Philippe Anres

Enthalpy of formation of the (Pt–Sn) system

Abstract With a fully automated high temperature calorimeter the enthalpy of formation of the [Pt–Sn] liquid system was determined on the molar fraction range 0 Δ mix H m °=x(1−x)(−123.76−96.27x−119.62x 2 +88.89x 3 +97.58x 4 ) with x=x Pt . The enthalpies are negative over the entire concentration range with a minimum ΔmixHm°=−46.8±2 kJ mol−1 at x=0.554, independent of temperature. The limiting partial molar enthalpy of mixing of platinum is determined as Δ mix h m ° ∞ ( Pt sc , x Pt =0)=−124±5 kJ mol −1 . Enthalpies of formation and fusion of PtSn and Pt3Sn, respectively, have been determined by calorimetric measurements. They show that PtSn exists in an high temperature (H.T.) and a low temperature (L.T.) form, respectively: Δ for H m °( Pt 0.5 Sn 0.5 (L.T.), sol )=−74 kJ mol −1 , Δ for H m °( Pt 0.5 Sn 0.5 (H.T.), sol )=−63.5 kJ mol −1 , Δ for H m °( Pt 0.75 Sn 0.25 , sol )=−55.3 kJ mol −1 . Moreover, some points of the equilibrium phase diagram were obtained by the calorimetric experiments. The integral and limiting partial enthalpies of mixing have been compared with the data previously obtained for other (T.M.–Sn) systems. The energetic effect is caused by sharing 3 electrons from Sn at most with the uppermost bands of Pt.

A chemometric approach for the elucidation of the parameter impact in the hyphenation of field-enhanced sample injection and sweeping in capillary electrophoresis.

The aim of this work was to elucidate the impacts of parameters influencing cation‐selective exhaustive injection coupled to sweeping and micellar electrokinetic chromatography (MEKC). A chemometric approach using cationic compounds, acidic conditions (phosphate buffer, pH 2.3) and polyacrylamide‐coated capillaries to suppress electroosmotic flow were used. It was demonstrated that the water plug was not useful because of long electrokinetic injections. If conductivity of the high conductivity buffer (HCB) and the HCB to sample conductivity ratio are sufficiently high (>1.66 S/m and >30, respectively), variations of HCB conductivity do not impact sensitivity. The length of the HCB must be long enough so that the most mobile cation remains stacked in this zone for a given injection time. SDS concentration should be as high as possible (the maximum concentration is dictated by MEKC, here 90 mM), so sensitivity is not impacted. We have shown analytes can be lost after electrokinetic injection, when the polarity of the voltage is reversed. Introducing a plug of micellar electrolyte before polarity reversal avoids these losses. Following these recommendations only injection time and sample conductivity impacted sensitivity enhancement. Sample conductivity had to be the lowest as possible and controlled in real case analyses to obtain repeatable enrichment factors.

Influence of high‐conductivity buffer composition on field‐enhanced sample injection coupled to sweeping in CE

The aim of this work was to clarify the mechanism taking place in field‐enhanced sample injection coupled to sweeping and micellar EKC (FESI‐Sweep‐MEKC), with the utilization of two acidic high‐conductivity buffers (HCBs), phosphoric acid or sodium phosphate buffer, in view of maximizing sensitivity enhancements. Using cationic model compounds in acidic media, a chemometric approach and simulations with SIMUL5 were implemented. Experimental design first enabled to identify the significant factors and their potential interactions. Simulation demonstrates the formation of moving boundaries during sample injection, which originate at the initial sample/HCB and HCB/buffer discontinuities and gradually change the compositions of HCB and BGE. With sodium phosphate buffer, the HCB conductivity increased during the injection, leading to a more efficient preconcentration by staking (about 1.6 times) than with phosphoric acid alone, for which conductivity decreased during injection. For the same injection time at constant voltage, however, a lower amount of analytes was injected with sodium phosphate buffer than with phosphoric acid. Consequently sensitivity enhancements were lower for the whole FESI‐Sweep‐MEKC process. This is why, in order to maximize sensitivity enhancements, it is proposed to work with sodium phosphate buffer as HCB and to use constant current during sample injection.

