Cai Weiping

Synthesis and structural and optical properties of mesoporous silica containing silver nanoparticles

Mesoporous silica with silver (Ag) nanoparticles within its pores was synthesized by thermal decomposition of silver nitrate. The structure of this new material was examined by x-ray diffraction, transmission electron microscope and Brunauer - Emmett - Teller techniques, and its optical absorption spectra were measured. It has been shown that Ag nanoparticles are isolated from each other and highly uniformly dispersed in pores which are less than 8 nm in diameter. The size of Ag particles follows a log-normal distribution function. Ag particle doping leads to a large red shift of the absorption edge and the edge position can be controlled across the whole visible region by varying the amount of Ag doping. There is no surface plasmon resonance peak other than an absorption edge on the absorption spectra. These facts are explained in terms of interband absorption and dipole interaction of Ag particles in silica, and interaction between pore walls and Ag particles.

Characterization and the optical switching phenomenon of porous silica dispersed with silver nano-particles within its pores

Porous silica dispersed with silver nano-particles (about 3 nm) within its pores (cages) has been prepared by a new method. The microstructures, particle size distribution and optical absorption have been examined. We have found that in the process of alternating exposure to the ambient air and annealing, this new material assumes a optical switching and memory effect in the visible wave band or a reversible transition between transparency and opacity.

Surface residual stresses of LSM-treated martensitic stainless steel

This is an investigation into the effects of laser surface melting (LSM) on martensitic stainless steel, commonly used for steam turbine blades. The principal result is that the magnitude of overlap between neighbouring melted tracks determines whether or not the surface residual stress is tensile.

Fractal structure of uniform corrosion surface for Fe-based alloys

Abstracts are not published in this journal

Endothermic effects in porous silica doped with silver nanoparticles and the formation of by atmospheric oxygen via chemisorption

Porous silica dispersed with silver (Ag) nanoparticles (about 3 nm in diameter) within its pores has been prepared by a new method. The microstructures and the size distribution of particles within pores have been examined by transmission electron microscopy and the Brunauer - Emmett - Teller technique. The Ag nanoparticles are uniformly dispersed within the pores of silica; the particle size follows the log-normal distribution function. The thermal effect of this porous composite, exposed to ambient air for different times, has been investigated by differential scanning calorimetry and thermogravimetric analysis. An endothermic peak has been found for all the doped samples measured. At room temperature (298 K), a short exposure (2 d) to dry air leads to a wide endothermic peak at around 400 K; long exposure (1 month) results in a wider endothermic peak at around 450 K; when the sample was exposed to ambient air with relative humidity greater than 60%, a much higher endothermic peak exists at around 460 K. From the experimental results and discussions of adsorption and oxidation, the endothermic peaks for the samples exposed to dry air can be mainly attributed to the desorption of oxygen physisorbed and chemisorbed on the surface of the Ag particles within the pores, for lower- and higher-temperature peaks, respectively, and the corresponding desorption enthalpy values were estimated to be about 0.26 eV and 0.90 eV, respectively. For the sample exposed to humid air, the endothermic peak originates from the decomposition of silver oxide () formed on the surface layer of the Ag particles, and the bond energy of Ag - O in the film was estimated to be about 1.8 eV.

A new kinetic model for non-equilibrium grain boundary segregation

The author proposes a new kinetic model for non-equilibrium grain boundary segregation. The model is based on three assumptions: that non-equilibrium grain boundary segregation is caused by diffusion of solute-vacancy complexes to the grain boundary; that the grain boundary is a sink for the complexes; and that the grain boundary and grain dimensions are sufficiently large.

An investigation of the purification of cerium in aluminium by the method of internal friction

In this letter, the relation between the purification effect and measurements of internal friction is established, including the grain boundary and dislocation internal friction. Corresponding internal frictions were measured for 4N pure aluminium samples with cerium content 0-0.1 wt.% (four in number) in Kes vacuum torsion pendulum. From the changes of the grain boundary internal friction peak height, the unpinning stress, and the slope of the GL plot with Ce content; it has been shown that there are different Ce purification effects in the grain boundary and in the interior of the grain of Al; a small amount of Ce (<0.01%) has a significant purification effect, but somewhat higher Ce content will decrease this effect because of segregation, especially in the grain boundary.

An investigation of the influence of cerium on the recrystallization of aluminium from background internal friction measurements

The relation between the recrystallization of metals and background internal friction is established. Internal friction as a function of temperature was measured, after annealing at 720 K for 2 h, for 4 N pure aluminium samples with cerium content of 0.0-3.0 wt% (six in number) in Kes vacuum torsion pendulum. From the changes of the background internal friction with cerium content, it has been shown that when cerium content (Ce%) is less than 0.5%, cerium has an insignificant effect on the recrystallization of aluminium; when Ce% is more than 0.5%, the opposite is true: cerium increases the recrystallization temperature of aluminium significantly.