Zhang Jinxiu

Structure and Raman Spectroscopy of Nanocrystalline TiO2 Powder Derived by Sol-Gel Process

Nanocrystalline TiO2 powder was prepared by sol-gel process. The structures of the as-prepared and the TiO2 powder heat-treated at different temperatures were studied by thermogravimetric analyzer, differential thermal analysis, x-ray diffraction, and Raman spectra. As the powder was heat-treated at 350°C, it turned into tetragonal anatase structure. A structural transformation from anatase to rutile type occurred and the grains of the powder grew drastically when the powder was heat-treated at above 550°C. The structural transformation from anatase to rutile type completed at 750°C. The Raman spectra of TiO2 nanocrystalline powder were also studied.

Characterization Method of Polycrystalline Materials Using Conductive Atomic Force Microscopy

An apparatus for characterization of polycrystalline materials based on conductive atomic force microscopy (cAFM) is developed and a quantitative measurement of electrical characteristics of individual grains in polycrystalline ZnO ceramic is demonstrated. Improvement of the experimental method is presented. Experimental results illuminate unambiguously the different electrical characteristics between individual grains, suggesting the suitability and maneuverability of this method in the study of local structure or properties and their relationship in polycrystalline materials such as semi-conducting ceramics.

Imaginary Part of the Surface Tension of Water

We report a direct measurement of the imaginary part of the surface tension of water through a dynamic scheme using a thin vertical glass fiber of diameter of 3 μm with one end glued onto a cantilever beam and the other end touching a water-air interface. The frequency dependence of the dissipation factor experienced by the glass fiber is exactly calculated through measuring the phase delay with various frequencies when the glass fiber is forced to oscillate vertically. We find the same intercept at the dissipation factor axis for different frequency dependences of the dissipation factor for different depths by which the glass fiber is dipped into water. This nonzero dissipation factor at zero frequency presents direct evidence of the existence of the imaginary part of surface tension of water and yields a complex surface tension of water σ* = 0.073 + i(0.017 ± 0.002) N/m at room temperature.

Resonant Absorption Mechanical Spectrometer and Its Applications in Solids

An improved apparatus is developed from Ke-pendulum. This new apparatus, resonant absorption mechanical spectrometer (RAMS), can measure the internal friction of solids under a forced vibration mode and the measuring frequency can change quasi-continually from a frequency that is much lower than the resonant frequency of the pendulum system, fr, to the one that is much higher than fr. The internal friction measurement is able to cover the frequency range from 10-3 Hz to kHz. The measurement method and the calculation formula of the internal friction measured by a RAMS in the full frequency range are derived. A series of resonant absorption peaks are observed in copper, aluminium, zinc, iron samples by the RAMS. The resonant absorption characteristics of the copper sample are studied in details. The experimental results indicate that the position (frequency) of the resonant absorption peaks are independent of the resonant frequency of the pendulum system. The reality of resonant absorption mechanical spectra is discussed and an inference based on the experimental results is presented such that the RAMS is able to characterize some feature of solid materials.

Non-Contact to Contact Transition: Direct Measurements of Interaction Forces between a Solid Probe and a Planar Air–Water Interface

The interaction force between a solid probe and a planar air–water interface is measured by using an atomic force microscope. It is demonstrated that during the approach of the probe to the air–water interface, the force curves decline all the time due to the van der Waals attraction and induces a stable profile of water surface raised. When the tip approaches very close to the water surface, force curves jump suddenly, reflecting the complex behaviour of the unstable water surface. With a theoretical analysis we conclude that before the tip touches water surface, two water profiles appear, one stable and the other unstable. Then, with further approaching, the tip touches water surface and the non-contact to contact transition occurs.