Search Results
Abstract
The capillary porosity of clinker phases, i.e. 3CaOSiO2, β2CaOSiO2, 3CaOAl2O3 and 4CaOAl2O3Fe2O3, at the early stages of hydration has been studied by the methods of Differential Scanning Calorimetry and nitrogen adsorption (BET). It was established that pores of 3–70 nm were formed during the hydration of 3CaOSiO2 and the maximum of their distribution was found at about 10 nm. The hydration of 2CaOSiO2 is much slower and the porosity is one order of magnitude lower. During the hydration of 3CaOAl2O3 the content of crystalline hexagonal hydrates prevailed and the porosity was in the range 5–90 nm with the average pore diameter of about 16 nm. This average pore diameter was much smaller for thermoporosimetry and lay at about 7 nm. The hydrated 4CaOAl2O3Fe2O3 sample had the porosity in the range 3–90 nm with the maximum of the pores distribution at about 4 nm. There are some differences between the porosities measured by BET and thermoporosimetry. Principally thermoporosimetry gives no information about larger capillary pores in the range 30–50 nm.
Abstract
α-Hemihydrate was allowed to hydrate in the presence of tartaric, succinic, malic or citric acids at room temperature at a water/ binder ratio of 0.35. Hydration of hemihydrate leading to the crystallisation of calcium sulphate dihydrate is an exothermic process. The temperature rise during hydration was measured as a function of time using a semi-adiabatic method. The temperature rise–time curves are similar for all investigated systems but with different induction period. The results showed that calcium sulphate dihydrate crystallisation is a nucleation controlled process and different acids are chemisorbed at the surface of forming nuclei to different extent. Processes taking place during nucleation may control the morphology of resultant crystals. Infrared spectral and differential scanning calorimetric studies confirmed the adsorption of carboxylic acids at the surface of dihydrate crystals.
Abstract
A simple method for determination of the hydrate numbers of saturating multi-hydrate salts in developed. The method demonstrated for scandium sulfate is based upon estimation of the enthalpy of solution of the hydrates from the solubility smoothing equations. It is shown that in the Sc2(SO4)3–H2O system, contrary to common opinion, the equilibrium solid phases are: Sc2(SO4)3.6H2O at 273–295 K, Sc2(SO4)3.5H2O at 295–333 K and Sc2(SO4)3.4H2O at 333–373 K. The solubility smoothing equations for the hexa-, penta- and tetrahydrate of scandium sulfate are given.
Abstract
In this study a calorimeter was applied to investigate the hydration of cements with fly ash (pulverised fuel ash – PFA) admixture. Four cements were used to produce the binders containing from 5 to 60% fly ash. The process of hydration in cementitious systems with fly ashes is slower than in reference pastes without admixtures. However, the calorimetric calculations and the shape of heat evolution curves seem to indicate a complex interaction between the components of cement and ash resulting in the increasing total heat evolved values per unit of cement. At higher fly ash content the accelerating effect of alkalis and alumina should be taken into account and discussed in terms of the composition of initial cement. The modifications of hydration kinetics and mechanism in this case is very well visualised by means of calorimetry.
Abstract
Medium reactive magnesium oxide reacts incompletely with available water to form magnesium hydroxide. To enhance the hydration of medium reactive magnesium oxide, the effect of magnesium acetate as hydrating agent was studied. The extent to which different parameters (concentration of magnesium acetate, solution temperature and solid to liquid ratio of MgO to magnesium acetate) influence the hydration rate of a medium reactive industrial sample of magnesium oxide were evaluated. The degree of rehydration measured as percentage Mg(OH)2being formed, increases from approximately 56% using 0.5 M magnesium acetate solutions at 25C to 64% at 50C, to more than 70% at 70C. The major part of rehydration of the medium reactive MgO sample occurs within the first few minutes of the reaction for all three temperatures studied.
Abstract
Reverse micelles formed from sodium bis (2-ethylhexyl)sulfosuccinate in n-heptane containing cytochrome c, horseradish peroxidase (HRP) and catalase in water pools preferentially scavenge electrons produced radiolytically in oil phase. Both initial absorbance at 720 nm and the half-lifetime of hydrated electron depend on the kind of hemoprotein and on the overall protein concentration. The possibility of electron capture by the protein molecule before its hydration is discussed. It is shown that the entrappment of cytochrome c and HRP into reverse micelles changes the reduction ability of the protein, whereas ferric iron in catalase remains unaccesible fore aq – like in homogeneous aqueous solution.
Abstract
Fly ash is the ash precipitated from the exhaust fumes of coal-fired power stations. It consists mainly of active silica and alumina, with large amounts of glass. The aim of this work was to study the pozzolanic activity of fly ash with lime by means of DTA as a function of the lime content and the curing time. The curves revealed that the rate of hydration, as indicated by the residual lime and hydrated compounds, increases with increasing lime content and curing time. It is concluded that fly ash can be used as a blending material in pozzolanic cement.
Abstract
The thermal behaviour of halloysite fully expanded with hydrazine-hydrate has been investigated in nitrogen atmosphere under dynamic heating and at a constant, pre-set decomposition rate of 0.15 mg min-1. Under controlled-rate thermal analysis (CRTA) conditions it was possible to resolve the closely overlapping decomposition stages and to distinguish between adsorbed and bonded reagent. Three types of bonded reagent could be identified. The loosely bonded reagent amounting to 0.20 mol hydrazine-hydrate per mol inner surface hydroxyl is connected to the internal and external surfaces of the expanded mineral and is present as a space filler between the sheets of the delaminated mineral. The strongly bonded (intercalated) hydrazine-hydrate is connected to the kaolinite inner surface OH groups by the formation of hydrogen bonds. Based on the thermoanalytical results two different types of bonded reagent could be distinguished in the complex. Type 1 reagent (approx. 0.06 mol hydrazine-hydrate/mol inner surface OH) is liberated between 77 and 103C. Type 2 reagent is lost between 103 and 227C, corresponding to a quantity of 0.36 mol hydrazine/mol inner surface OH. When heating the complex to 77C under CRTA conditions a new reflection appears in the XRD pattern with a d-value of 9.6 , in addition to the 10.2 Ĺ reflection. This new reflection disappears in contact with moist air and the complex re-expands to the original d-value of 10.2 in a few h. The appearance of the 9.6 reflection is interpreted as the expansion of kaolinite with hydrazine alone, while the 10.2 one is due to expansion with hydrazine-hydrate. FTIR (DRIFT) spectroscopic results showed that the treated mineral after intercalation/deintercalation and heat treatment to 300C is slightly more ordered than the original (untreated) clay.
Abstract
Nine rare earth citrate hydrates (RE(C6H5O7)·nH2O,RE=La, Nd, Sm) were prepared and characterized by chemical analysis, elementary analysis, thermal analysis and IR spectra. The thermal decomposition processes were studied by using TG-DTG and IR spectra techniques. Dehydration enthalpies and dehydration entropies of 3 neodymium and 3 samarium citrate hydrates were also determined by means of DSC.
Abstract
The aim of this work was to study the solubility in supercritical CO2 of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO2, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility in supercritical CO2 than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical interaction with the acid supercritical fluid, mediated by crystal water.
