Research Interests:
ABSTRACT
Research Interests:
Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature... more
Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature stating that fluctuations are possible only between an equilibrium and a non-equilibrium phase. The basic conditions used to describe fluctuations are well suited to calculate the limits for fluctuations
Research Interests:
... Under these conditions, the plasma is not too far from thermal equilibrium. One observes temperatures significantly above 4,000 K; (Rao et al. ... Nozzle design reach from very simple to highly sophisticated ones with hypersonic gas... more
... Under these conditions, the plasma is not too far from thermal equilibrium. One observes temperatures significantly above 4,000 K; (Rao et al. ... Nozzle design reach from very simple to highly sophisticated ones with hypersonic gas veloc-ities (Rao et al. 1999; Kim 2005). ...
Research Interests:
ABSTRACTSuperparamagnetic behavior is characterized by a thermally fluctuating vector of magnetization, leading to magnetization curves free of hysteresis: it is a property of isolated ferrite particles with sizes below ca. 10 nm. These... more
ABSTRACTSuperparamagnetic behavior is characterized by a thermally fluctuating vector of magnetization, leading to magnetization curves free of hysteresis: it is a property of isolated ferrite particles with sizes below ca. 10 nm. These particles fulfil the condition Kv < kT with K … energy of unisotropy, v … volume of the particle, kT has the usual meaning. To produce a superparamagnetic macroscopic part it is necessary to avoid the interaction of the particles. This can be achieved by coating the particles with a second non-magnetic phase. This special material can be synthesized using the microwave plasma process. Because of the specific interaction of charged particles with an oscillating electrical field, microwave plasmas excel in relatively low reaction temperatures. The low reaction temperature and the electrical charging of the particles in the plasma reduce the probability of agglomeration. Therefore, it is possible to pass the gas stream with the as produced particles ...
Research Interests:
ABSTRACT Nanocrystalline ZrO2 and TiO2 (n-ZrO2, n-TiO2), synthesized in a microwave plasma, have been investigated by X-ray and electron diffraction and by perturbed angular correlation (PAC) measurements of the nuclear electric... more
ABSTRACT Nanocrystalline ZrO2 and TiO2 (n-ZrO2, n-TiO2), synthesized in a microwave plasma, have been investigated by X-ray and electron diffraction and by perturbed angular correlation (PAC) measurements of the nuclear electric quadrupole interaction (QI) of the probe nucleus 181Ta residing on the cation site. The microwave synthesis produces zirconia in the cubic/tetragonal phase, titania in the anatase structure. Grain growth and phase transformations have been studied in bare and Al2O3-coated zirconia particles. Coating the nanoparticles with an amorphous Al2O3 layer obstructs grain growth and may suppress the monoclinic phase.
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Nanoparticle, Electrical, and 13 morePhase Transitions, Nanocrystalline Material, TEM, XRD, Ceramic Coatings, XPS, Anatase, Zirconia Based Nanocrystalline, Magnetic Properties of Soft Ferrites, Perturbed Angular Correlation, SEM EDS, Nanocrystalline titania, and TiO
Research Interests:
Research Interests:
Research Interests:
Irradiation effects on ionic conductivity of pure and Al-doped lithium orthosilicate (Li4SiO4 and Li3.7Al0.1SiO4) during and after irradiation were studied in the temperature ranges 423 to 523 K for Li4SiO4 and 383 to 473 K for... more
Irradiation effects on ionic conductivity of pure and Al-doped lithium orthosilicate (Li4SiO4 and Li3.7Al0.1SiO4) during and after irradiation were studied in the temperature ranges 423 to 523 K for Li4SiO4 and 383 to 473 K for Li3.7Al0.1SiO4 using 120 MeV oxygen-ion and 60 MeV lithium-ion irradiation. The conductivity of Li4SiO4 in the post-irradiation condition increased with the ion fluence in the temperature range 423 to 523 K. On the other hand, the conductivity of Li3.7Al0.1SiO4 in the post-irradiation condition increased with the fluence at 383 and 413 K, while decreased slightly at 443 and 473 K. The conductivity during irradiation for both Li4SiO4 and Li3.7Al0.1SiO4 was larger than that before and after irradiation, and it increased with the ion flux. From such behavior of conductivity, irradiation damage and irradiation effects on lithium-ion and tritium diffusion were discussed.
