CORDIS provides links to public deliverables and publications of HORIZON projects.
Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Deliverables
Precursor materials were modified to meet with the requirements for the laser-sintering process, and to match with specific applications. Aqueous based precursor solutions were preferred in the project. Zirconia sols were prepared by an electrolysis process. The electrolysis has been applied to an aqueous solution of zirconyl chloride. The remaining chloride content of the Zirconia sols causes corrosion on steel during the coating process, in combination with the low pH-values of 2 of the sols. Therefore the sol has been dialysed. This process achieved a suitable reduction of chloride.
The reduction of chloride gives the opportunity to address more of these sol-gel applications in which water-based processing is preferred (instead of using organic solvents) but chloride causes substrate corrosion. In combination with laser-curing of thin sol-gel films of Zirconia on metallic substrates, reduced surface friction or corrosion protection are possible.
Xaar Jet AB (former MIT-inkjet) was in charge of building the ACERLINK demonstrator, a tool which combines ink-jet facility with a high-precision table for the substrates to be printed on. We have used an ANORAD x/y/z-table set-up on a granite base. Software was written to drive both the ANORAD-table as well the print heads from a master, with internal synchronisation between the table and the print-head driver to assure controlled drop-ejection, and dot placement accuracy.
The Acerlink demonstrator comprises two print heads, driven by two evaluation printer kits as described before. It further comprises a maintenance station, in which the print-heads can be purged, and wiped, as well as being capped in order to prevent drying out of the print-head, and clogging of the ink-jet nozzles.
In the Acerlink project dot placement accuracies of +/- 6µm normal to the relative substrate motion, and +/- 1µm in the direction of the relative substrate motion were shown. Ceramic-loaded Acerlink ink was used for this test.
Xaar Jet AB (former MIT-Inkjet) has designed and built evaluation printer kits to run the piezo-type print heads, which were delivered to the project partners.
These kits comprise a print head, together with a driver card, electronics, and software. The user can download a CAD print-pattern from a PC onto the evaluation printer kit. When disconnected from the PC, the kits act as a stand-alone version, and will print the stored pattern.
In this fashion the user can print certain test patterns, e.g. to evaluate the drop placement accuracy, or other kind of print quality parameters.
Some of Xaar Jet ABs customers use the kit actually in their production lines to print e.g. logos, text, bar codes etc.
Xaar Jet AB (former MIT-Inkjet) has improved the passivation layer on the channel electrodes. It was demonstrated within the Acerlink-project that any kind of direct contact between the metal electrodes and the water-based, electrically conductive Acerlink ink, which contains nano-sized ceramic particles, did lead to immediate disintegration of the ink. With a pin-hole-free passivation layer it was finally possible to print such sensitive Acerlink inks.
The XaarJet print heads were adapted to make smaller drop volumes. Xaar Jet AB (former MIT-Inkjet) has shown that its 360 DPI print head can be modified to eject drops of smaller volume than the standard 32 pico-litres. The parameters modified were the geometrical ink channel dimensions, the nozzle outlet diameter, and the voltage pulse shape that drives the shear-mode motion of the piezo-channel walls. In this fashion the drop volume could be reduced from 32 pico-litres of the standard 360 DPI print head to below eight pico-litres. This made it possible to print lines as narrow as 60µm with the Acerlink inks onto metal or glass substrates.
The feasibility of the additive Acerlink process (ink-jet printing using inks with ceramic precursors and laser-sintering) was demonstrated for making locally wear resistant coatings and electrically conductive structures.
Special precursor materials were developed for the Acerlink process. Several of these were formulated into ink-jet inks and subsequently applied to substrates by ink-jet printing. Conversion to ceramic or conducting layers was done by laser-heating. All precursors (except Ni/ZrO2) could be laser-sintered on fused silica with a CO2 laser. Laser-sintering on other substrates was more complicated, and required different laser settings or lasers with a different wavelength.
A special laser process (with very steep temperature gradients) was developed for the laser sintering of Alumina coatings from amorphous sols. Dense, homogenous and cracks-free nano-crystalline corundum coatings of about 100nm thickness have been produced on different glass substrates to give a strongly improved abrasion resistance.
A pulsed laser treatment on cemented carbide samples with a coating of nano-crystalline Alumina powders was used to densify those coatings. Melting of the Alumina coatings has been achieved without destruction of the cemented carbide substrates. Wear-resistant coatings on steel substrates were made, improving the lifetime of cutting tools made from it. Application of the Acerlink technology using present and different precursors is potentially possible in the electronics industry and in solar cells.
All precursors (except Ni/ZrO{2}) could be laser-sintered to conductive or ceramic layers on fused silica. Several ZrO(2) precursors could be laser-sintered on steel. The fast laser-sintering process was compared with the conventional sintering process using oven heating with much longer times. A mutual agreement was found. In both cases completely densified layers could be obtained. Sintering of the Al2O3 precursors on cemented carbides was not successful, but melting of these layers was possible, which offers new opportunities.
Sintering behaviour of Zirconia sol-gel from amorphous zirconium hydroxide to crystalline Zirconia was very different at different stages in the process. The final obtainable mechanical properties and structure of the layer depend on both the temperature reached and the type of starting material. With an amorphous precursor, a high degree of densification occurs, followed by crystallisation at higher temperatures, resulting in mechanically stable and hard layers. Initially, very small grains with tetragonal structure are found, which grow with temperature and time, and change to the monoclinic crystal structure.
The hydroxyl content of the silica precursor, which is influenced by temperature and heating rate, seems to be very important in relation to the densification behaviour, in contrast to the size of the starting particles. If the heating rate is very large, the peak temperature must be higher to obtain the same degree of densification.
Especially with laser treatments, peak temperature and heating and cooling times are very important. Modelling is an ongoing project serving the insight in temperature-time history. During the Acerlink project some modifications were made, such as the incorporation of the sample dimensions and of temperature-dependent parameters. It became clear that the printed layer must be thicker than 1 micron before some real temperature increase will be obtained from the in-coupling of the laser in the layer. With thinner layers, the laser energy is completely dissipated in the substrate.
A special method using a fast pyrometer was developed to control the laser sintering process by a continuous temperature measurement. The method is suitable to improve the reproducibility of laser-heating processes in production, although only relative temperatures are measured because the emissivity of the surface is not known.
Newly developed Zirconia ink meets with nearly all requirements for the ACERLINK processes. It is applicable for steel and fused silica substrates. The additives used, transform the basic Zirconia sol into a liquid (ink) that meets the rheological needs for being printed with the Xaar Jet AB print-head. The inks properties allow precise placement of small amounts of the ceramic material in a micrometric scale onto the substrate surface using ink-jet technology. The selected additives are non-corrosive either to the print head material or to the substrates.
Wetting and drying properties of the ink are controlled in a way that the deposited ink wets the surface properly and leaves compact and sharp prints without cracks after drying. For example, lines 80 to 100µm wide can be placed with an accuracy of <5µm if the Xaar Jet AB print-head is used. The ink dries within seconds if printed on warm substrates and can immediately be cured by the Laser to sinter the dried print pattern.
The Zirconia ink is suitable for industrial use (e.g. friction reduction of steel) even though sinter density needs to be optimised. Furthermore, it demonstrates a model approach for inks, which are applicable for non-adsorbing surfaces. It has the potential to be adapted to other colloidal materials; e.g. electrically conductive particles or colour pigments. In addition, it may be used for the additive construction of micro-parts (stereostiction) after specific optimisation.
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