Influences of High Calcination Temperature on Densification and Magnetic Properties of Low-Temperature-Fired NiCuZn Ferrites
Traditional low-temperature-fired NiCuZn ferrites (900 °C sintered) were generally prepared at relatively low calcination temperatures to increase the activity of the calcined powders and promote sintering. However, in this study, we changed the calcination temperature from 700 °C to 1000 °C to investigate the influences of high calcination temperature on the densification characteristic and magnetic properties of the low-temperature-fired NiCuZn ferrites. It was found that although a high calcination temperature decreased the activity of the calcined powder, the NiCuZn ferrite could attain a higher sintered density with an adequate sintering aid. Furthermore, a uniform microstructure with small average grain size was obtained for the sample calcined at 1000 °C with 1 wt% Bi2O3 sintering aid. It also displayed high performances on Q-factor and permeability. Hence, choosing a high calcination temperature and adding more sintering aid was also an option for obtaining high performance and low-temperature-fired NiCuZn ferrites.
Functional degradation of NiZnCu-based multilayer chip inductors during nickel electroplating
Functional degradation of NiZnCu-based multilayer chip inductors (MLCI) during nickel electroplating and subsequent lateral growth of metal coating on the ferrite substrate were studied. It was found that the resistivity of the NiZnCu ferrite and inductance of MLCI decreased continuously during the electroplating. Scanning electron microscopy (SEM) analysis showed that the surface morphology of the ferrite had changed significantly after the electroplating. However, the resistance-degraded specimens can be restored partially through air annealing at elevated temperature. Based on the results obtained, it was inferred that the ceramics surface had suffered hydrogen reduction during the electroplating, which led to the functional degradation of ferrite material and the lateral growth of nickel coating.
MAS-NMR spectroscopy studies in the setting reaction of glass ionomer cements.
OBJECTIVES
The main objective is the characterisation of the setting reaction in glass ionomer cements based on experimental ionomer glasses with different fluorine content and a commercial glass ionomer cement liquid by using 13C CP/MAS-NMR, 29Si, 27Al and 31P MAS-NMR spectroscopy in order to receive information specifically about the cross-linking process.


METHODS
Different fluorine containing glass compositions based on 4.5SiO2-3Al2O3-1.5P2O5-(5-z)CaO-zCaF(2) where z=0-3, were mixed with a commercially available polymer liquid to form glass ionomer cements. The cements were subjected to 27Al, 13C CP/MAS, 29Si, and 31P MAS-NMR analysis.


RESULTS
The 27Al spectra showed clearly the formation of six-fold coordinate Al(VI), that may crosslink the carboxyl groups in the poly-acid molecules. A shift towards to more positive values of the carboxyl peak in the 13C CP/MAS-NMR spectra showed clearly the proton dissociation of the carboxyl groups. A shift towards more negative values was observed in the 29Si MAS-NMR spectra, suggesting formation of hydrated silica gel and consequently formation of additional Si-O-Si bonds. 31P MAS-NMR spectra also reflected changes in the coordination state around a PO4(3-) tetrahedron. Increasing the fluorine content of the glasses resulted generally in increased reactivity during setting, due to promoting cross-linking and repolymerisation of the silicate phase, followed by clear changes in the MAS-NMR spectra.


CONCLUSIONS
The cross-linking process during the setting reaction of glass ionomer cements can be followed by MAS-NMR spectroscopy observing the conversion of Al(IV) to Al(VI). The acid base setting reaction is completed in 1 day and no further significant changes in the MAS-NMR spectra can be observed. Further study is required in order to understand the role of phosphorus.