Iron oxide (α-Fe₂O₃) nanoparticles with very small size, high crystallinity, and narrow size distribution were synthesized by infiltration of Fe(NO₃)₃.9H₂O as an oxide precursor into mesoporous silica (SBA-15 and SBA-16) molds using a wetimpregnation technique. High resolution transmission electron microscopy shows that during the hydrothermal treatment of the precursor at 140 °C for 2 days, stable α-Fe₂O₃ nanoparticles inside the silica pores are formed. Subsequent leaching out of the silica template by NaOH resulted in well dispersed nanoparticles with an average diameter of ~ 4 nm.

Cobalt nanoparticles were prepared at room temperature by reducing cobalt sulfate heptahydrate with sodium borohydride and using functionalized SBA-15 mesoporous silica as a hard template. It was found that both external and internal fuctionalization of silica walls play a crucial role on the infiltration and reaction of the reagents in the silica framework. Subsequent heat treatment of the impregnated silica at 500 °C in air or nitrogen atmospheres leads to growth of crystals of the deposited cobalt and formation of cobalt and cobalt oxide nanoparticles, respectively. Dissolution of the silica template by NaOH resulted in well dispersed Co and Co₃O₄ nanoparticles ranging in size from 2 to 4 nm. The functionalization of the silica was studied by FTIR, N2-physisorption, and thermogravimetric techniques and the obtained nanoparticles were characterized by XRD, TEM and EDX analysis.

Phase transformations during annealing of coatings sprayed with the High Velocity Oxy-Fuel technique using Ti₂AlC powder have been investigated by in-situ x-ray diffraction. The asdeposited coatings, consisting of Ti2AlC, Ti₃AlC₂, TiC, Ti-Al, and oxides, are stable up to 500 °C. Ti3AlC2 forms above 550 °C and Ti₂AlC forms above 700 °C by intercalation of Al into TiC_x. For temperatures between 900 and 1100 °C, Ti₃AlC₂ and Ti₂AlC decompose by losing Al to the surrounding matrix resulting in TiCx, and Al₂O₃. The thermal expansion coefficient between ambient and 700°C is 11.9·10^-6 K^-1. The thermal diffusivity at room temperature is 1.9·10^-6 m²/s.

A solution based wet chemistry approach has been developed for synthesizing Li(2)SiO(3) using LiNO(3) and mesoporous silica as starting materials at 550 degrees C. A reaction path where NO and O(2) are formed as side-products is proposed. The crystals synthesized exhibit dendritic growth where the as-prepared nanodendrite is a typical 1-fold nanodendrite composed of one several microns long and some tenth of nanometers wide trunk with small branches, which are several hundreds of nanometers long and up to 70 nm in diameter. The effect of the structure of the mesoporous silica for the final morphology is discussed.

The performance of a magnetic resonance imaging contrast agent (CA) depends on several factors, including the relaxation times of the unpaired electrons in the CA. The electron spin relaxation time may be a key factor for the performance of new CAs, such as nanosized Gd2O3 particles. The aim of this work is, therefore, to study changes in the magnetic susceptibility and the electron spin relaxation time of paramagnetic Gd2O3 nanoparticles diluted with increasing amounts of diamagnetic Y2O3. Nanoparticles of (GdxY1-x)2O3 (0 e x e 1) were prepared by the combustion method and thoroughly characterized (by X-ray di.raction, transmission electron microscopy, thermogravimetry coupled with mass spectroscopy, photoelectron spectroscopy, Fourier transform infrared spectroscopy, and magnetic susceptibility measurements). Changes in the electron spin relaxation time were estimated by observations of the signal line width in electron paramagnetic resonance spectroscopy, and it was found that the line width was dependent on the concentration of yttrium, indicating that diamagnetic Y2O3 may increase the electron spin relaxation time of Gd2O3 nanoparticles.

