Determination of a partial phase composition in calcined gypsum by calorimetric analysis of hydration kinetics

A calorimetric method for the determination of a partial phase composition in calcined gypsum is presented. The method is based on the separation of the reaction heat of the transformation of ??-anhydrite III to ??-hemihydrate from the main hydration reaction transforming ??-anhydrite III to dihydrate. Using the known hydration heats of ??-anhydrite III to dihydrate and ??-hemihydrate to dihydrate, the content of ??-calcium sulfate anhydrite III and ??-calcium sulfate hemihydrate as well as the amount of non-hydrating parts in gypsum can be determined. Practical application of the method is illustrated on three industrial products.     

Simplified x-ray diffraction method for determining the framework composition of high-silica faujasites

Conclusions The x-ray diffractograms of high-silica Y zeolites have four reflections whose relative intensities correlate with the framework composition, and this relationship can be used to evaluate the Si/Al ratio in Y zeolites.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1497–1501, July, 1988.     

Heat of hydration prediction for blended cements

Prediction and control of concrete temperature rise due to cement hydration is of great significance for mass concrete structures since large temperature gradients between the surface and the core of the structure can lead to cracking thus reducing durability of the structure. Cement replacement with supplementary cementitious materials (SCMs) is frequently used to reduce the concrete temperature rise. Several models have been proposed for predicting heat release of blended cements; however, none of them address incorporation of metakaolin into the mixture. Isothermal calorimetry measurements, based on statistical experimental design, were taken on pastes incorporating combinations of SCMs and chemical admixtures. The data were then used to develop equations to predict the total heat reduction with the incorporation of chemical admixtures and SCMs. Analysis of the calorimetry data indicated that chemical admixtures do not have a significant effect on heat evolution beyond 12 h. SCMs investigated in this study (fly ash, slag, silica fume and metakaolin), on the other hand, were found to have a significant effect at hydration ages of 12, 24, 48 and 72 h.     

Capillary electrophoresis as a method for determining dissociation constants of aldohexose isomers

Capillary electrophoresis was first employed for the determination of pKa values of 6 aldohexose isomers based on their differential migrations within the capillary tubing. The pKa values obtained were found to be independent of the separation voltages. The quantitative basis of pKa determination was also discussed.     

Quasielastic light scattering as a method for determining the distribution of relaxation times in a polymer system

Amongst other techniques, dynamic light scattering may be used to obtain molar mass distributions. The first step in this process consists in the Laplace inversion of the time correlation function that was measured by dynamic light scattering. This inversion gives a distribution of diffusion coefficients. In order to convert this distribution into the corresponding molar mass distribution, a relationship between diffusion coefficient and molar mass of monodisperse fractions has to be known. Such a relationship can be derived for linear and star-branched macromolecules from measurements of polydisperse systems, since the polydispersity of the distributions does not change with the molar mass. The problem is more involved with randomly branched materials, since in these cases the polydispersity increases strongly as the point of gelation is approached. A procedure is suggested for deriving the diffusion-molar mass dependence of monodisperse samples from polydisperse systems. After an outline of this background the method is applied to the three selected systems (i) radically polymerized linear PMMA, (ii) a star-branched microgel where monodisperse arms are attached to a microgel center and (iii) a randomly branched poly(dicyanate) sample based on bisphenol A. The results are compared with the combined column chromatography SEC/LALLS/VISC. Good agreement was found up to molar masses of about 10 millions g/mol, but systematic deviations occured in the high molar mass region. These differences result from the limitations of size permeation chromatography. Finally it is shown that the size distribution can be determind by this method, even for associates.     

Influence of the calcined paper sludge on the development of hydration heat in blended cement mortars

The present study is based on the influence of the addition of a pozzolanic material as a result of the activation of an industrial waste coming from the Spanish paper industry on the heating as well as hydration heat of the cement mortars made with 10 or 20% of active addition. Once the sludge has been calcined at different temperatures (700–800°C) and stays in furnace (2 and 5 h), the calcined products showed high pozzolanic activity. The maximum activity corresponded to the paper sludge calcined at 700°C for 2 h (S1). Besides, it can be proved that there was an increase both of the heating and also of the hydration heat in the first 23–25 h for both additions (10 and 20% of S1) regarding the reference cement mortar. This behaviour would be related to the influence of different effects: filler and pozzolanic during the first hours of reaction, and by the dilution effect for longer hydration times, mainly when 20% of S1 was added.     

