Heating rate dependence of Tg and Tx in Zr-based BMGs with characteristic structures

Heating rate dependence of glass transition and crystallization temperatures is applicable for evaluation of glass structural stability and also for discussion on the apparent activation energies for glass transition and crystallization. The glass-structure stabilities of the Zr-based BMGs (Zr₅₀Cu₄₀Al₁₀, Zr₇₀Cu₂₀Al₁₀ and Zr₇₀Ni₂₀Al₁₀) and the conventional amorphous alloys (Zr₇₀Cu₃₀ and Zr₇₀Ni₃₀) are assessed by the densely packed glass structure as well as the complicated crystallization process. By the reverse Monte Carlo (RMC) simulation with X-ray and neutron diffraction data, it is shown that the densely packed structure is built by icosahedron-like clusters. In Zr₆₅Al_7.5Ni₁₀Pd_17.5 and Zr₆₅Al_7.5Ni₁₀Cu_17.5, the effect of Pd atoms on the glass structure is also described.     

Numerical modeling for potential relaxation of charged oil incontainers

A numerical model that simulates the relaxation process for surface potential at the surface of a charged oil in a grounded metal vessel is developed. In the model, constant (ohmic) conductivity of the oil is assumed, and a surface conduction mechanism for the dissipation of electric surface charge is introduced. Calculations for a cylindrical vessel of diameter D_t, height H_t, and fill fraction F show that the charge relaxation is influenced by vessel geometry and fill level, as expected, and by the absolute size of the vessel as well. In fact, it is found that the effective relaxation time of the surface potential correlates quite well to a dimensionless quantity D_tκ/λ, where κ (in Siemens per meter) is the bulk conductivity of the oil, and λ (in Siemens) is the effective surface conductivity at the oil/air interface     

An ultraprecision positioning system using a twist-roller friction drive

For ultraprecision positioning, the use of the twist-roller friction drive is proposed. To improve the positioning accuracy of conventional twist-roller friction drives, the proposed design has two features: (1) the twist angle between the driving shaft and the driven rollers is very small, and (2) the driven rollers are supported by hydrostatic bearings. The twist-roller friction drive is mechanically a kind of lead screw, and the small twist angle makes the lead of the friction drive less than 0.1 mm. The use of hydrostatic bearing is effective for improving the rotational accuracy of the driven rollers and for eliminating the influence of the fluctuation in roller rotation on positioning accuracy. It has been shown by experiments that the resolution of positioning can be less than 10 nm, and the twist-roller friction drive is suitable for an ultraprecision positioning system.     

Heat transfer and fluid flow characteristics in a swirling impinging jet

An experimental study on heat transfer and fluid flow has been carried out for a swirling round impinging jet. A thermosensitive liquid crystal sheet was used for the heat transfer measurements and the three velocity components were measured with LDV in the stagnation region for cases where the Swirl number Sw = 0.0, 0.22, and 0.45 at the Reynolds number Re = 8100. The formation of recirculation flow due to a swirl near the impinging wall was found to deteriorate the heat transfer coefficient in the stagnation region and results in a more uniform distribution of the Nusselt number with an increasing Swirl number. The heat transfer mechanism of the swirling impinging jet is discussed based on the flow characteristics of the mean velocities and turbulence quantities. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 324–335, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20068     

Theoretical analysis of experimental densification kinetics in final sintering stage of nano-sized zirconia

The experimental densification kinetics of 7.8 mol% Y₂O₃-stabilized zirconia was analyzed theoretically during isothermal sintering in the final stage. By taking concurrent grain growth into account, a possible value of the grain-size exponent n was examined. The Coble’s corner-pore model recognized widely was found not to be applicable for explaining the densification kinetics. The corner-pore model of n = 4 shows a significant divergence in the kinetics at different temperatures. Microstructural observation shows that most pores are not located at grain corners and have a size comparable to the surrounding grains. The observed pore structure is similar to the diffusive model where single pore is surrounded by dense body. The diffusive model combined with theoretical sintering stress predicts n = 1 or n = 2, which shows a good consistence to the measured densification kinetics. During sintering of nano-sized powder, it is found that the densification kinetics can be explained distinctively by the diffusive single-pore model.     

Effect of Grain Contiguity on the Thermal Diffusivity of Aluminum Nitride

Thermal diffusivity of AlN-based ceramics was studied as a function of second-phase amount and heat-treatment time. The Y₂O₃·Al₂O₃ contents varied over the range of 13-31 vol%. The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850°C, the AlN ceramics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5-50 h at 1800°C resulted in microstructures that consisted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat-treatment step, and the incremental improvement was essentially constant for the three compositions that have been studied. The amount of second phase was unchanged during heat treatment; therefore, the increase in thermal diffusivity is assumed to be a direct result of the enhanced contiguity of AlN grains.     

Spherical ultrasonic motor drive system for camera orientation in pipe inspection

We propose a camera actuating system using a spherical ultrasonic motor for inspection of the inside wall of a small pipe. The spherical ultrasonic motor has advantages that include three degrees of freedom, high responsiveness and high accuracy all within a compact body. We describe here the development of an outer rotor spherical ultrasonic motor (OR-SUSM) that enables a camera to rotate by more than 360° along the side of the pipe. All components, including the OR-SUSM, the sensing system, and the electric circuits, are designed to be assembled in the pipe inspection device with outer diameter of 52?mm. To control the system, the phase difference and frequency of the applied voltages are used. The rotational direction is determined by the phase difference and the angular velocity is controlled by the frequency. The completed system can be controlled to within 2° in an experimental pipe inspection test.