Svyatoslav Gnyloskurenko

Influence of wetting conditions on bubble formation at orifice in an inviscid liquid. Transformation of bubble shape and size

Abstract This paper presents experimental results of the surface phenomena effect on bubble formation from a single orifice (1 mm diameter) submerged in water with air blowing at an extremely small flow rate (2 cm3 min−1). Bubble formation was studied for a wide range of contact angles (68°≤θ0≤110°) at liquid–orifice plate–gas interface using key geometrical parameters of a bubble: volume (V), surface area (S), radius at the tip (R0) and the dimension of bubble periphery at the base (D). The meaningful stages, termed (1) nucleation period, (2) under critical growth, (3) critical growth and (4) necking, were identified during bubble formation. It was determined that bubble volume essentially depends on wettability. It increases by more than half as wetting conditions worsen, e.g. equilibrium contact angle, θ0, increases from 68° to 110°. Bubble formation is found to be substantially controlled by hysteresis of contact angle.

DEVELOPMENT OF LIGHTWEIGHT AL ALLOY AND TECHNIQUE

Abstract A most promising lightweight material termed cellular metal is of growing interest to industry because of its combination of strength and energy absorption. A new foaming agent, calcium carbonate, along with an appropriate technique are suggested to improve the metal structure and control the foaming process. An applied coating enhances wetting of the agent particles and improves the homogeneity of the foam. Structure and mechanical properties of the foams obtained were also studied. The results showed that calcium carbonate ensured an aluminum foam with comparable density and smaller pores than with the conventional foaming agent, titanium hydride. The present study confirmed that calcium carbonate and the described technique have good applicability for foamed metal production. Un matériel léger très prometteur qu’on appelle métal cellulaire est d’un intérêt croissant dans l’industrie grâce à sa combinaison de force et de capacité d’absorption d’énergie. On suggère un nouvel agent moussant, le carbonate de calcium, ainsi qu’une technique appropriée, pour améliorer la structure du métal et pour contrôler l’opération de moussage. L’application d’un revêtement favorise le mouillage des particules de l’agent et améliore l’homogénéité de la mousse. On a également étudié la structure et les propriétés mécaniques des mousses ainsi obtenues. Les résultats ont montré que le carbonate permettait l’obtention d’une mousse d’aluminium de densité comparable et avec de plus petits pores qu’avec l’agent de moussage conventionnel, l’hydrure de titane. La présente étude a confirmé que le carbonate de calcium, ainsi que la technique décrite, s’appliquait à la production de métal cellulaire.

The role of foaming agent and processing route in mechanical performance of fabricated aluminum foams

The results of this study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affects the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al/Al-alloys by the Alporas like melt process, all performed with and without Ca additive and processed either with conventional TiH2 foaming agent or CaCO3 as an alternative one. Damage behavior of contaminations was believed to affect the micromechanism of foam deformation, favoring either plastic buckling or brittle failure of cell walls. No discrepancy between experimental values of compressive strengths for Al-foams comprising ductile cell wall constituents and those prescribed by theoretical models for closed-cell structure was found while the presence of low ductile and/or brittle eutectic domains and contaminations including particles/layers of Al3Ti, residues of partially reacted TiH2, and Ca bearing compounds, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density.

Improvement of Structure and Deformation Behaviour of High Strength Al-Zn-Mg Foam

Metal foams based on high-strength Al-Zn-Mg alloy are promising material for energy absorption application. The performance of coated calcium carbonate (CaCO3) as foaming agent for Alporas like route is studied in the present paper by comparison with the conventional titanium hydride (TiH2). Compressive response of the foams was examined and microstructure of cell wall was investigated. The advantages of CaCO3–foam are shown and discussed.

Effect of Mass Fraction of Dolomite on the Foaming Behavior of AlSiCu Alloy Foam by Powder Metallurgy Route

AbstarctMetallic foams are commonly produced using hydride foaming agents. Carbonates are safer to handle than hydrides; furthermore, a fine and homogenous cell structure can be obtained by carbonates in the powder metallurgy route. In this study, the principle of foaming by dolomite, which is a carbonate, for AlSiCu alloy was investigated by observing foaming with a high-temperature transmission X-ray system and identifying the foaming gas with a gas chromatography–mass spectrometry technique. During foaming by dolomite, two stages of expansion were observed. The first stage of expansion was induced by the water vapor absorbed onto the AlSiCu powder surface, and the second stage of expansion was induced by the decomposition of dolomite. The coarse cells of the first stage of expansion were filled with H2, and the fine cells of the second stage of expansion were filled with CO. A fine and homogenous cell structure was achieved by controlling the mass fraction of dolomite with the fraction of adsorbed water, which induced cell coarsening.