Characterised by a number of shared properties, it is their exceptionally high melting points that most separate these elements form others in the periodic table and which identifies them as members of group known as the refractory metals. The entry criteria for inclusion in this group vary, however. Some authorities cite a minimum melting point of 2200 °C as the entry point for membership, and name molybdenum, niobium, rhenium, tantalum, and tungsten as the only five valid members. Others choose to set this criterion a bit lower at around 1850 °C, thus enabling the inclusion of a further nine elements in the form of chromium, hafnium, iridium, osmium, rhodium, ruthenium, titanium, vanadium, and zirconium.
Regardless of whether the group should actually number five or fourteen in total, each of these elements displays several of the other characteristic properties of refractory metals that have made them and their alloys so valuable in a wide range of industrial applications. These include high density and exceptional resistance to wear and tear and to various forms of corrosion. One of the first commercial applications for tungsten was in the manufacture of the filaments used in incandescent light globes, the first to offer consumers a product with an acceptable lifespan. Along with molybdenum and tantalum, tungsten is also a suitable choice for the manufacture of the vessels and tools used in the smelting of glass, as well as providing efficient heat sinks.
Just as important as their resistance to heat, their equally exceptional resistance to wear and abrasion serves to make refractory metals an obvious choice for the manufacture of valve seats, nozzles, and gaskets for use in engines and other types of machinery in which exposure to wear tends to be high. Their extreme hardness has led to the use of alloys such as tungsten carbide to make hand tools such as chisels, while, in a less formal capacity, their high density has also made them the ideal choice for the manufacture of golf clubs.
Another group member, molybdenum, may be best known for the anti-friction qualities that qualify it as an additive able to improve the performance of engine oil. A brief look at tantalum, niobium, and rhenium reveals some of the more exotic applications for refractory metals within the fields of electronics and nuclear power, for example. Less exotic but no less valuable are the non-consumable tungsten electrodes use in arc welding.
The latter are just one of the quality products in the range of components and tools designed for use in high-temperature and other specialised applications, and available to industries in South Africa from LIT Africa.