Biopolymer immobilization during the crystalline growth of layered double hydroxide

Alginic acid, a biopolymer produced by brown seaweed, is incorporated between the sheets of a layered double hydroxide (LDH) via direct coprecipitation. The growth of the inorganic crystalline seeds over the polymer gives rise to a lamellar structure. The obtained nanocomposite presents a basal spacing in agreement with the ideal picture of the polymer lying perpendicularly to the inorganic sheets. A study using FTIR and ¹³C CP-MAS spectroscopies suggests that the interaction between the organic guest and the inorganic framework is weak. However, the polymer has a stabilizing effect in temperature, since ZnO is observed at 350°C, whereas it appears at 200°C for the chloride LDH pristine material.     

Determination calorimetrique de l'enthalpie de formation des alliages (Al,Ba) riches en aluminum

The heats of formation of some aluminium-barium alloys have been determined by drop calorimetry at high temperature. The heats of mixing of pure liquid Al and Ba to give the liquid alloy are Δ_mH(x_Ba=O.056, 1215 K)=?6.6 kJ mole^?1 and Δ_mH(x_Ba=O.333, 1215 K)=?31.0 kJ mole^-1. To measure its heat of formation, the solid compound Al₄Ba was precipitated by addition of pure barium from a liquid (Al, Ba) bath. It was found that Δ_fH(Al_0.8Ba_O.2, solid, 1215 K)=-(37.1 ? 1.5) kJ mole^?1 with reference to the pure metals in the solid state.     

Precipitation sequence during ageing in β1 phase of Cu–Al–Ni shape memory alloy

The shape memory alloys based on the ternary system Cu–Al–Ni are able to produce a memory effect at high temperatures. However, if the material undergoes an accidental overheating, a transformation process leads to progressive loss of its characteristics. In this study, the effect of ageing on the metastable β₁ (austenite) phase of a Cu–13.3 %Al–4 %Ni shape memory alloy was investigated. In addition, the effects of heating rate between 450 and 580 °C on the structural transformations of austenite after cooling to room temperature were studied. Observation by transmission electron microscopy of the structure that has undergone an isothermal ageing shows that the precipitation process depends on the maximum ageing temperature. Furthermore, calorimetric analysis shows that precipitates dissolution is possible when rapid heating between 450 and 580 °C. This behaviour is observed on the cooling diagram which shows a martensitic transformation.     

Enthalpies of formation of Ni-Sn compounds

Enthalpies of formation (Δ_fH) of nickel-tin compounds have been measured by direct reaction calorimetry: (approximate value); .Standard states are solid Ni and liquid Sn at the respective working temperatures: 728, 1288, 1389, 1332, 943 and 846 K.The enthalpy of formation of the Ni₃Sn high-temperature form is measured for the first time, while that of Ni₃Sn₂_LT must be considered as approximate because the corresponding calorimetric reaction was incomplete.The chemical and phase compositions of the specimens have been verified by electron probe microanalyses and by high- and room-temperature X-ray diffraction analyses. Unidentified thermal effects have been observed in the Ni₃Sn₂ phases region.     

Calorimetric and phase equilibria studies of the Ni–Sn–Bi system

The phase equilibria at 1273 K were investigated and an isothermal section of the Ni‐Sn‐Bi phase diagram was constructed. The phase boundaries are inclined to the Bi‐rich region that is agreement with phase equilibria at lower temperatures. The molar enthalpies of formation of liquid ternary Ni–Sn–Bi alloys have been determined at 833, 873 and 933 K by direct reaction calorimetry using pellets of 325 mesh powders of pure Ni, Sn and Bi. Measurements were performed with alloys containing from 0.05 to 0.10 mole fractions of nickel, and at ratios of tin and bismuth mole fractions X_Sn/X_Bi = 2.8, 1.2 and 0.43. The experimental calorimetric data were used to calculate a regular solutions parameter of the ternary liquid phase by means of two different thermodynamic data files. It was found that the Ni–Sn–Bi ternary liquid phase could be described as temperature independent ternary regular solution. The assessed values of the ternary interaction parameter are ‐280 J·mol^–1 and 56 000 J·mol^–1, depending on the binary parameters used. Enthalpies of formation of solid binary phases were measured, too. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)