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Abstract
Nedocromil sodium has a number of known hydrate states, a monohydrate, a trihydrate and a heptahemihydrate, including an amorphous state. Effect of grinding on the hydration states of nedocromil sodium crystals was studied. After grinding the trihydrate, heptahemihydrate was observed in the ground sample, even though, the water content in the ground sample was not sufficient to cover the heptahemihydrate’s hydration level. On the other hand, in the ground heptahemihydrate, trihydrate was existed. Apparent activation energies (ΔE) for hydrates, monohydrate→anhydrate, trihydrate→monohydrate and heptahemihydrate→amorphous(anhydrate), were calculated using TG data. ΔE for the dehydration of heptahemihydrate was significantly lower than that of other hydrates. Obtained ΔE data explained the inter-conversion behavior of nedocromil sodium induced by grinding.
Abstract
The adsorption behaviour of99Mo in the form of molybdate and of99mTc in the form of pertechnetate on hydrated titanium dioxide was investigated at different molarities of hydrochloric acid. The adsorption capacity of molybdate on hydrated TiO2 is higher than on Al2O3. A99mTc-generator is suggested. This generator is based on the adsorption of (99Mo) molybdate on hydrated TiO2, at acidities of 0.05–0.1M. HCl.99mTc is eluted with 0.9% NaCl. Radionuclidic, radiochemical and chemical purities of the eluates were checked. This generator seems to have a great potential as compared to the traditional alumina generators.
Abstract
The mechanism of the reduction reaction of lanthanide(III) ions by hydrated electrons in polar solvents has been investigated. The theoretical rate constants for the reaction of hydrated electrons with a number of lanthanide ions have been calculated using the energy gap laws of the charge shift reaction(D+−A→D−A+) and compared with experimental values. With these results, we have explained the large difference of the reaction rates of lanthanide ions with hydrated electrons, which depend upon the kind of lanthanide ion. The calculated results agree almost quantitatively with the experimental values.
Abstract
This paper presents results of thermokinetic studies on the early stages of hydration of some slag minerals, slag alkaline binders of traditional and new-generation compounds. A possibility of adjustment and control of hardening processes through thermokinetic indices of hydration (intensity and completeness of heat evolution) for various compounds, types and quantities of the alkaline components and temperatures is proved.
Activation energies for the thermal decomposition reactions of hydrates and basic salts of FeSO4 were calculated using both conventional and statistical methods. The advantage and disadvantage of both methods is brought out. A combined method is proposed.
Abstract
The physicochemical properties of spent fluidized bed cracking catalyst and its influence on hydration process of cement slurry were studied. The samples were cement slurries prepared with water/solid=0.5 and additions of used catalyst amounted to 0, 5, 10, 15, 20 and 25%with resp. to the solid. After definite time they were subjected to thermogravimetric analysis (TG, DTG, DTA) and, in order to determine the progress of reaction with water, the heat of hydration was measured by means of isotherm calorimetry. The studies disclosed that the spent cracking catalyst is not merely an inactive filler in cement slurries, but it modifies the course of the hydration process. The spent catalyst is a pozzolana additive and its presence leads to a decrease of calcium hydroxide contents in the system. The spent catalyst affect on the heat of cement hydration. Small amounts additive accelerate the process of binding.
Abstract
The rate of some heterogeneous isotopic exchange reactions can be enhanced by the simultaneous hydration of the solid participating in the exchange process. The results presented here show that the concomitant hydration of anhydrous sodium sulphate enhances the Na2SO4–22Na+ isotopic exchange reaction in a water-acetone medium. The reaction rate is further enhanced by creating a controlled number of vacancies in the crystal lattice of sodium sulphate by doping.
Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)2·8H2O and Sr(OH)2·8H2O are promising latent heat storage materials.
Abstract
A simple isothermal calorimeter ideal to study hydration of cementitious systems is described together with an ampoule design to allow addition of water and mixing with the ampoule inside the calorimeter. An overview of dynamic corrections is given, and the utilisation of the different dynamic corrections on the calorimeter output is discussed. Correction of data on b-hemihydrate hydration to form gypsum has shown good kinetic agreement with data from synchrotron X-ray diffraction.
Abstract
This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate (C3A) paste at water to cement ratio of 0.5 and C3A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted clinker minerals to gel-like hydration products in the cement-Na2CO3 pastes takes place rapidly between 1st to 24th h. Contrary the Ca(OH)2 formation within the same time interval is retarded in the excess of CO3 2− ions due to intensive rise and growth of CaCO3 crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents of calcite and vaterite relative to that of Ca(OH)2 in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na2CO3 are observed. C3A hydrates very quickly with sodium carbonate between 1st and 24th h forming hydration products rich in bound water and characterized also by complex salts of (x)C3A�(y)CO2�(zH2O type, whereas C3A-H2O system offers C3AH6 as the main hydration product. Higher content of the formed calcium aluminate hydrates in C3A-Na2CO3-H2O system also contributes to early strength increase of Portland cement paste.