In this article, the reactivity of Ti(2)AlC powders, with 3 and 10 mu m alumina, Al(2)O(3), fibers during pressure-assisted sintering is explored. Samples were fabricated by hot-isostatic-pressing (HIPed) or hot-pressing (HPed), and characterized by X-ray diffraction, differential thermal analysis, and electron microscopy-both scanning and transmission-equipped with energy dispersive X-ray spectroscopes. Samples prepared at 1300 degrees C were fully dense, with no apparent reaction between fiber and matrix. In samples HPed to 1500 degrees C, even pure Ti(2)AlC powders dissociated to Ti(3)AlC(2) according to: 2 Ti(2)AlC = Ti(3)AlC(2) + TiAl(x) (l) + (1-x) Al (l/v), with x andlt; 1. More severe Al loss results in the formation of TiC(y). The presence of the Al(2)O(3) fibers delayed densification enough to allow most of the Al and some of the Ti to escape into the vacuum of the hot press or react with the encapsulating glass during HIPing a resulting in a more intensive dissociation of the Ti(2)AlC. Although, in principle Ti(2)AlC can be reinforced with Al(2)O(3) fibers, the processing/use temperature will have to be kept below 1500 degrees C, as, at that temperature the fibers, used here, sinter together.

Dispersed SBA-15 rods have been synthesized with varying lengths, widths, and pore sizes in a low-temperature synthesis in the presence of heptane and NH4F. The pore size of the material can systematically be varied between 11 and 17 nm using different hydrothermal treatment times And/or temperatures. The particle length (400-600 nm) and width (100-400 nm) were tuned by varying the HCl concentration. All the synthesized materials possess a large surface area of 400-600 m(2)/g And a pore volume of 1.05-1.30 cm(3). A, mechanism for the effect of the HCl concentration on the particle morphology is suggested. Furthermore, it is shown that the reaction time an be decreased to 1 h, with well-retained pore size and morphology. This work has resulted in SBA-15 rods with the largest pore size reported for this morphology.

The synthesis of spherical copper nanoparticles with extremely narrow size distribution by electroless copper deposition on mesoporous silica support is described. The materials were characterized by nitrogen sorption, transmission electron microscopy, x-ray diffractometry and Fourier transform infrared spectroscopy. The copper nanoparticles have a cubic crystalline structure and an average particle size of 5.5 +/- 0.8 nm. The copper nanoparticles are stable, without detectable oxidation or further agglomeration under ambient conditions even after months. These results demonstrate that electroless copper reduction can be conducted and constrained within the mesoporous silica framework, which pave the way for engineered mesoreactors.

Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent. tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH4F. The size of these spheres is in the range of 10 to 30 mu m. The shell is about 700 nm thick and consists of large pores, similar to 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m(2)/g. The formation mechanism of the silica hollow spheres is discussed.

The reactivities of commercially available Ti2AlC or Ti3SiC2 powders with uncoated SiC fibers or SiC powders were evaluated in this paper. When Ti2AlC-SiC samples were hot pressed or hot isostatically pressed at temperatures up to 1500 degrees C, fully dense composites were obtained. The latter were characterized by X-ray diffraction and electron-dispersive spectroscopy in a scanning and transmission electron microscope. Differential thermal analysis up to 1550 degrees C was also carried out. In all cases, SiC reacted with the Ti2AlC powder resulting in the formation of Ti-3(Al1-xSix)C-2 TiC and Al1+xTi1-x, where x ranges from 0 to 1. In the limit x=1, pure Al forms. Conversely, Ti3SiC2 samples, reinforced with uncoated SiC fibers or powders, can be hot pressed in vacuum at temperatures as high as 1500 degrees C to produce fully dense composites with no apparent reaction between the matrix and fibers. Based on these results, Ti3SiC2 can, but Ti2AlC cannot, be reinforced with SiC. Such reinforcements will be needed if the MAX phases are to be used as structural materials at very high temperatures.