Microstructural Characterization of Mg-Al Spinel Powders

Mg-Al spinel powders have been prepared by thermal decomposition of a mixture of: A-aluminium and magnesium nitrates; B-aluminium and magnesium hydroxides; and C-aluminium hydroxide and magnesium oxalate. The initial and the final powders were both characterized by specific surface area measurements, mercury intrusion porosimetry, X-ray diffraction, and scanning electron microscopy. The results showed that the preparation process sharply influences the final microstructure of the spinel powders. In particular while the shape and particle dimensions of the samples prepared by mixture of aluminium and magnesium nitrates are mainly influenced by crushing process, the preparation via mixed magnesium and aluminium hydroxides precipitation permits use of spinel formation temperatures as low as 350°C. Characteristically this powder is very uniform and consists of small particle sizes (0.1 micrometers)

Discrete Damage Modelling for Computer Aided Acoustic Emissions.

This chapter is conceived as an essay on modern multiscale discrete damage modelling, providing a brief personal perspective about its foreseeable applications-implications for structural health monitoring purposes. In particular, it is argued that this sort of damage modelling could be potentially useful in damage detection by acoustic emissions (AE), which is a class of non-destructive techniques (NDT) used to capture damage evolution in a number of materials (e.g. from concrete systems such as bridges and beam elements to composites in aircraft components and pressure equipments) and from a number of external actions (e.g. sustained load, monotonic testing, fatigue, corrosion, etc.) (Biancolini & Brutti, 2006 ; Carpinteri & Lacidogna, 2008 ; Grosse & Ohtsu, 2008). With AE it is possible to “hear” the microcracking phenomenon and characterize the location and magnitude of a single microcrack (of size and “strength”1 beyond certain thresholds) acting as an acoustic source. Hence, it is routinely possible to plot the released energy of each crack as a time series or to map them over a 2D spatial domain by counting and locating individual acoustic events in time. Yet the analysis of this type of output is not straightforward and major difficulties exist, let alone sensitivity issues of equipment, material dependence, and other practical issues. The scope of this discussion covers two issues of general interest: 1. the randomness of the AE signal, 2. the need for structure-property relations as companion to AE monitoring

Si-substituted hydroxyapatite nanopowders by precipitation: Synthesis, thermal stability, and sintering behaviour

Synthetic hydroxyapatites incorporating small amounts of Si show improved biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. Si-substituted hydroxyapatite (Si 1.40 % wt) nanopowders were synthesised by titration of Ca(OH)2. Samples were characterized by electron microscopy, induced coupled plasma-atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N2 adsorption measurements, X-ray diffraction and dilatometry

Synthesis and characterization of Mg-substituted hydroxyapatite nanopowders

Hydroxyapatite and Mg-substituted hydroxyapatite nanopowders were obtained by precipitation. Composition was determined by ICP-AES and specific surface area measured by N2 adsorption. Characteristic functional groups were evidenced by FT-IR and thermal behaviour followed by DTA. Thermal stability evaluated by XRD and HT-XRD. Crystallinity degree, average crystallite size and cell parameters were calculated. Density and microstructure of sintered ceramics were also determined

Preparation of NiCo metal powders by co-reduction of Ni (II) and Co(II) hydroxides for magnetoresistive sensors

The preparation of Ni-Co powder for magnetoresistive sensors was studied. A submicron Ni-Co powder was obtained in good yield by reduction of freshly prepared Ni(II) and Co(II) hydroxides in ethylene glycol. The product was a chemically homogeneous powder alloy with a fcc lattice and a Ni/Co atomic ratio of 70/30. The morphology and the composition of the solid solution are the most suitable for the preparation of thick films for physical sensors

Nanostructured F-substituted hydroxyapatite

Hydroxyapatite and F-halfsubstituted hydroxyapatite nanopowders were obtained by precipitation. Particle size and morphology were studied by TEM and specific surface area measured by N2 adsorption. Characteristic functional groups were evidenced by FT-IR, thermal behavior followed by DTA and thermal stability evaluated by XRD. Crystallinity degree, average crystallite size and cell parameters were calculated. Density and microstructure of sintered ceramics were also determined