Mesoporous molecular sieves (MCM-41) consist of an ordered array of silica tubules comprised of pores with uniform controllable diameters in the nanometer range. Tin was successfully incorporated into MCM-41 using wet chemical techniques. Detailed structural analysis via x-ray diffraction and high resolution transmission electron microscopy confirm this, and indicate that, after sintering samples in air, SnO2 crystal nanoclusters formed in the channels. These conclusions are further supported by a study of the positron annihilation spectrum. In particular, the insensitivity, after incorporation of tin, of the long-lived component of the positron annihilation spectrum to whether an air or a vacuum annealing atmosphere is used indicates that tin in the MCM-41 channels hinders the entry of quenching oxygen from the air. Furthermore, after sintering, the complete loss of this long-lived component indicates that SnO2 nanoclusters fill the channels.
A synthesis method for the production of porous bulk metallic glass (BMG) is introduced. This method utilizes the superplastic forming ability of amorphous powder in the supercooled liquid (SCL) state and intenerating salt mixture as a placeholder to produce BMG foam by using a hot die pressing method. Scanning electron microscope (SEM), x-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to characterize the morphologies of foaming structure, the crystallization and percentage of amorphous phase of the as-produced porous BMG. The results suggest that the formation of porous structure by superplastic forming process is feasible. Good bonding effect was observed between amorphous powder particles. None of crystalline phases was formed during hot pressing, and less than 3.5% percent of residual salt was enclosed in the foam. In order to remove any residual salt particles, salt preform with three-dimensional network and good connectivity is necessary.
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