Kusuhiro Mukai

SURFACE TENSION, WETTABILITY AND REACTIVITY OF MOLTEN TITANIUM IN TI/YTTRIA-STABILIZED ZIRCONIA SYSTEM

Abstract The wettability and the interaction between pure liquid titanium and yttria-stabilized zirconia were investigated by the sessile drop method in argon atmosphere at 1973 K. The micrographic observations made on cross sections perpendicular to the interface using EPMA show that interfacial reactions occurred at high temperature. However, the contact angles are relative stable and larger than 90° within experimental duration. The density and surface tension of molten titanium found equal to 4.12±0.01 g cm−3 and 1.46±0.05 N m−1, respectively. The contact angle increases with increasing the substrate porosity. The influence of porosity on the wettability can be explained by analogy with the influence of surface roughness.

Effect of boron on the surface tension of molten silicon and its temperature coefficient.

The influence of boron concentration (C(B)/mass%) on the surface tension of molten silicon has been investigated with the sessile drop method under oxygen partial pressure P(O(2))=1.62x10(-25)-2.63x10(-22) MPa, and the results can be summarized as follows. The surface tension increases with C(B) in the range below 2.09 mass%, and the maximum increase rate of the surface tension is about 30 mN m(-1)(mass% C(B))(-1). The temperature coefficient of the surface tension, ( partial differential sigma/ partial differential T)C(B), was found to increase with the boron concentration in molten silicon. At the interface between molten silicon and the BN substrate, a discontinuous Si(3)N(4) layer was reckoned to form and the layer might prevent BN from dissolving into the molten silicon. Since dissolved boron from the BN substrate into the molten silicon is below 0.054 mass% and the associated increase in surface tension is below 1.5 mN m(-1), the contamination from the BN substrate on the surface tension can be ignored. The relation between the surface tension and C(B) indicates negative adsorption of boron and can be well described by combining the Gibbs adsorption isotherm with the Langmuir isotherm.

Wettability, surface tension, and reactivity of the molten manganese/zirconia-yttria ceramic system

A basic research study for improvement of plasma-sprayed zirconia coatings has been conducted. The contact angle and surface tension of the molten manganese/zirconia-yttria ceramic system were measured at 1573 K by the sessile drop method, suggesting that molten manganese would spontaneously infiltrate open pores in zirconia coatings. Structure and elementary composition development of zirconia ceramics caused by reaction with manganese were examined by using scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), and an X-ray diffractometer (XRD). Manganese not only stabilized cubic zirconia but also contributed to the growth and volume increase of zirconia particles. In this article, the mechanism of making zirconia coatings dense with manganese is discussed based on the results of experiments.

Asymmetric Distribution of Oxygen Concentration in the Si Melt of a Czochralski System

Oxygen concentration in the Si melt of a Czochralski system was measured by immersing an oxygen sensor in the melt. The measurement clarified the existence of an inhomogeneous distribution of oxygen whose pattern was similar to the temperature distribution in the melt. This result suggests that the oxygen profile in the Si melt is not axisymmetric, although the furnace structure is axisymmetric. This oxygen fluctuation is proposed to be one reason for striations appearing in the grown crystals.

Penetration Dynamics of Solid Particles into Liquids High-Speed Experimental Results and Modelling

Penetration of model solid particles (polymer, teflon, nylon, alumina) into transparent model liquids (distilled water and aqueous solutions of KI) were recorded by a high speed (500 frames per second) camera, while the particles were dropped from different heights vertically on the still surface of the liquids. In all cases a cavity has been found to form behind the solid particle, penetrating into the liquid. For each particle/liquid combination the critical dropping height has been measured, above which the particle was able to penetrate into the bulk liquid. Based on this, the critical impact particle velocity, and also the critical Weber number of penetration have been established. The critical Weber number of penetration was modelled as a function of the contact angle, particle size and the ratio of the density of solid particles to the density of the liquid.

