Refractory metals are different. As a group they provide a number of unique characteristics – such as resistance to high heat, corrosion and wear – making them useful in a multitude of applications. What are refractory metals? Refractory metals have one characteristic in common: an exceptionally high melting point. Tungsten, for example, melts at 3410oC (6170oF), which is more than double that of iron and ten times that of lead.
As a group, they are found in one section of the periodic table of elements. Although there are twelve refractory metals, we specialise in four:
Tungsten, Molybdenum, Niobium, and Tantalum.
The paradox of refractory metals is that, despite their wide and constantly growing list of applications, many people – sometimes even engineers, working with one of the metals – do not fully understand how and where each is mined, how it is processed, how it is formed, or even understand the full extent of the diversity of refractory metals’ applications.
Very high melting point (2468oC/4474oF to 3410oC/6170oF): High melting points of Tungsten, Tantalum, Niobium and Molybdenum make them useful in processing molten metals and minerals such as glass making.
Excellent strength at high temperatures. Even when heated to 1000oC (1832oF) Tungsten rocket nose cones still have twice the tensile strength iron has at room temperature.
Exceptional resistance to corrosion. Stainless steel piping in chemical plants contains Molybdenum and Niobium.
Excellent wear and abrasion resistance: Refractory metals, often in alloy form extend the life of seals, bushings, nozzles, valve seats and many points of high wear. Alloys with gold and silver also make excellent long-life contact points or electronic equipment.
High resistance to thermal shock. The stresses of rapid expansion due to heat would destroy most metal filaments in just a few on-off cycles. A Tungsten filament, because of its high melting point and good non- sag characteristic, will withstand thousands of on-off cycles and still remain intact.
Some of the refractory metals are among the highest in density…they are used as a weight for precision ballasts on gyroscopes of aircraft and as weights in golf club heads.
Good Electrical and heat conducting properties: Besides their use in many electrical and electronic applications, refractory metals are often used as heat sinks…this semiconductor chip is set in a molybdenum or tungsten sink.
