Search

A chemical solution deposition route to synthesize silver-gold alloy colloids in thin films with diameters between 8-35 nm has been developed. Ag-Au alloy colloids were synthesized by the addition of silver ions to a polymer protected aqueous gold sol in presence of a seeding agent 'hydroxylamine hydrochloride', followed by a heat-treatment under reducing atmosphere at temperatures ranging from 150-550°C. The resonance wavelength of Ag-Au alloy colloids exists between those of pure Ag (410 nm) and pure Au (525 nm) colloids, which can easily be controlled by selecting the molar ratio of Ag to Au. This allows the tunability of the absorption wavelength (hence the color) by using Ag-Au alloy colloids in thin films.

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.

29Si and 13C MAS NMR spectroscopy, DTA-TG and elemental analysis were used to study the evolution of metastable oxycarbide phases starting from thin gel sheets derived from methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS) and a colloidal silica containing sol, up to 1450°C under a nitrogen atmosphere. The stoichiometric formulae of the glasses obtained by the semi-quantitative analysis of 29Si MAS NMR spectra were found to be in good agreement with those obtained by chemical analysis. It was found that the addition of colloidal silica sol delays the decomposition of methyl groups in MTEOS containing condensates. This delayed decomposition of the methyl groups was attributed to facilitate the strengthening of the matrix, thus leading to crack free sintering of sheets up to 400°C in air and for T>900°C under nitrogen. A significant portion (>40%) of the total carbon present in the glasses was found to exist as free carbon. 13C NMR showed that unsaturated C=C bonds exist in gels heat treated at 1000 °C, but they disappear in heat treated gels at 1200 and 1450°C. Both 29Si and 13C NMR spectra indicate the formation of a ca. 15 atom% SiC phase in the glass sheets sintered at 1450°C, which were found to be amorphous up to 1200°C.

The influence of SiO2 sol-gel coatings on the bending strength of soda lime plate glass samples has been investigated by 3 point bending and double ring bending strength measurements. The samples were prepared by manual glass cutting and were coated with two different types of SiO2 coating: A TEOS coating (thickness of about 100 nm) was obtained from sols synthesized by acid catalysis of tetraethoxysilane and a MTKS coating (thickness of about 1 µm) was obtained from a methyl modified nanoparticulate SiO2 sol. The coatings were applied by dipping and were densified at 500'°C for 1 h. The fracture strength σ0 of edge coated plate glass (60 x 25 x 3.8 mm), determined by 3 point bending test (according to EN 843-1), was increased after coating with TEOS from σ0 = 24 MPa to 40 MPa (67% increase). The fracture strength increased to σ0 = 56 MPa (133% increase) on applying MTKS or a double coating of TEOS followed by MTKS. The evaluation of these measurements using Weibull statistical analysis resulted in m values of 4.1 and 4.2 for the TEOS and MTKS coating and 3.5 for double coating (uncoated glasses m = 5.7), respectively. These results combined with high resolution secondary electron microscopy investigations led to the conclusion that the strengthening effect of the two different sol-gel systems is due to a partial flaw healing and clamping of the crack sides.

The electronic structure of nano-scaled Au-colloids embedded in thin glass-like sol-gel coatings on glass substrates was investigated by small-angle X-ray scattering (SAXS) in grazing incidence and by UV-VIS spectroscopy as a function of the densification temperature of the coatings and of kind and concentration of the stabilizer used in the sol. Special interest was concentrated on the structure of the interface between matrix and colloids. It was found that the structure of this interface changes with the preparation of the coatings. Depending on densification temperature and stabilizer, it was observed that the structure of the surface of the colloids or the interface region between matrix and colloids is changing continuously from a structure similar to a fractal surface to a sharp phase boundary. Further densification leads partially to a 'fuzzy' colloid surface which is supposed to be due to the formation of a highly densified shell around the colloids caused by the ligands.

