Experimental Densities, Speeds of Sound, Isentropic Compressibilties and Shear Relaxation Times of CaSO4·2H2O + CaCl2 + H2O and CaSO4·2H2O + NaCl + H2O Systems at Temperatures 30 and 35 °C

摘要

Speeds of sound, u, have been measured as a function of concentration for the systems, CaSO4·2H2O +CaCl2 + H2O and CaSO4·2H2O + NaCl + H2O, at temperatures of 30 and 35 °C. Derived parameters such as the isentropic compressibility, κ S , and the shear relaxation time,τ,were calculated using the experimental speed of sound data in combination with viscosity values from our earlier work. Results have been compared with those of the CaCl2+ H2Oand NaCl + H2O systems reported in literature,to examine the effect of adding CaSO4·2H2O(s).Values of κ S for the system,CaSO4·2H2O + CaCl2+H2O,are smaller compared with those for the CaCl2+ H2O system.Values of τ are lower at lower concentrations and then cross over in a narrow concentration region.Values of κ S for the system,CaSO4·2H2O+NaCl+H2O, are also smaller when compared with those forthe NaCl +H2O system.For this system the τ values are higher. These τ values reach a minimum at a certain concentration of NaCl in the solution and then increase with further increases in concentration.The influenceof solvent-separated and/or solvent-shared ion pairs plays a dominant role at higher concentrations for both systems.Results have been interpreted and discussed in terms of the expansion and contraction of the primary hydration shell of the ionic species present in the studied systems.