Ion-pair formation in aqueous strontium chloride and strontium hydroxide solutions under hydrothermal conditions by AC conductivity measurements

Abstract

Frequency-dependent electrical conductivities of solutions of aqueous strontium hydroxide and strontium chloride have been measured from T = 295 K to T = 625 K at p = 20 MPa, over a very wide range of ionic strength (3 × 10(-5) to 0.2 mol kg(-1)), using a high-precision flow AC conductivity instrument. Experimental values for the concentration-dependent equivalent conductivity, Λ, of the two electrolytes were fitted with the Turq-Blum-Bernard-Kunz ("TBBK") ionic conductivity model, to determine ionic association constants, K(A,m). The TBBK fits yielded statistically significant formation constants for the species SrOH(+) and SrCl(+) at all temperatures, and for Sr(OH)2(0) and SrCl2(0) at temperatures above 446 K. The first and second stepwise association constants for the ion pairs followed the order K(A1)(SrOH(+)) > K(A1)(SrCl(+)) > K(A2)[Sr(OH)2(0)] > K(A2)[SrCl2(0)], consistent with long-range solvent polarization effects associated with the lower static dielectric constant and high compressibility of water at elevated temperatures. The stepwise association constants to form SrCl(+) agree with previously reported values for CaCl(+) to within the combined experimental error at high temperatures and, at temperatures below ∼375 K, the values of log10 KA1 for strontium are lower than those for calcium by up to ∼0.3-0.4 units. The association constants for the species SrOH(+) and Sr(OH)2(0) are the first accurate values to be reported for hydroxide ion pairs with any divalent cation under these conditions.

High proportion strontium-doped micro-arc oxidation coatings enhance early osseointegration of titanium in osteoporosis by anti-oxidative stress pathway

“…This resulted in an increase of SrO proportions, which corresponded to an increase of Sr 2+ . The enhanced SrO component in the high Sr coatings would easily react with water to generate Sr(OH) 2 and subsequently dissolve in aqueous solution [ 42 ], resulting in a greater release rate of Sr 2+ in the Sr100% group than in the Sr25% group, as demonstrated in our work ( Fig. S4 ).…”

Water mediated growth of oriented single crystalline SrCO3 nanorod arrays on strontium compounds

“…Aside from such discrepancy, there is a general consensus that hydrated Sr 2+ clusters have flexible structures freely exchanging H 2 O and OH − between the first and second shells 74,75 . This indicates that Sr 2+ hydroxide clusters with Sr 2+ -OH − interaction (mostly mono/dihydroxides 75 ) are always present in high pH aqueous solutions (OH − abundant); however, Sr 2+ and OH − are not directly connected in both Sr(OH) 2 •8H 2 O and Sr(H 2 O) 7 (OH) + solid phases (instead, only Sr 2+ -H 2 O interaction exists unless further hydrated) 69,76 .…”

Internally consistent thermodynamic data for aqueous species in the system Na–K–Al–Si–O–H–Cl

“…The partial molal standard state properties and HKF parameters of the neutral ion pairs NaCl 0 , KCl 0 , NaOH 0 , and KOH 0 were refined using the OptimB optimization program (Shvarov, 2015), using equilibrium constants derived from recent conductance experiments. These experimental data have the advantage over the older datasets that the conductance was measured in very dilute solutions (Ho and Palmer 1997;Ho et al, 2000a, b;Ho et al, 2001;Sharygin et al, 2002;Zimmerman et al, 2007;Arcis et al, 2014) and that equilibrium constants were derived with more theoretically sound models for the conductivity of electrolyte solutions (Tagirov et al, 1997;Ho and Palmer 1997;Ho et al, 2000 a, b;Ho et al, 2001;Tagirov et al, 1997;Zimmerman et al, 2007;Plumridge et al, 2015). This makes the equilibrium constants retrieved from the conductance data largely independent from the aqueous activity model employed.…”