Sabry A. El-Korashy

Characterization and evaluation of the pozzolanic activity of Egyptian industrial by-products. I: Silica fume and dealuminated kaolin

Abstract Silica fume (SF) and dealuminated kaolin (DK) from Egyptian sources have been characterized chemically and mineralogically, and a comparative study of their reactivities toward lime were conducted using isothermal conduction calorimetry and an accelerated chemical method. The kinetics of SF–lime and DK–lime reaction were investigated in suspension. Unreacted lime and combined water were determined as function of time, and the hydration products were identified with X-ray diffraction (XRD) and SEM combined with EDX. DK has a much higher surface area (90.5 m 2 /g) than SF (18.6 m 2 /g) and exhibits much higher pozzolanic activity, especially during early hydration. A low-density sponge-like CSH was formed, from both SF and DK at low lime contents (20% CH), and a more dense CSH was formed at higher lime contents (40% CH).

Synthesis and fluorescence properties of Eu-anthracene-9-carboxylic acid towards N-acetyl amino acids and nucleotides in different solvents

Europium (III) complex with anthracene-9-carboxylic acid (9-AA) has been synthesized and characterized by elemental analysis, FT-IR, and TG-DTG techniques. The results indicated that the composition of this complex is Eu (9-AA)(3). The luminescence properties of the complex in different solvents and at different pH values have been investigated. The results show that the complex exhibits more efficient luminescence in THF and ethyl acetate. The interactions of Eu-complex with different N-acetyl amino acids and nucleotides in different solvents have been investigated by fluorescence measurements. Enhancement of the fluorescence intensities has been observed in cyclohexane, acetone, acetonitrile, and tetrahydrofuran whereas the fluorescence intensities of the investigated complex in ethanol, water, and ethyl acetate exhibit relatively low intensity.

Activity of silica fume and dealuminated kaolin at different temperatures

Abstract Silica fume (SF) and dealuminated kaolin (DK) were investigated for their pozzolanic activities. The kinetics of the SF–lime and DK–lime reactions were investigated in pastes at room temperature, 100°C, and 180°C by the determination of unreacted lime and combined water. The hydration products were identified by X-ray diffraction (XRD). The variations in mechanical properties were correlated with the reaction kinetics and the hydration products formed. DK exhibited higher reactivity than SF at all temperatures studied. Tobermorite was formed at 100°C in the high-lime DK mix at 14 days and extensively formed by autoclaving at 180°C curing due to the presence of Al and sulfate in the DK. The very low C/S ratios of SF mixes and low-lime DK mix prevent tobermorite formation and promote the formation of poorly crystalline C-S-H with a higher surface area.

High-throughput sensing microtiter plate for determination of biogenic amines in seafood using fluorescence or eye-vision

A new optical sensing microplate was developed for rapid screening for the presence of biogenic amines (BAs) in seafood samples with high sensitivity. The deposition of a sensing spot (containing a chameleon dye (Py-1) in a polymeric cocktail) on the bottom of the wells of a standard microplate renders the plate a new sensing tool for a rapid and parallel detection of up to 96 (real) samples. This sensing microplate enables (1) a semi-quantitative readout of analyte concentration by eye-vision, (2) a rapid fluorescence readout of 96 samples with standard instrumentation in less than two minutes (unlike chromatographic and electrophoretic methods), (3) a statistically robust data evaluation (with 8-12 replicates) and (4) a rapid parallel sample preparation with standard 8 or 12-channel micropipettes. On reaction with biogenic amines, the dye shows a significant visible color change from blue over green to red color. The appearance of red color favorably coincides with the concentration of BAs that can induce symptoms of poisoning. The linear ranges of fluorescence calibration data for six biogenic amines cover the clinical toxicological relevant range of BAs that is too low to be detected by the human nose. The LODs range from 0.16 to 0.56 μg mL(-1), with correlation coefficients (r(2)) between 0.985 and 0.999. Finally, the evolution of spoilage of four fish samples (monitored by determination of their BA status) and the increase of their total amine content were found to agree well with previous data on time-dependent evolution of BAs in fish.

Hydration characteristics of Portland cement – Electric arc furnace slag blends

Abstract Utilization of electric arc furnace slag (EAF slag) as blending material for Portland cement has been examined. This was done via the investigation of the hydration characteristic of EAF slag – Portland cement blended mixtures. Various ratios of EAF slag were used namely; 5, 10 and 20 wt% of solid mix. The hydration properties investigated for the various mixtures were; compressive strength, chemically combined water and free lime contents as a function of hydration times. The hydration ages were; 1, 3, 7, 28 and 90 days. In addition, phase composition of the formed hydrates was examined using XRD technique as well as differential thermal analysis (DTA) for some selected samples. The results showed that as the ratio of EAF slag increases the values of compressive strength decrease at all the hydration ages. Hydration kinetics of the investigated mixes was followed by determining the variation of free lime and chemically combined water contents with time of hydration. It was observed that hydration proceeds in four different stages. The values of chemically combined water of the cement pastes blended with EAF slag were less than those of the neat Portland cement paste at all hydration ages. The mode of variation of free lime content with time was nearly similar to that of combined water content. The results of chemically combined water, free lime, XRD analysis as well as thermal analysis were correlated well with those of compressive strength. All these results indicate that the used EAF slag has no significant pozzolanic reactivity.