New enantioselective method for hydration of alkenes using cyclodextrins as phase transfer catalyst

A new enantioselective/inverse phase transfer catalysis (IPTC) reaction for the Markovnikov hydration of double bounds by an oxymercuration-demercuration reaction with cyclodextrins as catalysts was disclosed. Moderate ee (up to 32%) and yields (14-60%) were obtained for allylic amines and protected allylic alcohols as starting materials.     

Histogram analysis as a method for determining the line tension of a three-phase contact region by Monte Carlo simulations

A method is proposed for determining the line tension, which is the main physical characteristic of a three-phase contact region, by Monte Carlo (MC) simulations. The key idea of the proposed method is that if a three-phase equilibrium involves a three-phase contact region, the probability distribution of states of a system as a function of two order parameters depends not only on the surface tension, but also on the line tension. This probability distribution can be obtained as a normalized histogram by appropriate MC simulations, so one can use the combination of histogram analysis and finite-size scaling to study the properties of a three phase contact region. Every histogram and results extracted therefrom will depend on the size of the simulated system. Carrying out MC simulations for a series of system sizes and extrapolating the results, obtained from the corresponding series of histograms, to infinite size, one can determine the line tension of the three phase contact region and the interfacial tensions of all three interfaces (and hence the contact angles) in an infinite system. To illustrate the proposed method, it is applied to the three-dimensional ternary fluid mixture, in which molecular pairs of like species do not interact whereas those of unlike species interact as hard spheres. The simulated results are in agreement with expectations.     

A modified and a new straight-line method for determining the composition of weak complexes of the form AmBn

A modified Asmus method and a new method are described for determining the composition and stability of weak complexes of the form A_mB_n. The modified method is applicable to polynuclear complexes and is not based on the approximation necessary originally. The second method is based on variation of the concentration of the reactant being maintained in excess. The method gives a straight line for the correct quotient of n/m and the stability constant can easily be calculated from data extracted from the diagram. The main advantage is that, in combination with the original straight-line method, this method permits the determination of both coefficients m andn in the presence of an excess of one of the reactants     

Hydroxyethyl methyl cellulose as a modifier of gypsum properties

Journal of Thermal Analysis and Calorimetry - The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivatives—hydroxyethyl methyl...     

Extraction-scintillation method for determining the concentration of radioisotopes

A method is presented for the determination of uranium isotopes in waters by the scintillation-extraction method. By extraction with tributyl phosphate (TBP) in toluene as a liquid scintillator it was established that the presence of TBP in the solvent does not affect the photo-yield substantially. The optimum measuring conditions and the sensitivity of the method have been studied.     

In situ neutron powder diffraction investigation of the hydration of tricalcium aluminate in the presence of gypsum

The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca₃Al₂O₆, to gypsum, CaSO₄·2D₂O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca₆[Al(OD)₆]₂(SO₄)₃·∼26D₂O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction.     

A new method for determining the composition and stability constant of complexes of the form ambn

A new method is reported for determining the composition of complexes of the form A_mB_n; it can be used to differentiate mono- and polynuclear complexes. The method is based on that of Holme and Langmyhr. Good results were obtained for several complexes.     

Using a two-jet arc plasmatron for determining the trace element composition of powdered biological samples

Weak effects of organic matrix and the chain length of the organic substituent on the analytical line intensities of the elements in the exciting emission spectra in a two-jet arc plasmatron were found. Using animal organs, hair, and plants as examples, it was demonstrated that the plasmatron is promising for determining trace elements in powdered biological samples without sample dissolution.     

A method for determining a basis set suitable for the description of radiationless decay

Quantitative conditions are derived which a basis set must satisfy if it is to be used for describing radiationless decay. The derivation is valid for both internal conversion and intersystem crossing.     

A precise instrumental neutron activation analysis method for determining the elemental composition of Mn−Mg−Zn ferrites

An accurate instrumental method is developed for analyzing nine Mn−Mg−Zn ferrite compositions with a wide range of macrocomponent concentrations. For the overall error of instrumental neutron activation analysis an expression is formulated where partial errors are most accurately taken into account. Brief analysis of the error sources is given. An expression is obtained allowing for the effects of contamination of the standard by the element under investigation with the accuracy of analysis being within 1–2 relative per cent.