Different formulations, composed of the diglycidyl ether of bisphenol-A, diepoxidized cardanol as reactive diluent, an anhydride as curing agent, and a tertiary amine as curing catalyst, with/without the use of an epoxy fortifier, were analysed. The effect of the fortifier on the diluent was also observed. The overall kinetics of curing was observed to follow a simple Arrhenius-type temperaturedependence, with an activation energy in the range 54–120 kJ/mol, with first-order kinetics up to 85% conversion. An increase in activation energy was observed with an increase of diluent content. The curing reaction was found to follow a three-step mechanism, involving a nucleophilic bimolecular displacement reaction, for which an explanation was offered. Incorporation of the fortifier lowers the curing temperature, but does not alter the final degree of reaction.
The hydrogen-isotope exchange reaction (T-for-H exchange reaction) between each solid material having two different kinds of functional groups and HTO vapor has been observed at several temperatures. Solid materials used were monosubstituted aminobenzenes. The rate constant (k) for each functional group was obtained by applying both the A"-McKay plot and the date obtained. Comparing these k values quantitatively leads to the followings: (1) the A"-McKay plot is useful in obtaining the reactivity of the compounds having two different kinds of functional groups; (2) as to m-aminobenzenesulfonic acid, the reactivity of the SO3H group is about 6.6-8 times larger than that of the NH2 group, and the temperature dependence of the reactivity of the SO3H group is also larger than the dependence of that of the NH2 one; (3) the reactivity of the NH2 group of some kinds of monosubstituted aminobenzenes may follow the Hammett rule; (4) the substituent constant (s) of SO3H group is estimated as follows: sm is 0.38, and sp is 0.64; (5) the substituent-effect of SO3H group is generally larger than that of other substituents; and (6) the subsutituent-effect unknown can be estimated by applying both the Hammett rule and A"-McKay plot.
Authors:Robert Ianoş, Ioan Lazău, and Cornelia Păcurariu
The reactivity of LiNO3 and Al(NO3)3 with respect to urea and β-alanine was investigated. Experimental results proved that β-alanine is a more suitable fuel for
LiNO3, whereas urea seems to be more adequate for Al(NO3)3. Based on the different metal nitrate/fuel mixture reactivity, nanocrystalline γ-LiAlO2 powders were prepared by solution combustion synthesis using a fuel mixture of urea and β-alanine. This fuel mixture yielded
single-phase nanocrystalline γ-LiAlO2 (32.6 nm) directly from the combustion reaction. The resulted powder had a specific surface area of 3.2 m2/g and no supplementary annealing was required. On the other hand, pure γ-LiAlO2 could not be obtained by using a single fuel (urea, β-alanine) unless annealing at 900 °C for 1 h was performed.
Authors:M. Villanueva, I. Fraga, J. Rodríguez-Añón, and J. Proupín-Castiñeiras
The rheological behaviour of the materials diglycidil ether of bisphenol A (n = 0), 1, 2 diamine-cyclohexane and the epoxy reactive diluent vinylcyclohexane dioxide have been studied both separately
and mixed before the beginning of the curing reaction. Different kinds of tests such as: preshear and time sweep, flow curve
and stress sweep experiments were carried out. From these experiments, interesting information about: viscosity-shear stress
and viscosity-shear rate dependences, storage modulus and the linear viscoelastic region were found out. Relationships between
concentration of diluent and the final viscosity of the mixed sample and also between percentage of diluent and storage modulus
Authors:Celestyna Mila-Kierzenkowska, Alina Woźniak, B. Woźniak, G. Drewa, Bogumiła Chęsy, T. Drewa, Ewa Krzyżyńska-Malinowska, and R. Ceraficki
In this study we examined superoxide dismutase (SOD) activity and thiobarbituric acid reactive substances (TBARS) concentration in liver and muscles of four fish species: the carp, the brown trout, the white cod and the flounder. Higher SOD activity and higher TBARS concentration was revealed in the tissues of marine fish in comparison to freshwater fish. The highest SOD activity was observed in the cod while the highest TBARS concentration was in the flounder. The observed differences are probably an effect of the different living mode of the compared fish.
The present study deals with the radiolysis of tetracycline hydrochloride dissolved in aerated alkaline aqueous solutions containing 0.1, 0.5 and 1M NaOH, at 77 K, as followed by ESR. The rate constants for the reactions between the electron and physical and chemical traps which are present in these solutions are calculated. These values are kph= =9.6·1015 l·mol–1·s–1 and kch=1.3·1010 l·mol–1·s–1. The reactivity of electrons that are formed in the radiolysis of water decreases in the following proportions: physical traps: chemical traps: molecules of water: 4.8·1014: 6.5·108: 1.0. The electrons react preferentially with the solute instead of the solvent.
The effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol /p-NPH/ towards orthopositronium atom has been investigated by performing positron lifetime measurements in methanol and methanol containing 0.5M NaOH solutions, respectively. In the latter case the solute exists in anionic form /p-NP–/. It has been found that as a result of dissociation, both the rate constant /k/ and the inhibition coefficient // decrease significantly. Their values are k=/7.5±0.4/×108 s–1 M–1 and =6.8±0.2 M–1 for p-NPH and kd=/0.6±0.2/×108 s–1 M–1 and
d=4.0±0.2 M–1 for p-NP–. The possible reasons for these effects are discussed.
Authors:C.A. d’Azevedo, F.M.S. Garrido, and M.E. Medeiros
of the MgO–Al2O3–SiO2
ternary system, constituted by 28.5 mol% ofMgO, 28.5 mol% of Al2O3
and 43mol%of SiO2, were activated in a roll mill and
calcined at different temperatures. The influence of the grinding time, the
used SiO2 precursor and activation medium, furthermore
the mass ratio between the powdered sample and zirconia cylinders was investigated
on the reactivity of the MgO–Al2O3–SiO2
ternary system. FTIR spectra and the X-ray powder diffraction patterns indicates
the formation of Mg(OH)2 at 393 K, of forsterite (MgSi2O5)
and enstatite (MgSiO3) at 1223 K and of spinel (MgAl2O4)
between 1223 and 1523 K in some samples. The presence of cordierite (Mg2Al2Si5O18) was observed at 1523 K, a reaction pathway concerning
its formation was proposed.