Thomas Graule

High solids loading ceramic colloidal dispersions in UV curable media via comb-polyelectrolyte surfactants.

Ceramic articles and ceramic/polymer composites with complex 3d shapes can be produced by rapid prototyping techniques such as stereolithography of ceramic dispersions in UV curable resins. Nanometer and submicrometer ceramic particles are advantageous for high resolution microstructures, surface quality and reduced sintering temperatures. Frequently, special surfactants are needed to maximize solids loading while maintaining suitable rheological properties for stereolithography applications (viscosity <5 Pa s, 301/s). We present here a general scheme for relatively high loading/low viscosity dispersions of nanometer and submicrometer particles in UV curable resins using comb-polyelectrolyte surfactants. In the present approach, adsorption is favorably carried out in aqueous media and the dry particles with adsorbed surfactant are transferred to the organic media through centrifugation, washing, drying and dry milling. The method is demonstrated for Al(2)O(3), ZnO and mixed Al(2)O(3)/ZnO colloidal dispersions. Dispersions containing >48 vol% particles suitable for stereolithography have been achieved. Dispersions containing 36 vol% particles are predicted to have viscosities in the range suitable for direct inkjet printing applications at 75 degrees C. The particle stabilization and transfer schemes, rheological behavior and UV curing characteristics are presented.

Homogeneous functional Ni–P/ceramic nanocomposite coatings via stable dispersions in electroless nickel electrolytes

Stable nanoparticle dispersions in concentrated electrolytes are prerequisite for a variety of advanced nanocomposites prepared by deposition techniques. In this work we investigate the synthesis of electroless Ni-P/functional ceramic coatings from concentrated electrolytes containing functional nanoparticles such as TiO(2), α-Fe(2)O(3), ITO, and CeO(2). Stable nanoparticle dispersions in both low and high phosphorus electrolytes are achieved at plating temperatures (80-90 °C) by a generalized scheme employing comb-polyelectrolyte and antifreeze additives. Dispersion stability at room temperature is achieved in both low and high phosphorus EN media using anionic comb-polyelectrolyte surfactants with polyether side chain of 1100 g/mol. The optimal surfactant concentration is determined by zeta-potential and thermo-gravimetric analysis. Without additives the dispersions flocculate and sediment between 65 and 80 °C. Such phenomenon is believed to be associated with a critical flocculation temperature (CFT). The CFT is also weekly dependent on the particle type and the high ionic strength media. Addition of antifreeze additives such as propylene glycol and urea to the dispersions restores stability and increase the CFT for all particles. We estimate an average increase of the CFT by 1.5-2 °C per 1% additive for all particles and electrolytes. While the particle stabilization scheme is generalized in this work, the composite EN plating proved highly dependent on particle type. Baths containing ITO nanoparticles showed no plating reactions and those containing α-Fe(2)O(3) no nanoparticle co-deposition. In contrast, homogeneous Ni-P/TiO(2) and Ni-P/CeO(2) nanocomposites with up to 22 vol.% nanoparticles are produced. The possible application of the stabilization principles developed here for other functional nanocomposite systems is discussed.

Self-organised microdots formed by dewetting in a highly volatile liquid

Dewetting induced self-organisation was used to prepare an ordered microstructure from a highly volatile liquid. Dewetting of an evaporating iron oxide precursor solute on silicon substrate resulted in arrays of microdots with nearly hexagonal and tetragonal symmetries. Ordered structures form either by stick-slip motion or fingering instability at the receding contact line of evaporating droplets. Subsequent thermal treatment at 550 °C yields crystalline Fe(2)O(3) microdots with a diameter range of 1-4 μm. The size, density and shape of the microdots can be changed by using patterned substrates with different surface energies.

Superhydrophilic ceramic glazes for sanitaryware

Based on industrial ZrSiO4 glazes for sanitaryware, a new glaze with photoactive oxides was developed. The development aimed to produce a glaze that is smooth in order to decrease contamination of the ware and increase superhydrophilic wetting behaviour for easier cleanability. The glazes were characterized with profilometry, atomic force microscopy, x-ray diffraction and scanning electronmicroscopy. For reactivity under UV light, the wetting angles in the dark and after irradiation, aswell as the degradationofmethylene blueweremeasured. SampleswithTiO2 showed no improvement in wetting, neither in the dark, nor under UV irradiation. However, compared with the industrial ZrSiO4 tile, the cleaning properties were improved in the case of bulk contaminants likemustard. Evenmore promising resultswere achieved by replacingZrSiO4withZnO.The glazes developed in thiswork showed surface roughness of less than 20 nm and superhydrophilic wetting under UV illumination.