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  • Author or Editor: W. Swiątkowski x
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The DTA method has been used for determination of the initial crystallization temperatureT A for the vitreous selenium samples remelted in the different temperaturesT f. The decrease of theT A values with increase ofT f temperatures was observed. These results may be explained by assumption that the increase of concentration of the chains accelerates the nucleation process in the vitreous selenium.

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The rate of transformation of the chains in amorphous sulphur was examined by calorimetry at 298 K. The amorphous samples were remelted at the temperatureT f in the range from 458 to 573 K. Increase ofT f decreased the transformation rate. The results satisfy the equationX=1-exp[-(kt)z] (X=transformation degree,t=time, andk andz=constants). A one-stage transformation was observed for samples remelted atT f≤473 K. ForT f ≥523 K, transformation in two stages was observed.

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Abstract  

The transformation rate of the chains in amorphous sulphur doped with 0.43, 0.86 and 1.28% at. P was examined by calorimetric method at 298 K. The samples were remelted at T f=443 K. For description of the results the equation X=1–exp[–(kt)z] was used (X — transformation degree, t — time, k and z — constants). The admixtures of phosphorus inhibit the transformation strongly. The constants k and z are less smaller for the samples S+P than for pure sulphur.Samples S+1.28% at. P were examined in the range of the temperatures from 203 to 308 K. The activation energy is equal to E=86.6 kJ mol–1 with standard error S E=12.0 kJ –1.The effect of the admixture of phosphorus on the kinetics of the nucleation and the growth of the nuclei was discussed.

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The influence of remelting temperatureT f on allotropic transformation of amorphous sulfur with admixtures 2, 4 and 6 at.% Se has been investigated.

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Abstract  

The heatQ of transformation of the chains in amorphous sulphur was measured calorimetrically. The mean value ¯Q for samples remelted atT f=443 K increases from 31.5 to 45.9 J g−1 in the measurement temperature range from 288 to 303 K. For samples remelted in theT f range from 443 to 573 K, the ¯Q values are from 30.6 to 24.0 J g−1. The results are discussed on the basis of the theory of nucleation and growth of nuclei.

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Abstract  

The transformation of the chains in the amorphous sulphur was investigated by calorimetric method at the temperature range from 288 to 303 K. The results satisfy the equationX=1−exp [−(kt)2] (X-transformation degree,t—time,k andz—constants). It was found that thez values increasevs. the temperature The activation energy is equal toE=21 kJ/mol with standard deviation 5 kJ/mol. The results were explained on the basis of the theory of the nucleation and the growth of the nuclei.

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Abstract  

The heat of transformation (Q ) of the chains in amorphous sulfur doped with selenium (0, 2, 4 and 6 at%Se) and phosphorous (0, 0.43, 0.86 and 1.28 at%P) was measured calorimetrically. All samples were remelted at temperature T f =443 K. The admixtures decrease the Q : at the measurement temperature 298 K the mean value of is equal to 37.6, 20.4 and 9.1 J g−1 for the samples S, S+6 at%Se and S+1.28 at%P respectively. The quantity of the evolved heat increases vs. the elevation of the measurement temperature. For the samples S+6 at%Se the value is equal 16.2 and 28.8 J g−1 at 288 to 303 K. For the samples S+1.28 at%P the value of increases from 9.1 to 25.0 J g−1 in the range of the measurement temperature from 293 to 308 K. The results are discussed on the basis of the theory of nucleation and growth of nuclei.

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Abstract  

The DTA method has been used for determination of the initial crystallization temperatureT A of the vitreous selenium with admixtures of sulphur (crystallization inhibitor) and tellurium (crystallization catalyst). It was found that both admixtures raise the value ofT A. The obtained results suggest that each foreign atom distorts the structures of the chain in vitreous selenium and consequently inhibits the nucleation. The values of the heat of transformation and degree of crystallization have been also determined.

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The kinetics of transformations of freshly-prepared amorphous and monoclinic sulphur were determined with a nonisothermal — nonadiabatic calorimeter at 35– 45° and 25–45°, respectively. The experimental data were fitted to the equation of Avrami and the coefficients of the equation were calculated. From the results it was evident that only a process of rhombic sulphur formation proceeds in monoclinic sulphur, while two processes proceed in amorphous sulphur: a rapid one, consisting in the formation of S8 rings from biradical chains, and a slow one, consisting in the formation of rhombic sulphur.

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