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Vanadium - Its Increasing Role in the Twenty First Century

Vanadium Steels for High-Energy, High-Speed Autogenous Welding

New autogenous welding processes are being developed which make use of the high energy available in lasers and electron beams to increase the speed and reduce the cost of welding. these processes also avoid the use of filler materials as commonly required in arc welding.

Arc welds often contain significant quantities of the oxides introduced via the welding consumables that promote fine grained microstructures associated with toughness in the welds. The beam welding processes however have fused zones which contain very few oxide particles and as a result, coarse microstructures are often developed in the fused zone tending to give brittleness.Unlike most other alloys vanadium tends to stabilise ferrite and produces a special microstructure known as intragranular ferrite which increases the toughness of welds at low temperatures. Vanadium steels therefore have a possible advantage over other steels for use in structures welded by these processes.

The laser welding process has many applications and is being considered for shipbuilding.

Laser welding can also be used on board ship and the process has a potential for use on barges laying oil and gas pipes in deep water where the pipes have to be welded using a single pass with the pipes in the vertical position. Vanadium steels therefore with their characteristic of giving a fine grained, tough weld have a potential for use in offshore pipelines to be laid in deep water for which there will be an increasing demand.

The electron beam process has an even higher power source and can be used for welding thicker plates (50-100mm). It is being developed for the seam and girth welding of thick walled oil and gas pipes and for offshore structures. The beneficial microstructures of welds offered by vanadium steels make them candidates for all these applications.

Vanadium Steels in Electric Generating Plant of the Future

In the quest for increase efficiency and lower cost of electric power generation, combine cycle plant is now being developed. In this plant the primary unit is a gas turbine which will be driven by natural gas. The exhaust gases from this turbine will be used to generate steam which will drive a steam turbine generator.

Developments are also taking place in the use of steam above the critical temperature which would mean that steam temperatures of the order of 650°C will be involved, giving an increase of generating efficiency from the present maximum of 43% to above 45%. Steels in such power plant are required to have exceptional creep properties but chromium steels containing vanadium, niobium and tungsten appear to be effective.

Large scale energy storage systems

The Vanadium redox flow battery is becoming increasingly important for the storage of energy. In these batteris, which resemble small chemical plants, vanadium salts of different valency are circulated from storage tanks, by pumps, round both the positive and negative half cells of the battery. The electrolytes on both sides of the cell are prevented from mixing by a membrane. Even if they do cross contaminate any problems which may be associated with this are minimised because vanadium salts are used on both sides of the battery.

Current flows within the cell when the positiive electrode reacts with ions from the negative electrode via the ion selective membrane. The current is collected using condicting polymer electrode plates which have a graphite felt surface.

In such batteries voltage is a function of the number of cells, the maximum current is a function of the electrode surface area in each cell and the storage capacity is a function of the volume of the electolyte and its concentration. Consequently, the power rating and the energy rating of the battery are decoupled.

It is anticipated that the batteries will find applications in telecommunications, in association with renewable and primary energy systems, as load levelling devices used in conjunction with electricity generation and also in mobile systems such as fork lift trucks, electric vehicles, golf carts etc.

Fusion Reactors

There is increasing concern about the environmental effects (global climatic changes and the impact of acidic emissions) of burning fossil fuels. There is also public unease over the safety of nuclear fission. These considerations will make it difficult for these energy sources to meet the large increases in demand that will inevitably result from population increases in the less developed countries over the next 50 years. Fusion energy represents an alternative that has been shown to have major potential safety and environmental advantages over all other means of base-load electricity generation, at broadly comparable cost.

Several decades of research and development will be needed before commercial fusion energy can be realised but the property requirements of the materials to be used in the most critical parts of a reactor are already fairly well defined. Furthermore, it is clear that the physical and nuclear properties of vanadium make vanadium-based alloys, probably containing chromium and titanium, strong candidates for the structural material of the core.

The properties of vanadium that make its alloys attractive to the nuclear engineer include its high melting point of 1887°C and the fact that 80% vanadium alloys containing chromium and titanium additions possess high creep resistance at temperatures in the region of 698-797°C. They are therefore likely to have the required strength for the core structure and would maintain this strength at relatively high operating temperatures. Vanadium also has a high resistance to attack by lithium and lithium-lead alloys, which could be used as coolants.

Vanadium, together with chromium and titanium, also exhibits a low rate of nuclear transmutation. This is associated with low production rates of hydrogen and helium thus minimising the risk of swelling and embrittlement of the alloys. Moreover, radioactive transmutation products of vanadium are few in number and decay relatively quickly compared with most other metals. This property would possibly have advantages both in operational safety and in management of expired materials and offers the potential for recycling.

Ultra-Light, Ultra-Strong, Complex Alloys for Aircraft

New low density, aluminium-iron-silicon-vanadium alloys with improved corrosion resistance and higher strength at temperatures up to 315°C are being developed for the compressors of aero-engine gas turbines. These will enable higher intake temperatures to be used which will reduce fuel consumption. The alloys also have a potential for aircraft wheels particularly for military aircraft where severe braking produces high temperatures.

Metal Matrix Composites for Aero-Engine Components

Metal matrix composites of silicon carbide continuous reinforced titanium-vanadium alloys offer the possibility of lower density materials which will operate at considerably higher temperatures than those at present used for compressors and other aero-engine parts.

Vanadium High Carbon Grey Cast Irons for Brake Discs and Drums

Heavy trucks operating at high speeds put a strain on the discs and drums in braking systems and there is a demand for improved materials. Vanadium, when added to grey cast iron, refines the graphite and increases the strength without reducing the thermal conductivity or thermal fatigue resistance. These irons are therefore candidate materials for brake drums and discs of the future.