High temperature gas corrosion of metal and alloy refractories

Many sectors of human activity involve techniques and devices that require the use of sophisticated materials capable of withstanding extreme conditions in terms of durability, mechanical strength and operating temperature. For reasons such as increasing thermal efficiency, or limiting pollution, it is necessary to select materials that can withstand high temperatures, continuously or not, for varying lengths of time, but which are crucial to the success of the operations in question.

One example is the need to increase the maximum operating temperature of aircraft engines wherever possible. Carnot's principle states that the greater the difference between the temperature of the hot and cold sources, the greater the efficiency of a heat engine. The development of materials capable of meeting this requirement has been the subject of a great deal of successful research and development over the last fifty years. For example, the temperature of aircraft engines has risen from 650-750°C, towards the end of the Second World War, to 1,250-1,350°C (or more...) for the hot parts of today's jet engines... This represents an average gain of around 10°C per year!... An absolutely remarkable result.

Such high and alternating operating temperatures must be reached and maintained for periods ranging from a few hours for fighter aircraft, to several tens of hours for today's long-haul aircraft. Thermal cycles must also be repeated many times over the life of the aircraft engine.

This imperative to increase thermodynamic efficiency, which remains a permanent objective, can however be applied in very different conditions of use. For example, we may be dealing with huge engines such as terrestrial turbines for energy production, with very long operating times, but in quasi-isothermal conditions... or, on the contrary, with smaller engines which, for their part, must be very reliable for fairly short periods (from a few tens of seconds to a few tens of minutes), as in the case of propellant combustion chambers, with oxygen/hydrogen gas mixtures, for the Vulcain and Vinci engines providing propulsion for Ariane rockets, for example.

In addition to the above-mentioned applications for heat engines, there are many other industrial sectors that require materials to withstand high temperatures. These include, for example, tools for shaping metals and alloys (forging, stamping, extruding, drawing, rolling, etc.), or those required for heat treatment installations (electrical resistors for furnaces). High temperatures are also required for processes encountered in various industries, such as cement, glass and ceramics, or for incineration of household or industrial waste, and for coal combustion or transformation (gasification, liquefaction)....