Research Interests:
Phase relations, thermal stability and preparation methods of the Li 2 O-rich silicates Li 8 SiO 6 and “Li 6 SiO 5 ” have been investigated experimentally, the application of these compounds as solid breeder materials is discussed. In the... more
Phase relations, thermal stability and preparation methods of the Li 2 O-rich silicates Li 8 SiO 6 and “Li 6 SiO 5 ” have been investigated experimentally, the application of these compounds as solid breeder materials is discussed. In the second part of this contribution, the results of thermal expansion measurements on the silicates Li 2 SiO 3 , Li 4 SiO 4 and Li 8 SiO 6 are presented.
Research Interests:
ABSTRACTPyrolytically prepared ceramic powders usually exhibit excellent homogeneity and small grain sizes. The energy efficiency of those methods for synthesis is, particularly in systems heated electrically, very poor. The situation can... more
ABSTRACTPyrolytically prepared ceramic powders usually exhibit excellent homogeneity and small grain sizes. The energy efficiency of those methods for synthesis is, particularly in systems heated electrically, very poor. The situation can be improved drastically using a microwave plasma as a source of energy. This has been confirmed by the synthesis of alumina- and zirconia-based ceramic powders for which an efficiency of more than 80% was found. Aqueous solutions of nitrates of zirconium, yttrium, and aluminum were used as starting materials. Electron microscopy revealed that, through proper selection of the experimental conditions, it is possible to obtain nanocrystalline powders with cubic structure. Because of the extreme conditions during synthesis, it is possible to prepare solid solutions in systems without solubility.
Research Interests:
ABSTRACTMorphology, chemistry and microstructure of zirconia and alumina based ceramic powders synthesized by microwave plasma pyrolysis were studied by transmission electron microscopy. Electron diffraction was used to determine the... more
ABSTRACTMorphology, chemistry and microstructure of zirconia and alumina based ceramic powders synthesized by microwave plasma pyrolysis were studied by transmission electron microscopy. Electron diffraction was used to determine the phases present, while conventional bright field and dark field imaging were used to characterize grain size and density variations. Materials analyzed in this study were either pure zirconia, pure alumina, or a ternary zirconia-yttria-alumina oxide. Solid spheres, hollow spheres, and fragments of hollow spheres were observed. All three modifications of zirconia were observed in the pure zirconia powder. In alumina, the predominant phase was cubic, gamma alumina. In the ternary oxide, most structures exhibited cubic zirconia diffraction patterns. Energy dispersive x-ray spectroscopy revealed chemical inhomogeneities in the ternary oxide powder.
Research Interests:
ABSTRACT
Research Interests:
Research Interests:
ABSTRACT Research News: Microwave plasma synthesis can be used to coat individual ceramic nanoparticles with both ceramic and polymer coatings. as reported here. This enables the production of technical parts with properties... more
ABSTRACT Research News: Microwave plasma synthesis can be used to coat individual ceramic nanoparticles with both ceramic and polymer coatings. as reported here. This enables the production of technical parts with properties characteristic of the isolated particles, such as superparamagnetism. The Figure shows the very narrow size distribution of poly(methacrylic acid)-coated maghemite particles produced with this method.
Research Interests:
Research Interests:
ABSTRACTNanocomposites made of an oxide core of a wide band gap insulator, a lumophore monolayer of anthracene and an outer protecting layer of PMMA are studied regarding their luminescence properties and the influence of halides stemming... more
ABSTRACTNanocomposites made of an oxide core of a wide band gap insulator, a lumophore monolayer of anthracene and an outer protecting layer of PMMA are studied regarding their luminescence properties and the influence of halides stemming either from the precursor used for synthesis or from the lumophore itself. Halide-free nanocomposites exhibit luminescence spectra resembling to that of anthracene with some significant differences concerning the intensity ratio and an additional peak at 420 nm. Nanocomposites made from chlorides show excimer-like spectra with broad maxima. In microanalysis residual chlorine can be detected. Chlorine-free oxide kernels, coated with 9, 10 dichloroanthracene exhibit luminescence spectra resembling to a superposition of the pure lumophores 9 chloro- and 9, 10 dichloroanthracene. It can be shown that the origin of the halide strongly influences, but does not quench the luminescence spectra of the powders. Suspensions of the chlorine containing nanocomposites in ethanol exhibit modified anthracene like spectra. This is a strong indication for dechlorination by proton-transfer in ethanol. Suspensions of the same material in water lead to spectra showing a superposition of exci-mer spectrum and modified anthracene spectrum. Here a partial dechlorination occurs.
