Tungsten fills niche in new innovations

President-elect Joe Biden's plans to spend $2 trillion on infrastructure and move the world's biggest economy toward greener policies is brightening the outlook for base metals, including tougher-than-nails tungsten.

Many countries, including the United States, have designated tungsten as a critical metal after China, which accounts for 80% of annual global tungsten production of 85,000 metric tons, have placed restrictions on its exports of the metal.

Tungsten is often overshadowed by other elements in discussions about the global supply of critical minerals meeting growing demand from industry and high-tech applications. Minerals such as lithium, cobalt and rare earth elements have soaked up the limelight in recent years, while tungsten in both alloys and compounds have increasingly been used in manufacturing new technologies, from aerospace and defense to medical devices.

A critical element

The European Commission recently recognized tungsten as having the highest economic importance of all raw materials. The mineral is already listed as critical in the United States, Japan, India and Australia.

A U.S. Geological Survey assessment to identify which mineral commodities are most at risk to supply disruptions also ranked tungsten near the top of the list in 2020.

Though tungsten resources are plentiful in Canada and the United States, with significant deposits in 12 states, including Alaska, neither country currently has producing tungsten mines.

"However, the United States may have future production potential from U.S. projects that are currently in the advanced exploration stage," said Jeff Mauk, research geologist at the USGS Geology, Geophysics, and Geochemistry Science Center.

The U. S. government has supplemented American tungsten supply in recent years from its reserves. According to USGS data, roughly 3,390 metric tons of tungsten has been sold out of government stockpiles since 2017.

A hard, versatile metal

It is tungsten's unique properties that make it the go-to mineral for certain industrial and high-tech applications. In its raw form, tungsten is an extremely hard steel-grey metal that is often brittle and hard to work. If made very pure, tungsten retains its hardness (which exceeds that of many steels), but becomes malleable enough that it can be easily worked by forging, drawing, extruding, or more commonly sintering, which is the process of compacting powdered minerals into a solid material without melting them.

Of all metals in pure form, tungsten has the highest melting point (6,192 degrees Fahrenheit), lowest vapor pressure (above 3,000 degrees Fahrenheit at temperatures), and the highest tensile strength. Though carbon remains solid at higher temperatures than tungsten, carbon sublimes, or becomes a vapor, at atmospheric pressure instead of melting, so it has no melting point.

Tungsten also has the lowest co-efficient of thermal expansion of any pure metal. The low thermal expansion, high melting point and tensile strength of tungsten originate from strong metallic bonds formed between tungsten atoms. Thus, alloying small quantities of tungsten with steel greatly increases its toughness.

Demand for tungsten carbide

Tungsten alloys and compounds play important roles in industry. Tungsten carbide, for example, is used extensively in cutting tool materials, mining and drilling tools and wear parts. This extremely hard alloy contains equal parts of tungsten and carbon atoms. It is a dense, metal-like substance, light gray with a bluish tinge, that decomposes, rather than melts, at 4,712 degrees Fahrenheit. Tungsten carbide is prepared by heating powdered tungsten with carbon black in the presence of hydrogen at high temperatures.

Nearly 60% of the tungsten consumed used in the United States in 2019 was used to make cemented tungsten carbide, a compound of roughly equal parts tungsten and carbon.

About twice as strong as steel, tungsten carbide is often found on the working end of drill bits, saw blades, wear plates and other items that require the compound's toughness.

The hardness and density of tungsten carbide also makes it ideal for making armor-piercing projectiles for the military.

Elemental tungsten is also used in manufacturing heating elements, light-bulb filaments, rocket engine nozzles and TIG (tungsten inert gas) welding, as well as many applications that take advantage of tungsten's ability to hold up to heat.

The global tungsten carbide market is projected to grow at a compound annual growth rate of 5.1% during the next five years. Growing potential for tungsten carbide in the aerospace and defense industry is the chief contributor to growth in this market.

Tungsten in tech

The use of tungsten in new technologies varies widely across industries as researchers develop new applications and use the mineral in different ways to improve on existing products.

In the quest to build a better and safer lithium-ion battery for use in cell phones, laptops and electric vehicles, a team of engineers at Rensselaer Polytechnic Institute in New York recently demonstrated how they could use aqueous electrolytes instead of the typical organic electrolytes to assemble a battery that still performs well.

Aqueous electrolytes had been eyed for that role for some time because of their non-flammable nature and because they are not sensitive to moisture in the manufacturing process, making them easier to work with and less expensive. The biggest challenge with this material has been maintaining performance.

The breakthrough came from dense-packing niobium tungsten oxide particles in the battery's electrode, which greatly improved its storage capacity without affecting its fast-charging capability, the researchers said.

"It turns out that niobium tungsten oxide is outstanding in terms of energy stored per unit of volume," said Nikhil Koratkar, who headed the research team at Rensselaer.

An inexpensive material, made from tungsten disulfide flakes just a few atoms thick, has helped to improve the performance of organic solar cells. The discovery by Saudi Arabian researchers could be an important step toward bringing these photovoltaic cells into wider use for generating clean electricity. The team found that the tungsten disulfide layer has a lower resistance than the conjugated polymer previously used, and is also better at gathering electron vacancies, or "holes" than the other materials, leading to improved performance.

In May 2020, a Hong Kong-California research collaboration reported building an artificial eye with capabilities that come close to those of the human eye. The artificial eye is made with an aluminum-lined tungsten shell that serves as a round casing.

Metal 3D printing has become well-established and the range of metals that can be 3D printed is increasing quickly. Industrial 3D printer supplier ExOne Dec. 13 reported adding iron infiltrated with bronze and bonded tungsten to the range of metal and ceramic powders that can be used with its multi-material M-Flex machines. The company said one of the main reasons it has seen demand for using iron to 3D print parts instead of stainless steel is lower costs. Using bonded tungsten for 3D printing, ExOne collaborated with partner companies to produce products to replace lead parts in medical imaging and aerospace applications.