A Novel Method for Tantalum Powder Preparation

Tantalum powder is one of the most important materials in the electronics industry, particularly for the production of tantalum capacitors. Tantalum capacitors are most desirable for their high capacitance-to-volume ratio, thermal stability, and consistency. As the demand for miniaturized and high-performance electronic equipment grows, so does demand for finer and purer and more specialized powders of tantalum. A novel development in preparation offers shining solutions to age-old issues in the production of tantalum powder.

What Is Tantalum Powder and Why It Matters

Tantalum is a valve metal that can produce a stable and insulating oxide covering, and therefore an ideal candidate for use as the anode in solid electrolyte capacitors. The quality of a tantalum capacitor depends to a very large extent on the qualities of the tantalum powder employed—i.e., its purity, particle size, morphology, and specific surface area.

High-quality tantalum powder has the advantage of a large surface area to unit volume, and hence increased capacitance. More fine powders, with intricate particle structure and greater porosity, while enhancing capacitance, introduce the disadvantages of greater leakage currents and lower breakdown voltages. Thus, a compromise has to be achieved in particle design, purity, and controlled porosity.

How to Make Tantalum Powder and the Advance

The most commonly used traditional method for the production of capacitor-grade tantalum powder has been sodium reduction of potassium fluotantalate (K₂TaF₇). Although the process is well-established, it is limited for economically producing powders with surface areas of greater than 4.5 m²/g. It generally involves the use of excess diluents and sintering retardants that complicate purification and limit scalability.

Moreover, although theoretically feasible to make high-surface-area tantalum powders, control of tight porosity, impurity content, and grain morphology at the industrial level remains difficult. These limitations drive research towards novel preparation routes that are less costly, less environmentally degrading, and can produce uniform high-performance powders.

How to Prepare Tantalum Powder with the New Method

A new process, patented in patent CN201610236819.7, offers a low-cost and scalable method for the production of high-capacity tantalum powders from tantalum oxide (Ta₂O₅), eliminating fluotantalate intermediates. High surface area, high purity, and particle shape as per user are guaranteed in this multi-step reduction and deoxidation process.

Step-by-Step Process

1. Composite Mixing

Ultrafine, spherical Ta₂O₅ (300–500 g) is blended with a carbon-based reducing agent (95–165 g) in deionized or distilled water to form a uniform slurry.

2. Filtration and Pre-Drying

The slurry is pressure filtered (0.1–0.2 MPa) to form a filter cake, which in turn is heated (100–200°C), dried (50–100°C), crushed, and sieved (70 mesh) to provide a precursor powder.

3. Carbon-Based Reduction

This precursor is vacuum-heated—first to 1450°C (1 hr), then to 1700°C (10–30 min)—activating reduction of Ta₂O₅. Slower air passivation on cooling stabilizes the produced low-oxygen tantalum powder (5–10 wt% O).

4. Primary Deoxidation

The powder is blended with 0.8–1.5 wt% magnesium (based on oxygen content) and heated at 780–860°C for 4–8 hours. Controlled passivation is then followed.

5. Acid Cleaning

Excess magnesium and byproducts are removed by washing with 10–15% nitric acid followed by deionized water rinsing to neutral pH. The powder is vacuum-dried at 60°C for 12 hours and then sieved, resulting in high-oxygen tantalum powder (1.5–4 wt% O).

6. Phosphorus Addition

A precise quantity of ammonium dihydrogen phosphate (NH₄H₂PO₄) is added in order to obtain ~150 ppm phosphorus, which improves the electrical properties of the powder.

7. Secondary Deoxidation and Nitriding

A second deoxidation with 1–1.5 wt% magnesium is performed at 780–860°C for 3–5 hours. Nitrogen is supplied for surface modification during cooling (170–300°C). Controlled passivation ensures safety.

8. Final Purification

The final wash is conducted to eliminate residues, and thereafter drying and sieving are performed. The result is capacitor-grade tantalum powder of high purity that is tailored for electrical performance and reliability.

Advantages of the New Method

This new oxide reduction process conserves cost and waste by avoiding halide intermediates, but its stepwise reduction/deoxidation method keeps particle size and impurities tightly under control for consistent, scalable manufacture. Oxygen and phosphorus levels being variable, manufacturers can tailor powders to the high CV per gram demanded of high-end capacitors. Added passivation and nitriding also improve safety and shelf stability by mitigating storage and handling oxidation.

Conclusion

This new procedure for the production of tantalum powder is a significant advance in electronic components materials science. It avoids some of the significant drawbacks of traditional processes in being less costly, more manageable, and cleaner to high-performance powders. As demand for high-capacitance, miniature devices continues to grow, this process should bring about the next generation of tantalum-based capacitors. For more tantalum powder and tech information, please check Advanced Refractory Metals (ARM).