ABSTRACT Melting temperature and entropy of metallic nanoparticles are, to a large extent, poorly known, or unknown, because they are extremely difficult to measure. Based on equations published in the literature an improved system of... more
ABSTRACT Melting temperature and entropy of metallic nanoparticles are, to a large extent, poorly known, or unknown, because they are extremely difficult to measure. Based on equations published in the literature an improved system of equations to estimate the thermodynamic behavior of nanoparticles is developed. The special excitement of this improved set of equations is based on the fact that it allows these estimations based on bulk data only. The only problematic point in the system of equations is the unknown contribution of the electrons to the entropy of melting. However, this is a minor contribution. The presented system of equations leads to a characteristic particle size where entropy and enthalpy of melting are zero. For smaller particle sizes, an inversion of the phase sequence is predicted. This phenomenon is well documented by a series of experimental results and modeling studies. The calculation of the size of stable nuclei for crystallization, based on the presented set of equations, leads to conclusions that are well in accordance with experimental and theoretical results. This study establishes the thermodynamic background for crystallization and melting phenomena observed in connection to nanoparticles and bulk systems.
Research Interests:
Research Interests:
Research Interests:
ABSTRACT ABSTRACTA systematic study is presented of the properties of autofocus criteria. Special importance is attributed to their behaviour with respect to noise, working range and image sharpness, whose reproducibility has been... more
ABSTRACT ABSTRACTA systematic study is presented of the properties of autofocus criteria. Special importance is attributed to their behaviour with respect to noise, working range and image sharpness, whose reproducibility has been investigated. It can be demonstrated that autofocus algorithms have either a large working range and do not focus in an unambiguous way or vice versa. From considerations of the properties of autofocus algorithms two novel algorithms have been developed which are insensitive to noise. One of these algorithms is characterized by a particularly large working range, whereas the other is capable of achieving maximum sharpness in a reproducible manner.
Research Interests:
Research Interests:
Applying the Karlsruhe Microwave Plasma Process, alumina and zirconia particles with particle sizes in the range from 2 to 5 nm were synthesized. Additionally, the influence of small amounts of iron(III)-oxide, chromia, and magnesia on... more
Applying the Karlsruhe Microwave Plasma Process, alumina and zirconia particles with particle sizes in the range from 2 to 5 nm were synthesized. Additionally, the influence of small amounts of iron(III)-oxide, chromia, and magnesia on the crystallization and phase transitions in alumina powders was investigated. It is shown that these dopants may influence the crystallization behavior significantly. Especially, the addition of 1 mol% iron(III)-oxide reduced the temperature of the formation of a-alumina from 1200 °C to 300 °C.
Research Interests:
This paper describes the possibilities of synthesising ceramic nanoparticles in a microwave plasma. The properties of these particles can be modzped by coating them with a layer of a second material. A two-step process to produce this... more
This paper describes the possibilities of synthesising ceramic nanoparticles in a microwave plasma. The properties of these particles can be modzped by coating them with a layer of a second material. A two-step process to produce this type of particle is described. The structure of these nanocoated particles depends strongly on the crystaliisation behaviour of the phases forming the kernel and the coating. The main applications of these new nanocoated particles may either be seen in the formation of dzjiision barriers to avoid grain growth or in the modzjication of physical properties of the core and the chemical properties of the surface.
Nanocrystalline Cr,O, particles were synthesized in a microwave plasma using chromium hexacarbonyl as precursor. Electron microscopy revealed that the particle diameter is, depending on the process parameters, in the range from 7 to 9 nm... more
Nanocrystalline Cr,O, particles were synthesized in a microwave plasma using chromium hexacarbonyl as precursor. Electron microscopy revealed that the particle diameter is, depending on the process parameters, in the range from 7 to 9 nm or from 5 to 6 nm. In the case of the larger particles, additionally elongated ones with a diameter from 6 to 7 nm and a length from 10 to 15 nm, were found. The larger particles were found to be single crystals. The smaller particle fraction showed a granular substructure, resembling to a polycrystalline particle. The size of these granules is in the range from 2 to 3 nm. The structure of the material was determined by electron diffraction to be the rhombohedral corundum structure. In the temperature range from 10 to 300 K the magnetic behavior can be described by a modified Langevin function but with a magnetic moment having a thermally activated component. In any event, in this temperature range the assumption Kv < kT is valid, where K is the ...
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT