Steps in the titanium anodizing process

Titanium anodizing is a carefully sequenced process. While at its core it is an electrochemical reaction, the success of the results depends greatly on the precision employed at each step. Let’s take a closer look at each stage of the titanium anodizing process.

Step 1: Cleaning and Pretreatment

Before anodizing, it is critical to ensure that the titanium surface is free of contaminants, oil, or any previous oxide layer.

1.Degreasing: First, the titanium piece is immersed in a degreasing solution to remove organic residue or oil. Common solvents include acetone or isopropyl alcohol.

2.Rinsing: After degreasing, the piece is rinsed thoroughly with distilled or deionized water to eliminate solvent residue.

3.Pickling: The titanium is then immersed in an acid solution (usually a mixture of nitric and hydrofluoric acids) to remove the natural oxide layer and any remaining contaminants. This step also helps etch the surface, promoting better adhesion of the newly formed oxide layer.

Step 2: Electrolyte Preparation

The electrolyte solution (usually dilute sulfuric acid) acts as a medium that facilitates the flow of electrical current during the anodizing process. Its concentration and pH need to be optimized to obtain consistent results. The acid is mixed with distilled water in the correct proportions to ensure uniform concentration. Then, the temperature of the electrolyte is monitored and controlled. Lower temperatures may cause the oxide layer to harden.

Step 3: Anodizing

This is the center stage where the magic of color and protection happens. The titanium piece is connected to the positive terminal (anode) of a power source, while the cathode (usually made of lead or stainless steel) is connected to the negative terminal. Both the anode (titanium) and cathode are immersed in the electrolyte solution, ensuring that they do not touch each other. A direct current is then applied. As the voltage is increased, the oxygen ions in the electrolyte form an oxide layer on the surface of the titanium. The thickness of the oxide layer, and the resulting color, is directly related to the voltage applied.

Step 4: Post-anodizing Rinse

Once the desired oxide layer thickness (and color) is achieved, the titanium piece is removed from the electrolyte and rinsed. Immediately rinse with distilled or deionized water to stop the anodizing process and remove any acid residue.

Step 5: Sealing (Optional)

Sealing the anodized layer is an optional step that may be required for some applications to enhance corrosion resistance. Hydration sealing involves boiling or steaming the workpiece, which converts the titanium oxide into hydrated titanium oxide, effectively sealing the surface pores. Another method is cold sealing, where the workpiece is immersed in a nickel acetate solution at a lower temperature.

Step 6: Quality Inspection

Anodized titanium undergoes various tests to ensure it meets the required specifications. For example, the thickness of the oxide layer is measured using equipment such as an eddy current meter, and the color uniformity and appearance are visually inspected to detect any inconsistencies or defects.