3,617 research outputs found
Speciation of Al3+ in fairly concentrated solutions(20-200 mmol L-1) at I = 1 molL-1 (NaNO3), in the acidic pH range, at different temperatures
No full textThe hydrolysis of Al3+ was studied in aqueous 1 mol L-1 NaNO3 solution at different concentrations (20 –
200 mmol L-1) and temperatures (283.15 –343.15 K) by potentiometry (ISE-H+, glass electrode). Many
different speciation models were considered in the calculations and it was found that the best model is represented by the following species: Al(OH)2+, Al3(OH)45+, Al13(OH)327+. Hydrolysis constants and
enthalpy changes at different temperatures are reported
Enhancement of Hydrolysis through the Formation of Mixed Heterometal Species: Al3+/CH3Sn3+ Mixtures
No full textABSTRACT: The hydrolysis of mixed-metal cations (Al3+/CH3Sn3+)
was studied in aqueous solutions of NaNO3, at I = 1.00 ± 0.05
mol·dm−3 and T = 298.15 K, by potentiometric technique. Several
hydrolytic mixed species are formed in this mixed system, namely,
Alp(CH3Sn)q(OH)r with (p, q, r) = (1, 1, 4), (1, 1, 5), (1, 1, 6), (2, 1,
4), (1, 2, 5), (1, 4, 11), (1, 3, 8), and (7, 6, 32). The stability of these
species, expressed by the equilibrium: pAl3+ + qCH3Sn3+ + rOH− =
Alp(CH3Sn)q(OH)r
3(p+q)−r, βpqr
OH, can be modeled by the empirical
relationship: log βpqr
OH = −3.34 + 2.67p + 9.23(q + r). By using the
equilibrium constant Xpqr relative to the formation reaction:
pAl(p+q)(OH)r + q(CH3Sn)(p+q)(OH)r = (p + q)Alp(CH3Sn)q(OH)r,
it was found that the formation of heterometal mixed species is
thermodynamically favored, and the extra stability can be expressed as
a function of the difference in the stability of parent homometal species. This leads, in turn, to a significant enhancement of
hydrolysis and solubility
Speciation of tin(II) in aqueous solution: thermodynamic and spectroscopic study of simple and mixed hydroxocarboxylate complexes
No full textThis contribution reports the results of potentiometric and Mossbauer investigations on the formation, stability, and structure of binary and ternary mono- and binuclear complexes of Sn2+ with three hydroxocarboxylic ligands (namely L = tartrate, malate, and citrate) and chloride at T = 298.15 K in different ionic media and ionic strengths (0.15 and 1.00 mol dm(-3) in NaCl(aq) and 1.00 mol dm(-3) in NaNO3(aq)). The stability constants of various simple Sn (i) H (j) L (k) ((2i+j-kz)) and mixed Sn (i) H (j) L (k) Cl (l) ((2i+j-kz-l)) species obtained in the different experimental conditions are reported, and various speciation diagrams of the simple and mixed systems are shown in different conditions. The sequestering ability of the three ligands toward Sn2+ was assessed by means of the calculation of the pL(0.5) parameter at different ionic strengths and in the different ionic media. The effect of the chloride anion on the stability of various species and on the sequestering ability of the investigated ligands toward Sn2+ was also evaluated. The structural results obtained by Mossbauer spectroscopy supported the speciation schemes obtained by the potentiometric investigations and indicated the possible trigonal bipyramidal arrangement of various Sn2+/ligand species. Measurements at different temperatures were also performed in the case of citrate, in order to estimate the temperature dependence of the stability of these species. A modified version of the computer program STACO is briefly presented here for the first time and allows the simultaneous determination of the stability constants and the enthalpy changes of various species from potentiometric titrations at different temperatures
The 2D/3D dynamics of wall-bounded low-Rm magnetohydrodynamic (MHD) turbulence
No full textWith this experimental study, we give evidence that the dynamics of low-Rm MHD turbulence depends on the diffusion length l_z, which corresponds to the distance over which the Lorentz force is able to diffuse momentum before it is balanced by inertia
Speciazione di Sn(II) in presenza di leganti O-donatori di interesse biologico
No full textLo stagno è il ventiquattresimo elemento più abbondante nella crosta terrestre ed ha il più elevato numero di isotopi stabili (dieci). Generalmente questo elemento non viene annoverato tra gli inquinanti più importanti, in quanto lo stagno inorganico non risulta particolarmente tossico. Tuttavia, molti dei suoi sali lo sono. Infatti, la corrosione di contenitori in stagno da parte di cibi e bevande acide ha causato in passato numerosi intossicazioni ad opera di composti solubili di questo metallo. Inoltre, la bioalchilazione dello stagno inorganico porta alla formazione di composti ancor più nocivi per l’ambiente. Per tali ragioni, per esempio, la Food Standards Agency del Regno Unito ha imposto dei limiti di 200 e 150 