1. Thermal and Optical Analysis of the Doped Cerium Calcium Aluminate Obtained by the Gel Process Using Ethylenediamine Tetraacetic Acid

   Valéria Rejane Silva Brito, Raquel Jovita dos Santos, Paulo Neilson Marques dos Anjos

   Abstract: In this work, we synthesized calcium aluminates doped with trivalent cerium ions (Ce³⁺) by gel process with ethylenediamine tetraacetic acid (EDTA) as a chelating agent. The synthesized material was characterized by means of thermogravimetry and differential thermal analysis and spectrofluorimetry. The results were similar to literature.

   Keywords: Calcium aluminate, cerium ions, luminescence.

   Pages: 247 – 252 | Full PDF Paper

2. Combined Synthesis of Sodium and Potassium Alkoxides Using Electrochemical Methods

   Kudryavtsev Pavel, Kudryavtsev Nikolay

   Abstract: The alkoxides of chemical elements form a class of compounds, the practical value of which are large and are growing. In the present work generalizes the experience of creation of small-tonnage chemical production of alkoxides of different chemical elements and their use in technological processes of production of various chemicals and composites. In this paper the authors presented an overview of the main synthetic methods, obtaining alkoxides of chemical elements and, in particular, alkali metal alkoxides. Describe their basic physical and chemical properties. Have been analyzed the main methods of production of alkali metal alkoxides.Four basic methods of synthesis of chemical elements alkoxides have been allocated. Consider the direct methods for the synthesis of metal alkoxides by reaction with alcohols. Also have been considered, options for obtaining chemical elements alkoxides by reacting their oxides and hydroxides, with the corresponding alcohols. To implement this method has been described the functioning, the process plant scheme for obtaining potassium i-butoxide, by azeotropic distillation of water. For alkoxides of chemical elements, has been considered a variant of their synthesis method using exchange reactions with alcohols, and processes such as transesterification. The combined process of electrochemical synthesis, of sodium and potassium alkoxides has been proposed. To slow down the rate of interaction of sodium and potassium with alcohols, their amalgam has been used. The amalgam was prepared by electrolysis of sodium hydroxide. The interaction process alkali metal amalgam flows quietly enough, even in the case of methyl alcohol and potassium amalgam. Technological scheme includes three stages: electrolysis of NaOH solution at ordinary electrolyze with flow mercury cathode; dissolving amalgam on the anode in an alcohol solution and recovering sodium or potassium, in the form of alkoxides.

   Keywords: electrochemical synthesis, sodium alkoxide, potassium alkoxide.

   Pages: 253 – 264 | Full PDF Paper

3. Surface Recombination Processes in Silicon with Nano- Structured Porous Layers Formed by Photocatalysis

   Vitaliy P. Kostylyov, Volodymyr V. Chernenko, Olexandr A. Serba, Roman M. Korkishko, Viktor M. Vlasiuk

   Abstract: Experimental verification for simultaneous realization of effective antireflection and passivation coating of the back-contact back-junction silicon solar cell (BCBJ SC) front surface by using porous silicon nanostructured layers obtained applying the electrochemical method has been carried out. It has been shown that, using mixed ethanol and concentrated hydrofluoric acid electrolyte on the SC n⁺-surface, the porous silicon film with optimized values of the refractive index and thickness can be grown, which can be reached varying duration of the electrochemical etching process. It has been found that, after formation of the porous silicon film on the n-base BCBJ SC material, the effective surface recombination velocity decreases due to passivation of surface recombination-active centers by hydrogen atoms that are released during the electrochemical reaction, but this effect is unstable because of hydrogen atom desorption from the porous layer.

    

   Keywords: Microporous silicon, electrochemical etching, surface recombination.

   Pages: 265 – 271 | Full PDF Paper

4. Temperature Dependence Magnetoresistance of Fe_73.5 –Cu₁ –Ta₃ –Si_13.5 –B₉ Magnetic Alloy

   M Z Ahsan, F A Khan and M. Perven

   Abstract: Fe_73.5-Cu₁– Ta₃-Si_13.5-B₉ magnetic alloy, in the form of ribbon, was synthesized by single roller melt-spinning technique in air. The magneto transport properties of the sample were studied as a function of temperature using conventional 4-probe technique. The sample exhibits semiconducting behavior at low temperature (35 – 295 K) and metallic behavior at high temperature (350 – 700 K). The magnetoresistance (MR) found to increase with both the temperature and field in the low temperature range due to the ordering effect of microcrystallites in the amorphous matrix. A significant dispersion of negative MR obtained at 700 K due to more disorderliness of spins in the amorphous matrix of the sample. Its Zero Field Cool (ZFC) and field cool (FC) measurement demonstrates both the positive and negative slopes of Magnetoresistance below and above a critical transition temperature, 175 K that resulted from the difference of magnetic and thermal energies. Up to this critical temperature, the system makes a transition from ferromagnetic (FM) to antiferromagnetic(AFM) and above this temperature from AFM to FM, which is an indicative of reentrant ferromagnetic phase, which leads to be used it in sensors and magnetic devices.

   Keywords: Magnetic alloy, Normalized resistivity, Magnetoresistance, Microcrystallites.

   Pages: 272 – 278 | Full PDF Paper