By Ron B. Davis Jr., Georgetown University
The strong trend of increasing melting points and density is clear as one descends from chromium to molybdenum and tungsten in the periodic table. The latter two are well known for their durability and use in high-temperature applications such as lighting, where tungsten filaments can literally be heated to white-hot temperatures and remain solid.
Tungsten
Tungsten’s position in the sixth period gives it an awesome density, at 19 grams per cubic centimeter, rivaling that of uranium. Tungsten has two stable isotopes which means that it can be used, for example, to forge conventional military munition projectiles with the density and hardness of so-called ‘depleted uranium,’ but without the radiological, toxicological and environmental challenges that depleted-uranium poses.
Many modern armor-piercing munitions are made partially or completely of tungsten. Tungsten was even once considered for the payload of a weapon that could deliver the destructive force of a tactical nuclear bomb, but without any of that pesky radioactive fallout.
Project Thor
In the 1950s, as it became clear that nuclear weapons were on their way to becoming a standard part of the superpower military arsenal, the US military received a proposal from Boeing employee and later science-fiction writer, Jerry Pournelle, for a different weapons technology named ‘Project Thor’.
The proposal was to place an array of satellites containing metallic rods the size of telephone poles into orbit above the Earth, where they could be called to drop onto targets anywhere in the world within minutes, striking the ground at ten times the speed of sound with a force similar to a small asteroid.
Understandably, such a projectile had to be dense, hard, and able to withstand the high temperatures of re-entry. And what better material to accomplish all of this, than tungsten.
But tungsten’s ideal traits for dropping also made it impractical for raising into place. A six-meter rod of pure tungsten would weigh in excess of 9 tons. The cost of delivering all that mass into space made it more affordable for warring nations to just lob lighter-weight missiles at their targets, packed with radioactive explosives.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Niobium and Tantalum
Just left of molybdenum and tungsten, and below vanadium are two less well-known metals that are no less useful in engineering and manufacturing.
Niobium and tantalum aren’t just vertical neighbors on the table. These two elements in group 5 of the table share so many similarities that it was more than four decades after their initial discoveries, in 1801 and 1802, that they were finally separated from one another, in 1846, and conclusively proven to be separate elements.
Their similar electron configurations and similarly-sized atomic radii cause them to often be found comingled in nature, sharing similar spaces in minerals like columbite.
Even their names suggest this close relationship: ‘niobium’ refers to the Greek mythological goddess Niobe, daughter of king Tantalus, for whom the larger element Tantalum is named.
From Gas Pipelines to Aerospace Industry
Based on their position in the table, would one expect niobium and tantalum to be hard, high-melting-point metals with a colorful chemistry? Yes—And that is exactly what they are.
Much like vanadium above them, niobium and tantalum both have significant strengthening effects when alloyed with steel and other metals. This property has made both of these elements useful in alloys for manufacturing applications from gas pipelines to the aerospace industry.
Niobium
Also like vanadium—niobium can deliver a pop of color to materials. Thus, niobium has recently been used to produce selectively colored silver coins by several nations including Canada and Austria.
By alloying silver with niobium, then carefully and specifically oxidizing the niobium atoms in the alloy just the right amount, a range of brilliant colors can be created with the beauty and permanence worthy of collectible coins.
Being low and centered within the d-block, both niobium and tantalum also have very high melting points. So high, in fact, that niobium originally competed with tungsten as the preferred metal for incandescent light filaments. Niobium’s high heat resistance even led to it being used as the principal metal for fabrication of rocket nozzles on some of NASA’s most famous vehicles, like the Apollo Service Module.
Common Questions about Tungsten, Niobium and Tantalum: The Metals with High Melting Points
The proposal made under Project Thor was to place an array of satellites containing metallic rods the size of telephone poles into orbit above the Earth, where they could be called to drop onto targets anywhere in the world within minutes, striking the ground at ten times the speed of sound with a force similar to a small asteroid.
Tungsten’s very ideal trait for dropping it also made it impractical for raising the rods into place. A six-meter rod of pure tungsten would weigh in excess of 9 tons. The cost of delivering all that mass into space made it more affordable for warring nations to just lob lighter-weight missiles at their targets, packed with radioactive explosives.
Niobium and tantalum both have significant strengthening effects when alloyed with steel and other metals. This property has made both of these elements useful in alloys for manufacturing applications from gas pipelines to the aerospace industry.