mg di stagno per kg di alimento solido e bevanda, rispettivamente. In virtù della diversa attività biologica delle differenti specie dello stagno, la conoscenza della sua speciazione nell’ambiente è di importanza fondamentale. Ciò nonostante, la conoscenza del comportamento chimico e della distribuzione delle specie dello stagno in sistemi naturali è praticamente inesistente, e i pochi dati di letteratura disponibili consentono soltanto una vaga predizione della sua speciazione in questi sistemi. In particolare, il comportamento in soluzione dello stagno(II) non è ben definito, e per tale motivo recentemente è stato intrapreso uno studio sistematico della sua speciazione in sistemi acquosi multicomponente. Dopo aver valutato le proprietà acido-base e le interazioni di Sn2+ con i principali leganti inorganici presenti nei fluidi naturali, in questo contributo sono presentati alcuni risultati preliminari sulla stabilità delle specie che questo catione forma con alcuni leganti organici a basso peso molecolare di interesse biologico e ambientale. In particolare, è stata studiata la speciazione di Sn2+ in presenza di acidi policarbossilici (acetico, malonico, malico, tartarico, citrico, lattico, gluconico), a t = 25°C a diverse forze ioniche in NaNO3aq e NaClaq. La capacità sequestrante di questi leganti nei confronti di Sn2+ è stata poi confrontata attraverso il calcolo di diversi valori di pL50, un parametro semiempirico proposto di recente che rappresenta la concentrazione totale (come antilogaritmo) di legante necessaria per sequestrare il 50% di catione presente (in tracce) in un sistema
Triangular Constellations in Flows
No full textParticles advected on the surface of a fluid can exhibit fractal clustering. The local structure of a fractal set is described by its dimension , which is the exponent of a power-law relating the mass in a ball to its radius : . It is desirable to characterise the {\em shapes} of constellations of points sampling a fractal measure, as well as their masses. The simplest example is the distribution of shapes of triangles formed by triplets of points, which we investigate for fractals generated by chaotic dynamical systems. The most significant parameter describing the triangle shape is the ratio of its area to the radius of gyration squared. We show that the probability density of has a phase transition: is independent of and approximately uniform below a critical flow compressibility , which we estimate. For the distribution appears to be described by two power laws: when , and when
Exact two-dimensionalization of low-magnetic-Reynolds-number flows subject to a strong magnetic field
No full textWe investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical? We restrict attention to low-magnetic-Reynolds number (Rm) flow. Because liquid metals have low magnetic Prandtl number, such low- flows can have a kinetic Reynolds number as large as one million and therefore be strongly turbulent. We first focus on the quasi-static approximation, i.e. the asymptotic limit of vanishing magnetic Reynolds number Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided the interaction parameter N is larger than a threshold value. We call this property absolute two-dimensionalization: the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full-magnetohydrodynamic equations and we prove that, for low enough Rm and large enough N, the flow becomes exactly two-dimensional in the long-time limit provided the initial vertically-dependent perturbations are infinitesimal. We call this phenomenon linear two-dimensionalization: the (possibly turbulent) 2D flow is an attractor of the dynamics, but it is not necessarily the only attractor of the system. Some 3D attractors may also exist and be attained for strong enough initial 3D perturbations. These results shed some light on the existence of a dissipative anomaly for magnetohydrodynamic flows subject to a strong external magnetic field
The Decay of Wall Bounded MHD Turbulence at Low RM
No full textWe have developed a new spectral method to simulate flows with very fine boundary layers present. We apply it to calculate the evolution of freely decaying MHD turbulence between isolating walls. By comparison them with results obtained in fully periodic domain we quantify the influence of the channel walls on the character of freely decaying MHD turbulence
A basis of a certain module for the hyperalgebra and some applications
No full textIn the hyperalgebra of the -th Frobenius kernel of the algebraic group , we construct a basis of the
-module generated by a certain element which was given by the
author before. As its applications, we also prove some results on the
-modules and the algebra .Comment: 30 page
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