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- 2016 (3) (entfernen)
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- Agglomeration (1)
- Analytical centrifuge (1)
- Barium titanate nanopowder (1)
- Ceramic dispersion (1)
- Nanopulver (1)
- Particle size analysis (1)
- Partikelgröße (1)
- Shelf life prediction (1)
- Stability assessment (1)
- Stabilized dispersions (1)
Resolution of capacitive sensors can be improved enormously by replacement of the dielectric material between the capacitor plates (e.g. air-dielectric) by a dielectric fluid with high permittivity. High dielectric liquid dispersions of ceramic micro and nano powders should be qualified as dielectric fluid with longtime shelf life.
For this purpose it was necessary to produce stabilized ceramic suspensions with high particle concentration and to investigate sedimentation processes of the particles. Characterization of particles was done by use of zeta potential measurement, gas adsorption measurements (BET), density measurement with gas pycnometer as well as particle sizing by ultrasound spectroscopy and by use of an optical centrifuge.
Shelf life of optimized electrostatic and steric stabilized ceramic suspension was investigated by use of an optical centrifuge, a LUMISizer 651 MW (LUM Ltd.) with STEP technology and front tracking analysis. Two different wave lengths – NIR (865 nm) and blue light (470 nm) were available for examination. Centrifugation measurements with different rotation speed were used to study the rheological behavior and the sedimentation process. By this way it was possible to achieve accelerated stability determination. Measured values could be used to simulate the sedimentation process under gravity acceleration and to predict shelf life for suspensions with different dispersants.
Fünf verschiedene Messverfahren wurden zur Partikelgrößenanalyse von nanodispersen ZrO₂-Pulver verglichen. Mit der Laserstreulichtanalyse, der dynamischen Lichtstreuung (heterodyne DLS und homodyne DLS-PCS), der Sedimentationsanalyse im Zentrifugalfeld und der Ultraschallspektrometrie wurden wässrige ZrO₂-Suspensionen mit verschiedenen Feststoffkonzentrationen hinsichtlich ihrer Partikelgrößenverteilung analysiert. Als Referenz diente die REM-Analyse zur Ermittlung der Primärpartikelgröße (ca. 40 nm). Mit den hier vorgestellten Messverfahren konnten in den entsprechenden Suspensionen nur Sekundärpartikel im Bereich von 105 nm bis 224 nm detektiert werden, die somit auf das Vorhandensein von Aggregaten bzw. harten Agglomeraten hinweisen.
Resolution of special capacitive sensors can be improved enormously by replacement of the gaseous material between the capacitor plates by a ceramic dispersion with high permittivity. High dielectric liquid dispersions of ceramic submicron and nano barium titanate powders should be qualified as dielectric fluid with long-term shelf life for this use.
Investigations for the production of stabilized barium titanate dispersions in aqueous and organic liquids by use of different dispersant aids were performed. Characterization of dispersed particles and agglomerates was done by use of zeta potential measurements for aqueous dispersions as well as particle sizing by laser diffraction, ultrasound spectroscopy and dynamic light scattering for aqueous and organic dispersions. Optimization of stability was evaluated by accelerated sedimentation measurements with an optical centrifuge. Best results were achieved for barium titanate dispersions in silicone oil.