Marangoni flow of molten silicon

Abstract Marangoni flow of molten silicon was studied for a half-zone liquid-bridge configuration. Through flow visualization using an X-ray radiography technique with tracer particles and temperature oscillation measurements, the instability mode for the Marangoni flow was determined. It was found that m=1 and 2 modes appeared depending on the aspect ratio ( Γ= height h/ radius r ) of the liquid bridge. The critical Marangoni number for transition from an oscillatory flow with single frequency to that with multiple frequencies was deduced to be about Ma=1300, based on the calibrated-temperature difference between hot and cold solid/liquid interfaces. A transition was also observed when the oxygen partial pressure of the ambient atmosphere was changed. The flow velocity observed using a tracer particle also showed a dependence on the oxygen partial pressure; the velocity decreased with increasing oxygen partial pressure. By observing surface oscillation using a spatial-phase measurement technique, Marangoni oscillation at the melt surface was successfully distinguished from natural oscillation with eigenfrequencies. Marangoni oscillation ( >1 Hz ) that was not revealed by flow visualization and temperature measurement using thermocouples was also observed. Marangoni flow at a flat surface should be studied, so that the heat and mass transfer process for the Czochralski system can be more clearly understood and controlled.

Thermal, optical and surface/interfacial properties of molten slag systems

Abstract In modelling mass and heat transfer steps in metallurgical processes, it is important to have knowledge of the physical properties of slags, the most important among these being the surface and interfacial tensions, thermal diffusivities, optical properties and viscosities. A critical review is presented of work reported in the past two decades relating to the following properties of slag systems: (i) surface/interfacial tensions and related interfacial phenomena; (ii) thermal diffusivities and thermal conductivities; (iii) velocities and coefficients of absorption of ultrasonic waves; (iv) optical properties. A perspective for further work is also provided.

The effect of surface movements on nitrogen mass transfer in liquid iron

Marangoni convection due to surface tension gradients set up in a nitrogen-liquid iron system at 1873K has been mathematically simulated and experimentally confirmed by measuring the rate of nitrogen absorption into liquid iron and by observing the free surface motion of liquid ironvia zirconium oxide particles using X-ray radiography. This surface flow was created by blowing nitrogen gas through a small lance over the free surface of the liquid iron contained in an alumina boat under resistance heating. Absorption measurements indicated that the mass-transfer coefficient of nitrogen in liquid iron due to Marangoni convection (km1>=1.5×10−4 m/s) is slightly less than that due to induction stirring (km1=2.1×10−4 to 1.5×10−4 m/s). The free surface velocity induced by the surface tension gradient, with an initial composition difference of 425 to 10 ppm, was found to be of the order of 0.05 to 0.11 m/s. Mathematical modeling was also carried out to determine the velocity and nitrogen concentration profiles in the alumina boat. It was found that Marangoni convection creates mildly turbulent flows in liquid iron. Good agreements between the experimentally obtained data (nitrogen concentration and surface velocity) and the computed results were attained when a constant eddy viscosity which was five times the molecular value was assumed. This prescription allows both the predicted apparent mass-transfer coefficient and the predicted surface velocity to match the experimental results simultaneously. Note that the transport coefficients in the momentum and the convective-diffusive equations are correlated by the turbulent Schmidt number. The dimensionless mass-transfer correlation obtained for the present N-Fe system at 1873 K under resistance heating was found to be Sh=0.104 Re0.7·Sc0.7 with Sc=79.5 (3500

Density measurement of liquid Ni−Ta alloys by a modified sessile drop method

The density of liquid Ni−Ta alloys was measured by using a modified sessile drop method. It is found that the density of the liquid Ni−Ta alloys decreases with the increasing temperature, but increases with the increase of tantalum concentration in the alloys. The molar volume of liquid Ni−Ta binary alloys increases with the increase of temperature and tantalum concentration.

An analysis of the specific heat capacity of liquid Au-Sn alloy based on the ideal-associated solution model

The specific heat capacity of Au Sn liquid alloy was analyzed using the ideal associated solution model assuming associated compounds Au,Sn, AuSn, and AuSn2. Based on this model, all of the specific heat capacity. heat of mixing and activity are described over a wide temperature range, Further, it became clear that (he summation of mole numbers of the species in the liquid alloy shows a minium at the stoichiometric composition of Au3Sn, which implies that the liquid is the most ordered at this composition,