Properties and typical uses of tantalum

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This post was last edited by Shaobin Fluid on 2026-3-13 at 14:01. It explains that for most people in the metallurgy industry, tantalum is an unusual metal. Due to its obscurity, its nature is often unknown or misunderstood. Frequently asked questions include, “What kind of steel is that?” ”Or \"Isn’t tantalum one of the hardest metals?\" ”This article describes some properties of tantalum, aiming to clear up some existing confusions. Table IV at the end of this article presents most of the general properties of tantalum in tabular form. Classification of tantalum Tantalum is an active metal and a refractory metal. The periodic table shows that it lies between reactive metals (titanium, zirconium, and hafnium) and refractory metals (molybdenum and tungsten). Tantalum and its sister element niobium are similar to these two elements in many ways, but there are also many differences between them. Refer to Figure 1. Figure 1. The relationship between tantalum and active and refractory metals (excerpt from the periodic table of elements). Tantalum reacts with carbon, nitrogen, oxygen, and hydrogen, as shown in Figure 2. These reactions are common in active metals. The reaction of tantalum with oxygen endows it with excellent corrosion resistance, which will be discussed later. Figure 2. The reaction of tantalum with oxygen. This reaction occurs at room temperature, and an oxide layer forms rapidly to protect tantalum from further erosion. However, when the temperature exceeds 200°C, the oxide layer becomes thicker and more pronounced. This layer is brownish in color, in contrast to the typical gray metal. As the temperature rises, oxygen will begin to migrate through the tantalum matrix, ultimately leading to oxygen embrittlement. The concentration of oxygen and external pressure affect the oxidation rate and oxygen absorption rate. It’s difficult to summarize, but tantalum in an oxygen-rich environment can usually only be exposed to temperatures below 200°C. Nitrogen, carbon, and hydrogen also undergo similar reactions. Hydrogen embrittlement is an important issue for tantalum, and it will be discussed in the context of corrosion resistance. Refractory properties: Tungsten shares many common properties with the refractory metals molybdenum and tungsten. It has an extremely high melting point of 2996°C, which is within the range of melting points of other refractory metals. Its high melting point makes it an excellent choice for high-temperature applications. However, there is one thing to keep in mind. Since it reacts with carbon, nitrogen, oxygen, and hydrogen, it cannot be used in environments where these elements or their compounds exist as gases or volatile substances. Therefore, its use at high temperatures is limited to vacuum or inert gas environments. Density, ductility, and formability of tantalum Tantalum is one of the metals with the highest density. Its density is 16.6 grams per cubic centimeter (0.600 pounds per square inch), and its weight is about twice that of more common materials such as nickel, copper, and steel with the same volume. Tantalum has a higher density than lead, but lower than tungsten and platinum ； Refer to Figure 3. Figure 3. Select the density of the metal. Tantalum is easy to bend, stretch, and shape. Its annealed hardness is on the lower end of the Rockwell B scale, similar to that of pure copper. As shown in Figure 4, its yield strength is similar to that of many more common non-ferrous elements. Figure 4. Strength of the selected metal. The common alloy of tantalum, Ta-2.5W, has a higher yield strength and can provide greater strength with a thinner cross-section. It provides greater strength while maintaining good ductility and formability. Processing and welding of tantalum: The welding and processing of tantalum and its alloys are challenging. Their high melting point and reaction with gases pose challenges to manufacturers. However, the experience of Apex Engineering Products shows that although tantalum and Ta-2.5%W differ from other alloys, their manufacturing is not necessarily difficult if the correct procedures are followed. Table 1: Successful processing of tantalum requires experience. High speeds and low cooling rates generate heat, causing tantalum to react with carbon, oxygen, and hydrogen to form extremely hard particles. These particles quickly dull the tool and cause more heat to be generated. Tantalum is also a soft, gelatinous material that tends to gel. To compensate for these characteristics, a very low rotational speed must be used, and a large amount of coolant is required. Water-soluble oils are suitable for most cooling applications ； Fluorocarbon lubricants can provide additional benefits when needed. Table 1 shows some suggestions. Tantalum welding is typically carried out using the Tungsten Inert Gas Welding (TIG) process, which employs a tungsten electrode and argon as a shielding gas. Special care must be taken to keep the air away from any heated surfaces. Welding should be carried out in a glove box filled with high-purity argon or helium. Alternatively, argon or helium can be used together with long-tail shielding and backshielding (or back purification). Preventive measures must be taken to prevent warm surfaces from being exposed to air, as welding embrittlement may occur. Tantalum and its common alloy containing 2.5% tungsten (Ta-2.5%W) can both be welded in this way. Since the melting points of tantalum and tungsten are similar, no segregation occurs in the alloy during solidification. Therefore, post-weld heat treatment is unnecessary. Compared to materials such as nickel alloys of groups B and C, Ta-2.5%W retains its resistance to corrosion by wrought metals during welding. Due to segregation, the corrosion resistance of nickel alloys in welds is always significantly lower than the published corrosion data for forged alloys. The cleanliness of the tantalum surface has a significant impact on the welding quality. Hydrocarbons (oils) react during welding, forming brittle hydrides and carbides. Before welding, the surface of tantalum should be degreased. Other methods can also be used, such as electron beam welding (EBW) and plasma arc welding (PAW). The preventive measures to prevent hot surfaces from being exposed to air also apply. Corrosion resistance of tantalum: Tantalum is a metal with extremely high corrosion resistance. The most commonly used alloy is Ta-2.5%W, which can