Mechanically agitated calorimetric cells working under pressure at macro and micro scale: application to gas hydrates

Originally applied to fields related to oil and gas production and flow assurance, high pressure differential scanning calorimetry (HP-DSC) has now been involved in several new studies such as carbon dioxide sequestration by CO2/CH4 exchange in naturally occurring gas hydrates or CO2 hydrate reversible formation/dissociation for refrigeration loops. However, the technique still has some limitations, which are linked to the fact that the gas hydrate formation occurs at the gas/liquid interface, and because the hydrate nucleation can be rather difficult in small volumes especially in quiescent conditions. It leads to several problems such as inefficient gas dissolution, long induction times, formation of a hydrate crust covering the gas/liquid interface, low hydrate to water conversion, etc. As a result, it is very difficult to determine accurately the heat capacities and the kinetics of formation/dissociation of several systems involving gas hydrates. This study presents two prototypes of calorimetric cells equipped with an in-situ mechanical agitation system, which allow performing experiments under pressure (150 bar maximum for the cells used in this work). The first system presented, called MIXCEL®, was developed for macro-calorimetry analysis (experiments carried out with a BT 2.15 Calvet Calorimeter from SETARAM Instrumentation). Very recently, we have developed a novel prototype of micro-calorimetric agitated cell (called MICROMIXCEL®) for microDSC analyses (experiments carried out using a microDSC7 evo from SETARAM Instrumentation). Both technical aspects, and results obtained at macro and micro scales with gas hydrate systems are presented and discussed

Experience with tacrolimus in children with steroid-resistant nephrotic syndrome

Children with steroid-resistant nephrotic syndrome (SRNS) are at risk of developing renal failure. We report here the results of a single-center retrospective observational study of the remission rate in pediatric patients with SNRS receiving tacrolimus. Serial renal biopsies from children on tacrolimus therapy were evaluated for tubulointerstitial fibrosis and transforming growth factor-β immunostaining. Of the 16 children with SRNS, 15 went into complete remission after a median of 120 days of therapy. Nine children were able to stop steroids, while the others were on tapering doses. Forty-seven percent had relapses, most of which were steroid-responsive. Serial renal biopsies were obtained from seven children after a median treatment duration of 24 months; two of these children had increased tubulointerstitial fibrosis and four showed increased transforming growth factor-β tissue staining. Children with worsening histological findings were younger. There was no significant association between tacrolimus exposure and biopsy changes, although the average trough level was higher in those children with worsening histological findings. In conclusion, tacrolimus may be a safe and effective alternative agent for inducing remission in children with SRNS. However, caution needs to be taken when prescribing this agent due to its narrow therapeutic index. Serial renal biopsies are necessary to check for subclinical nephrotoxicity, especially in younger children and those with higher trough levels

Thermodynamics of NiAl 2O 4-NiFe 2O 4 spinel solid solutions

NiAl 2O 4, NiFe 2O 4, and their solid solution Ni(Fe zAl 1-z) 2O 4 have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B 2O 3 at 973 K. X-ray absorption near edge structure (XANES) measurements and Mössbauer spectroscopy investigation of the cation distribution showed that the Ni fraction in octahedral sites increases with increasing iron content. Despite the zero heat of mixing, the solid solution is not thermodynamically ideal in the sense of Raoult's law. The entropies of mixing are similar to those for a solid solution of two inverse spinels and the activities are approximated as the square of the mole fractions. The stability of the solid solutions relative to oxide components (NiO, Al 2O 3, Fe 2O 3) increases with increasing iron content. The solid solution is a suitable waste form for nickel from industrial processing with higher iron content potentially beneficial to its stability. © 2011 The American Ceramic Society.link_to_subscribed_fulltex

