- Phosphoric acid: 10-20% by volume in deionized water
- Trisodium phosphate (TSP): 50-100 g/L in deionized water (safer alternative)
- Sodium hydroxide (NaOH): 5-10 g/L (used in some formulations)
Cathode Requirements
- Material: Platinum-coated titanium, stainless steel 316, or graphite
- Surface area: Minimum equal to workpiece area
- Must not dissolve or contaminate the electrolyte
Surface Preparation
Cleaning
Thorough cleaning is essential before anodizing. Any contamination on the surface will result in uneven oxide growth and inconsistent colors:
- Degrease with acetone or alkaline cleaner
- Rinse with deionized water
- Acid pickle in 10-20% nitric acid + 2-5% hydrofluoric acid
- Rinse thoroughly with deionized water
- Anodize immediately (do not allow surface to air-dry or re-contaminate)
Mechanical Preparation
Surface finish affects the final appearance of anodized titanium:
- Polished surfaces: Bright, metallic luster with vivid interference colors
- Bead-blasted surfaces: Matte finish with softer, more diffuse colors
- As-machined surfaces: May show machining marks through the color
- Satin finishes: Uniform directional grain produces consistent color
Applications by Industry
Medical Devices
- Color coding of surgical instruments by size or type
- Identification of different titanium alloy grades
- Enhanced biocompatibility for implants (Type III anodizing)
- Surface hardening for wear-resistant joint replacements
Aerospace
- Component identification and traceability
- Corrosion protection for airframe components
- Hydrogen embrittlement prevention (Type I anodizing removes absorbed hydrogen)
- Fastener identification by color coding
Jewelry and Consumer Products
- Decorative colors for rings, pendants, watch cases
- Multi-color designs using selective masking techniques
- Permanent color that does not fade, chip, or peel
Automotive and Motorsport
- Decorative exhaust tips and trim
- Identification of performance components
- Weight-critical decorative parts (anodizing adds negligible weight)
Quality Control
Oxide Thickness Measurement
- Eddy current measurement (non-destructive)
- Optical interferometry
- Cross-section metallography (destructive)
Color Verification
- Visual comparison against standard color chips under controlled lighting
- Spectrophotometer measurement for CIE L*a*b* color values
- Voltage record kept for each batch as process documentation
Adhesion and Durability Testing
- Bend test: No cracking or flaking when bent to 180° around 3mm mandrel
- Tape test: No oxide removal when tested with standard adhesion tape
- Salt spray test: 500+ hours without visible corrosion
CoreMetal Steel Titanium Products
CoreMetal Steel supplies premium titanium sheet, plate, tube, bar, and fabricated components in commercially pure (Grade 1-4) and alloy (Ti-6Al-4V, Ti-6Al-4V ELI) grades. Our products are suitable for anodizing and other surface treatments. All materials include full Mill Test Certificates with chemical composition and mechanical property verification.
Conclusion
Titanium anodizing is a versatile surface treatment that provides both functional benefits (corrosion resistance, biocompatibility, hardness) and decorative possibilities (permanent, vivid colors through voltage-controlled oxide thickness). Understanding the process parameters, color-voltage relationship, and quality control requirements enables manufacturers to produce consistent, high-quality anodized titanium components.
Contact CoreMetal Steel for titanium product specifications, surface treatment consultation, and quotations for your project.