Calcite,vaterite and aragonite forming on cement hydration from liquid and gaseous phase

Cement hydration products were studied as influenced by the hydration conditions (hydration time in liquid phase; relative humidity, RH, in gaseous phase). The formation of calcium hydroxide (portlandite, P) and its transformation to calcium carbonates is mainly discussed here. More hydration products, including P, were formed in liquid phase (paste) than in water vapor (powder), due to the higher availability of water molecules. Full hydration was observed only in the paste hydrated for 6 month, otherwise the P content, estimated from its water escape, DM(400-800°C), increased after storage in water vapor of the prehydrated paste. All the three polymorphs of CaCO₃ (calcite, vaterite and aragonite) were found on prolonged contact with air of the hydrated powder (XRD, HRTEM). Their content was dependent on sequence of RH conditions on hydration: higher after water retention, WR, on lowering RH=1.0→0.95→0.5, than after water sorption, WS, on increasing RH in the inverse order. It increased also on wetting and drying, both of hydrated powder and paste. Ca was found to accumulate on the micro-surfaces of WR samples (SEM, TEM), whereas more Al was observed on WS samples and the crystallinity of hydration products was here higher (ED). Dissolution-diffusion-recrystallization was possible: small Al-ions concentrated at one end and the bigger Ca ions - at the other end of some needles (TEM). At 400-500°C the P in cement transforms in air into CaCO₃, which decomposes at 600-700°C. Thus the sensitivity to carbonation was estimated from ΔM(600-800°C). This value was similar in pastes hydrated for 1 month and in powder (WR). It was lower in powder WS and much lower in the paste (6 months). It increased pronouncedly when the prehydrated paste was stored in water vapor in WS. The nanocrystals of portlandite, vaterite and aragonite, embedded in the amorphous matrix, were observed by HRTEM in the hydrated powder. They may contribute to the cement strength. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of sodium-tetramethylammonium decamolybdate

Sodium-tetramethylammonium decamolybdate in acidified solution has been crystallized. Chemical analysis, thermogravimetric and X-ray studies have been performed.     

Four wave mixing in a waveguide — Two radiation and two guided modes interaction

The theory of nonlinear interaction between two radiation modes as a pump waves and two guided modes: the input beam and the generated backward beam, is presented. In the degenerate case, for all waves at the same frequency, we demonstrate the possibility of the input wave amplification and the phase conjugate replica generation as well as of the interaction between modes of different polarization. The nondegenerate case, with the phase matching achieved by pump waves amplitude modulation is also considered.     

On the nature of the boundary layers instabilities in a flow between a rotating and a stationary discSur la nature des instabilités de couche limite dans un écoulement entre un disque fixe et un disque tournant

Both theoretical linear stability analysis and direct numerical simulation are performed to study the transition flow between a stationary and a rotating disc. This paper concerns three-dimensional spiral and annular patterns computed with a high-order (spectral) numerical method and related to Bödewadt layer instabilities. The characteristic parameters of these boundary layer patterns are compared to the theoretical results and interpreted in terms of type I and type II generic instabilities. Moreover, the absolute instability regions are also theoretically identified and the critical Reynolds numbers of the convective/absolute transition in both layers are given. To cite this article: E. Tuliska-Sznitko et al., C. R. Mecanique 330 (2002) 91–99.     

On the regular part of varieties of algebras

We show that the regular part of a variety of algebras may not consist entirely of subalgebras of Plonka sums; indeed, the latter may not be closed under homomorphic images. In addition we give an example of a finitely based variety whose regular part has no finite basis (but is finitely based in a different similarity type).Our examples contrast with known results for semigroups, and contradict a published claim for the general case.To the memory of András HuhnPresented by Boris Schein.     

Infinite sheet structure of disodium tetra-μ-acetato- dichlorodirhodate(II) tetrahydrate

The binuclear rhodium(II) complex Na2[Rh2Cl2(OAc)4]· 4H2O has an infinite sheet structure. Binuclear anionic complexes [Rh2Cl2(OAc)4]2– are bound with cationic entities. The Na+ cation has pseudooctahedral coordination and is surrounded by two chloro ligands and two oxygen atoms of bridging acetato ligands of two [Rh2Cl2(OAc)4]2– anions and two water molecules. Both Cl and H2O are bridging ligands involved in formation of the Na+ chains. The remaining water molecules are located between sheets.     

Ion transport across model lipid membranes containing light-harvesting complex II: an effect of light

The effect of light on proton transport across lipid membranes of small unilamellar liposomes containing incorporated major light-harvesting pigment-protein complex of Photosystem II (LHCII) has been studied with the application of pH-sensitive dyes entrapped inside vesicles. Proton permeability coefficient for LHCII-modified membranes was found to be about twice as high as in the case of the control pure lipid vesicles. Illumination of the samples with light absorbed by the LHCII-bound photosynthetic pigments considerably affects the kinetics of proton transport: it increases the rate and decreases the steady-state level of proton gradient across the membranes. The effect was interpreted in terms of heat-induced conformational changes of LHCII molecular structures that affect proton buffering capacity of this protein. Both the control and the LHCII-modified lipid membranes have been found to be practically impermeable to Ca(++) ions, as demonstrated by fluorescence of liposome-entrapped calcium-sensitive probe calcium crimson. The slight differences in the proton transport across the LHCII-containing membranes under the presence of Ca(++) suggest calcium binding to this antenna protein.     

Determination of the lipophilicity of quinolinesulfonamides by reversed-phase HPLC and theoretical calculations

Reversed-phase high-performance liquid chromatography analyses were used for the determination of the retention factor (log k) of a set of quinolinesulfonamides. The analyses utilized a mixture of acetonitrile/water as the mobile phase. The log k values were linearly dependent on the concentration of acetonitrile and extrapolated to 100% water and gave the lipophilicity parameter log k_w. The parameter log P_HPLC was determined from log k_w values using the calibration curve obtained for five standards. The log P_HPLC parameters are discussed in terms of structure–lipophilicity relationships. Furthermore, the theoretical lipophilic parameters (log P_calc) for all compounds were calculated using chemical programs (e.g., Advanced Chemistry Development (ACD/ logP), miLogP, AlogP, ClogP, and Pallas). The determined log P_HPLC and calculated log P_calc values were compared by linear regression analysis.