Effect of solvent, host precursor, dopant concentration and crystallite size on the fluorescence properties of Eu(III) doped yttria

A systematic spectroscopic study of Eu3+ doped yttria powder phosphors are reported. Fluorescence study of this system has been investigated under the different solvent systems, e.g ethanol and water. In this study, the effect of the precursor of yttria, e.g. acetate, nitrate and chloride, on the fluorescence behaviour of Eu3+ have been observed in particular. Attention was paid to their effect on the emission intensity of the 5D0 -> 7F2 transition which is characteristic of the \u27red fluorescence\u27 of the Eu3+ ion. Results show that the CH3COO- ion has a tremendous effect on the enhancement of emission intensity, greater than NO3- and Cl- ions. The Fourier transformed infrared (FTIR) spectroscopy was used for chemical and structural analysis. It has also been stated that the concentration quenching of dopant was more pronounced in the powders derived from yttrium chloride than from yttria precursor. In the case of Y(CH3COO)3 as a precursor, the concentration quenching was totally absent and emission intensity increased with an increase in the concentration of dopant. This paper also includes some interesting results on the effect of modifiers, which are a mixture of Tween-80 with ε-caprolactum/ β-alanine/emulsogen-OG, on the 5D0 -> 7F2 transition of Eu3+ doped yttria in terms of crystallite size in brief

Correlation of the precursor type with densification behavior and microstructure of sintered mullite ceramics

The effect of alumina component in diphasic mullite precursors containing alkoxy-derived silica on the crystallization and sintering behavior of compacts was studied. The phenomena observed were characterized using differential thermal analysis (DTA), powder X-ray diffraction (XRD), dilatometry and transmission and scanning electron microscopy (TEM, SEM). In order to change the characteristics of as-prepared gels, the alumina source was varied while keeping the silica source constant. Al(NO3)(3).9H(2)O, gamma-Al2O3 and boehmite (gamma-AlOOH) were used as the alumina source and TEOS as the silica source. Clear differences were found in the microstructure of sintered samples derived from the precursors with aluminum nitrate nonahydrate in comparison to the samples containing gamma-Al2O3 or boehmite (gamma-AlOOH). The former exhibited elongated mullite grains embedded into the "equiaxial mullite matrix". This morphology is due to the overlapping of mullite crystallization and viscous flow sintering temperatures. Transient alumina, either added as gamma-Al2O3 or formed in situ by decomposition of boehmite, shifts the mullite formation above the sintering temperature, and enables formation of equiaxial mullite. The smaller are the transient alumina particles, the smaller are mullite grains of sintered bodies

Crystallization kinetics of mullite formation in diphasic gels containing different alumina components

The crystallization kinetics of mullite formation in diphasic gels containing TEOS-derived amorphous silica and alumina component in different crystalline form and particle size has been studied using quantitative X-ray diffraction (QXRD) with 3:2 mullite as a standard and transmission electron microscopy (TEM). As the source of alumina component, aluminum nitrate nonahydrate, commercial gamma-Al2O3 and boehmite (gamma-AlOOH) were used. The results were consistent with previous studies which indicated that mullite forms initially by nucleation and growth. During the second slow stage of transformation, mullite with approximate 2:1 composition subsequently converts further into 3:2. This process is the fastest in the precursor with the smallest particle size of alumina, and the slowest in the sample with boehmite-derived alumina. In very fine scale of morphology the conversion of 2:1 mullite started even in the first stage of transformation

Role of organic components in sol-gel glasses

Organic groupings play an important role for the preparation of glasses by the sol-gel route. They are responsible for the solubility of precursors, interact during the polycondensation process, the drying and ageing step and during firing. For processing, important parameters e.g. hydrolysis rates and the SiOH formation can be controlled by proper choice of the hydrolysable group. If organics remain in the glass network, remarkable changes of properties (density, hardness, refractive index) occur

Ultrafiltration conducting membranes and coatings from redispersable, nanoscaled, crystalline SnO2:Sb particles

