The sol-gel process as a basic technology for nanoparticle-dispersed inorganic-organic composites

Nanoparticles containing hybrid materials became of interest for many areas in the last decade. The reason for this is the fact that, in addition to the molecular inorganic-organic hybrid network, the physical, electronical, optical or catalytical properties of nanoparticles resulting from the inorganic crystalline, glassy or metallic properties also can be used for the material tailoring. For this reason, a survey is given over some interesting developments. Furthermore, in case studies, examples are given for the effect of nanoparticles on the two component Ormosil type of hybrids composed of ethyl ortho-silicate (TEOS) and methylethoxy(methoxy)triethoxy silane (MTEOS, MTMOS). It was shown that the 6 nm SiO2-containing nanocomposite hybrid sols can be dried in form of thick films up to 14 µm after a one step dip-coating process and densified crack-free. This is attributed to the increase of relaxation ability and flexibility. This nanocomposite based on TEOS, MTEOS and particulate SiO2 has been used to develop an industrial process for a new type of environmentally friendly glass fiber mat with a temperature resistance up to 600°C

New sol-gel based coatings as corrosion- and wear-protection on non-ferrous metals

Es wurde ein neuer Beschichtungswerkstoff auf Basis von anorganisch-organischen Kompositen zum Schutz von Metalloberflächen, besonders von Aluminium entwickelt. Das Beschichtungsmaterial wurde über den Sol-Gel-Prozeß synthetisiert, ausgehend von Epoxy-funktionalisierten Alkoxysilanen und aromatischen Diolen als Quervernetzer. Als Lösungsmittel wurden Alkohole und Glykolether verwendet. Die Viskosität der Systeme wurde so eingestellt, dass sowohl Sprüh-, als auch Tauch- und Flut-Beschichtungen durchgeführt werden konnten. Sie lag zwischen 7 und 55 mPas. Nach dem thermischen Verdichtungsprozeß bei 100-220°C wurden transparente Beschichtungen mit ausgezeichneter Haftung auf Al-Mg-, Zn-und Messing-Oberflächen (Gitterschnitt- und Tape-Test: Klasse 0) erhalten. Die Korrosionsfestigkeit beschichteter Aluminiumlegierungen (Al 99.5, AlMg3, AlMgSi I) wurde mit dem Salzsprühverfahren (DIN 50021) und dem CASS-Test (NaCl, CuCl2•2H2O, Essigsäure, pH=3) geprüft und auch nach 3000 Stunden trat keine Unterwanderung der Grenzfläche Metall / Schicht auf. Ebenso wurde keine Filiform-Korrosion beobachtet. Messingproben zeigten nach 500 h Salzsprühnebel-Test weniger als 4 mm mittlere Unterwanderungsbreite. Darüber hinaus wurde die Abriebbeständigkeit der Proben überprüft. Die Schichten zeigten keine sichtbare Beschädigung nach Prüfung des Abriebes mit dem Reibradverfahren (1000 Zyklen, Räder: CS 10-F). Es konnten stabile Dispersionen von organischen Farbpigmenten im transparenten Basissystem hergestellt werden, wodurch eine große Vielfalt farbiger Beschichtungen erhalten wurde.A new composite coating material has been developed for the protection of non-ferrous alloys (e.g. aluminum, magnesium, zinc and brass). The coating materials were prepared by the sol-gel process from epoxyalkoxysilanes and aromatic diols to act as crosslinking agents. As solvent, alcohols and glycol ethers have been used. The viscosity of the system (7 - 55 mPa·s) was established in a way to be used in spray, dip or flow coating processes. The transparent coatings were cured at T = 100 - 220°C. In corrosion tests, 3000 hours salt-spray climate and 240 hours CASS-test = Copper chloride and Acetic acid added Salt Spray, no infiltration of the metal-coating interface and no "filiform-corrosion" on A199.5, AlMg3 and AIMgSi1 was observed. Brass samples showed less than 4 mm extension of a scribe after 500 hours salt-spray-test. The coatings showed no visible traces of abrasion after 1000 cycles taber abrader test and an excellent adhesion (cross cut and tape-test: grade 0). The transparent basic systems were pigmented by 5-10 wt. % of colored organic pigments to obtain all kind of colored coatings

Sol-gel derived thick coatings and their thermomechanical and optical properties

The preparation of crackfree and transparent SiO2 coatings on soda lime glass with thicknesses of about 8 µm after densification at 500°C is presented. The high thickness can be obtained by using on 80:20 mixture of methyltriethoxysilane and tetraethyl orthosilicate as alkoxide precursors in combination with an aqueous colloidal SiO2 sol with particle sizes of about 7 nm. This principle of synthesis is also applied to ZrO2 containing coatings yielding to thickness of about 3 µm. Refractive index measurements indicate that the coatings are nearly completely densified. At higher temperatures tensile stresses appear within the layers and are transmitted to the substrate, increasing its thermal stability

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

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

Flame retardent coatings on glass

The objective of the investigations was to develop a sol-gel coating to increase the thermal instability of glass substrates like plate glass, weavings or glass wool. An organically modified mixed polymer/colloidal SiO2 basic sol has been synthesised, which allows the crackfree densification of coatings with thicknesses up to 80 µm after densification by 500 °C with a one step dipcoating process. The basic system has been adapted to plate glass and glass weavings. It has been shown, that the heat resistance of the substrate materials could be improved substantially by the coating

Flame retardent coatings on glass

The objective of the investigations was to develop a sol-gel coating to increase the thermal instability of glass substrates like plate glass, weavings or glass wool. An organically modified mixed polymer/colloidal SiO2 basic sol has been synthesised, which allows the crackfree densification of coatings with thicknesses up to 80 µm after densification by 500 °C with a one step dipcoating process. The basic system has been adapted to plate glass and glass weavings. It has been shown, that the heat resistance of the substrate materials could be improved substantially by the coating