Tetragonal to monoclinic transformation and microstructural evolution in ZrO2–9.7 mol% MgO during cyclic heating and cooling

The tetragonal (t) to monoclinic (m) transformation behaviour and its relationship to microstructural evolution were investigated by means of dilatometry and transmission electron microscopy for ZrO2–9.7 mol% MgO during cyclic heating and cooling between room temperature and 1490 K. In the as-sintered specimens, fine oblate ellipsoidal t-phase precipitates, 20–50 nm in diameter and 100–200 nm long, were distributed in the cubic (c)-phase matrix. They were below a critical size for transformation and exhibited no transformation in the first three cycles. In the fourth and further cycles, transformation occurred in two distinct stages. A low-temperature stage appeared at 850–1000 K on heating and at 400–700 K on cooling, while a high-temperature stage appeared at 1350–1400 K on heating and at 1000–1200 K on cooling. With the increasing number of cycles, at first the size of low-temperature stages increased and then decreased above ten cycles accompanying the development of the high-temperature stage. During cyclic heating and cooling, coarsening of ellipsoidal precipitates and decomposition of c- and t-phases occurred. As a result of the decomposition, MgO particles and a new m-phase containing a very low concentration of MgO were produced. The coarsened ellipsoidal t-phase precipitates were responsible for the low-temperature stage. The new m- or t-phase containing very low MgO produced by the decomposition was responsible for the high-temperature stage.     

IMPINGING JET DRYER

In coating and gravure printing, an impinging jet nozzle with high thermal efficiency for drying of coated film was developed.

Trial production 0f 40 kinds of nozzle enables to develop a high-performance impinging jet nozzle with heat transfer coefficient 1.5 times larger than that of current slit nozzle, through measurement of heat transfer coefficient, visualizations of air flow and heat transfer, and measuremenu of jet velocity and turbulence distribution. The purpose of the trial production was to expand a range of high heat transfer and promote turbulence compared with the current nozzle.

Paying attention to mass transfer within gravure ink coated film, drying characteristic of the film was analyzed by numerical solution of a set of equations governing the drying process in which concentration dependencies 0f the diffusion coefficient and the equilibrium vapor pressure were considered.

Applying these analyses. an industrial scale dryer with excellent drying efficiency has finally been developed.     

Analytical Electron Microscope Analysis of the Formation of BaO · 6Al2O3

The formation process of barium hexaaluminate (BaO 6Al₂O₃) from BaCO₃/γ-Al₂O₃ powders or hydrolyzed alkoxides was studied by analytical electron microscopy. Barium hexaaluminate is produced by a two-step solid-state reaction from BaCO₃ and Al₂O₃ via formation of BaO·Al₂O₃. Marked grain growth and inclusion of nonequilibrium phase were inevitable in this powder mixture process. However, in an alkoxide-derived precursor, homogeneous mixing of components is attained and hence the formation of BaO·6Al₂O₃ proceeds readily. Powders obtained by this latter route consisted of fine planar particles with a uniform size and retained a large surface area (20.2 m²/g) even after heating at 1300°C. Electron diffraction results implied that suppression of crystal growth along the c axis is the reason for the large surface area of BaO·6Al₂O₃.     

Oxidation of CVD Si3N4 at 1550° to 1650°C

A thermo gravimetric study of the oxidation behavior of chemically vapor-deposited amorphous and crystalline Si₃N₄ (CVD Si₃N₄) was made in dry oxygen (0.1 MPa) at 1550° to 1650°C. The specimens were prepared under various deposition conditions using a mixture of SiCl₄, NH₃, and H₂ gases. The crystalline CVD Si₃N₄ indicated a parabolic oxidation kinetics over the whole temperature range, whereas the amorphous CVD Si₃N₄ changed from a parabolic to a linear law with increased temperature. The oxidation mechanism is discussed in terms of the activation energy for the oxidation and the microstructure of the formed oxide films.     

Magnetorefractive Effect for Co/Ru Multilayer Film with Antiferromagnetic Interlayer Exchange Coupling

The spin‐dependent scattering of conduction electron in metallic magnetic multilayers was investigated to reveal the optical properties which corresponded to the magnetization state. From the measurement of magnetorefractive effect in antiferro‐magnetically exchange coupled Co/Ru multilayers, it was found that (1) the transmittance varied around 1% at wavelength of 1550 nm during the parallel/antiparallel spin alignment changes, (2) as a result of number of repetition and Co thickness for the multilayers, transmittance difference between the parallel and antiparallel spin alignment states had trade‐off relationship with the magnitude of transmittance, and (3) asymmetric Co/Ru/Co stacking structure brought different interlayer exchange coupling fields in each layer, which resulted in magnetic field sensitive transmittance.     

The minimal time control of multi-system problems with energy constrained inputs†

This paper presents an. application, of functional analysis to the minimal?time control problem where two or more energy constrained systems of the same order must be taken to an initially unknown common point in state space. Two different types of problems with different forms of the energy constraint are described in detail. The development depends on the fact that the reachable region of a system with an energy constraint on the input vector is an ellipsoid.     

Effect of Milling on the Intrinsic Coercivity of Barium Ferrite Powders

The effect of milling on the intrinsic coercive force of Ba ferrite powders has been ascribed to (1) thermal fluctuations caused by superparamagnetic fine particles and (2) lattice defects introduced by milling. To test these interpretations, the Moessbauer absorption spectra and angular variation of coercive force for ball-milled powders were determined. With increasing milling time, the Moessbauer absorption spectrum becomes ambiguous, and the absorption lines are broadened; the quadrupole-split center line corresponding to superparamagnetic BaFe₁₂O₁₉ cannot be detected. The angular variation of coercive force shows that milling considerably lowers either the nucleation field of the reverse domain or the effective anisotropy field or both. It is concluded that lattice defects, rather than superparamagnetic fine particles introduced by milling, greatly affect the intrinsic coercive force of Ba ferrite powders.     

Synthesis of minimum-time control functions with multiple constraints by functional analysis!

This paper presents the functional analysis and iterative procedure for the minimum-time control problem subject to energy and magnitude constraints on the control functions. The necessary change of Swiger's method is described to solve a multi-boundary problem and numerical results are presented for a linear control system.     

An experimental study on self-output-control characteristics of micro downwind rotor with coning soft blades

In this short paper,we have treated the aerodynamic performance of micro downwind rotor with coning soft blades experimentally.The test wind rotor has the tip diameter of 1.5 m and three two-dimensional NACA0018 blades of 0.15 m chord whose material is light,soft and pliable foam plastic for perfect safety.From the wind tunnel test,it is realized that the performance is manageable by the coning angle of the rotor blade.In the present case,an improvement of the performance in lower wind speeds is achieved by...