High Purity Tantalum Powder

In addition to sputtering films in semiconductor technology, this tantalum powder can also be used for other applications, such as medical applications and surface coating.

The following method for manufacturing high-purity tantalum powder comprises the following steps in sequence.

1 ) hydrogenating the high-purity tantalum ingot

2 ) crushing and sieving the tantalum chips obtained from the hydrogenation of the tantalum ingots and then purifying them by acid washing to remove the contamination of impurities brought in by the ball milling process

3 ) High-temperature dehydrogenation of the resulting tantalum powder

4 ) deoxidation of the resulting tantalum powder

5 ) acid washing, water washing, drying, and sieving of the tantalum powder

6 ) The tantalum powder is subjected to low-temperature heat treatment, then cooled, passivated, discharged, and sieved to obtain the finished product.

In the manufacturing process, high-purity tantalum ingots are defined as those with a tantalum content of 99.995% or more. These ingots can be obtained in a variety of ways, for example by sintering or electron bombardment at high temperatures using tantalum powder produced by various processes as the raw material. These ingots are also commercially available.

There is no restriction on how the hydrogenated tantalum chips can be crushed, for example by means of an airflow crushing plant or a ball mill, but preferably all the crushed tantalum powder particles should be able to pass through a screen of 400 mesh or higher, e.g. 500 mesh, 600 mesh or 700 mesh. The higher the mesh size, the finer the tantalum powder, but if the powder is too fine, e.g. above 700 mesh, it is more difficult to control the oxygen content of the tantalum powder. Therefore, the sieving in step 2) preferably refers to sieving between 400 and 700 mesh. For the purpose of illustration and not limitation, ball mill crushing is used in the implementation.

Unlike low-temperature dehydrogenation, which is used in the field to save energy, high-temperature dehydrogenation is preferably carried out in the manufacture by heating the tantalum powder under inert gas protection and keeping it warm for about 60-300 minutes (e.g. about 120 minutes, about 150 minutes, about 240 minutes, about 200 minutes) at about 800-1000°C (e.g. about 900°C, about 950°C, about 980°C, about 850°C, about 880°C). The tantalum powder is then cooled down, removed from the furnace, and sieved to obtain the dehydrogenated tantalum powder. Surprisingly, the inventors found that the higher temperature described for dehydrogenation made it possible to reduce surface activity at the same time as the dehydrogenation.

In step 4, the tantalum powder is deoxidized at a low temperature, i.e. the maximum temperature of the process is preferably not higher than the dehydrogenation temperature, which is generally about 50-300 °C below the dehydrogenation temperature (e.g. about 100 °C, about 150 °C, about 180 °C, about 80 °C, about 200 °C), which is sufficient to achieve the purpose of deoxygenation while ensuring that the tantalum particles do not sinter or grow so that the magnesium or magnesium oxide particles do not become encapsulated in the tantalum particles. The magnesium or magnesium oxide particles are encapsulated within the tantalum particles and cannot be easily removed during the subsequent pickling process, resulting in a high magnesium content in the finished product.

Deoxidation is carried out by adding a reducing agent to the tantalum powder. Preferably, the said deoxidation process is usually carried out under inert gas protection. Generally, the reducing agent in question has a greater affinity for oxygen than tantalum does for oxygen. Such reducing agents are, for example, alkaline earth metals, rare earth metals, and their hydrides, most commonly magnesium powder. As a specific preferred embodiment, this can be achieved by mixing tantalum powder with 0.2-2.0 % magnesium metal powder by weight of tantalum powder, loading the tray using the method described in Chinese patent CN 102120258A, heating under inert gas protection, holding at approx. 600-750°C (e.g. approx. 700eC) for approx. 2-4 hours, then evacuating and holding again under evacuation for approx. 2-4 hours. The temperature is then lowered, passivated, and removed from the furnace to obtain a deoxidized, high-purity tantalum powder.

The advantage of this method is the combination of high-temperature dehydrogenation, low-temperature deoxidation, and low-temperature heat treatment. As the raw tantalum powder contains hydrides that are inevitably generated by the absorption of hydrogen, its properties (e.g. lattice constant, electrical resistance, etc.) are altered in ways that cannot yet be completely eliminated by conventional low-temperature dehydrogenation. The purpose of using low-temperature dehydrogenation is to avoid the growth of sintered particles caused by high deoxygenation temperatures.

The above-mentioned combination of high-temperature dehydrogenation, low-temperature deoxidation, and low-temperature heat treatment avoids the sintering and growth of tantalum powder particles caused by high temperatures in the conventional process (i.e. dehydrogenation and deoxidation at the same time) and the encapsulation of magnesium or magnesium oxide particles inside the tantalum particles, resulting in poorly controllable particle size and high magnesium content in the final product; it also avoids the problem of incomplete dehydrogenation caused by low temperatures, resulting in high hydrogen content. The problem of high hydrogen content due to incomplete dehydrogenation caused by low temperatures is also avoided. The low-temperature heat treatment mainly removes the residual magnesium metal after deoxidation, the impurities such as H and F from the pickling, and ensures that the particles do not grow, so that the impurity content is well controlled while achieving the particle size requirements. In the end, the method of the invention resulted in a high-purity tantalum powder with a purity of >99.995% by GDMS.

Tantalum powder performance comparison

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