Although mesoporous silica particles
are useful building blocks
for colloidal crystals, mesoporous silica nanoparticles smaller than
100 nm with sufficient monodispersity and colloidal stability to enable
thermodynamic assemblies have not been reported. Here, we report that
highly monodisperse colloidal mesoporous silica nanoparticles (CMS)
can be prepared by combining the preparation of colloidal mesoporous
silica nanoparticles with a shortened nucleation time. The nanoparticles
exhibited a uniform shape and relatively smooth surface because an
undesirable aggregate dispersion process was avoided. In addition,
the diameter of the nanoparticles was controlled by seed-growth without
spontaneous nucleation, which enabled the investigation of fundamental
CMS properties. Using monodisperse CMS, the dependence of the ζ-potential
of CMS on the diameter was revealed. Colloidal crystals composed of
mesoporous silica nanoparticles were fabricated by drying the colloidal
solution. This is the first report regarding the fabrication of colloidal
crystals composed of mesoporous silica nanoparticles with a small
particle size.
316L stainless steel plates were friction stir processed using polycrystalline cubic boron nitride tools. Mechanical properties and microstructure evolution of the friction stir processing (FSP) zone were investigated. Tensile test results showed that the tensile strengths of the defect free FSP zones were equal to those of base metals. All the samples fractured at the base metal side. Microstructural observation results showed that the grains in the FSP zone were refined by the tool. The FSP zone was a roughly equiaxed grain structure and the grain size was in the range of 10-30 mm, which was smaller than that in the base metal (30-80 mm). Moreover, transmission electron microscopy observation revealed that sigma phases formed in this zone during FSP.
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