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Abstract
The adsorption of Ce3+ on hydrated manganese dioxide (HMD) was studied as a function of concentration, temperature and pH of the cerium solution labelled with141Ce. The steady state values of cerium adsorption at various concentrations fit well with the classical Freundlich isotherm. The effect of temperature on equilibrium adsorption values was utilized to determine the change in the standard enthalpy ΔH o of the cerium uptake process and its value (ΔH o=10.57) indicates that the uptake process proceeds via ion exchange.141Ce desorption studies, from HMD in water, HCl and unlabelled CeCl3 solution, confirmed the ion exchange nature of the cerium uptake process as well as its reversibility.
Thermal behaviour of hydrated copper(II) complexes
Correlation of dehydration steps with structural properties
Abstract
Dehydration steps of aquacopper(II) complexes with homogeneous and heterogeneous coordination sphere are investigated from the view point of structural changes taking place under their heating to the decomposition temperature and during the dehydration. The role of loosening of intra-and intermolecular hydrogen bonds in the decomposition reaction for the structure changes of the remainder, the structural presumptions of the reactants for lower hydrates formation are discussed. Activation parameters of dehydration were found to be the lower, the smaller are the structure differences between the reactants and products. They do not reflect the bond length central atomvolatile ligand, much more the overall structure differences between the starting and resulting compounds. From all data on crystal and molecular structures of dehydrated compounds is the reaction pathway best indicated by anisotropic temperature parameters of donor atoms corrected for the thermal movement of the central atom: the higher these values in the bond direction are, the lower the values of activation energies of dehydration are.
Abstract
The time required for maximum hydration of MgO obtained from the calcination of magnesite was determined. The MgO samples were hydrated for different time intervals in both water and magnesium acetate. A thermogravimetric analysis (TG) method was used to determine the degree of hydration to Mg(OH)2. Increasing the hydration time, the degree of hydration of MgO and surface area of the formed Mg(OH)2 increased. A leveling effect was observed on the percentage Mg(OH)2 obtained from hydration in magnesium acetate, and an optimum amount of 85% was obtained after 500 min. For the hydration in water, the leveling effect was only observed after 800 min giving a maximum of 65% Mg(OH)2.
Abstract
A series of six nitrates(V) hydrates of 4d-metals as well as mercury and cadmium thermal decomposition was examined by DTA, TG and EGA techniques. It was found that thermal decomposition of d-metals nitrate(V) hydrates proceeds in three stages: partial dehydration, oxo-nitrates and hydroxide nitrates formation and metal oxides formation. General chemical equations for all decomposition stages were proposed. It was found that dehydration of hydrated salts is accompanied by partial decomposition of nitrate(V) groups.
The thermal evolution of a very fine-grained hydrated cobalt molybdate, CoMoO4 · · 0.9H2O, has been studied by dilatometry, DTA, X-ray crystallography and scanning electron microscopy. Four principal stages have been detected between 25 and 1000°: dehydration, polymorphism (or precipitation), recrystallization, and high-temperature phase change. Such phenomena also occurred with some other hydrated molybdates (Ni, Mn).
Abstract
This paper presents results of thermochemical and thermokinetic studies of the hydration of portland cement, alkaline cements with mineral additives and slag alkaline binder. The influence of the modulus of basicity of the binders on the thermochemical and thermokinetic characteristics of hydration was estimated.
Abstract
Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, 
Mo, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.
Abstract
A microcalorimeter (Setaram c-80) was used to study the thermokinetics of the hydration process of calcium phosphate cement (CPC), a biocompatible biomaterial used in bone repair. The hydration enthalpy was determined to be 35.8 J g–1 at 37.0°C when up to 80 mg CPC was dissolved in 2 mL of citric buffer. In the present study, parameters related to time constants of the calorimeter were obtained by fitting the recorded thermal curves with the function θ=Ae–?t(1– e–?2t). The real thermogenetic curves were then retrieved with Tian function and the transformation rate of the hydration process of CPC was found to follow the equation α=1–[1–(0.0075t)3]3. The microstructures of the hydrated CPC were examined by scanning electron microscopy. The nano-scale flake microstructures are due to crystallization of calcium phosphate and they could contribute to the good biocompatibility and high bioactivity.
ZnO added to the system Portland cement — water changes the kinetics of the hydration process substantially. Amorphous zinc hydroxide is formed and inhibits the reaction of tricalcium silicate with water, resulting in an induction period prolongation. This effect depends on the amount of ZnO added to the hydrated paste. The transformation of zinc hydroxide into calcium hydrozincate provokes the further hydration.
A study was made of the thermal decompositions of the hydrates of 5 neutral sulphate complexes and 5 hydroxy-sulphate complexes of uranium(IV). The hydrates did not yield corresponding stable anhydrous compounds. After dehydration, the complexes decomposed in endothermic reactions involving progressive substitution of sulphur trioxide (that is liberated) by oxygen, giving oxy-sulphates and other compunds.