Inorganic membranes prepared by the sol-gel method are promising candidates for use as filters in separation processes. Conducting supported membranes and coatings have been produced from redispersable nanoscaled crystalline Sb-doped SnO2 powders with Sb contents up to 10 mol%. The crystalline particles (ca. 4 nm) are fully redispersable in aqueous solution at ph ≥ 8 with a solid content up to 37 vol.% and are monosized. After thermal treatment at different temperatures and times, the pore size diameter of such a powder can be adjusted from 4-20 nm with a very narrow pore size distribution (ca. ±1 nm) and a total porosity of 63%, practically independent of the sintering parameters. Uniaxial compacted substrates (unsupported membranes) present similar characteristics but with a larger pore size distribution (± 5 nm) and 80% total porosity. Their electrical resistance decreases with sintering temperature and time to 4 Ω (800 °C, 8 h). Crack free transparent conducting coatings on glasses and ceramics have been obtained by spin-coating using fully dispersed aqueous solutions of the powder with volume content up to 7.8%. After thermal treatment (1 h at 550 °C) single layers 200 nm thick are still porous and exhibit specific electrical resistivity as low as p = 2.5 x 10-2 Ω cm with 90% transmission in the visible range

Synthesis and processing of nanoscaled ceramics by chemical routes

Nanocrystalline boehmite and TiN powders have been used as model systems for testing the conception of small-molecule surface modification for the preparation of processable nanoscaled slips and pastes with a high solid content. It was found that after surface modification of boehmite with carboxylic acids like acetic or propionic acid and the addition of 5 to 6 vol.-% of organic processing additives pastes with a solid content of about 45 vol.-% can be prepared. The nanocrystalline pastes have been extruded to tubes which after drying exhibit green densities of about 55 to 60 % of the theory. In the case of TiN it was shown that deagglomeration with short-chained organic bases gives low viscous slips with a solid content of 40 wt.-%. Green bodies with a green density of about 50 % of the theory have been prepared by vacuum-assisted pressure filtration. The nanocrystalline material exhibits a very high sintering activity so that a density above 96 % of the theory could be achieved at 1150°C leading to a microstructure consisting of an average grain size of about 50 nm. This clearly demonstrates the potential of nanosized starting material for separating the densification regime from the grain growth regime in the sintering step

What If Your Car Would Care? Exploring Use Cases For Affective Automotive User Interfaces

In this paper we present use cases for affective user interfaces (UIs) in cars and how they are perceived by potential users in China and Germany. Emotion-aware interaction is enabled by the improvement of ubiquitous sensing methods and provides potential benefits for both traffic safety and personal well-being. To promote the adoption of affective interaction at an international scale, we developed 20 mobile in-car use cases through an inter-cultural design approach and evaluated them with 65 drivers in Germany and China. Our data shows perceived benefits in specific areas of pragmatic quality as well as cultural differences, especially for socially interactive use cases. We also discuss general implications for future affective automotive UI. Our results provide a perspective on cultural peculiarities and a concrete starting point for practitioners and researchers working on emotion-aware interfaces

The use of colloidal and surface chemistry for processing nanosized ceramic powders

Surface and colloidal chemistry have been applied to the synthesis and processing of nanoscale ceramic powders. Redispersable oxides, e.g. ZrO2 and Y2O3/ZrO2 with particle sizes less than 20 nm have been prepared by the microemulsion technique as well as by thermodynamically controlled growth reaction in the presence of surface active compounds. By surface modification with short-chained organic molecules which provided short-range steric repulsive forces, nano-scale boehmite and TiN could be processed to high green density compacts. Due to the small particle size of TiN (40nm) and homogeneous green microstructure, nearly full density (>98%) was achieved below 1300°C with negelctable grain growth. The system SiC/B4C/C has been investigated for the improvement of the carbon black distribution within the green specimens prepared by casting techniques and electrohporesis, respectively. For slip casting it was found that nano-scale carbon black can be directly deposited on the surface on the SiC-particles which leads to significantly improved processing and properties of the sintered material (Tb>600 MPa, HV05=31 GPa). An excellent sintering aid distribution within the green parts was achieved by electrophoresis after careful adjustment of the electrophoretic velocity of the different components by surface modification with a polymeric base