Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.     

Alkali activated fly ash: effect of admixtures on paste rheology

In this paper, an investigation related to the rheological behaviour of alkali-activated fly-ash pastes (AAFA) is described. Those pastes were prepared by mixing the fly ash with an alkaline dissolution containing 85% of a 12.5 M NaOH solution and 15% of waterglass and adding some commercial chemical admixtures usually used in the Portland cement concrete fabrication, like lignosulphonates, melamines (first and second generation products) and polycarboxylates (latest generation). The fly ash rheological data were determined by rotational viscometry measurements as well as by the use of the flow table test. Results indicate that chemicals admixtures used do not work the same in the Portland cement systems than in alkali-activated fly ash systems. As a general rule, it seems that the most efficient admixtures for these new cementitious pastes (AAFA) are those based in polycarboxylates.     

The Accuracy of Senum and Yang's Approximations to the Arrhenius Integral

The accuracy of the integral of the Arrhenius equation, as determined from the 1^st to the 4^th degree rational approximation proposed by Senum and Yang, has been calculated. The precision of the 5^th to 8^th rational approximations, here proposed for the first time, has also been analyzed. It has been concluded that the accuracy increases by increasing the order of the rational approximation. It has been shown that these approximations to the Arrhenius equation integral would allow an accuracy better than 10⁻⁸ % in the E/RT range generally observed for solid state reactions. Moreover, it has been demonstrated that errors closed to 10⁻² % can be obtained even for E/RT=1, provided that high enough degrees of rational approximation have been used. Thus, it would be reasonable to assume that high degree rational approximations for the Arrhenius integral could be used for the kinetic analysis of processes, like adsorption or desorption of gases on solid surfaces, which can take place at low temperatures with very low values of E/RT. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic properties of magnetite prepared by ball-milling of hematite with iron

Magnetic properties of magnetite powder prepared by ball-milling of stoichiometric mixture of hematite and iron in an inert atmosphere are reported. Hysteresis loops, isothermal remanence acquisition curves and temperature dependence of magnetic susceptibility measurements are used to characterise this material and to examine the effects of heating in air and in an argon atmosphere. Ball-milling of hematite with iron during periods ranging from 30 min up to almost 5 h yields magnetite which exhibits high magnetic hardness, characterised by coercive force three times higher than that typical for single-domain natural magnetites. However, the magnetite produced is unstable upon heating in air, reoxidising almost completely to hematite. Heating in an argon atmosphere causes enhancement of typical magnetic parameters, but decreases the magnetic hardness.     

About the remarks on the application of the combined Kolmogorov-Erofeev-Kazeev-Avrami-Mampel equation in the kinetics of non-isothermal transformations

An analysis is made of the method proposed by Gorbachev for the kinetic study of non-isothermal transformations using the KEKAM equation=1–exp(–kt ⁿ). It is demonstrated that the procedure cannot be used to determine either the kinetic exponentn or the activation energyE.     

The accuracy of equation approximating the integral of the Arrhenius equation to perform the kinetic analysis of solid state reactions

The accuracies of the approximation of the temperature integral of the Arrhenius law proposed by Coats and Redfern(CR), Doyle(D), Gyulai and Greenhow(GG), and MacCallum and Tanner(McT) have been tested. It has been demonstrated that these methods (only with the exception of the MacCallum and Tanner procedure) generally lead to accurate enough values of the activation energy of solid state reactions. The accuracy of these methods increases in the sequence: CC > D ? GG ? McT.