Analysis of Titanium Rod Substrates for Electrodes: Intrinsic Material Properties of Titanium Rods Dedicated to Electrolytic Working Conditions

In electrochemical systems such as water electrolysis for hydrogen production, chlor-alkali chemical industry, electrochemical water treatment and non-ferrous metal electrowinning, Titanium Rods act as the core substrate of MMO coated anodes. They perform multiple functions including conducting electricity for support, resisting anodic corrosion and carrying noble metal active coatings. Many projects suffer premature electrode failure, abnormal rise in cell voltage and coating peeling. Most of these faults stem not from coating process defects, but improper selection and substandard metallurgical quality of titanium rod substrates.

Many purchasers only focus on external dimensional parameters of titanium rods such as outer diameter and length, while ignoring the internal metallographic structure, impurity control and surface condition of substrates. As a result, the whole electrolytic system fails to reach its designed service life. Starting from material fundamentals, this paper analyzes the intrinsic characteristics of titanium rods dedicated to electrolytic environments, providing technical references for engineering type selection and incoming material inspection.

In the article “Titanium Anode Tubes: Special Pipes Exclusive to the New Energy Electrolysis Sector, the Core Substrate for Cost Reduction and Efficiency Improvement in Electrolysis Systems,” we discussed the applications of titanium anode tubes in the field of electrolysis. For more details, please read the original article.

I. Special Requirements of Electrolytic Working Conditions for Titanium Rod Substrates

There is almost no difference in appearance between ordinary Industrial Titanium Rods and electrode-specific titanium rods, yet their internal control standards vary greatly. Under long-term anodic polarization in electrolytic environments containing chloride ions and acidic media, together with heavy current, temperature cycling and bubble scouring, substrates must meet four rigid requirements:

1. Excellent anodic corrosion resistance: Under electrified anodic conditions, a titanium dioxide passive film forms on the surface of titanium rods. This passive film must be continuous and dense. Once local rupture occurs, rapid pitting corrosion of the substrate follows, directly causing substrate damage, massive peeling of active coatings and permanent electrode failure.
2. Stable electrical conductivity: The substrate must have a homogeneous structure free from local segregation to ensure uniform current transmission. Enrichment of impurities inside titanium rods leads to locally elevated resistance, forming hot spots and overloading local current density, which accelerates electrode degradation.
3. Coating compatibility and adhesion: The metallographic grain structure and surface quality of titanium rod substrates directly affect the adhesion of noble metal oxide coatings. Coarse grains, surface oxide scale or excessively deep machining marks easily induce coating blistering and cracking during sintering.
4. Structural and dimensional stability: Repeated temperature fluctuations inside electrolytic cells require substrates to withstand thermal stress without bending deformation. Distortion of titanium rods shifts electrode spacing, disrupting current distribution across the electrolytic cell, raising energy consumption and increasing side reactions.

⚠️ Special Reminder: Titanium Alloy TC4 is not suitable as an electrolytic anode substrate. Alloying elements aluminium and vanadium precipitate under anodic polarization, destroying the passive film and leading to rapid electrode failure. High-purity commercially pure titanium TA1/TA2 is preferred for electrolytic anode substrates, while TA10 titanium rods are selected for special highly corrosive working conditions.

II. Performance Comparison of Mainstream Grades of Electrode-Grade Titanium Rods

Titanium rods used in the electrolysis industry comply with Chinese standard GB/T 3620.1 and American standard ASTM-B348. Oxygen, iron, nitrogen and hydrogen are key impurity elements affecting the quality of electrode-grade titanium rods. Oxygen content directly determines passive film quality; iron segregates at grain boundaries and readily induces intergranular corrosion; excessive hydrogen leads to hydrogen embrittlement and significantly raises the risk of crack initiation under high-current operating conditions.