Hydraulic activity of water-cooled slag and air-cooled slag at different temperatures

Water-cooled slag (WS) and air-cooled slag (AS) with similar chemical compositions and produced from the same blast furnace were investigated for their hydraulic activities at different temperatures. The kinetics of hydration of WS ‐ lime and AS ‐ lime pastes were investigated at room temperature, 100∞C, and 180∞C by the determination of unreacted lime and combined water. The hydration products were identified by XRD. The variations in mechanical properties were correlated with the reaction kinetics and the types of the hydration products. The change in the mechanism of slag hydration was also predicted. The AS studied exhibited significant reactivity at room temperature. Increasing the temperature to 100∞C has no significant effect on the reactivity of either type of slag except during early hydration. However, the reactivity of AS increased much more than WS with hydrothermal activation at 180∞C. Calcium silicate hydrate (CSH) and plazolite formed in AS mixes. CSH, plazolite, and a-C2SH formed in WS mixes at 180∞C. D 2001 Elsevier Science Ltd. All rights reserved.

Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-CaSO4 systems

Mixtures of CaO, amorphous SiO2 and kaolinite in the presence or absence of SO42−ions (added as CaSO4·2H2O) were treated in suspension under hydrothermal conditions at temperatures of 80–200 °C. Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO2 mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO42−ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and α-C2SH by increasing the autoclaving temperature. In the C-S-A-C¯s system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-alumirtate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, α-C2SH and anhydrite II are formed. In both systems the excess Al2O3 appeared as a hydrogarnet phase, C3ASH4.

Studies on divalent ion uptake of transition metal cations by calcite through crystallization and cation exchange process

The uptake of transition metal cations of Fe, Cu, Zn, Cd and Pb with calcium carbonate in the form of calcite was investigated. The uptake reaction was found to be in the following order: Pb2+ > Cu2+ Zn2+ > Cd2+ ≈ Fe2+; and the amount of uptake (meq/g) cations has been found to increase with the increase of the metal ion concentration and reaction time. The uptake of these ions was mainly considered to be due to the crystallization that happens through decomposition reaction mechanism as in case of Pb2+, Cu2+ and Zn2+ and cation exchange of surface Ca2+-ions present in lattice structure of carbonate solid with metal cations, as in the case of Fe2+ and Cd2+. The different affinities of calcite toward these cations can be used for waste ions fixations or decontamination.

Experimental and spectroscopic studies of charge transfer reaction between sulfasalazine antibiotic drug with different types of acceptors

The charge-transfer (CT) interactions between the electron donor sulfasalazine (SS) and the acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL), picric acid (PA) and iodine have been studied spectrophotometrically in CHCl(3) or CH(3) OH solutions. The formed solid CT complexes were also isolated and characterized through infrared, (1) H-NMR, mass spectra as well as elemental and thermal analysis. The CT complexes were discussed in terms of formation constant (K(CT) ), molar extinction coefficient (ε(CT) ), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (µ), resonance energy (R(N) ) and ionization potential (I(D) ). The stoichiometry of these complexes was found to be 1:1 molar ratio and having the formulae [(SS)(DDQ)], [(SS)(CHL)], [(SS)(PA)] and [(SS)(2) I](+) · I(3) (-) , respectively. The charge transfer interaction was successfully applied to the determination of SS drug using mentioned σ and π-acceptors also, the results obtained herein are satisfactory for estimation of SS compound in the pharmaceutical form.

Divalent ion uptake of heavy metal cations by (aluminum + alkali metals) – substituted synthetic 1.1 nm-tobermorites

The reactions of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+ or Hg2+ synthetic (Al + alkali metal) – substituted tobermorites were studied. Among these cations, Mn2+, Fe2+, Cu2+, Zn2+, pb2+ and Hg2+ appears to exchange with outer planar surface of Ca2+ of tobermorites due to the break down of structural Ca-O bonds, in addition to the substituted alkali metals in the structure. But it is difficult to delineate the extent of this reaction from the precipitation of the concerned ions as carbonates, hydroxy carbonates, hydroxy nitrates or hydroxides. The uptake of metal ions by these solids led to their amorphization in many cases due to the partial exchange and the acidic nature of metal solutions, and hence their reactions are not strictly analogous to cation exchange in zeolites and clays. The order of ion uptake has been found in the following order: Fe2+ > Ni2+ > Co2+ > Zn2+ > Cu2+ > Mn2+ > Hg2+ > Cd2+ > pb2+.