SUMMARY of the STARELIGHT project
Project finished December 2003
Abstract
The main objective is the development of
significantly improved alumina ceramics with an extremely reduced grain
size, having the following properties: very high mechanical strength
(approx. 700 MPa instead of approx. 300 MPa now), high transparency
(conventional alumina ceramics is only translucent or opaque), improved
corrosion resistance (e.g., against metal halides), having a complex hollow
shape (now only cylindrical shapes are possible). The improved material will
solve problems in existing applications (e.g., metal halide lamps) and will
lead to new applications such as scratch-resistant windows for bar-code
scanners (now saphire). Metal halide lamps with improved alumina ceramics
will enable to replace energy-wasting halogen lamps on a larger scale which
is not possible now. This can lead to substantial energy savings up to 7
billion KWh in Europe which corresponds to one big power station or 4.5
million tons CO2.
Main Objective
The main objective is the development of significantly improved alumina
ceramics with an extremely reduced grain size, having the following
properties: very high mechanical strength (approx. 700 MPa instead of
approx. 300 MPa now), high transparency (conventional alumina ceramics is
only translucent or opaque), improved corrosion resistance (e.g., against
metal halides), having a complex hollow shape (now only cylindrical shapes
are possible). This requires the development of an ultra-fine high-purity
alumina powder, a suitable ceramic shaping method, and an improved sintering
technique. The benefits of these improved material properties will be
demonstrated for metal halide lamps and robust, scratch-resistant windows.
The project will enable the co-operation of European top-players in order to
reach the very innovative goal of the project and to catch up with Japan
that is technologically leading in this field.
Technical approach
1. Development of high-purity alpha-alumina nano-powder with a mean
particle size of 100 nm, a narrow size distribution, and without hard
agglomerates. Therefore the milling process has to be optimised and an
improved control of the gamma-to-alpha phase-transition is necessary. New
raw materials and processes will also be investigated. Characterisation of
the powder, testing it for the desired applications, and comparison to
existing powders.
2. Investigation of three different ceramic shaping methods (slip-,
pressure-, and gel-casting) for making the desired alumina ceramics in
complex shapes. This requires the development of special moulds, a slurry
injection technique, and a method to release the green product from the
moulds. It requires also the optimisation of the slurry (de-agglomeration,
binders, rheology, etc.). This is essential for the moulding as well as
for the final material properties after sintering (extremely small grain
size at virtually zero porosity and low defect density). Continuous
comparison of the three techniques and choice of the best one before the
end of the project.
3. Investigation and comparison of three different sintering
techniques (pressure less sintering, Hot Isostatic Pressing,
Millimeter-wave sintering). Hot Isostatic Pressing and Millimetre-wave
sintering will be investigated because of the possibility to obtain a
significantly smaller grain size at virtually zero porosity compared to
conventional pressure less sintering as already observed for various types
of ceramics. Continuous comparison of the different techniques and choice
of the best one before the end of the project.
4. Material testing such as density, microstructure (SEM/TEM),
mechanical strength, surface roughness, light transmission, and hardness
in view of the desired applications. Lamp making and testing. Practical
tests of the windows.
The Consortium
Scantech BV. (NL)
Fraunhofer Gesellschaft IKTS (D)
Forschungszentrum Karlsruhe GmbH (D)
Bodycote IMT N.V. (B)
Baikowski Chimie (F)
Philips Research (NL)
|