The table below compares key parameters and applicable scenarios of titanium rod grades commonly used in electrolytic environments:

III. Adverse Impacts of Metallographic Structure and Impurity Defects on Electrode-Grade Titanium Rods

Many users experience rapid failure after commissioning even with qualified material test certificates. The root cause usually lies in metallographic structure. Even if chemical composition meets the lower limits of national standards, inadequate control of ingot forging and rolling processes can trigger metallurgical defects.

1. Excessively large grain size: Improper annealing of titanium rods results in coarse grains. Coarse α-titanium grains cause uneven grain boundary distribution on the substrate surface. After coating sintering, stress concentrates at grain boundaries, facilitating coating cracking and peeling during service and shortening overall electrode service life. Electrode-specific titanium rods ideally possess uniform fine equiaxed α structures, avoiding coarse columnar grains.
2. Segregation of impurity elements: Local enrichment of iron and nitrogen at grain boundaries forms secondary phases. Under anodic polarization, grain boundaries corrode preferentially, initiating internal intergranular corrosion of titanium rods. Such damage is difficult to detect externally; by the time cell voltage rises sharply, irreversible substrate deterioration has already occurred.
3. Surface defects of bar stock: Cracks, laps, deep machining tool marks and hard oxide scale. Deep-seated defects cannot be completely eliminated by subsequent grinding. In electrolytic environments, these defects act as corrosion initiation sites, gradually expanding into pitting cavities that penetrate the substrate. Electrode-grade titanium rods must undergo strict surface defect control; deep laps and cracks are unacceptable.

Frequently Asked Questions (FAQ)

Q1: Is TA1 titanium rod always superior to TA2?

A: Not necessarily. TA1 delivers higher purity and better corrosion resistance yet comes with higher material costs. TA2 titanium rods fully meet the requirements for conventional water treatment and chlor-alkali working conditions. TA1 is prioritized for seawater systems and long-service-life projects with high current density. Blindly specifying higher grades brings unnecessary costs; upgrading material grades cannot further improve electrode performance if overmatched for operating conditions.

Q2: Chemical composition meets specifications on material certificates, why does severe corrosion still occur during electrolytic operation?

A: Material certificates only reflect the chemical composition of sampled positions and cannot represent the metallographic structure of the entire titanium rod. Out-of-control ingot casting, forging and annealing processes lead to local impurity segregation and metallurgical defects along the bar. For critical projects, additional metallographic sampling inspection is recommended, rather than relying solely on material test reports.

Q3: Does a brighter titanium rod surface indicate higher substrate quality?

A: Brightness merely reflects surface machining status, not internal metallurgical quality. Finely turned and polished low-quality titanium rods may still suffer from coarse grains and impurity segregation internally. When purchasing electrode-grade titanium rods, both internal metallographic quality and surface machining quality should be evaluated; appearance gloss alone is not a reliable criterion.

Q4: Can TC4 Titanium Alloy Rods be used as anodic titanium rod substrates?

A: TC4 is not recommended for anodic working conditions. TC4 contains aluminium-vanadium alloy phases that corrode preferentially under anodic polarization, breaking down the passive film and directly triggering coating peeling and substrate perforation. TC4 titanium alloy can only serve as cathode structural parts in electrolytic cells and must never be used as MMO anode substrates.

Q5: What pre-treatment procedures are required for titanium rods before coating sintering?

A: Sandblasting and pickling are needed to remove surface oxide layers and machining stress. The original surface quality of titanium rod substrates directly determines the base state after pre-treatment. If laps and cracks exist on the raw substrate surface, these defects will be exposed after sandblasting and pickling, leaving hidden risks.

Conclusion

The overall service life of electrolytic electrodes is jointly determined by substrate, coating and operating condition management. Coatings function as active layers for electrocatalytic reactions, while titanium rod substrates form the foundation of the entire electrode. Ignoring the intrinsic properties of titanium rod substrates and relying merely on optimized coating processes cannot effectively resolve premature electrode failure. Only by selecting titanium rod substrates with matching grades and qualified metallographic quality according to electrolyte medium, current density and temperature conditions can electrolytic systems achieve long-term stable operation and reduce maintenance and replacement costs.