Water and salt transport in plaster/substrate systems

The transport of salt and water during drying has been studied in systems consisting of a substrate covered with either one or two plaster layers. The drying behaviour of these systems was modelled with invasion percolation (IP) algorithms. The model outcomes were compared with experimental results obtained with Nuclear Magnetic Resonance (NMR). It was found that drying behaviour of the plaster layers was strongly influenced by the properties of the substrate. When the substrate has the widest pores, the plaster layers stay wet while the substrate dries out. As a consequence most salt, present in the substrate, moves to the plaster layers and accumulates at the external surface. In the case that the substrate has the smallest pores, the plaster layers dry out first. In this case salts also crystallize in the substrate. Further we have tried to make an accumulating plaster system consisting of two layers on top of a substrate, which would function purely on the basis of differences in pore sizes between the layers. The drying behaviour in the presence of pure water was as predicted by the model. However, in the case of a salt solution the salt modified the drying behaviour such that the accumulation properties of the system were reduced. Therefore, we conclude that for transporting systems tuning the pore-sizes of the layers suffices, but for accumulating systems it seems that additives , for example water repellents, have to be used

Magnetic susceptibilities, specific heat, and crystal structure of four S = 3/2, three-dimensional antiferromagnets

The zero-field, ac magnetic susceptibilities of single crystals of four S=3/2 trigonal salts containing the tris(1,2-diaminoethane)chromium(III) cation, [Cr(en)3]3+, and heat-capacity measurements on one of them, [Na(OH2)6][Cr(en)3]2Cl7, are reported. The crystal structures of two of them, [Na(OH2)6][Cr(en3]2Cl7 and [Na(OH)2)6][Cr(en)3]2Br6Cl, have been determined. They both belong to the trigonal P3¯cl space group, with a=11.513(2), c=15.566(6) Å; Z=2; and a=11.740(5), c=16.008(9) Å; Z=2, respectively, and contain discrete octahedral hexaquasodium (i) cations. The salt [K(OH2)6][Cr(en)3]2Cl7 appears to be isomorphous with its sodium analog, and [Cr(en)3]Cl3·3H2O belongs to the same space group. The magnetic measurements on the four salts extend over the temperature interval 60 mK to 4.2 K, and antiferromagnetic ordering is found in all of them. The zero-field-splitting energy is of the same order of magnitude as the magnetic exchange energy. The susceptibility data have been fitted with the parameters 2D/kB=-0.091(8) K, g?=1.994, g¿=1.988, and zJ/kB=-0.061(2) K for [Cr(en)3]Cl3·3H2O; 2D/kB=-0.058(8) K, g?=2.01, g¿=2.00, and zJ/kB=-0.068(4) K for [Na(OH2)6][Cr(en)3]2Cl7; 2D/kB =-0.060(8) K, g?=1.993, g¿=1.951, and zJ/kB=-0.046(4) K for [K(OH2)6][Cr(en)3]2Cl7; and 2D/kB=+0.064(8) K, g?=2.001, g¿=1.991, and zJ/kB=-0.066(4) K for [Na(OH2)6][Cr(en)3]2Br6Cl, where longitudinal (¿) and transverse (¿) refer to the unique threefold crystallographic axis. The ordering temperatures are 0.124(5), 0.116(5), 0.093(5), and 0.112(5) K, respectively. The easy axis for the chloride compounds lies parallel to the longitudinal axis, whereas the easy axis for the bromide lies in the transverse plane. Heat-capacity measurements on [Na(OH2)6][Cr(en)3]2Cl7 confirm that magnetic ordering takes place at 0.112(5) K. The heat-capacity curve and magnetic entropy calculations agree with the three-dimensional character of the ordering of an S=3/2, effective bcc magnetic lattice

Phase diagram of S=1/2 two-leg XXZ spin ladder systems

We investigate the ground state phase diagram of the S=1/2 two-leg $XXZ$ spin ladder system with an isotropic interchain coupling. In this model, there is the Berezinskii-Kosterlitz-Thouless transition which occurs at the XY-Haldane and the XY-rung singlet phase boundaries. It was difficult to determine the transition line using traditional methods. We overcome this difficulty using the level spectroscopy method combined with the twisted boundary condition method, and we check the consistency. We find out that the phase boundary between XY phase and Haldane phase lies on the $\Delta=0$ line. And we show that there exist two different XY phases, which we can distinguish investigating a $XX$ correlation function

Phase diagrams of spin ladders with ferromagnetic legs

The low-temperature properties of the spin S=1/2 ladder with anisotropic ferromagnetic legs are studied using the continuum limit bosonization approach. The weak-coupling ground state phase diagram of the model is obtained for a wide range of coupling constants and several unconventional gapless ''spin-liquid'' phases are shown to exist for ferromagnetic coupling. The behavior of the ladder system in the vicinity of the ferromagnetic instability point is discussed in detail.Comment: 11 pages, 4 figure