An increase of light absorption by light trapping is a key issue for the design of thin film solar cells from crystalline silicon. According to our numerical work, the deposition of crystalline silicon layers of thickness, W= 4 µm, on textured glass substrates doubles the cell current for facet angles, α = 75°, and texture periods, p < 16 µm, without the need for anti reflection coatings. We demonstrate the fabrication of such micron-sized light traps by embossing of sol-gel glasses.

Anti-reflection coatings on glass substrates were prepared by the application of sol-gel coatings of silica containing crystalline tin oxide particles. The sol was coated on commercially available float glass by dip-coating and spin-coating techniques. Increasing the surface roughness of the float glass (factor of 50) by a particulate coating material resulted in anti-reflection effects comparable to frosted glass. Haze and clarity, which are a measure for the contrast and definition of an optical system, were determined and compared to the uncoated and the commercial frosted glass. The reflectivity of the float glass could be reduced from 9% to 3%, which is a factor of two better than that of glasses.

An organic-inorganic (O-I) hybrid glass hosting photochromic spirooxazine dyes has been prepared via the sol-gel method with organically modified silican alkoxides as starting materials. The utilization of methyltrimethoxysilane (MTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) at appropriate mole ratios led to different shaped of the glassy materials. The photochromic response, colour-decay speed, thermal and photochemical stabilities of the dye in the hybrid glass were studied and compared with the dye-in-ethanol (DIE) and dye-in-polymer (DIP) systems. The results reveal that (1) the photochromic response is better than both the DIE and DIP systems; (2) the colour-decay speed is similar to the DIE and much higher than the DIP system, and (3) the thermal stability is better than the DIE and similar to the DIP system, while the photostability is between them. Matrix effect is discussed on the photochromism of the dye in the hybrid glass.

Self organising gradient coatings for a variety of substrate materials were developed. The coatings are highly photocatalytically active and are transparent. The coatings show self cleaning properties and exhibit long term stability in weathering experiments.

Bei den holografischen Lichtlenkelementen (LLE) handelt es sich um brechungsindexmodulierte Filme, die in Abhängigkeit vom Betrachtungswinkel sowohl lichtstreuende als auch transparente Eigenschaften in sich vereinen. Eine Brechungsindexmodulation kann z. B. durch einen kontaktlithografischen Prozess innerhalb eines photosensitiven Materials erzeugt werden. Ein geeignetes photosensitives Material ist ein s.g. Photopolymerfilm. Die Brechungsindexmodulation basiert auf der Schaffung von lokalen Konzentrationsgradienten von Verbindungen, die sich in ihrem Brechnungsindex hinreichend unterscheiden. Bei den organisch-anorganischen Nanokompositen (Photoanomere) wird durch den Einsatz von nanoskaligen, anorganischen Partikeln (z.B. ZrO2), dispergiert in einer flüssigen, härtbaren Matrixphase, der im Vergleich zu organischen Verbindungen, höhere Brechnungsindex von geeigneten anorganischen Partikeln (z. B. TiO2, Ta2O5, ZrO2) ausgenutzt. Dadurch gelingt die Steigerung der Brechungsindexmodulation gegenüber photopolymeren Filmen. In einer speziellen Belichtung des Photoanomers können LLE-Filme hergestellt werden, die senkrecht einfallendes Licht in einem kleinen Winkelbereich stark streuen, schräg einfallendes Licht dagegen viel stärker gerichtet transmittieren. Dieses Verhalten eignet sich hervorragend für Projektionsschirme, die das einfallende Licht sehr viel effizienter ins Auge des Betrachters lenken als konventionelle Leinwände und zudem unempfindlicher sind gegen diffuses Streulicht. Ziel der vorgestellten Untersuchungen ist die Herstellung entsprechender Photoanomer basierender LLE-Filme (PN-LLE) direkt auf Glas- bzw. Spiegeloberflächen zur Verwendung als Projektionsschirme.

