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MicrobondFirebird
All over the world, in millions of fluorescent tubes and energy-saving lamps, amalgam spheres create the chemical conditions for the conversion of electrical energy into agreeable light.
Energy conservation is the most important element for climate protection and C02 reduction. It is great for Umicore to be able to contribute to this with
Application in compact fluorescent lamps(CFL) & fluorescent tube lamps (FTL)
The mercury vapor pressure in the discharge vessel of the lamp controls the luminous flux of the lamp. CFL & FTL lamps work on the low-pressure mercury discharge principle. The discharge tube has an electrode sealed into each of its ends and is filled with an inert gas and a little mercury, the latter being present in both liquid and vapour form. A discharge is obtained by sending electrons through the gas from one electrode to the other. If the speed of the electrons is moderate, the collision with an electron of the mercury atom will eject it temporarily into a higher orbit, a process called excitation. These so-called exciting collisions result in the emission of electromagnetic radiation, which occurs when the excited electron falls back into an orbit of lower energy. The inside of the tube is coated with fluorescent powder. This coating converts the ultraviolet radiation of the mercury discharge into longer wavelengths within the visible range. The mercury vapour pressure above an amalgam is always lower than that of pure mercury. It implies that the number of mercury atoms in the discharge is too low at starting, resulting in a low luminous flux and long time to reach a temperature at which the lamp gives the expected amount of light.
An amalgam is a chemical compound consisting of mercury and one or more other metals
The vapor pressure of mercury in the lamp is a function of the working temperature of the lamp. These characteristics (see below figure : Hg vapor pressure as function of working temperature) make the amalgam very suitable for compact and tube fluorescent lamps, where a relatively large amount of energy is generated in a small volume, causing higher temperatures. The luminous flux of the lamp is directly triggered by the vapor pressure of mercury, which depends on amalgam characteristics. Figure 1. illustrates the function of amalgam in a lamp compared to a traditional lamp. Umicore amalgam alloys enable optimum luminous flux over widest ambient temperature range. The requirement that the lamp has to operate properly in all burning positions makes the search for an optimum more complex. The mercury is present in the lamp in both its liquid and gaseous forms. An increase in temperature will lead to mercury evaporation, resulting in a higher vapor pressure. A decrease in temperature implies mercury condensation resulting in a drastically reduced vapor pressure.
Development towards more accurate mercury dosage & Pb-free amalgam alloys
To achieve further development of the CFL (Compact Fluorescent Lamp) towards freedom from lead and towards more dimensions and less mercury discharge in the environment, it was necessary to find new amalgam alloys. Those have to work efficiently and ensure a long service life for a more compact CFL, operating at high temperatures. The new “Restriction of Hazardous Substances (RoHS)” imposes limitations on the amount of lead and mercury content in the amalgam spheres. For this reason, the use of alloys containing lead is extremely limited. Therefore, the amalgam alloys based on BiIn, BiInHg, BiPbSnHg and SnHg are used in the form of spheres. Also only a low amount of mercury is permitted to be used for the spheres and therefore a low amount of amalgam for the lamps. So far, common spheres have had a diameter of 2.5 mm - 2.8 mm and a weight of about 100 mg. The new CFL need amalgam spheres with a diameter of 0.8 mm - 2.0 mm and a weight of 5 mg - 50 mg. Therefore, a new process for the production of the spheres had to be developed.
With its new process, Microbond EPM can manufacture these small spheres in the required quality. With the ability to adapt the diameter of the amalgam spheres, an exact proportioning of the mercury for every type of lamp is possible.
General product specification
Diameter range: 0.8 to 3 mm
Tolerance: ± 0.025 mm to 0.2 mm (depending on sphere diameter)
Batch size: mass production 35,0 kg / sampling 0.5 kg
Alloy Melting range by DSC analysis BiSn32.2Pb19.0Hg5.4% 70 - 110°C BiSn33.0Pb19.4Hg3.0% 75 - 110°C BiIn29.0 98 - 112°C BiIn28.8Hg3.9% 92 - 110°C InSn38.8Pb19.4Hg4.5% 107 - 126°C BiSn38.5 Pb4.0Hg0.7% 85 - 115° C
Please click here to download an article from the newspaper "Licht", issue 05/2007.
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http://www.electronicmaterials.umicore.com/de/microbond/produkte/microbondFirebird/