The surface organic modification of TiO2 particles with titanate coupling reagent,which was pre-coated with double layers of SiO2 and Al2O3,was studied.Experiments showed that the modified particles exhibited hydrophobic characteristics.The modification state of the particle surface was characterized by IR spectroscopic measurement,pyrolytic gas chromatography,thermogravimetric analysis and X-ray photoelectron spectra.The titanate coupling reagent binding with the hydroxyl on the particle surface was analyzed.The surface characteristics of pre-modification and post-modification particles were compared.
The characteristics of dynamic pressure in an impinging jet were experimentally studied. The instantaneous signals of dynamic pressure resulted from the turbulence in the jetting fluid were measured through a piezoelectric sensor and recorded by a computer. The pressure signals at central axial position of the jetting fluid were sampled at different fluid pressure. The measured signals obviously possessed periodical characteristics. After analyzing the signals with FFT method, it was found that there was an inherent frequency in the dynamic pressure signals. The inherent frequency increases with the average velocity of the jetting fluid at the nozzle outlet, which is consistent with the theoretical analysis. It was supposed that the dynamic pressure signals are transformed from the fluctuating fluid velocities resulted from the turbulence in the jetting fluid. The inherent frequency corresponds to the minimum eddy scale in the turbulent jet. The smaller the eddy scale is, the higher the inherent frequency is. Higher velocity of the fluid at the outlet leads to a stronger turbulent strength. The fluctuation velocities with high inherent frequency resulted in a strong shear force field, which enables the fluid to be micro-mixed fleetly and the agglomerate of solid particles to be dispersed effectively.
