T Górecki

Relations between the cohesive energy, atomic volume, bulk modulus and sound velocity in metals

By analysing the experimental data available in the literature, it has been found that the bulk modulus B of metals is proportional to the cohesive energy density Ec/V. For metals which start to melt having the close packed structure A1 or A3 the proportionality factor in the forementioned correlation is distinctly greater than that for metals melting from the A2 type structure. The existence of the correlation between the bulk modulus and the cohesive energy density leads to another, hitherto unrevealed correlation between the sound velocity, cohesive energy and the molar mass of metals: u2 ~ Ec/μ.

Phase transitions in some n-alkanes and petroleum waxes — investigation by photoacoustic and exoelectron emission techniques

Abstract The use of the photoacoustic (PA) effect and photostimulated exoelectron emission (EEE) technique in the investigation of first- and second-order phase transitions in pure n -alkanes such as n -C 22 , n -C 28 and n -C 32 and in three petroleum waxes having different carbon number distributions, have been examined. Changes in the amplitude and phase of the PA signal with temperature and the temperature dependence of the intensity of photostimulated EEE across the phase transitions have been measured. These measurements have shown that both the polymorphic phase transitions and melting of these hydrocarbons are accompanied by jumps or peaks of the PA amplitude and phase and EEE intensity, thus enabling the detection of the solid–solid and solid–liquid phase transitions. These results are further confirmed by a comparison with those obtained by differential thermal analysis (DTA) control measurements performed at the same heating and/or cooling rate. The PA and EEE results thus obtained are discussed in the light of phase transition temperatures obtained from other techniques.

Thermal stability of the Fe80−xVxB20 metallic glasses as studied by the EEE and DTA methods

The surface and volume crystallization of Fe80−xVxB20 (x=6, 10, 20) metallic glasses, produced by the melt spinning method, have been investigated by means of exoelectron emission (EEE) and differential thermal analysis (DTA). A comparison of the results of the EEE and DTA measurements shows clearly that surface crystallization occurs at temperatures ∼ 200 K lower than volume crystallization. The activation energy for the surface crystallization is also distinctly lower than that for crystallization in the bulk.

Structural transformations in surface layers of amorphous ribbons Ni78SixB22−x

The thermal stability of NI78SixB22−x (x = 6, 9, 12, 15) metallic glasses, produced by the single-roll melt spinning method, has been investigated by differential thermal analysis (DTA) and by measuring the temperature dependences of the exoelectron emission (EEE) and contact potential difference (CPD) relative to platinum. It has been found that both CPD and EEE show anomalies at temperatures corresponding to the structural transformations in the surface layer of investigated materials. The surface crystallization occurs at temperature of ∼ 150 K lower than the volume crystallization. The activation energy for the surface crystallization is also distinctly lower than that for crystallization in bulk.

Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique

The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA heating run is higher compared with that measured in the first heating run. Irradiation with X-rays accelerates both the surface and volume retrification of amorphous selenium.

Investigation of the effect of intensive ball milling in a planetary ball mill on the thermal decomposition of cadmium carbonate and basic zinc carbonate

The kinetics of thermal decomposition of cadmium carbonate CdCO3 and basic zinc carbonate ZnCO3?nZn(OH)2 and the effect of intensive milling in a planetary ball mill on its parameters, have been investigated. The values of the reaction heat and of the activation energies of thermal decomposition have been determined for both the compounds. Investigations of the thermal decomposition of the products of ball milling of investigated compounds revealed a slight effect of milling conditions on the reaction temperature and heat consumed during the thermal decomposition of ZnCO3?nZn(OH)2. No effect of ball milling on the thermal decomposition of CdCO3 has been found.

Exoelectron emission accompanying the phase transformations in the AgI-type superionic conductors

Abstract Results of experimental investigations of the photostimulated exoelectron emission (EEE) accompanying the polymorphic phase changes in some superionic conductors (silver, copper and mercury iodides) are reported for the first time. The measurements of the temperature dependence of the intensity of photostimulated EEE were performed in air at atmospheric pressure, the (exo)electrons being detected with an open air point-counter with saturated ethanol quenching vapour. The DTA control measurements were performed at the same heating and/or cooling rate. A comparison of the results of the EEE and DTA measurements shows clearly that the polymorphic phase transitions and melting of investigated materials are accompanied by an enhancement (peak) of the EEE intensity. This enables the detection of the phase transformations in inorganic compounds by the EEE technique.

Effect of the milling conditions on the degree of amorphization of selenium by milling in a planetary ball mill

The effect of the milling parameters (rotation speed of the milling device and duration of milling) on the phase composition of the products of milling of fully crystalline selenium has been investigated. The milling was conducted using a planetary micromill and the phase composition of the milling products was determined by differential thermal analysis. It has been found that ball milling leads to the partial amorphization of the starting crystalline material. The content of amorphous phase in the milling products depends, in a rather complicated way, on the milling parameters. At the milling parameters adopted in the present study, the milling product was never fully amorphous. The complicated way the milling parameters affect the content of amorphous phase in the milling products is a result of competition of two processes: amorphization due to deformation and refinement of grains of milled material and crystallization of the already produced amorphous material at the cost of heat evolved in the milling vial during the milling process.

Kinetics of phase transitions in vitreous chalcogenide semiconductors AsxSe100m-x-yBiy as studied by the differential thermal analysis and exoelectron emission methods

Kinetics of glass transition (retrification) in chalcogenide semiconductors AsxSe100-x-yBy (x = 20 or 30, and y = 0 and 1) has been investigated by parallel differential thermal analysis (DTA) and exoelectron emission (EEE) measurements. EEE is a surface effect accompanying the structural transformations in the surface layer, whereas the DTA technique gives information about the transformations occurring in the volume of the sample. Temperature dependencies of the DTA signal and of the EEE intensity have been determined and the values of the activation energy for both the volume and the surface retrification have been determined by the Ozawa method for each of the four investigated materials. It has been found that addition of Bi into the vitreous AsxSe100-x glass changes distinctly the kinetics of both the surface and volume retrification. Addition of Bi causes a distinct decrease in the value of the activation energy for retrification process in both the surface layer and in the volume, i.e. reduces the thermal stability of investigated materials.

Effect of electrolytical hydrogenation on the thermal stability and crystallization kinetics of METGLASS MBF-50

The effect of electrolytical hydrogenation on both the surface and volume crystallization kinetics and thermal stability of amorphous alloy METGLASS MBF-50 has been investigated. The surface crystallization has been investigated by the exoelectron emission (EEE) technique, whereas the volume crystallization has been followed by differential thermal analysis (DTA). It has been found that both the surface and volume crystallization of investigated material occur in two stages. The surface crystallization occurs at temperature lower and with activation energy distinctly smaller than the volume crystallization. Hydrogenation of the investigated metallic glass enhances its thermal stability by increasing the activation energies for both the surface and volume crystallization. The results of DTA measurements indicate that hydrogenation causes an increase in the enthalpy of both stages of volume crystallization.