Es wurden neue Kompositpartikel zur Abtrennung von Schwermetallionen aus wässrigen Abwasserströmen entwickelt. Die Kompositpartikel bestehen aus superparamagnetischen Eisenoxid-Nanopartikeln in einer Borosilikatglasmatrix. Die Oberfläche der Kompositpartikel ist mit Organosilanen modifiziert. Eine Siloxanfunktion erlaubt die chemische Anbindung an die Partikel, eine Komplexbildnerfunktionalität erlaubt die reversible Bindung von Metallionen. Die Kombination der großen freien Oberfläche der superparamagnetischen Kompositpartikel (SPMK) mit einer schnellen Bindungskinetik ermöglicht Abtrennungen insbesondere bei geringen Schwermetallkonzentrationen, die mit herkömmlichen Trennverfahren nur unzureichend durchführbar sind. Ein möglicher Einsatz der neuen Technik lohnt sich daher vor allem dann, wenn das abzutrennende Schwermetall hochgiftig ist (z.B. Cd) und deshalb besonders niedrige Grenzwerte zu erfüllen sind.

A sol-gel route to synthesize semiconductor cuprous halide CuX (X = Cl, Br) nanoparticles in a glassy matrix has been developed. Cu2O and HCl or HBr were used as the precursors for CuX and the matrix was prepared from 3-glycidoxypropyl trimethoxysilane (GPTS)/tetraethoxysilane (TEOS). Samples were dip-coated and cured either by ultraviolet (UV) irradiation at a temperature of 150 degreesC or in an oven at temperatures of 150-250 degreesC. Thin films (thicknesses 0.7-1.0 mm) containing cubic CuCl and CuBr nanoparticles with diameters ranging from 4-16 nm and 2-28 nm, respectively, were obtained. The ultraviolet-visible (UV-Vis) absorption spectra recorded at room temperature exhibited peaks at 371 and 379 nm for CuCl and at 410 and 391 nm for CuBr, corresponding to the Z(1,2) and Z(3) excitons respectively. X-Ray diffraction patterns showed the characteristic (111), (220) and (311) peaks of cuprous halides. High resolution transmission electron microscopy (HR-TEM) characterization proved that the lattice plane spacings correspond to copper halide nanocrystals.

Die etablierten Techniken zur Aufarbeitung schwermetallbelasteter Industrieabwässer haben verschiedene Nachteile. Sie haben geringe Selektivitäten, produzieren große Mengen von Schlämmen oder sind nur schwer im Sinne eines Recyclings in den Produktionsprozeß integrierbar. Außerdem versagen sie oft bei geringen Schwermetallkonzentrationen. Durch die Kombination von gekapselten superparamagnetischen Eisenoxidpartikeln mit einer Oberflächenmodifikation durch Komplexbildner sollte ein Partikelsystem zur Abtrennung von Schwermetallionen aus wässrigen Systemen entwickelt werden. Diese Partikel sollten Metallionen komplexieren und anschließend magnetisch abgetrennt werden. Nach einer Aufarbeitung sollten die Partikel resuspendiert und wiederverwendet werden. Aus Gründen der chemischen Stabilität ebenso wie einer leichteren magnetischen Abtrennung und eines verbesserten Handlings war dazu die Entwicklung eines glasgekapselten Kompositpartikelsystems nötig.

2024, Besonders in der chemischen und pharmazeutischen Industrie ist die Korrosion und Alterung von Glas in Produktionsmaschinen, Laborausrüstungen und auch in Fenstern ein großes Problem. Nahezu alle Forschungen auf dem Gebiet resistenter Materialien beschäftigen sich mit einer hermetischen Versiegelung der zu schützenden Glasoberfläche mit Substanzen, die gegen korrosiven Angriff stabil sind. Nachteile der meisten Beschichtungen sind ihre geringe thermische Resistenz und/oder optische Undurchlässigkeit. So zeigen Polyethylene, -styrole oder -propylene eine gute Transparenz, sind aber auf Temperaturen bis maximal 150 °C begrenzt, was für viele Anwendungen zu niedrig ist. Auch Polyurethane und -ester werden häufig verwendet, sind aber ebenfalls in ihrem thermischen Einsatzbereich limitiert. Einige hochtemperaturstabile Materialien wie Tibesputterte BN-Schichten sind extrem korrosionsunempfindlich, sind jedoch technisch aufwendig und damit sehr teuer, nicht transparent und können auch nicht auf geometrisch anspruchsvolle Gläser appliziert werden. Weitere gebräuchliche Methoden des Alkaliund Korrosionsschutzes sind spezielle Glasmischungen, z.B. mit B2O3, BaO, CaO und Al2O3 oder synthetische Saphir-Gläser. Diese Gläser sind aufgrund ihres hohen Preises ebenfalls für Massenprodukte in der chemischen Industrie ungeeignet. Die sich aus o. g. Gründen ableitende Zielstellung ist die Entwicklung einer transparenten Sol-Gel-Beschichtung, die Korrosionsschutz gegen Alkaliangriff bietet, bis 500 °C stabil ist und nach Möglichkeit auch UV-Schutz besitzt, um die UV-bedingte Alterung von Substanzen zu verhindern.

