How is the cleanliness of titanium foil material tested?

The cleanliness of titanium foil must be assessed comprehensively using multi-dimensional metrics, including particulate contamination, organic residues, inorganic ions, and surface energy, to ensure its reliable performance in high-sensitivity applications such as electronics, medical devices, and aerospace. Given the extremely thin gauge of titanium foil—typically less than 0.1 mm—inspection methods must balance high sensitivity with non-destructive testing.

I. Core Testing Items and Methods

Particulate Pollutant Analysis

Test items: the quantity, size distribution, and composition of solid contaminants such as metal chips, fibers, dust, and polymer particles.
Testing method:
Ultrasonic extraction is used to transfer surface particles onto a filter membrane, followed by counting and morphological analysis using optical or electron microscopy.
Perform chemical composition analysis of particles using energy-dispersive X-ray spectroscopy (EDS) to identify the source of contamination.

Organic Residue Testing

Test items: organic substances such as lubricating oils, cutting fluids, rust-preventive oils, mold release agents, fingerprint residues, and plasticizers.
Testing method:
Total Carbon/Organic Carbon Analyzer: Determines the organic carbon content in surface extraction solutions via high-temperature catalytic oxidation, thereby quantifying the total pollutant load.
Fourier-transform infrared spectroscopy (FTIR): identifies specific functional groups in organic compounds, enabling qualitative analysis.

Inorganic Salt Residue Testing

Test parameters: soluble salt ions such as chloride, sulfate, and nitrate.
Testing method:
Ion Chromatograph (IC): Separates and quantifies extracts from cleaning solutions, with detection limits down to the ppm level for ionic species.
Particular attention should be paid to the Cl⁻ content, as it readily induces stress corrosion cracking in titanium materials.

Surface Energy and Wettability Assessment

Testing method:
The effect of surface cleanliness on wettability is evaluated through droplet shape analysis (contact angle measurement). A clean surface should exhibit high surface energy and a small contact angle.
Suitable for determining the thoroughness of cleaning processes, particularly for verification prior to coating or bonding.

Correlation Analysis Between Surface Finish and Cleanliness

Surface roughness (Ra value) is measured using a profilometer to evaluate the distribution of contaminants within the microtopography.
High-precision applications require Ra ≤ 0.4 μm, with no localized contamination or enrichment.
II. Cleanliness Control in Special Process Stages
Titanium foil for additive manufacturing: As a raw material for laminated bonding, it is essential to rigorously inspect thickness uniformity, surface finish, cleanliness, and interlayer adhesion performance to prevent inclusions from causing forming defects.
Pre-weld area inspection: Conduct targeted inspections of the weld and the adjacent areas on both sides to ensure there is no residual grease, oxide scale, or coating, thereby preventing any adverse impact on weld quality.
Regenerated/recycled titanium foil: Must be tested for cross-contaminants such as fragments of old coatings, label adhesives, and corrosion products.