Axel Kalleder

Nanometer sized particles for viscosity controlled binders for silk screen printing

Abstract A water based synthesis route to PbOSiO2B2O3ZnO gels and glasses has been developed. In the present study the gel was used for the substitution of organic silk screen printing media and additives in a silk screen printing paste for the decoration of glass with a black enamel. Interparticle forces of the gel particles can control the viscosity of a paste, containing 30 wt% of the wet gel and 70 wt% of a commercially available black enamel powder. Beside the rheology controlling function, a consequence of polycondensation of the gel during drying of the printed pastes is, that the sol—gel material acts as a binder. The composition of the gel ensured that during firing the sol—gel material is densified to a glass with properties suitable for the firing process at temperatures between 560°C and 640°C. Because of the particular inorganic gel which was used, no residual organic groups have to be removed during firing.

Sol—gel coatings for the substitution of fluoride or lead containing white decorations on glass

Abstract A SiO2-based sol was developed, which allows the deposition of thick (10 μm), crack free coatings on soda-lime glass. By homogeneous dispersion of TiO2 particles (10 nm to 250 nm in radius) lead and fluorine free white paints are obtained, which can be applied by spray coating to as produced glass without any pretreatment. The coatings can be densified using rapid firing in a tunnel furnace at a temperature of about 560°C for about 30 min, which is typical for firing of enamels. After this densification step, the coatings show good adhesion on soda-lime glass (class 0 of cross hatch cut and tape test) and excellent chemical durability according to Kesternich-Tests.

Fluorescent Er2O3 doped lead silicate glass for optical amplifiers

A hot-pressing method is investigated for the fabrication of a planar optical waveguide amplifier. Therefore commercially available LaSFN15 produced by Schott is used as substrate and cladding material in combination with Er2O3 doped lead silicate glass as core material, synthesised by a hybrid sol-gel melting technique. The lead silicate glass is selected for its low melting temperature required for the waveguide processing. The core glass is adapted to the LaSFN15 with respect to the thermal expansion coefficient and the refractive index. The composition suited for the hot-pressing technology is evaluated to be 45 mole% PbO and 55 mole% SiO2. The influence of increasing Er2O3 content to these parameters is compensated by changing the molar ratio of PbO/SiO2. The optimal composition of the doped core glass is found out to be a glass containing around 3 wt.% Er2O3 because concentration quenching accurs above.

Glasartige Beschichtungen auf keramischen Partikeln über die Sol-Gel-Technik

Fur eine Reihe von Anwendungen ist es von Interesse, die Oberflache von keramischen Partikeln durch Aufbringen von Glasschichten zu modifizieren. Beispiele sind die Realisierung von Diffusionssperrschichten oder eine gezielte Einstellung der Rauhigkeit, Farbe oder Oberflachenladung von einzelnen Pulverteilchen durch geeignete Glasbeschichtungen. Solche Beschichtungen auf einzelnen Partikeln sind nicht mit makroskopischen Beschichtungsmethoden (wie z.B. Dip-, Spin-, Spraycoating, u.a.) aufzutragen, sie konnen jedoch durch Abscheidungsprozesse aus der flussigen oder gasformigen Phase realisiert werden. [1-3]. Im vorliegenden Fall wurde zur Herstellung derartiger Beschichtungen der Spruhtrocknungsprozes [4-7] verwendet. Bei diesem Verfahren konnen Partikel mit einer Grose im unteren MIkrometerbereich mittels Spruhtrocknen mit einem Sol beschichtet werden. Hierbei wird jedes einzelne Partikel mit einer homogenen und gleichmasigen Schicht uberzogen. Als geeignetes Substrat hierfur kommen Teilchen zwischen 5 und 1000 µm in Betracht. Idealierweise haben die zu beschichteten Partikel Kugelform, jedoch konnen auch stark von der Kugelform abweichende Substrate, wie z.B. Glimmerpartikel beschichtet werden.

Preparation and characterisation of thermomechanical properties of sol-gel derived glasses in the PbO-SiO2-B2O3-ZnO system

Silicate glasses with high contents of lead oxide are for example used as optical glasses and as solder glasses. In spite of the numerous usabilities their manufacturing is sometimes difficult, since these melts are chemically aggressive, and the evaporation of lead during melting cannot be avoided. The sol-gel process may be assumed to be an alternative preparation route, since lower temperatures can be used and more homogeneous glasses can be obtained. Thus mixing problems of SiO2 and PbO due to very different densities could be avoided.