氦的化合物和粒子的固化

就宇宙而言,氦不是稀有气体,同样,也非惰性气体,因为氦可以与其它元素生成化合物. 衰变而发射 粒子, 俘获电子而变为氦气 ,导致钚体积年增加6.8% ,损害钚晶格.所谓”固化 粒子”, 即使 粒子与其它原子生成固态离子化合物, 最有希望的生成碳或铝的氦化合物.可以基本消除氦泡的影响.这是举世瞩目的.     

Effect of ternary addition and γ-irradiation on the characteristics of rapidly solidified Pb-base alloys

The properties of a series of rapidly solidified Pb-Sb 3 -Sn x alloys ( x =0-2.5 r wt.%) irradiated with n -rays were studied. Variations in the internal friction, Q m 1 , thermal diffusivity D th and dynamic Young's modulus Y were traced before and after irradiation by applying the resonance technique. Variations of specific heat C p were obtained from DTA thermograms. Structure parameters were obtained from the X-rays diffraction patterns. A marked change in the behaviour of the measured parameters was observed at 1.5 r wt.% Sn addition. Besides, irradiation induced defects increased the level of the measured hardening parameters.     

An Enthalpy Control Volume Method for Transient Mass and Heat Transport with Solidification

A single domain enthalpy control volume method is developed for solving the coupled fluid flow and heat transfer with solidification problem arising from the continuous casting process. The governing equations consist of the continuity equation, the Navier–Stokes equations and the convection–diffusion equation. The formulation of the method is cast into the framework of the Petrov–Galerkin finite element method with a step test function across the control volume and locally constant approximation to the fluxes of heat and fluid. The use of the step test function and the constant flux approximation leads to the derivation of the exponential interpolating functions for the velocity and temperature fields within each control volume. The exponential fitting makes it possible to capture the sharp boundary layers around the solidification front. The method is then applied to investigate the effect of various casting parameters on the solidification profile and flow pattern of fluids in the casting process.     

Role of non-stoichiometry in the cracking of oxide crystals

The cracking and stoichiometric deviations frequently observed in crystals of mixed oxides have generally been perceived to be unrelated phenomena. The present study pertains to the cracking in Czochralski grown crystals of three different materials, viz. CdWO₄, PbWO₄ and ZnWO₄. The results obtained on the single-crystal growth as well as on the thermal stability of melts of these materials and of their constituent oxides demonstrate, for the first time, that stoichiometric deviations manifest as cracks in the crystals. An important outcome of this investigation is that materials exhibiting a small degree of super-cooling with stable melting and solidification temperatures should be less prone to cracking.     

Eutectic solidification patterns: Interest of microgravity environment

The solidification of binary eutectic alloys produces two-phase composite materials in which the microstructure, that is, the geometrical distribution of the two solid phases, results from complex pattern-formation processes at the moving solid–liquid interface. Since the volume fraction of the two solids depends on the local composition, solidification dynamics can be strongly influenced by thermosolutal convection in the liquid. In this contribution, we review our experimental and numerical work devoted to the understanding of eutectic solidification under purely diffusive conditions, which will soon be tested and extended during the microgravity experiment TRANSPARENT ALLOYS planned by the European Space Agency (ESA).     

Thermal conductivity and interfacial energy of solid Bi solution in the Bi–Al–Zn eutectic system

The equilibrated grain boundary groove shapes for solid Bi solution (Bi–6.1 at.%Zn–0.38 at.%Al) in equilibrium with the Bi–Al–Zn eutectic liquid have been observed from quenched sample with a radial heat flow apparatus. The Gibbs–Thomson coefficient, solid–liquid interfacial energy and grain boundary energy of solid Bi solution have been determined from the observed grain boundary groove shapes. The variations of thermal conductivity with temperature for solid Bi solution (Bi–6.1 at.%Zn–0.38 at.%Al) has been measured up to five degree below the melting temperature by using radial heat flow technique. The ratio of thermal conductivity of equilibrated Bi–Al–Zn eutectic liquid phase to solid Bi solution (Bi–6.1 at.%Zn–0.38 at.%Al) phase has also been measured with a Bridgman type growth apparatus at the melting temperature.     

Inertial and coriolis effects on oscillatory flow in a horizontal dendrite layer

Flow instability due to oscillatory modes of disturbances in a horizontal dendrite layer during alloy solidification is investigated under an external constraint of rotation. The flow in the dendrite layer, which is modeled as flow in a porous layer and with the inertial effects included, is assumed to rotate about the vertical axis at a constant angular velocity. The investigation is an extension of the work in Riahi (On stationary and oscillatory modes of flow instablity in a rotating porous layer during alloy solidification. J. Porous Media, 6, 177–187, 2003), which was for the case in the absence of the inertial effects. Results of the stability analyses indicate, in particular, that the Coriolis effect can enhance the physical domain for the oscillatory flow, while the inertial effect tends to reduce such domain. Sufficiently strong inertial effect can eliminate presence of the oscillatory mode only for the rotation rate beyond some value. The effect of interaction between the local volume fraction of solid and the flow associated with the Coriolis term was found to be stabilizing.     

Solidification/stabilization of lead with the aid of bagasse as an additive to Portland cement

Solidification/stabilization (S/S) of hazardous waste is a widely used technology; therefore, it is crucial to evaluate its effectiveness and make attempts to improve the technique. A better matrix for S/S of hazardous waste was designed that is effective and economically feasible. This was accomplished by adding bagasse (byproduct of milling or diffusing sugar cane) to the waste/cement matrix. Lead nitrate was used as the model heavy metal waste with a 10 or 15% lead by weight to cement loading. Samples were cured for 7, 14, and 28 days at 24°C. Samples containing bagasse typically resulted in TCLP (modified) extract lead concentrations of approximately 0.5 mg/l of lead for all samples, while samples containing no bagasse had lead extract concentrations of approximately 5 mg/l for 10% samples and 45 mg/l for 15%. Results indicate that using bagasse as an additive to cement effectively improved the S/S of lead.