First thermodynamic approach of the (Ir+Ga) system

With a fully automated high temperature calorimeter the enthalpy of formation of the [Ir+Ga] liquid system was determined between 1106<Te<1471 K, in the molar fraction range 0<x<0.54 (with x=xtr). The molar enthalpy of formation of the [Ir+Ga] liquid alloys [ΔmaxHm°] corresponding to the reaction, at Te and p°: Ga(liq) + b lr(liq) → Ga, lr(1-a)(liq) can be described by the following Redlich-Kister equation (in kJ mol−1) ΔmaxHm°=x(1−x)ξ(y) with ξ(y)=−257.68−63.09y+76.47y2+14.39y3 and y=xtr − xGa. This function is negative with an estimated minimum ΔmaxHm°=−65±4 kJ mol−1 at x=0.55, and independent of temperature, within the experimental error. The limiting partial molar enthalpy of mixing of iridium, deduced from experiments performed at 1155 and 1482 K, is: Δmaxhm°(Ir supercooled liquid in ∞ liq Ga) = − 132±5 kJ mol−1. On the other hand, by extrapolation of the ξ-function to x = 1, the limiting enthalpy of Ga in supercooled liquid Ir was predicted with a larger uncertainty: Δmaxhm°(Ga liq. in ∞ supercooled liquid Ir) = − 230±30 kJ mol−1. For three compositions (x=0.141, 0.182 and 0.25), the molar heat capacities of the solid alloys have been measured between 423 and 763 K and the enthalpy of formation of IrGa3 was determined by dissolution calorimetry : ΔmaxHm°(Ir0.25Ga0.75; Tamb, sol) = −80 kJ mol−1. Moreover, from these calorimetric experiments, some points of the equilibrium phase diagram were obtained; thus the first shape of the liquidus of the Ir + Ga system (in the Ga-rich region, has been proposed. The integral and limiting partial enthalpies of mixing have been compared with the data previously obtained for the (transition metal + Ga) systems.

Thermodynamics of the [Ir–In] system

Abstract The molar enthalpy of formation of the [Ir–In] liquid alloys [ΔmixHm°] corresponding to the reaction, at Te and p°: a In (liq) +b Ir (liq) → In x Ir (1−x) (liq) was determined on the following temperature and molar fraction ranges 1175 Δ mix H m °=x.(1−x)ξ(y) with ξ(y)=−74.27+18.51y+27.74 y2−15.28 y3and y=(xIr−xIn). In this case, the coordinates of the minimum are estimated to be at ΔmixHm°=−19±1 kJ.mol−1 and x=0.45±0.01. The limiting partial molar enthalpy of mixing of iridium, deduced from experiments performed at 1154 K, is: Δ mix h m ° ( Ir supercooled liquid in ∞ liq In)=−50±2 kJ.mol −1 . The integral and limiting partial enthalpies of mixing have been compared with the data predicted by Miedema and co-workers. The trend of the ΔmixHm°=f(x) diagrams obtained at the lower temperature (below 1175 K and between 1200 and 1300 K) allow us to conclude that the solid phases IrIn3 and IrIn2 are in equilibrium with the liquid phase. For three compositions (x=0.186, 0.25 and 0.33), the molar heat capacities have been measured between 423 and 763 K. These results are compared with the values calculated with the Neumann-Kopp law. The weak thermal effect appearing in the Cp°=f(T) graph with the alloy x=0.186 can be due to a change of structure. So, some information concerning the [Ir–In] equilibrium phase diagram (eutectic, peritectic and liquidus temperatures) was obtained. Thus, in the In-rich region, a preliminary shape of the liquidus of the [Ir–In] system has been proposed. Finally, thermodynamic results obtained under the same condition, on the one hand, for the Co–In system and, on the other hand, for the Ir–In system, have been compared: the existence of a liquid–liquid miscibility gap at high temperature could also be assumed for this last system.