Shapes of the icosahedral quasicrystalline phase in melt-spun ribbons

The shapes of icosahedral quasicrystalline (IQC) particles were determined in melt-spun ribbons of alloys based on the Al-Mn-Be alloy system. The sizes of the quasicrystalline particles ranged from a few tenths of nanometres up to 1 μm. Therefore, different methods were employed for characterizing their shapes: projection of quasicrystalline particles using transmission electron microscopy (TEM), cross-sections of IQCs on metallographically polished surfaces, and observation of deep-etched samples and extracted particles using a scanning electron microscope (SEM). It was discovered that icosahedral quasicrystalline particles preferentially grow in three-fold directions and have a tendency for faceting and adopting the shape of a pentagonal dodecahedron. The evolution of quasicrystalline shapes is systematically presented

Utjecaj brizne hlađenja na mikrostrukturu legure Al94Mn2Be2Cu2

In this study the effect of the cooling rate on the microstructure of Al94Mn2Be2Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K•min-1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K•s-1) and the rapid solidification was performed by melt spinning (up to 106 K•s-1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29Mn6Cu4, Al4Mn, θ-Al2Cu and Be4Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2Cu. Particles of i-phase and θ-Al2Cu were much smaller and more uniformly distributed in melt-spun ribbons.U ovoj je studiji istraživan utjecaj brzine hlađenja na mikrostrukturu legure Al94Mn2Be2Cu2. Legura sintetizirana vakuumskim indukcionim taljenjem i postupkom lijevanja bila je izložena različitim brzinama hlađenja. Najsporije je bilo hlađenje kod DSC (10 K•min-1), umjerene brzine hlađenja prilikom lijevanja u bakreni kalup (≈1 000 K•s-1) a najviše brzine skrućivanja postignute su pomoću metode melt spinning (do 106 K•s-1). Mikrostruktura DSC uzoraka sastoji se od matrice α-Al i nekoliko intermetalnih faza: τ1-Al29Mn6Cu4, Al4Mn, θ-Al2Cu i Be4Al(Mn,Cu). Mikrostruktura legura umjereno i brzo hlađenih sastoji se od matrice α-Al, i-faze i θ-Al2Cu. Čestice i-faze i θ-Al2Cu mnogo su manje i ravnomjerno raspoređene u trakama izrađenima metodom melt spinning

In situ TEM study of precipitation in a quasicrystal-strengthened AL-alloy

Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300°C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect

Salt-specific effects in lysozyme solutions

The effects of additions of low-molecular-mass salts on the properties of aqueous lysozyme solutions are examined by using the cloud-point temperature, T_{cloud}, measurements. Mixtures of protein, buffer, and simple salt in water are studied at pH=6.8 (phosphate buffer) and pH=4.6 (acetate buffer). We show that an addition of buffer in the amount above I_{buffer} = 0.6 mol dm^{-3} does not affect the T_{cloud} values. However, by replacing a certain amount of the buffer electrolyte by another salt, keeping the total ionic strength constant, we can significantly change the cloud-point temperature. All the salts de-stabilize the solution and the magnitude of the effect depends on the nature of the salt. Experimental results are analyzed within the framework of the one-component model, which treats the protein-protein interaction as highly directional and of short-range. We use this approach to predict the second virial coefficients, and liquid-liquid phase diagrams under conditions, where T_{cloud} is determined experimentally