Opis termodynamiczny trójskładnikowych układów Fe-B-X. Część 3: Fe-B-Mn

A thermodynamic optimization of the ternary Fe-B-Mn system is presented. The thermodynamic parameters of the binary sub-systems, Fe-Mn, Fe-B and B-Mn, are taken from earlier assessments slightly modifying the B-Mn system description. The thermodynamic parameters of the Fe-B-Mn system are optimized in this study using literature experimental thermodynamic and phase equilibrium data. The solution phases of the system are described using the substitutional solution model and the borides are treated as stoichiometric or semi-stoichiometric phases of the (A,B)pCq type described with the two-sublattice models.Przedstawiono termodynamiczny opis trójskładnikowego układu Fe-B-Mn. Parametry termodynamiczne dwuskładnikowych stopów Fe-Mn, Fe-B i B-Mn zostały zaczerpnięte z wcześniejszych opracowań, przy tym opis układu B-Mn został nieznacznie zmodyfikowany. Parametry termodynamiczne dla układu Fe-B-Mn zostały zoptymalizowane w tej pracy w oparciu o eksperymentalne równowagi fazowe i dane termodynamiczne zaczerpnięte z literatury. Roztwory stałe w układzie Fe-B-Mn opisano przy użyciu modelu roztworu substytucyjnego, a borki traktowane sa jako fazy stechiometryczne lub półstechiometryczne typu (A,B)pCq opisane przy użyciu modelu dwu podsieci

Thermodynamic Description of Ternary Fe-B-X Systems. Part 3: Fe-B-Mn/ Opis Termodynamiczny Trójskładnikowych Układów Fe-B-X. Część 3: Fe-B-Mn

A thermodynamic optimization of the ternary Fe-B-Mn system is presented. The thermodynamic parameters of the binary sub-systems, Fe-Mn, Fe-B and B-Mn, are taken from earlier assessments slightly modifying the B-Mn system description. The thermodynamic parameters of the Fe-B-Mn system are optimized in this study using literature experimental thermodynamic and phase equilibrium data. The solution phases of the system are described using the substitutional solution model and the borides are treated as stoichiometric or semi-stoichiometric phases of the (A,B)pCq type described with the two-sublattice models.Przedstawiono termodynamiczny opis trójskładnikowego układu Fe-B-Mn. Parametry termodynamiczne dwuskładnikowych stopów Fe-Mn, Fe-B i B-Mn zostały zaczerpnięte z wcześniejszych opracowań, przy tym opis układu B-Mn został nieznacznie zmodyfikowany. Parametry termodynamiczne dla układu Fe-B-Mn zostały zoptymalizowane w tej pracy w oparciu o eksperymentalne równowagi fazowe i dane termodynamiczne zaczerpnięte z literatury. Roztwory stałe w układzie Fe-B-Mn opisano przy użyciu modelu roztworu substytucyjnego, a borki traktowane sa jako fazy stechiometryczne lub półstechiometryczne typu (A,B)pCq opisane przy użyciu modelu dwu podsieci

Thermodynamic study of orthorhombic Tx and tetragonal T′ lanthanum cuprate, La2CuO4

The enthalpies of transition among the Tx, T′, and T–La2CuO4 phases are obtained from a combination of differential scanning calorimetry, high temperature oxide melt solution calorimetry, and transposed temperature drop calorimetry. The enthalpy of transformation of Tx to T is 2.32±0.07 kJ/mol and the corresponding entropy of transition is 4.38±0.13 J/(mol K). The T′ modification, with an average of 1.40 kJ/mol, is less stable in enthalpy than Tx but at 0.96 kJ/mol, more stable in enthalpy than T. Although we cannot rule out a small stability field at temperatures near the Tx–T transition at 530 K, T′ is most likely metastable at all temperatures

On the synthesis of Bi-based precursors for lead-free solders development

Preliminary studies on the design of lead-free solders precursors by wet chemistry methods are presented. The main objective is to assess the impact of the way of hydroxide precipitates preparation on the metal elements content of the precipitates. Namely, ternary hydroxide mixtures of three systems: a. Cu(II), Bi(III), Sn(II); b. Cu(II), Bi(III), Sb(III); and c. Cu(II), Bi(III), Zn(II) were prepared, firstly, by single-element precipitation and, secondly, by co-precipitation. Thereafter, all mixtures were reduced by using hydrogen gas. Both, the initial mixtures and the reduced samples were studied by X-ray diffraction, optical and scanning electron microscopes. The chemical compositions of the precipitates were determined experimentally and their dependence on the pH was verified. It was found that alloying occurred during the reduction procedure, but in some cases the reduction was not complete (i.e. oxide phases rest in the samples). This might be a huge obstacle to use such an approach for the preparation of lead-free solders. Moreover, the materials obtained after reductions apparently are bulk alloys, thus, the preparation of small-sized metal particles would be a challenge. Another key feature to be addressed in future studies is the correlation between the chemical compositions of the parent solution and these of the corresponding precipitates