Thin films containing semiconducting nanocrystals of CuClxBr1-x( x = 0 1) were synthesized by the sol gel process, by stepwise substitution of chloride ions by bromide ions. Cuprous oxide was used as the precursor for copper, HCl and HBr as halide sources, and the matrix sol was synthesized from 3-glycidoxypropyl-(trimethoxy)silane (GPTS) and tetraethoxysilane (TEOS). The films were characterized using ultraviolet visible (UV-VIS) spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction analysis. Thin films (thickness 0.7-1.0 mum) containing cubic CuClxBr1-x (x = 1-0) nanoparticles were obtained. For the samples having no bromide, the absorption spectrum showed a sharp absorption edge at 371 nm. Addition of HBr shifted the peak towards a higher wavelength, giving a peak that is characteristic of CuClxBr1-x; the addition of 1.85 x 10(-2) mole of HBr leads to the complete substitution of chloride by bromide ions. The same observations were also made using X-ray diffraction.

An amino-epoxy-silane based coating system (GAMAL) for glass surfaces was developed, which can efficiently protect bottles from the damages of a bottling plant. Testing bottles with a ramp pressure tester show an identical value of about (40 ± 4) bar for conventionally hot- and cold-end coated bottles and bottles coated with the developed organic-inorganic composite (GAMAL) system. After already 2 min of wet line-simulation testing, all species of a conventionally coated probe fall short of the critical limit of 16 bar, whereas bottles coated with GAMAL (thickness about 7 µm) show a value of (21 ± 3) bar. Coating is possible by dip and spray application on cold or hot (80°C) substrates, the coating is cured at 120°C for 5 to 10 min. Additional functions such as colour or UV protection can be added easily, without reduction of the protection potential. The low content of carbon (about 0.5 g per 11 soft drink bottle) should not disturb the recycling process of such coated bottles.

Thin glasses are very important for display applications. If high bending strength is required, state-of-the-art technologies cannot be applied due to the small thickness. SiO2 coatings derived from tetraorthosilicate and also from a methyl modified silane in combination with a nanoparticulate silica sol are applied to 0 5 nn thick soda-lime glasses by dipping and are fired at 500°C. The bending strength of the glass (double ring method) is increased from about 450 MPa to 1100 MPa by a combination of filling and clamping of the micro flaws in the glass surface. An organic-inorganic coating of only 10 µm in thickness is introduced, which can protect 2 mm thick float glass with extremely high bending strength (600 MPa) completely against the mechanical load of a sand falling test, whereas the bending strength of uncoated float glass is decreased down to 10 % of its initial value by this test. In addition, coatings with optical functions, useful for display applications like antireflective properties, NIR reflectance or colour neutral absorbance of visible light for contrast enhancement, are introduced briefly.

The use of sol-gel derived nanoparticles leads to interesting new materials and systems for optics. The basic principle, to combine transparent matrices with nanoparticles in sizes below remarkable scattering losses opens up new material technologies. The processing is almost as simple as sol-gel processing, and the use of polymerizable nanoparticle even leads to high performance coatings by using simple polymer techniques.