Papers by Keyword: Nanophases

Abstract: Nanopowders of Cr and Al2O3 was fabricated from CrO3 and 2Al by high energy ball milling. Dense nanocrystalline Cr-Al2O3 composite was consolidated by pulsed current activated sintering (PCAS) method within 1 min from mechanically alloyed powders. Highly dense Cr-Al2O3 with relative density of up to 99% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. The average grain size and mechanical properties of the composite were investigated.

Abstract: Although compositional gradients could be manufactured for the functionally graded coating that was showed to improve bonding strength between the coating and the substrate, the biological efficacy of the graded coatings remained unclear. In this study, a functionally graded nanophase hydroxyapatite/bioglass (n-HA/bioglass) coating was prepared on a titanium (Ti) substrate for evaluating peri-implant osteogenesis in a canine model. The bone apposition and osteointegration of n-HA/bioglass coating were investigated at the interface compared with plasma spraying HA (PS-HA) coating. The results showed that the coating degraded gradually over time but not as fast as PS-HA coating did, and that more active bone apposition appeared on the n-HA/bioglass coating. The in vivo study indicated that an early osteogenesis and osteointegration at the interface could be stimulated by the use of n-HA/bioglass coating in biological environment.

Abstract: The yttrium-aluminium garnet phase (YAG) represents a suitable host material for solidstate lasers and is widely used for various display applications being doped with rare-earth ions. Introduction of Ce3+ ion as a luminescence centre transforms it from insulating to effective phosphor material capable of emitting radiation in the visible spectrum. In this work Ce3+ doped YAG powder was obtained via aerosol route using nitrate precursor solution. Well-crystallized targeted phase was obtained after additional thermal treatment. A combination of different analysis techniques (differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy with determination of image metrology, energy dispersive spectroscopy, transmission electron microscopy) is used to obtain detailed information about the structural and morphological powder properties. The effects of both processing parameters and post annealing treatment conditions are discussed from the viewpoint of establishing the best relationship between them and produced YAG:Ce3+ crystal structure.

Abstract: Pt/Ru-doped ZnO nanophase particles were synthesized using ultrasonic spray pyrolysis. Particles were obtained through decomposition of zinc nitrate and newly developed Pt(IV) and Ru(III) complexes. The particle morphology, phase composition and chemical structure were revealed in accordance to various analysis methods (XRD, DSC, SEM/EDS, TEM) and discussed in terms of precursor chemistry and process parameters. The shape of DSC curves, indicating two exothermic effects above 6000C in both ZnO:Ru and ZnO:Pt, gave an indication of irreversible structural changes and high reactivity of as-prepared powders. The hexagonal wurtzite-type ZnO phase was revealed in both powdered samples. Small content of an intermediate Zn5(NO3)2(OH)8·2H2O and cubic Zn2PtO4 phase were detected in the Pt-doped ZnO particles. Structural refinements, performed by Koalariet-XFit, suggest the composite internal particle structure composed of primary particles sized less than 100 nm. The estimated values for the unit cell parameters and Zn-O bond lengths imply noble metal ions incorporation into ZnO matrix interstitially, probably in octahedral interstitial environment. It has been shown that different particle growing morphologies (either spheroidally or pyramidally shaped) were influenced by the precursor chemistry, processing parameters and the presence of noble metal ions. Among the many parameters, attaining of the particle shape uniformity and homogeneous distribution of the noble metal cations in as-prepared particles are regarded as the most important factors for dominating microstructure evolution.

Abstract: We present results on microwave and millimeter-wave processing of materials. The research is primarily based on two systems– a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron based quasi-optical system. These systems have been used for a wide range of material processing experiments. We describe the capabilities of these systems and discuss some of the results, including nanophase material production, rapid sintering, coating removal and joining of high temperature ceramics.