Vol 53, No 2 (2017)

The basic features of the formation of a single crater under the influence of the pulse laser radiation on the surface of the titanium alloy and corrosion-resistant steel specimen are experimentally confirmed. In addition, a possible influence of the plasma–vapor cloud on the single crater formation. A calculation was carried out of an approximate estimate of the index, connecting the material mass destroyed under the impact of the phase transition with the absorption energy. This makes it possible to perform specific technological calculations needed while preparing for laser marking and milling.

The possibility of using the Cahn–Hilliard theory in the process of electrodeposition of nanostructures is studied. A correlation between the microscopic parameters included in the calculation formulas and the experimental kinetic coefficients is found. The theoretical results can explain the choice of the optimal parameters of electrochemical deposition.

Using the analogy between the charged drop which hangs in an electrostatic suspension and ball lightning (BL) with an electric charge and floating in the air in the superposition of the gravitational and electrostatic fields, the two phenomena which differ only by the role of the ascending force, inferences are deduced on the role of some physical properties of BL and the peculiarities of its movement and existence. It was shown that with the fixed physical parameters of BL its radius cannot exceed a certain value. The same can be said about the ratio of the densities of the substance of BL and the environment, as well as the value of its coefficient of surface tension.

Boronizing (boron diffusion) is one of the treatments applied to improve the surface properties of steels. In this study, an interstitial-free (IF) steel was boronized and titanium diffused in order to gain knowledge about the diffusion mechanism. Boronizing was carried out electrothermochemically at 900°C by applying a current density of 0.10 or 0.40 A/cm² for 45 or 120 minutes in a salt bath containing 100% Na₂B₄O₇ while titanium diffusion was performed thermally at 1000°C for 2 hours. Single-layered diffusion coatings were formed by either boronizing or titanium diffusion whereas multi-layered diffusion coatings were generated by both boronizing and titanium diffusion. One part of the study was concerned with first boronizing and then titanium diffusion while a reverse sequence of the process, i.e. first titanium diffusion and then boronizing, was applied in the other part. The generated single-layered and multi-layered diffusion coatings were characterised by using an optical microscope, a scanning electron microscope equipped with an energy dispersive spectrometer, and an X-ray diffractometer. Occurrence of six chemical reactions during titanium diffusion was assumed and the standard formation enthalpies of these reactions were calculated by using a database. On investigating the microstructure, it was understood that both a boride layer and a titanium based diffusion layer were formed by first boronizing and then titanium diffusion. However, it was observed that the previously formed titanium based diffusion layer inhibited the diffusion of boron atoms in case of first titanium diffusion and then boronizing. On the other hand, if the duration of boronizing and the current density applied during this treatment that was carried out after titanium diffusion were increased, formation of boride phases, as well as of a titanium based diffusion layer, was achieved. The semi-quantitative atomic per cent chemical analyses carried out by the energy dispersive spectrometer and X-ray diffraction analyses pointed out the formation of metastable boride phase of Fe₃B, as well as stable boride phases of Fe₂B and FeB on the surface of the IF steel that was only boronized. It was concluded that the standard formation enthalpies of the six supposed chemical reactions were negative, indicating that these reactions could occur at a normal atmospheric pressure. In addition, most of the products of these reactions were detected in the X-ray diffraction analyses.

The resistivity, ρ(T), and the magnetoresistance (MR) of Cu₂ZnSnS₄ (CZTS) single crystals are investigated at temperatures T = 2–300 K in pulsed magnetic fields of B up to 20 T. The Mott variable–range hopping (VRH) conductivity over localized states of the defect acceptor band is observed between T ~ 50–150 K. The Shklovskii–Efros (SE) VRH conduction over the states of the Coulomb gap is found below T ~ 3–4 K. The positive MR is observed at all temperatures and magnetic fields, its value decreasing with T. In the Mott VRH conduction region, MR follows the law ln ρ(B) ∝ B² up to the highest applied fields. The joint analysis of the resistivity and MR data in this region has yielded values of the localization radius as well as a set of important microscopic parameters, including the mobility threshold in the acceptor band, the values of the density of localized states near the Fermi level and the critical concentration of the metal–insulator transition. In the SE region, the MR law above is observed only in much smaller fields, transformed into those of lnρ(B) ∝ B^2/3 or ∝ B^3/4 when B increases. Such transformation, accompanied by a strong increase of the localization radius, give evidence for an important role of scattering and interference phenomena in the VRH conduction at low temperatures.

The behavior of three clays collected from different locations in Tunisia has been studied through their chemical and mineralogical composition, plasticity, specific surface area, cation exchange capacity, via dilatometry and infrared spectroscopy. The mineralogical composition is an indication of the presence of kaolinite, illite and smectite associated with quartz, calcite and hematite. The study of the chemical composition showed that the main oxides in the ClayTeb sample are SiO₂ and Al₂O₃, which were also found in the ClayHorb and ClayMed samples along with Fe₂O₃, CaO and K₂O. The mineralogical metamorphoses during the firing process were recorded via the X-ray diffraction of the raw clays and subsequent firing at 300, 600, 800, 1000 and 1200°C for 3 hours. Kaolinite transformed to metakaolinite was not observed at 600°C. Illite underwent total deshydroxylation at 1000°C. This latter temperature characterizes the main evolution of all samples and the start of the crystallization of mullite, which is dependent on the presence of impurities (Fe₂O₃) and K₂O (lent fondant). For the ClayMed clays, which have the maximum content of illite, only the spinel phase was defined at 1200°C. The samples were dry pressed and fired at temperatures of 950, 1050, and 1100°C and the characteristics of the ceramic were determined by firing shrinkage, water absorption, loss on ignition and flexural strength.