Crystalline hydroxyapatite (HAp) powders were prepared at room temperature from heterogeneous reaction between Ca(OH) 2 powders and (NH 4 ) 2 HPO 4 solutions via the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, thermogravimetric characterization, and chemical analysis were performed, and it was determined that the room temperature products were phase-pure, thermally stable HAp with a nearly stoichiometric composition. Dynamic light scattering revealed that the dispersed particle size distribution of the room temperature HAp powders was in the range of 0.15-3.0 m with a specific surface area of ≈90 m 2 /g. Both specific surface area measurements and scanning electron microscopy confirmed that the HAp powders consisted of agglomerates containing hundreds of ≈20 nm HAp crystals.Hydroxyapatite (HAp) with the chemical formula Ca 10 (PO 4 ) 6 (OH) 2 has been extensively used in medicine for implant fabrication and is one of the most biocompatible materials owing to its similarity with mineral constituents found in hard tissue (i.e., teeth and bones). 1-3 Multiple techniques have been used for preparation of HAp powders with wet methods 1,4-9 and solid state reactions 1,10 as the most popular. Depending upon the technique, materials with different morphology, stoichiometry, and level of crystallinity can be obtained. Recently, several papers regarding mechanochemical and mechanochemical-hydrothermal synthesis of HAp powders appeared in the literature. 11-18 Mechanochemical powder synthesis is a solid-state synthesis method that takes advantage of the perturbation of surface-bonded species by pressure to enhance thermodynamic and kinetic reactions between solids. 19 Pressure can be applied at room temperature by milling equipment ranging from low-energy ball mills to high-energy stirred mills (usually attrition, planetary, or vibratory). The main advantages of the mechanochemical synthesis of ceramic powders are simplicity and low cost.Since the mechanochemical synthesis involves only solid-state reactions, it should be clearly distinguished from the mechanochemical-hydrothermal synthesis (sometimes called "wet" mechanochemical), which takes advantage of the presence of an aqueous solution in the system. An aqueous solution can actively participate in the mechanochemical reaction by acceleration of dissolution, diffusion, adsorption, reaction rate, and crystallization (nucleation and growth). 20 The mechanochemical activation of slurries can generate local zones of high temperatures (up to 450-700°C) and high pressures due to friction effects and adiabatic heating of gas bubbles (if present in the slurry), while the overall temperature is close to the room temperature. 21 The mechanochemical-hydrothermal technique is thus located at the intersection of hydrothermal 20 and mechanochemical 19 processing. Correspondingly, if nonaqueous solutions were used we would define the process as mechanochemical-solvothermal. The mechanochemicalhydrothermal route produces comparable amounts of HAp powd...

Colloidal solids of monosized, solution-derived SiO2 were prepared under forced and unforced sedimentation conditions to tailor the level of particulate order. Photonic band gaps were observed in the blue part of the visible spectrum and their spectral shape is shown experimentally to correlate directly to the degree of long- and short-range particulate order. These results are discussed by analogy to the x-ray diffraction of crystals and glasses as is the practical applicability of “photonic glasses” with respect to the more widely studied “photonic crystals.”

The sol-gel-type condensation of tin(1V) ethoxide [Sn(OEt),], (where OEt is ethoxide) under basic conditions produced spherical, submicrometer-sized tin(1V) oxide (cassiterite) particles. Transmission electron microscopy and powder X-ray diffraction data indicated that the grain size was approximately 20 to 30 A (2 to 3 nm). The mixed-metal alkoxide compound [ZnSn(OEt)s] was hydrolyzed under analogous conditions to give either spherical or octahedral submicrometer-sized crystalline particles of ZnSn(0H)r depending on the solvents used. These data demonstrated that the stoichiometry of the mixed-metal alkoxide precursor was retained during Condensation. Thermal treatment of ZnSn(OH)6 resulted in crystallization of ZnSn03 at approximately 676°C. At neutral pH, hydrolysis of [ZnSn(OEt)6] resulted in formation of a high surface area (261 m2/g) amorphous powder. [

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A general route to low temperature synthesis of ternary metal tin oxides with controlled stoichiometries from single component molecular metal alkoxide precursors is described. The solid state and solution structures of homoleptic tin(IV) alkoxide compounds have been investigated to establish criteria for the determination of their solution structure. Tin alkoxide compounds suitable for metathesis reactions have been synthesized and used to prepare the mixed metal alkoxide compounds [ZnSn(OEt) 6 ] and [((COD)Rh) 2 Sn(OEt)6] (where Et = ethyl and COD = 1,5-cyclooctadiene). Hydrolysis of [ZnSn(OEt)6] at neutral pH results in the formation of a high surface area, mainly amorphous hydrous oxide powder which forms Zn2SnO 4 and SnO2 on heating to 600 0 C and ZnSnO3 on heating to 1000 0 C.Thermolysis of [ ((COD)Rh } 2 Sn(OEt) 6 ] results in formation of rhodium and tin(IV) oxide (cassiterite phase).

Structure/optical property relationships in photonic bandgap structures are evaluated by a novel combination of sample sectioning, microscopy, and image analysis. Disordered colloidal crystals of solution-derived, monosized SiO 2 particles were sectioned by focused ion beam (FIB) milling and then imaged using field emission scanning electron microscopy (FE-SEM). Pair correlation and radial distribution functions of the particulate arrangement were generated directly from a binary color scale rendering of the FE-SEM images, therein defining the level of order or disorder in the structure. These experimentally obtained spatial correlation functions were used to compute the scattering spectral properties in an analogous, although inverse (i.e., solving the inverse scattering problem), method to that used in X-ray diffraction for structure determination. Using a first-order approximation to the scattering from a disordered structure, the bandwidth and midgap values for the colloidal crystal photonic bandgap materials were within 15% of those measured. This new methodology promises to provide a simple and direct approach for quantifying the structure/optical property relationships in ordered and disordered photonic crystals directly from standard microstructural imaging techniques.

Molecular Routes to Tin Oxides -(general route to low-temp. synthesis of ternary metal Sn oxides with controlled stoichiometries from single component molecular metal alkoxide precursors; 48 refs.). -(WARK, T. A.; GULLIVER, E. A.; JONES, L. C.; HAMPDEN-SMITH, M. J.; RHEINGOLD, A. L.; HUFFMAN, J. C.; Mater. Res. Soc. Symp. Proc. 180 (1990) 4, 61-72; Cent. Micro-Eng. Ceram., Univ. N. Mex., Albuquerque, NM 87131, USA; EN)

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