Martin Klinecky, left, testing customer materials in the vacuum test chamber
View into the Vacuum test chamber
Increasingly, coating processes in photovoltaics, for semi-conductors and also for other products in glass or metal, require vacuum conditions or inert gases. Infrared emitters transfer energy without contact and are consequently ideal heat sources for vacuum processes. It is of great advantage if the infrared system is precisely matched to the vacuum application.
Heraeus Noblelight has created a vacuum test chamber in its in-house Application Centre in Kleinostheim. Since its foundation, the test centre has helped to allow infrared emitters to be matched precisely to product and process. In-house tests keep track, in a targeted manner, of the influences of vacuum conditions on infrared heat; they allow customers to investigate their materials and processes more precisely, so that they can design infrared systems of maximum efficiency.
In photovoltaics, for semi-conductors and even generally for glass- or metal-coatings, heating processes under vacuum conditions are being increasingly used. Plates, discs or work pieces are processed at very high temperatures and, during this, in many cases oxidation must be prevented.
Generally, infrared heating technology is used for the heating process, as infrared radiation transfers energy without contact and at high power.
“We have quickly established that the ambient atmosphere can influence the efficiency of the infrared radiation,” says Martin Klinecky, specialist for vacuum applications at Heraeus, “we carry out tests in conditions as near to those met in practice as possible, so that we can design infrared systems in the most optimum fashion.” When, for example, metals oxidize when they are heated in air, then often their surface character and color change and thus their capacity to absorb infrared radiation. Consequently, test results cannot be simply extrapolated to vacuum conditions.
Because customers have asked increasingly for tests of infrared radiation under vacuum, Heraeus have set up a vacuum chamber with infrared heating technology in their in-house Application Centre, where pressures of 1000 mbar up to 10-6 mbar can be generated according to customer requirements. For these tests, short wave infrared emitters or medium wave Carbon Infrared (CIR) emitters can be used. These heat the materials either directly in the chamber or via a quartz glass sheathing tube. When a sheathing tube is used, it is possible to replace the emitter simply from outside. The tests are recorded by computer with the aid of temperature sensors and are evaluated in collaboration with the customer.
Sometimes with striking results: “Some metals heat up under vacuum twice as quickly as in normal atmospheres, with others there is practically no difference,” says Martin Klinecky, “this very much depends on the conditions of the heating process!”
One example is that of aluminum components which are heated at 1000 mbar and then, in comparison, at 10-4 mbar with short wave infrared emitters. In normal atmospheres, 150ºC is reached in 4 minutes; under vacuum, the same temperature is achieved after 2 minutes.
The color and the type of the material and the color and the thickness of the coating, as well as the required temperature and drying time all affect the design of the heating process. Even with innovative coatings and new materials, tests are very much worthwhile to ensure that systems are designed and built in the most energy-efficient ways possible.Box: Infrared emitters for vacuum conditions
With the QRC reflector, Heraeus has been successful in producing for the first time in producing a reflector which sits directly on the emitter for vacuum applications. Infrared emitters with quartz reflectors are already used in the manufacture of solar cells. They heat carrier materials before and during the coating especially effectively because this process takes place under vacuum or at very high ambient temperatures.
Heraeus Noblelight GmbH with its headquarters in Hanau and with subsidiaries in the USA, Great Britain, France, China, Australia and Puerto Rico, is one of the technology and market leaders in the production of specialty light sources. In 2009, Heraeus Noblelight had an annual turnover of 71.6 Million € and employed 707 people worldwide. The organisation develops, manufactures and markets infrared and ultraviolet emitters for applications in industrial manufacture, environmental protection, medicine and cosmetics, research, development and analytical laboratories.
Heraeus, the precious metals and technology group headquartered in Hanau, Germany, is a global, private company with over 155 years of tradition. Our businesses include precious metals, sensors, biomaterials and medical products, dental products, quartz glass, and specialty light sources. With product revenues of € 2.6 billion and precious metal trading revenues of € 13.6 billion, as well as more than 12,300 employees in over 110 subsidiaries worldwide, Heraeus holds a leading position in its global markets.
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