Search Results
Abstract
An analytical methodology has been developed for the separation of arsenic from ground water using inorganic material in neutral medium. The separation procedure involves the quantitative retention of arsenic on hydrated manganese dioxide, in neutral medium. The validity of the separation procedure has been checked by a standard addition method and radiotracer studies. Neutron activation analysis (NAA), a powerful measurement technique, has been used for the quantitative determination of arsenic.
The thermal decomposition of iron sulphate hexahydrate was studied by thermogravimetry at a heating rate of 5°C min−1 in static air. The kinetic parameters were evaluated using the integral method by applying the Coats and Redfern approximation. The thermal stabilities of the hydrates were found to vary in the order. Fe2(SO4)3·6H2O → Fe2(SO4)3·4.5H2O → Fe2(SO4)3·0.5H2O
Abstract
Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was t h=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water content, EV (110C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m2 g-1 (C-33, 1 m) to 166 m2 g-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m2 g-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m2 g-1 in C-33 (1 and 6 m) and 198-210 m2 g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m).
Abstract
In order to study the thermal properties of new type environment-friendly binary hydrate for cold storage in air-conditioning system, tests have been carried out by DSC comprehensively on the phase-change temperature and fusion heat of TBAB hydrate, THF hydrate, and TBAB–THF hydrate mixture. The results show a good trend that TBAB–THF hydrate has the superiority for more proper phase-change temperature and increased fusion heat. A broader and more developed view is that adding appropriate amount of hydrate with lower phase-change temperature to hydrate with higher one can make the hydrate mixture more suitable for cold storage (especially for 278–281 K); some hydrates with lower phase-change temperature can even make the fusion heat of mixture hydrate increased greatly. Several new environmental working pairs for binary gas hydrates have been listed to help to promote the application.
The thermal decompositions of two beryllium periodate hydrates, Be(IO4)2·8H2O and Be(H4IO6)2·2H2O, were studied by DTA and TG in the temperature range from 298 to 1073 K, and by DSC from 298 to 723 K. The intermediates of the thermal decompositions were identified via quantitative analysis, IR spectroscopy and the TG curves. The data obtained were utilized to suggest a scheme for the thermal decompositions of the two periodates. Both compounds decompose via an anhydrous beryllium iodate, and the final residue is beryllium oxide.
Abstract
A new approach to dating ancient obsidian artifacts based on the modeling of water diffusion profiles is evaluated using multiple archaeological test cases of known age. Hydrogen profiles from hydrated obsidian surfaces have been collected by secondary ion mass spectrometry (SIMS). The H2O concentration versus depth profiles are modeled and diffusion ages have been produced. SIMS based dates for fourteen obsidian specimens of well-known age, ranging from 300-7000 years old, have been compared with radiocarbon ages. The convergence between the two dating methods is excellent and validates the new dating approach.
Abstract
Hydration properties of lipid bilayer systems are compared for symmetric chain sphingomyelin (N-palmitoylsphingomyelin) and asymmetric chain sphingomyelin (N-lignoceroylsphingomyelin). These sphingomyelins were semisynthesized by a deacylation- reacylation process with a natural sphingomyelin used as a starting material. The number of differently bound water molecules was estimated by a deconvolution analysis of the ice-melting curves obtained by a differential scanning calorimetry (DSC) and was used to construct a water distribution diagram for these water molecules. Similarly to a natural sphingomyelin used for comparison, the asymmetric chain sphingomyelin was found to form small size vesicles having an internal cavity and incorporate 15 water molecules per molecule of lipid into its cavity, in contrast with 5 H2O/lipid for freezable interlamellar water observed for large size multilamellar vesicles formed by the symmetric chain sphingomyelin.
The composition of a hydrated aluminium oxide was determined and the course of its thermal decomposition was investigated. The stages of the dissociation were established and all the solid and gaseous intermediates of the decomposition were identified. A correlation was observed between the peak temperatures for boehmite and the particle size and degree of crystallinity.
Hydrate hypothesis of living matter origination (LOH-hypothesis)
Thermodynamic grounds of formation of living matter simplest elements from hydrocarbons and niter
Abstract
In the context of the LOH-hypothesis, the following questions are discussed: (1) Could N-bases and riboses originate from CH4-hydrocarbons and niter at the expense of internal energy? (2) How had methane-hydrate originated? (3) How had CH4 and NO3 − met together? (4) Why are DNA and RNA monomer links similar and limited in size? (5) Why were N-bases and riboses limited in their chemical growth? (6) Why are the sequences of N-bases in DNA and RNA molecules not random? (7) Why do DNA and RNA compositions usually contain only five chemical elements? (8) Why do only five N-bases usually enter the DNA and RNA compositions, and why are other ones random? (9) Could D-ribose, desoxy-D-ribose, thymine, and uracil be simultaneously produced in the reaction of niter with methane? (10) Why did Nature select D-riboses for DNA and RNA construction?
The study by thermal methods of the dehydration/rehydration phenomena of crystal hydrates shows that it is possible to separate the total heat of rehydration of previously dehydrated crystals into two contributions, attributed to surface and bulk, respectively. Values obtained for a number of salt hydrates are given and the ratio between the surface portion and the total heat is found to be of the order of 1%. Such findings are in agreement with results previously obtained by optical microscopy and are discussed in terms of recent views about the reversible reactions of crystalline solids.