resist most common acids at various concentrations and processing temperatures. Table 2 shows a summary of the corrosion rates. Table 2: Tantalum is commonly used in applications involving high temperatures, high concentrations of sulfuric and hydrochloric acids, and contact with bromine. Tantalum is commonly used when the process employs multiple media or when the media are frequently changed in batch processing. A serious limitation of tantalum is its lack of resistance to fluorides and fluoride ions, as well as to most strong bases. In many aspects, the corrosion resistance of tantalum and Ta-2.5%W is similar to that of glass. Tantalum is usually the preferred material when other materials fail. Sulfuric acid services are a great example. Figure 5 is the equal corrosion diagram of many materials in sulfuric acid. These lines represent the temperatures and concentrations at which a corrosion rate of 0.13 mm/year or 5 mils per year (mpy) occurs. Figure 5. Corrosion rate chart – sulfuric acid: 0.13 mm/year (0.005 inches/year). It is clear from the chart that many metals can function at lower temperatures and concentrations. Tantalum is significantly superior at high temperatures and high concentrations. This is a common situation in other acidic media, and tantalum can address the severe corrosion problems in such media. Figure 6 shows the bayonet heater used for sulfuric acid applications. Except for the tube sheet, the entire assembly is made of tantalum-2.5% tungsten; the tube sheet is lined with tantalum and a tantalum-2.5% tungsten alloy, with a thickness of 0.020 inch–0.024 inch (0.51 mm–0.64 mm). The typical pipe size for bayonet heaters is a diameter of 1 inch (25.4 mm), with a wall thickness of 0.015 inch–0.025 inch (0.38 mm–0.64 mm). Figure 6. Bayonet heater with sulfuric acid application. The most serious cause of failure of tantalum in acidic media is hydrogen embrittlement. Ta & Ta-2.5%W react readily with hydrogen to form a brittle solid solution matrix. Generally, there is no free hydrogen in the process medium, but in applications with lower temperatures of the aqueous liquid, hydrogen can be released through the electrochemical reaction shown in Figure 7. The combination of two different metals in an aqueous solution will produce hydrogen on one of the metals. Breaking the electrical connection between tantalum and other metals can prevent the galvanic cell, which is the best solution to the problem. It is usually feasible to place a non-conductive washer between the metals. If this is not possible, Apex Engineered Products can use plated platinum dots to force hydrogen to be released onto the platinum surface, thereby minimizing the impact of hydrogen on tantalum (see Figures 8 and 9). Figure 10. Corrosion rates of tantalum and Ta-2.5%W in sulfuric acid, with and without platinum dots. Results were very promising when pure Ta and Ta-2.5%W materials (with or without Pt spots) were tested in high-temperature, high-concentration sulfuric acid. Table 3 shows the results of the test program. Compared with the corrosion rates of other tantalum and tantalum alloys shown in Figure 10, the Ultra 76 tantalum alloy with a platinum-group alloy additive exhibits excellent resistance to hydrogen embrittlement, and its corrosion resistance in HCl and H2SO4 environments gradually improves. Table 3 shows that, as illustrated in Figure 10, adding tungsten to tantalum can significantly improve the material’s resistance to hydrogen absorption and corrosion. Typical uses of tantalum: Tantalum has a wide range of applications in the modern world. The most common use is tantalum capacitors. Today, anodized tantalum capacitors are used in many common electronic devices. Most other applications take advantage of tantalum’s corrosion resistance or its high-temperature resistance. The pharmaceutical industry finds tantalum very attractive due to its extremely low corrosion resistance. Corrosion by-products contaminate the process medium and introduce contaminants into the product. Figure 11 shows the spiral condenser used in the pharmaceutical industry. Figure 11. Spiral condensers used in the pharmaceutical industry. In the chemical processing industry, few materials can surpass tantalum in acidic media. Tantalum is commonly used as a lining for tanks and pipes in processing vessels, as well as as a heat exchange material in shell-and-tube heat exchangers, condensers, and heaters. In many high-temperature and high-pressure applications, it is often used as a liner for autoclaves. Tantalum can also be used to repair glass-lined containers. Tantalum is generally considered to be used only in small-device applications. However, tantalum devices can be quite large. Figure 12 is a typical example of a large application. This tantalum liner post has a diameter of 72 inches. X, 117 feet long), replaced acid brick, whose maintenance costs were very high and caused long downtime for customers. Figure 12. Examples of large-scale applications. Tantalum is also used for heating elements and insulation shields in high-temperature vacuum furnaces, as well as as crucible materials for many high-temperature applications. The film industry uses tantalum as a sputtering target material for many electronic applications. Tantalum is also used in the medical field for hemostatic clips, stents, and pacemaker components. Due to its corrosion resistance, tantalum is inert in the human body. Conclusion The industry has long recognized that tantalum and its alloys are a solution to some of the most difficult problems. As is well known, tantalum has been in use for decades, while other materials fail very quickly. People usually choose tantalum over cheaper materials because it provides long-term performance and reduces downtime. Figure 13 is an excellent example of the short-life-cycle return of tantalum compared to graphite. Figure 13. The short lifespan of tantalum compared to graphite. Tantalum is also a widely used and easily manufacturable material, whose properties are often superior to those of almost all alternatives. Although its properties are not widely known and it is often misunderstood, differing from more common materials in certain cases, it often provides industrial applications with practical solutions to difficult problems. Some properties of tantalum are given in Table 4 below. Table 4. Atomic and crystallographic properties of tantalum. Table 5. Thermal properties of tantalum. Table 6. Thermal conductivity of tantalum. Table 7. Various properties of tantalum.