Processing Technology of Tantalum Bar to Wire

The production of tantalum wire is usually carried out by powder metallurgy or other isostatic pressing, vacuum sintering to obtain a tantalum rod, followed by cold rolling and surface cleaning to obtain a tantalum strip, and then the wire is obtained by surface oxidation coating, stretching, pickling, water washing, and annealing. The processing process of the tantalum bar to wire includes the following steps.

Isostatic molding

The chemical composition of the tantalum powder raw material for preparing the tantalum should meet the specified requirements, and the particle size distribution should satisfy the requirement that 100% is less than 0.074 m, and the content of less than 0.038 m (400) is not less than 60%. The bar blank after press forming requires no defects on the surface, no cracks, and has a certain strength, reaching 70% of the theoretical density.

Isostatic-molding
Isostatic-molding

Vacuum sintering

Usually, the melt sintering is performed, the sintering vacuum should be less than 0.133Pa, and the highest sintering temperature should be controlled within 2600 °C. Generally, after two times of vertical melting and sintering, the relative density of the tantalum can reach about 98%, and the surface of the tantalum is required to be smooth, without cracks, melted tumor knots, and bubbling.

Cold rolling

The production of tantalum wire and the forging of tantalum bars are generally carried out by cold rolling. It can be used as a manufacturing process before die forging, or it can be directly rolled into an ingot. Roll forging is a process in which a tantalum rod is passed through a pair of rotating wrought rolls equipped with circular arc dies, and plastically deformed by means of a cavity to obtain the desired ingot.

Cold rolling
Cold rolling

Anodizing

The purpose of anodizing is to uniformly coat an oxide film on the surface of the tantalum ingot (wire). As a carrier of the lubricant, the oxide film can uniformly and firmly adhere the lubricant, which can reduce the tensile friction coefficient, ensure the surface quality of the silk, and cannot directly contact the metal and the mold, then prevent the bonding and improve the tensile performance.

The standard of the oxide film is that the adhesion is strong, the micro-tightness is firm, the color is not easy to fall off, the thickness is uniform, the insulation is good, the residual current is small, and the surface is less crystalline.

Stretching

Stretching is a major process in the production of tantalum wire. The choice of lubricant, drawing die, stretching pass and stretching speed will directly affect the quality of the wire. The stretching of tantalum is divided into the thick wire and fine wire. Solid wax is generally used as a lubricant for roughening the thick tantalum wire with an oxide film, an aqueous solution of grease soap is generally used as a lubricant when the tantalum wire with oxide film is finely drawn. The tensile die has cemented carbide and diamond, the latter is better but more expensive. The processing rate of the stretching pass depends mainly on the quality of the oxide film and the quality of the lubricant.

The surface of the wire after stretching is stuck with oil and residual oxide film, so it is necessary to clean the surface with acid and then with pure water. For the fine wire, the acidity of the pickling and the pickling time are strictly controlled. When the oxygen content and the surface brightness are good, the acidity and pickling time should be minimized.

Tantalum wire
Tantalum wire

Vacuum annealing

Annealing of the tantalum wire includes two parts, intermediate annealing and finished annealing. The purpose of intermediate annealing is to eliminate work hardening and improve the processing plasticity of the wire to continue stretching, while annealing is to achieve the desired properties of the finished product.

Tantalum has good plasticity at room temperature, and the work hardening tendency at room temperature is not large. The practice has shown that the billet produced by powder metallurgy can be processed until the total deformation rate is about 95%; the total deformation rate of the extruded billet by electron beam melting and consumable arc melting can reach more than 99%. After the recrystallization annealing, the plasticity of tantalum at room temperature is completely recovered.

Wire rewinding

In order to facilitate the material leaving the factory after the wire has been annealed, it is generally necessary to rewind on a certain winding machine. When rewinding, it is necessary to prevent the surface from being stained or scratched and to prevent twisting.

Stanford Advanced Materials supplies high-quality tantalum products to meet our customers’ R&D and production needs. Please visit https://www.samaterials.com/ for more information.

Is tantalum Toxic?

Tantalum is a shiny, silvery metal which is soft when is pure. It is almost immune to chemical attack at temperatures below 150℃. Tantalum is virtually resistant to corrosion due to an oxide film on its surface.

Applications of tantalum

Tantalum is used to manufacture surgical implants, capacitors, aircraft engines, and alloys. It is used to produce high-temperature devices because of its high melting point. The element also has application in the chemical industry because of its good corrosion resistance. It is used to manufacture refractive index glass, electron tubes, and alloys for missiles, nuclear reactors, chemical equipment, and jet engines.

However, the element is rarely added to alloys because it makes some metals more brittle. Tantalum is used to manufacture tubes because it forms oxides and nitrides that create the vacuum. In addition, it is used to manufacture special optical glasses, non-ferrous alloys for aerospace and nuclear applications, metallurgical and chemical processing equipment, high-voltage surge arresters, and more. It is also used to make circuitry for devices and computers, electrolytic capacitors, and tantalum compounds and alloys. Glass-line equipment is also manufactured. Its compounds are used to produce clips, mesh, surgical equipment, and machinery.

solid-tantalum-chip-capacitors
Solid Tantalum Chip Capacitors

The harm of tantalum

Tantalum powder is not as serious as other metals (zirconium, titanium, etc.), but it has the risk of fire and explosion.

Tantalum-related jobs often carry the risk of burns, electric shocks, eyes, and trauma. The refining process involves toxic and dangerous chemicals such as hydrogen fluoride, sodium, and organic solvents.

Toxicity

Both tantalum oxide and tantalum metal have low systemic toxicity, which may be due to their poor solubility. However, there are also skin, eye, and respiratory hazards. In alloys of cobalt, tungsten, and niobium, tantalum is considered to be the cause of pneumoconiosis and skin damage caused by hard metal dust.

Tantalum hydroxide has no toxic effect on chicken embryo, and intraperitoneal injection of tantalum oxide has no toxic effect on rats. However, when tantalum chloride has an LD50 of 38mg/kg(Ta), the compound salt K2TaF7 is about one-fourth toxic.

tantalum-chloride
Tantalum Chloride

Safety precautions

In most operations, general ventilation can maintain the dust concentration of tantalum and its compounds below the exposure limit. Flame, arc, and spark should be avoided in the area where tantalum powder is handled. If workers are regularly exposed to dust concentrations close to the critical value, regular physical examinations should be conducted, with emphasis on lung function. For operations containing tantalum fluoride and hydrogen fluoride, precautions applicable to these compounds should be followed.

Tantalum bromide (TaBr5), tantalum chloride (TaCl5) and tantalum fluoride (TaF5) shall be stored in a clearly labeled and cool, ventilated place away from compounds affected by acid or acid smoke, and the persons concerned should be reminded of the danger.

Stanford Advanced Materials supplies high-quality tantalum products to meet our customers’ R&D and production needs. Please visit https://www.samaterials.com/ for more information.