The 3D packing structures of microcrystals in framboidal pyrite have been investigated by morphological observations and crystallographic orientation analyses using the EBSD technique to understand its self-organization process. The packing structures are basically classified into three types: (i) face-centered cubic (fcc), (ii) icosahedral and (iii) random packings. The orientation analyses on many ordered (fcc) framboids revealed that about a half of the microcrystals in a framboid involve high-angle (~ 90°) misorientation. This means that even in morphologically highly ordered framboids, the crystallographic orientations of microcrystals are not uniform, suggesting that the self-organization process of framboidal microcrystals is not crystallographically controlled. We propose a three-step model for the self-organization: (1) simultaneous nucleation of monodispersive pyrite microcrystals in a fixed volume (from precursor FeS), (2) aggregation of the randomly oriented microcrystals driven by surface forces and the reduction in total surface energy associated with both the individual microcrystals and the whole aggregate, resulting in the formation of the framboidal texture, and 3) reorientation of the microcrystals driven by further reduction in surface energy associated with the grain boundaries.
Peridotite xenoliths derived from the upper mantle give us important information about partial melting and subsequent modification processes, i.e., mantle metasomatism. We examined a large number of mantle peridotite xenoliths from Avacha volcano, located on the volcanic front of southern Kamchatka arc, to reveal that they are residues of high degree of mantle melting and experienced extensive silica addition. We inferred that the slab-derived fluids are closely related with both of the processes, and the degrees of melt extraction and silica addition to the mantle wedge tend to decrease with an increase of the distance from the trench. In addition, we found several new mantle metasomatic events recorded in the Avacha peridotite xenoliths: e.g., the mantle reduction and Ni metasomatism. We consider such peculiar metasomatisms are possibly specific to the sub-frontal mantle, although detailed petrological features and metasomatic processes from other volcanic front regions have not been fully understood due to the paucity of mantle peridotite xenoliths there. More thorough research about the petrological nature of sub-arc mantle and the mantle processes is needed for complete understanding of sub-arc mantle and its metasomatism by slab-derived fluids or melts.
Hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is a major inorganic component of bone and teeth tissues and has the excellent biocompatibility and high osteoconductivity. The interactions between HAp and protein or cell have been studied. The HAp related bioceramics such as bone substitute, coating substance of metal implants, inorganic-polymer composites, and cell culture. We described two methods; (1) surface modification of HAp using organosilane; (2) fabrication of HAp ultra-thin layer on gold surface for protein adsorption analyzed with QCM-D technique. The interfacial interaction between collagen and HAp in a nano-region was controlled by depositing the organosilane of n-octadecyltrimethoxysilane (ODS: -CH3) or aminopropyltriethoxysilane (APTS: -NH2) with a chemical vapor deposition method. The morphologies of collagen adsorbed on the surfaces of HAp and HAp deposited with APTS were similar, however that of the surface with ODS was apparently different, due to the hydrophobic interaction between the organic head group of -CH3 and residual groups of collagen. We present a method for coating gold quartz crystal microbalance with dissipation (QCM-D) sensor with ultra-thin layer of hydroxyapatite nanocrystals evenly covering and tightly bound to the surface. The hydroxyapatite sensor operated in liquid with high stability and sensitivity. The in-situ adsorption mechanism and conformational change of fibrinogen on gold, titanium and hydroxyapatite surfaces were investigated by QCM-D technique and Fourier-transform infrared spectroscopy. The study indicates that the hydroxyapatite sensor is applicable for qualitative and conformational analysis of protein adsorption.