Papers by Keyword: Precursor

Abstract: Ceramic Matrix Composites (CMC) have a wide interest for high temperature applications. The materials can be modified by the selection of the matrix precursor as well as of the reinforcing materials. C/C-composites can be easily modified by post-treatments with silicon in order to acquire different tribological properties from good sliding behaviour up to braking systems only depending on the manufacturing technique of these materials. It will be demonstrated during the presentation that the manufacturing depends on one hand side on the material which has to be manufactured and on the other side on the structural component and the number of parts which are required. Furthermore, it will also be shown, that silicon treatments can be performed up to a full conversion of C/C materials creating a new family of monolithic ceramic materials. Within the presentation detailed information will be given on possible processing routes as well as the resulting physical and mechanical properties of the materials.

Abstract: Main applications for preceramic polymers (precursors) are ceramic fibres, ceramic matrices and coatings. The requirements for the polymer are determined by the intended application and differ from a cross-linkable liquid to meltable and curable or unmeltable but soluble solid. For applying these precursors on a larger scale, they must be processable by conventional polymer processing techniques. Furthermore, the starting material should be cheap and readily available, and the synthesis should be uncomplicated. Considering these criteria, specially tailored precursors in the system Si-C-N (silazanes) were synthesized in a laboratory scale by ammonolysis of different chlorosilanes. After investigating the properties suitable precursors were produced in a pilot plant (approx. 5 kg). Variation of both the functional groups of the chlorosilane educts and the synthesis conditions lead to precursors with tailored properties (liquid, solid, soluble) and a special cross-linking behaviour (catalyst, initiator, electron-beam). Selected applications with the special precursors were presented for producing ceramic SiCN-fibres via melt-spinning also with a precursor modified with multi-walled carbon nanotubes as well as for processing a new kind of metal-ceramic gradient compound by reaction of SiCN-precursors with Ti-powders during pyrolysis.

Abstract: Spherical LiAlxMn2-xO4 fine powders were continuously produced by Internal Combustion Type Spray Pyrolysis Apparatus Using Gas Burner from metal nitrate precursor solutions. XRD showed
that LiAlxMn2-xO4 powders were well crystallized in a spinel structure with the Fd3m space group. As-prepared powders have a spherical particle shape with a diameter of 2.3 μm. As-prepared samples were calcined at 800
 for 10 h in air. The charge/discharge capacity of LiAlxMn2-xO4 was over 100 mAh/g. A powder production capacity speed of 1 kg/h was attained by this system.

Abstract: A new photochromic ZrO2 precursor solution was prepared using zirconium tetra-n-butoxide, 4-(phenylazo)benzoic acid and ethyleneglycol monomethylether. The ZrO2 precursor solution was irradiated with ultraviolet light (UV) at room temperature. After that, UV-irradiated precursor solution was irradiated with visible light (Vis) at room temperature. UV-Vis spectra were measured before irradiation, after UV irradiation and Vis irradiation. Changes of UV-Vis spectra indicated that the new ZrO2 precursor including 4-(phenylazo)benzoic acid shows photochromism. The phenomena have synchronized with reversible photoisomerization of 4-(phenylazo)benzoic acid in the precursor. In addition, the difference of peak position originated from Zr-O CT transition between before UV irradiation and after UV irradiation increased with increasing the concentration of 4-(phenylazo)benzoic acid. Furthermore, the optimized structure of the new ZrO2 precursor was derived by density functional theory (DFT) calculation.

Abstract: The development of lead-free piezoelectric materials has been required from the viewpoint of environmental preservation. We focused the lead-free KNbO3-based systems, and used a chemical solution deposition (CSD) process to obtain their precursor. (Na1-xKx)NbO3 precursor solutions were prepared from metal alkoxides and solvents such as absolute ethanol and 2-methoxyethanol. Crystallization behavior of the precursor gels obtained from the above solutions was investigated by the thermogravimetry differential thermal analysis (TG-DTA) measurement.

Abstract: A method is presented for more than doubling the volume yield from an AlPO4 precursor, aluminium chlorophosphate ethanolate, from approximately 20% to 50% by replacing the ethanol ligands with water. It is shown that this increases the volume yield from about 20% to 50%. The precursor is used to make an Al2O3 powder bonded with an amorphous AlPO4 with a Young modulus of 80 GPa and a strength of 60 MPa.

Abstract: Extensive interfacial reactions are known to occur between Fe-Co based perovskite cathode materials and the standard solid oxide fuel cell (SOFC) yttria stabilized zirconia (YSZ) electrolyte. Thin films of gadolinia doped ceria (GDC) could be used as a diffusion barrier between the cathode and the electrolyte. The present work investigates spin coating thin diffusion reaction inhibiting films onto SOFC electrolytes. The chemical and structural evolution of ethylene glycol based precursor solution is studied by means of rheology, x-ray diffraction (XRD), high temperature XRD (HT-XRD), Fourier-transformed infrared spectroscopy (FTIR) and differential thermal analysis (DTA). The studies show that cerium formate is formed as an intermediate resin. Thin films, up to 500 nm thick, of gadolinia doped ceria (GDC) are successfully produced by multiple spin coating of polymerized ethylene glycol derived solutions on 200 1m thick YSZ tapes. The GDC and YSZ interfacial surface morphology and film thickness are studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). These films are shown to successfully prevent the creation of non-conducting reaction phases at the cathode-electrolyte interface by blocking interdiffusion.

Abstract: The microstructure of the polyacrylonitrile (PAN) precursors can strongly affect the structure of the carbon fibers which determine the final mechanical properties of carbon fibers. The orientation factors ( n f
) of PAN precursors under different draw ratios were characterized by the birefringence (
n f ), which was obtained through polarized microscopy. The results show that the increasing of the draw ratio may enhance the degree of orientation, which can correspondingly improve the mechanical properties. However the increasing speed of the orientation factor slows down as the draw ratio reached to 8.

Abstract: The main purpose of this paper is to present a spray dryer device developed to synthesize ammonium niobium-oxalate precursor powder with controlled grain size. The dryer device is manufactured using stainless steel 304 and measures 0,48m in outside diameter and 1,9m in height. The spray dryer has a cylindrical shape assembled on a conical base. The central chamber is heated by three 4 KW resistances and is equipped with serpentine coil heaters placed around its main body. This configuration guarantees that the air is at the same temperature of the chamber walls and the adherence of the powder particles on the wall is prevented. The precursor solution is atomized on the air stream downwards from the top to the bottom, at low rates. Powder particles are collected on a 0,4m diameter horizontal plate placed at the bottom portion of the dryer and the wet air is released from the chamber by the opening located under the collecting plate. The synthesis of the niobium oxalate precursor and the results of the decomposition process are described.